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Office: EKA

FXUS66 KEKA 211320
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
520 AM PST Wed Nov 21 2018

.SYNOPSIS...Breezy south winds and frontal rains will continue to
impact the area this morning. Thereafter, showers and thunderstorms
will occur this afternoon and evening, followed by several rounds of
heavy rain and strong winds Thursday and Friday.


&&

.DISCUSSION...Very breezy southerly winds are currently ongoing
across the region this morning ahead of an approaching cold front.
Mountain RAWS sites are indicating wind gusts in excess of 40 mph
with even lower elevation stations seeing winds in excess of 20
mph. These strong winds will stay with us through early afternoon
before gradually diminishing as the cold front moves through. A
band of precipitation is now evident on radar associated with the
cold front across the outer waters as of 4am. This band is
expected to move inland after sunrise. This first band of
precipitation will lead to widespread light to moderate rain. Once
the front clears the area later this morning a more convective
air mass will move in. 500mb temperatures near
-25C will aid in steepening lapse rates leading to modest amount
 of MUCAPE nearing 500 J/Kg. Therefore a few thunderstorms will be
 possible across the ocean and coastal locations this afternoon
 and evening. Thunderstorms will be able to mix strong winds aloft
 down to the surface therefore erratic strong winds as well as
 small hail will be possible with any thunderstorm or stronger
 shower that develops.

Heaviest rains will develop across the region Thursday afternoon
into Friday in two distinct waves. The first wave is expected to
quickly move north to south across the region Thursday afternoon and
then become fairly stationary across Mendocino County. Therefore
Del Norte and northern Humboldt counties may see a brief break
late Thursday night into early Friday morning while other areas
will continue to see precipitation. Then a secondary surface low
develops and moves towards the coast just to the north of our
area. This system is expected to bring even heavier rain as
moisture flux vectors are pointed into our coast. This means that
area wide heavy rain will be possible especially for locations
that see topographical enhancements Friday morning through Friday
afternoon. Debated issuing an aerial flood watch for Thursday into
Friday however due to very dry antecedent conditions it seems
likely that the soils, rivers, and creeks will be able to hold a
lot of the moisture and therefore widespread flooding would not be
likely. Decided to continue the hydrologic outlook mentioning the
potential for localized urban and small creek flooding at this
time. For mountain locations it appears that snow levels will
remain above 5000 feet during this event which will keep snow
levels above all the area passes except Scott Mountain Pass on Hwy
3 where minimal impacts will be possible.

The other hazard for Thursday will be extremely gusty southerly
winds ahead of the next front for coastal locations north of Cape
Mendocino. A strong pressure gradient combined with a LLJ in excess
of 50 kts suggests very strong winds above 45 mph will be possible
for exposed coastal headlands and elevated ridges and mountains.
These conditions would easily meet wind advisory criteria however
a high wind watch was contemplated for this period for coastal
zones however confidence in high wind criteria being reached is
not yet high enough. These strong winds will bring some tree limbs
down and cause sporadic power outages.

Looking into the weekend, ridging will redevelop across the
Pacific which will dampen our rain chances this weekend. Model
guidance indicates a weak system attempting to move to the north
of our area Sunday however we would only experience the tail end
of the front. Therefore, only a few showers may be possible
across the far northern portions of the area on Sunday. Models
are in better agreement regarding a stronger weather system
impacting the North Coast Monday into Tuesday which will bring
another round of rain and winds to the area. /WCI


&&

.AVIATION...The cold front is 30 to 40 miles off the coast this
morning. South winds have started to pick up this morning. At the
surface they remain fairly light, but they have increased above the
surface so have continued the wind shear in the tafs. A band of
heavier rain is expected this morning as this front moves onshore
bringing periods MVFR conditions. This afternoon and evening models
are showing the potential for thunderstorms so have added VCTS to
the tafs. The best chance looks to be along the coast and over the
waters, but have them in Ukiah as well. MKK


&&

.MARINE...The south to southeast winds ahead of the cold front are
moving into the waters this morning. The strongest winds are in the
outer waters and near cape Mendocino. This has brought steep waves
of around 6 to 8 feet. A few gale force gusts are possible this
morning, but the coverage doesn't look to be enough with this system
for a gale warning. The northern inner waters continue to be
sheltered due to the southeast winds so don't expect small craft
conditions there in the majority of the zone. In addition to the
winds a mid period swell has started to build into the waters.
Currently it is about 2 ft at 16 seconds. This will build to around
7 feet at 13 seconds tonight. This afternoon the winds will diminish
behind the front, but showers and thunderstorms are expected as the
trough moves over the area. Some of these showers could bring
locally gusty winds to 30 kt.

Late Thursday night southerly winds will start to increase once
again as the next system approaches the area. This front is expected
to bring gale force winds to the northern waters. Confidence is
growing that this will brings gale to the waters north of Cape
Mendocino. A few storm force gusts are possible as well. Added a
Gale watch to the northern inner waters as the hi-res models show a
good portion of this with gale force gusts. While these winds are
ongoing an 8 to 10 feet swell at 12 seconds will increase the
seas and create a confused sea state.

Thursday afternoon the winds will quickly diminish behind front.
Another system will bring additional strong winds Friday morning.
Current models show the winds staying below gale force with this
system. The swell will continue to bring seas of 8 to 9 feet at 12
to 14 seconds in addition to wind driven waves.

Models have finally come into better agreement on light winds over
the weekend. There will be lingering swell of 9 feet at 11 seconds
on Saturday, but this will diminish on Sunday.

Early next the models are showing another system, but they are
struggling with the strength at this point. MKK


&&

.HYDROLOGY...Multiple rounds of moderate to heavy rain are
forecast to occur across NWRN CA today through Friday. A cold front
will move east across northwest California early this morning. The
front will bring widespread moderate rains to the region and also
aid in the development of gusty south winds. After the front passes
east, showers and thunderstorms will spread across the area during
the afternoon and evening.

Heavy rainfall and strong south winds are forecast to develop
Thursday afternoon and persist through Friday. This next round of
precipitation will push storm total rainfall amounts to 2 to 5
inches for most of the region, with locally higher amounts in excess
of 6 inches occurring across west facing mountain and ridge slopes.
Rapid rises on area rivers will be possible, but river flooding is
not expected. However, heavy rainfall may cause small streams and
low-lying urban areas to flood.


&&

.COASTAL FLOODING...Current tidal anomalies in the vicinity of
Humboldt Bay are around 0.7 feet. Applying that anomaly to the
astronomical tide this Friday of 7.9 feet combined with strong
southwest winds, minor flooding around Humboldt Bay, including
King Salmon and Jackson Ranch Road, will be possible. In
addition, a west swell yielding breaking waves of 15 feet may lead
to enhanced wave run up on area beaches.


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 4 PM PST this afternoon for CAZ102-104>113.

     Flash Flood Watch from noon PST today through Friday morning for
     CAZ107-110-113.

NORTHWEST CALIFORNIA COASTAL WATERS...Gale Watch from Thursday morning through Thursday afternoon for
     PZZ450.

     Gale Watch from Thursday morning through Thursday afternoon for
     PZZ470.

     Small Craft Advisory until 1 AM PST Thursday for PZZ455-470-475.

&&

$$

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Office: HNX FXUS66 KHNX 211201 AFDHNX Area Forecast Discussion National Weather Service San Joaquin Valley - Hanford CA 401 AM PST Wed Nov 21 2018 .SYNOPSIS...A low pressure system will bring cooler temperatures, increased moisture and precipitation to the area by this afternoon. Rain and mountain snow will continue into Thanksgiving Day. Another system will bring precipitation chances to the area on Friday and Friday Night then move east of the area over the weekend as high pressure returns along with a drier airmass. && .DISCUSSION...METARs and webcams are indicating much better visibility across the San Joaquin Valley than what was observed on Tuesday morning as an incoming trough has provided for increased atmospheric mixing. IR imagery is indicating some thin high clouds streaming over central CA while the deeper moisture and precipitation remain to the north and west of our area. After several days of a dry and stagnant airmass prevailing over the area, a big change is in store as the offshore trough continues to approach the CA coast today and move inland across our area tonight. RH progs are trending slower with the arrival of the deeper moisture moving into our area, but there is still the potential for light precipitation from Fresno County northward by late this morning spreading southward this afternoon. The more significant precipitation is expected to arrive by this evening as the WRF is indicating a 170kt 250mb jet max slicing through central CA. With the northern portion of our CWFA expected to be in the favored LFQ this evening, moderate to locally heavy precipitation will be possible in the Southern Sierra Nevada from Fresno County northward. The biggest concern at this time remains how the Ferguson Fire burn area in Mariposa County responds to the first significant precipitation across our area in a month and a half. The potential exists for mudslides and debris flows in this area so a Flash Flood Watch has been posted for late this afternoon through Thanksgiving morning. This is also expected to be the first significant snowfall of the season across the higher elevations of the Southern Sierra Nevada and a Winter Storm Warning remains in effect for elevations above 7000 feet from for late this afternoon through Thanksgiving morning as well. This system will move east of our area by afternoon on Thanksgiving Day. However, a second system is expected to push through Norcal on Thanksgiving Night and spread precipitation southward across our area by Friday morning. Although amounts are progged to be light with this second system, QPF progs are trending a bit higher with it; and this will need to be watched for possible impacts across the Ferguson Fire burn area for Friday. By Saturday the second system will move to the east of our area and a dry upper ridge will push into CA on Saturday Night and Sunday. The medium range models are in fair agreement with the ridge remaining the dominant weather feature across our area Sunday through Tuesday which will result in a warming trend and lowering daytime humidities. It will also increase the potential for significant fog in the San Joaquin Valley on Monday and Tuesday mornings. The ridge is progged to break down by next Wednesday, and both the GFS and ECMWF are indicating a potentially strong storm moving through Central CA by the end of next week which would bring additional precipitation to our area. && .AVIATION...Smoke and haze will continue to create widespread MVFR and areas of IFR visibilities in the San Joaquin Valley and southern Sierra foothills through 18Z today. Gusty south winds will be possible over the Sierra Nevada after 18Z today. Precipitation spreading from north to south across the region. SHRA by 18Z MER,MCE to 21Z at FAT,VIS then BFL by 03Z. Mountain obscuration in precipitation. && .AIR QUALITY ISSUES... Please see SFOAQAHNX for an Air Quality Alert On Wednesday November 21 2018... Unhealthy for sensitive groups in Fresno... Kern... Kings... Madera... Merced and Tulare Counties and Sequoia National Park and Forest. Fireplace/Wood Stove Burning Status is: No Burning For All in Fresno... Kern... Kings... Madera... Merced... Sequoia National Park and Forest and Tulare Counties. Further information is available at Valleyair.org && .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information an/or to provide feedback. && .HNX Watches/Warnings/Advisories... Winter Storm Warning from 4 PM this afternoon to 8 AM PST Thursday ABOVE 7000 FEET CAZ096-097. Flash Flood Watch from this afternoon through Thursday morning CAZ093-096. && $$ public...DS avn/fw...JDB synopsis...DS weather.gov/hanford
Office: LOX FXUS66 KLOX 211737 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 937 AM PST Wed Nov 21 2018 .SYNOPSIS...21/728 AM. Rain will spread across the region today and early tonight, then turn to scattered showers by Thanksgiving morning. There is a slight chance of thunderstorms across portions of the region tonight. Dry weather is expected Friday through Tuesday, except there is a slight chance of showers across north of Point Conception Friday and Friday night. Temperatures will be below normal through Friday, then rise to near normal levels Saturday, and above to normal levels Sunday through Tuesday. && .SHORT TERM (TDY-FRI)...21/936 AM. Some lower stratocu were noted over parts of the area this morning, otherwise some hi clouds were streaming overhead and coming in from the SW. Over far NW SLO County, there were more extensive clouds associated with an approaching cold front, and a few light showers were noted on RADAR in this area. As the day progresses and the front approaches the Central Coast, skies will become mostly cloudy over much of SLO/SBA Counties with rain becoming likely this afternoon especially over central and western SLO County and the SBA County Central Coast. Dry weather with increasing clouds can be expected for VTU/L.A. County thru this afternoon. South to southeast winds will increase especially over SLO/SBA Counties thru the afternoon, with gusts up to 25 to 35 mph possible. Temps across the forecast area today are expected to be several degrees below normal, with highs in the 60s across the coast and vlys. The models continue to advertise a rather sharp upper level trof over the E Pac pushing toward the CA coast thru today. The upper trof will accelerate with a 160-170 kt jet tonight and push inland over the state after midnight. Its associated cold front will push into the Central Coast early this evening then move quickly E overnight, passing thru VTU/L.A. Counties after midnight. Flat upper level ridging should prevail over srn CA Thu afternoon thru Fri, with a broad WNW flow aloft. The front will spread rain across the rest of the forecast area tonight. There will also be enough instability with the upper trof and front to warrant a slight chance of thunderstorms this evening over SLO/SBA Counties and over most of the forecast area later tonight, including the Woolsey and Hill burn areas. The main jet core should stay over northern and central parts of the district tonight which is not the most favorable location for heavy rain across srn VTU/L.A. Counties, but some enhance rainfall will be possible even in these areas, especially if any thunderstorms develop. PWAT values are forecast to be in the 1.00 to 1.20 inch range, enough to contribute to moderate to locally heavy rain at times with the front especially in any thunderstorms and along S facing slopes. Rain will turn to scattered showers in L.A. County by Thu morning, with showers mostly ending elsewhere. Skies should become partly cloudy in all areas Thu afternoon. Rainfall totals of 0.50 to 0.75 inches can be expected across SLO and SBA Counties, with local totals of 1 to 1.50 inches in the foothills and mountains. Isolated totals up to 2 inches are possible across the higher terrain of northwestern SLO County. Across Ventura and Los Angeles Counties, models show rainfall totals of generally between 0.30 and 0.70 inches. Local totals of 0.70 inches to 1.25 inches are possible in the foothills and mountains of VTU and L.A. Counties, especially in western Ventura County and in the Santa Monica Mountains. The rain should still be significant enough to cause some issues in and around the recent burn areas, especially the Woolsey and Hill burn areas, with the potential for rock slides, mud slides and minor debris flows. Residents in and near the burn areas should stay tuned to the latest forecasts and any future advisories or statements on this rain event. Broad west to northwest flow pattern will set up across the region Thu night through Fri night. The tail end of the frontal system may bring a few showers to SLO County Fri, which could spread into northern SBA County Fri night. If any rain falls, it looks as though it will be very light. Elsewhere, expect partly cloudy skies Thu night through Fri night. Max temperatures will be below normal Thu and Fri, altho there could be a couple of degrees of warming in most areas Fri. .LONG TERM (SAT-TUE)...21/421 AM. It will be dry across the region on Sat, and height rises could bring a couple of degrees of warming to most areas, generally back to normal levels. A weak trough will drop southward into the forecast area on Sunday, causing heights to fall a bit, but no rain is expected. Low level flow will turn offshore. This could bring some warming to areas west of the mountains, and cooling in the mtns and deserts. An upper ridge will build to the north of the region Monday and Tue. Dry weather is expected, with temperatures a few degrees above normal. && .AVIATION...21/1101Z. At 0923Z at KLAX...There was no inversion near LAX. N of Point Conception...Low to moderate confidence with 12z TAFs. Low clouds are expected to fill in across coast and valleys N of Point Conception with mostly MVFR CIGs this morning and then remain mostly cloudy through the day. Light rain will develop along the Central Coast later this mering which could bring Vsbys down to IFR with rain. Rain will then begin to push inland late this morning into this afternoon. There will be a chance of TSRA this evening. S of Point Conception... Little in the way of inversion this morning, low clouds will form randomly anywhere W of the mountains this morning. Expect mostly MVFR cigs, but a few valley locations could see IFR conds this morning. Low confidence if stratus will stick around most of the morning or scour out to VFR conds this afternoon. High Clouds are expected to increase late this afternoon into this evening. Rain should begin late this afternoon or early evening for areas S of Point Conception. SHRA will likely start to form as early as 12Z north of Point Conception, and after around 23Z for Ventura County. It now looks like L.A County will start seeing rain this evening through the overnight hours. Widespread RA expected tonight into early Thursday morning. Some lingering showers Thursday. KLAX...Low to moderate confidence in 12Z TAF in respect to timing of MVFR cigs as well as confidence for scouring out CIGs. High clouds will increase late this afternoon. 50 percent chance of east winds 8 kt or stronger between through 19Z today. -RA possible after 23Z, but more likely after 03Z Thursday. KBUR...Moderate confidence in 12Z TAF. . Higher probability for MVFR cigs after a couple hours of IFR cigs this morning. Lower confidence if MVFR cigs will scour out by late this morning. -RA possible after 23Z, but more likely after 03Z Thursday. && .MARINE...21/910 AM. A storm system will impact the area today into Thursday. Gusty SE winds will impact most waters, with SCA conditions likely north of Point Conception into the evening hours. Thunderstorms are possible tonight anywhere, but especially off the Central Coast. Gusty west to northwest winds will follow Thursday and Friday south and east of Point Conception, then expand to the Central Coast on Saturday. A long duration of SCA conditions is likely with building short period seas, including the Santa Barbara Channel and Santa Monica Basin. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 9 PM PST this evening for zones 645-670-673. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK (FRI-TUE). No significant hazards expected. && $$ PUBLIC...Sirard/DB AVIATION...kaplan MARINE...Kittell SYNOPSIS...DB/RAT weather.gov/losangeles
Office: STO FXUS66 KSTO 211316 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 516 AM PST Wed Nov 21 2018 .SYNOPSIS... Cooler and wetter weather spreads into the area by today and continues into early Saturday. Newly burned areas could experience ash/debris flows. Snow over the higher elevations of the Sierra will make travel difficult for the Thanksgiving travel period. && .DISCUSSION... Satellite imagery this morning shows the first of a series of storm systems pushing towards the West Coast with the radar showing some light rain over the coastal range. This will continue to advance eastwards and eventually bring widespread rain to the area later this afternoon and evening. Snow levels will be falling during this time frame as well, with the Sierra seeing accumulating snow around 6000 feet. These conditions will make driving conditions hazardous so motorists should take extra precautions if they must go out. As we head into Thanksgiving, the first storm system will be exiting the region with a second and more potent system arriving late in afternoon and into the evening hours. Periods of heavy rain and mountain snow are expected with this system in addition to gusty southerly winds. These conditions will continue as we head into Friday, so travelers will once again have to take extra precautions as these conditions will make driving difficult. By late Friday night and into Saturday morning, the low will be exiting the region. Showers will likely linger over the Sierra and its associated foothills, but elsewhere conditions should be dry. Finally, we're still concerned about the newly burned areas as they will likely see debris/ash flow from moderate rain. The major question is whether rain intensity could reach sufficient levels to cause more hazardous debris/ash flows. There is still quite a bit uncertainty, but there is enough potential to keep the Flash Flood Watch in effect for debris flows at the Mendocino Complex, the Carr, Delta, Hirz fires and the Camp Fire. Flooding outside of the burn areas is not expected, except for local ponding on roads with clogged drains. .EXTENDED DISCUSSION (Sunday THROUGH Wednesday) Drier weather is expected into early next week as high pressure builds into California. A weak system could bring a few showers over the northern mountains on Sunday, but guidance has trended drier with this feature, so only light precipitation amounts are expected. A return of precipitation is likely during the second half of next week across interior NorCal. However, model uncertainty is evident in terms of precipitation amounts, and timing, with the latest ECMWF run being quicker than the GFS. Regardless, widespread precipitation, locally gusty winds, and cooler temperatures could be possible. Seasonal temperatures expected across the area during the extended period, with Valley highs in the mid 50s to low 60s, and 40s to 50s over the mountains. && .AVIATION... Areas of MVFR/IFR with local IFR conditions possible next 24 hours as Pacific storm moves inland. Southerly wind gusts 15-25 kts possible between 18z Wed - 03z Thurs mainly from KSAC southward. Wind gusts over the Sierra up to 45 kts are possible. && .STO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch from noon PST today through Friday morning for Central Sacramento Valley-Clear Lake/Southern Lake County- Mountains Southwestern Shasta County to Northern Lake County- Northeast Foothills/Sacramento Valley-Northern Sacramento Valley- Shasta Lake Area / Northern Shasta County-Western Plumas County/Lassen Park. Winter Storm Warning from noon today to 10 AM PST Friday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. Wind Advisory from 4 PM Thursday to 7 AM PST Friday for Central Sacramento Valley-Northern Sacramento Valley-Southern Sacramento Valley. && $$
Office: SGX FXUS66 KSGX 211717 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 917 AM PST Wed Nov 21 2018 .SYNOPSIS... High temperatures will be slightly cooler today with increasing high clouds during the day as a trough of low pressure approaches the West Coast. For tonight and Thursday, that trough of low pressure will move inland through California bringing a period of light showers mainly from late this evening through early Thursday morning. A second round of scattered light showers is expected for late Friday night into Saturday along and west of the mountains with the passage of another upper trough. For Sunday and Monday, high pressure aloft near the California coast and surface high pressure over the Great Basin are expected to bring offshore flow and a warming trend with periods of gusty northeast winds for the mountains and inland valleys. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... High clouds are beginning to stream across the area this morning in advance of the upper trough now located off the northern California coast. The 12Z Miramar sounding continues to show a dry and stable airmass across the area with PW of 0.66 inch. Expect slightly cooler max temps today compared to the last couple of days given the increased cloud cover. Moisture will deepen this evening with the approach the upper trough. Expect low clouds to develop beginning this evening with a period of light showers late evening through early Thursday morning in association with the trough and a weak surface front crossing the area. Current forecast looks good and no changes will be made at this time. From previous discussion... .SHORT TERM (Today through Friday)... There is very little change to much of the forecast into early next week with only minor adjustments to the forecast. A trough of low pressure off the West Coast will move inland through California tonight and Thursday and then into the Great Basin. The marine layer is deepening, but aircraft soundings late Tuesday evening showed the marine inversion to be fairly weak with satellite imagery show mostly patchy coverage of stratus across the coastal waters and adjacent coastal areas. The cold frontal band of precipitation with this trough of low pressure is expected to reach Orange County and southwestern San Bernardino County after midnight and reach the southern San Diego County coast by about daybreak on Thursday. While some lighter precipitation with lesser coverage may precede the front from this evening into tonight, the bulk of the rainfall for most areas is expected with the frontal passage. For tonight into Thursday morning, rainfall amounts are expected to range from one tenth to one quarter inch near the Orange County and northern San Diego County coast to one half to one inch in the San Bernardino County mountains with locally greater amounts. Rainfall amounts are expected to be less farther south with amounts in San Diego County ranging from around one tenth inch near the central and southern coast to one quarter to one third inch in the mountains with locally greater amounts to around one half inch. In the deserts, the high desert areas are expected to receive around one tenth inch or less with a few hundredths of an inch or less in the lower deserts. The snow level will lower to around 6500 feet for late tonight into Thursday morning with a few inches of snowfall possible on the higher peaks in San Bernardino County, mostly above 7000 feet. Stronger onshore flow will bring areas of southwest to west winds in the mountains and deserts Thursday into Thursday evening with strongest gusts to around 45 mph in the windier locations. Friday is expected to be dry with high temperatures a little warmer than on Thursday, but still near to slightly below average. && .LONG TERM (Friday night through Tuesday)... A low pressure system will move inland through the Pacific Northwest for late Friday and Friday night, quickly through the Great Basin and central Rockies on Saturday, and into the plains on Saturday night. This will bring stronger onshore flow across Southern California with stronger and gusty west winds in the mountains and deserts with strongest gusts mostly less than 45 mph. There is also a slight chance for light showers along and west of the mountains for late Friday night into Saturday, mostly for San Diego County. The extended forecast continues to follow mostly the ECMWF though the latest GFS is not all that different. High pressure near the California coast will bring a warming trend for Sunday and Monday with surface high pressure over the Great Basin bringing periods of mostly weak offshore flow. There will be periods of gusty northeast winds at times, mainly for the coastal slopes of the mountains into the inland valleys and below passes and canyons, with the stronger gusts mostly 35 mph or less. This offshore flow will also bring a drier air mass into inland areas. By the middle of next week, the flow will be more zonal across the central and eastern Pacific with the main band of westerlies mostly between 35N and 40N latitude. This will begin to bring a series of low pressure systems into the West Coast beginning around Wednesday. For Southern California, onshore flow is expected to return on Tuesday and begin to spread some cooling inland. && .AVIATION... 201630Z...Coasts/Valleys...FEW-SCT clouds AOA 20000 ft MSL and unrestricted vis will prevail into the afternoon. More widespread low clouds with bases mostly 2000-4000 ft MSL and tops to 6000 ft MSL developing in the early evening. -SHRA will begin to spread into the region around 06Z Thursday beginning in Orange County and progressing eastward into all other areas. Bases expected to lower to around 1500 ft MSL. Mountains/Deserts...Increasing clouds AOA 20000 ft MSL this afternoon and unrestricted vis through this evening. Low clouds and precipitation will obscure coastal mountain slopes after 22/06Z. && .MARINE... No hazardous marine weather is expected through Thursday. Wind gusts 20-25 kt may develop over the outer coastal waters Friday evening through Saturday evening, creating conditions hazardous to small craft. && .FIRE WEATHER... For Sunday and Monday, high pressure aloft near the California coast and surface high pressure over the Great Basin will bring a warming trend with periods of mostly weak offshore flow. The humidity for inland areas will be much lower, falling to around 10 to 15 percent each day. There will be periods of gusty northeast winds near the coastal slopes of the mountains at times with gusts mostly 35 mph or less. Those winds combined with the lower humidity will elevate fire weather conditions at times, mainly for the coastal slopes of the mountains into the inland valleys. A return of weak onshore flow is expected for Tuesday which will begin to spread cooling and higher coastal humidity inland. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...Moreland AVIATION/MARINE...APR
Office: MTR FXUS66 KMTR 211721 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 921 AM PST Wed Nov 21 2018 .SYNOPSIS...An approaching weather system will bring widespread light to moderate rain and gusty winds to the region through the day, with scattered showers continuing through Wednesday night and into Thanksgiving morning. A second system is expected to bring additional rainfall to the area from Thursday evening through Friday. Dry weather is expected over the weekend before another chance of rain returns by the middle part of next week. && .DISCUSSION...as of 09:20 AM PST Wednesday...Prefrontal rain has moved into the SF Bay Area this morning. Areas on the west side of the Bay, including San Francisco, Half Moon Bay, and San Rafael, have seen moderate to locally heavy rainfall rates with around 0.2 inches of rain in the past hour. This area of rain will continue to spread north and east, impacting the North Bay over the next couple of hours. Another round of rainfall is expected this afternoon as a cold front sweeps across the area. Prefrontal southerly winds have helped to scour out some of the smoke across the area, with visibilities greatly improved and the air quality back into the moderate category in San Francisco as of 9 AM. Expect the rain and breezy southerly winds to continue to remove any lingering smoke from the region. Expecting the cold front to pass through the area late this morning through the afternoon. Another round of rainfall is likely with the frontal passage. Behind the front, winds will shift to southwesterly and decrease into the evening. Showers will remain possible in the unstable environment into the evening and overnight, with isolated thunderstorms possible near the coast this evening. Rainfall totals today will range from around a 0.25 inches in the rain-shadowed valleys, 0.25-0.75 inches along the coast and the North Bay valleys, and 0.5-1.5 inches in the North Bay Hills, Santa Cruz Mountains, and the Santa Lucia Range. With the rainfall occuring on a busy travel day, expect travel impacts and slick roadways. Another round of rainfall is expected late Thanksgiving and into Friday. && .PREV DISCUSSION...as of 2:44 AM PST Wednesday...Mid and high level clouds are starting to arrive at the North Bay this early Wednesday morning in advance of an upper level low that is approaching the West Coast. Over the next several days, the San Francisco Bay Area and central California coast will finally see the long-awaited and highly beneficial rainfall. For some locations, particularly in the East and South Bays, the incoming system will almost certainly provide the first wetting rain since April (wetting rain defined as >= 0.10"). It has been 223 days since the Oakland Airport has received >= 0.10" of rain in a calendar day (a record for the station), and 218 days for San Jose Airport and Moffett Field (a record for Moffett Field). Other locations throughout the region such as Santa Rosa, Napa, San Francisco, and even south to Monterey and Salinas managed to surpass 0.10" during an early October system. As the system approaches the coast, the communities in the North Bay will be the first to see the rain within several hours of sunrise today. KMUX radar is already showing some weak echos over the area, though anything reaching the ground at this time is expected to be very light. The rain is then forecast to spread southeastward through the day. Overall, rain amounts during the day are expected to be generally light to locally moderate. In addition to the rain, expect breezy southerly winds over much of the area. With today being a busy travel day, it's very realistic to expect travel impacts with the rain-slickened roads for Thanksgiving travelers. If your travel plans are taking you outside the Bay Area, note there will be accumulating snowfall across the higher elevations of the Sierra Nevada. Be sure to keep up the the latest weather reports by visiting weather.gov, and road conditions through CalTrans. For Thanksgiving Day, expect continued showers to impact the area, particularly during the morning hours. A second system will then take aim on the area, arriving first to the North Bay sometime on Thursday afternoon or evening. Rain will then advance south overnight and into Friday. Over the course of these two systems, expect rain totals to range from about 2.5-3.5 inches in the North Bay Mountains (orographically-favored locations may exceed 4 inches); 1.5-3 inches in the North Bay Valleys, Santa Cruz Mountains, and Big Sur Coast/Coastal Range; 1-2 inches for San Francisco and the East Bay, and generally 0.5-1 inch for the rain-shadowed South Bay/Santa Clara Valley, the Salinas Valley, and San Benito County. With the absence of any recent and significant burn areas across the Bay Area and central California coast, the threat of debris flows will be rather limited, though can't rule out some minor rock slides that would ordinarily happen during events such as these. Specifically for the San Francisco Bay Area and central California coast, these two systems will bring welcomed and very beneficial rainfall to the area. The debris flow threat will change outside of our area, such as in Northern California, the Sierra foothills, and southern California where there have been recent and significant burn areas. For additional forecast details for these locations, please checkout our neighboring offices' discussions from NWS Eureka, NWS Sacramento, NWS Hanford/San Joaquin Valley, and NWS Los Angeles/Oxnard. Expect dry weather to return to the area on both Saturday and Sunday as an upper level ridge develops just off the California coast. By early next week models suggest another incoming system to the area. The ECMWF is a bit quicker with bringing the rain onshore by Tuesday, while the GFS waits until Tuesday night and is wetter. Long story short: beneficial rains are expected to finally arrive to the area over the next few days with continued rain chances into the last week of November. && .AVIATION...As of 3:49 AM PST Wednesday...Reports of light rain are increasing as a cold front approaches from the northwest, southerly wind flow will precede frontal passage today. VFR areas MVFR except very locally IFR this morning in residual hazy and smoky conditions. Poor slant range visibilities still possible in the Bay Area this morning improving by afternoon and evening. Vicinity of KSFO...MVFR with light to occasionally moderate rain tapering to showers later today, tonight, and Thursday. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...VFR occasionally MVFR in light to moderate rain. Gusty SE winds today ahead of cold front. Showers tonight and Thursday morning. && .FIRE WEATHER...as of 2:44 AM PST Wednesday...Southerly winds will increase into the morning hours, especially along the coast and in the hills. Some strong gusts are likely just before rain begins this morning. Periods of light rain on today with some brief heavy rainfall possible as the front moves through. The typical rain shadowed valleys of the East Bay, Santa Clara Valley and Salinas Valley will see the lightest rain amounts. Thursday will be mainly dry with just some lingering showers. Next warm front arrives by Thursday night with rain developing in the North Bay and then slowly sliding southward on Friday. The heaviest rain will be in the North Bay and Santa Cruz mountains. By Friday night most areas should have received season-ending rains. Long range looks dry Saturday through the middle of next week but already signs of another storm before the end of the month. && .MARINE...as of 3:35 AM PST Wednesday...Increasing southerly winds will precede a cold front that will sweep southeastward over the coastal waters and bays today bringing rain and possibly thunderstorms. Winds weaken by late afternoon, but another storm system will once again strengthen southerly winds Thursday night. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm SCA...SF Bay until 3 PM SCA...Mry Bay until 3 PM SCA...Pt Arena to Pt Reyes 0-10 nm until 3 PM SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 PM SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 PM SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 PM && $$ PUBLIC FORECAST: ST AVIATION: Canepa MARINE: Canepa FIRE WEATHER: Rowe/RWW Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea