FXUS66 KEKA 211320
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.
CA...Wind Advisory until 4 PM PST this afternoon for CAZ102-104>113.
Flash Flood Watch from noon PST today through Friday morning for
NORTHWEST CALIFORNIA COASTAL WATERS...Gale Watch from Thursday morning through Thursday afternoon for
Gale Watch from Thursday morning through Thursday afternoon for
Small Craft Advisory until 1 AM PST Thursday for PZZ455-470-475.
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FXUS66 KHNX 211201
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
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
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.
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
FXUS66 KLOX 211737
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
937 AM PST Wed Nov 21 2018
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
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
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.
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
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.
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.
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.
FXUS66 KSTO 211316
Area Forecast Discussion
National Weather Service Sacramento CA
516 AM PST Wed Nov 21 2018
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.
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.
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.
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
Winter Storm Warning from noon today to 10 AM PST Friday for
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Wind Advisory from 4 PM Thursday to 7 AM PST Friday for Central
Sacramento Valley-Northern Sacramento Valley-Southern Sacramento
FXUS66 KSGX 211717
Area Forecast Discussion
National Weather Service San Diego CA
917 AM PST Wed Nov 21 2018
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
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.
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.
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
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 activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
FXUS66 KMTR 211721
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
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
.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.
.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
FIRE WEATHER: Rowe/RWW
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