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Office: EKA

FXUS66 KEKA 182247
AFDEKA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
247 PM PST Sun Feb 18 2018

.SYNOPSIS...A cold storm system will bring rain and snow showers to
northwest California through early Monday morning. Some showers may
contain small hail. Behind this system a cold air mass settles
over the area. The coldest temperatures will be Tuesday morning.

&&

.DISCUSSION...The upper level trough moving over the area is
bringing widespread showers to Humboldt and Del Norte counties.
Snow levels have dropped to around 2,000 feet as of noon. Snow
levels will continue to fall tonight to around 1,000 feet.
Additional snow accumulations of up to 3 inches are possible
tonight in Humboldt and Del Norte counties. Locally lower snow
levels are possible in the heavier showers. A few flakes are
possible at the coast towards morning, but nothing is expected to
stick. Along the coast below the snow level numerous showers are
producing small hail. This has been accumulating on roadways. One
of these storms produced a couple lightning strikes. So have added
a slight chance for thunder and small hail this evening. These
showers are expected to continue tonight and start to diminish
towards morning.

Monday isolated showers will diminish through the day.
Temperatures are expected to only warm into the 40s and snow
levels will be around 1,000 to 1,500 feet, but no significant
accumulation is expected. Monday night into Tuesday morning looks
like the coldest morning. Temperatures at the coast look to drop
to around 30 at the immediate coast with 20s just a mile two
inland. The hard freeze watch for the coastal areas looks to be on
track and confidence is growing that we will see these
temperatures. Farther inland temperatures will drop into the low
20s and teens. Single digit temperatures are possible in the
northern mountains. There will likely be some clouds around from
a system off the coast, but models have slowed down this system
and come into better agreement that these clouds will not impact
temperatures too much. Tuesday afternoon temperatures will warm
slightly, but most areas will remain in the 40s. Tuesday evening
and overnight a few showers and some clouds likely as the weak
system moves by just off the coast. Snow levels will be fairly
low, but only a dusting of snow is expected.

Wednesday the airmass starts to warm slightly with temperatures
warming back into to low 50s. Northwest flow persists and a few
sprinkles are possible with some clouds around. Thursday into the
Weekend the models are showing additional systems moving over the
area from the northwest. There is not very good agreement in the
models on these systems yet. However, there is reasonable
confidence that temperatures will be fairly cool and there will be
periods of light rain and snow. MKK

&&

.AVIATION...An active day of showers at the coastal terminals
today will continue trough the evening before diminishing in
intensity and coverage later tonight.  The showers have and will
bring brief periods of mvfr conditions otherwise sites will mainly
observe VFR conditions through the next taf cycle. Some interior
valley locations sheltered from the north winds could see some ground
fog develop very early tomorrow morning.

&&

.MARINE...Gusty Northwest to north winds will continue through
tomorrow across all waters. Some of these winds are also enhanced
from passing showers...although the shower activity should diminish
over night. Meanwhile, a large swell from the northwest will move
through the waters this evening through Monday morning. The
combination of steep wind-driven seas and the arriving swell will
result in very large and hazardous seas with combined wave heights
reaching 20 to 25 feet throughout much of the waters. As a result, a
Gale Warning remains in effect for the outer waters from late this
morning through Monday afternoon. Hazardous Seas Warning has been
issued for the nearshore waters of Humboldt, Del Norte, and
Mendocino counties. Winds will steadily decrease through the day
Tuesday, allowing seas to slowly subside.  Tuesday and Wednesday,
north winds of 15 to 20 kt will maintain somewhat elevated seas,
likely with wave heights between 7 and 9 feet. However, north winds
will increase again Thursday through the end of the week, resulting
in the buildup of steeper seas that will last through at least the
end of Friday. /KAR/JT

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Hard Freeze Watch from late Monday night through Tuesday morning
     for CAZ101-103-109.

     High Surf Advisory from 1 AM to noon PST Monday for CAZ109.

     Winter Weather Advisory until 4 AM PST Monday for CAZ102-104>108.

     High Surf Advisory from 7 PM this evening to 4 AM PST Monday for
     CAZ101-103-104.

NORTHWEST CALIFORNIA COASTAL WATERS...Gale Warning until 3 PM PST Monday for PZZ470-475.

     Small Craft Advisory for winds until 3 PM PST Monday for PZZ450-
     455.

     Hazardous Seas Warning until 3 PM PST Monday for PZZ450-455.

&&

$$

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Office: HNX FXUS66 KHNX 182335 AFDHNX Area Forecast Discussion National Weather Service San Joaquin Valley - Hanford CA 335 PM PST Sun Feb 18 2018 .SYNOPSIS... A southward moving cold front will bring an unseasonably cold air mass into the central California interior by this evening. Blustery winds will accompany the change to colder weather this afternoon through Monday and snow showers are possible in the mountains and foothills by this evening. Below freezing temperatures are likely in the San Joaquin Valley Tuesday morning and Wednesday morning. Colder than normal weather will continue for the remainder of the week. && .DISCUSSION... Change is finally in store for Central California as a cold front from the Gulf of Alaska continues to descend toward the district. While the sun continued to shine this Sunday, clouds and showers have spread into Northern California behind the cold front. Surface Frontal analysis has the cold front over Northern California and quickly approaching the Central California Interior. Many surface observations are already showing a more northwesterly wind component which places the cold front nearby. Satellite IR imagery is showing the cold air cellular cloud formations pushing past the Bay area and moving further southward. Therefore, the cold air-mass will descend down into the region tonight with elevated wind speed being the saving grace from a very cold night. Clouds development from marginal instability will be the other saving grace, but will also produce spotty showers tonight as snow level could reach down into the foothills. However, moisture continues to lack which will keep precipitation on the lower accumulation-side with a few inches possible over the higher terrain of the Sierra Nevada. Current model prog timing still has the disturbance and associated cold front crossing into Central California today as surface winds have already started to increase. The cold front is entering the region and should reach the southern portion of the district just after sunset. At which time, the disturbance aloft will drop into the region and place a good portion of its energy offshore along the Central Coast. Model prog is still showing the flow pattern in a more channel flow pattern characteristic. This channel flow pattern is more indicative of strong winds than precipitation. Satellite imagery and surface observations are already showing this trend. Therefore, the higher confidence levels are with the strong winds then the lower confidence of possible precipitation. Yet, a portion of the wind component could become perpendicular to the Sierra Nevada Range and Tehachapi Mountains. Therefore, can not rule out precipitation over the higher terrain. However, forecast precipitation accumulation is small for this event as Central California is not favored in this flow pattern. Yet, the lack of precipitation and the fact that lower elevations may see snow will warrant the winter weather advisories for tonight. Behind Today's cold front, models have been very consistent in prog sub-freezing temperatures across the San Joaquin Valley from around Tuesday through Thursday morning. While during the early onset of the cold frontal passage, the coldest air will reside over the area with possible moderation in conditions going into Thursday morning. Therefore, the best chances of a hard freeze [min's < 28F] will exist on Tuesday morning (once the winds settle down and the skies clear out from Monday's event) with a good chance of freezing [min's < 32F but > 28F] Wednesday morning. While not as widespread as Wednesday morning, freezing will still be possible on Thursday morning. By Friday, Modification of the air-mass will make the potential for freezing less likely. Furthermore, another disturbance will enter the region on Thursday afternoon, which will increase winds and clouds along with mixing of the atmosphere to prevent the freeze potential. While the potential for precipitation is very low, will at least mention a potential as very low accumulation will be likely. By next weekend, an inside slider will maintain clouds, winds and possible mixing of the atmosphere to moderate temperatures. && .AVIATION... Strong surface winds with gusts to 45 knots developing this evening across the Kern County Mountains and Deserts. IFR conditions in Blowing Dust will be also be possible across the Mojave Desert overnight. Increasing clouds this afternoon with clouds and showers obscuring the mountains after 00Z Monday. Otherwise, VFR conditions will prevail across the Central CA Interior during the next 24 hours. && .AIR QUALITY ISSUES... None. && .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.php for additional information an/or to provide feedback. && .HNX Watches/Warnings/Advisories... Winter Weather Advisory from 9 PM this evening to 3 AM PST Tuesday CAZ095. Wind Advisory until 9 PM PST this evening CAZ095. Winter Weather Advisory from 6 PM this evening to 4 PM PST Monday CAZ093-094. Hard Freeze Warning from midnight Monday night to 8 AM PST Tuesday CAZ089>092. Freeze Watch from late Tuesday night through Thursday morning CAZ089>092. Wind Advisory until 4 PM PST Monday CAZ098-099. && $$ public...Molina avn/fw...JEB synopsis...Molina weather.gov/hanford
Office: LOX FXUS66 KLOX 190411 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 811 PM PST Sun Feb 18 2018 .SYNOPSIS...18/345 PM. Light rain and mountain snow will fall across much of the region tonight and Monday with snow falling as low as 1500 feet Monday morning. Gusty winds and a blast of cold air will create very cold wind chill temperatures through Monday with frost or freezing conditions Tuesday and Wednesday mornings. Conditions will be dry but cool for the remainder of the week. && .UPDATE... 18/811 PM Very difficult forecast this evening as a weak and fairly dry but very cold system moves in from the north. There are a fair amount of showers over MRY county and these will move over SLO and western SBA counties in a few hours. The forecasted eddy and convergent flow for SE LA county really did not materilize so the odd of that area seeing a shower tonight are much reduced. This system will very likely produce highly changable skies but not much rain. There is a pretty good chc that SLO and most of SBA county (but not the SBA south coast) will see some light showers. The best chc of showers will occur after midnight with the cold north flow impinges on the north faceing slopes near the Kern County line. Current suite of winter...wind and freeze products looks good. Updated the forecast to raise pops in the advisory areas as well as SLO and western SBA counties. Al;so play with the cloud wording a little to reflect current conditions. && .SHORT TERM (SUN-WED)... 18/400 PM Skies were mostly clear early this afternoon with some partly cloudy skies across portions of the Central Coast down to Ventura County coastal areas. Surface gradients between LAX and DAG have trended over +8 mb in the last 24 hours. A wind advisory is now in effect for the Antelope Valley due to the strong onshore gradients causing SW winds to increase to around 30 to 35 mph with gusts expected to be around 45 to 50- mph through this evening. There will be locally gusty winds across the Highway 14 corridor as well, including the Soledad Pass through this evening as well. Motorists driving high profile vehicles should slow down if encountering gusty cross winds. There will be gusty NW winds developing this afternoon across the Central Coast this afternoon but remain below advisory thresholds. Temps were trending down 6-10 degrees in most areas today compared to yesterday at this time. Highs today are expected to be around normal for this time of year. For this evening, NW winds will expand across the Santa Barabara County Mtns and adjacent wind prone south coast as well as the Los Angeles and Ventura County Mountains. Wind advisories will be in effect by 8 pm this evening in these locations. Synoptically, an upper level low located in the PAC NW will begin to dive south into the Great Basin tonight while the base of the low continues to dig into southern California. The trajectory of the trough will remain mainly over land, therefore not expecting much precip with this system. However, the combination of strong height falls and cold temperatures expected with this system will help squeeze out what little moisture there is to tap into to tonight through Monday evening. The best chance for light showers will be across L.A. County, especially the southern and eastern areas where the cyclonic flow aloft will be most most favorable. Otherwise, broad NW to N flow will bring a chance of rain and snow to the north facing slopes of SBA/Ventura and the NW portion of the LA County Mtns near the Grapevine and I-5 Corridor. The NW portion of the Antelope Valley could see a few showers as well through Monday eve. Snow levels will plummet tonight, dropping from between 5000 and 5500 feet this evening, to between 2500 and 3000 feet late tonight, and to 1500 to 2000 feet Monday morning. This could bring snow showers into foothills areas Monday morning. Little or no snow accumulation is expected in the foothills, but in the mountains above 2500 feet, snow accumulations of 2 to 4 inches are possible. 1-2 inches possible for the Santa Barbara County Mountains, and around an inch of snow for portions of the Cuyama Valley including highway 166. A winter weather advisory is in effect for the mtns of L.A. and VTU Counties as well as the Santa Barbara mountains and the Cuyam Valley this evening through Monday night for the snow and advisory level northwest winds. There could be a dusting of snow across the Antelope Valley foothills as well. Especially across the western portion, but not expecting valley floor accumulations. Gusty northwest winds will begin to shift out of the north and filter into the Santa Clarita and San Fernando Valleys and likely into West L.A. monday night into Tuesday morning. Additional wind advisories might be needed during that time. It will be very cool on Monday, with highs only in the 50s in most coastal and lower valley areas, in the mid to upper 40s in the interior valleys, in the upper 30s to mid 40s in the lower mountains and the Antelope Valley and in the mid 20s to mid 30s at higher mountain locations. With the cold conditions and added wind, it will feel much colder. In fact, wind chill values could drop to between 10 degrees and -10 degrees in the higher elevation of the mountains late tonight and Monday. This is unusually cold for Southern California. People planning to hike, camp, ski or snowboard in the mountains on the holiday are urged to plan for the unusual cold and low wind chill values. Winds are expected to decrease rather suddenly Monday night in most areas. With light winds and clear skies expected Monday night into Tuesday morning, radiational cooling will help temps drop significantly. The Hard Freeze Watches have been converted to Hard Freeze Warnings for both Monday night into Tue and Tuesday night into Wednesday morning for the Central Coast, the Santa Ynez and Cuyama Valleys, and the interior valleys of Ventura County, especially for the Ojai Valley. In these areas, temperatures will drop to 28 degrees or lower for at least two hours Monday night. Some areas within the Hard Freeze Warning will experience lows in the lower 20s. A Freeze Watch has also been converted to a Freeze Warning for the same time periods across South Coast of SBA County, coastal sections of VTU County, and the VTU County coastal valleys. Temperatures in these areas could bottom out between 29 and 32 degrees for at least two hours Monday night. It will also be very cold in the interior valleys of SLO County and the Antelope Valley, with temps between 17 and 27 degrees there, but those locations have already experienced two hard freezes this season. Frost is likely in the colder locations in the valleys of L.A. County Monday night, and a Frost Advisory will likely be needed for those areas. Tuesday will be mostly sunny but it will continue to be very cool across the region. .LONG TERM (THU-SUN)... 18/154 PM The EC and GFS are coming into better agreement with large scale features from Wednesday through Saturday. Temperatures will remain quite cool through the extended period as a broad upper trough across the west will persist. Skies should be mostly sunny Tuesday through Thursday before clouds increase Thursday night. Another trough will drop southward through the Pac NW Thursday. The GFS shows this trough moving eastward into Arizona Thu night and Fri, while the EC is farther west and slower with it, tracking just to the northeast of the area Fri morning. Slight chance POPs have been added across most of the forecast area except the Antelope Valley for Thursday night into Fri at this time. High temps will remain quite cool and there could be more issues for anyone going across the I-5 Corridor Thurday night and Friday. Again, this looks like a light precip maker at this point, but will have to continue to monitor. Models were hinting at a more significant and another cold system the following Monday and Tuesday. So expect the cooler than normal pattern to continue for a while. && .AVIATION... 19/0013Z At 23Z over KLAX, a weak inversion bottom was at 2000 ft and 9 degrees Celsius, and a top at 2600 ft and 11 degrees Celsius. Challenging next 24 hour forecast. Low confidence on timing and heights of ceilings. 30 percent chance of occasional -SHRA and BKN015-025 through 16Z KPRB KSBP KSMX KSMO KLAX KLGB KBUR KVNY. Moderate confidence on timing and strength of winds, with fairly widespread gusty westerly winds. Occasional LLWS and turbulence anywhere, especially over KSBA tonight. KLAX...Low confidence on ceilings, moderate confidence in winds. Periods of BKN015-025 with -SHRA possible through around 12Z. North winds likely over airport 12-16Z Monday, either surfacing or creating LLWS issues. KBUR...Low confidence on ceilings, moderate confidence in winds. Periods of BKN015-025 with -SHRA possible through around 12Z. 10KT LLWS possible from North winds over airport 12-16Z Monday. && .MARINE... 18/709 PM Updated marine forecast, with significant larger sea heights for the next 48 hours, and expanded Gale Warnings to the Santa Barbara Channel and western Santa Monica Basin. High confidence in Gale Force winds (around 35 KT) everywhere by 3 AM tonight, except for the eastern Santa Barbara Channel and the nearshore waters of Los Angeles and Ventura Counties. With the strong winds however, all areas will see dangerous and large short period seas developing tonight. High confidence in the winds expanding and peaking Monday afternoon, with gusts of 30 to 40 KT over all waters. The winds will continue through Monday evening, then weaken through Tuesday, but Small Craft Advisory (SCA) are likely from the Central Coast to San Nicolas Island. Improved conditions are likely on Wednesday. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...High Surf Advisory in effect from 6 AM Monday to 2 PM PST Tuesday for zones 34-35. (See LAXCFWLOX). Hard Freeze Warning in effect from 1 AM to 9 AM PST Tuesday for zones 34>36-38-44. (See LAXNPWLOX). Hard Freeze Warning in effect from 1 AM to 9 AM PST Wednesday for zones 34>36-38-44. (See LAXNPWLOX). Winter Weather Advisory in effect until 3 AM PST Tuesday for zones 38-52>54. (See LAXWSWLOX). Wind Advisory in effect until 10 PM PST Monday for zones 39-52-59. (See LAXNPWLOX). Freeze Warning in effect from 1 AM to 9 AM PST Tuesday for zones 39-40-45. (See LAXNPWLOX). Freeze Warning in effect from 1 AM to 9 AM PST Wednesday for zones 39-40-45. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 9 AM PST Monday for zone 645. (See LAXMWWLOX). Gale Warning in effect from 9 AM to 9 PM PST Monday for zone 645. (See LAXMWWLOX). Gale Warning in effect until 9 PM PST Monday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 1 AM PST Monday for zone 655. (See LAXMWWLOX). Gale Warning in effect from 1 AM to 9 PM PST Monday for zone 655. (See LAXMWWLOX). Gale Warning in effect until 3 AM PST Tuesday for zones 670-673-676. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK (WED-SUN). Widespread temperatures around or below freezing is expected early Wednesday morning away from the beaches, posing a risk for hypothermia and plant damage. && $$ PUBLIC...Kaplan/Kaplan/Bruno AVIATION...Kittell MARINE...Kittell SYNOPSIS...Kj weather.gov/losangeles
Office: STO FXUS66 KSTO 182303 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 303 PM PST Sun Feb 18 2018 .SYNOPSIS... A COLD WEATHER SYSTEM BRINGS BREEZY WINDS AND SNOW OVER THE MOUNTAINS AND FOOTHILLS INTO MONDAY, IMPACTING TRAVEL. THIS WILL BE FOLLOWED BY NEAR RECORD COLD TEMPERATURES WITH A POSSIBLE WIDESPREAD FREEZE. && .DISCUSSION... SCATTERED SHOWERS ARE SPREADING ACROSS THE MOUNTAINS, WITH THE HEAVIEST SHOWERS CURRENTLY OVER THE NORTHERN SIERRA NORTH OF HIGHWAY 50. WEBCAMS ON I80 SHOW MODERATE TO HEAVY SNOW SHOWERS. SNOW SHOWERS OVER THE SIERRA ARE EXPECTED TO BRING SLIPPERY ROADS AND TRAVEL DELAYS. A WINTER WEATHER ADVISORY CONTINUES TO BE IN EFFECT UNTIL 4 PM MONDAY. USE CAUTION IF TRAVELING IN THE MOUNTAINS AND UPPER FOOTHILLS. A DUSTING OF SNOW WILL BE POSSIBLE ACROSS THE FOOTHILLS OVERNIGHT INTO MONDAY. SNOW ACCUMULATIONS ARE NOT EXPECTED TO BE IMPRESSIVE, BUT THIS HOLIDAY WEEKEND TRADITIONALLY SEES A HIGH VOLUME OF TRAFFIC OVER THE MOUNTAINS AND SNOW COULD CAUSE EXACERBATED IMPACTS. WHAT WILL LIKELY BE THE COLDEST AIR OF THE WINTER SEASON WILL BEGIN TO IMPACT PORTIONS OF THE REGION TONIGHT. FOR LOWER ELEVATIONS, THE COLDEST TEMPERATURES TONIGHT WILL LIKELY BE ACROSS THE NORTHERN VALLEY, WHERE SKIES CLEAR AND WINDS SLACKEN. SKIES SHOULD CLEAR FURTHER MONDAY NIGHT INTO TUESDAY MORNING, AND CURRENTLY APPEARS TO BE THE COLDEST NIGHT OF THIS EVENT. WIDESPREAD FREEZE CONDITIONS MAY CONTINUE TUESDAY NIGHT. WIDESPREAD FROST IS EXPECTED. AGRICULTURAL IMPACTS COULD BE SIGNIFICANT, DUE TO AN EARLY BLOOM FROM UNUSUALLY MILD WEATHER IN RECENT WEEKS. PEOPLE SHOULD BEGIN PLANNING NOW ON WAYS TO PROTECT SENSITIVE PLANTS, OUTDOOR PETS, AND OUTDOOR PIPES. ANOTHER SYSTEM WILL BRING LIGHT SNOW SHOWERS TO THE MOUNTAINS ON WEDNESDAY. SNOW LEVELS WILL BE AROUND 1000 FEET, POSSIBLY LOWER, BUT JUST A DUSTING OF SNOW IS EXPECTED. && .EXTENDED DISCUSSION (Thursday THROUGH Sunday) A series of cold shortwave troughs will pass through NorCal for the extended period. Models are more aligned today with timing and placement. The first system arrives Wednesday night into Thursday and will bring precip chances for both the Valley and higher elevations. The best chances for Valley showers will be Thursday afternoon when some weak instability builds in and the trough axis swings through. With not a ton of moisture to work with, precip totals should remain rather low. Low snow levels will be a concern though as they will be 1000 to 2500 feet. Hazardous Mountain travel will be possible Thursday lasting into Friday morning. A weak ridge builds in Friday into early Saturday with another short wave trough passing just to our east on Saturday. This will bring the chances for light showers mainly to the northern Mountains. Another system arrives Sunday into Monday. The EC is just a bit further to the west with it and is able to pull in higher moisture levels but the GFS is drier. Cool temperatures will remain in place for the period running 5-10 below normal to start but will gradually warm a few degrees each day. -CJM && .AVIATION... Generally VFR conditions are expected at the TAF sites the next 24 hours. SCT to BKN clouds between 5000 and 10000 feet can be expected this afternoon rising to around 10000 feet overnight. Scattered snow showers continue in the higher elevations through 15z Monday and MVFR/IFR conditions can be expected in any showers. Breezy northerly winds 15-30 knots diminish to 5-11 knots overnight. -CJM && .STO WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 4 PM PST Monday for West Slope Northern Sierra Nevada. Freeze Warning from 2 AM Monday to 8 AM PST Wednesday for Carquinez Strait and Delta-Central Sacramento Valley-Clear Lake/Southern Lake County-Motherlode-Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta County- Southern Sacramento Valley. && $$
Office: SGX FXUS66 KSGX 190548 AAA AFDSGX Area Forecast Discussion National Weather Service San Diego CA 945 PM PST Sun Feb 18 2018 .SYNOPSIS... Onshore flow will be increasing tonight, becoming strong and gusty over the mountains and deserts as a cold low pressure trough drops south into the Great Basin. Scattered, light rain and snow showers will pop over and west of the mountains late tonight into Monday as the marine layer builds. Expect the coldest days of the winter so far on Monday and Tuesday. Dry and a little warmer for Wednesday and Thursday. Then cooler again into Friday, with a chance for some more scattered showers as another cold low pressure system drops into the Great Basin from the north. Dry and a little warmer into next weekend as temperatures edge back toward average. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... ...Evening Update... Rain showers are developing offshore, likely to move onshore after 10 pm. Most of this activity will be quite light as it moves inland through the night. Snow showers will be likely in the mountains late tonight but again on the light side. With temperatures already down into the mid 40s in the high desert, there is a slight chance of seeing some snow flurries by Monday morning there as well once the cooler air is ushered in by the vigorous trough which will be dropping through California overnight. No significant changes were needed to the forecast this evening. ...Remainder of previous discussion... A longwave trough will dive into the Great Basin on Monday, grazing SoCal with strong onshore winds and scattered light precipitation. It will also bring the coldest air of the season, plunging maximum temps on Monday into the 15 to 20 degrees below normal range. given the extended period of well above normal temps this winter, it will be a profound change. This wave is actually the beginning of a more sustained cooler weather pattern for the SoCal as the longwave is maintained for sometime in the model runs. Various shorter wavelength disturbances will periodically drop into the longwave, creating gusty onshore flow over the coastal waters, mts and deserts, and chances for light precip. So for the foreseeable future, daytime temperatures will be mostly below average. A variety of Warnings and Advisories are in effect from frost/freeze to wind and winter conditions. Please visit our webpage for more detail on all of these. Of most significance will be the strong westerly winds late tonight into Monday. Gusts over 70 MPH are expected on the upper desert slopes and ridge tops, while on the desert floor, it will be breezy, but potentially damaging gusts look to be more isolated and near the foothills late tonight into Monday morning. windy conditions are also expected for coastal San Diego County on Monday. Precipitation will be light and scattered, but it will be cold enough so that some light snow accumulations are forecast above 4000 FT. Freezing conditions on the passes, could create a hazard to travelers. As this system moves east, another, weaker trough slips south across the area midweek with little weather. Temps will moderate some, then a stronger disturbance drops south for Friday. this one could generate more light showers, and gusty winds over the mts/deserts/ coastal waters. Slightly warmer and dry into the weekend, then both the 12Z GFS/ECMWF runs are advertising a stronger system early next week. Who knows, we may be able to salvage some precip before the end of the month. && .AVIATION... 190515Z...Mostly BKN-OVC clouds with bases 2000-4000 ft MSL will prevail through Monday afternoon from the mountains to the coast, with scattered -SHRA, most frequent 07Z-13Z, plus scattered -SHSN in the mountains. Higher terrain will be obscured, with tops to 8000 ft MSL possible, but at TAF sites, most vis will remain above 5 miles. By Monday evening, most areas will have SCT clouds, generally above 3000 ft MSL. Southwest to west winds 25-35 kt with gusts to 55 kt will continue to spread over the mountain crests and desert mountain slopes tonight with these strong winds continuing through Monday afternoon. Areas of west winds 20-30 kt will occur near the coast Monday and will likely bring gusts around 30 kt at KSAN at times. && .MARINE... West-northwest winds will increase to 20-30 kt tonight and continue through Monday night, with gusts 35 to 40 kt possible in the outer waters Monday morning. Combined seas of 9-13 ft with steep waves are likely Monday through Monday evening in the outer waters with 7-11 ft in the inner waters. Conditions will improve Tuesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Winter Weather Advisory from 6 PM this evening to 10 PM PST Monday for Riverside County Mountains-San Bernardino County Mountains-San Diego County Mountains. Wind Advisory from 2 PM this afternoon to 6 PM PST Monday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass Near Banning. High Wind Warning from 2 PM this afternoon to 6 PM PST Monday for Apple and Lucerne Valleys. Frost Advisory from 10 PM Monday to 9 AM PST Tuesday for San Diego County Valleys-San Gorgonio Pass Near Banning. Wind Advisory from 8 AM to 6 PM PST Monday for San Diego County Coastal Areas-San Diego County Valleys. Frost Advisory from 10 PM Tuesday to 8 AM PST Wednesday for San Bernardino and Riverside County Valleys-The Inland Empire. Freeze Warning from 10 PM Monday to 9 AM PST Tuesday for San Bernardino and Riverside County Valleys-The Inland Empire. PZ...Gale Warning from 10 PM this evening to 6 AM PST Tuesday for Waters from San Mateo point to the Mexican Border Extending 30 to 60 nm out including San Clemente Island. Small Craft Advisory from 10 PM this evening to 6 AM PST Tuesday for Coastal Waters from San Mateo Point to the Mexican Border and out to 30 nm. && $$ PUBLIC...jad/jmb AVIATION/MARINE...Maxwell
Office: MTR FXUS66 KMTR 190512 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 912 PM PST Sun Feb 18 2018 .SYNOPSIS...Blustery and much colder weather conditions developed across the region today in wake of a strong frontal passage. Scattered post frontal showers will occur tonight into Monday morning, mainly near the coast and in Santa Cruz and Santa Lucia Mountains. Snow levels are forecast to drop to or below 1,000 feet by Monday morning. Widespread freezing temperatures are then expected for inland areas once winds subside Monday night into Tuesday morning. Cool and unsettled weather is expected to persist through the end of the week and into early next week. && .DISCUSSION...As of 9:10 PM PST Sunday...A strong, but mostly dry, cold front swept across our region earlier today. As expected, blustery and much cooler conditions developed behind the front. Local wind gust of up to 45 mph were observed along the coast and in the hills today. Today's high temperatures were generally 10 to 20 degrees cooler compared to Saturday. Scattered showers developed late this afternoon in the cold and unstable post frontal environment. Most of these showers were confined to the coastal waters, as well as coastal San Mateo and Santa Cruz Counties, and northwest Monterey County. These showers have been brief and rain totals thus far have been just a few hundredths. Models have been consistent in developing more widespread shower activity overnight as the upper trough continues to dig south and drags an even colder and more unstable airmass across our region. Precipitation overnight is expected to be concentrated in coastal areas and especially in the Santa Cruz Mountains and northern Santa Lucia mountain range of Monterey County. Very little, if any, precipitation is expected in the North and East Bay (except northwest Sonoma County). In general, the bulk of tonight and tomorrow morning's rain and snow is expected to fall west of highway 101. Snow levels are currently at about 2000-2500 feet but are expected to drop to 1500 feet overnight and 1000 feet on Monday morning. Snow could even fall briefly as low as 500 feet in heavier showers. Latest HRRR and WRF models agree on where the greatest precipitation totals will occur through midday Monday. Both models forecast liquid precipitation of about a quarter to a third of an inch in the Santa Cruz Mountains and maximum amounts of a half inch (HRRR) and 1 inch (WRF) in the Santa Lucias. Given the anticipated low snow levels these QPF values would translate into between 2 and 4 inches of snow at the higher elevations of the Santa Cruz Mountains and from 5 to 10 inches in the Santa Lucia Mountains. The primary impact from a travel standpoint will be near the summit of highway 17 in Santa Cruz County and along Skyline Boulevard (highway 35) in the Santa Cruz Mountains. A Winter Weather Advisory is in effect from midnight tonight until 10 am Monday for the Santa Cruz Mountains and Santa Lucia Mountains. The models agree that precipitation will taper off by mid morning on Monday and mostly end by midday. Blustery conditions continue near the coast and locally in the hills this evening with northwest winds gusting between 30 and 40 mph. Expect gusty winds to persist overnight and then increase slightly again by Monday afternoon, especially along the coast. Based on the 12Z WRF wind output, a wind advisory may be needed for coastal areas on Monday afternoon, but it looks like a marginal event. Therefore, will wait for all the 00Z model data before making a determination on any possible wind advisories. Winds will subside in all areas on Monday evening. Once precipitation and clouds depart on Monday, and winds subside on Monday evening, the stage will be set for very cold temperatures late Monday night into Tuesday morning. Latest model guidance is consistent with previous guidance in indicating widespread overnight lows ranging from the mid 20s to lower 30s across inland areas early Tuesday morning and mostly in the 30s near the coast. A Freeze Warning is in effect for all of our inland areas late Monday night into Tuesday morning. In addition, a Frost Advisory has been issued for all of our coastal and bayside zones (except the city of San Francisco) for the same time period. A shortwave trough is forecast to drop south just offshore on Tuesday night. The models agree that nearly all precipitation with this disturbance will remain offshore. However, enough clouds are expected to spread across our area on Tuesday night to keep temperatures from dropping below freezing at most locations. Therefore, it appears unlikely that freeze warnings/frost advisories will need to be reissued for Tuesday night/Wednesday morning. The models maintain a cool and unsettled pattern through the rest of the week with another system forecast to drop in from the north Wednesday night into Thursday. The 12Z ECMWF brings in yet another system Thursday night into Friday. These systems are forecast to be cold, but not as cold as our current system. Thus snow levels will likely remain above 1500 feet. Longer range models show a potentially more potent and wetter system arriving sometime early next week. && .AVIATION...As of 5:30 PM PST Sunday...Cold northwest flow settling over the area with scattered cumulus clouds. A few showers are developing offshore and coming onshore around Monterey Bay. This should continue through this evening with possibly an increase in activity after 10Z from the MRY Bay Area south. Winds gusting as high as 30-35 kt through at least 04Z. Vicinity of KSFO...VFR. West winds 25 kt gusting to 35 kt through at least 04Z. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...A few passing showers in MRY early tonight but mainly VFR. MVFR cigs with shower activity increasing after 10Z. && .CLIMATE... Here are record low temperatures and the years they occurred for Monday through Wednesday this week. Location Monday Tuesday Wednesday SF Bay Area Healdsburg 28 in 1932 22 in 1922 28 in 1929 Santa Rosa 26 in 1932 26 in 1913 26 in 1913 Calistoga 25 in 1918 25 in 2006 25 in 2006 Kentfield 27 in 1932 27 in 1913 29 in 1953 San Rafael 32 in 1990 32 in 2006 33 in 1955 Napa 29 in 1990 28 in 1920 29 in 1955 San Francisco 38 in 1897 38 in 1897 36 in 1890 SFO Airport 36 in 1990 37 in 2011 34 in 1955 Half Moon Bay 34 in 1954 32 in 2013 31 in 2006 Oakland Airport 35 in 1955 34 in 2006 33 in 1955 Richmond 35 in 1990 35 in 1990 35 in 1981 Livermore 27 in 1956 28 in 1942 27 in 1955 Moffett Field 35 in 1949 34 in 2006 32 in 1955 San Jose 32 in 1990 30 in 1897 25 in 1897 Gilroy 27 in 1964 30 in 1990 31 in 1976 Monterey Bay Area Santa Cruz 30 in 1990 29 in 1913 30 in 1955 Salinas 29 in 1990 31 in 2006 31 in 1970 Salinas Airport 29 in 1933 28 in 1953 30 in 1953 Monterey 35 in 1990 35 in 2006 36 in 1952 King City 25 in 1955 22 in 1953 23 in 1953 && .MARINE...As of 9:02 PM PST Sunday...A 1039 mb high is centered 800 miles west of Cape Mendocino while a 995 mb low is over Utah. The strong pressure gradients will bring gusty northerly winds through Monday night. Winds will decrease Tuesday as the low moves east but another system may affect the area later in the week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...Winter Weather Advisory...Santa Cruz Mountains and Santa Lucia Mountains SCA...SF Bay SCA...Mry Bay SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pt Reyes to Pigeon Pt 0-10 nm SCA...Pigeon Pt to Pt Pinos 0-10 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm GLW...Pt Arena to Pigeon Pt 10-60 nm GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm && $$ PUBLIC FORECAST: Dykema AVIATION: W Pi MARINE: W Pi 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