Area Forecast Discussion
FXUS66 KMTR [Monterey CA] 280448 AFDMTR ∨
FXUS66 KMTR 280448 AFDMTR [HEAD]
National Weather Service San Francisco Bay Area 8:48pm PST Fri Nov 27 2015 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 848 PM PST FRI NOV 27 2015 [HEAD]
Synopsis. Dry and cool weather will continue through the weekend with areas of nighttime freezing temperatures forecast across inland areas. Temperatures will begin to moderate early next week. There is also a chance of rain developing by the middle portion of next week. ∨
.SYNOPSIS...DRY AND COOL WEATHER WILL CONTINUE THROUGH THE WEEKEND WITH AREAS OF NIGHTTIME FREEZING TEMPERATURES FORECAST ACROSS INLAND AREAS. TEMPERATURES WILL BEGIN TO MODERATE EARLY NEXT WEEK. THERE IS ALSO A CHANCE OF RAIN DEVELOPING BY THE MIDDLE PORTION OF NEXT WEEK. [DISC]
Discussion. As of 8:45pm PST Friday… north winds brought a drier airmass into our region last night and today. This drier airmass allowed temps to climb a bit higher today compared to yesterday and a few locations managed to make it into the lower 60s. Even so… temperatures remained below normal in most areas even with a full day of sunshine. ∨
.DISCUSSION...AS OF 8:45 PM PST FRIDAY...NORTH WINDS BROUGHT A DRIER AIRMASS INTO OUR REGION LAST NIGHT AND TODAY. THIS DRIER AIRMASS ALLOWED TEMPS TO CLIMB A BIT HIGHER TODAY COMPARED TO YESTERDAY AND A FEW LOCATIONS MANAGED TO MAKE IT INTO THE LOWER 60S. EVEN SO...TEMPERATURES REMAINED BELOW NORMAL IN MOST AREAS EVEN WITH A FULL DAY OF SUNSHINE. [DISC]
The main weather story continues to be cold nighttime temperatures. Winds persisted longer than expected last night and these winds helped hold temps up… particularly in the North Bay valleys. But temperatures did drop to freezing or below in most inland areas from Santa Clara County southward last night. Four minimum temperature records were set or tied early this morning (see record event report for more details). ∨
THE MAIN WEATHER STORY CONTINUES TO BE COLD NIGHTTIME TEMPERATURES. WINDS PERSISTED LONGER THAN EXPECTED LAST NIGHT AND THESE WINDS HELPED HOLD TEMPS UP...PARTICULARLY IN THE NORTH BAY VALLEYS. BUT TEMPERATURES DID DROP TO FREEZING OR BELOW IN MOST INLAND AREAS FROM SANTA CLARA COUNTY SOUTHWARD LAST NIGHT. FOUR MINIMUM TEMPERATURE RECORDS WERE SET OR TIED EARLY THIS MORNING (SEE RECORD EVENT REPORT FOR MORE DETAILS). [DISC]
North winds remain locally moderate and gusty in the North Bay mountains this evening… but winds in the valleys have eased and so temperatures at 8pm were running as much as 9° cooler than last evening in the North Bay valleys. Expect winds to be lighter in most areas tonight which will likely result in cooler overnight temps. Overnight lows are expected to dip into the mid and upper 20s in the coldest inland valleys by daybreak Saturday. Elsewhere overnight lows will mostly be in the low to mid 30s. A Freeze Warning is in effect for all inland locations from late tonight through mid-morning Saturday. A Frost Advisory is in effect for coastal areas (except San Francisco) during this same time period. ∨
NORTH WINDS REMAIN LOCALLY MODERATE AND GUSTY IN THE NORTH BAY MOUNTAINS THIS EVENING...BUT WINDS IN THE VALLEYS HAVE EASED AND SO TEMPERATURES AT 8 PM WERE RUNNING AS MUCH AS 9 DEGREES COOLER THAN LAST EVENING IN THE NORTH BAY VALLEYS. EXPECT WINDS TO BE LIGHTER IN MOST AREAS TONIGHT WHICH WILL LIKELY RESULT IN COOLER OVERNIGHT TEMPS. OVERNIGHT LOWS ARE EXPECTED TO DIP INTO THE MID AND UPPER 20S IN THE COLDEST INLAND VALLEYS BY DAYBREAK SATURDAY. ELSEWHERE OVERNIGHT LOWS WILL MOSTLY BE IN THE LOW TO MID 30S. A FREEZE WARNING IS IN EFFECT FOR ALL INLAND LOCATIONS FROM LATE TONIGHT THROUGH MID-MORNING SATURDAY. A FROST ADVISORY IS IN EFFECT FOR COASTAL AREAS (EXCEPT SAN FRANCISCO) DURING THIS SAME TIME PERIOD. [DISC]
The synoptic pattern is not forecast to change much through the weekend. A cold cutoff low [A closed upper-level low which has become completely displaced (cut off) from basic westerly current, and moves independently of that current. Cutoff lows may remain nearly stationary for days, or on occasion may move westward opposite to the prevailing flow aloft] will remain centered over the Great Basin while a high amplitude ridge persists just off the West Coast. The temperature of the airmass aloft is forecast to warm slightly through the weekend. However… with light winds and low sun angle there will be no mechanism to scour out the cold airmass in the low levels and so cold nights will persist through the weekend. In fact… most model guidance indicates that Saturday night will be a bit colder than tonight in most inland locations… probably due to winds becoming light and variable by then. For example… the NAM [North American Meso (formerly Eta) model] MOS [Model Output Statistics] guidance forecasts a low of 20° at the Napa Airport early Sunday morning. So it's highly likely that the Freeze Warning/Frost Advisory will be re-issued for Saturday night/Sunday morning. Slight moderation in temps is expected by Sunday night… but even so we will likely meet Freeze Warning criteria for one more night. ∨
THE SYNOPTIC PATTERN IS NOT FORECAST TO CHANGE MUCH THROUGH THE WEEKEND. A COLD CUTOFF LOW WILL REMAIN CENTERED OVER THE GREAT BASIN WHILE A HIGH AMPLITUDE RIDGE PERSISTS JUST OFF THE WEST COAST. THE TEMPERATURE OF THE AIRMASS ALOFT IS FORECAST TO WARM SLIGHTLY THROUGH THE WEEKEND. HOWEVER...WITH LIGHT WINDS AND LOW SUN ANGLE THERE WILL BE NO MECHANISM TO SCOUR OUT THE COLD AIRMASS IN THE LOW LEVELS AND SO COLD NIGHTS WILL PERSIST THROUGH THE WEEKEND. IN FACT...MOST MODEL GUIDANCE INDICATES THAT SATURDAY NIGHT WILL BE A BIT COLDER THAN TONIGHT IN MOST INLAND LOCATIONS...PROBABLY DUE TO WINDS BECOMING LIGHT AND VARIABLE BY THEN. FOR EXAMPLE...THE NAM MOS GUIDANCE FORECASTS A LOW OF 20 DEGREES AT THE NAPA AIRPORT EARLY SUNDAY MORNING. SO IT`S HIGHLY LIKELY THAT THE FREEZE WARNING/FROST ADVISORY WILL BE RE-ISSUED FOR SATURDAY NIGHT/SUNDAY MORNING. SLIGHT MODERATION IN TEMPS IS EXPECTED BY SUNDAY NIGHT...BUT EVEN SO WE WILL LIKELY MEET FREEZE WARNING CRITERIA FOR ONE MORE NIGHT. [DISC]
The models agree that the high amplitude ridge offshore will begin to weaken and shift eastward early next week. Previous model runs had indicated that a weak Pacific frontal system would reach the West Coast by late Monday and produce at least light precipitation in our area. But recent model runs… particularly the 00Z [4pm PST] NAM [North American Meso (formerly Eta) model] and 00Z [4pm PST] GFS [Global Forecast System: global spectral model used primarily for aviation weather forecasts; provides guidance out to 384 hours at 00, 06, 12 and 18UTC.]… show that system completely washing out offshore prior to reaching the coast. Have therefore gone ahead and almost entirely removed rain chances for late Monday and Monday night. We should at least get an increase in clouds by late Monday and an influx of warmer air as the flow aloft changes from north to west. Thus… nighttime temps are expected to finally moderate and climb above freezing in nearly all areas by Monday night. ∨
THE MODELS AGREE THAT THE HIGH AMPLITUDE RIDGE OFFSHORE WILL BEGIN TO WEAKEN AND SHIFT EASTWARD EARLY NEXT WEEK. PREVIOUS MODEL RUNS HAD INDICATED THAT A WEAK PACIFIC FRONTAL SYSTEM WOULD REACH THE WEST COAST BY LATE MONDAY AND PRODUCE AT LEAST LIGHT PRECIPITATION IN OUR AREA. BUT RECENT MODEL RUNS...PARTICULARLY THE 00Z NAM AND 00Z GFS...SHOW THAT SYSTEM COMPLETELY WASHING OUT OFFSHORE PRIOR TO REACHING THE COAST. HAVE THEREFORE GONE AHEAD AND ALMOST ENTIRELY REMOVED RAIN CHANCES FOR LATE MONDAY AND MONDAY NIGHT. WE SHOULD AT LEAST GET AN INCREASE IN CLOUDS BY LATE MONDAY AND AN INFLUX OF WARMER AIR AS THE FLOW ALOFT CHANGES FROM NORTH TO WEST. THUS...NIGHTTIME TEMPS ARE EXPECTED TO FINALLY MODERATE AND CLIMB ABOVE FREEZING IN NEARLY ALL AREAS BY MONDAY NIGHT. [DISC]
The medium range models agree in bringing a reasonably robust storm system into northern and central California by next Wednesday night or Thursday and this appears to be our next best shot at rainfall. ∨
THE MEDIUM RANGE MODELS AGREE IN BRINGING A REASONABLY ROBUST STORM SYSTEM INTO NORTHERN AND CENTRAL CALIFORNIA BY NEXT WEDNESDAY NIGHT OR THURSDAY AND THIS APPEARS TO BE OUR NEXT BEST SHOT AT RAINFALL. [DISC]
Aviation. As of 3:50pm PST Friday… VFR [Visual Flight Rules] conditions expected to continue to through the night at all terminals as the air mass remains dry and the flow offshore. ∨
.AVIATION...AS OF 3:50 PM PST FRIDAY...VFR CONDS EXPECTED TO CONTINUE TO THROUGH THE NIGHT AT ALL TERMINALS AS THE AIR MASS REMAINS DRY AND THE FLOW OFFSHORE. [AVIA]
Vicinity of KSFO [San Francisco CA]… VFR [Visual Flight Rules]. Light winds. ∨
VICINITY OF KSFO...VFR. LIGHT WINDS. [AVI2]
KSFO [San Francisco CA] bridge approach… VFR [Visual Flight Rules]. Light winds. ∨
KSFO BRIDGE APPROACH...VFR. LIGHT WINDS. [AVI2]
Monterey Bay Area terminals… VFR [Visual Flight Rules]. Light winds. ∨
MONTEREY BAY AREA TERMINALS...VFR. LIGHT WINDS. [AVI2]
Marine. As of 2:03pm PST Friday… little change expected over the coastal waters with light winds and seas continuing through Saturday. Winds and seas are expected to increase early Monday as a weak frontal system moves into the California coastal waters. ∨
.MARINE...AS OF 2:03 PM PST FRIDAY...LITTLE CHANGE EXPECTED OVER THE COASTAL WATERS WITH LIGHT WINDS AND SEAS CONTINUING THROUGH SATURDAY. WINDS AND SEAS ARE EXPECTED TO INCREASE EARLY MONDAY AS A WEAK FRONTAL SYSTEM MOVES INTO THE CALIFORNIA COASTAL WATERS. [AVIA]
.MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...FROST ADVISORY...ALL COASTAL ZONES EXCEPT SAN FRANCISCO FREEZE WARNING...ALL INLAND ZONES [WARN]
Public Forecast: Dykema; Aviation: Blier; Marine: DRP ∨
PUBLIC FORECAST: DYKEMA AVIATION: BLIER MARINE: DRP [CRED]
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27 Nov 9:15pm PST
Tonight Clear, with a low around 38°. South wind 9 to 14 mph becoming NNE in the evening. Winds could gust as high as 18 mph.
Saturday Sunny, with a high near 58°. Breezy, with an ENE wind 14 to 22 mph, with gusts as high as 26 mph.
Saturday Night Mostly clear, with a low around 39°. East wind around 14 mph.
Sunday Sunny, with a high near 59°. ENE wind 6 to 13 mph.
Sunday Night Partly cloudy, with a low around 41°. East wind 3 to 6 mph.
Monday Partly sunny, with a high near 59°.
Monday Night A 20% chance of rain. Mostly cloudy, with a low around 41°.
Tuesday Partly sunny, with a high near 61°.
Tuesday Night Mostly cloudy, with a low around 43°.
Wednesday Partly sunny, with a high near 61°.
Wednesday Night A slight chance of rain. Mostly cloudy, with a low around 46°.
Thursday A chance of rain. Partly sunny, with a high near 61°.
Thursday Night A chance of rain. Mostly cloudy, with a low around 45°.
Friday A slight chance of rain. Partly sunny, with a high near 61°.
Clear, with a low around 38. South wind 9 to 14 mph becoming north northeast in the evening. Winds could gust as high as 18 mph.
Sunny, with a high near 58. Breezy, with an east northeast wind 14 to 22 mph, with gusts as high as 26 mph.
Mostly clear, with a low around 39. East wind around 14 mph.
Sunny, with a high near 59. East northeast wind 6 to 13 mph.
Partly cloudy, with a low around 41. East wind 3 to 6 mph.
Partly sunny, with a high near 59.
A 20 percent chance of rain. Mostly cloudy, with a low around 41.
Partly sunny, with a high near 61.
Mostly cloudy, with a low around 43.
Partly sunny, with a high near 61.
A slight chance of rain. Mostly cloudy, with a low around 46.
A chance of rain. Partly sunny, with a high near 61.
A chance of rain. Mostly cloudy, with a low around 45.
A slight chance of rain. Partly sunny, with a high near 61.