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Area Forecast Discussion

FXUS66 KMTR [Monterey CA] 121729 AFDMTR ∨

FXUS66 KMTR 121729
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 9:29am PST Wed Dec 12 2018 ∨

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
929 AM PST WED DEC 12 2018 [HEAD]

Synopsis. Dry conditions are forecast to continue across our region through Thursday night. Daytime temperatures will be mild while nights will be seasonably cool. Patchy fog could redevelop tonight across the area, especially in the valleys. A weak weather system will likely produce light rain on Friday and Friday night, especially for areas north of the Golden Gate. Periods of light rain may continue into Saturday and Saturday night, mainly in the North Bay. A stronger and wetter system is then expected to produce widespread rain across our entire region Sunday and Sunday night. Dry weather will likely return by late Monday. ∨

.SYNOPSIS...DRY CONDITIONS ARE FORECAST TO CONTINUE ACROSS OUR
REGION THROUGH THURSDAY NIGHT. DAYTIME TEMPERATURES WILL BE MILD
WHILE NIGHTS WILL BE SEASONABLY COOL. PATCHY FOG COULD REDEVELOP
TONIGHT ACROSS THE AREA, ESPECIALLY IN THE VALLEYS. A WEAK
WEATHER SYSTEM WILL LIKELY PRODUCE LIGHT RAIN ON FRIDAY AND FRIDAY
NIGHT, ESPECIALLY FOR AREAS NORTH OF THE GOLDEN GATE. PERIODS OF
LIGHT RAIN MAY CONTINUE INTO SATURDAY AND SATURDAY NIGHT, MAINLY
IN THE NORTH BAY. A STRONGER AND WETTER SYSTEM IS THEN EXPECTED TO
PRODUCE WIDESPREAD RAIN ACROSS OUR ENTIRE REGION SUNDAY AND
SUNDAY NIGHT. DRY WEATHER WILL LIKELY RETURN BY LATE MONDAY. [DISC]

Discussion. As of 09:15am PST Wednesday… a system moving to our north brought high clouds overnight, which limited fog formation. Fog remained patchy this morning and was generally not dense, with only the North Bay reporting localized areas of visibilities below one mile at times. A few locations across the Bay Area experienced light drizzle from low clouds, with San Jose managing to record one hundredth of an inch of precipitation from the drizzle. Low clouds will dissipate by late morning and the afternoon will feature only occasional high clouds. High temperatures today will be similar to yesterday with perhaps a couple degrees of warming in some locations. Mostly clear skies are expected tonight under a ridge of high pressure. This will allow temperatures to drop to values cooler than what was experienced this morning, and likely the coolest for the next several nights. Temperatures will fall into the 30s across most inland valley locations with 40s near the coast or the SF Bay. The cool overnight temperatures and mostly clear skies will allow for patchy fog to redevelop overnight. Looking ahead, a series of storm systems will then impact the area, one on Friday and into Saturday and other on Sunday and into Monday. See the previous discussion for additional details. No updates planned this morning as short term forecast remains on track. ∨

.DISCUSSION...AS OF 09:15 AM PST WEDNESDAY...A SYSTEM MOVING TO
OUR NORTH BROUGHT HIGH CLOUDS OVERNIGHT, WHICH LIMITED FOG
FORMATION. FOG REMAINED PATCHY THIS MORNING AND WAS GENERALLY NOT
DENSE, WITH ONLY THE NORTH BAY REPORTING LOCALIZED AREAS OF
VISIBILITIES BELOW ONE MILE AT TIMES. A FEW LOCATIONS ACROSS THE
BAY AREA EXPERIENCED LIGHT DRIZZLE FROM LOW CLOUDS, WITH SAN JOSE
MANAGING TO RECORD ONE HUNDREDTH OF AN INCH OF PRECIPITATION FROM
THE DRIZZLE. LOW CLOUDS WILL DISSIPATE BY LATE MORNING AND THE
AFTERNOON WILL FEATURE ONLY OCCASIONAL HIGH CLOUDS. HIGH
TEMPERATURES TODAY WILL BE SIMILAR TO YESTERDAY WITH PERHAPS A
COUPLE DEGREES OF WARMING IN SOME LOCATIONS. MOSTLY CLEAR SKIES
ARE EXPECTED TONIGHT UNDER A RIDGE OF HIGH PRESSURE. THIS WILL
ALLOW TEMPERATURES TO DROP TO VALUES COOLER THAN WHAT WAS
EXPERIENCED THIS MORNING, AND LIKELY THE COOLEST FOR THE NEXT
SEVERAL NIGHTS. TEMPERATURES WILL FALL INTO THE 30S ACROSS MOST
INLAND VALLEY LOCATIONS WITH 40S NEAR THE COAST OR THE SF BAY. THE
COOL OVERNIGHT TEMPERATURES AND MOSTLY CLEAR SKIES WILL ALLOW FOR
PATCHY FOG TO REDEVELOP OVERNIGHT. LOOKING AHEAD, A SERIES OF
STORM SYSTEMS WILL THEN IMPACT THE AREA, ONE ON FRIDAY AND INTO
SATURDAY AND OTHER ON SUNDAY AND INTO MONDAY. SEE THE PREVIOUS
DISCUSSION FOR ADDITIONAL DETAILS. NO UPDATES PLANNED THIS MORNING
AS SHORT TERM FORECAST REMAINS ON TRACK. [DISC]

Previous discussion… as of 3:20am PST Wednesday. A weather system moving inland to our north brought considerable high clouds to our region overnight, but no rainfall. Also, areas of low clouds developed overnight, but only patchy light fog has formed thus far. Given the amount of cloud cover in place, feel it's unlikely we will see widespread fog develop prior to sunrise. ∨

.PREV DISCUSSION...AS OF 3:20 AM PST WEDNESDAY...A WEATHER SYSTEM
MOVING INLAND TO OUR NORTH BROUGHT CONSIDERABLE HIGH CLOUDS TO OUR
REGION OVERNIGHT, BUT NO RAINFALL. ALSO, AREAS OF LOW CLOUDS
DEVELOPED OVERNIGHT, BUT ONLY PATCHY LIGHT FOG HAS FORMED THUS
FAR. GIVEN THE AMOUNT OF CLOUD COVER IN PLACE, FEEL IT`S UNLIKELY
WE WILL SEE WIDESPREAD FOG DEVELOP PRIOR TO SUNRISE. [DISC]

The system to our north will move quickly off to the east today while an upper ridge offshore builds inland over California. After morning low clouds and fog clear, expect a mostly sunny day except for occasional high clouds. High temperatures today should be slightly warmer than yesterday. Mostly clear skies and light winds will mean chilly conditions tonight with lows dipping into the lower to mid 30s in the coolest inland valleys. Also, expect patchy fog again by late tonight, especially in the valleys. The upper ridge will maintain dry and mild conditions on Thursday, along with a continued warming trend across the southern portion of our region where high temperatures will climb into the mid and upper 60s. Increasing high clouds on Thursday night are expected to hold temps up a bit. ∨

THE SYSTEM TO OUR NORTH WILL MOVE QUICKLY OFF TO THE EAST TODAY
WHILE AN UPPER RIDGE OFFSHORE BUILDS INLAND OVER CALIFORNIA. AFTER
MORNING LOW CLOUDS AND FOG CLEAR, EXPECT A MOSTLY SUNNY DAY EXCEPT
FOR OCCASIONAL HIGH CLOUDS. HIGH TEMPERATURES TODAY SHOULD BE
SLIGHTLY WARMER THAN YESTERDAY. MOSTLY CLEAR SKIES AND LIGHT WINDS
WILL MEAN CHILLY CONDITIONS TONIGHT WITH LOWS DIPPING INTO THE
LOWER TO MID 30S IN THE COOLEST INLAND VALLEYS. ALSO, EXPECT
PATCHY FOG AGAIN BY LATE TONIGHT, ESPECIALLY IN THE VALLEYS. THE
UPPER RIDGE WILL MAINTAIN DRY AND MILD CONDITIONS ON THURSDAY,
ALONG WITH A CONTINUED WARMING TREND ACROSS THE SOUTHERN PORTION
OF OUR REGION WHERE HIGH TEMPERATURES WILL CLIMB INTO THE MID AND
UPPER 60S. INCREASING HIGH CLOUDS ON THURSDAY NIGHT ARE EXPECTED
TO HOLD TEMPS UP A BIT. [DISC]

Rain chances return to our region on Friday when a frontal system arrives over Northern California. Models agree that most rainfall will hold off until Friday afternoon, but both the NAM [North American Meso (formerly Eta) model] and ECMWF [European Center for Medium-Range Weather Forecasts model] forecast spotty light warm advection rainfall as early as Friday morning in advance of the main frontal rain band. Models have come into better agreement with respect to rainfall location and amounts with this system. Widespread light rain is forecast to spread across the North Bay Friday afternoon and evening, with only spotty light rain expected across the San Francisco Peninsula and East Bay, and little or no rain for points south. The front is forecast to stall and mostly dissipate over the SF Bay Area by Friday night. This weak remnant frontal boundary is then expected to remain draped across the Bay Area through Saturday and Saturday night, producing periods of light precipitation, mainly over the North Bay. Rainfall accumulations from Friday through Saturday night are generally forecast to be a quarter inch or less, except up to a half inch in the North Bay. Most of this rain will likely fall on Friday afternoon and evening. ∨

RAIN CHANCES RETURN TO OUR REGION ON FRIDAY WHEN A FRONTAL SYSTEM
ARRIVES OVER NORTHERN CALIFORNIA. MODELS AGREE THAT MOST RAINFALL
WILL HOLD OFF UNTIL FRIDAY AFTERNOON, BUT BOTH THE NAM AND ECMWF
FORECAST SPOTTY LIGHT WARM ADVECTION RAINFALL AS EARLY AS FRIDAY
MORNING IN ADVANCE OF THE MAIN FRONTAL RAIN BAND. MODELS HAVE
COME INTO BETTER AGREEMENT WITH RESPECT TO RAINFALL LOCATION AND
AMOUNTS WITH THIS SYSTEM. WIDESPREAD LIGHT RAIN IS FORECAST TO
SPREAD ACROSS THE NORTH BAY FRIDAY AFTERNOON AND EVENING, WITH
ONLY SPOTTY LIGHT RAIN EXPECTED ACROSS THE SAN FRANCISCO PENINSULA
AND EAST BAY, AND LITTLE OR NO RAIN FOR POINTS SOUTH. THE FRONT
IS FORECAST TO STALL AND MOSTLY DISSIPATE OVER THE SF BAY AREA BY
FRIDAY NIGHT. THIS WEAK REMNANT FRONTAL BOUNDARY IS THEN EXPECTED
TO REMAIN DRAPED ACROSS THE BAY AREA THROUGH SATURDAY AND
SATURDAY NIGHT, PRODUCING PERIODS OF LIGHT PRECIPITATION, MAINLY
OVER THE NORTH BAY. RAINFALL ACCUMULATIONS FROM FRIDAY THROUGH
SATURDAY NIGHT ARE GENERALLY FORECAST TO BE A QUARTER INCH OR
LESS, EXCEPT UP TO A HALF INCH IN THE NORTH BAY. MOST OF THIS RAIN
WILL LIKELY FALL ON FRIDAY AFTERNOON AND EVENING. [DISC]

The models have consistently indicated that the following system, due to arrive by Sunday afternoon, will be both stronger and wetter, producing widespread moderate rainfall across our region from Sunday afternoon through Sunday night. There could be a brief period of heavy rain just prior to frontal passage, especially in the North Bay on Sunday afternoon. Rainfall totals with the Sunday/Sunday night system are projected to range from 0.50–1.50", with potentially higher amounts in the North Bay. Gusty south winds are also likely for a short period of time just ahead of the front on Sunday, with the strongest winds expected along the North Bay coast and in the coastal hills. ∨

THE MODELS HAVE CONSISTENTLY INDICATED THAT THE FOLLOWING SYSTEM,
DUE TO ARRIVE BY SUNDAY AFTERNOON, WILL BE BOTH STRONGER AND
WETTER, PRODUCING WIDESPREAD MODERATE RAINFALL ACROSS OUR REGION
FROM SUNDAY AFTERNOON THROUGH SUNDAY NIGHT. THERE COULD BE A BRIEF
PERIOD OF HEAVY RAIN JUST PRIOR TO FRONTAL PASSAGE, ESPECIALLY IN
THE NORTH BAY ON SUNDAY AFTERNOON. RAINFALL TOTALS WITH THE
SUNDAY/SUNDAY NIGHT SYSTEM ARE PROJECTED TO RANGE FROM
0.50-1.50", WITH POTENTIALLY HIGHER AMOUNTS IN THE NORTH BAY.
GUSTY SOUTH WINDS ARE ALSO LIKELY FOR A SHORT PERIOD OF TIME JUST
AHEAD OF THE FRONT ON SUNDAY, WITH THE STRONGEST WINDS EXPECTED
ALONG THE NORTH BAY COAST AND IN THE COASTAL HILLS. [DISC]

Showers may linger into Monday morning, but the models agree that dry conditions will develop in most areas by Monday afternoon. An upper ridge is forecast to build in quickly behind the departing system on Monday and this ridge will likely bring dry and mild weather to most of our region from late Monday through at least Thursday of next week. However, the ECMWF [European Center for Medium-Range Weather Forecasts model] indicates that moist flow over the top of the ridge may result in rain across portions of the North Bay late Monday night and Tuesday. ∨

SHOWERS MAY LINGER INTO MONDAY MORNING, BUT THE MODELS AGREE THAT
DRY CONDITIONS WILL DEVELOP IN MOST AREAS BY MONDAY AFTERNOON. AN
UPPER RIDGE IS FORECAST TO BUILD IN QUICKLY BEHIND THE DEPARTING
SYSTEM ON MONDAY AND THIS RIDGE WILL LIKELY BRING DRY AND MILD
WEATHER TO MOST OF OUR REGION FROM LATE MONDAY THROUGH AT LEAST
THURSDAY OF NEXT WEEK. HOWEVER, THE ECMWF INDICATES THAT MOIST
FLOW OVER THE TOP OF THE RIDGE MAY RESULT IN RAIN ACROSS PORTIONS
OF THE NORTH BAY LATE MONDAY NIGHT AND TUESDAY. [DISC]

Aviation. As of 9:30am PST Wednesday… for 18Z [10am PST] TAFs [Terminal Aerodrome Forecasts]. VFR [Visual Flight Rules] expected today except early at Livermore where some residual tule fog [Radiation fog in the Central Valley of California. It forms during night and morning hours in late fall and winter months following the first significant rainfall.] is impacting visibilities. Should clear out by 20Z [12pm PST]. Winds will be mostly light offshore with high cirrus clouds. ∨

.AVIATION....AS OF 9:30 AM PST WEDNESDAY...FOR 18Z TAFS. VFR
EXPECTED TODAY EXCEPT EARLY AT LVK WHERE SOME RESIDUAL TULE FOG IS
IMPACTING VISIBILITIES. SHOULD CLEAR OUT BY 20Z. WINDS WILL BE
MOSTLY LIGHT OFFSHORE WITH HIGH CIRRUS CLOUDS. [AVIA]

Vicinity of KSFO [San Francisco CA]… VFR [Visual Flight Rules]. ∨

VICINITY OF KSFO...VFR. [AVI2]

SFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨

SFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2]

Monterey Bay terminals… VFR [Visual Flight Rules] except at KSNS [Salinas CA] until 19Z [11am PST]. ∨

MONTEREY BAY TERMINALS...VFR EXCEPT AT KSNS UNTIL 19Z. [AVI2]

Marine. As of 8:41am PST Wednesday… breezy northerly winds behind a passing cold front will gradually subside later this afternoon and evening over the coastal waters. Winds will then become southerly by late Thursday and Friday ahead of a weekend system. A series of west to northwest swell trains will arrive to the waters over the coming days, creating hazardous conditions for small vessels. The most significant long-period swell is forecast to arrive by late Sunday or Monday, which has the potential to bring open water swells of 20 feet or more. ∨

.MARINE...AS OF 8:41 AM PST WEDNESDAY...BREEZY NORTHERLY WINDS
BEHIND A PASSING COLD FRONT WILL GRADUALLY SUBSIDE LATER THIS
AFTERNOON AND EVENING OVER THE COASTAL WATERS. WINDS WILL THEN
BECOME SOUTHERLY BY LATE THURSDAY AND FRIDAY AHEAD OF A WEEKEND
SYSTEM. A SERIES OF WEST TO NORTHWEST SWELL TRAINS WILL ARRIVE TO
THE WATERS OVER THE COMING DAYS, CREATING HAZARDOUS CONDITIONS FOR
SMALL VESSELS. THE MOST SIGNIFICANT LONG- PERIOD SWELL IS
FORECAST TO ARRIVE BY LATE SUNDAY OR MONDAY, WHICH HAS THE
POTENTIAL TO BRING OPEN WATER SWELLS OF 20 FEET OR MORE. [AVIA]

MTR Watches/Warnings/Advisories

Today: Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Pinos [Monterey CA] 0–10 nm [11 miles] from 3pm Small Craft Advisory…Pt Arena [Mendocino CA] to Pt Reyes [San Francisco CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Reyes [San Francisco CA] to Pigeon Pt [Pescadero CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Pinos [Monterey CA] to Pt Piedras Blancas [San Simeon CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon CA] 10–60 nm [69 miles] ∨

.MTR WATCHES/WARNINGS/ADVISORIES...
.TDAY...SCA...PIGEON PT TO PT PINOS 0-10 NM FROM 3 PM
SCA...PT ARENA TO PT REYES 0-10 NM
SCA...PT REYES TO PIGEON PT 0-10 NM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
SCA...PT ARENA TO PIGEON PT 10-60 NM
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM [WARN]

Public Forecast: ST; Aviation: Sims; Marine: Sims ∨

PUBLIC FORECAST: ST
AVIATION: SIMS
MARINE: SIMS [CRED]

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WWW.YOUTUBE.COM/NWSBAYAREA [DISC]

Weather NWS glossary About NWS point forecasts Hourly Weather Graph Long-range forecast Radar Satellite Max Temps Graphical Forecast	Area Forecast Discussion FXUS66 KMTR [Monterey CA] 121729 AFDMTR ∨ FXUS66 KMTR 121729 AFDMTR [HEAD] National Weather Service San Francisco Bay Area 9:29am PST Wed Dec 12 2018 ∨ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 929 AM PST WED DEC 12 2018 [HEAD] Synopsis. Dry conditions are forecast to continue across our region through Thursday night. Daytime temperatures will be mild while nights will be seasonably cool. Patchy fog could redevelop tonight across the area, especially in the valleys. A weak weather system will likely produce light rain on Friday and Friday night, especially for areas north of the Golden Gate. Periods of light rain may continue into Saturday and Saturday night, mainly in the North Bay. A stronger and wetter system is then expected to produce widespread rain across our entire region Sunday and Sunday night. Dry weather will likely return by late Monday. ∨ .SYNOPSIS...DRY CONDITIONS ARE FORECAST TO CONTINUE ACROSS OUR REGION THROUGH THURSDAY NIGHT. DAYTIME TEMPERATURES WILL BE MILD WHILE NIGHTS WILL BE SEASONABLY COOL. PATCHY FOG COULD REDEVELOP TONIGHT ACROSS THE AREA, ESPECIALLY IN THE VALLEYS. A WEAK WEATHER SYSTEM WILL LIKELY PRODUCE LIGHT RAIN ON FRIDAY AND FRIDAY NIGHT, ESPECIALLY FOR AREAS NORTH OF THE GOLDEN GATE. PERIODS OF LIGHT RAIN MAY CONTINUE INTO SATURDAY AND SATURDAY NIGHT, MAINLY IN THE NORTH BAY. A STRONGER AND WETTER SYSTEM IS THEN EXPECTED TO PRODUCE WIDESPREAD RAIN ACROSS OUR ENTIRE REGION SUNDAY AND SUNDAY NIGHT. DRY WEATHER WILL LIKELY RETURN BY LATE MONDAY. [DISC] Discussion. As of 09:15am PST Wednesday… a system moving to our north brought high clouds overnight, which limited fog formation. Fog remained patchy this morning and was generally not dense, with only the North Bay reporting localized areas of visibilities below one mile at times. A few locations across the Bay Area experienced light drizzle from low clouds, with San Jose managing to record one hundredth of an inch of precipitation from the drizzle. Low clouds will dissipate by late morning and the afternoon will feature only occasional high clouds. High temperatures today will be similar to yesterday with perhaps a couple degrees of warming in some locations. Mostly clear skies are expected tonight under a ridge of high pressure. This will allow temperatures to drop to values cooler than what was experienced this morning, and likely the coolest for the next several nights. Temperatures will fall into the 30s across most inland valley locations with 40s near the coast or the SF Bay. The cool overnight temperatures and mostly clear skies will allow for patchy fog to redevelop overnight. Looking ahead, a series of storm systems will then impact the area, one on Friday and into Saturday and other on Sunday and into Monday. See the previous discussion for additional details. No updates planned this morning as short term forecast remains on track. ∨ .DISCUSSION...AS OF 09:15 AM PST WEDNESDAY...A SYSTEM MOVING TO OUR NORTH BROUGHT HIGH CLOUDS OVERNIGHT, WHICH LIMITED FOG FORMATION. FOG REMAINED PATCHY THIS MORNING AND WAS GENERALLY NOT DENSE, WITH ONLY THE NORTH BAY REPORTING LOCALIZED AREAS OF VISIBILITIES BELOW ONE MILE AT TIMES. A FEW LOCATIONS ACROSS THE BAY AREA EXPERIENCED LIGHT DRIZZLE FROM LOW CLOUDS, WITH SAN JOSE MANAGING TO RECORD ONE HUNDREDTH OF AN INCH OF PRECIPITATION FROM THE DRIZZLE. LOW CLOUDS WILL DISSIPATE BY LATE MORNING AND THE AFTERNOON WILL FEATURE ONLY OCCASIONAL HIGH CLOUDS. HIGH TEMPERATURES TODAY WILL BE SIMILAR TO YESTERDAY WITH PERHAPS A COUPLE DEGREES OF WARMING IN SOME LOCATIONS. MOSTLY CLEAR SKIES ARE EXPECTED TONIGHT UNDER A RIDGE OF HIGH PRESSURE. THIS WILL ALLOW TEMPERATURES TO DROP TO VALUES COOLER THAN WHAT WAS EXPERIENCED THIS MORNING, AND LIKELY THE COOLEST FOR THE NEXT SEVERAL NIGHTS. TEMPERATURES WILL FALL INTO THE 30S ACROSS MOST INLAND VALLEY LOCATIONS WITH 40S NEAR THE COAST OR THE SF BAY. THE COOL OVERNIGHT TEMPERATURES AND MOSTLY CLEAR SKIES WILL ALLOW FOR PATCHY FOG TO REDEVELOP OVERNIGHT. LOOKING AHEAD, A SERIES OF STORM SYSTEMS WILL THEN IMPACT THE AREA, ONE ON FRIDAY AND INTO SATURDAY AND OTHER ON SUNDAY AND INTO MONDAY. SEE THE PREVIOUS DISCUSSION FOR ADDITIONAL DETAILS. NO UPDATES PLANNED THIS MORNING AS SHORT TERM FORECAST REMAINS ON TRACK. [DISC] Previous discussion… as of 3:20am PST Wednesday. A weather system moving inland to our north brought considerable high clouds to our region overnight, but no rainfall. Also, areas of low clouds developed overnight, but only patchy light fog has formed thus far. Given the amount of cloud cover in place, feel it's unlikely we will see widespread fog develop prior to sunrise. ∨ .PREV DISCUSSION...AS OF 3:20 AM PST WEDNESDAY...A WEATHER SYSTEM MOVING INLAND TO OUR NORTH BROUGHT CONSIDERABLE HIGH CLOUDS TO OUR REGION OVERNIGHT, BUT NO RAINFALL. ALSO, AREAS OF LOW CLOUDS DEVELOPED OVERNIGHT, BUT ONLY PATCHY LIGHT FOG HAS FORMED THUS FAR. GIVEN THE AMOUNT OF CLOUD COVER IN PLACE, FEEL IT`S UNLIKELY WE WILL SEE WIDESPREAD FOG DEVELOP PRIOR TO SUNRISE. [DISC] The system to our north will move quickly off to the east today while an upper ridge offshore builds inland over California. After morning low clouds and fog clear, expect a mostly sunny day except for occasional high clouds. High temperatures today should be slightly warmer than yesterday. Mostly clear skies and light winds will mean chilly conditions tonight with lows dipping into the lower to mid 30s in the coolest inland valleys. Also, expect patchy fog again by late tonight, especially in the valleys. The upper ridge will maintain dry and mild conditions on Thursday, along with a continued warming trend across the southern portion of our region where high temperatures will climb into the mid and upper 60s. Increasing high clouds on Thursday night are expected to hold temps up a bit. ∨ THE SYSTEM TO OUR NORTH WILL MOVE QUICKLY OFF TO THE EAST TODAY WHILE AN UPPER RIDGE OFFSHORE BUILDS INLAND OVER CALIFORNIA. AFTER MORNING LOW CLOUDS AND FOG CLEAR, EXPECT A MOSTLY SUNNY DAY EXCEPT FOR OCCASIONAL HIGH CLOUDS. HIGH TEMPERATURES TODAY SHOULD BE SLIGHTLY WARMER THAN YESTERDAY. MOSTLY CLEAR SKIES AND LIGHT WINDS WILL MEAN CHILLY CONDITIONS TONIGHT WITH LOWS DIPPING INTO THE LOWER TO MID 30S IN THE COOLEST INLAND VALLEYS. ALSO, EXPECT PATCHY FOG AGAIN BY LATE TONIGHT, ESPECIALLY IN THE VALLEYS. THE UPPER RIDGE WILL MAINTAIN DRY AND MILD CONDITIONS ON THURSDAY, ALONG WITH A CONTINUED WARMING TREND ACROSS THE SOUTHERN PORTION OF OUR REGION WHERE HIGH TEMPERATURES WILL CLIMB INTO THE MID AND UPPER 60S. INCREASING HIGH CLOUDS ON THURSDAY NIGHT ARE EXPECTED TO HOLD TEMPS UP A BIT. [DISC] Rain chances return to our region on Friday when a frontal system arrives over Northern California. Models agree that most rainfall will hold off until Friday afternoon, but both the NAM [North American Meso (formerly Eta) model] and ECMWF [European Center for Medium-Range Weather Forecasts model] forecast spotty light warm advection rainfall as early as Friday morning in advance of the main frontal rain band. Models have come into better agreement with respect to rainfall location and amounts with this system. Widespread light rain is forecast to spread across the North Bay Friday afternoon and evening, with only spotty light rain expected across the San Francisco Peninsula and East Bay, and little or no rain for points south. The front is forecast to stall and mostly dissipate over the SF Bay Area by Friday night. This weak remnant frontal boundary is then expected to remain draped across the Bay Area through Saturday and Saturday night, producing periods of light precipitation, mainly over the North Bay. Rainfall accumulations from Friday through Saturday night are generally forecast to be a quarter inch or less, except up to a half inch in the North Bay. Most of this rain will likely fall on Friday afternoon and evening. ∨ RAIN CHANCES RETURN TO OUR REGION ON FRIDAY WHEN A FRONTAL SYSTEM ARRIVES OVER NORTHERN CALIFORNIA. MODELS AGREE THAT MOST RAINFALL WILL HOLD OFF UNTIL FRIDAY AFTERNOON, BUT BOTH THE NAM AND ECMWF FORECAST SPOTTY LIGHT WARM ADVECTION RAINFALL AS EARLY AS FRIDAY MORNING IN ADVANCE OF THE MAIN FRONTAL RAIN BAND. MODELS HAVE COME INTO BETTER AGREEMENT WITH RESPECT TO RAINFALL LOCATION AND AMOUNTS WITH THIS SYSTEM. WIDESPREAD LIGHT RAIN IS FORECAST TO SPREAD ACROSS THE NORTH BAY FRIDAY AFTERNOON AND EVENING, WITH ONLY SPOTTY LIGHT RAIN EXPECTED ACROSS THE SAN FRANCISCO PENINSULA AND EAST BAY, AND LITTLE OR NO RAIN FOR POINTS SOUTH. THE FRONT IS FORECAST TO STALL AND MOSTLY DISSIPATE OVER THE SF BAY AREA BY FRIDAY NIGHT. THIS WEAK REMNANT FRONTAL BOUNDARY IS THEN EXPECTED TO REMAIN DRAPED ACROSS THE BAY AREA THROUGH SATURDAY AND SATURDAY NIGHT, PRODUCING PERIODS OF LIGHT PRECIPITATION, MAINLY OVER THE NORTH BAY. RAINFALL ACCUMULATIONS FROM FRIDAY THROUGH SATURDAY NIGHT ARE GENERALLY FORECAST TO BE A QUARTER INCH OR LESS, EXCEPT UP TO A HALF INCH IN THE NORTH BAY. MOST OF THIS RAIN WILL LIKELY FALL ON FRIDAY AFTERNOON AND EVENING. [DISC] The models have consistently indicated that the following system, due to arrive by Sunday afternoon, will be both stronger and wetter, producing widespread moderate rainfall across our region from Sunday afternoon through Sunday night. There could be a brief period of heavy rain just prior to frontal passage, especially in the North Bay on Sunday afternoon. Rainfall totals with the Sunday/Sunday night system are projected to range from 0.50–1.50", with potentially higher amounts in the North Bay. Gusty south winds are also likely for a short period of time just ahead of the front on Sunday, with the strongest winds expected along the North Bay coast and in the coastal hills. ∨ THE MODELS HAVE CONSISTENTLY INDICATED THAT THE FOLLOWING SYSTEM, DUE TO ARRIVE BY SUNDAY AFTERNOON, WILL BE BOTH STRONGER AND WETTER, PRODUCING WIDESPREAD MODERATE RAINFALL ACROSS OUR REGION FROM SUNDAY AFTERNOON THROUGH SUNDAY NIGHT. THERE COULD BE A BRIEF PERIOD OF HEAVY RAIN JUST PRIOR TO FRONTAL PASSAGE, ESPECIALLY IN THE NORTH BAY ON SUNDAY AFTERNOON. RAINFALL TOTALS WITH THE SUNDAY/SUNDAY NIGHT SYSTEM ARE PROJECTED TO RANGE FROM 0.50-1.50", WITH POTENTIALLY HIGHER AMOUNTS IN THE NORTH BAY. GUSTY SOUTH WINDS ARE ALSO LIKELY FOR A SHORT PERIOD OF TIME JUST AHEAD OF THE FRONT ON SUNDAY, WITH THE STRONGEST WINDS EXPECTED ALONG THE NORTH BAY COAST AND IN THE COASTAL HILLS. [DISC] Showers may linger into Monday morning, but the models agree that dry conditions will develop in most areas by Monday afternoon. An upper ridge is forecast to build in quickly behind the departing system on Monday and this ridge will likely bring dry and mild weather to most of our region from late Monday through at least Thursday of next week. However, the ECMWF [European Center for Medium-Range Weather Forecasts model] indicates that moist flow over the top of the ridge may result in rain across portions of the North Bay late Monday night and Tuesday. ∨ SHOWERS MAY LINGER INTO MONDAY MORNING, BUT THE MODELS AGREE THAT DRY CONDITIONS WILL DEVELOP IN MOST AREAS BY MONDAY AFTERNOON. AN UPPER RIDGE IS FORECAST TO BUILD IN QUICKLY BEHIND THE DEPARTING SYSTEM ON MONDAY AND THIS RIDGE WILL LIKELY BRING DRY AND MILD WEATHER TO MOST OF OUR REGION FROM LATE MONDAY THROUGH AT LEAST THURSDAY OF NEXT WEEK. HOWEVER, THE ECMWF INDICATES THAT MOIST FLOW OVER THE TOP OF THE RIDGE MAY RESULT IN RAIN ACROSS PORTIONS OF THE NORTH BAY LATE MONDAY NIGHT AND TUESDAY. [DISC] Aviation. As of 9:30am PST Wednesday… for 18Z [10am PST] TAFs [Terminal Aerodrome Forecasts]. VFR [Visual Flight Rules] expected today except early at Livermore where some residual tule fog [Radiation fog in the Central Valley of California. It forms during night and morning hours in late fall and winter months following the first significant rainfall.] is impacting visibilities. Should clear out by 20Z [12pm PST]. Winds will be mostly light offshore with high cirrus clouds. ∨ .AVIATION....AS OF 9:30 AM PST WEDNESDAY...FOR 18Z TAFS. VFR EXPECTED TODAY EXCEPT EARLY AT LVK WHERE SOME RESIDUAL TULE FOG IS IMPACTING VISIBILITIES. SHOULD CLEAR OUT BY 20Z. WINDS WILL BE MOSTLY LIGHT OFFSHORE WITH HIGH CIRRUS CLOUDS. [AVIA] Vicinity of KSFO [San Francisco CA]… VFR [Visual Flight Rules]. ∨ VICINITY OF KSFO...VFR. [AVI2] SFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨ SFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2] Monterey Bay terminals… VFR [Visual Flight Rules] except at KSNS [Salinas CA] until 19Z [11am PST]. ∨ MONTEREY BAY TERMINALS...VFR EXCEPT AT KSNS UNTIL 19Z. [AVI2] Marine. As of 8:41am PST Wednesday… breezy northerly winds behind a passing cold front will gradually subside later this afternoon and evening over the coastal waters. Winds will then become southerly by late Thursday and Friday ahead of a weekend system. A series of west to northwest swell trains will arrive to the waters over the coming days, creating hazardous conditions for small vessels. The most significant long-period swell is forecast to arrive by late Sunday or Monday, which has the potential to bring open water swells of 20 feet or more. ∨ .MARINE...AS OF 8:41 AM PST WEDNESDAY...BREEZY NORTHERLY WINDS BEHIND A PASSING COLD FRONT WILL GRADUALLY SUBSIDE LATER THIS AFTERNOON AND EVENING OVER THE COASTAL WATERS. WINDS WILL THEN BECOME SOUTHERLY BY LATE THURSDAY AND FRIDAY AHEAD OF A WEEKEND SYSTEM. A SERIES OF WEST TO NORTHWEST SWELL TRAINS WILL ARRIVE TO THE WATERS OVER THE COMING DAYS, CREATING HAZARDOUS CONDITIONS FOR SMALL VESSELS. THE MOST SIGNIFICANT LONG- PERIOD SWELL IS FORECAST TO ARRIVE BY LATE SUNDAY OR MONDAY, WHICH HAS THE POTENTIAL TO BRING OPEN WATER SWELLS OF 20 FEET OR MORE. [AVIA] MTR Watches/Warnings/Advisories Today: Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Pinos [Monterey CA] 0–10 nm [11 miles] from 3pm Small Craft Advisory…Pt Arena [Mendocino CA] to Pt Reyes [San Francisco CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Reyes [San Francisco CA] to Pigeon Pt [Pescadero CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Pinos [Monterey CA] to Pt Piedras Blancas [San Simeon CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon CA] 10–60 nm [69 miles] ∨ .MTR WATCHES/WARNINGS/ADVISORIES... .TDAY...SCA...PIGEON PT TO PT PINOS 0-10 NM FROM 3 PM SCA...PT ARENA TO PT REYES 0-10 NM SCA...PT REYES TO PIGEON PT 0-10 NM SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM SCA...PT ARENA TO PIGEON PT 10-60 NM SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM [WARN] Public Forecast: ST; Aviation: Sims; Marine: Sims ∨ PUBLIC FORECAST: ST AVIATION: SIMS MARINE: SIMS [CRED] VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK] Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea ∨ FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSBAYAREA WWW.TWITTER.COM/NWSBAYAREA WWW.YOUTUBE.COM/NWSBAYAREA [DISC]	Point Forecast Half Moon Bay CA 12 Dec 12:55pm PST This Afternoon Sunny, with a high near 60°. NNE wind 14 to 20 mph, with gusts as high as 25 mph. Tonight Mostly clear, with a low around 45°. ENE wind 8 to 16 mph, with gusts as high as 22 mph. Thursday Sunny, with a high near 62°. ENE wind 11 to 15 mph, with gusts as high as 20 mph. Thursday Night Increasing clouds, with a low around 48°. ENE wind 9 to 11 mph becoming south in the evening. Friday Rain likely, mainly after 11am. Mostly cloudy, with a high near 61°. Breezy, with a south wind 11 to 16 mph increasing to 17 to 22 mph in the morning. Winds could gust as high as 29 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible. Friday Night A 50% chance of showers. Mostly cloudy, with a low around 49°. New precipitation amounts of less than a tenth of an inch possible. Saturday Partly sunny, with a high near 60°. Saturday Night A slight chance of showers. Mostly cloudy, with a low around 52°. Sunday Rain. Cloudy, with a high near 60°. Sunday Night Rain likely. Cloudy, with a low around 50°. Monday A chance of showers. Partly sunny, with a high near 59°. Monday Night Mostly cloudy, with a low around 48°. Tuesday Mostly sunny, with a high near 61°. This Afternoon Sunny, with a high near 60. North northeast wind 14 to 20 mph, with gusts as high as 25 mph. Tonight Mostly clear, with a low around 45. East northeast wind 8 to 16 mph, with gusts as high as 22 mph. Thursday Sunny, with a high near 62. East northeast wind 11 to 15 mph, with gusts as high as 20 mph. Thursday Night Increasing clouds, with a low around 48. East northeast wind 9 to 11 mph becoming south in the evening. Friday Rain likely, mainly after 11am. Mostly cloudy, with a high near 61. Breezy, with a south wind 11 to 16 mph increasing to 17 to 22 mph in the morning. Winds could gust as high as 29 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible. Friday Night A 50 percent chance of showers. Mostly cloudy, with a low around 49. New precipitation amounts of less than a tenth of an inch possible. Saturday Partly sunny, with a high near 60. Saturday Night A slight chance of showers. Mostly cloudy, with a low around 52. Sunday Rain. Cloudy, with a high near 60. Sunday Night Rain likely. Cloudy, with a low around 50. Monday A chance of showers. Partly sunny, with a high near 59. Monday Night Mostly cloudy, with a low around 48. Tuesday Mostly sunny, with a high near 61.
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