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FXUS66 KMTR [Monterey CA] 070047 AFDMTR 

FXUS66 KMTR 070047
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 4:47pm PST Mon Dec 6 2021 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
447 PM PST MON DEC 6 2021 [HEAD]

Synopsis. Scattered rain showers this evening into Tuesday with light rain accumulations. Quiet through mid week with rain chances returning for Wednesday night and Thursday. Cool temperatures for late week into the weekend with frost likely in the valleys. 

.SYNOPSIS...SCATTERED RAIN SHOWERS THIS EVENING INTO TUESDAY
WITH LIGHT RAIN ACCUMULATIONS. QUIET THROUGH MID WEEK WITH
RAIN CHANCES RETURNING FOR WEDNESDAY NIGHT AND THURSDAY. COOL
TEMPERATURES FOR LATE WEEK INTO THE WEEKEND WITH FROST LIKELY IN
THE VALLEYS. [DISC]

Discussion. As of 12:20pm PST Monday. 

.DISCUSSION...AS OF 12:20 PM PST MONDAY... [DISC]

This afternoon through Tuesday: 

THIS AFTERNOON THROUGH TUESDAY: [DISC]

As of early Monday afternoon our area was along the northeast periphery of an expansive mid-level ridge centered near 30°N [520 mi south of Half Moon Bay]/110°W [680 mi east of Half Moon Bay]. However heights were dropping aloft and high clouds were streaming into the area ahead of a shortwave trough located west of Washington/Oregon. This shortwave should evolve into a closed low while dropping SSE across the eastern Pacific to locate west of the Central Coast by Tuesday. 

AS OF EARLY MONDAY AFTERNOON OUR AREA WAS ALONG THE NORTHEAST
PERIPHERY OF AN EXPANSIVE MID-LEVEL RIDGE CENTERED NEAR 30N/110W.
HOWEVER HEIGHTS WERE DROPPING ALOFT AND HIGH CLOUDS WERE STREAMING
INTO THE AREA AHEAD OF A SHORTWAVE TROUGH LOCATED WEST OF WA/OR.
THIS SHORTWAVE SHOULD EVOLVE INTO A CLOSED LOW WHILE DROPPING SSE
ACROSS THE EASTERN PACIFIC TO LOCATE WEST OF THE CENTRAL COAST BY
TUESDAY. [DISC]

As the trough approaches rain chances will increase from north to south across the area this afternoon and into this evening. Rain is already encroaching on far northern portions of Sonoma County, and current timing has chances starting from early to mid afternoon for the North Bay, early evening for SF, and later tonight for Monterey Bay and points south. Shower chances persist overnight before diminishing from north to south during the day on Tuesday. 

AS THE TROUGH APPROACHES RAIN CHANCES WILL INCREASE FROM NORTH TO
SOUTH ACROSS THE AREA THIS AFTERNOON AND INTO THIS EVENING.
RAIN IS ALREADY ENCROACHING ON FAR NORTHERN PORTIONS OF SONOMA
COUNTY, AND CURRENT TIMING HAS CHANCES STARTING FROM EARLY TO MID
AFTERNOON FOR THE NORTH BAY, EARLY EVENING FOR SF, AND LATER
TONIGHT FOR MONTEREY BAY AND POINTS SOUTH. SHOWER CHANCES PERSIST
OVERNIGHT BEFORE DIMINISHING FROM NORTH TO SOUTH DURING THE DAY ON
TUESDAY. [DISC]

As for rain amounts, a quick perusal of our model certainty tool suggests light totals overall with 50th percentile values of 0.05" to 0.1". However 75th/90th percentiles (which can be thought of as "reasonable worst case" amounts) suggest at least localized potential for 0.15" to 0.25". This chance is greatest for higher terrain locations in the North Bay and along the Big Sur coast. 

AS FOR RAIN AMOUNTS, A QUICK PERUSAL OF OUR MODEL CERTAINTY TOOL
SUGGESTS LIGHT TOTALS OVERALL WITH 50TH PERCENTILE VALUES OF 0.05"
TO 0.1". HOWEVER 75TH/90TH PERCENTILES (WHICH CAN BE THOUGHT OF AS
"REASONABLE WORST CASE" AMOUNTS) SUGGEST AT LEAST LOCALIZED
POTENTIAL FOR 0.15" TO 0.25". THIS CHANCE IS GREATEST FOR HIGHER
TERRAIN LOCATIONS IN THE NORTH BAY AND ALONG THE BIG SUR COAST. [DISC]

Given elevated instability associated with the nearby upper low can't rule out a rumble of thunder late tonight into Tuesday morning, but this chance should be confined to the Pacific waters and perhaps along the immediate shoreline. 

GIVEN ELEVATED INSTABILITY ASSOCIATED WITH THE NEARBY UPPER LOW
CAN`T RULE OUT A RUMBLE OF THUNDER LATE TONIGHT INTO TUESDAY
MORNING, BUT THIS CHANCE SHOULD BE CONFINED TO THE PACIFIC WATERS
AND PERHAPS ALONG THE IMMEDIATE SHORELINE. [DISC]

Some fog is possible late tonight into Tuesday morning as the low levels saturate. The strongest signal for this among the near-term guidance is over the North Bay valleys. Temperatures will be seasonal with highs mostly in the 50s to lower 60s and lows mostly in the 40s. 

SOME FOG IS POSSIBLE LATE TONIGHT INTO TUESDAY MORNING AS THE LOW
LEVELS SATURATE. THE STRONGEST SIGNAL FOR THIS AMONG THE NEAR-TERM
GUIDANCE IS OVER THE NORTH BAY VALLEYS. TEMPERATURES WILL BE
SEASONAL WITH HIGHS MOSTLY IN THE 50S TO LOWER 60S AND LOWS MOSTLY
IN THE 40S. [DISC]

Wednesday through Sunday: 

WEDNESDAY THROUGH SUNDAY: [DISC]

An upper trough will deepen along the West Coast on Wednesday into Thursday. This system will bring additional rain chances to the area beginning on Wednesday night. In general this system appears to remain progressive with light rain amounts under one quarter of an inch. So as previously noted this doesn't look like something that's going to make a dent in the ongoing long-term drought. With cold air pouring in behind this system some of the precipitation may end as light snow at the higher elevations (~2500 ft+) on Thursday. Thereafter cool temperatures should prevail into the weekend. Valley frost is a good possibility on Thursday and Friday mornings so those with agricultural interests should monitor the forecast. 

AN UPPER TROUGH WILL DEEPEN ALONG THE WEST COAST ON WEDNESDAY INTO
THURSDAY. THIS SYSTEM WILL BRING ADDITIONAL RAIN CHANCES TO THE AREA
BEGINNING ON WEDNESDAY NIGHT. IN GENERAL THIS SYSTEM APPEARS TO
REMAIN PROGRESSIVE WITH LIGHT RAIN AMOUNTS UNDER ONE QUARTER OF AN
INCH. SO AS PREVIOUSLY NOTED THIS DOESN`T LOOK LIKE SOMETHING
THAT`S GOING TO MAKE A DENT IN THE ONGOING LONG-TERM DROUGHT. WITH
COLD AIR POURING IN BEHIND THIS SYSTEM SOME OF THE PRECIPITATION
MAY END AS LIGHT SNOW AT THE HIGHER ELEVATIONS (~2500 FT+) ON
THURSDAY. THEREAFTER COOL TEMPERATURES SHOULD PREVAIL INTO THE
WEEKEND. VALLEY FROST IS A GOOD POSSIBILITY ON THURSDAY AND FRIDAY
MORNINGS SO THOSE WITH AGRICULTURAL INTERESTS SHOULD MONITOR THE
FORECAST. [DISC]

Looking forward our next rain chances are on the horizon around December 13th and 14th. 

LOOKING FORWARD OUR NEXT RAIN CHANCES ARE ON THE HORIZON AROUND
DECEMBER 13TH AND 14TH. [DISC]

Aviation. As of 4:00pm PST Monday… for the 00Z [4pm PST] TAFs [Terminal Aerodrome Forecasts]. MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules] with isolated LIFR [Low Instrument Flight Rules] ceilings and visibilities lasting through 15–18Z [7–10am PST] as rain/VCSH [Rain Showers in the Vicinity] moves through the area tonight, ahead of a weak and progressive frontal passage Tuesday afternoon. Winds reamin at or below 12 kts [14 mph] through 18Z [10am PST], with mostly at or below 5 kts [6 mph] and variable. Light rain/VCSH [Rain Showers in the Vicinity] is to approach the Bay Area around 01Z [5pm PST]. VCSH [Rain Showers in the Vicinity] will last through 09–12Z [1–4am PST] for most areas. Isolated pockets of patchy fog and LIFR [Low Instrument Flight Rules] conditions is possible overnight in sheltered valley locations. Winds will be out of the northwest Tuesday afternoon and breezy as the boundary passes through, but subsiding overnight. 

.AVIATION...AS OF 4:00 PM PST MONDAY...FOR THE 00Z TAFS. MVFR/IFR
WITH ISOLATED LIFR CEILINGS AND VISIBILITIES LASTING THROUGH
15-18Z AS RA/VCSH MOVES THROUGH THE AREA TONIGHT, AHEAD OF A WEAK
AND PROGRESSIVE FROPA TUESDAY AFTERNOON. WINDS REAMIN AOB 12KTS
THROUGH 18Z, WITH MOSTLY AOB 5KTS AND VARIABLE. -RA/VCSH IS TO
APPROACH THE BAY AREA AROUND 01Z. VCSH WILL LAST THROUGH 09-12Z
FOR MOST AREAS. ISOLATED POCKETS OF PATCHY FOG AND LIFR CONDITIONS
IS POSSIBLE OVERNIGHT IN SHELTERED VALLEY LOCATIONS. WINDS WILL
BE OUT OF THE NORTHWEST TUESDAY AFTERNOON AND BREEZY AS THE
BOUNDARY PASSES THROUGH, BUT SUBSIDING OVERNIGHT. [AVIA]

Vicinity of KSFO [San Francisco CA]MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules] ceilings and visibilities tonight as rain/VCSH [Rain Showers in the Vicinity] will move through the area. Rain will start around 01–02Z [5–6pm PST] and last through 10–12Z [2–4am PST] tonight. Fog/mist will be possible as heavy rain/rain weakens to VCSH [Rain Showers in the Vicinity]/light rain after 07Z [11pm PST]. VFR [Visual Flight Rules] after 18Z [10am PST] for Monday afternoon with northwest winds and skies few-scattered 030. More broken-overcast ceilings will move inland Tuesday night. 

VICINITY OF KSFO...MVFR/IFR CEILINGS AND VISIBILITIES TONIGHT AS
RA/VCSH WILL MOVE THROUGH THE AREA. RA WILL START AROUND 01-02Z
AND LAST THROUGH 10-12Z TONIGHT. FG/BR WILL BE POSSIBLE AS +RA/RA
WEAKENS TO VCSH/-RA AFTER 07Z. VFR AFTER 18Z FOR MONDAY AFTERNOON
WITH NORTHWEST WINDS AND SKIES FEW-SCT030. MORE BKN-OVC CEILINGS
WILL MOVE INLAND TUESDAY NIGHT. [AVI2]

KSFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]

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

Monterey Bay… IFR [Instrument Flight Rules] ceilings will continue to fill in and last through the night tonight. Light rain/VCSH [Rain Showers in the Vicinity] will begin around 04Z [8pm PST] and and last through 10Z [2am PST], with potential for mist/haze from 09Z [1am PST] to 15Z [7am PST]. VFR [Visual Flight Rules] Tuesday afternoon and northwest winds. 

MONTEREY BAY...IFR CEILINGS WILL CONTINUE TO FILL IN AND LAST
THROUGH THE NIGHT TONIGHT. -RA/VCSH WILL BEGIN AROUND 04Z AND AND
LAST THROUGH 10Z, WITH POTENTIAL FOR BR/HZ FROM 09Z TO 15Z. VFR
TUESDAY AFTERNOON AND NORTHWEST WINDS. [AVI2]

Marine. As of 8:48am PST Monday… winds remain out of the northwest and gusty, forecast to last through Tuesday morning that can generate steep wind waves which can be hazardous to smaller vessels. A system moving over the waters Monday afternoon and into this evening provides a chance of rain and a slight chance for thunder. While the sea state will be mostly dominated by wind waves, the next moderate period northwest swell is forecast to arrive on Wednesday. 

.MARINE...AS OF 8:48 AM PST MONDAY...WINDS REMAIN OUT OF THE
NORTHWEST AND GUSTY, FORECAST TO LAST  THROUGH TUESDAY MORNING
THAT CAN GENERATE STEEP WIND WAVES WHICH  CAN BE HAZARDOUS TO
SMALLER VESSELS. A SYSTEM MOVING OVER THE WATERS MONDAY AFTERNOON
AND INTO THIS EVENING PROVIDES A CHANCE  OF RAIN AND A SLIGHT
CHANCE FOR THUNDER. WHILE THE SEA STATE WILL BE MOSTLY DOMINATED
BY WIND WAVES, THE NEXT MODERATE PERIOD NORTHWEST SWELL IS
FORECAST TO ARRIVE ON WEDNESDAY. [AVIA]

MTR Watches/Warnings/Advisories

.MTR WATCHES/WARNINGS/ADVISORIES...
.TNGT...SCA...MRY BAY UNTIL 9 PM
SCA...PIGEON PT TO PT PINOS 0-10 NM UNTIL 9 PM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM UNTIL 3 AM [WARN]

Public Forecast: SPM; Aviation: Dhuyvetter; Marine: DK 

PUBLIC FORECAST: SPM
AVIATION: DHUYVETTER
MARINE: DK [CRED]
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK]

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WWW.YOUTUBE.COM/NWSBAYAREA [DISC]

Point Forecast

Half Moon Bay CA

06 Dec 06:00pm PST

Tonight Rain likely, mainly before 10pm. Cloudy, with a low around 48°. WNW wind around 6 mph becoming calm. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.
Tuesday A 10% chance of rain before 7am. Mostly cloudy through mid morning, then gradual clearing, with a high near 60°. NE wind 15 to 20 mph becoming north 9 to 14 mph in the afternoon. Winds could gust as high as 25 mph.
Tuesday Night Increasing clouds, with a steady temperature around 51°. West wind 6 to 9 mph.
Wednesday Mostly cloudy, with a high near 60°. WNW wind 9 to 16 mph, with gusts as high as 21 mph.
Wednesday Night A 50% chance of rain after 10pm. Cloudy, with a low around 46°. NW wind around 15 mph, with gusts as high as 20 mph. New precipitation amounts of less than a tenth of an inch possible.
Thursday A 40% chance of rain before 10am. Mostly sunny, with a high near 56°.
Thursday Night Mostly clear, with a low around 41°.
Friday Sunny, with a high near 56°.
Friday Night Mostly clear, with a low around 40°.
Saturday Sunny, with a high near 57°.
Saturday Night A slight chance of rain. Partly cloudy, with a low around 42°.
Sunday A chance of rain. Partly sunny, with a high near 57°.
Sunday Night A chance of rain. Mostly cloudy, with a low around 45°.
Monday Rain likely. Mostly cloudy, with a high near 57°.
Tonight
Rain likely, mainly before 10pm. Cloudy, with a low around 48. West northwest wind around 6 mph becoming calm. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.
Tuesday
A 10 percent chance of rain before 7am. Mostly cloudy through mid morning, then gradual clearing, with a high near 60. Northeast wind 15 to 20 mph becoming north 9 to 14 mph in the afternoon. Winds could gust as high as 25 mph.
Tuesday Night
Increasing clouds, with a steady temperature around 51. West wind 6 to 9 mph.
Wednesday
Mostly cloudy, with a high near 60. West northwest wind 9 to 16 mph, with gusts as high as 21 mph.
Wednesday Night
A 50 percent chance of rain after 10pm. Cloudy, with a low around 46. Northwest wind around 15 mph, with gusts as high as 20 mph. New precipitation amounts of less than a tenth of an inch possible.
Thursday
A 40 percent chance of rain before 10am. Mostly sunny, with a high near 56.
Thursday Night
Mostly clear, with a low around 41.
Friday
Sunny, with a high near 56.
Friday Night
Mostly clear, with a low around 40.
Saturday
Sunny, with a high near 57.
Saturday Night
A slight chance of rain. Partly cloudy, with a low around 42.
Sunday
A chance of rain. Partly sunny, with a high near 57.
Sunday Night
A chance of rain. Mostly cloudy, with a low around 45.
Monday
Rain likely. Mostly cloudy, with a high near 57.

This page is generated dynamically from the National Weather Service's NWS point forecast and Area Forecast Discussion, reformatted for readability. NWS glossary; about point forecasts. For more information, visit the Lobitos Weather Project home page. Comments and corrections are welcome: