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FXUS66 KMTR [Monterey CA] 171534 AFDMTR 

FXUS66 KMTR 171534
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 8:34am PDT Sat Apr 17 2021 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
834 AM PDT SAT APR 17 2021 [HEAD]

Synopsis. A warming trend will continue through the weekend, with Sunday expected to be the warmest day. Cooling will begin on Monday, mainly in coastal areas. More widespread cooling is forecast for Tuesday as temperatures return to seasonal averages. Rain is not expected through Friday. 

.SYNOPSIS...A WARMING TREND WILL CONTINUE THROUGH THE WEEKEND,
WITH SUNDAY EXPECTED TO BE THE WARMEST DAY. COOLING WILL BEGIN ON
MONDAY, MAINLY IN COASTAL AREAS. MORE WIDESPREAD COOLING IS
FORECAST FOR TUESDAY AS TEMPERATURES RETURN TO SEASONAL AVERAGES.
RAIN IS NOT EXPECTED THROUGH FRIDAY. [DISC]

Discussion. As of 08:34am PDT Saturday… Saturday morning visible satellite looks very summer like - June gloom. A solid marine layer developed overnight and pushed pretty far inland blanketing much of the inland valleys. Despite the inland push the marine layer depth is somewhat shallow at approximately 1,000 feet. Also seeing a few reports of patchy fog this morning as well. Needless to say, but a cool and damp start to the day for areas under the marine layer. Above the marine layer is a different story with sunny skies, mild temperatures, and drier conditions. 

.DISCUSSION...AS OF 08:34 AM PDT SATURDAY...SATURDAY MORNING
VISIBLE SATELLITE LOOKS VERY SUMMER LIKE - JUNE GLOOM. A SOLID
MARINE LAYER DEVELOPED OVERNIGHT AND PUSHED PRETTY FAR INLAND
BLANKETING MUCH OF THE INLAND VALLEYS. DESPITE THE INLAND PUSH THE
MARINE LAYER DEPTH IS SOMEWHAT SHALLOW AT APPROXIMATELY 1,000
FEET. ALSO SEEING A FEW REPORTS OF PATCHY FOG THIS MORNING AS
WELL. NEEDLESS TO SAY, BUT A COOL AND DAMP START TO THE DAY FOR
AREAS UNDER THE MARINE LAYER. ABOVE THE MARINE LAYER IS A
DIFFERENT STORY WITH SUNNY SKIES, MILD TEMPERATURES, AND DRIER
CONDITIONS. [DISC]

For the rest of today, given the shallow nature of the marine layer cloud deck will erode relatively early - midmorning. Expecting mostly sunny skies this afternoon with a noticeable warm up. Did a quick update this morning to nudge a few interior locations in the N and East Bay upward a few degrees into the mid 80s. More details below. 

FOR THE REST OF TODAY, GIVEN THE SHALLOW NATURE OF THE MARINE
LAYER CLOUD DECK WILL ERODE RELATIVELY EARLY - MIDMORNING.
EXPECTING MOSTLY SUNNY SKIES THIS AFTERNOON WITH A NOTICEABLE WARM
UP. DID A QUICK UPDATE THIS MORNING TO NUDGE A FEW INTERIOR
LOCATIONS IN THE N AND E BAY UPWARD A FEW DEGREES INTO THE MID
80S. MORE DETAILS BELOW... [DISC]

Previous discussion… as of 3:10am PDT Saturday. The primary focus in the short-term is the anticipated warming trend through the weekend, and specifically the amount of warming we can expect. 

.PREV DISCUSSION...AS OF 3:10 AM PDT SATURDAY...THE PRIMARY FOCUS IN
THE SHORT-TERM IS THE ANTICIPATED WARMING TREND THROUGH THE
WEEKEND, AND SPECIFICALLY THE AMOUNT OF WARMING WE CAN EXPECT. [DISC]

A high amplitude upper ridge centered over the West Coast has compressed the marine layer overnight. Latest profiler [instrument designed to measure horizontal winds directly above its location, and thus measure the vertical wind profile. Profilers operate on the same principles as Doppler radar.] data at both Fort Ord and Bodega Bay reveals the marine layer depth has decreased to about 1000 feet. Surface flow remains onshore and so low clouds remain near the ocean and bays, and low clouds have developed locally inland as well. Given the relatively shallow nature of the marine layer, and the light offshore flow starting to develop aloft, would expect low clouds to clear in most areas by mid morning, except near Monterey Bay where clouds may linger until midday. Warming aloft, a compressed marine layer, and the influx of drier air from light offshore flow aloft, will combine to produce warming across our entire area today. Warming will be most pronounced in the North Bay where offshore flow will develop in the hills more quickly and where light north winds will inhibit afternoon seabreezes. North Bay valleys are forecast to warm into the lower 80s today, which is 15° warmer than yesterday. Most other locations are forecast to see a 5–10° warmup. 

A HIGH AMPLITUDE UPPER RIDGE CENTERED OVER THE WEST COAST HAS
COMPRESSED THE MARINE LAYER OVERNIGHT. LATEST PROFILER DATA AT
BOTH FORT ORD AND BODEGA BAY REVEALS THE MARINE LAYER DEPTH HAS
DECREASED TO ABOUT 1000 FEET. SURFACE FLOW REMAINS ONSHORE AND SO LOW
CLOUDS REMAIN NEAR THE OCEAN AND BAYS, AND LOW CLOUDS HAVE
DEVELOPED LOCALLY INLAND AS WELL. GIVEN THE RELATIVELY SHALLOW
NATURE OF THE MARINE LAYER, AND THE LIGHT OFFSHORE FLOW STARTING
TO DEVELOP ALOFT, WOULD EXPECT LOW CLOUDS TO CLEAR IN MOST AREAS
BY MID MORNING, EXCEPT NEAR MONTEREY BAY WHERE CLOUDS MAY LINGER
UNTIL MIDDAY. WARMING ALOFT, A COMPRESSED MARINE LAYER, AND THE
INFLUX OF DRIER AIR FROM LIGHT OFFSHORE FLOW ALOFT, WILL COMBINE
TO PRODUCE WARMING ACROSS OUR ENTIRE AREA TODAY. WARMING WILL BE
MOST PRONOUNCED IN THE NORTH BAY WHERE OFFSHORE FLOW WILL DEVELOP
IN THE HILLS MORE QUICKLY AND WHERE LIGHT NORTH WINDS WILL INHIBIT
AFTERNOON SEABREEZES. NORTH BAY VALLEYS ARE FORECAST TO WARM INTO
THE LOWER 80S TODAY, WHICH IS 15 DEGREES WARMER THAN YESTERDAY.
MOST OTHER LOCATIONS ARE FORECAST TO SEE A 5 TO 10 DEGREE WARMUP. [DISC]

More widespread light offshore flow is forecast to develop in the hills, and locally near sea level, by late tonight and early Sunday. In addition, the upper ridge will strengthen a bit further and we should see the marine layer continue to become more shallow, while the airmass aloft continues to warm. Widespread 80s are forecast for inland areas on Sunday and a few lower 90s are possible in the warmest inland locations. The difficult part of the forecast are coastal temps on Sunday. Although light offshore flow will likely develop briefly at the surface late Saturday night and Sunday morning, a seabreeze will almost certain develop in the afternoon. But even a brief period of offshore flow should allow coastal temps to warm into the 70s and there may even be a few lower 80s in the warmer coastal spots such as Santa Cruz and Big Sur on Sunday. Sunday's highs are forecast to be from 10–15° warmer than normal in most locations. Sunday's temps will likely be the warmest so far this year across most of our area, although the record breaking warmth that occurred on March 31 and April 1 may not be matched at some locations. 

MORE WIDESPREAD LIGHT OFFSHORE FLOW IS FORECAST TO DEVELOP IN THE
HILLS, AND LOCALLY NEAR SEA LEVEL, BY LATE TONIGHT AND EARLY
SUNDAY. IN ADDITION, THE UPPER RIDGE WILL STRENGTHEN A BIT FURTHER
AND WE SHOULD SEE THE MARINE LAYER CONTINUE TO BECOME MORE
SHALLOW, WHILE THE AIRMASS ALOFT CONTINUES TO WARM. WIDESPREAD 80S
ARE FORECAST FOR INLAND AREAS ON SUNDAY AND A FEW LOWER 90S ARE
POSSIBLE IN THE WARMEST INLAND LOCATIONS. THE DIFFICULT PART OF
THE FORECAST ARE COASTAL TEMPS ON SUNDAY. ALTHOUGH LIGHT OFFSHORE
FLOW WILL LIKELY DEVELOP BRIEFLY AT THE SURFACE LATE SATURDAY
NIGHT AND SUNDAY MORNING, A SEABREEZE WILL ALMOST CERTAIN DEVELOP
IN THE AFTERNOON. BUT EVEN A BRIEF PERIOD OF OFFSHORE FLOW SHOULD
ALLOW COASTAL TEMPS TO WARM INTO THE 70S AND THERE MAY EVEN BE A
FEW LOWER 80S IN THE WARMER COASTAL SPOTS SUCH AS SANTA CRUZ AND
BIG SUR ON SUNDAY. SUNDAY`S HIGHS ARE FORECAST TO BE FROM 10 TO 15
DEGREES WARMER THAN NORMAL IN MOST LOCATIONS. SUNDAY`S TEMPS WILL
LIKELY BE THE WARMEST SO FAR THIS YEAR ACROSS MOST OF OUR AREA,
ALTHOUGH THE RECORD BREAKING WARMTH THAT OCCURRED ON MARCH 31 AND
APRIL 1 MAY NOT BE MATCHED AT SOME LOCATIONS. [DISC]

The upper ridge is forecast to begin breaking down on Monday and onshore flow will fully develop by afternoon. Thus, we can expect 10–15° of cooling near the coast on Monday, while the inland valleys cool by only about 5°. Inland areas will then cool an additional 10° on Tuesday and temperatures will return to near normal in all areas. 

THE UPPER RIDGE IS FORECAST TO BEGIN BREAKING DOWN ON MONDAY AND
ONSHORE FLOW WILL FULLY DEVELOP BY AFTERNOON. THUS, WE CAN EXPECT
10 TO 15 DEGREES OF COOLING NEAR THE COAST ON MONDAY, WHILE THE
INLAND VALLEYS COOL BY ONLY ABOUT 5 DEGREES. INLAND AREAS WILL
THEN COOL AN ADDITIONAL 10 DEGREES ON TUESDAY AND TEMPERATURES
WILL RETURN TO NEAR NORMAL IN ALL AREAS. [DISC]

Both the 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.] and ECMWF [European Center for Medium-Range Weather Forecasts model] drop a couple of weak systems into Northern California from the NNW around the middle of next week, but model details differ. The deterministic models keep scattered precipitation with these systems to our north and east, as do most ensemble members. Just a couple ensemble members develop light precipitation in our area around the middle of next week, not enough to add rain chances to the forecast at this time. Rain chances improve by late next weekend and into the early part of the following week when several 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.] and ECMWF [European Center for Medium-Range Weather Forecasts model] ensemble members forecast precipitation. However, this must be taken with a grain of salt considering the long range models have been giving us hope for rain for much of the past month, with nothing to show for it. 

BOTH THE GFS AND ECMWF DROP A COUPLE OF WEAK SYSTEMS INTO
NORTHERN CALIFORNIA FROM THE NNW AROUND THE MIDDLE OF NEXT WEEK,
BUT MODEL DETAILS DIFFER. THE DETERMINISTIC MODELS KEEP SCATTERED
PRECIPITATION WITH THESE SYSTEMS TO OUR NORTH AND EAST, AS DO
MOST ENSEMBLE MEMBERS. JUST A COUPLE ENSEMBLE MEMBERS DEVELOP
LIGHT PRECIP IN OUR AREA AROUND THE MIDDLE OF NEXT WEEK, NOT
ENOUGH TO ADD RAIN CHANCES TO THE FORECAST AT THIS TIME. RAIN
CHANCES IMPROVE BY LATE NEXT WEEKEND AND INTO THE EARLY PART OF
THE FOLLOWING WEEK WHEN SEVERAL GFS AND ECMWF ENSEMBLE MEMBERS
FORECAST PRECIPITATION. HOWEVER, THIS MUST BE TAKEN WITH A GRAIN
OF SALT CONSIDERING THE LONG RANGE MODELS HAVE BEEN GIVING US HOPE
FOR RAIN FOR MUCH OF THE PAST MONTH, WITH NOTHING TO SHOW FOR IT. [DISC]

Aviation. As of 4:58am PDT Saturday… for the 12Z [5am PDT] TAFs [Terminal Aerodrome Forecasts]. A mix of VFR [Visual Flight Rules]/MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules]/LIFR [Low Instrument Flight Rules] across terminals, as stratus continues its push further inland. A well established marine layer sits in place at a depth between 1300 and 1500 ft, with the more compressed end further to the north, as per coastal profilers. This morning expecting most terminals to go under ceilings at IFR [Instrument Flight Rules]/MVFR [Marginal Visual Flight Rules] levels, though terminals furthest inland may see only scattered clouds/patchy ceilings. Also, LIFR [Low Instrument Flight Rules] in North Bay terminals with areas of fog. Stratus burns off around 17Z [10am PDT] for most Bay Area terminals, but perhaps a couple of hours later around Monterey Bay. 

.AVIATION...AS OF 4:58 AM PDT SATURDAY...FOR THE 12Z TAFS. A MIX
OF VFR/MVFR/IFR/LIFR ACROSS TERMINALS, AS STRATUS CONTINUES ITS
PUSH FURTHER INLAND. A WELL ESTABLISHED MARINE LAYER SITS IN PLACE
AT A DEPTH BETWEEN 1300 AND 1500 FT, WITH THE MORE COMPRESSED END
FURTHER TO THE NORTH, AS PER COASTAL PROFILERS. THIS MORNING
EXPECTING MOST TERMINALS TO GO UNDER CIGS AT IFR/MVFR LEVELS,
THOUGH TERMINALS FURTHEST INLAND MAY SEE ONLY SCT CLOUDS/PATCHY
CIGS. ALSO, LIFR IN NORTH BAY TERMINALS WITH AREAS OF FOG. STRATUS
BURNS OFF AROUND 17Z FOR MOST BAY AREA TERMINALS, BUT PERHAPS A
COUPLE OF HOURS LATER AROUND MONTEREY BAY. [AVIA]

Light northerly to northeasterly flow aloft Saturday afternoon will usher in a drier airmass, keeping skies clear. Coastal terminals will still experience an afternoon sea breeze, but inland terminals will have more northerly winds. The marine layer will compress, keeping VFR [Visual Flight Rules] conditions through Saturday night, except for possibly Monterey Bay terminals where stratus may return. 

LIGHT NORTHERLY TO NORTHEASTERLY FLOW ALOFT SATURDAY
AFTERNOON WILL USHER IN A DRIER AIRMASS, KEEPING SKIES CLEAR.
COASTAL TERMINALS WILL STILL EXPERIENCE AN AFTERNOON SEA BREEZE,
BUT INLAND TERMINALS WILL HAVE MORE NORTHERLY WINDS. THE MARINE
LAYER WILL COMPRESS, KEEPING VFR CONDITIONS THROUGH SATURDAY
NIGHT, EXCEPT FOR POSSIBLY MONTEREY BAY TERMINALS WHERE STRATUS
MAY RETURN. [AVI2]

Vicinity of KSFO [San Francisco CA]… currently IFR [Instrument Flight Rules] with overcast 008 reported at terminal. Satellite night imagery shows stratus has progressed through the Golden Gate, and is encircling the Bay, under light WNW winds. Onshore winds will become breezy Saturday afternoon, reaching 15–20 kt [17–23 mph] late afternoon/early evening. VFR [Visual Flight Rules] expected Saturday into Sunday, with a drier airmass filtering in. 

VICINITY OF KSFO...CURRENTLY IFR WITH OVC008 REPORTED AT
TERMINAL. SATELLITE NIGHT IMAGERY SHOWS STRATUS HAS PROGRESSED
THROUGH THE GOLDEN GATE, AND IS ENCIRCLING THE BAY, UNDER LIGHT
WNW WINDS. ONSHORE WINDS WILL BECOME BREEZY SATURDAY AFTERNOON,
REACHING 15-20KT LATE AFTERNOON/EARLY EVENING. VFR EXPECTED
SATURDAY INTO SUNDAY, WITH A DRIER AIRMASS FILTERING IN. [AVI2]

SFO [San Francisco CA] bridge approach… patchy stratus observed on satellite over the approach, and filling in. High-resolution ensembles indicate clearing around 16Z [9am PDT], but low clouds may linger through 17Z [10am PDT]

SFO BRIDGE APPROACH...PATCHY STRATUS OBSERVED ON SATELLITE OVER
THE APPROACH, AND FILLING IN. HI-RES ENSEMBLES INDICATE CLEARING
AROUND 16Z, BUT LOW CLOUDS MAY LINGER THROUGH 17Z. [AVI2]

Monterey Bay terminals… MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules]. Satellite imagery reveals stratus over the Bay, surrounding coast, and progressing down the Salinas Valley. Clearing expected around 18Z [11am PDT] for VFR [Visual Flight Rules] Saturday, but perhaps later along the immediate coast. Breezy WNW winds 10–15 kt [12–17 mph] return in the afternoon. Possible ceilings/low clouds again Saturday night. 

MONTEREY BAY TERMINALS...MVFR/IFR. SATELLITE IMAGERY REVEALS
STRATUS OVER THE BAY, SURROUNDING COAST, AND PROGRESSING DOWN THE
SALINAS VALLEY. CLEARING EXPECTED AROUND 18Z FOR VFR SATURDAY,
BUT PERHAPS LATER ALONG THE IMMEDIATE COAST. BREEZY WNW WINDS
10-15 KT RETURN IN THE AFTERNOON. POSSIBLE CIGS/LOW CLOUDS AGAIN
SATURDAY NIGHT. [AVI2]

Marine. As of 03:04am PDT Saturday… moderately breezy to locally gusty northwest winds will persist across the waters today. The strongest winds will blow along the coast north of Point Reyes [San Francisco CA], south of Pigeon Point [Pescadero CA] and along the Big Sur coast south of Point Sur [Big Sur CA]. These stronger winds will produce steep to very steep wind waves and hazardous conditions for smaller vessels. More widespread stronger winds will move into the outer waters Sunday evening, persisting into early next week. A moderate northwest swell prevails through the period with a smaller longer period southerly swell. 

.MARINE...AS OF 03:04 AM PDT SATURDAY...MODERATELY BREEZY TO
LOCALLY GUSTY NORTHWEST WINDS WILL PERSIST ACROSS THE WATERS
TODAY. THE STRONGEST WINDS WILL BLOW ALONG THE COAST NORTH OF
POINT REYES, SOUTH OF PIGEON POINT AND ALONG THE BIG SUR COAST
SOUTH OF POINT SUR. THESE STRONGER WINDS WILL PRODUCE STEEP TO
VERY STEEP WIND WAVES AND HAZARDOUS CONDITIONS FOR SMALLER
VESSELS. MORE WIDESPREAD STRONGER WINDS WILL MOVE INTO THE OUTER
WATERS SUNDAY EVENING, PERSISTING INTO EARLY NEXT WEEK. A MODERATE
NORTHWEST SWELL PREVAILS THROUGH THE PERIOD WITH A SMALLER LONGER
PERIOD SOUTHERLY SWELL. [AVIA]

MTR Watches/Warnings/Advisories

  • Today: Small Craft AdvisoryPigeon Pt [Pescadero CA] to Pt Pinos [Monterey CA] 0–10 nm [11 miles] from 1pm Small Craft AdvisoryPt Arena [Mendocino CA] to Pt Reyes [San Francisco CA] 0–10 nm [11 miles] Small Craft AdvisoryPt Pinos [Monterey CA] to Pt Piedras Blancas [San Simeon CA] 0–10 nm [11 miles] 
.MTR WATCHES/WARNINGS/ADVISORIES...
.TDAY...SCA...PIGEON PT TO PT PINOS 0-10 NM FROM 1 PM
SCA...PT ARENA TO PT REYES 0-10 NM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM [WARN]

Public Forecast: MM/Dykema; Aviation: Lorber; Marine: Lorber 

PUBLIC FORECAST: MM/DYKEMA
AVIATION: LORBER
MARINE: LORBER [CRED]
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK]

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WWW.YOUTUBE.COM/NWSBAYAREA [DISC]

Point Forecast

Half Moon Bay CA

17 Apr 09:15am PDT

Today Mostly sunny, with a high near 64°. West wind 6 to 9 mph.
Tonight Mostly clear, with a low around 46°. Light and variable wind becoming NNE 5 to 7 mph after midnight.
Sunday Sunny, with a high near 73°. NNE wind 6 to 9 mph becoming NW in the afternoon.
Sunday Night Partly cloudy, with a low around 46°. WNW wind 5 to 9 mph becoming light WSW.
Monday Mostly sunny, with a high near 65°. WSW wind 6 to 9 mph.
Monday Night Partly cloudy, with a low around 46°.
Tuesday Partly sunny, with a high near 59°.
Tuesday Night Mostly cloudy, with a low around 46°.
Wednesday Mostly sunny, with a high near 60°.
Wednesday Night Partly cloudy, with a low around 45°.
Thursday Mostly sunny, with a high near 65°.
Thursday Night Partly cloudy, with a low around 45°.
Friday Partly sunny, with a high near 61°.
Today
Mostly sunny, with a high near 64. West wind 6 to 9 mph.
Tonight
Mostly clear, with a low around 46. Light and variable wind becoming north northeast 5 to 7 mph after midnight.
Sunday
Sunny, with a high near 73. North northeast wind 6 to 9 mph becoming northwest in the afternoon.
Sunday Night
Partly cloudy, with a low around 46. West northwest wind 5 to 9 mph becoming light west southwest.
Monday
Mostly sunny, with a high near 65. West southwest wind 6 to 9 mph.
Monday Night
Partly cloudy, with a low around 46.
Tuesday
Partly sunny, with a high near 59.
Tuesday Night
Mostly cloudy, with a low around 46.
Wednesday
Mostly sunny, with a high near 60.
Wednesday Night
Partly cloudy, with a low around 45.
Thursday
Mostly sunny, with a high near 65.
Thursday Night
Partly cloudy, with a low around 45.
Friday
Partly sunny, with a high near 61.

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: