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FXUS66 KMTR [Monterey CA] 191150 AFDMTR 

FXUS66 KMTR 191150
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 4:50am PDT Thu Oct 19 2017 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
450 AM PDT THU OCT 19 2017 [HEAD]

Synopsis. A cold front remains on track to push through our district later today and tonight, bringing our first widespread rainfall event of the season, along with cooler temperatures. Look for the most rainfall to be in the coastal ranges and across the North Bay. Along with cooler temperatures, breezy onshore winds can be expected through Friday. Dry conditions will return on Friday and a warming trend is forecast over the weekend and into the first part of next week. Temperatures are forecast to be well above seasonal averages during the first half of next week. 

.SYNOPSIS...A COLD FRONT REMAINS ON TRACK TO PUSH THROUGH OUR
DISTRICT LATER TODAY AND TONIGHT, BRINGING OUR FIRST WIDESPREAD
RAINFALL EVENT OF THE SEASON, ALONG WITH COOLER TEMPERATURES. LOOK
FOR THE MOST RAINFALL TO BE IN THE COASTAL RANGES AND ACROSS THE
NORTH BAY. ALONG WITH COOLER TEMPERATURES, BREEZY ONSHORE WINDS
CAN BE EXPECTED THROUGH FRIDAY. DRY CONDITIONS WILL RETURN ON
FRIDAY AND A WARMING TREND IS FORECAST OVER THE WEEKEND AND INTO
THE FIRST PART OF NEXT WEEK. TEMPERATURES ARE FORECAST TO BE WELL
ABOVE SEASONAL AVERAGES DURING THE FIRST HALF OF NEXT WEEK. [DISC]

Discussion. As of 3:43am PDT Thursday… the marine layer deepened yesterday and cool air filtered inland with help from an increased onshore flow. Currently the marine layer depth is around 1000 feet per the Fort Ord 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.] and the latest surface pressure gradient between SFO [San Francisco CA] and SAC [Sacramento CA] was up to 2.6 mb. Latest temperature trends are warmer than yesterday at most locations due to increased cloud cover as coastal stratus has spread into inland valleys. 

.DISCUSSION...AS OF 3:43 AM PDT THURSDAY...THE MARINE LAYER
DEEPENED YESTERDAY AND COOL AIR FILTERED INLAND WITH HELP FROM AN
INCREASED ONSHORE FLOW. CURRENTLY THE MARINE LAYER DEPTH IS AROUND
1000 FEET PER THE FORT ORD PROFILER AND THE LATEST SURFACE
PRESSURE GRADIENT BETWEEN SFO AND SAC WAS UP TO 2.6 MB. LATEST
TEMPERATURE TRENDS ARE WARMER THAN YESTERDAY AT MOST LOCATIONS DUE
TO INCREASED CLOUD COVER AS COASTAL STRATUS HAS SPREAD INTO
INLAND VALLEYS. [DISC]

Satellite imagery shows the approaching cold from now along the Washington and Oregon coasts. Models continue to bring the system to our area later today, with rainfall reaching the Sonoma and Marin coasts by this afternoon, then spreading south through the greater San Francisco Bay Area by late evening, and then down through the remainder of the CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map] around midnight and through the early morning hours. The 00Z [5pm PDT] NAM [North American Meso (formerly Eta) model] forecasts local rain totals up to 0.75" in the North Bay mountains tomorrow afternoon and evening, and up to 0.25" in the Santa Cruz Mountains tomorrow night. Elsewhere in the hills and North Bay valleys, expect rain totals from 0.10–0.25", while all other valley locations will likely see a tenth of an inch or less. Rainfall is expected to end by Friday morning with partly cloudy and relatively cool and breezy conditions. 

SATELLITE IMAGERY SHOWS THE APPROACHING COLD FROM NOW ALONG THE
WASHINGTON AND OREGON COASTS. MODELS CONTINUE TO BRING THE SYSTEM
TO OUR AREA LATER TODAY, WITH RAINFALL REACHING THE SONOMA AND
MARIN COASTS BY THIS AFTERNOON, THEN SPREADING SOUTH THROUGH THE
GREATER SAN FRANCISCO BAY AREA BY LATE EVENING, AND THEN DOWN
THROUGH THE REMAINDER OF THE CWA AROUND MIDNIGHT AND THROUGH THE
EARLY MORNING HOURS. THE 00Z NAM FORECASTS LOCAL RAIN TOTALS UP TO
0.75" IN THE NORTH BAY MOUNTAINS TOMORROW AFTERNOON AND EVENING,
AND UP TO 0.25" IN THE SANTA CRUZ MOUNTAINS TOMORROW NIGHT.
ELSEWHERE IN THE HILLS AND NORTH BAY VALLEYS, EXPECT RAIN TOTALS
FROM 0.10-0.25", WHILE ALL OTHER VALLEY LOCATIONS WILL LIKELY SEE
A TENTH OF AN INCH OR LESS. RAINFALL IS EXPECTED TO END BY FRIDAY
MORNING WITH PARTLY CLOUDY AND RELATIVELY COOL AND BREEZY
CONDITIONS. [DISC]

A warming trend is forecast during the weekend as an upper level ridge begins to build over California. The ridge is then expected to strengthen along the West Coast early next week, resulting in a marked warming trend. Light offshore flow is also forecast to develop early next week resulting in warm and dry conditions across our entire area on Monday and Tuesday, with widespread highs in the 80s to around 90. Slight cooling is indicated by midweek at the coast with a return to onshore flow, but warm conditions will persist inland. 

A WARMING TREND IS FORECAST DURING THE WEEKEND AS AN UPPER LEVEL
RIDGE BEGINS TO BUILD OVER CALIFORNIA. THE RIDGE IS THEN EXPECTED
TO STRENGTHEN ALONG THE WEST COAST EARLY NEXT WEEK, RESULTING IN
A MARKED WARMING TREND. LIGHT OFFSHORE FLOW IS ALSO FORECAST TO
DEVELOP EARLY NEXT WEEK RESULTING IN WARM AND DRY CONDITIONS
ACROSS OUR ENTIRE AREA ON MONDAY AND TUESDAY, WITH WIDESPREAD
HIGHS IN THE 80S TO AROUND 90. SLIGHT COOLING IS INDICATED BY
MIDWEEK AT THE COAST WITH A RETURN TO ONSHORE FLOW, BUT WARM
CONDITIONS WILL PERSIST INLAND. [DISC]

Aviation. As of 4:46am PDT Thursday… for 12Z [5am PDT] TAFs [Terminal Aerodrome Forecasts]. A complicated aviation forecast over the next 24–36 hours in store for Bay Area terminals. Current fog product shows widespread stratus/low clouds affecting all TAF [Terminal Aerodrome Forecast] terminals. Most sites are MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules], with some isolated LIFR [Low Instrument Flight Rules] ceilings right now. Clearing time is still uncertain at this moment. With sufficient onshore flow, it's possible some sites, such as KMRY [Monterey CA], may not clear at all today, though ceilings may lift some later this morning. This will have to be closely monitored and updated as the morning progresses. A cold front will bring a chance of rain this evening and overnight, enough to wet the runways at most TAF [Terminal Aerodrome Forecast] sites. Winds ahead of the front will be moderate, occasionally gusty along and behind the front, out of the SW/WSW. Winds will eventually turn more out of the W/NW after the front passes. 

.AVIATION...AS OF 4:46 AM PDT THURSDAY...FOR 12Z TAFS. A
COMPLICATED AVIATION FORECAST OVER THE NEXT 24-36 HOURS IN STORE
FOR BAY AREA TERMINALS. CURRENT FOG PRODUCT SHOWS WIDESPREAD
STRATUS/LOW CLOUDS AFFECTING ALL TAF TERMINALS. MOST SITES ARE
MVFR/IFR, WITH SOME ISOLATED LIFR CIGS RIGHT NOW. CLEARING TIME IS
STILL UNCERTAIN AT THIS MOMENT. WITH SUFFICIENT ONSHORE FLOW,
IT`S POSSIBLE SOME SITES, SUCH AS KMRY, MAY NOT CLEAR AT ALL
TODAY, THOUGH CIGS MAY LIFT SOME LATER THIS MORNING. THIS WILL
HAVE TO BE CLOSELY MONITORED AND UPDATED AS THE MORNING
PROGRESSES. A COLD FRONT WILL BRING A CHANCE OF RAIN THIS EVENING
AND OVERNIGHT, ENOUGH TO WET THE RUNWAYS AT MOST TAF SITES. WINDS
AHEAD OF THE FRONT WILL BE MODERATE, OCCASIONALLY GUSTY ALONG AND
BEHIND THE FRONT, OUT OF THE SW/WSW. WINDS WILL EVENTUALLY TURN
MORE OUT OF THE W/NW AFTER THE FRONT PASSES. [AVIA]

Overall forecast confidence: low to moderate 

OVERALL FORECAST CONFIDENCE: LOW TO MODERATE [AVI2]

Vicinity of KSFO [San Francisco CA]MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules] ceilings will prevail through much of the morning, possibly into the early afternoon hours. Low confidence with respect to clearing times. WSW winds through much of the period until the cold front passes around 06Z [11pm PDT]. Rain/showers possible as early as 03Z [8pm PDT]

VICINITY OF KSFO...MVFR/IFR CIGS WILL PREVAIL THROUGH MUCH OF THE
MORNING, POSSIBLY INTO THE EARLY AFTERNOON HOURS. LOW CONFIDENCE
WITH RESPECT TO CLEARING TIMES. WSW WINDS THROUGH MUCH OF THE
PERIOD UNTIL THE COLD FRONT PASSES AROUND 06Z. RAIN/SHOWERS
POSSIBLE AS EARLY AS 03Z. [AVI2]

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

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

Monterey Bay terminals… LIFR [Low Instrument Flight Rules]/IFR [Instrument Flight Rules] ceilings will continue through majority of the morning. Low confidence with respect to clearing times. Light to moderate WSW winds for KMRY [Monterey CA] today, with winds varying through the day at KSNS [Salinas CA]. Rain/showers possible as early 06Z [11pm PDT]

MONTEREY BAY TERMINALS...LIFR/IFR CIGS WILL CONTINUE THROUGH
MAJORITY OF THE MORNING. LOW CONFIDENCE WITH RESPECT TO CLEARING
TIMES. LIGHT TO MODERATE WSW WINDS FOR KMRY TODAY, WITH WINDS
VARYING THROUGH THE DAY AT KSNS. RAIN/SHOWERS POSSIBLE AS EARLY
06Z. [AVI2]

Fire weather. As of 3:43am PDT Thursday… relative humidity recoveries have improved this morning with even most hilltop areas seeing 80–100% values. Onshore winds will continue to gradually increase today and moderate and locally gusty winds are expected. Models continue to move an early season cold front through the district late today and tonight. Rainfall will begin in the North Bay this afternoon and spread across most of the remainder of the district tonight. The models have just recently trended slightly wetter with this system, although rainfall amounts are still expected to be mostly light. Wetting rains are most likely in the North Bay mountains and perhaps locally in the Santa Cruz Mountains. Rainfall should end in most areas by Friday morning. Friday will be a cool day with brisk northwest winds. 

.FIRE WEATHER...AS OF 3:43 AM PDT THURSDAY...RELATIVE HUMIDITY
RECOVERIES HAVE IMPROVED THIS MORNING WITH EVEN MOST HILLTOP AREAS
SEEING 80-100% VALUES. ONSHORE WINDS WILL CONTINUE TO GRADUALLY
INCREASE TODAY AND MODERATE AND LOCALLY GUSTY WINDS ARE EXPECTED.
MODELS CONTINUE TO MOVE AN EARLY SEASON COLD FRONT THROUGH THE
DISTRICT LATE TODAY AND TONIGHT. RAINFALL WILL BEGIN IN THE NORTH
BAY THIS AFTERNOON AND SPREAD ACROSS MOST OF THE REMAINDER OF THE
DISTRICT TONIGHT. THE MODELS HAVE JUST RECENTLY TRENDED SLIGHTLY
WETTER WITH THIS SYSTEM, ALTHOUGH RAINFALL AMOUNTS ARE STILL
EXPECTED TO BE MOSTLY LIGHT. WETTING RAINS ARE MOST LIKELY IN THE
NORTH BAY MOUNTAINS AND PERHAPS LOCALLY IN THE SANTA CRUZ
MOUNTAINS. RAINFALL SHOULD END IN MOST AREAS BY FRIDAY MORNING.
FRIDAY WILL BE A COOL DAY WITH BRISK NORTHWEST WINDS. [AVIA]

A warming trend will begin over the upcoming weekend as a high pressure ridge begins to build over California. This ridge will strengthen into early next week and result in warm and dry conditions districtwide from Monday through Wednesday. Will need to be wary of possible gusty offshore winds in the hills by Sunday night and especially Monday night. 

A WARMING TREND WILL BEGIN OVER THE UPCOMING WEEKEND AS A HIGH
PRESSURE RIDGE BEGINS TO BUILD OVER CALIFORNIA. THIS RIDGE WILL
STRENGTHEN INTO EARLY NEXT WEEK AND RESULT IN WARM AND DRY
CONDITIONS DISTRICTWIDE FROM MONDAY THROUGH WEDNESDAY. WILL NEED
TO BE WARY OF POSSIBLE GUSTY OFFSHORE WINDS IN THE HILLS BY SUNDAY
NIGHT AND ESPECIALLY MONDAY NIGHT. [AVI2]

Marine. As of 2:47am PDT Thursday… a cold front is forecast to pass through the region later this evening. Winds will increase along and just behind the front, occasionally gusting around 25 knots [29 mph] at times. Showers will be possible ahead of and along the cold front, as well. A very robust northwest, long period swell will arrive late this afternoon and through the evening, generating large waves and hazardous seas through at least Saturday. Operators of small crafts are urged to use extreme caution if out at sea over the next several days. 

.MARINE...AS OF 2:47 AM PDT THURSDAY...A COLD FRONT IS FORECAST
TO PASS THROUGH THE REGION LATER THIS EVENING. WINDS WILL INCREASE
ALONG AND JUST BEHIND THE FRONT, OCCASIONALLY GUSTING AROUND 25
KNOTS AT TIMES. SHOWERS WILL BE POSSIBLE AHEAD OF AND ALONG THE
COLD FRONT, AS WELL. A VERY ROBUST NORTHWEST, LONG PERIOD SWELL
WILL ARRIVE LATE THIS AFTERNOON AND THROUGH THE EVENING,
GENERATING LARGE WAVES AND HAZARDOUS SEAS THROUGH AT LEAST
SATURDAY. OPERATORS OF SMALL CRAFTS ARE URGED TO USE EXTREME
CAUTION IF OUT AT SEA OVER THE NEXT SEVERAL DAYS. [AVIA]

MTR Watches/Warnings/Advisories

  • Today: Small Craft AdvisoryPt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] from 5pm Small Craft AdvisoryPt Pinos [Monterey CA] to Pt Piedras Blancas [San Simeon CA] 0–10 nm [11 miles] until 6am 
.MTR WATCHES/WARNINGS/ADVISORIES...
.TDAY...SCA...PT ARENA TO PIGEON PT 10-60 NM FROM 5 PM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM UNTIL 6 AM [WARN]

Public Forecast: Sims; Aviation: BAM; Marine: BAM; Fire Weather: Sims 

PUBLIC FORECAST: SIMS
AVIATION: BAM
MARINE: BAM
FIRE WEATHER: SIMS [CRED]
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK]

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Point Forecast

Half Moon Bay Airport

19 Oct 5:15am PDT

Overnight A 20% chance of rain. Patchy fog. Otherwise, cloudy, with a low around 47°. West wind around 6 mph.
Thursday A 20% chance of rain before 11am. Patchy fog before 8am. Otherwise, mostly cloudy, with a high near 60°. West wind 5 to 11 mph becoming south in the morning. New precipitation amounts of less than a tenth of an inch possible.
Thursday Night A chance of rain before 11pm, then a chance of showers after 11pm. Mostly cloudy, with a low around 49°. South wind 16 to 21 mph becoming WNW after midnight. Winds could gust as high as 25 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.
Friday Mostly sunny, with a high near 59°. WNW wind 11 to 16 mph, with gusts as high as 21 mph.
Friday Night Mostly clear, with a low around 45°. NW wind around 16 mph, with gusts as high as 21 mph.
Saturday Mostly sunny, with a high near 62°.
Saturday Night Mostly clear, with a low around 48°.
Sunday Sunny, with a high near 68°.
Sunday Night Clear, with a low around 48°.
Monday Sunny, with a high near 72°.
Monday Night Clear, with a low around 51°.
Tuesday Sunny, with a high near 74°.
Tuesday Night Mostly clear, with a low around 50°.
Wednesday Sunny, with a high near 71°.
Overnight
A 20 percent chance of rain. Patchy fog. Otherwise, cloudy, with a low around 47. West wind around 6 mph.
Thursday
A 20 percent chance of rain before 11am. Patchy fog before 8am. Otherwise, mostly cloudy, with a high near 60. West wind 5 to 11 mph becoming south in the morning. New precipitation amounts of less than a tenth of an inch possible.
Thursday Night
A chance of rain before 11pm, then a chance of showers after 11pm. Mostly cloudy, with a low around 49. South wind 16 to 21 mph becoming west northwest after midnight. Winds could gust as high as 25 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.
Friday
Mostly sunny, with a high near 59. West northwest wind 11 to 16 mph, with gusts as high as 21 mph.
Friday Night
Mostly clear, with a low around 45. Northwest wind around 16 mph, with gusts as high as 21 mph.
Saturday
Mostly sunny, with a high near 62.
Saturday Night
Mostly clear, with a low around 48.
Sunday
Sunny, with a high near 68.
Sunday Night
Clear, with a low around 48.
Monday
Sunny, with a high near 72.
Monday Night
Clear, with a low around 51.
Tuesday
Sunny, with a high near 74.
Tuesday Night
Mostly clear, with a low around 50.
Wednesday
Sunny, with a high near 71.

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: