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Area Forecast Discussion

FXUS66 KMTR [Monterey CA] 180508 AFDMTR 

FXUS66 KMTR 180508
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 10:08pm PDT Wed Sep 17 2014 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1008 PM PDT WED SEP 17 2014 [HEAD]

Synopsis. A Pacific weather system will bring a chance of light rain to much of the region tonight and Thursday… mainly across the north and also in coastal areas. There is also a slight chance of thunderstorms on Thursday… mainly across the North and East Bay. Temperatures will cool below seasonal averages through the remainder of the work week. Dry conditions will return and temperatures will rebound during the upcoming weekend as low pressure moves off to the east. 

.SYNOPSIS...A PACIFIC WEATHER SYSTEM WILL BRING A CHANCE OF LIGHT
RAIN TO MUCH OF THE REGION TONIGHT AND THURSDAY...MAINLY ACROSS
THE NORTH AND ALSO IN COASTAL AREAS. THERE IS ALSO A SLIGHT
CHANCE OF THUNDERSTORMS ON THURSDAY...MAINLY ACROSS THE NORTH AND
EAST BAY. TEMPERATURES WILL COOL BELOW SEASONAL AVERAGES THROUGH
THE REMAINDER OF THE WORK WEEK. DRY CONDITIONS WILL RETURN AND
TEMPERATURES WILL REBOUND DURING THE UPCOMING WEEKEND AS LOW
PRESSURE MOVES OFF TO THE EAST. [DISC]

Discussion. As of 9:15pm PDT Wednesday… an upper trough is located off the Northern California coast along 130°W [410 mi west of Montara] this evening. An associated cold front swept into northwest California late this afternoon and early evening… producing widespread rainfall north of Point Arena [Mendocino CA] and even scattered thunderstorms near Eureka. The front has since weakened quite a bit… but light rain has made it as far south as occidental and Santa Rosa within the past hour. The 00Z [5pm PDT] NAM [North American Meso (formerly Eta) model] is consistent with previous NAM [North American Meso (formerly Eta) model] output in spreading light rain across most of the North Bay overnight… as well as into all of our coastal areas by late tonight. Current forecast looks on track except have taken out mention of thunderstorms for tonight as it appears there is no longer any convection along the front and the models show very little instability for the remainder of tonight. 

.DISCUSSION...AS OF 9:15 PM PDT WEDNESDAY...AN UPPER TROUGH IS
LOCATED OFF THE NORTHERN CALIFORNIA COAST ALONG 130W THIS EVENING.
AN ASSOCIATED COLD FRONT SWEPT INTO NORTHWEST CALIFORNIA LATE THIS
AFTERNOON AND EARLY EVENING....PRODUCING WIDESPREAD RAINFALL NORTH
OF POINT ARENA AND EVEN SCATTERED THUNDERSTORMS NEAR EUREKA. THE
FRONT HAS SINCE WEAKENED QUITE A BIT...BUT LIGHT RAIN HAS MADE IT
AS FAR SOUTH AS OCCIDENTAL AND SANTA ROSA WITHIN THE PAST HOUR.
THE 00Z NAM IS CONSISTENT WITH PREVIOUS NAM OUTPUT IN SPREADING
LIGHT RAIN ACROSS MOST OF THE NORTH BAY OVERNIGHT...AS WELL AS
INTO ALL OF OUR COASTAL AREAS BY LATE TONIGHT. CURRENT FORECAST
LOOKS ON TRACK EXCEPT HAVE TAKEN OUT MENTION OF THUNDERSTORMS FOR
TONIGHT AS IT APPEARS THERE IS NO LONGER ANY CONVECTION ALONG THE
FRONT...AND THE MODELS SHOW VERY LITTLE INSTABILITY FOR THE
REMAINDER OF TONIGHT. [DISC]

Shower activity will continue into Thursday as the upper trough gradually digs southeast along the coast. Instability will increase on Thursday as a colder air moves in aloft. Based on latest model guidance… the best chance of isolated thunderstorms on Thursday will be across the North and East Bay. 

SHOWER ACTIVITY WILL CONTINUE INTO THURSDAY AS THE UPPER TROUGH
GRADUALLY DIGS SOUTHEAST ALONG THE COAST. INSTABILITY WILL
INCREASE ON THURSDAY AS A COLDER AIR MOVES IN ALOFT. BASED ON
LATEST MODEL GUIDANCE...THE BEST CHANCE OF ISOLATED THUNDERSTORMS
ON THURSDAY WILL BE ACROSS THE NORTH AND EAST BAY. [DISC]

The trough is forecast to drop south on Thursday night and Friday and eventually form a 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] near Point Conception [Santa Barbara CA]. Earlier runs of the NAM [North American Meso (formerly Eta) model] had indicated that showers and thunderstorms might still be a possibility across the far southeastern part of our forecast area into Friday… but now now the NAM [North American Meso (formerly Eta) model] is on board with the other models in keeping all precipitation out of our area after Thursday evening. 

THE TROUGH IS FORECAST TO DROP SOUTH ON THURSDAY NIGHT AND FRIDAY
AND EVENTUALLY FORM A CUTOFF LOW NEAR POINT CONCEPTION. EARLIER
RUNS OF THE NAM HAD INDICATED THAT SHOWERS AND THUNDERSTORMS MIGHT
STILL BE A POSSIBILITY ACROSS THE FAR SOUTHEASTERN PART OF OUR
FORECAST AREA INTO FRIDAY...BUT NOW NOW THE NAM IS ON BOARD WITH
THE OTHER MODELS IN KEEPING ALL PRECIP OUT OF OUR AREA AFTER
THURSDAY EVENING. [DISC]

850 mb temps are forecast to drop by about 8°C by tomorrow and so we can expect widespread cooling with temperatures falling below normal in most areas. Temps will then gradually warm from Friday through the weekend as the low first sinks south of our area and then moves off to the east. 

850 MB TEMPS ARE FORECAST TO DROP BY ABOUT 8 DEG C BY TOMORROW AND
SO WE CAN EXPECT WIDESPREAD COOLING WITH TEMPERATURES FALLING
BELOW NORMAL IN MOST AREAS. TEMPS WILL THEN GRADUALLY WARM FROM
FRIDAY THROUGH THE WEEKEND AS THE LOW FIRST SINKS SOUTH OF OUR
AREA AND THEN MOVES OFF TO THE EAST. [DISC]

During past few days the medium range models had been forecasting a rather robust warming trend during the first half of next week when a strong upper ridge was expected to develop off the California coast. But the latest models now show another upper trough approaching the West Coast with rain possible across at least the northern portion of our area by Tuesday night or Wednesday of next week. 

DURING PAST FEW DAYS THE MEDIUM RANGE MODELS HAD BEEN FORECASTING
A RATHER ROBUST WARMING TREND DURING THE FIRST HALF OF NEXT WEEK
WHEN A STRONG UPPER RIDGE WAS EXPECTED TO DEVELOP OFF THE
CALIFORNIA COAST. BUT THE LATEST MODELS NOW SHOW ANOTHER UPPER
TROUGH APPROACHING THE WEST COAST WITH RAIN POSSIBLE ACROSS AT
LEAST THE NORTHERN PORTION OF OUR AREA BY TUESDAY NIGHT OR
WEDNESDAY OF NEXT WEEK. [DISC]

Aviation. As of 10:00pm PDT Wednesday… rain… mostly light in intensity and on the immediate coast continues to move south this evening. Ceilings at area terminals will gradually lower to MVFR [Marginal Visual Flight Rules] levels overnight. 

.AVIATION...AS OF 10:00 PM PDT WEDNESDAY...RAIN...MOSTLY LIGHT IN
INTENSITY AND ON THE IMMEDIATE COAST CONTINUES TO MOVE SOUTH THIS
EVENING. CIGS AT AREA TERMINALS WILL GRADUALLY LOWER TO MVFR
LEVELS OVERNIGHT. [AVIA]

Vicinity of KSFO [San Francisco CA]… light drizzle reported at KSFO [San Francisco CA] now. The lower to mid level clouds will move in later tonight. MVFR [Marginal Visual Flight Rules] ceilings with light rain late tonight. Wet runways. 

VICINITY OF KSFO...LIGHT DRIZZLE REPORTED AT KSFO NOW. THE LOWER TO
MID LEVEL CLOUDS WILL MOVE IN LATER TONIGHT. MVFR CIGS WITH LIGHT
RAIN LATE TONIGHT. WET RUNWAYS. [AVI2]

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

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

Monterey Bay Area terminals… VFR [Visual Flight Rules] holding together so far but potential is there for low cloud development ahead of the incoming low. Cloud layers tonight forecast to be primarily MVFR [Marginal Visual Flight Rules]

MONTEREY BAY AREA TERMINALS...VFR HOLDING TOGETHER SO FAR BUT POTENTIAL
IS THERE FOR LOW CLOUD DEVELOPMENT AHEAD OF THE INCOMING LOW.
CLOUD LAYERS TONIGHT FORECAST TO BE PRIMARILY MVFR. [AVI2]

Marine. As of 6:35pm PDT Wednesday… very large long period southwesterly swell will impact the waters through Thursday. A low is centered 350 miles west of Ukiah. This low will move through the northern waters on Thursday resulting in light southerly winds with a chance of showers. There will be a slight chance of thunderstorms this evening north of Point Reyes [San Francisco CA] and in the San Francisco Bay Thursday. Winds will become light to moderate northwest Friday through Sunday after the low moves inland. 

.MARINE...AS OF 6:35 PM PDT WEDNESDAY...VERY LARGE LONG PERIOD
SOUTHWESTERLY SWELL WILL IMPACT THE WATERS THROUGH THURSDAY. A LOW
IS CENTERED 350 MILES WEST OF UKIAH. THIS LOW WILL MOVE THROUGH
THE NORTHERN WATERS ON THURSDAY RESULTING IN LIGHT SOUTHERLY WINDS
WITH A CHANCE OF SHOWERS. THERE WILL BE A SLIGHT CHANCE OF
THUNDERSTORMS THIS EVENING NORTH OF POINT REYES AND IN THE SAN
FRANCISCO BAY THURSDAY. WINDS WILL BECOME LIGHT TO MODERATE
NORTHWEST FRIDAY THROUGH SUNDAY AFTER THE LOW MOVES INLAND. [AVIA]

MTR Watches/Warnings/Advisories

  • Tonight: none. 
.MTR WATCHES/WARNINGS/ADVISORIES...
.TNGT...NONE. [WARN]

Public Forecast: Dykema; Aviation: Canepa; Marine: W PI/Canepa 

PUBLIC FORECAST: DYKEMA
AVIATION: CANEPA
MARINE: W PI/CANEPA [CRED]
VISIT US AT WEATHER.GOV/SANFRANCISCO [LINK]

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WWW.YOUTUBE.COM/NWSBAYAREA [DISC]

Point Forecast

Montara CA

9:05pm PDT Sep 17 2014

Overnight. A 40% chance of showers. Cloudy, with a low around 58°. SSW wind around 14 mph, with gusts as high as 18 mph.


Thursday. A 30% chance of showers. Cloudy, with a high near 68°. South wind 10 to 14 mph.

Thursday Night. Cloudy, with a low around 57°. WNW wind 5 to 13 mph.


Friday. Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 67°. West wind 7 to 9 mph.

Friday Night. Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 57°. West wind 7 to 13 mph.


Saturday. Patchy fog before 11am. Otherwise, partly sunny, with a high near 66°.

Saturday Night. Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 57°.


Sunday. Patchy fog before 11am. Otherwise, partly sunny, with a high near 66°.

Sunday Night. Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 56°.


Monday. Patchy fog before 11am. Otherwise, partly sunny, with a high near 67°.

Monday Night. Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 56°.


Tuesday. Patchy fog before 11am. Otherwise, mostly sunny, with a high near 67°.

Tuesday Night. Mostly cloudy, with a low around 57°.


Wednesday. Mostly sunny, with a high near 69°.

  • Overnight A 40 percent chance of showers. Cloudy, with a low around 58. South southwest wind around 14 mph, with gusts as high as 18 mph.
  • Thursday A 30 percent chance of showers. Cloudy, with a high near 68. South wind 10 to 14 mph.
  • Thursday Night Cloudy, with a low around 57. West northwest wind 5 to 13 mph.
  • Friday Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 67. West wind 7 to 9 mph.
  • Friday Night Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 57. West wind 7 to 13 mph.
  • Saturday Patchy fog before 11am. Otherwise, partly sunny, with a high near 66.
  • Saturday Night Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 57.
  • Sunday Patchy fog before 11am. Otherwise, partly sunny, with a high near 66.
  • Sunday Night Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 56.
  • Monday Patchy fog before 11am. Otherwise, partly sunny, with a high near 67.
  • Monday Night Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 56.
  • Tuesday Patchy fog before 11am. Otherwise, mostly sunny, with a high near 67.
  • Tuesday Night Mostly cloudy, with a low around 57.
  • Wednesday Mostly sunny, with a high near 69.

  • 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: