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FXUS66 KMTR [Monterey CA] 240552 AFDMTR 

FXUS66 KMTR 240552
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 10:52pm PDT Fri Aug 23 2019 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1052 PM PDT FRI AUG 23 2019 [HEAD]

Synopsis. Little change is forecast through the first half of the weekend. A modest warming trend is then expected from Sunday into Monday as high pressure strengthens over California. The ridge will weaken slightly by Tuesday and Wednesday as the remnants of Tropical Storm Ivo Pass west of the Golden Gate. Ivo remnants may bring increasing mid and high clouds and more humidity to the region next week. 

.SYNOPSIS...LITTLE CHANGE IS FORECAST THROUGH THE FIRST HALF OF
THE WEEKEND. A MODEST WARMING TREND IS THEN EXPECTED FROM SUNDAY
INTO MONDAY AS HIGH PRESSURE STRENGTHENS OVER CALIFORNIA. THE
RIDGE WILL WEAKEN SLIGHTLY BY TUESDAY AND WEDNESDAY AS THE
REMNANTS OF TROPICAL STORM IVO PASS WEST OF THE GOLDEN GATE. IVO
REMNANTS MAY BRING INCREASING MID AND HIGH CLOUDS AND MORE
HUMIDITY TO THE REGION NEXT WEEK. [DISC]

Discussion. As of 8:55pm PDT Friday… the combination of a deeper marine layer and southerly low level flow resulted in cooling across most of our region today. Today's cooling was most pronounced in the North Bay valleys where south winds enhanced the inland transport of marine air. Highs in the North Bay valleys today were as much as 15° cooler than yesterday. Similarly, Santa Cruz on the north side of Monterey Bay cooled by 11°. By contrast, today's high of 80 in Monterey was 10° warmer than yesterday due to downslope flow off the Santa Lucia Mountains to the south. 

.DISCUSSION...AS OF 8:55 PM PDT FRIDAY...THE COMBINATION OF A
DEEPER MARINE LAYER AND SOUTHERLY LOW LEVEL FLOW RESULTED IN
COOLING ACROSS MOST OF OUR REGION TODAY. TODAY`S COOLING WAS MOST
PRONOUNCED IN THE NORTH BAY VALLEYS WHERE SOUTH WINDS ENHANCED THE
INLAND TRANSPORT OF MARINE AIR. HIGHS IN THE NORTH BAY VALLEYS
TODAY WERE AS MUCH AS 15 DEGREES COOLER THAN YESTERDAY. SIMILARLY,
SANTA CRUZ ON THE NORTH SIDE OF MONTEREY BAY COOLED BY 11
DEGREES. BY CONTRAST, TODAY`S HIGH OF 80 IN MONTEREY WAS 10
DEGREES WARMER THAN YESTERDAY DUE TO DOWNSLOPE FLOW OFF THE SANTA
LUCIA MOUNTAINS TO THE SOUTH. [DISC]

An upper level ridge currently dominates the eastern Pacific between 30 and 40° north latitude, and extends eastward across California. The models agree that the ridge will gradually strengthen over California through the weekend and into the early part of next week. However, warming due to the strengthening ridge will likely be tempered over the weekend by continued southerly low level flow. In fact, most model guidance indicates little change in temperatures on Saturday. Modest warming is then likely on Sunday and especially Monday as the marine layer compresses and southerly flow tapers off and gradually veers more to the west and northwest. Even with the expected warming on Sunday and Monday, heat risk is projected to only rise into the moderate category across our inland areas, with just a few pockets of high heat risk expected in the inland hills where temperatures will remain warm during the overnight hours. Persistent onshore flow will keep heat risk mostly in the low category in coastal areas. 

AN UPPER LEVEL RIDGE CURRENTLY DOMINATES THE EASTERN PACIFIC
BETWEEN 30 AND 40 DEGREES NORTH LATITUDE, AND EXTENDS EASTWARD
ACROSS CALIFORNIA. THE MODELS AGREE THAT THE RIDGE WILL GRADUALLY
STRENGTHEN OVER CALIFORNIA THROUGH THE WEEKEND AND INTO THE EARLY
PART OF NEXT WEEK. HOWEVER, WARMING DUE TO THE STRENGTHENING RIDGE
WILL LIKELY BE TEMPERED OVER THE WEEKEND BY CONTINUED SOUTHERLY
LOW LEVEL FLOW. IN FACT, MOST MODEL GUIDANCE INDICATES LITTLE
CHANGE IN TEMPERATURES ON SATURDAY. MODEST WARMING IS THEN LIKELY
ON SUNDAY AND ESPECIALLY MONDAY AS THE MARINE LAYER COMPRESSES
AND SOUTHERLY FLOW TAPERS OFF AND GRADUALLY VEERS MORE TO THE WEST
AND NORTHWEST. EVEN WITH THE EXPECTED WARMING ON SUNDAY AND
MONDAY, HEAT RISK IS PROJECTED TO ONLY RISE INTO THE MODERATE
CATEGORY ACROSS OUR INLAND AREAS, WITH JUST A FEW POCKETS OF HIGH
HEAT RISK EXPECTED IN THE INLAND HILLS WHERE TEMPERATURES WILL
REMAIN WARM DURING THE OVERNIGHT HOURS. PERSISTENT ONSHORE FLOW
WILL KEEP HEAT RISK MOSTLY IN THE LOW CATEGORY IN COASTAL AREAS. [DISC]

The upper ridge axis is forecast to shift to our east by Tuesday as remnants of Tropical Storm Ivo drift north offshore. There remains quite a bit of uncertainty as to the exact trajectory of Ivo's moisture, but current model consensus indicates that the bulk of the moisture will remain offshore from the Bay Area as it drifts north, and then shift eastward and inland across northwest California sometime between Tuesday afternoon and Wednesday morning. The 12Z [5am PDT] ECMWF [European Center for Medium-Range Weather Forecasts model] forecasts some of this mid/upper level moisture clipping at least the northern half of our forecast area late Tuesday. Will need to continue to monitor this situation closely as high-based thunderstorms and dry lightning are possible in conjunction with this tropical moisture. 

THE UPPER RIDGE AXIS IS FORECAST TO SHIFT TO OUR EAST BY TUESDAY
AS REMNANTS OF TROPICAL STORM IVO DRIFT NORTH OFFSHORE. THERE
REMAINS QUITE A BIT OF UNCERTAINTY AS TO THE EXACT TRAJECTORY OF
IVO`S MOISTURE, BUT CURRENT MODEL CONSENSUS INDICATES THAT THE
BULK OF THE MOISTURE WILL REMAIN OFFSHORE FROM THE BAY AREA AS IT
DRIFTS NORTH, AND THEN SHIFT EASTWARD AND INLAND ACROSS NORTHWEST
CALIFORNIA SOMETIME BETWEEN TUESDAY AFTERNOON AND WEDNESDAY
MORNING. THE 12Z ECMWF FORECASTS SOME OF THIS MID/UPPER LEVEL
MOISTURE CLIPPING AT LEAST THE NORTHERN HALF OF OUR FORECAST AREA
LATE TUESDAY. WILL NEED TO CONTINUE TO MONITOR THIS SITUATION
CLOSELY AS HIGH-BASED THUNDERSTORMS AND DRY LIGHTNING ARE POSSIBLE
IN CONJUNCTION WITH THIS TROPICAL MOISTURE. [DISC]

A gradual cooling trend is forecast during the second half of next week as the upper ridge continues to drift slowly to our east. 

A GRADUAL COOLING TREND IS FORECAST DURING THE SECOND HALF OF NEXT
WEEK AS THE UPPER RIDGE CONTINUES TO DRIFT SLOWLY TO OUR EAST. [DISC]

Aviation. As of 10:52pm PDT Friday… in most places winds have eased since earlier today, the SMX [Santa Maria CA]-SFO [San Francisco CA] gradient has decreased to 1 mb while the onshore gradient SFO [San Francisco CA]-SAC [Sacramento CA] is 2.8 mb. 925 mb south winds ease tonight but resume to gusty again Saturday, 850 mb south winds hold steady tonight and Saturday based on WRF [Weather Research and Forecasting model] output. Very localized low level wind shear remains a possibility on the coast and over the coastal waters Saturday, not enough to place in 06Z [11pm PDT] TAFs [Terminal Aerodrome Forecasts] for now. Otherwise it's VFR [Visual Flight Rules] inland for the period and IFR [Instrument Flight Rules]-MVFR [Marginal Visual Flight Rules] coastal sections and nearby valleys tonight and Saturday morning. 

.AVIATION...AS OF 10:52 PM PDT FRIDAY...IN MOST PLACES WINDS HAVE
EASED SINCE EARLIER TODAY, THE SMX-SFO GRADIENT HAS DECREASED TO
1 MB WHILE THE ONSHORE GRADIENT SFO-SAC IS 2.8 MB. 925 MB SOUTH
WINDS EASE TONIGHT BUT RESUME TO GUSTY AGAIN SATURDAY, 850 MB
SOUTH WINDS HOLD STEADY TONIGHT AND SATURDAY BASED ON WRF OUTPUT.
VERY LOCALIZED LOW LEVEL WIND SHEAR REMAINS A POSSIBILITY ON THE
COAST AND OVER THE COASTAL WATERS SATURDAY, NOT ENOUGH TO PLACE IN
06Z TAFS FOR NOW. OTHERWISE IT`S VFR INLAND FOR THE PERIOD AND
IFR-MVFR COASTAL SECTIONS AND NEARBY VALLEYS TONIGHT AND SATURDAY
MORNING. [AVIA]

Vicinity of KSFO [San Francisco CA]VFR [Visual Flight Rules] conditions will prevail with IFR [Instrument Flight Rules]/MVFR [Marginal Visual Flight Rules] ceilings briefly possible Saturday morning. Low confidence. 

VICINITY OF KSFO...VFR CONDITIONS WILL PREVAIL WITH IFR/MVFR CIGS
BRIEFLY POSSIBLE SATURDAY MORNING. LOW CONFIDENCE. [AVI2]

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

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

Monterey Bay terminals… IFR [Instrument Flight Rules] ceilings tonight and Saturday morning. VFR [Visual Flight Rules] returning by late morning Saturday. 

MONTEREY BAY TERMINALS...IFR CEILINGS TONIGHT AND SATURDAY MORNING.
VFR RETURNING BY LATE MORNING SATURDAY. [AVI2]

Marine. As of 9:34pm PDT Friday… northwest winds will continue to diminish across the coastal waters through tonight with strongest winds remaining over the northern outer waters. Steep, short period northwesterly swells will also diminish tonight and through the weekend with period becoming 7–8 seconds. Southwesterly winds are forecast over the near shore coastal waters this weekend. A moderate southerly swell will arrive on Sunday and persist through early next week with light northwesterly swell continuing through the period. 

.MARINE...AS OF 9:34 PM PDT FRIDAY...NORTHWEST WINDS WILL
CONTINUE TO DIMINISH ACROSS THE COASTAL WATERS THROUGH TONIGHT
WITH STRONGEST WINDS REMAINING OVER THE NORTHERN OUTER WATERS.
STEEP, SHORT PERIOD NORTHWESTERLY SWELLS WILL ALSO DIMINISH
TONIGHT AND THROUGH THE WEEKEND WITH PERIOD BECOMING 7 TO 8
SECONDS. SOUTHWESTERLY WINDS ARE FORECAST OVER THE NEAR SHORE
COASTAL WATERS THIS WEEKEND. A MODERATE SOUTHERLY SWELL WILL
ARRIVE ON SUNDAY AND PERSIST THROUGH EARLY NEXT WEEK WITH LIGHT
NORTHWESTERLY SWELL CONTINUING THROUGH THE PERIOD. [AVIA]

MTR Watches/Warnings/Advisories

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

Public Forecast: Dykema; Aviation: Canepa; Marine: CW 

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

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WWW.YOUTUBE.COM/NWSBAYAREA [DISC]

Point Forecast

Half Moon Bay CA

23 Aug 11:40pm PDT

Overnight Mostly cloudy, with a low around 55°. SSW wind around 9 mph.
Saturday Mostly cloudy, then gradually becoming sunny, with a high near 71°. SSW wind around 10 mph.
Saturday Night Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 55°. WSW wind 5 to 7 mph becoming calm in the evening.
Sunday Sunny, with a high near 73°. Calm wind becoming WSW 5 to 8 mph in the afternoon.
Sunday Night Mostly clear, with a low around 55°. WSW wind 3 to 8 mph.
Monday Mostly sunny, with a high near 74°.
Monday Night Partly cloudy, with a low around 56°.
Tuesday Mostly sunny, with a high near 74°.
Tuesday Night Mostly clear, with a low around 57°.
Wednesday Mostly sunny, with a high near 71°.
Wednesday Night Partly cloudy, with a low around 58°.
Thursday Mostly sunny, with a high near 70°.
Thursday Night Partly cloudy, with a low around 57°.
Friday Mostly sunny, with a high near 70°.
Overnight
Mostly cloudy, with a low around 55. South southwest wind around 9 mph.
Saturday
Mostly cloudy, then gradually becoming sunny, with a high near 71. South southwest wind around 10 mph.
Saturday Night
Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 55. West southwest wind 5 to 7 mph becoming calm in the evening.
Sunday
Sunny, with a high near 73. Calm wind becoming west southwest 5 to 8 mph in the afternoon.
Sunday Night
Mostly clear, with a low around 55. West southwest wind 3 to 8 mph.
Monday
Mostly sunny, with a high near 74.
Monday Night
Partly cloudy, with a low around 56.
Tuesday
Mostly sunny, with a high near 74.
Tuesday Night
Mostly clear, with a low around 57.
Wednesday
Mostly sunny, with a high near 71.
Wednesday Night
Partly cloudy, with a low around 58.
Thursday
Mostly sunny, with a high near 70.
Thursday Night
Partly cloudy, with a low around 57.
Friday
Mostly sunny, with a high near 70.

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