Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 282159
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
259 PM PDT FRI AUG 28 2015

.SYNOPSIS...A PACIFIC WEATHER SYSTEM WILL BRING A CHANCE OF LIGHT
RAIN TO THE NORTHERN PORTION OF OUR DISTRICT LATE TONIGHT AND
SATURDAY MORNING. MUCH COOLER WEATHER WILL DEVELOP BY THE WEEKEND.
DRY AND SEASONABLY COOL WEATHER IS EXPECTED NEXT WEEK.

&&

.DISCUSSION...AS OF 3:00 PM PDT FRIDAY...A BIT OF A SURPRISE TODAY
AS TEMPS AGAIN BECAME VERY WARM TO HOT TODAY. QUICK SCAN OF
CURRENT READINGS SHOWS WIDESPREAD 70S AND 80S AT THE COAST WITH
90S TO LOWER 100S FOR MANY INLAND SPOTS. HAD EXPECTED TEMPS TO
ACTUALLY BE A FEW DEGREES COOLER TODAY DUE TO A SLIGHT ONSHORE
PUSH PLUS FLATTENING OF THE RIDGE. HOWEVER...CURRENT ANALYSIS
SHOWS THAT DID NOT COME TO FRUITION.

STILL LOOKS LIKE COOLER WEATHER WILL RETURN TO OUR REGION OVER THE
WEEKEND AS THE RIDGE PROGRESSES TO THE EAST WHILE A LONGWAVE TROF
ADVANCES TO THE WEST COAST. AT THE SAME TIME A COLD FRONT WILL
PUSH ACROSS NORCAL/PACNW OVERNIGHT INTO SATURDAY WHICH WILL HELP
TO BRING RAINFALL (MOSTLY NORTH OF OUR AREA) PLUS COOLER WEATHER.
MODELS REMAIN IN GOOD AGREEMENT THAT THE SOUTHERN EXTENT OF THE
MOISTURE WILL MOVE INTO OUR NORTHERN OUTWER WATERS WATER THIS
EVENING AND EASTWARD TO THE NORTH BAY PLUS SF BAY AREA OVERNIGHT
INTO SATURDAY. AMOUNTS WILL LIKELY BE VERY LIGHT WITH THE GREATEST
AMOUNTS OVER THE NORTH BAY MOUNTAINS. STILL LOOKS LIKE JUST A
HUNDREDTH OR SO FOR MOST URBAN SPOTS. UP TO A TENTH MAY FALL
LOCALLY FOR HIGHER ELEVATION SPOTS IN NAPA/SONOMA. HUMIDITY
VALUES ARE MOSTLY IN THE 20 TO 30 PERCENT RANGE ALTHOUGH VALUES
SHOULD RECOVER ENOUGH OVERNIGHT TO ALLOW SOME OF THE RAIN TO REACH
THE GROUND. PRECIPITATION IS NOT EXPECTED FOR THE SOUTHERN HALF OF
OUR AREA. HIGHS WILL BE NOTICEABLY COOLER WITH MANY INLAND SPOTS
15 OR MORE DEGREES COOLER OVER THE WEEKEND.

BIG PICTURE VIEW ACROSS THE CONUS FOR NEXT WEEK CONTINUES TO SHOW
LOWER THAN NORMAL HEIGHTS OVER THE WESTERN CONUS WITH ABOVE NORMAL
HEIGHTS TO THE EAST. THIS WILL LEAD TO COOLER THAN NORMAL TEMPS
ESPECIALLY FOR INLAND SPOTS. THE STORM TRACK SHOULD STAY TO THE
NORTH SO NO ORGANIZED RAINFALL FORECAST.
&&

.AVIATION...AS OF 11:15 PM PDT FRIDAY.... VFR CIGS WITH BKN TO OVC
HIGH LEVEL CLOUDS MOVING OVER THE AREA AHEAD OF AN APPROACHING
BAGGY TROUGH. MODEL GUIDANCE UNRELIABLE FOR TONIGHT... WITH WIDE
VARIANCES IN DURATION...CIGS...AND ONSET/MIX OUT TIMES... THUS
VERY LOW CONFIDENCE ON CIGS TONIGHT. THE MODEL NUDGING TOWARDS LOW
CIGS/LONG DURATION IS THE NAM...WHICH HAS CONSISTENTLY
UNDERPERFORMED COMPARED TO THE RUC13...WHICH HAS HIGHER CIGS/SHORTER
DURATION. FORT ORD PROFILER SHOWS EXTREMELY COMPRESSED MARINE LAYER
THAT WOULD STRUGGLE TO PUSH INLAND... ONSHORE FLOW WILL WEAKEN INTO
TOMORROW... AND HIGH CLOUDS WILL INHIBIT OVERNIGHT COOLING... THUS
HAVE LEANED CLOSER TO MODELS...SPECIFICALLY THE RUC...WITH HIGHER
OVERNIGHT CIGS WITH SHORT DURATION. THERE IS A POSSIBILITY OF LOW
CIGS ALONG THE COASTLINE... WHICH ARE NOT ACCOUNTED FOR IN THE TAFS.

VICINITY OF KSFO...VFR. LIGHT TO MODERATE WINDS. STRONGEST WIND
EXPECTED DURING THE AFTERNOON. MVFR CIGS POSBL AFTER 06-8Z... THEN
MIXING OUT BY SUNRISE...HOWEVER READ DISCUSSION...VERY LOW
CONFIDENCE FOR TONIGHT.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...VFR TODAY. LIGHT WINDS. POSSIBLE
MVFR TO IFR CIGS AFTER 08-10Z TONIGHT...READ DISCUSSION...VERY
LOW CONFIDENCE.

&&

.BEACHES...AS OF 11:30 AM PDT FRIDAY...A LONG PERIOD WEST SWELL
HAS ARRIVED AND WILL CONTINUE TO ADVANCE ON WEST FACING BEACHES
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK. THESE LONG PERIOD
SWELLS CAN PRODUCE HAZARDOUS RIP CURRENTS THAT CAN QUICKLY PULL
SWIMMERS OUT TO SEA. THE HIGHEST RISK OF HAZARDOUS CONDITIONS WILL
BE THIS WEEKEND WHEN ONSHORE WINDS WEAKEN AND THE PERIOD
INCREASES FROM 15 TO 18 SECONDS. SWIMMERS CAUGHT IN A RIP CURRENT
SHOULD SWIM PARALLEL TO THE COAST TO ESCAPE THE RIP CURRENTS.

&&

.MARINE...AS OF 02:15 PM PDT FRIDAY...PREDOMINATELY LIGHT WESTERLY
WINDS AND SEAS WILL CONTINUE ACROSS THE COASTAL WATERS. A LONG
PERIOD SWELL HAS BEGUN TO MOVE INTO THE AREA. A MORE ENERGETIC
WESTERLY SWELL WILL IMPACT THE REGION THIS WEEKEND.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...NONE.

$$

PUBLIC FORECAST: BELL
AVIATION: DRP
MARINE: DRP


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