Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
540 PM PDT MON APR 27 2015

.SYNOPSIS...A DRY COLD FRONT WILL APPROACH THE COAST RESULTING IN
INCREASING ONSHORE FLOW AND A MODEST COOLING TREND TUESDAY AND
WEDNESDAY. DRY AND SEASONABLE WEATHER IS THEN FORECAST FROM
WEDNESDAY THROUGH THE UPCOMING WEEKEND.

&&

.DISCUSSION...AS OF 3:00 PM PDT MONDAY...SUNNY ACROSS ALMOST ALL
OF OUR CWA TODAY WITH TEMPERATURES RUNNING 8 TO 15 DEGREES AHEAD OF
YESTERDAY AT THIS TIME. LOOK AT THE LATEST READINGS SHOW SAN
FRANCISCO AT 73...SAN RAFAEL 79...LIVERMORE 84...AND SAN JOSE PLUS
SALINAS AT 80. THE WESTERLY SURFACE GRADIENT WHICH HAD BEEN NEARLY
NEUTRAL HAS BEEN SLOWLY INCREASING THROUGH THE DAY TO WEAK
WESTERLY WHILE AT THE SAME TIME THE NORTHERLY GRADIENT HAS BEEN
CUT IN HALF. ALONG WITH THE INLAND HEATING...THOSE FACTORS HAVE
ALLOWED CLOUDS TO MOVE TO MANY COASTAL SPOTS ALONG SAN
MATEO...MARIN...AND SONOMA COUNTIES. ALSO RECEIVED A REPORT OF
LESS THAN 1 MILE VISIBILITY AT THE FARALLONES DUE TO FOG. 

FOR TONIGHT...WITH THE WESTERLY GRADIENT EXPECTED TO INCREASE AND
A LARGE AREA OF CLOUDS UPSTREAM EXPECT CLOUDS ALONG THE COAST PLUS
ADJACENT VALLEYS. WILL LIKELY GET REPORTS OF FOG DURING THE
MORNING COMMUTE PARTICULARLY ALONG HIGHWAY 1. AT THE SAME TIME AN
UPPER LEVEL TROF WILL ADVANCE TO THE PACNW/BC COAST BY TOMORROW.
ALTHOUGH ALL ASSOCIATED MOISTURE WITH THIS FEATURE WILL STAY WELL
TO OUR NORTH...IT WILL HELP TO DROP TEMPS LOCALLY BY MORE THAN 10
DEGREES.

QUIET WEATHER WILL CONTINUE FOR THE REMAINDER OF THE WEEK AS THE
FLOW BECOMES WEAKLY ZONAL WITH THE MAIN STORM TRACK WELL TO THE
NORTH. TEMPERATURES WILL WARM BACK CLOSE TO THE VALUES WE SAW
TODAY BY FRIDAY. STILL NO CHANCE OF RAIN AT LEAST INTO THE FIRST
PART OF NEXT WEEK.
&&

.AVIATION...AS OF 5:17 PM PDT MONDAY...A STRONG UPPER RIDGE IS
COMPRESSING THE MARINE LAYER TO 600-1000 FEET DEEP. A LARGE AREA OF
STRATUS CAN BE SEEN FROM EUREKA TO THE BIG SUR COAST AND THE STRATUS
HAS FILLED IN QUICKLY AROUND THE MONTEREY BAY REGION IN THE LAST
1-2 HOURS. THINK THE KEY TO CIG/VSBY FORECASTS FOR THIS PERIOD
HINGE ON THE SHALLOW MARINE LAYER HOLDING IN PLACE OVERNIGHT INTO
TUESDAY. OVERALL THE MARINE LAYER MAY FLUCTUATE A LITTLE IN DEPTH
OVERNIGHT INTO TUESDAY BUT SHOULD HOLD FAIRLY CLOSE TO 1000 FEET.
THE 04/27 18Z NAM MODEL RUN INITIALIZED TOO LOW ON THE NORTH-SOUTH
GRADIENTS...BUT DID WELL INITIALIZING THE SFO-SAC GRAD. MODELS ARE
TRENDING STRONGER WITH THE W-NW GRADIENTS AND WINDS...ESPECIALLY OVER
THE BAY AREA...BY THIS TIME TOMORROW AND AGAIN WEDNESDAY AFTERNOON
AND EVENING.

VICINITY OF KSFO...IT'S A HIGH CONFIDENCE VFR FORECAST FOR THE
EVENING DUE TO THE SHALLOW MARINE CLOUD LAYER. DECENT LATE PM
OCEAN-LAND TEMP DIFFERENCES...LOCAL ONSHORE GRADIENTS AND A SHALLOW
MARINE LAYER WILL COMBINE TO PRODUCE MORE WESTERLY WIND GUSTS IN
THE 20 TO 30 KNOT RANGE TIL 04Z. NOT ENTIRELY CONFIDENT THE STRATUS
WILL REACH KSFO TUESDAY MORNING IF THE MARINE LAYER DOES STAY
COMPRESSED. THEREFORE DECIDED TO SCALE BACK THE DURATION OF 
FORECASTED MVFR CIGS TO A TEMPO GROUP 13Z-17Z. OVERALL THE BIGGER
STORY IS LIKELY TO BE THE STRENGTH OF THE WESTERLY WINDS OVER NEXT
24-36 HOURS ESPECIALLY IN THE LATTER FORECAST PERIOD. COORD AND IN
AGREEMENT WITH THE CWSU OFFICE.

SFO BRIDGE APPROACH...VFR EXCEPT A FEW BRIEF PATCHES OF STRATUS ARE
POSSIBLE TUESDAY MORNING.
 
MONTEREY BAY AREA TERMINALS...IFR CIGS ARE LIKELY TO DEVELOP THIS
EVENING AS THE STRATUS CONTINUES TO MOVE IN FROM THE NORTHWEST.
EXPECTING THE STRATUS CLOUDS TO MIX OUT BY LATE TUESDAY MORNING
BUT MOST LIKELY TO BE POISED TO MOVE BACK IN WEDNESDAY EVENING.

&&

.MARINE...AS OF 02:09 PM PDT MONDAY...HIGH PRESSURE WILL MAINTAIN
MODERATE NORTHWESTERLY WINDS ACROSS THE COASTAL WATERS THROUGH
TONIGHT. WINDS ARE ANTICIPATED TO STRENGTHEN MIDWEEK AS A COLD
FRONT PUSHES TOWARDS THE CALIFORNIA COAST. STRONG WINDS WILL
PERSIST THROUGH THE END OF THE WEEK AS THE FRONTAL SYSTEM MOVES
ACROSS THE REGION.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...SF BAY NORTH OF THE BAY BRIDGE UNTIL 9 PM
             SCA...SF BAY SOUTH OF THE BAY BRIDGE UNTIL 9 PM
             SCA...MONTEREY BAY UNTIL 9 PM
             SCA...PIGEON PT TO PT PINOS 0-10 NM UNTIL 9 PM
             SCA...PT ARENA TO PT REYES 10-60 NM
             SCA...PT REYES TO PIGEON PT 10-60 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...PT ARENA TO PT REYES 0-10 NM
             SCA...PT REYES TO PIGEON PT 0-10 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 10-60 NM FROM 9 PM

&&

$$

PUBLIC FORECAST: BELL
AVIATION: CANEPA
MARINE: RGASS

VISIT US AT WEATHER.GOV/SANFRANCISCO

FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSBAYAREA
WWW.TWITTER.COM/NWSBAYAREA
WWW.YOUTUBE.COM/NWSBAYAREA

National Weather Service Glossary of Abbreviations