867  
FXUS66 KMTR 190623  
AFDMTR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA  
1023 PM PST SUN FEB 18 2018  
   
SYNOPSIS
 
BLUSTERY AND MUCH COLDER WEATHER CONDITIONS  
DEVELOPED ACROSS THE REGION TODAY IN WAKE OF A STRONG FRONTAL  
PASSAGE. SCATTERED POST FRONTAL SHOWERS WILL OCCUR TONIGHT INTO  
MONDAY MORNING, MAINLY NEAR THE COAST AND IN SANTA CRUZ AND SANTA  
LUCIA MOUNTAINS. SNOW LEVELS ARE FORECAST TO DROP TO OR BELOW  
1,000 FEET BY MONDAY MORNING. WIDESPREAD FREEZING TEMPERATURES ARE  
THEN EXPECTED FOR INLAND AREAS ONCE WINDS SUBSIDE MONDAY NIGHT  
INTO TUESDAY MORNING. COOL AND UNSETTLED WEATHER IS EXPECTED TO  
PERSIST THROUGH THE END OF THE WEEK AND INTO EARLY NEXT WEEK.  
 

 
   
DISCUSSION...AS OF 9:10 PM PST SUNDAY
 
A STRONG, BUT MOSTLY  
DRY, COLD FRONT SWEPT ACROSS OUR REGION EARLIER TODAY. AS  
EXPECTED, BLUSTERY AND MUCH COOLER CONDITIONS DEVELOPED BEHIND THE  
FRONT. LOCAL WIND GUST OF UP TO 45 MPH WERE OBSERVED ALONG THE  
COAST AND IN THE HILLS TODAY. TODAY'S HIGH TEMPERATURES WERE  
GENERALLY 10 TO 20 DEGREES COOLER COMPARED TO SATURDAY.  
 
SCATTERED SHOWERS DEVELOPED LATE THIS AFTERNOON IN THE COLD AND  
UNSTABLE POST FRONTAL ENVIRONMENT. MOST OF THESE SHOWERS WERE  
CONFINED TO THE COASTAL WATERS, AS WELL AS COASTAL SAN MATEO AND  
SANTA CRUZ COUNTIES, AND NORTHWEST MONTEREY COUNTY. THESE SHOWERS  
HAVE BEEN BRIEF AND RAIN TOTALS THUS FAR HAVE BEEN JUST A FEW  
HUNDREDTHS.  
 
MODELS HAVE BEEN CONSISTENT IN DEVELOPING MORE WIDESPREAD SHOWER  
ACTIVITY OVERNIGHT AS THE UPPER TROUGH CONTINUES TO DIG SOUTH AND  
DRAGS AN EVEN COLDER AND MORE UNSTABLE AIRMASS ACROSS OUR REGION.  
PRECIPITATION OVERNIGHT IS EXPECTED TO BE CONCENTRATED IN COASTAL  
AREAS AND ESPECIALLY IN THE SANTA CRUZ MOUNTAINS AND NORTHERN  
SANTA LUCIA MOUNTAIN RANGE OF MONTEREY COUNTY. VERY LITTLE, IF  
ANY, PRECIPITATION IS EXPECTED IN THE NORTH AND EAST BAY (EXCEPT  
NORTHWEST SONOMA COUNTY). IN GENERAL, THE BULK OF TONIGHT AND  
TOMORROW MORNING'S RAIN AND SNOW IS EXPECTED TO FALL WEST OF  
HIGHWAY 101.  
 
SNOW LEVELS ARE CURRENTLY AT ABOUT 2000-2500 FEET BUT ARE EXPECTED  
TO DROP TO 1500 FEET OVERNIGHT AND 1000 FEET ON MONDAY MORNING.  
SNOW COULD EVEN FALL BRIEFLY AS LOW AS 500 FEET IN HEAVIER  
SHOWERS. LATEST HRRR AND WRF MODELS AGREE ON WHERE THE GREATEST  
PRECIPITATION TOTALS WILL OCCUR THROUGH MIDDAY MONDAY. BOTH MODELS  
FORECAST LIQUID PRECIPITATION OF ABOUT A QUARTER TO A THIRD OF AN  
INCH IN THE SANTA CRUZ MOUNTAINS AND MAXIMUM AMOUNTS OF A HALF  
INCH (HRRR) AND 1 INCH (WRF) IN THE SANTA LUCIAS. GIVEN THE  
ANTICIPATED LOW SNOW LEVELS THESE QPF VALUES WOULD TRANSLATE INTO  
BETWEEN 2 AND 4 INCHES OF SNOW AT THE HIGHER ELEVATIONS OF THE  
SANTA CRUZ MOUNTAINS AND FROM 5 TO 10 INCHES IN THE SANTA LUCIA  
MOUNTAINS. THE PRIMARY IMPACT FROM A TRAVEL STANDPOINT WILL BE  
NEAR THE SUMMIT OF HIGHWAY 17 IN SANTA CRUZ COUNTY AND ALONG  
SKYLINE BOULEVARD (HIGHWAY 35) IN THE SANTA CRUZ MOUNTAINS. A  
WINTER WEATHER ADVISORY IS IN EFFECT FROM MIDNIGHT TONIGHT UNTIL  
10 AM MONDAY FOR THE SANTA CRUZ MOUNTAINS AND SANTA LUCIA  
MOUNTAINS. THE MODELS AGREE THAT PRECIPITATION WILL TAPER OFF BY  
MID MORNING ON MONDAY AND MOSTLY END BY MIDDAY.  
 
BLUSTERY CONDITIONS CONTINUE NEAR THE COAST AND LOCALLY IN THE  
HILLS THIS EVENING WITH NORTHWEST WINDS GUSTING BETWEEN 30 AND 40  
MPH. EXPECT GUSTY WINDS TO PERSIST OVERNIGHT AND THEN INCREASE  
SLIGHTLY AGAIN BY MONDAY AFTERNOON, ESPECIALLY ALONG THE COAST.  
BASED ON THE 12Z WRF WIND OUTPUT, A WIND ADVISORY MAY BE NEEDED  
FOR COASTAL AREAS ON MONDAY AFTERNOON, BUT IT LOOKS LIKE A  
MARGINAL EVENT. THEREFORE, WILL WAIT FOR ALL THE 00Z MODEL DATA  
BEFORE MAKING A DETERMINATION ON ANY POSSIBLE WIND ADVISORIES.  
WINDS WILL SUBSIDE IN ALL AREAS ON MONDAY EVENING.  
 
ONCE PRECIPITATION AND CLOUDS DEPART ON MONDAY, AND WINDS SUBSIDE  
ON MONDAY EVENING, THE STAGE WILL BE SET FOR VERY COLD  
TEMPERATURES LATE MONDAY NIGHT INTO TUESDAY MORNING. LATEST MODEL  
GUIDANCE IS CONSISTENT WITH PREVIOUS GUIDANCE IN INDICATING  
WIDESPREAD OVERNIGHT LOWS RANGING FROM THE MID 20S TO LOWER 30S  
ACROSS INLAND AREAS EARLY TUESDAY MORNING AND MOSTLY IN THE 30S  
NEAR THE COAST. A FREEZE WARNING IS IN EFFECT FOR ALL OF OUR  
INLAND AREAS LATE MONDAY NIGHT INTO TUESDAY MORNING. IN ADDITION,  
A FROST ADVISORY HAS BEEN ISSUED FOR ALL OF OUR COASTAL AND  
BAYSIDE ZONES (EXCEPT THE CITY OF SAN FRANCISCO) FOR THE SAME TIME  
PERIOD.  
 
A SHORTWAVE TROUGH IS FORECAST TO DROP SOUTH JUST OFFSHORE ON  
TUESDAY NIGHT. THE MODELS AGREE THAT NEARLY ALL PRECIPITATION  
WITH THIS DISTURBANCE WILL REMAIN OFFSHORE. HOWEVER, ENOUGH CLOUDS  
ARE EXPECTED TO SPREAD ACROSS OUR AREA ON TUESDAY NIGHT TO KEEP  
TEMPERATURES FROM DROPPING BELOW FREEZING AT MOST LOCATIONS.  
THEREFORE, IT APPEARS UNLIKELY THAT FREEZE WARNINGS/FROST  
ADVISORIES WILL NEED TO BE REISSUED FOR TUESDAY NIGHT/WEDNESDAY  
MORNING.  
 
THE MODELS MAINTAIN A COOL AND UNSETTLED PATTERN THROUGH THE REST  
OF THE WEEK WITH ANOTHER SYSTEM FORECAST TO DROP IN FROM THE NORTH  
WEDNESDAY NIGHT INTO THURSDAY. THE 12Z ECMWF BRINGS IN YET  
ANOTHER SYSTEM THURSDAY NIGHT INTO FRIDAY. THESE SYSTEMS ARE  
FORECAST TO BE COLD, BUT NOT AS COLD AS OUR CURRENT SYSTEM. THUS  
SNOW LEVELS WILL LIKELY REMAIN ABOVE 1500 FEET.  
 
LONGER RANGE MODELS SHOW A POTENTIALLY MORE POTENT AND WETTER  
SYSTEM ARRIVING SOMETIME EARLY NEXT WEEK.  
 

 
   
AVIATION...AS OF 10:00 PM PST SUNDAY
 
HI-RES MODELS INDICATE SHOWER  
ACTIVITY IS EXPECTED TO PICK UP BETWEEN 09Z AND 18Z ALONG THE  
COAST AND OVER THE MRY BAY AREA. STRONG PRESSURE GRADIENTS BETWEEN  
HIGH PRESSURE OVER THE WATERS AND LOW PRESSURE OVER UTAH PRODUCING  
GUSTY WINDS UP TO 30 KT. THESE WINDS WILL SLOWLY DECREASE DURING  
THE NIGHT.  
 
VICINITY OF KSFO...POSSIBLE MVFR CONDITIONS BETWEEN 10Z AND 17Z AS  
SHOWERS MOVE THROUGH WEST OF THE AIRPORT. WEST WINDS GUSTING TO 30  
KT UNTIL 10Z.  
 
SFO BRIDGE APPROACH...SIMILAR TO KSFO.  
 
MONTEREY BAY TERMINALS...SHOWER ACTIVITY WILL INCREASE AFTER 10Z  
AND LAST THROUGH 16-17Z. PREDOMINANTLY MVFR CIGS BECOMING VFR  
AFTER 17Z.  
 

 
   
CLIMATE
 
 
HERE ARE RECORD LOW TEMPERATURES AND THE YEARS THEY OCCURRED FOR  
MONDAY THROUGH WEDNESDAY THIS WEEK.  
 
LOCATION MONDAY TUESDAY WEDNESDAY  
 
SF BAY AREA  
 
HEALDSBURG 28 IN 1932 22 IN 1922 28 IN 1929  
SANTA ROSA 26 IN 1932 26 IN 1913 26 IN 1913  
CALISTOGA 25 IN 1918 25 IN 2006 25 IN 2006  
KENTFIELD 27 IN 1932 27 IN 1913 29 IN 1953  
SAN RAFAEL 32 IN 1990 32 IN 2006 33 IN 1955  
NAPA 29 IN 1990 28 IN 1920 29 IN 1955  
SAN FRANCISCO 38 IN 1897 38 IN 1897 36 IN 1890  
SFO AIRPORT 36 IN 1990 37 IN 2011 34 IN 1955  
HALF MOON BAY 34 IN 1954 32 IN 2013 31 IN 2006  
OAKLAND AIRPORT 35 IN 1955 34 IN 2006 33 IN 1955  
RICHMOND 35 IN 1990 35 IN 1990 35 IN 1981  
LIVERMORE 27 IN 1956 28 IN 1942 27 IN 1955  
MOFFETT FIELD 35 IN 1949 34 IN 2006 32 IN 1955  
SAN JOSE 32 IN 1990 30 IN 1897 25 IN 1897  
GILROY 27 IN 1964 30 IN 1990 31 IN 1976  
 
MONTEREY BAY AREA  
 
SANTA CRUZ 30 IN 1990 29 IN 1913 30 IN 1955  
SALINAS 29 IN 1990 31 IN 2006 31 IN 1970  
SALINAS AIRPORT 29 IN 1933 28 IN 1953 30 IN 1953  
MONTEREY 35 IN 1990 35 IN 2006 36 IN 1952  
KING CITY 25 IN 1955 22 IN 1953 23 IN 1953  
 

 
   
MARINE...AS OF 10:14 PM PST SUNDAY
 
A 1039 MB HIGH IS CENTERED  
800 MILES WEST OF CAPE MENDOCINO WHILE A 995 MB LOW IS OVER UTAH.  
THE STRONG PRESSURE GRADIENTS WILL BRING GUSTY NORTHERLY WINDS  
THROUGH MONDAY NIGHT. WINDS WILL DECREASE TUESDAY AS THE LOW MOVES  
EAST BUT ANOTHER SYSTEM MAY AFFECT THE AREA LATER IN THE WEEK.  
 

 
   
MTR WATCHES/WARNINGS/ADVISORIES
 
 
.TDAY...WINTER WEATHER ADVISORY...CAZ512-517  
SCA...SF BAY  
SCA...MRY BAY  
SCA...PT ARENA TO PT REYES 0-10 NM  
SCA...PT REYES TO PIGEON PT 0-10 NM  
SCA...PIGEON PT TO PT PINOS 0-10 NM  
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM  
GLW...PT ARENA TO PIGEON PT 10-60 NM  
GLW...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM  
SCA...ROUGH BAR ADVISORY FOR SF BAR  
 

 
 

 
 
PUBLIC FORECAST: DYKEMA  
AVIATION: W PI  
MARINE: W PI  
 
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