383  
FXUS66 KMTR 210629  
AFDMTR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA  
1029 PM PST MON FEB 20 2017  
   
SYNOPSIS
 
THE COLD FRONTAL RAIN BAND IS NOW MOVING SOUTHEASTWARD  
THROUGH MONTEREY COUNTY, WITH LOCALLY GUSTY WINDS AND SCATTERED  
SHOWERS LEFT IN ITS WAKE. FLOODING REMAINS A CONCERN AS WATER  
CONTINUES TO FLOW DOWN THE SLOPES FROM THE RECENT HEAVY RAINS, BUT  
WILL DIMINISH LATER TONIGHT AND TUESDAY ASIDE FROM SOME OF THE  
SLOWER TO RESPOND MAINSTEM RIVERS. SHOWERS AND WINDS WILL  
GRADUALLY TAPER OFF OVER THE NEXT 24 HOURS, WITH MAINLY DRY THOUGH  
COOLER CONDITIONS EXPECTED FOR WEDNESDAY THROUGH FRIDAY. MORE  
ACTIVE WEATHER LOOKS TO RETURN TO OUR AREA NEXT WEEKEND HOWEVER,  
WITH A COLD AND WET STORM SYSTEM POTENTIALLY MOVING IN.  
 

 
   
DISCUSSION...AS OF 09:35 PM PST MONDAY
 
THE STRONG STORM SYSTEM  
AND ATMOSPHERIC RIVER EVENT THAT BATTERED OUR AREA OVER THE PAST  
24 HOURS IS NOW FINALLY WEAKENING AND MOVING OUT. RAINFALL TOTALS  
GENERALLY RANGED IN THE 1.25 TO 2.5 INCH RANGE AT LOWER ELEVATIONS,  
AND TO OVER A HALF A FOOT AT SEVERAL LOCATIONS UP IN THE COASTAL  
HILLS. OUR SITE IN DOWNTOWN SAN FRANCISCO RECEIVED 1.86 INCHES OF  
RAIN, WITH THE WET SPOT THUS FAR BEING MINING RIDGE IN THE MOUNTAINS  
ABOVE BIG SUR, WITH 7.24 INCHES AS OF 8:30 PM. WILL ALSO NOTE THAT  
MINING RIDGE HAD THE MAXIMUM 7-DAY RAINFALL TOTAL FOR OUR AREA,  
14.91 INCHES.  
 
WINDS ALSO GOT QUITE STRONG, ESPECIALLY ALONG THE COAST AND UP  
IN THE HILLS. AT THE LOS GATOS RAWS SITE AT 1842 FT UP IN THE  
SANTA CRUZ MOUNTAINS FOR EXAMPLE, NOTED A MAXIMUM SUSTAINED WIND  
OF 46 MPH WITH A PEAK GUST TO 77 MPH, BOTH REPORTED AT 5:32 PM.  
 
CURRENT RADAR AND SATELLITE DATA SHOW THE PRIMARY COLD FRONTAL  
RAINBAND EXTENDING NORTHEAST TO SOUTHWEST THROUGH SOUTHERN SANTA  
CLARA COUNTY AND NORTHERN MONTEREY COUNTY, AND WEAKENING AS IT  
PROGRESSES INLAND. ASIDE FROM THESE TWO COUNTIES AND SAN BENITO  
COUNTY, SIGNIFICANT RAINFALL HAS NOW PRETTY MUCH ENDED, BUT  
SCATTERED SHOWERS WILL CONTINUE TONIGHT AND TUESDAY IN THE COOL  
AND MOIST AIR MASS LEFT IN ITS WAKE.  
 
NO LIGHTNING REPORTS WERE NOTED TODAY OVER EITHER OUR LAND OR  
WATER AREAS. WILL NONETHELESS RETAIN SLIGHT CHANCE OF THUNDERSTORMS  
IN THE FORECAST FOR TONIGHT AND TUESDAY. HAVE NOTED SOME LIGHTNING  
DETECTION IN SHOWERS WELL OFFSHORE (AND A LIGHTNING STRIKE JUST  
NOW OFF THE MENDOCINO COUNTY COAST) AND LATEST MODEL AND MOS  
OUTPUT CONTINUE TO INDICATE MARGINALLY FAVORABLE CONVECTIVE  
CONDITIONS, ESPECIALLY MORE NORTHERN PORTIONS OF OUR AREA TUESDAY  
AFTERNOON.  
 
FOR WEDNESDAY THROUGH FRIDAY, GENERALLY DRY WEATHER SHOULD  
PREVAIL, THOUGH NEW 00Z NAM IN PARTICULAR DOES NOW INDICATE A VERY  
WEAK DISTURBANCE SLIDING SOUTH DOWN OUR COAST ON THURSDAY ALONG  
WITH THE POSSIBILITY OF A FEW ASSOCIATED SHOWERS. TEMPERATURES  
WILL BE SIGNIFICANTLY COOLER HOWEVER FOR THE LATTER PART OF THE  
WEEK. THE 850 MB TEMPERATURE IN THE 4 PM MONDAY KOAK SOUNDING WAS  
6.15 DEG C, BUT WITH BOTH THE 00Z NAM AND GFS BRINGING IT DOWN TO  
AROUND -2 DEG C BY 12Z WEDNESDAY AND -3 TO -4 DEG C BY 12Z  
THURSDAY. DAYTIME TEMPS UP AT HIGHER ELEVATIONS ESPECIALLY WILL BE  
CHILLY, WITH NIGHT AND EARLY MORNING FROST BECOMING POSSIBLE IN  
THE VALLEYS.  
 
THEN FURTHER INTO THE EXTENDED PORTION OF THE FORECAST, AS WE  
HEAD INTO NEXT WEEKEND, INCLEMENT WEATHER CONDITIONS LOOK TO  
RETURN. LATEST RUNS OF THE GFS (00Z TUESDAY) AND ECMWF AND  
CANADIAN MODELS (12Z MONDAY) ARE IN GOOD AGREEMENT IN BRINGING IN  
A COOL AND WET WEATHER SYSTEM TO OUR DISTRICT. ALTHOUGH QUITE A  
WAYS OUT, AND THUS SIGNIFICANT CHANGES IN SOLUTION COULD WELL  
OCCUR, PRESENT MODEL OUTPUT INDICATES POTENTIAL ENTRAINMENT OF  
SUBTROPICAL MOISTURE AS THE COLD UPPER LOW DROPS SOUTHWARD  
TOWARDS US FROM THE PACIFIC NW.  
 

 
   
AVIATION...AS OF 10:15 PM PST MONDAY
 
FRONTAL SYSTEM CURRENTLY  
MOVING INTO SOUTHERN MONTEREY/SAN BENITO COUNTIES. POST FRONTAL  
SHOWERS ARE NOW MOVING INTO THE SFO AND MRY BAY AREAS WITH CIGS  
FLUCTUATING ABOVE AND BELOW THE MVFR RANGE. STRONG SOUTHWEST  
WINDS HAVE APPEARED AS THE LOW CENTER MAKES ITS CLOSEST PASS TO  
THE DISTRICT THIS EVENING. WINDS WILL SLOWLY DECREASE AFTER 11Z  
WITH SHOWERS CONTINUING THROUGH TUESDAY. LOW LEVEL WIND SHEAR IS  
POSSIBLE IN THESE STRONG WINDS UP TO 2000 FEET.  
 
VICINITY OF KSFO...CIGS MOSTLY IN THE MVFR RANGE BUT WILL  
OCCASIONALLY BE HIGHER. SHOWERS THROUGH TUESDAY. SOUTHWEST WINDS  
25-30 KT GUSTING TO 40 KT THROUGH 12Z. WINDS DECREASING AFTER  
12Z.  
 
SFO BRIDGE APPROACH...SIMILAR TO SFO.  
 
MONTEREY BAY TERMINALS...CIGS EXPECTED TO STAY AT OR ABOVE 3000  
FEET WITH SHOWERS THROUGH TUESDAY. SOUTHEAST WINDS GUSTING TO 25 KT  
DECREASING AFTER 12Z.  
 

 
   
MARINE...AS OF 09:04 PM PST MONDAY
 
A 999 MB LOW CENTERED 200  
MILES WEST OF CAPE MENDOCINO IS MOVING NORTHEAST. THIS WILL BRING  
GALE FORCE WINDS TO MUCH OF THE COASTAL WATERS THROUGH TUESDAY  
MORNING. THERE IS A SLIGHT CHANCE FOR THUNDERSTORMS THROUGH  
TUESDAY. HIGH PRESSURE WILL BUILD OVER THE EASTERN PACIFIC  
WEDNESDAY THROUGH FRIDAY BRINGING LIGHT TO MODERATE NORTHWEST  
WINDS.  
 

 
   
MTR WATCHES/WARNINGS/ADVISORIES
 
 
.TNGT...HIGH WIND WARNING...HIGHER TERRAIN BAY AREA TO MONTEREY  
AND SAN BENITO COUNTIES.  
FLOOD WATCH...ENTIRE FORECAST AREA.  
WIND ADVISORY...ENTIRE FORECAST AREA.  
GLW...PT REYES TO PIGEON PT 0-10 NM  
GLW...PIGEON PT TO PT PINOS 0-10 NM  
GLW...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM  
SCA...PT ARENA TO PT REYES 0-10 NM  
SCA...PT ARENA TO PIGEON PT 10-60 NM  
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM FROM 1 AM  
GLW...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 1 AM  
SCA...ROUGH BAR ADVISORY FOR SF BAR  
SCA...MRY BAY FROM 10 PM  
GLW...MRY BAY UNTIL 10 PM  
SCA...SF BAY FROM 11 PM  
GLW...SF BAY UNTIL 11 PM  
 

 
 

 
 
PUBLIC FORECAST: BLIER  
AVIATION: W PI  
MARINE: W PI  
 
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO  
 
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