261  
FXUS66 KSGX 231153  
AFDSGX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN DIEGO CA  
353 AM PST MON JAN 23 2017  
   
SYNOPSIS
 
 
A LARGE LOW PRESSURE SYSTEM NEAR THE WEST COAST WILL MOVE SLOWLY  
INLAND THROUGH TUESDAY. MUCH COLDER AIR ALOFT WILL SPREAD  
SOUTHWARD ACROSS SOUTHERN CALIFORNIA TODAY. THIS IS EXPECTED TO  
INCREASE SHOWER COVERAGE AND INTENSITY TODAY AND BRING A SLIGHT  
CHANCE OF THUNDERSTORMS WITH SMALL HAIL. SHOWERS WILL GRADUALLY  
DECREASE FOR TONIGHT AND TUESDAY. DRY AND SLOWLY WARMER FOR  
WEDNESDAY THROUGH FRIDAY. FOR SATURDAY THROUGH MONDAY...HIGH  
PRESSURE ALOFT NEAR THE WEST COAST AND SURFACE HIGH PRESSURE OVER  
THE GREAT BASIN WILL BRING GREATER WARMING AND PERIODS OF GUSTY  
NORTHEAST WINDS.  
 

 
   
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
 
 
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO  
COUNTIES...  
 
A LARGE LOW PRESSURE SYSTEM NEAR THE WEST COAST WILL MOVE SLOWLY  
INLAND THROUGH TUESDAY. MUCH COLDER AIR ALOFT WILL SPREAD  
INTO SOUTHERN CALIFORNIA TODAY. 500 MB TEMPERATURES NEAR -30 C  
EXTEND AS FAR TO THE SOUTHEAST AS POINT CONCEPTION EARLY THIS  
MORNING AND WILL SPREAD SOUTHEASTWARD ACROSS SOUTHERN CALIFORNIA  
TODAY...THEN REMAIN ENTRENCHED ACROSS SOUTHERN CALIFORNIA INTO  
TUESDAY.  
 
PERIODS OF SHOWERS WILL CONTINUE TODAY WITH GREATEST  
PRECIPITATION TOTALS MOSTLY NEAR THE MOUNTAINS. THE COMBINATION  
OF DAYTIME HEATING AND THE COOLING ALOFT WILL INCREASE THE  
INSTABILITY TODAY. THIS IS EXPECTED TO INCREASE SHOWER COVERAGE  
AND INTENSITY TODAY...ESPECIALLY FROM LATE THIS MORNING THROUGH  
THE AFTERNOON...AND BRING A SLIGHT CHANCE OF THUNDERSTORMS WITH  
SMALL HAIL. SHOWERS WILL GRADUALLY DECREASE FOR TONIGHT AND  
TUESDAY.  
 
GUIDANCE HAS TRENDED A LITTLE WEAKER WITH THE WINDS FOR TODAY  
THOUGH STRONGER AND GUSTY WEST WINDS WILL CONTINUE IN THE  
MOUNTAINS AND DESERTS TODAY. GUSTY WEST WINDS IN COASTAL AND  
VALLEY AREAS ARE MOSTLY EXPECTED TO REMAIN BELOW ADVISORY STRENGTH  
TODAY WITH STRONGEST GUSTS NEAR THE COAST AND NEAR STRONGER  
SHOWERS AND ISOLATED THUNDERSTORMS.  
 
SNOW LEVELS EARLY THIS MORNING ARE NEAR 5000 FEET IN THE MOUNTAINS  
OF SAN BERNARDINO COUNTY AND 5500 IN THE MOUNTAINS OF SAN DIEGO  
COUNTY AND CONTINUING TO FALL AND ARE EXPECTED TO FALL TO 3500 TO  
4000 FEET FOR LATER THIS AFTERNOON INTO THIS EVENING.  
 
COOL WEATHER WILL CONTINUE THROUGH TUESDAY WITH HIGH TEMPERATURES  
REMAINING MOSTLY IN THE 50S EVEN AT THE LOWEST ELEVATIONS NEAR THE  
COAST AND IN THE LOWER DESERTS.  
 
FOR WEDNESDAY THROUGH FRIDAY...DRY WEATHER IS EXPECTED WITH A  
SLOW WARMING TREND WITH HIGH TEMPERATURES REMAINING BELOW AVERAGE.  
 
FOR SATURDAY THROUGH MONDAY...HIGH PRESSURE ALOFT NEAR THE WEST  
COAST AND SURFACE HIGH PRESSURE OVER THE GREAT BASIN WILL BRING  
GREATER WARMING AND PERIODS OF GUSTY NORTHEAST WINDS.  
 

 
   
AVIATION
 
 
231100Z...WEST OF THE MTNS...BKN-OVC CLOUDS LAYERED FROM 1000-12000  
FT MSL WILL CONTINUE TODAY, WITH VIS MOSTLY UNRESTRICTED EXCEPT  
WHERE CLOUDS AND TERRAIN INTERSECT. DURING PERIODS OF RAINFALL, CIGS  
COULD LOWER TO 1500 FT MSL OR LESS WITH VIS 3-5SM EVEN AT LOWER  
ELEVATIONS. A DECREASE IN SHOWERS AND SOME SCATTER OUT IS EXPECTED  
AFTER 04Z TONIGHT PARTICULARLY VCNTY KSNA.  
 
IN THE DESERTS...CLOUDS LAYERED 5000-15000 FT MSL WILL PREVAIL  
TODAY, WITH PERIODS OF BKN CIGS 800-1500 FT MSL AND VIS ABOUT 2SM  
DURING RAIN SHOWERS THIS MORNING. EXPECT OBSCURATIONS IN HIGHER  
TERRAIN AT TIMES.  
 
SOUTH TO SOUTHWEST WINDS 15-20 KT GUSTING TO 30 KT WILL CONTINUE  
TODAY INTO TONIGHT. THIS WILL PRODUCE STG-SVR UP/DOWNDRAFTS AND LLWS  
OVER AND N, NE, AND E OF THE MOUNTAINS.  
 

 
   
MARINE
 
 
STRONG WINDS WITH GUSTS APPROACHING GALE FORCE WILL CONTINUE TODAY  
INTO TONIGHT. LARGE SWELL AND HAZARDOUS SEAS WILL CONTINUE THROUGH  
MOST OF TUESDAY. A GALE WARNING CONTINUES THROUGH TONIGHT. WINDS  
WILL DIMINISH TONIGHT AND TUESDAY WITH SEAS VERY GRADUALLY  
DECREASING LATER TUESDAY.  
 
THE STORM WILL ALSO BRING HEAVY RAIN SQUALLS AT TIMES THROUGH THIS  
AFTERNOON, WITH A SLIGHT CHANCE OF THUNDERSTORMS TODAY AND TONIGHT.  
WATERSPOUTS WILL BE POSSIBLE AS WELL. A MARINE WEATHER STATEMENT  
CONTAINS MORE DETAILS.  
 

 
   
BEACHES
 
 
HIGH SURF WILL CONTINUE TODAY THROUGH TUESDAY THREATENING DAMAGE TO  
COASTAL STRUCTURES AND THE BEACHES. STRONG RIP CURRENTS WILL ADD TO  
THE BIG SURF TO MAKE DANGEROUS SWIMMING CONDITIONS. A HIGH SURF  
WARNING CONTINUES IN EFFECT AND CONTAINS MORE DETAILS. EARLY MORNING  
HIGH TIDES WILL ONLY BE AROUND 5 FT, SO ANYTHING MORE SERIOUS THAN  
MINOR COASTAL FLOODING IS NOT EXPECTED FROM THE LARGE SURF. SWELL  
AND SURF WILL DECREASE LATE TUESDAY AND WEDNESDAY.  
 
IN ADDITION, THERE WILL BE A SLIGHT CHANCE OF THUNDERSTORMS TODAY  
AND TONIGHT.  
 
MORE HIGH SURF IS EXPECTED FRIDAY AS A LARGE NORTHWEST SWELL WITH A  
LONG PERIOD ARRIVES.  
 

 
   
HYDROLOGY
 
 
PERIODS OF SHOWERS WILL CONTINUE TODAY WITH GREATEST  
PRECIPITATION TOTALS MOSTLY NEAR THE MOUNTAINS. THE COMBINATION  
OF DAYTIME HEATING AND THE COOLING ALOFT WILL INCREASE THE  
INSTABILITY TODAY. THIS IS EXPECTED TO INCREASE SHOWER COVERAGE  
AND INTENSITY TODAY...ESPECIALLY FROM LATE THIS MORNING THROUGH  
THE AFTERNOON...AND BRING A SLIGHT CHANCE OF THUNDERSTORMS WITH  
SMALL HAIL. SHOWERS WILL GRADUALLY DECREASE FOR TONIGHT AND  
TUESDAY.  
 
THROUGH TUESDAY...ADDITIONAL RAINFALL FOR ORANGE...SOUTHWESTERN  
SAN BERNARDINO...AND RIVERSIDE COUNTIES...  
 
COAST...........0.25 TO 0.5 INCH.  
VALLEYS.........0.5 TO 1 INCH.  
MOUNTAINS.......1 TO 2 INCHES WITH LOCAL AMOUNTS TO 3 INCHES.  
UPPER DESERTS...0.25 TO 0.5 INCH.  
 
THROUGH TUESDAY...ADDITIONAL RAINFALL FOR SAN DIEGO COUNTY...  
 
COAST...........0.5 TO 1 INCH.  
VALLEYS.........0.75 TO 1.5 INCHES.  
MOUNTAINS.......1.5 TO 2.5 INCHES WITH LOCAL AMOUNTS TO 3.5 INCHES.  
DESERTS.........MOSTLY 0.25 INCH OR LESS.  
 
GIVEN THE CONVECTIVE NATURE OF THE PRECIPITATION...LOCALLY GREATER  
AMOUNTS ARE POSSIBLE IN BANDS OF SHOWERS...STRONGER SHOWERS WITH  
HEAVIER RAINFALL...AND ISOLATED THUNDERSTORMS.  
 
SNOW LEVELS EARLY THIS MORNING ARE NEAR 5000 FEET IN THE MOUNTAINS  
OF SAN BERNARDINO COUNTY AND 5500 IN THE MOUNTAINS OF SAN DIEGO  
COUNTY AND CONTINUING TO FALL AND ARE EXPECTED TO FALL TO 3500 TO  
4000 FEET FOR LATER THIS AFTERNOON INTO THIS EVENING...THEN  
FLUCTUATE NEAR 3000 TO 3500 FEET FOR LATER TONIGHT INTO TUESDAY.  
 
GIVEN SATURATION FROM RECENT RAINFALL...URBAN AND SMALL STREAM  
FLOODING AND ISOLATED FLASH FLOODING CAN OCCUR QUICKLY WITH  
ADDITIONAL HEAVY RAINFALL. A FLASH FLOOD WATCH REMAINS IN EFFECT  
INTO THIS EVENING...EXCEPT FOR MOUNTAIN AREAS ABOVE THE SNOW  
LEVEL.  
 
FLOOD WARNINGS REMAIN IN EFFECT FOR THE SANTA MARGARITA RIVER AND  
FOR THE WHITEWATER RIVER IN THE COACHELLA VALLEY. THE SANTA  
MARGARITA RIVER AT YSIDORA CRESTED AT 14.6 FEET AT 11:45 PM SUNDAY  
EVENING. THAT IS THE FIFTH HIGHEST CREST ON RECORD AND THE HIGHEST  
CREST SINCE THE HIGHEST CREST ON RECORD OF 20.47 FEET IN JANUARY  
1993. THE RIVER LEVEL IS CONTINUING TO FALL EARLY THIS MORNING BUT  
REMAINS ABOVE FLOOD STAGE. THE SAN DIEGO RIVER AT FASHION VALLEY  
HAS REMAINED BELOW FLOOD STAGE OVERNIGHT. IT REACHED A CREST OF  
8.7 FEET AROUND 1:30 AM AND IS SLOWLY FALLING. THAT LEVEL IS  
SUFFICIENT TO AFFECT SOME OF THE LOWER CROSSINGS.  
 

 
   
SKYWARN
 
 
SKYWARN ACTIVATION IS REQUESTED TODAY FROM 10 AM TO 6 PM.  
 

 
   
SGX WATCHES/WARNINGS/ADVISORIES
 
 
CA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR APPLE AND LUCERNE  
VALLEYS-COACHELLA VALLEY-ORANGE COUNTY COASTAL AREAS-ORANGE  
COUNTY INLAND AREAS-RIVERSIDE COUNTY MOUNTAINS-SAN  
BERNARDINO COUNTY MOUNTAINS-SAN BERNARDINO AND RIVERSIDE  
COUNTY VALLEYS-THE INLAND EMPIRE-SAN DIEGO COUNTY COASTAL  
AREAS-SAN DIEGO COUNTY DESERTS-SAN DIEGO COUNTY MOUNTAINS-  
SAN DIEGO COUNTY VALLEYS-SAN GORGONIO PASS NEAR BANNING-  
SANTA ANA MOUNTAINS AND FOOTHILLS.  
 
WINTER STORM WARNING UNTIL 6 PM PST THIS EVENING FOR RIVERSIDE  
COUNTY MOUNTAINS-SAN BERNARDINO COUNTY MOUNTAINS-SAN DIEGO  
COUNTY MOUNTAINS.  
 
WIND ADVISORY FROM 6 AM THIS MORNING TO 6 PM PST THIS EVENING  
FOR SAN DIEGO COUNTY DESERTS-SAN GORGONIO PASS NEAR BANNING.  
 
WIND ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR APPLE AND  
LUCERNE VALLEYS.  
 
HIGH SURF WARNING UNTIL 10 PM PST TUESDAY FOR ORANGE COUNTY  
COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS.  
 
PZ...GALE WARNING UNTIL 4 AM PST TUESDAY FOR COASTAL WATERS FROM SAN  
MATEO POINT TO THE MEXICAN BORDER AND OUT TO 30 NM-WATERS  
FROM SAN MATEO POINT TO THE MEXICAN BORDER EXTENDING 30 TO  
60 NM OUT INCLUDING SAN CLEMENTE ISLAND.  
 

 
 

 
 
PUBLIC/HYDROLOGY...17  
AVIATION/MARINE/BEACHES...MM  
 
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