002
FXUS66 KSGX 161017
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
217 AM PST MON DEC 16 2024
SYNOPSIS
FAIR AND WARMER WEATHER IS EXPECTED THIS WEEK AND THE WARMEST DAYS
WILL BE WEDNESDAY AND THURSDAY. WEAK TO MODERATE SANTA ANA WINDS
WILL DEVELOP TUESDAY AND CONTINUE THROUGH WEDNESDAY. WEAKER WINDS
AND A COOLING TREND SHOULD TAKE PLACE THURSDAY THROUGH SUNDAY.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
MOSTLY CLEAR SKIES COVER THE REGION THIS MORNING. A WEAK AND
SPEEDY TROUGH OF LOW PRESSURE WILL MOVE THROUGH THE WEST WELL TO
THE NORTH OF SOCAL TODAY AND TUESDAY. THIS WILL DRAPE A BAND OF
THICKER HIGH CLOUDS ACROSS SOCAL TODAY, FILTERING OR OCCASIONALLY
BLOCKING OUR SUNSHINE, AND WILL TURN OUR FLOW WEAKLY AND BRIEFLY
ONSHORE. IT COULD BRING SOME COASTAL LOW CLOUDS AND FOG TONIGHT
INTO TUESDAY, BUT COVERAGE WOULD BE PATCHY AT MOST. ON TUESDAY,
THE TROUGH BRINGS COLDER AIR INTO THE WESTERN INTERIOR, ALLOWING A
STRONGER SURFACE HIGH PRESSURE TO DEVELOP THERE, AND SETTING UP
AN OFFSHORE PRESSURE GRADIENT INTO SOCAL. THERE IS ALSO A LITTLE
NORTHERLY WIND FLOW AT 850 MB, ROUGHLY 5-6 THOUSAND FEET ABOVE SEA
LEVEL. GENERALLY, IN SOCAL WE NEED TWO FACTORS FOR OFFSHORE WINDS
AND STRONG ONES WE CALL SANTA ANAS: 1) THE MID LEVEL NORTHEAST
WINDS WE CALL UPPER SUPPORT, AND 2) A STRONG SURFACE PRESSURE
GRADIENT ALIGNED BETWEEN THE GREAT BASIN AND SOCAL. ON TUESDAY THE
UPPER SUPPORT PEAKS. IT IS NOT STRONG, BUT WILL BE THE GREATER
DRIVING FACTOR FOR NORTHEAST SANTA ANA WINDS. ON WEDNESDAY WE LOSE
THE UPPER SUPPORT, BUT THE SURFACE PRESSURE GRADIENT IS A LITTLE
STRONGER THAN ON TUESDAY. THE END RESULT IS A WEAK TO MODERATE
SANTA ANA EPISODE FROM AROUND MIDDAY TUESDAY THROUGH AROUND MIDDAY
WEDNESDAY. TOP GUSTS ARE PROJECTED TO BE 35 TO 45 MPH WITH
ISOLATED HIGHER GUSTS IN THE FOOTHILLS AND ADJACENT VALLEYS BELOW
CAJON PASS AND THE NORTHERN SANTA ANA MOUNTAINS OF EASTERN ORANGE
COUNTY. WEAKER OFFSHORE BREEZES WILL FOLLOW INTO THURSDAY, MAINLY
IN FOOTHILLS. HIGH PRESSURE ALOFT AND THE OFFSHORE FLOW WILL
COMBINE TO BOOST TEMPERATURES WEST OF THE MOUNTAINS TUESDAY AND
ESPECIALLY WEDNESDAY. ON WEDNESDAY, OUR WARMEST DAY THIS WEEK,
HIGHS WILL REACH THE MID 70S INTO THE 80S, WHICH WOULD BE 10-18
DEGREES ABOVE AVERAGE. A SHIFT TO WEAK ONSHORE FLOW APPEARS TO
HAPPEN FRIDAY AND CONTINUES THROUGH THE WEEKEND. THAT WILL BRING
DOWN TEMPERATURES, BUT THEY WILL REMAIN A FEW DEGREES ABOVE
NORMAL, ESPECIALLY INLAND. A LONG WAVE PATTERN ENSURING A WEAK
HIGH PRESSURE RIDGE OVER THE WEST WILL KEEP THE FAIR AND DRY
WEATHER COMING, SEEMINGLY WITH NO END IN SIGHT. NOT TO PUT IT ON
SANTA'S WISH LIST, BUT THERE ARE SOME ENSEMBLE MEMBERS SHOWING
SOME PRECIPITATION IN SOCAL AROUND CHRISTMAS DAY.
AVIATION
161000Z....COASTS...MOSTLY CLEAR WITH UNRESTRICTED VIS THROUGH LATE
TONIGHT. PATCHY LOW CLOUDS WILL DEVELOP OVER THE NEARSHORE WATERS 07-
09Z TUE. THESE HAVE A LOW TO MODERATE CHANCE OF MAKING IT BRIEFLY
INTO COASTAL SITES, WITH THE HIGHEST CHANCE AT KSAN (25-40%) 09-12Z
TUE. CHANCES FOR SITES IN NORTH SD AND ORANGE COUNTIES ARE LOWER (10-
20%). BASES FOR CLOUDS THAT DO MAKE IT INLAND AT ABOUT 400-700 FT
MSL, WITH LOCALIZED AREAS OF BR 3-5 SM OVER HIGHER COASTAL TERRAIN.
VALLEYS/MOUNTAINS/DESERTS
MOSTLY CLEAR EXCEPT FOR HIGH CLOUDS AT
OR ABOVE 25,000 FT MSL AND UNRESTRICTED VIS TODAY AND TONIGHT.
MARINE
STRONGER NORTHWEST WINDS EXPECTED IN THE OUTER COASTAL WATERS
STARTING THIS AFTERNOON, WITH ISOLATED GUSTS 20-25 KTS NEAR SAN
CLEMENTE ISLAND THIS EVENING THROUGH EARLY TUESDAY MORNING.
OTHERWISE, NO HAZARDOUS MARINE WEATHER EXPECTED THROUGH FRIDAY.
FIRE WEATHER
SANTA ANA WINDS WILL DEVELOP TUESDAY, PEAKING TUESDAY NIGHT AND
WEDNESDAY MORNING FOR ORANGE, SAN BERNARDINO, AND RIVERSIDE
COUNTIES, AND LATE WEDNESDAY MORNING INTO WEDNESDAY AFTERNOON FOR
SAN DIEGO COUNTY. PEAK GUSTS ARE CURRENTLY PROJECTED IN THE 35-45
MPH RANGE THROUGH AND BELOW CAJON PASS AND ADJACENT COASTAL SLOPES
OF THE SAN BERNARDINO COUNTY MOUNTAINS, PARTS OF THE INLAND
EMPIRE AND IN THE SANTA ANA MOUNTAINS. PEAK WINDS WILL BE CLOSER
TO 30-40 MPH FOR MUCH OF THE SAN DIEGO COUNTY MOUNTAINS AND
FOOTHILLS, WITH ISOLATED GUSTS TO 50 MPH ON THE FAVORED COASTAL
SLOPES. WINDS FOR ALL LOCATIONS WILL SLOWLY SUBSIDE WEDNESDAY
NIGHT INTO THURSDAY.
MINIMUM RELATIVE HUMIDITY ON TUESDAY WILL BE AROUND 20 PERCENT FOR
THE VALLEYS AND FOOTHILLS, LOWERING TO 15-20 PERCENT ON WEDNESDAY
FOR ALL AREAS EXCEPT THE COAST, WITH ONLY SMALL IMPROVEMENTS ON
THURSDAY. MODERATE TO POOR OVERNIGHT RECOVERY IS EXPECTED NEAR
THE PASSES AND FOOTHILLS EACH NIGHT TUESDAY THROUGH THURSDAY.
WITH THE COMBINATION OF ABOVE NORMAL TEMPERATURES, LOW HUMIDITY,
AND GUSTY OFFSHORE WINDS, ELEVATED TO NEAR CRITICAL FIRE WEATHER
CONDITIONS WILL OCCUR TUESDAY THROUGH THURSDAY. THERE WILL LIKELY
BE AT LEAST A FEW HOURS OF CRITICAL FIRE WEATHER CONDITIONS
WEDNESDAY MORNING THROUGH EARLY WEDNESDAY AFTERNOON IN THE WIND
PRONE AREAS.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC/FIRE WEATHER...MM
AVIATION/MARINE...CSP
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