835
FXUS66 KSGX 302117
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
117 PM PST TUE DEC 30 2025
SYNOPSIS
CLOUDY AND WARM TODAY TODAY WITH PERIODS OF VERY LIGHT RAIN OR
SOWERS, NOT ENOUGH TO WET THE GROUND. GUSTY SANTA ANA WINDS
EARLY THIS AFTERNOON WILL WEAKEN BY THIS EVENING ACROSS THE
MOUNTAINS AND WESTERN VALLEYS. A LOW PRESSURE SYSTEM WILL BRING
PERIODS OF SHOWERS FOR NEW YEAR'S EVE AND NEW YEAR'S DAY WITH THE
POTENTIAL FOR MORE CLOUDY AND WET WEATHER BY THE END OF THE WEEK
INTO EARLY NEXT WEEK.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
THIS AFTERNOON...SFC PRESSURE GRADIENTS ARE WEAKENING. CURRENTLY,
NORTHEAST TO EAST WINDS ARE GUSTING 25-40 MPH IN THE WIND-PRONE
AREAS. THE OFFSHORE WINDS AT THE SURFACE WILL CONTINUE TO WEAKEN
THIS AFTERNOON, BECOMING LIGHT TONIGHT. A VERY DRY LAYER OF THE
ATMOSPHERE EXTENDS UPWARD FROM THE SFC TO ABOUT 12,000 FT. ABOVE
THAT, WIDESPREAD CLOUDS IN A DEEP, MOIST LAYER ARE MOVING FROM
SOUTH TO NORTH IN A WARM ADVECTION PROCESS ON THE EASTERN SIDE OF
AN UPPER LEVEL LOW ABOUT 650 MILES SOUTHWEST OF SAN DIEGO. THESE
MID TO HIGH LEVEL CLOUDS ARE PRODUCING LIGHT RAIN/SHOWERS BUT A
PERCENTAGE OF THE PRECIP IS EVAPORATING IN THE DRY SUB-CLOUD
LAYER. AS A RESULT, THE PRECIP REACHING THE SURFACE IS LIKELY NOT
ENOUGH TO MAKE THE ROADS WET EXCEPT POSSIBLY AT HIGHER ELEVATIONS
WHERE THE DRY LAYER IS NOT AS DEEP. THIS PATTERN HAS ALSO PRODUCED
GENERALLY WARMER CONDITIONS AT THE SFC, AND HIGH TEMPERATURES
WILL BE IN THE LOW TO HIGH 70S - POSSIBLY REACHING 80 - WEST OF
THE MTNS.
THIS WARM OVERRUNNING PATTERN WILL CONTINUE THROUGH WEDNESDAY AS
THE LOW TO THE SOUTHWEST MOVES NORTHEAST. THE DEEP, MOIST LAYER
ALOFT WILL GRADUALLY EXTEND LOWER IN THE ATMOSPHERE AND OVER TIME,
MORE RAIN IS LIKELY TO REACH THE GROUND BUT STILL NOT ENOUGH TO
PRODUCE SIGNIFICANT IMPACTS. TEMPERATURES ON WED WILL BE LOWER BUT
WILL REMAIN NEAR OR SLIGHTLY ABOVE SEASONAL AVERAGES.
FOR WED EVENING THROUGH THU...THIS IS THE PERIOD OF TIME WHEN MOST
OF THE RAINFALL WILL OCCUR AS THE CLOSED LOW TO THE SOUTHWEST
ACCELERATES TO THE NORTHEAST AND BECOMES AN OPEN WAVE. IT WILL
PRODUCE ENOUGH DYNAMIC FORCING FOR DEEP CONVECTION, RESULTING IN
PERIODS OF HEAVIER SHOWERS WHICH WILL BE MORE EFFICIENT AT
EXTRACTING MOISTURE FROM THE ATMOSPHERE. RAINFALL RATES DURING
HEAVIER SHOWERS WILL LIKELY RANGE FROM 0.3"-0.5" PER HOUR, WITH
ABOUT A 50% CHANCE OF EXCEEDING 0.5" PER HOUR. THE GREATEST
ACCUMULATIONS WILL BE IN THE SAN BERNARDINO MOUNTAINS AND ON THE
COASTAL SLOPES WHERE TOTALS WILL RANGE FROM ABOUT 1.9" EAST OF
THE CAJON PASS TO ABOUT 5" NEAR THE LA COUNTY LINE. ELSEWHERE,
RAINFALL AMOUNTS WILL RANGE FROM 0.9"-1.8" IN THE COASTAL AREAS,
0.9"-1.8" IN THE INLAND VALLEYS, 1.1"-2.2" IN THE SAN DIEGO AND
RIVERSIDE COUNTY MTNS, 0.25"-0.75" IN THE LOW DESERTS, AND
0.25"-0.9" IN THE HIGH DESERT.
THERE WILL BE A BREAK FROM THE PRECIP ON FRI AS A WEAK DYNAMIC
RIDGE BUILDS BETWEEN THE TROUGH MOVING EAST AND A LOW PRESSURE
SYSTEM MOVING SOUTHEAST OUT OF THE GULF OF AK. TEMPS WILL RISE
SLIGHTLY, ESPECIALLY IN THE LOW DESERTS WHERE TEMPS COULD CLIMB
BACK INTO THE 70S.
THE LOW FROM THE GULF OF AK WILL RESUME THE PRECIP FOR SAT-SUN.
THIS SYSTEM WILL BRING COLDER AIR BUT WILL HAVE LESS AVAILABLE
MOISTURE. TEMPS ON SAT AND SUN WILL BE IN THE 60S WEST OF THE MTNS
AND PRECIP AMOUNTS WILL RANGE FROM A TRACE TO 0.25" IN THE SAN
DIEGO AND RIVERSIDE COUNTY MTNS AS WELL AS AREAS WEST OF THE
MTNS. THE DESERTS WILL BE LUCKY TO GET ANY MEASURABLE PRECIP AND
THE SAN BERNARDINO MOUNTAINS WILL LIKELY GET ABOUT
0.2"-0.8"...GREATEST WEST OF THE CAJON PASS.
A REINFORCING MAJOR SHORTWAVE TROUGH MOVING INTO THE BASE OF THE
EXISTING TROUGH OVER THE WEST COAST WILL CONTINUE THE UNSETTLED
WEATHER AND BRING CHANCES FOR ADDITIONAL PRECIP FOR MONDAY AND
TUESDAY. MOST PRECIP WILL FALL IN THE SAN BERNARDINO MOUNTAINS
WHERE MON-TUE TOTALS WILL RANGE FROM ABOUT 0.2" EAST OF THE CAJON
PASS TO ABOUT 0.7" WEST OF THE CAJON PASS. ELSEWHERE, AMOUNTS WILL
RANGE FROM A TRACE TO 0.25", EXCEPT THE LOW DESERTS WHICH MAY GET
NO MEASURABLE PRECIP.
SNOW LEVELS WILL LIKELY REMAIN ABOVE 8,000 FT THROUGH FRIDAY
BEFORE DROPPING DOWN TO ABOUT 6,500-7,500 FT FOR SAT THROUGH NEXT
TUE. SNOWFALL ESTIMATES NEAR RESORT LEVELS ARE FOR A TRACE TO
ABOUT 4 INCHES BETWEEN SAT AND NEXT TUE.
AVIATION
302100Z...GENERALLY VFR CONDITIONS TODAY AND TONIGHT TAF PERIOD WITH
BKN-OVC HIGH CLOUDS 8000-12000 FT. INTERMITTENT VERY LIGHT -RA/-SHRA
MOVING NORTHWARDS TODAY AND TONIGHT, BUT IS UNLIKELY TO CAUSE ANY
CIG/VIS IMPACTS. LOCALIZED OFFSHORE GUSTS NEAR 20-30 KTS IN THE
MOUNTAIN PASSES AND COASTAL SLOPES THROUGH EARLY EVENING BEFORE
OFFSHORE WINDS DIMINISH LATE EVENING. -SHRA BECOME MORE WIDESPREAD
AND SLIGHTLY HEAVIER WED MORNING AFTER 14Z, WITH INTERMITTENT
REDUCED VIS 5-6 SM AND WIDESPREAD CLOUDS 5000-7000 FT MSL. RA
CHANCES INCREASE AND SPREAD SUBSTANTIALLY WEDNESDAY EVENING,
BRINGING LOWERED VIS 1-4 SM IN HEAVIER SHOWERS AND LOCAL CIGS 1000-
3000 FT MSL.
MARINE
SOUTHEASTERLY WINDS START TO STRENGTHEN WEDNESDAY AFTERNOON, WITH
CONDITIONS HAZARDOUS TO SMALL CRAFT WEDNESDAY EVENING THROUGH
THURSDAY AFTERNOON, BRINGING SOUTH TO SOUTHEAST GUSTS TO 25 KNOTS.
WINDS CALM LATE THURSDAY AFTERNOON, THEN NO HAZARDOUS MARINE WEATHER
CONDITIONS EXPECTED THROUGH SATURDAY.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...FLOOD WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY EVENING FOR
ORANGE COUNTY COASTAL AREAS-ORANGE COUNTY INLAND AREAS-SAN
BERNARDINO COUNTY MOUNTAINS-SAN BERNARDINO AND RIVERSIDE
COUNTY VALLEYS-THE INLAND EMPIRE-SANTA ANA MOUNTAINS AND
FOOTHILLS.
PZ...SMALL CRAFT ADVISORY FROM 7 PM WEDNESDAY TO 3 PM PST THURSDAY
FOR COASTAL WATERS FROM SAN MATEO POINT TO THE MEXICAN
BORDER AND OUT TO 10 NM-WATERS FROM SAN MATEO POINT TO THE
MEXICAN BORDER EXTENDING 10 TO 60 NM OUT INCLUDING SAN
CLEMENTE ISLAND.
PUBLIC...PG
AVIATION/MARINE...CSP
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