025
FXUS66 KSGX 210435
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
835 PM PST SAT DEC 20 2025
SYNOPSIS
DRY WEATHER WITH ABOVE AVERAGE TEMPERATURES INLAND WILL CONTINUE
THROUGH MONDAY. PERIODS OF PATCHY FOG ALONG THE COAST AND IN THE VALLEYS
EACH MORNING THROUGH TUESDAY. AN ATMOSPHERIC RIVER WILL BRING
WIDESPREAD HEAVY RAIN AND MOUNTAIN SNOW ABOVE 8000 FT LATE TUESDAY
INTO THURSDAY (CHRISTMAS DAY). GUSTY SOUTHERLY WINDS DURING THIS
SAME PERIOD EXPECTED FOR MUCH OF THE AREA, INCLUDING THE
MOUNTAINS, MARINE WATERS, AND COAST. THERE MAY BE ADDITIONAL
SHOWERS LATE WEEK INTO NEXT WEEKEND BUT CHANCES ARE LOWER.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
UPDATE
NO SIGNIFICANT CHANGES FROM THE PREVIOUS FORECAST. MODEL GUIDANCE
FOR INTEGRATED WATER VAPOR TRANSPORT (IVT) CONTINUES TO HIGHLIGHT
VERY EARLY WEDNESDAY MORNING INTO LATE WEDNESDAY MORNING AS THE
MOST IMPACTFUL PERIOD, AND RAIN RATES MAY EXCEED 0.50"/HR AT
TIMES. GIVEN THIS IS STILL 4-5 DAYS OUT, TIMING WILL LIKELY SHIFT
FORWARDS OR BACKWARDS, POSSIBLY BY 12+ HRS, SO IT'S IMPORTANT TO
FOLLOW THE FORECAST CLOSELY AS THINGS CHANGE IN THE COMING DAYS.
REGARDLESS, HEAVY AND PERSISTENT RAIN CAN BE EXPECTED FROM LATE
TUESDAY EVENING INTO THURSDAY AFTERNOON, WITH ADDITIONAL CHANCES
FOR FRIDAY AND SATURDAY. IF PLANNING ON TRAVELING FOR THE
CHRISTMAS HOLIDAY, ENSURE YOU ARE AWARE OF ANY FLOOD WATCHES OR
FLASH FLOOD WARNINGS IN EFFECT, AVOID DRIVING AT NIGHT IN HEAVY
RAIN, HAVE EMERGENCY SUPPLIES IN YOUR CAR OR BAG, AND FIND
ALTERNATIVE ROUTES IF ROADS ARE COVERED WITH WATER (TURN AROUND,
DON'T DROWN!). THOSE LIVING IN MOUNTAIN COMMUNITIES WHERE THE
HEAVIEST RAINFALL IS EXPECTED WILL BE ESPECIALLY AT RISK, AS DIRT
ROADS MAY BE WASHED AWAY. FOLLOW ALL GUIDANCE FROM LOCAL EMERGENCY
OFFICIALS.
PREVIOUS DISCUSSION FROM 1225 PM
KEY POINTS:
* WIDESPREAD MODERATE TO HEAVY RAINFALL CHRISTMAS EVE AND CHRISTMAS
DAY WITH THE POTENTIAL FOR ROADWAY FLOODING. RAPID RISES IN SMALL
STREAMS AND INCREASED FLOW IN MAIN STEM RIVERS EXPECTED.
* SNOW LEVELS ARE FORECAST TO REMAIN ABOVE 8000 FT THROUGH CHRISTMAS
DAY, INCREASING POTENTIAL FOR ROCK AND MUDSLIDES ALONG MOUNTAIN
HIGHWAYS, AND DEBRIS FLOWS IN AND BELOW BURN SCARS.
* GUSTY SOUTHERLY WINDS ARE EXPECTED ACROSS THE AREA WITH 80-90%
CHANCE OF WIND GUSTS EXCEEDING 35 MPH ALONG THE COAST TUESDAY
NIGHT INTO WEDNESDAY. MAKE SURE TO SECURE OUTDOOR FURNITURE. TREE
DAMAGE IS POSSIBLE.
* ADDITIONAL CHANCES OF SHOWERS FRIDAY AND SATURDAY WITH LOWER SNOW
LEVELS, CREATING SLICK CONDITIONS ON MOUNTAIN HIGHWAYS.
AT 12 PM A COASTAL EDDY WAS SPINNING OVER THE COASTAL WATERS, WHICH
HAS HELPED MAINTAIN FAIRLY WIDESPREAD LOW CLOUD COVERAGE AT THE
COAST AND IN PORTIONS OF THE WESTERN VALLEYS. WITH MINIMAL CHANGES
IN THE WEATHER PATTERN EXPECTED INTO SUNDAY THE MARINE LAYER SHOULD
REMAIN DEEP ENOUGH FOR AREAS OF DENSE FOG TO DEVELOP ON HIGHER
COASTAL TERRAIN TONIGHT INTO SUNDAY MORNING. HIGHS WILL REMAIN 5 TO
10 DEGREES ABOVE AVERAGE FOR INLAND LOCATIONS THROUGH MONDAY, WITH
HIGHS ALONG THE COAST NEAR AVERAGE.
A SIGNIFICANT PATTERN CHANGE IS EXPECTED BY THE MIDDLE OF THE WEEK.
AN UPPER LEVEL TROUGH AND ASSOCIATED ATMOSPHERIC RIVER WILL AMPLIFY
OFF THE WEST COAST. A SHORT WAVE EMBEDDED IN THE TROUGH LIFTS INTO
SOUTHERN CALIFORNIA TUESDAY NIGHT INTO WEDNESDAY, USHERING IN THE
FIRST SURGE OF MOISTURE AND WIDESPREAD MODERATE TO HEAVY
PRECIPITATION. CURRENT FORECASTS FROM CW3E WRF MODELS ARE SHOWING
IVT FORECASTS AS HIGH AS 600-700 KG/M/S AIMED AT SOUTHERN CALIFORNIA
TUESDAY NIGHT THROUGH MUCH OF THE DAY WEDNESDAY. EVEN WITH THE
DIFFERENCES BETWEEN GLOBAL MODELS AND UNCERTAINTY IN EXACT DETAILS,
THERE IS INCREASING CERTAINTY THAT PERIODS OF MODERATE TO LOCALLY
HEAVY RAIN WILL OCCUR BETWEEN THE OVERNIGHT HOURS OF DECEMBER 23
THROUGH DECEMBER 25. SNOW LEVELS ARE EXPECTED TO STAY ABOVE 7500 FT
THROUGH DECEMBER 25, WITH SNOW LEVELS ABOVE 8500 FT AT THE ONSET OF
THE PRECIPITATION. THIS INCREASES THE CHANCES FOR FLOODING, DEBRIS
FLOWS, AND MUD SLIDES IN THE MOUNTAINS, ESPECIALLY NEAR BURN SCARS.
ADDITIONALLY IMPACTS FROM RIVER FLOODING, ESPECIALLY NEAR THE SAN
DIEGO RIVER, ARE POSSIBLE. SEE THE HYDROLOGY SECTION BELOW FOR
ADDITIONAL INFORMATION. GUSTY SOUTH WINDS ARE ALSO EXPECTED ACROSS
THE COASTAL AREAS, VALLEYS, AND THE SAN BERNARDINO MOUNTAINS INTO
THE ADJACENT DESERT FOOTHILLS LIKELY STARTING LATE TUESDAY
NIGHT/EARLY WEDNESDAY CONTINUING THROUGH WEDNESDAY AFTERNOON.
FROM THURSDAY ONWARDS, THERE IS INCREASING UNCERTAINTY IN THE
EVOLUTION OF THE UPPER LEVEL PATTERN, IN BOTH THE FORWARD
PROGRESSION OF THE LOW AND HOW FAR SOUTH IT WILL DIG. ABOUT 45
PERCENT OF ENSEMBLE SOLUTIONS DIG THE TROUGH OF LOW PRESSURE SOUTH
WITH THE AXIS OFF TO OUR WEST WHICH WOULD CONTINUE TO PULL MOISTURE
INTO THE AREA AND CONTINUE THE WETTER PATTERN FOR SOUTHERN
CALIFORNIA FOR THURSDAY AND FRIDAY. BY SATURDAY, 60 PERCENT OF
SOLUTIONS STILL HAVE THE TROUGH IN POSITION TO CONTINUE BRINGING
PRECIPITATION TO SOUTHERN CALIFORNIA. CURRENT FORECAST MAINTAINS
CHANCES OF PRECIPITATION THROUGH THE END OF THE FORECAST PERIOD
(NEXT SATURDAY). THE CLOSED LOW THAT MAY BRING ADDITIONAL
PRECIPITATION COULD BE COLDER, WHICH WOULD INCREASE CHANCES OF SNOW
IN THE MOUNTAINS ALTHOUGH UNCERTAINTY IN WHAT THE SNOW LEVELS WOULD
BE REMAINS QUITE HIGH. ADDITIONALLY, WESTERLY WINDS COULD INCREASE
DEPENDING ON THE FINAL TRACK OF THE LOW. REGARDLESS, MULTIPLE DAYS
OF PRECIPITATION, WHICH WILL LIKELY BE HEAVY AT TIMES, IS BRINGING A
RISK OF FLOODING AND DIFFICULT TRAVEL CONDITIONS AROUND THE HOLIDAY.
AVIATION
210340Z...COAST/WESTERN VALLEYS...LOW CLOUDS HAVE BEGUN THEIR
NIGHTLY INFILTRATION INTO SOUTHERN SAN DIEGO CO AND WILL MOVE
NORTHWARDS INTO ORANGE CO AFTER 05Z, THEN INLAND TO 15-20 MILES
OVERNIGHT. CLOUDS VERY LIKELY TO MAKE IT TO VCNTY KONT, WITH A 60%
CHANCE FOR CIGS AT THE AIRPORT ITSELF BY 10Z. CURRENTLY BASED AT
1300-1600 FT MSL, BASES LOWER SLIGHTLY OVERNIGHT AFTER 08Z TO 800-
1300 FT MSL, BRINGING VIS RESTRICTIONS 4-6 SM TO COASTAL
MESAS/HIGHLANDS. CLOUDS SCATTER BACK TO COASTS 17-19Z, THEN MOVING
BACK ONSHORE AFTER 22/02Z WITH SIMILAR BASES/INLAND EXTENT TO
TONIGHT.
OTHERWISE...SCT-BKN HIGH CLOUDS WITH UNRESTRICTED VIS TONIGHT AND
SUNDAY.
MARINE
NO HAZARDOUS MARINE CONDITIONS THROUGH TUESDAY MORNING. SOUTH WINDS
WILL STRENGTHEN LATE TUESDAY IN ADVANCE OF A PACIFIC STORM. STRONG
WINDS AND BUILDING SEAS ARE EXPECTED AS A RESULT, WITH SEAS NEAR 8-
10 FT AND WIND GUSTS UPWARD OF 30-35 KTS.
HYDROLOGY
DRY WEATHER CONTINUES THROUGH TUESDAY MORNING. A LOW PRESSURE
SYSTEM AND ASSOCIATED ATMOSPHERIC RIVER BRINGS INCREASING CHANCES
FOR WIDESPREAD HEAVY RAINFALL LATE TUESDAY INTO THURSDAY. TIMING
FOR HEAVIEST RAINFALL IS CURRENTLY TUESDAY NIGHT INTO WEDNESDAY
MORNING.
WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT FOR LYTLE CREEK ON THE
COASTAL SLOPES OF THE EASTERN SAN GABRIEL MOUNTAINS, THE CHANCE
FOR 3 INCHES OR MORE OF RAINFALL IS 92-95%, WITH A 70% CHANCE FOR
5 INCHES OR MORE AND A 30-35% CHANCE FOR 6 INCHES OR MORE. FOR
EARLY WEDNESDAY MORNING THROUGH THURSDAY NIGHT, THE CHANCE FOR 8
INCHES OR MORE OF RAINFALL AT LYTLE CREEK IS 50-60%.
PROBABILITIES OF RAINFALL TOTALS OF 2 INCHES OR MORE TUESDAY
NIGHT THROUGH THURSDAY NIGHT:
- OC/SANTA ANA MOUNTAINS/SAN BERNARDINO MOUNTAINS: 90%
- INLAND EMPIRE: 75-90%, HIGHEST WEST
- SD CO MTS/COAST/VALLEYS: 50-75%
- DESERTS: 15-25% (LOWER DESERTS), 50-70% (HIGH DESERT)
PROBABILITIES OF RAINFALL TOTALS OF 3 INCHES ORE MORE TUESDAY
THROUGH THURSDAY NIGHT:
- OC/SANTA ANA MOUNTAINS/SAN BERNARDINO MOUNTAINS: 70-85%
- INLAND EMPIRE: 50-60%, HIGHEST WEST
- SD CO MTS/COAST/VALLEYS: 25-55%
- DESERTS: 5-15% (LOWER DESERTS), 25-30% CHANCE (HIGH DESERT)
MOST OF THE PRECIPITATION ACROSS SOUTHWESTERN CALIFORNIA THROUGH
CHRISTMAS MORNING IS EXPECTED TO FALL AS RAIN WITH SNOW LEVELS
REMAINING ABOVE 8000 FEET. SNOW LEVELS MAY DROP CLOSER TO
6000-6500 FEET FRIDAY AND FURTHER INTO SATURDAY, BUT EXACT LEVELS
AND LOCATIONS REMAINS UNCERTAIN.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC...ZUBER
AVIATION/MARINE...CSP
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