174
FXUS66 KSGX 220021
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
420 PM PST SUN DEC 21 2025
SYNOPSIS
DRY CONDITIONS WITH ABOVE AVERAGE TEMPERATURES INLAND WILL CONTINUE
INTO EARLY THIS WEEK. PERIODS OF PATCHY FOG EXPECTED NEAR HIGHER
COASTAL TERRAIN AND IN THE VALLEYS TONIGHT INTO MONDAY MORNING. AN
ATMOSPHERIC RIVER WILL BRING WIDESPREAD HEAVY RAIN AND MOUNTAIN SNOW
ABOVE 8000 FT LATE TUESDAY INTO WEDNESDAY, WITH MORE SCATTERED
SHOWERS CONTINUING INTO THURSDAY (CHRISTMAS DAY). GUSTY SOUTHERLY
WINDS CAN BE EXPECTED ACROSS MUCH OF THE AREA, INCLUDING NEAR THE
COAST AND OVER THE COASTAL WATERS TUESDAY INTO WEDNESDAY. THERE ARE
ADDITIONAL CHANCES FOR SHOWERS FRIDAY THROUGH SUNDAY WITH DECREASING
CHANCES INTO SUNDAY.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
NEW AVIATION DISCUSSION...
KEY POINTS:
* WIDESPREAD MODERATE TO HEAVY RAINFALL CHRISTMAS EVE WITH THE
POTENTIAL FOR ROADWAY FLOODING AND LOCALIZED FLASH FLOODING FROM
THE COAST TO DESERTS. RAPID RISES IN SMALL STREAMS AND INCREASED
FLOW IN MAIN STEM RIVERS EXPECTED. 27% CHANCE OF THE SAN DIEGO
RIVER REACHING MINOR FLOOD STAGE.
* SNOW LEVELS ARE FORECAST TO REMAIN ABOVE 8000 FT INTO CHRISTMAS
MORNING, INCREASING POTENTIAL FOR ROCK AND MUDSLIDES ALONG
MOUNTAIN HIGHWAYS, AND DEBRIS FLOWS IN AND BELOW BURN SCARS,
ESPECIALLY IN THE SAN BERNARDINO COUNTY MOUNTAINS.
* GUSTY SOUTHERLY WINDS ARE EXPECTED ACROSS THE AREA WITH 70-90%
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 THURSDAY THROUGH SUNDAY. SNOW LEVELS
ARE EXPECTED TO LOWER TO 6500-7000 FT BY FRIDAY MORNING, CREATING
SLICK CONDITIONS ON MOUNTAIN HIGHWAYS.
HIGH CLOUDS WERE STREAMING ACROSS THE AREA AS OF 11 AM, WITH
BETTER CLEARING ALONG THE COAST COMPARED TO THIS TIME YESTERDAY.
AREAS OF HIGH CLOUDS ARE EXPECTED TO LINGER THROUGH THE AFTERNOON
WITH LOW CLOUDS EXPECTED FOR THE COAST AND VALLEYS AGAIN
OVERNIGHT. PATCHY DENSE FOG IS EXPECTED NEAR HIGHER COASTAL
TERRAIN AND IN PORTIONS OF THE VALLEYS INTO MONDAY MORNING. HIGHS
ON MONDAY ARE EXPECTED TO BE 5 TO 10 DEGREES ABOVE AVERAGE FOR
INLAND LOCATIONS, LOCALLY UP TO 15 DEGREES ABOVE AVERAGE FOR THE
MOUNTAINS AND DESERTS. TEMPERATURES ARE EXPECTED TO FALL TO NEAR
OR BELOW AVERAGE FOR THE REST OF THE WEEK.
AN ATMOSPHERIC RIVER IS STILL ON TRACK TO IMPACT SOUTHERN CALIFORNIA
ON WEDNESDAY. PERIODS OF LIGHT TO LOCALLY MODERATE RAIN MAY BEGIN AS
EARLY AS MID-DAY TUESDAY WITH INCREASING CHANCES OF PRECIPITATION
INTO THE OVERNIGHT HOURS. OVERNIGHT TUESDAY LOCALLY HEAVY RAIN MAY
DEVELOP, MOST LIKELY ON THE COASTAL SLOPES OF THE SAN BERNARDINO
COUNTY MOUNTAINS. THE HEAVIEST AND MOST WIDESPREAD RAIN IS EXPECTED
THROUGH THE DAY WEDNESDAY, WITH THE HEAVY RAIN MOVING NORTHWEST TO
SOUTHEAST FROM ORANGE TO SAN DIEGO COUNTY DESERTS. AFTER THE
RAIN BAND PASSES, SCATTERED SHOWERS ARE EXPECTED TO CONTINUE WITH
LOCALLY HEAVY RAIN INTO THURSDAY (CHRISTMAS DAY). LATEST GUIDANCE
SHOWS A SIGNIFICANT DECREASE IN IVT (ATMOSPHERIC MOISTURE) DURING
THE DAY THURSDAY, BRINGING THE POTENTIAL FOR PERIODS NO
PRECIPITATION. SNOW LEVELS ARE EXPECTED TO REMAIN QUITE HIGH
THROUGH THE DURATION OF THE HEAVIEST PRECIPITATION, BUT ARE
EXPECTED TO LOWER LATER IN THE WEEK. PLEASE SEE THE HYDROLOGY
SECTION BELOW FOR MORE INFORMATION ON EXPECTED RAINFALL RATES,
TOTALS, AND SNOW LEVEL INFORMATION. IN ADDITION TO PERIODS OF
HEAVY RAIN, GUSTY SOUTH WINDS ARE EXPECTED. WINDS ARE EXPECTED TO
INCREASE ON TUESDAY AFTERNOON, WITH THE STRONGEST WINDS EXPECTED
DURING THE DAY WEDNESDAY. PEAK WIND GUSTS OF 60-70 MPH POSSIBLE ON
THE COASTAL SLOPES OF THE SAN BERNARDINO COUNTY MOUNTAINS WITH
GUSTS 30-40 MPH POSSIBLE IN THE COASTS AND VALLEYS.
THERE STILL REMAINS SOME UNCERTAINTY IN THE UPPER LEVEL PATTERN FOR
FRIDAY THROUGH SUNDAY. GLOBAL MODELS CONTINUE TO STRUGGLE WITH THE
PROGRESSION OF THE LOW PRESSURE SYSTEM THAT DEVELOPS NEAR THE GULF
OF ALASKA. THE SOLUTIONS WITH MORE ECMWF ENSEMBLE MEMBERS SHOW A
FASTER EASTWARD MOVEMENT OF THE LOW WHICH WOULD BRING ADDITIONAL
CHANCES OF MORE WIDESPREAD PRECIPITATION TO THE AREA SOMETIME FRIDAY
INTO SATURDAY, BUT DRIER CONDITIONS SUNDAY. SOLUTIONS WITH MORE
INPUT FROM GEFS MEMBERS SHOW A SLOWER EASTWARD PROGRESSION OF THE
LOW WHICH WOULD CONTINUE OUR PRECIPITATION CHANCES INTO AT LEAST
SUNDAY. WE WILL HAVE TO SEE HOW THIS EVOLVES OVER THE NEXT FEW
DAYS, BUT OVERALL THE RAIN FOR LATE INTO THE WEEK INTO THE WEEKEND
LOOKS FAR LESS IMPACTFUL, THOUGH SNOW COULD MAKE TRAVEL DIFFICULT
IN THE MOUNTAINS SHOULD THE SNOW LEVEL LOWER ENOUGH.
AVIATION
212345Z....COAST/WESTERN VALLEYS...SATELLITE SHOWS LOW CLOUDS ARE
ALREADY BEGINNING TO DEVELOP ALONG THE COASTLINE WITH BASES AROUND
1000FT MSL. CLOUDS WILL PUSH INTO COASTAL TAF SITES 01-03Z MON, WITH
VIS 4-6SM IN HZ. BASES MAY FALL A BIT CLOSER TO 700-900FT MSL
THROUGH 10-12Z BEFORE CLEARING BACK TOWARDS THE COAST BY 16-18Z.
LOCALIZED DENSE FG WHERE TERRAIN INTERSECTS CLOUDS. LOW CLOUDS
DEVELOP AGAIN MONDAY EVENING, WITH SIMILAR BASES BUT WILL BE A BIT
SLOWER TO MOVE INLAND, LIKELY AFTER 02-04Z TUE.
OTHERWISE
SCT-BKN HIGH CLOUDS WITH UNRESTRICTED VIS
CONTINUES THROUGH MONDAY.
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 THEN THROUGH EARLY THURSDAY
MORNING. STEEP SEAS NEAR 8-10 FT EXPECTED WITH WIND GUSTS UPWARD OF
30-35 KTS.
HYDROLOGY
WHILE MODERATE TO LOCALLY HEAVY RAIN MAY BEGIN TUESDAY EVENING
(ESPECIALLY FOR THE MOUNTAINS) GUIDANCE IS COMING INTO BETTER
ALIGNMENT THAT THE HEAVIEST AND MOST WIDESPREAD RAINFALL IS EXPECTED
THROUGH THE DAY WEDNESDAY. RAIN WILL MOVE FROM NORTHWEST TO
SOUTHEAST THROUGH THE DAY WEDNESDAY, WITH SCATTERED SHOWERS
LINGERING INTO THE OVERNIGHT HOURS AND CHRISTMAS MORNING. THOSE
SCATTERED SHOWERS MAY BE LOCALLY HEAVY. ADDITIONALLY THERE IS A
SLIGHT CHANCE OF THUNDERSTORMS FOR WEDNESDAY EVENING INTO THURSDAY
MORNING AND HEAVY RAIN IS EXPECTED WHERE THUNDERSTORMS DEVELOP. PEAK
RAINFALL RATES ARE EXPECTED TO RANGE FROM 0.5-1 INCH PER HOUR, WITH
THE POTENTIAL TO BE LOCALLY HIGHER WHERE EMBEDDED CONVECTIVE
SHOWERS OR THUNDERSTORMS DEVELOP. THE COASTAL SLOPES OF THE SAN
BERNARDINO MOUNTAINS ARE EXPECTED TO RECEIVE A SIGNIFICANT AMOUNT
OF RAINFALL DUE TO STRONG SOUTHERLY FLOW ALOFT (30-50 KT) ALLOWING
FOR OROGRAPHIC ENHANCEMENT OF RAINFALL AND THE WARM AIRMASS
PREVENTING SNOW FORMATION BELOW 8000 FT DURING THE HEAVIEST
PRECIPITATION.
FOR THE SAN BERNARDINO/SAN GABRIEL MOUNTAINS 4 AM TUE THROUGH 4 AM
FRIDAY, THE CURRENT DETERMINISTIC FORECAST IS:
- CAJON PASS WESTWARD: 8-14"
- EAST OF CAJON PASS: 8-10"
MOST OF THE RAINFALL IS EXPECTED TO FALL ON WEDNESDAY.
FOR REMAINING AREAS 4 AM TUE THROUGH 4 AM FRIDAY...
PROBABILITIES OF RAINFALL TOTALS 3 INCHES OR MORE:
- ORANGE COUNTY/SANTA ANA MOUNTAINS: 70-85%
- INLAND EMPIRE: 40-80%, HIGHEST WEST
- RIVERSIDE/SAN DIEGO COUNTY MOUNTAINS: 70-90%
- SAN DIEGO COUNTY COAST/VALLEYS: 30-60%, HIGHEST NORTH
- DESERTS: 5-10% (LOWER DESERTS), 15-25% (HIGH DESERT)
PROBABILITIES OF 4 INCHES OR MORE:
- ORANGE COUNTY/SANTA ANA MOUNTAINS: 40-60%
- INLAND EMPIRE: 20-60%, HIGHEST WEST
- RIVERSIDE/SAN DIEGO COUNTY MOUNTAINS: 60-80%
- SAN DIEGO COUNTY COAST/VALLEYS: 20-40%, HIGHEST NORTH
- DESERTS: LESS THAN 5% (LOWER DESERTS), 10% CHANCE (HIGH DESERT)
CURRENT DETERMINISTIC FORECAST FOR TUESDAY THROUGH FRIDAY MORNING:
- ORANGE COUNTY: 3.3 - 4.75", HIGHEST NORTH
- INLAND EMPIRE: 3-4.75", HIGHEST NORTHWEST
- SAN DIEGO COUNTY COASTS/VALLEYS: 2.5-4", HIGHEST NORTH
- SANTA ANA MOUNTAINS: 4.5-6.5"
- RIVERSIDE/SAN DIEGO COUNTY MOUNTAINS: 3-6"
- HIGH DESERT: 1.5-3", HIGHEST WEST
- LOW DESERTS: 0.85-1.5", LOCALLY 2.5" NEAR THE SAN GORGONIO PASS
THE HIGHER RAINFALL AMOUNTS IN THE DETERMINISTIC RANGES ABOVE
WILL LIKELY BE MORE LOCALIZED TO WHERE HEAVIER, MORE CONVECTIVE
BANDS OF RAINFALL DEVELOP.
MOST OF THE PRECIPITATION ACROSS SOUTHWESTERN CALIFORNIA THROUGH
CHRISTMAS MORNING IS EXPECTED TO FALL AS RAIN WITH SNOW LEVELS
REMAINING ABOVE 7500-8000 FEET. SNOW LEVELS COULD DROP TO 6500-7000
FT BY FRIDAY MORNING, POTENTIALLY DOWN TO 5500-6000 FT BY SATURDAY.
CONFIDENCE IN SNOW LEVELS IS LOW AS THE SPREAD BETWEEN THE NBM 25TH
AND 75TH PERCENTILE SNOW LEVEL IS AROUND 1500-2000 FT.
THE SAN DIEGO RIVER AT FASHION VALLEY AND THE SANTA MARGARITA RIVER
AT YSIDORA ARE CURRENTLY EXPECTED TO REACH ACTION/MONITOR STAGE BY
WEDNESDAY EVENING. BASED ON CURRENT FORECAST, THE SAN DIEGO RIVER IS
EXPECTED TO PEAK AT 8.2 FT EARLY THURSDAY MORNING WITH THE SANTA
MARGARITA EXPECTED TO PEAK AT 10.9 FT LATE WEDNESDAY NIGHT. THERE IS
A 27% CHANCE THE SAN DIEGO RIVER COULD REACH MINOR FLOOD STAGE BY
FRIDAY DEPENDING ON THE LOCATION AND INTENSITY OF ADDITIONAL
RAINFALL.
SGX WATCHES/WARNINGS/ADVISORIES
CA...FLOOD WATCH FROM LATE TUESDAY NIGHT THROUGH LATE WEDNESDAY NIGHT
FOR SAN DIEGO COUNTY COASTAL AREAS-SAN DIEGO COUNTY DESERTS-
SAN DIEGO COUNTY MOUNTAINS-SAN DIEGO COUNTY VALLEYS.
FLOOD WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY 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 GORGONIO
PASS NEAR BANNING-SANTA ANA MOUNTAINS AND FOOTHILLS.
PZ...NONE.
PUBLIC...CO
AVIATION/MARINE...ZUBER
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