044
FXUS66 KSGX 211740
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
940 AM PST SUN DEC 21 2025
UPDATE
AVIATION DISCUSSION UPDATED FOR THE 18Z TAF PACKAGE.
SYNOPSIS
DRY WEATHER WITH ABOVE NORMAL TEMPERATURES INLAND WILL CONTINUE
THROUGH MONDAY. PERIODS OF PATCHY FOG IN THE COASTAL AREAS AND
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 FRIDAY THROUGH SUNDAY WITH CHANCES LOWERING FROM AROUND
70% ON FRIDAY TO 40% ON SATURDAY, AND ONLY AROUND 15-20% SUNDAY.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
KEY POINTS:
* WIDESPREAD MODERATE TO HEAVY RAINFALL AND A SLIGHT CHANCE OF
THUNDERSTORMS CHRISTMAS EVE AND CHRISTMAS DAY WITH THE
POTENTIAL FOR ROADWAY FLOODING AND LOCALIZED FLASH FLOODING.
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 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 60-70%
CHANCE OF WIND GUSTS EXCEEDING 35 MPH ALONG THE COAST TUESDAY
NIGHT INTO WEDNESDAY. MAKE SURE TO SECURE OUTDOOR OBJECTS. TREE
DAMAGE IS POSSIBLE.
* ADDITIONAL CHANCES OF SHOWERS FRIDAY THROUGH SUNDAY WITH LOWER
SNOW LEVELS, CREATING SLICK CONDITIONS ON MOUNTAIN HIGHWAYS.
LOW CLOUDS SPREAD INTO THE SAN DIEGO COUNTY VALLEYS EARLY IN THE
EVENING, BUT ARE MUCH SLOWER TO PUSH INTO ORANGE COUNTY THIS
MORNING. ELSEWHERE THERE ARE A FEW HIGH CLOUDS MOVING EAST OVER
THE AREA. LOW CLOUDS WILL CLEAR INLAND BY LATE MORNING, BUT COULD
STICK TO THE COASTAL AREAS THROUGH THE DAY. NOT MANY DAY-TO-DAY
CHANGES THROUGH MONDAY AS A WEAK UPPER LEVEL HIGH REMAINS TO OUR
SOUTH OR SOUTHEAST, WITH HIGH TEMPERATURES REMAINING AROUND 10-15
DEGREES ABOVE NORMAL INLAND, LOW CLOUDS AND PATCHY FOG ACROSS THE
COASTAL AREAS AND VALLEYS EACH NIGHT AND MORNING, AND OCCASIONAL
HIGH CLOUDS.
A PATTERN CHANGE AND SIGNIFICANT PRECIPITATION IS STILL ON TAP
MIDWEEK AS A LARGE UPPER LEVEL TROUGH AMPLIFIES OFF THE WEST
COAST, WITH THE BASE OF THE TROUGH EXTENDING AS FAR SOUTH AS
AROUND 15N LATITUDE. AN EXISTING ATMOSPHERIC RIVER WITH THIS
TROUGH WILL PUSH INTO SO CAL LATE TUESDAY, AND THE HIGHLY
AMPLIFIED TROUGH WILL ALSO HELP PULL IN ADDITIONAL MOISTURE FROM
OUR SOUTH, THOUGH MOST OF THIS IS FORECAST TO JUST BRUSH THE FAR
SOUTHEAST PORTION OF OUR FORECAST AREA, WITH THE BULK MOVING INTO
IMPERIAL COUNTY AND WESTERN AZ. BOTH THE GFS AND EC ARE STILL
SHOWING IVT IN EXCESS OF 700 KG/M/S. ENSEMBLE GUIDANCE SHOWS
LIGHT PRECIPITATION BEGINNING AS EARLY AS TUESDAY AFTERNOON FOR
THE NORTHERN AREAS, WITH THE WIDESPREAD HEAVIER PRECIPITATION
OCCURRING WEDNESDAY MORNING THROUGH WEDNESDAY EVENING. STRONG
SOUTHERLY FLOW WILL ACCOMPANY THIS INITIAL WAVE OF PRECIPIATION,
RESULTING IN GUSTY SOUTH WINDS ACROSS THE COASTAL WATERS, COASTAL
AREAS, AND SAN BERNARDINO MOUNTAINS AND ADJACENT DESERT FOOTHILLS.
850-700 MB FLOW OF 30-40 KT WILL ENHANCE PRECIPITATION ALONG THE
COASTAL SLOPES OF THE SAN BERNARDINO MOUNTAINS, WHERE STORM TOTAL
PRECIPITATION COULD END UP IN DOUBLE DIGITS IN SPOTS. THE SNOW
LEVEL WILL BE VERY HIGH DURING THE HEAVIEST PRECIPITATION,
GENERALLY BETWEEN 8500 AND 9000 FT. SEE THE HYDROLOGY SECTION FOR
DETAILS ON PRECIPITATION AMOUNTS.
DEEPER MOISTURE MOVES OUT OF THE AREA WEDNESDAY NIGHT INTO
CHRISTMAS DAY, BUT WEAK SHORT WAVES CONTINUING TO MOVE THROUGH THE
MEAN TROUGH WILL MAINTAIN CHANCES OF SHOWERS AND A SLIGHT CHANCE
OF THUNDERSTORMS. OVERALL PRECIPITATION WILL BE LIGHTER DURING
THIS PERIOD, BUT BRIEF HEAVY SHOWERS COULD OCCUR, ESPECIALLY IN
THUNDERSTORMS. THE SNOW LEVEL FALLS TO AROUND 7500-8000 FT BY
THURSDAY EVENING, SO ONLY THE HIGHER MOUNTAIN PEAKS WILL BE
GETTING A WHITE CHRISTMAS.
THE EVOLUTION OF THE UPPER LEVEL PATTERN IS UNCERTAIN AS WE HEAD
INTO FRIDAY, AROUND 41% OF THE MEMBERS HAVE THE UPPER TROUGH
FURTHER SOUTHEAST, WHICH WOULD PRODUCE HIGHER PRECIPITATION
AMOUNTS AND LOWER SNOW LEVELS ACROSS SO CAL, WHILE THE REMAINING
59% KEEP THE TROUGH FURTHER NORTHEAST FOR LESS PRECIPITATION AND
HIGHER SNOW LEVELS. NBM PRECIPITATION CHANCES ON FRIDAY ARE AROUND
70-80% FOR THE MOUNTAINS WESTWARD, AND 40-50% IN THE DESERTS. BY
SATURDAY, THE ENSEMBLE SOLUTIONS WITH THE MORE PROGRESSIVE TROUGH
ARE PRETTY MUCH DRY (AROUND 50% OF THE MEMBERS), WHILE THE SLOWER
SOLUTIONS HAVE AT LEAST LIGHT PRECIPITATION. THE SLOWEST CLUSTER,
ENCOMPASSING AROUND 34% OF THE MEMBERS, HAS PRECIPITATION
CONTINUING INTO SUNDAY. 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
211730Z...COAST/WESTERN VALLEYS...LOW CLOUDS CLEARED MUCH FASTER
COMPARED TO YESTERDAY, WITH ALL TERMINALS FREE OF LOW CLOUDS AS OF
1730Z THIS MORNING. ASIDE FROM SCT HIGH CLOUDS, VFR WILL PREVAIL
INTO THE AFTERNOON. LOW CLOUDS WILL REDEVELOP AND GRADUALLY FILL
BACK IN AFTER 02-03Z MONDAY, GRADUALLY FILLING IN 10-15 MILES INLAND
THROUGH 05-08Z. AS WITH LAST NIGHT, BASES WILL INITIALLY COME IN
AROUND 1000-1500FT MSL, BUT ARE EXPECTED TO GRADUALLY LOWER TO 800-
1100FT MSL OVERNIGHT. VIS RESTRICTIONS FROM THESE CLOUDS OF 0-3SM
LIMITED TO THE INLAND VALLEYS AND HIGHER TERRAIN, WITH VIS NEAR SEA
LEVEL GENERALLY 6SM OR HIGHER. LOW CLOUDS SCATTER BACK OUT AROUND 16-
18Z MONDAY MORNING.
OTHERWISE...SCT-BKN HIGH CLOUDS WITH UNRESTRICTED VIS
CONTINUES THROUGH MONDAY MORNING.
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 WEDNESDAY, WITH
SEAS NEAR 8-10 FT AND WIND GUSTS UPWARD OF 30-35 KTS.
HYDROLOGY
WIDESPREAD MODERATE TO HEAVY RAINFALL IS EXPECTED TUESDAY NIGHT
THROUGH THURSDAY, HEAVIEST AND MOST WIDESPREAD DURING THE DAY
WEDNESDAY. STRONG SOUTH WINDS WILL FAVOR THE COASTAL SLOPES OF THE
SAN BERNARDINO AND EASTERN SAN GABRIEL MOUNTAINS, GENERALLY FROM
THE CAJON PASS WESTWARD.
FOR THE SAN BERNARDINO/SAN GABRIEL MOUNTAINS 4 AM TUE THROUGH 4 AM
FRIDAY, PROBABILITIES OF RAINFALL TOTALS OF 5 INCHES OR MORE ARE
AS FOLLOWS:
- CAJON PASS WESTWARD: 75-85%
- EAST OF CAJON PASS: 35-65%
PROBABILITIES OF 8 INCHES OR MORE:
- CAJON PASS WESTWARD: 45-55%
- EAST OF CAJON PASS: 10-20%
PROBABILITIES OF 10 INCHES OR MORE:
- CAJON PASS WESTWARD: 10-20%
- EAST OF CAJON PASS: 5% OR LESS
FOR REMAINING AREAS 4 AM TUE THROUGH 4 AM FRIDAY, PROBABILITIES OF
RAINFALL TOTALS 2 INCHES OR MORE:
- ORANGE COUNTY/SANTA ANA MOUNTAINS: 85-95%
- INLAND EMPIRE: 50-90%, HIGHEST WEST
- RIVERSIDE/SAN DIEGO COUNTY MOUNTAINS: 60-80%
- SAN DIEGO COUNTY COAST/VALLEYS: 40-75%, HIGHEST NORTHWEST
- DESERTS: 10-15% (LOWER DESERTS), 25-45% (HIGH DESERT)
PROBABILITIES OF 3 INCHES OR MORE:
- ORANGE COUNTY/SANTA ANA MOUNTAINS: 65-80%
- INLAND EMPIRE: 30-75%, HIGHEST WEST
- RIVERSIDE/SAN DIEGO COUNTY MOUNTAINS: 40-60%
- SAN DIEGO COUNTY COAST/VALLEYS: 10-50%, HIGHEST NORTHWEST
- DESERTS: 5-10% (LOWER DESERTS), 10-20% CHANCE (HIGH DESERT)
CURRENT DETERMINISTIC FORECAST FOR TUESDAY THROUGH FRIDAY MORNING:
- ORANGE COUNTY: 3.3 - 4.5", HIGHEST NORTH
- INLAND EMPIRE: 2.5-4", HIGHEST NORTHWEST
- SAN DIEGO COUNTY COASTS/VALLEYS: 2-3.5", HIGHEST NORTH
- SAN BERNARDINO COUNTY MOUNTAINS: 4-9", HIGHEST WEST
- SANTA ANA MOUNTAINS: 4-5.5"
- RIVERSIDE/SAN DIEGO COUNTY MOUNTAINS: 2-4.5"
- HIGH DESERT: 1.5-3", HIGHEST WEST
- LOW DESERTS: 0.85-1.5", LOCALLY 2.5" NEAR THE SAN GORGONIO PASS
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 EVEN LOWER
FOR FRIDAY AND SATURDAY, BUT 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 IS CURRENTLY EXPECTED TO REACH
ACTION/MONITOR STAGE BY 10 PM WEDNESDAY. BASED ON CURRENT
FORECAST, THE RIVER IS EXPECTED TO PEAK AT 7.8 FT AT 1 AM
THURSDAY, BUT THE OFFICIAL FORECAST ONLY GOES THROUGH 4 AM
THURSDAY. THERE IS A 27% CHANCE THE RIVER COULD REACH MINOR FLOOD
STAGE BEYOND THE FORECAST PERIOD.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC...CO
AVIATION/MARINE...MUNYAN
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