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FXUS66 KSGX [San Diego/WFO CA] 090522 AFDSGX 

FXUS66 KSGX 090522
AFDSGX [HEAD]

National Weather Service San Diego California 9:22pm PST Mon Mar 8 2021 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
922 PM PST MON MAR 8 2021 [HEAD]

Synopsis. Tuesday will be cooler across the board, with gusty winds across the mountains and deserts preceding the approaching storm system. This system will bring widespread rain, heavy low-elevation snow, and a few thunderstorms to the region Wednesday and Thursday. The Winter Storm Watch was upgraded to a Winter Storm Warning this evening. The cold will be very noticeable mid week, with highs locally 20° below normal Wednesday and Thursday. Some showers may continue into Friday, especially in the mountains and high desert, before the storm exits the region and ushers in warmer and drier weather for the weekend. 

.SYNOPSIS...
TUESDAY WILL BE COOLER ACROSS THE BOARD, WITH GUSTY WINDS ACROSS
THE MOUNTAINS AND DESERTS PRECEDING THE APPROACHING STORM SYSTEM.
THIS SYSTEM WILL BRING WIDESPREAD RAIN, HEAVY LOW-ELEVATION SNOW,
AND A FEW THUNDERSTORMS TO THE REGION WEDNESDAY AND THURSDAY. THE
WINTER STORM WATCH WAS UPGRADED TO A WINTER STORM WARNING THIS
EVENING. THE COLD WILL BE VERY NOTICEABLE MID WEEK, WITH HIGHS
LOCALLY 20 DEGREES BELOW NORMAL WEDNESDAY AND THURSDAY. SOME
SHOWERS MAY CONTINUE INTO FRIDAY, ESPECIALLY IN THE MOUNTAINS AND
HIGH DESERT, BEFORE THE STORM EXITS THE REGION AND USHERS IN
WARMER AND DRIER WEATHER FOR THE WEEKEND. [DISC]

Discussion. For extreme southwestern California including Orange… San Diego… western Riverside and southwestern San Bernardino Counties. 

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES... [DISC]

Highlights 

HIGHLIGHTS... [CRED]

* Winter Storm Warning for mountains starting Tuesday night * heavy, low elevation snow to impact some major passes * widespread rain and isolated thunderstorms Wednesday–Thursday * much colder than normal mid week * showers may continue into Friday. Drier for the weekend. 

* WINTER STORM WARNING FOR MOUNTAINS STARTING TUESDAY NIGHT
* HEAVY, LOW ELEVATION SNOW TO IMPACT SOME MAJOR PASSES
* WIDESPREAD RAIN AND ISOLATED THUNDERSTORMS WED-THU
* MUCH COLDER THAN NORMAL MID WEEK
* SHOWERS MAY CONTINUE INTO FRIDAY. DRIER FOR THE WEEKEND. [DISC]

We may have recently entered meteorological spring, but winter is about to come knocking back at our door. The low pressure trough centered off the Pacific Northwest coast will continue to deepen into Tuesday, ushering in noticeably cooler temperatures, particularly for the mountains and deserts. As onshore pressure gradients tighten, winds will respond accordingly, with gusty west winds surfacing across the desert-facing mountain slopes and passes. These will persist into Wednesday, and locally longer, especially for the San Gorgonio Pass area. 

WE MAY HAVE RECENTLY ENTERED METEOROLOGICAL SPRING, BUT
WINTER IS ABOUT TO COME KNOCKING BACK AT OUR DOOR. THE LOW
PRESSURE TROUGH CENTERED OFF THE PACNW COAST WILL CONTINUE TO
DEEPEN INTO TUESDAY, USHERING IN NOTICEABLY COOLER TEMPERATURES,
PARTICULARLY FOR THE MOUNTAINS AND DESERTS. AS ONSHORE PRESSURE
GRADIENTS TIGHTEN, WINDS WILL RESPOND ACCORDINGLY, WITH GUSTY WEST
WINDS SURFACING ACROSS THE DESERT-FACING MOUNTAIN SLOPES AND
PASSES. THESE WILL PERSIST INTO WEDNESDAY, AND LOCALLY LONGER,
ESPECIALLY FOR THE SAN GORGONIO PASS AREA. [DISC]

It is not until Tuesday night that the first few pre-frontal showers will make an appearance, but the more widespread precipitation is still slated for Wednesday and Thursday. A mostly weak cold front Wednesday will bring largely moderate rain and the first round of heavy snow to the mountains. 700 mb temperatures lowering to around –10°C Wednesday will bring down snow levels to around 4,000 ft, locally lower in San Bernardino County. Instability will increase in the afternoon, with ample cold air aloft and favorable jet positioning leading to scattered post-frontal showers and likely a few thunderstorms west of the mountains. Temperatures will continue to fall, with highs a good 10–20° below normal Wednesday, and locally even 25° below average. 

IT IS NOT UNTIL TUESDAY NIGHT THAT THE FIRST FEW PRE-FRONTAL
SHOWERS WILL MAKE AN APPEARANCE, BUT THE MORE WIDESPREAD
PRECIPITATION IS STILL SLATED FOR WEDNESDAY AND THURSDAY. A MOSTLY
WEAK COLD FRONT WEDNESDAY WILL BRING LARGELY MODERATE RAIN AND THE
FIRST ROUND OF HEAVY SNOW TO THE MOUNTAINS. 700 MB TEMPERATURES
LOWERING TO AROUND -10 C WEDNESDAY WILL BRING DOWN SNOW LEVELS
TO AROUND 4,000 FT, LOCALLY LOWER IN SAN BERNARDINO COUNTY.
INSTABILITY WILL INCREASE IN THE AFTERNOON, WITH AMPLE COLD AIR
ALOFT AND FAVORABLE JET POSITIONING LEADING TO SCATTERED POST-
FRONTAL SHOWERS AND LIKELY A FEW THUNDERSTORMS WEST OF THE
MOUNTAINS. TEMPERATURES WILL CONTINUE TO FALL, WITH HIGHS A GOOD
10 TO 20 DEGREES BELOW NORMAL WEDNESDAY, AND LOCALLY EVEN 25
DEGREES BELOW AVERAGE. [DISC]

The cold will only reaffirm its grip over the region Wednesday night and Thursday, as the approaching low pressure center continues forcing snow levels to fall. Snow can be expected above 3,000–3,500 feet for northern portions of our forecast area Thursday, and around 500 ft higher in San Diego County. There is high confidence in significant travel impacts to cajon pass and potentially I-8 through laguna summit. Highs both days will struggle to hit the mid to high 50's across most of our coastal and valley areas. With the jet streak remaining due South Thursday as the trough digs over Southern California, we'll remain under a dynamically favorable environment for thunderstorms, with precipitation largely of showery characteristics. 

THE COLD WILL ONLY REAFFIRM ITS GRIP OVER THE REGION WEDNESDAY
NIGHT AND THURSDAY, AS THE APPROACHING LOW PRESSURE CENTER
CONTINUES FORCING SNOW LEVELS TO FALL. SNOW CAN BE EXPECTED ABOVE
3,000 TO 3,500 FEET FOR NORTHERN PORTIONS OF OUR FORECAST AREA
THURSDAY, AND AROUND 500 FT HIGHER IN SAN DIEGO COUNTY. THERE IS
HIGH CONFIDENCE IN SIGNIFICANT TRAVEL IMPACTS TO CAJON PASS AND
POTENTIALLY I-8 THROUGH LAGUNA SUMMIT. HIGHS BOTH DAYS WILL
STRUGGLE TO HIT THE MID TO HIGH 50`S ACROSS MOST OF OUR COASTAL
AND VALLEY AREAS. WITH THE JET STREAK REMAINING DUE SOUTH
THURSDAY AS THE TROUGH DIGS OVER SOCAL, WE`LL REMAIN UNDER A
DYNAMICALLY FAVORABLE ENVIRONMENT FOR THUNDERSTORMS, WITH
PRECIPITATION LARGELY OF SHOWERY CHARACTERISTICS. [DISC]

Although the bulk of the precipitation will fall through Thursday night, we're not entirely out of the woods for Friday either. As the low tracks inland and northerly flow rotates along its western periphery, there's decent potential for additional wrap-around moisture and showers, mainly for the mountains and high desert. Both ensemble guidance and local WRF [Weather Research and Forecasting model] products hint at this potential, and a glance at the ECMWF [European Center for Medium-Range Weather Forecasts model] shift of tails suggests we cannot rule out significant additional snowfall impacts for these areas if this scenario plays out. 

ALTHOUGH THE BULK OF THE PRECIPITATION WILL FALL THROUGH THURSDAY
NIGHT, WE`RE NOT ENTIRELY OUT OF THE WOODS FOR FRIDAY EITHER. AS
THE LOW TRACKS INLAND AND NORTHERLY FLOW ROTATES ALONG ITS WESTERN
PERIPHERY, THERE`S DECENT POTENTIAL FOR ADDITIONAL WRAP-AROUND
MOISTURE AND SHOWERS, MAINLY FOR THE MOUNTAINS AND HIGH DESERT.
BOTH ENSEMBLE GUIDANCE AND LOCAL WRF PRODUCTS HINT AT THIS
POTENTIAL, AND A GLANCE AT THE ECMWF SHIFT OF TAILS SUGGESTS WE
CANNOT RULE OUT SIGNIFICANT ADDITIONAL SNOWFALL IMPACTS FOR THESE
AREAS IF THIS SCENARIO PLAYS OUT. [DISC]

Weak ridging will fill in for the weekend, bringing us an increase in temperatures and drier weather. The pattern beyond the weekend looks like a "time will tell" situation, with a wide realm of possibilities. For now, the focus remains on the upcoming significant winter storm. For more information on snow totals and snow levels, see the Winter Storm Warning, and for more information on rainfall totals and rates, see the hydrology section below. 

WEAK RIDGING WILL FILL IN FOR THE WEEKEND, BRINGING US AN INCREASE
IN TEMPERATURES AND DRIER WEATHER. THE PATTERN BEYOND THE WEEKEND
LOOKS LIKE A "TIME WILL TELL" SITUATION, WITH A WIDE REALM OF
POSSIBILITIES. FOR NOW, THE FOCUS REMAINS ON THE UPCOMING
SIGNIFICANT WINTER STORM. FOR MORE INFORMATION ON SNOW TOTALS AND
SNOW LEVELS, SEE THE WINTER STORM WARNING, AND FOR MORE
INFORMATION ON RAINFALL TOTALS AND RATES, SEE THE HYDROLOGY
SECTION BELOW. [DISC]

Aviation. 090415Z [1:04am PST]… coast/valleys… mostly VFR [Visual Flight Rules] conditions through 22Z [2pm PST] Tuesday with scattered 020 broken 200 and only occasional broken 020 at times. West winds increasing after 18Z [10am PST] Tuesday to 15–25 kt [17–29 mph] at the coastal and valley airports with gusts to 30 kt [35 mph]

.AVIATION...
090415Z...COAST/VALLEYS...MOSTLY VFR CONDITIONS THROUGH 22Z TUESDAY
WITH SCT020 BKN200 AND ONLY OCNL BKN020 AT TIMES. WEST WINDS
INCREASING AFTER 18Z TUESDAY TO 15-25 KT AT THE COASTAL AND VALLEY
AIRPORTS WITH GUSTS TO 30 KT. [AVIA]

Mountains/deserts… gusty west winds 20–30 kt [23–35 mph] with gusts to 45 kt [52 mph] in the mountains and some desert areas through Tuesday with low-level wind shear and moderate up/downdrafts. 

MOUNTAINS/DESERTS...GUSTY WEST WINDS 20-30 KT WITH GUSTS TO 45 KT IN
THE MOUNTAINS AND SOME DESERT AREAS THROUGH TUESDAY WITH LLWS AND
MODERATE UP/DOWNDRAFTS. [AVI2]

Marine. A Small Craft Advisory is in effect through 9pm Tuesday. Northwest winds 15–25 kt [17–29 mph] over the outer waters will move into the inner waters after midnight and continue through Tuesday afternoon. 

.MARINE...
A SMALL CRAFT ADVISORY IS IN EFFECT THROUGH 9 PM TUESDAY. NORTHWEST
WINDS 15-25 KT OVER THE OUTER WATERS WILL MOVE INTO THE INNER WATERS
AFTER MIDNIGHT AND CONTINUE THROUGH TUESDAY AFTERNOON. [AVIA]

Gusty west winds at times Tuesday night, Wednesday and Thursday as a cold winter storm moves across Southern California. Rain is likely Wednesday with scattered showers Thursday. Thunderstorms with strong winds, rough seas and lightning are also possible. 

GUSTY WEST WINDS AT TIMES TUESDAY NIGHT, WEDNESDAY AND THURSDAY AS A
COLD WINTER STORM MOVES ACROSS SOUTHERN CALIFORNIA. RAIN IS LIKELY
WEDNESDAY WITH SCATTERED SHOWERS THURSDAY. THUNDERSTORMS WITH STRONG
WINDS, ROUGH SEAS AND LIGHTNING ARE ALSO POSSIBLE. [AVI2]

Beaches… elevated surf from 3–6 feet Tuesday. Gusty west winds 15–30 mph at the beaches in the afternoon. Above average surf from 3–6 feet continues Wednesday and Thursday with showers and possible thunderstorms. 

.BEACHES...
ELEVATED SURF FROM 3 TO 6 FEET TUESDAY. GUSTY WEST WINDS 15 TO 30
MPH AT THE BEACHES IN THE AFTERNOON. ABOVE AVERAGE SURF FROM 3 TO 6
FEET CONTINUES WEDNESDAY AND THURSDAY WITH SHOWERS AND POSSIBLE
THUNDERSTORMS. [DISC]

Hydrology. A slow moving storm system will bring periods of rain and mountain snow beginning early Wednesday, and possibly continuing through Friday, with the heaviest precipitation expected Wednesday into Thursday. The main frontal band will move through on Wednesday, with mostly moderate rain. This will be followed by widespread scattered showers and likely a few thunderstorms through Thursday. Thus, storm totals will be spread out over several days, with the main impact being snowfall. Since the storm will be quite cold, snow levels may be as low as 2500 ft at times with convective showers. Moisture will be limited with this event, so rainfall totals are not excessive for a winter storm. Current estimates range from 0.50 to locally 1.25 inches for the coast and valleys, and 1.5 to locally 2.5 inches (liquid equivalent) in the mountains (mostly as snow). The deserts will be drier, and are expected to mostly pick up 0.25" or less, with locally higher amounts up to around 0.30" for the high desert. 

.HYDROLOGY...
A SLOW MOVING STORM SYSTEM WILL BRING PERIODS OF RAIN AND MOUNTAIN
SNOW BEGINNING EARLY WEDNESDAY, AND POSSIBLY CONTINUING THROUGH
FRIDAY, WITH THE HEAVIEST PRECIPITATION EXPECTED WEDNESDAY INTO
THURSDAY. THE MAIN FRONTAL BAND WILL MOVE THROUGH ON WEDNESDAY,
WITH MOSTLY MODERATE RAIN. THIS WILL BE FOLLOWED BY WIDESPREAD
SCATTERED SHOWERS AND LIKELY A FEW THUNDERSTORMS THROUGH THURSDAY.
THUS, STORM TOTALS WILL BE SPREAD OUT OVER SEVERAL DAYS, WITH THE
MAIN IMPACT BEING SNOWFALL. SINCE THE STORM WILL BE QUITE COLD,
SNOW LEVELS MAY BE AS LOW AS 2500 FT AT TIMES WITH CONVECTIVE
SHOWERS. MOISTURE WILL BE LIMITED WITH THIS EVENT, SO RAINFALL
TOTALS ARE NOT EXCESSIVE FOR A WINTER STORM. CURRENT ESTIMATES
RANGE FROM 0.50 TO LOCALLY 1.25 INCHES FOR THE COAST AND VALLEYS,
AND 1.5 TO LOCALLY 2.5 INCHES (LIQUID EQUIVALENT) IN THE
MOUNTAINS (MOSTLY AS SNOW). THE DESERTS WILL BE DRIER, AND ARE
EXPECTED TO MOSTLY PICK UP 0.25" OR LESS, WITH LOCALLY HIGHER
AMOUNTS UP TO AROUND 0.30" FOR THE HIGH DESERT. [AVIA]

Rainfall rates will be light to moderate overall (0.10–0.30/hour.), with some briefly heavier rainfall rates possible during heavier showers and thunderstorms. Some runoff is likely, with the greatest impact in urban and poorly drained areas, but widespread flooding and mainstem river flooding is not likely. Snow levels near 4500 feet will lower to around 4000 feet Wednesday afternoon and 3500 feet or less for Wednesday night and Thursday. This will further limit any significant runoff, and eliminate the risk of debris flows for the El Dorado and apple burn scars. 

RAINFALL RATES WILL BE LIGHT TO MODERATE OVERALL (0.10 TO 0.30/HR.),
WITH SOME BRIEFLY HEAVIER RAINFALL RATES POSSIBLE DURING HEAVIER
SHOWERS AND THUNDERSTORMS. SOME RUNOFF IS LIKELY, WITH THE
GREATEST IMPACT IN URBAN AND POORLY DRAINED AREAS, BUT WIDESPREAD
FLOODING AND MAINSTEM RIVER FLOODING IS NOT LIKELY. SNOW LEVELS
NEAR 4500 FEET WILL LOWER TO AROUND 4000 FEET WEDNESDAY AFTERNOON
AND 3500 FEET OR LESS FOR WEDNESDAY NIGHT AND THURSDAY. THIS WILL
FURTHER LIMIT ANY SIGNIFICANT RUNOFF, AND ELIMINATE THE RISK OF
DEBRIS FLOWS FOR THE EL DORADO AND APPLE BURN SCARS. [AVI2]

Showers should taper off on Friday, but there's potential for wrap-around moisture to enhance snowfall totals in the mountains and generate additional showers for the high desert before the system completely exits the region Friday night. 

SHOWERS SHOULD TAPER OFF ON FRIDAY, BUT THERE`S POTENTIAL FOR
WRAP-AROUND MOISTURE TO ENHANCE SNOWFALL TOTALS IN THE MOUNTAINS
AND GENERATE ADDITIONAL SHOWERS FOR THE HIGH DESERT BEFORE THE
SYSTEM COMPLETELY EXITS THE REGION FRIDAY NIGHT. [AVI2]

SGX [San Diego/WFO CA] Watches/Warnings/Advisories

  • California: Winter Storm Warning from 10pm Tuesday to 10pm PST Thursday for Riverside County Mountains-San Bernardino County Mountains-San Diego County Mountains. 
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...WINTER STORM WARNING FROM 10 PM TUESDAY TO 10 PM PST THURSDAY
FOR RIVERSIDE COUNTY MOUNTAINS-SAN BERNARDINO COUNTY
MOUNTAINS-SAN DIEGO COUNTY MOUNTAINS. [WARN]
  • Wind Advisory until 4am PST Friday for San Gorgonio Pass near banning. 
     WIND ADVISORY UNTIL 4 AM PST FRIDAY FOR SAN GORGONIO PASS NEAR
BANNING. [WRN2]
  • Pacific Ocean: Small Craft Advisory until 9pm PST Tuesday for waters from San Mateo point to the Mexican border and out to 60 nm [69 miles]
PZ...SMALL CRAFT ADVISORY UNTIL 9 PM PST TUESDAY FOR WATERS FROM
SAN MATEO POINT TO THE MEXICAN BORDER AND OUT TO 60 NM. [WRN2]

Synopsis/Public Discussion/Hydrology: Rodriguez; Aviation/Marine/Beaches: Moede 

SYNOPSIS/PUBLIC DISCUSSION/HYDROLOGY...RODRIGUEZ
AVIATION/MARINE/BEACHES...MOEDE [CRED]

Point Forecast

Poway CA

Overnight Mostly cloudy, with a low around 46°. Calm wind.
Tuesday Mostly cloudy, with a high near 57°. West wind 5 to 15 mph, with gusts as high as 25 mph.
Tuesday Night A chance of rain. Mostly cloudy, with a low around 45°. West wind around 5 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.
Wednesday Rain, with thunderstorms also possible after 10am. Some of the storms could produce heavy rainfall. High near 52°. SW wind 10 to 15 mph, with gusts as high as 25 mph. Chance of precipitation is 80%. New rainfall amounts between a half and three quarters of an inch possible.
Wednesday Night Showers likely and possibly a thunderstorm. Mostly cloudy, with a low around 44°. SW wind around 5 mph becoming calm after midnight. Chance of precipitation is 60%. New rainfall amounts between a quarter and half of an inch possible.
Thursday Showers likely. Mostly cloudy, with a high near 51°. Chance of precipitation is 60%.
Thursday Night A chance of showers, mainly before 4am. Partly cloudy, with a low around 41°. Chance of precipitation is 50%.
Friday A chance of showers, mainly after 10am. Mostly sunny, with a high near 56°.
Friday Night Mostly clear, with a low around 41°.
Saturday Sunny, with a high near 64°.
Saturday Night Mostly clear, with a low around 45°.
Sunday Mostly sunny, with a high near 67°.
Sunday Night Partly cloudy, with a low around 47°.
Monday Mostly sunny, with a high near 66°.
Overnight
Mostly cloudy, with a low around 46. Calm wind.
Tuesday
Mostly cloudy, with a high near 57. West wind 5 to 15 mph, with gusts as high as 25 mph.
Tuesday Night
A chance of rain. Mostly cloudy, with a low around 45. West wind around 5 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.
Wednesday
Rain, with thunderstorms also possible after 10am. Some of the storms could produce heavy rainfall. High near 52. Southwest wind 10 to 15 mph, with gusts as high as 25 mph. Chance of precipitation is 80%. New rainfall amounts between a half and three quarters of an inch possible.
Wednesday Night
Showers likely and possibly a thunderstorm. Mostly cloudy, with a low around 44. Southwest wind around 5 mph becoming calm after midnight. Chance of precipitation is 60%. New rainfall amounts between a quarter and half of an inch possible.
Thursday
Showers likely. Mostly cloudy, with a high near 51. Chance of precipitation is 60%.
Thursday Night
A chance of showers, mainly before 4am. Partly cloudy, with a low around 41. Chance of precipitation is 50%.
Friday
A chance of showers, mainly after 10am. Mostly sunny, with a high near 56.
Friday Night
Mostly clear, with a low around 41.
Saturday
Sunny, with a high near 64.
Saturday Night
Mostly clear, with a low around 45.
Sunday
Mostly sunny, with a high near 67.
Sunday Night
Partly cloudy, with a low around 47.
Monday
Mostly sunny, with a high near 66.

This page is generated dynamically from the National Weather Service's NWS point forecast and Area Forecast Discussion, reformatted for readability. NWS glossary; about point forecasts. For more information, visit the Lobitos Weather Project home page. Comments and corrections are welcome: