200
FXUS01 KWBC 211911
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EST THU DEC 21 2023
VALID 00Z FRI DEC 22 2023 - 00Z SUN DEC 24 2023
...HEAVY RAINFALL AND FLASH FLASH FLOODING WILL CONTINUE TO IMPACT
AREAS OF SOUTHERN CALIFORNIA THROUGH FRIDAY, WITH THE THREAT
GRADUALLY EXPANDING INTO THE SOUTHWEST...
...UNSETTLED WEATHER WILL ADVANCE ACROSS THE PACIFIC NORTHWEST AND
THE INTERMOUNTAIN WEST GOING THROUGH SATURDAY WITH LOWER-ELEVATION
RAINS AND HIGHER-ELEVATION SNOWFALL...
...UNUSUALLY MILD TEMPERATURES ACROSS THE PLAINS AND MIDWEST WILL
PERSIST INTO THE EARLY PART OF THE CHRISTMAS HOLIDAY WEEKEND...
AN UPPER-LEVEL LOW OFFSHORE OF SOUTHERN CALIFORNIA WILL GRADUALLY
BEGIN TO ACCELERATE OFF TO THE EAST TONIGHT AND FRIDAY, AND WILL
MOVE INTO THE SOUTHWEST U.S. BY FRIDAY NIGHT. AREAS OF HEAVY
RAINFALL ASSOCIATED WITH THE STORM SYSTEM WILL CONTINUE ACROSS
ESPECIALLY THE COASTAL RANGES OF SOUTHERN CALIFORNIA THIS EVENING
AND INTO THE OVERNIGHT PERIOD, WITH LOCALLY SIGNIFICANT FLASH
FLOODING POSSIBLE. URBAN FLASH FLOODING WILL ALSO BE POSSIBLE
INCLUDING AREAS OF THE LOS ANGELES BASIN. DEBRIS FLOWS AND
MUDSLIDES WILL BE POSSIBLE NEAR BURN SCAR AREAS AND AREAS OF STEEP
TERRAIN. LOCALLY SEVERAL INCHES OF ADDITIONAL RAIN IS POSSIBLE BY
FRIDAY MORNING, AND THE WEATHER PREDICTION CENTER HAS MAINTAINED A
MODERATE RISK OF EXCESSIVE RAINFALL FOR THESE AREAS.
ON FRIDAY, THE HEAVY TO EXCESSIVE RAINFALL THREAT WILL STILL
IMPACT SOME AREAS OF SOUTHERN CALIFORNIA, INCLUDING THE PENINSULAR
RANGE, BUT THE RAINS WILL ADVANCE EAST INTO AREAS OF CENTRAL AND
SOUTHERN ARIZONA AS WELL GOING THROUGH FRIDAY NIGHT AND EARLY
SATURDAY. THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL DEPICTED
ACROSS THESE AREAS WHERE THERE MAY BE SOME ISOLATED TO SCATTERED
AREAS OF FLASH FLOODING. SOME OF THE LOCAL SLOT CANYONS AND BURN
SCARS CLOSER TO AREAS OF TERRAIN, AND ALSO THE DRY WASHES/ARROYOS
OVER THE DESERTS, WILL BE VULNERABLE TO SEEING THESE RUNOFF
IMPACTS. HOWEVER, GENERALLY MUCH OF THE RAINFALL ACROSS THESE
AREAS SHOULD BE BENEFICIAL.
MEANWHILE, A COLD FRONT WILL ADVANCE INLAND ACROSS THE PACIFIC
NORTHWEST AND INTERMOUNTAIN WEST GOING THROUGH FRIDAY AND
SATURDAY, AND THIS WILL BRING LOW-ELEVATION RAINS AND
HIGH-ELEVATION SNOWFALL TO THE REGION. THE HEAVIEST SNOWFALL WILL
BE OVER THE WASHINGTON CASCADES, AND THEN DOWNSTREAM OVER THE
NORTHERN AND CENTRAL ROCKIES INCLUDING THE BITTERROOTS, TETONS,
AND COLORADO HIGH COUNTY. THE SAN JUAN MOUNTAINS OF SOUTHWEST
COLORADO WILL SEE IMPACTS RELATING TO THE STORM SYSTEM TRAVERSING
THE SOUTHWEST, AND MULTI-DAY SNOWFALL AMOUNTS OF 1 TO 2 FEET WILL
BE POSSIBLE HERE GOING THROUGH SATURDAY.
AREAS FARTHER EAST ACROSS THE CENTRAL AND EASTERN U.S. WILL BE
SEEING GENERALLY VERY MILD TEMPERATURES THROUGH THE REMAINDER OF
THE WEEK AND INTO THE START OF THE CHRISTMAS HOLIDAY WEEKEND, WITH
AREAS OF THE PLAINS AND MIDWEST IN PARTICULAR SEEING TEMPERATURES
THAT WILL BE AS MUCH AS 15 TO 25 DEGREES ABOVE NORMAL. THESE
RELATIVELY WARM TEMPERATURES WILL BE THE RESULT OF INCREASING
SOUTHERLY FLOW WITH TIME AND THE RETURN OF MOISTURE FROM THE GULF
OF MEXICO, AND SOME RECORD WARM OVERNIGHT LOW TEMPERATURES IN
PARTICULAR MAY BE SET. EXPECT THESE WARMER TEMPERATURES TO BEGIN
OVERSPREADING THE OHIO VALLEY AND MID-SOUTH, WITH AT LEAST ABOVE
NORMAL TEMPERATURES REACHING THE EAST COAST.
ORRISON
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