848
FXUS01 KWBC 220801
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EST FRI DEC 22 2023
VALID 12Z FRI DEC 22 2023 - 12Z SUN DEC 24 2023
...HEAVY RAINFALL AND FLASH FLASH FLOODING WILL CONTINUE TO IMPACT
AREAS OF SOUTHERN CALIFORNIA TODAY, WITH THE THREAT GRADUALLY
EXPANDING INTO THE SOUTHWEST THROUGH TONIGHT...
...NEXT ROUND OF UNSETTLED WEATHER WILL REACH THE PACIFIC
NORTHWEST TODAY THEN QUICKLY MOVE THROUGH THE INTERMOUNTAIN WEST
GOING INTO SATURDAY...
...SNOW IS FORECAST TO OVERSPREAD THE CENTRAL ROCKIES SATURDAY
NIGHT BEFORE EXPANDING INTO THE NORTHERN PLAINS BY THE MORNING OF
CHRISTMAS EVE...
...UNUSUALLY MILD TEMPERATURES WILL PERSIST ACROSS THE PLAINS AND
MIDWEST THROUGH THE EARLY PART OF THE CHRISTMAS HOLIDAY WEEKEND...
A RELATIVELY SLOW-MOVING LOW PRESSURE SYSTEM OFF THE SOUTHERN
CALIFORNIA COAST WILL BEGIN TO GRADUALLY ACCELERATE OFF TO THE
EAST AND MOVE ONSHORE INTO THE SOUTHWEST U.S. BY TONIGHT. DEEP
SOUTHERLY FLOW AHEAD OF THE LOW CENTER WILL CONTINUE TO FEED
MOISTURE-LADEN AIR FROM THE SUBTROPICAL PACIFIC OCEAN TOWARD
SOUTHERN CALIFORNIA TODAY. HEAVY RAINFALL WILL MOST LIKELY BE
FOUND ONCE AGAIN ALONG THE WIND-FACING COASTAL RANGES OF SOUTHERN
CALIFORNIA WHERE PROLIFIC RAINFALL AMOUNTS HAD ALREADY BEEN
REPORTED IN THE PAST 24 HOURS, WITH ADDITIONAL SIGNIFICANT FLASH
FLOODING EXPECTED. URBAN FLASH FLOODING WILL ALSO BE POSSIBLE
INCLUDING AREAS OF THE LOS ANGELES BASIN EARLY THIS MORNING.
DEBRIS FLOWS AND MUDSLIDES WILL REMAIN LIKELY NEAR BURN SCAR AREAS
AND AREAS OF STEEP TERRAIN. THE WEATHER PREDICTION CENTER HAS
MAINTAINED A MODERATE RISK OF EXCESSIVE RAINFALL FOR THESE AREAS
EARLY THIS MORNING.
AS THE LOW PRESSURE SYSTEM MOVES ONSHORE LATER TODAY, THE HEAVY TO
EXCESSIVE RAINFALL THREAT WILL BEGIN TO SPREAD EAST INTO AREAS OF
CENTRAL AND SOUTHERN ARIZONA AS WELL BY FRIDAY NIGHT AND INTO
EARLY SATURDAY. A SLIGHT RISK OF EXCESSIVE RAINFALL IS 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 TODAY AND INTO SATURDAY, BRINGING
THE NEXT ROUND OF 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.
BY SATURDAY NIGHT INTO SUNDAY MORNING, THE MOISTURE ASSOCIATED
WITH THE COLD FRONT IS FORECAST TO HEAD TOWARD THE CENTRAL ROCKIES
AND WILL BEGIN TO INTERACT WITH THE MOISTURE LIFTING NORTHEASTWARD
FROM THE SOUTHWESTERN U.S. SYSTEM. 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. A LOW PRESSURE
SYSTEM IS FORECAST TO CONSOLIDATE AND STRENGTHEN OVER THE CENTRAL
HIGH PLAINS EARLY ON SUNDAY WITH SNOW EXPANDING NORTHEASTWARD INTO
THE NORTHERN PLAINS UNDER STRONG AND GUSTY NORTHERLY WINDS.
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.
KONG/ORRISON
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