819
FXUS21 KWNC 232116
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST JANUARY 23 2024
SYNOPSIS: A VERY STORMY PERIOD IS EXPECTED FOR PORTIONS OF THE WESTERN
CONTIGUOUS U.S., PARTICULARLY ACROSS CALIFORNIA AND ARIZONA. HEAVY
PRECIPITATION AND HIGHER-ELEVATION HEAVY SNOWFALL ARE STRONGLY INDICATED IN
MODEL GUIDANCE, ALONG WITH HIGH WINDS NEAR THE WEST COAST. AS THE SYSTEM
SPREADS EASTWARD, THERE IS AT LEAST A SLIGHT RISK OF HEAVY PRECIPITATION, HIGH
WINDS, AND HEAVY HIGH-ELEVATIONS SNOWFALL FOR SOME AREAS FROM THE ROCKIES AND
SOUTHERN HIGH PLAINS TO THE PACIFIC OCEAN THROUGHOUT WEEK-2. MUCH BELOW NORMAL
TEMPERATURES ARE POSSIBLE OVER PORTIONS OF MAINLAND ALASKA EARLY IN THE PERIOD,
WITH HIGH WINDS POSSIBLE DURING THIS PERIOD IN FAR SOUTHWESTERN PARTS OF THE
STATE AND MOST OF THE ALEUTIANS. DURING THE LAST HALF OF WEEK-2, AS THE STRONG
DISTURBANCE IN THE WEST BEGINS TO MOVE EASTWARD, HEAVY PRECIPITATION IS
POSSIBLE IN PORTIONS OF THE SOUTHEASTERN LOWER 48.
HAZARDS
HIGH RISK OF HEAVY PRECIPITATION FOR MUCH OF CALIFORNIA AND ARIZONA, AND SOME
ADJACENT LOCATIONS OF NEVADA AND NEW MEXICO, WED-SUN, JAN 31 - FEB 4.
HIGH RISK OF HEAVY SNOW FOR MOST OF THE SIERRA NEVADA, SOUTHERN CASCADES, AND
NORTHERN COASTAL RANGES OF CALIFORNIA, WED-SUN, JAN 31 - FEB 4.
MODERATE RISK OF HIGH WINDS ALONG THE WEST COAST AND IN THE GREAT BASIN,
WED-SUN, JAN 31 - FEB 4.
MODERATE RISK OF HEAVY PRECIPITATION FOR CALIFORNIA, ARIZONA, MOST OF THE GREAT
BASIN, AND SOME ADJACENT LOCATIONS IN THE FOUR CORNERS REGION AND SOUTHERN
OREGON, WED-MON, JAN 31 - FEB 5.
MODERATE RISK OF HEAVY SNOW FOR THE SIERRA NEVADAS, THE SOUTHERN CASCADES, THE
NORTHERN COASTAL RANGES OF CALIFORNIA, THE CENTRAL AND SOUTHERN GREAT BASIN,
AND SOME HIGHER ELEVATIONS IN UTAH, ARIZONA, AND WEST-CENTRAL NEW MEXICO,
WED-MON, JAN 31 - FEB 5.
SLIGHT RISK OF HEAVY PRECIPITATION FOR MUCH OF THE CONUS FROM THE ROCKIES
WESTWARD AND PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, WED-TUE, JAN 31 - FEB
6.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE SOUTHERN PLAINS AND MUCH OF THE
CONUS FROM THE ROCKIES WESTWARD AND PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, WED-TUE, JAN 31 - FEB 6.
SLIGHT RISK OF PERIODS OF HEAVY SNOW FOR MANY OF THE HIGHER ELEVATIONS ACROSS
THE INTERIOR WEST, WED-TUE, JAN 31 - FEB 6.
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR SOUTHWESTERN MAINLAND
ALASKA, WED-THU, JAN 31 - FEB 1.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR MUCH OF CENTRAL AND
SOUTHWESTERN MAINLAND ALASKA, WED-FRI, JAN 31 - FEB 2.
SLIGHT RISK OF HIGH WINDS FOR KODIAK ISLAND, SOUTHWESTERN MAINLAND ALASKA, AND
PARTS OF THE ALEUTIANS, WED-FRI, JAN 31 - FEB 2.
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEASTERN
CONUS, SAT-TUE, FEB 3-6.
POSSIBLE FLOODING ACROSS MUCH OF ARIZONA AND ADJACENT NEW MEXICO.
POSSIBLE FLOODING FOR WESTERN CALIFORNIA, AND ADJACENT OREGON.
DETAILED SUMMARY
FOR FRIDAY JANUARY 26 - TUESDAY JANUARY 30:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY JANUARY 31 - TUESDAY FEBRUARY 06: MULTIPLE MODELS STRONGLY FAVOR
A STORMY PERIOD FOR PORTIONS OF THE CONUS FROM THE ROCKIES WESTWARD, WITH THE
GREATEST ODDS FOR HEAVY PRECIPITATION AND HIGH-ELEVATION SNOW ACROSS CALIFORNIA
AND ARIZONA. HIGH WINDS ARE ALSO SIGNIFICANTLY INDICATED WITH A STRONG SURFACE
PRESSURE GRADIENT FAVORED ALONG MOST OF THE WEST COAST DURING THE FIRST HALF OF
WEEK-2.
THERE ARE MODEL DIFFERENCES IN THE DETAILS OF TIMING AND EVOLUTION, BUT
AGREEMENT IS A BIT BETTER THAN YESTERDAY WITH THE GEFS LOOKING MORE LIKE
YESTERDAY’S EUROPEAN AND CANADIAN ENSEMBLE MEANS. ALL MODELS SHOW A STRONG
MID-LEVEL TROUGH TRACKING FROM THE CENTRAL NORTH PACIFIC TOWARD THE WEST COAST
DURING WEEK-2, CREATING STRONG LOW-LEVEL FLOW FROM THE PACIFIC OCEAN INTO THE
WESTERN CONUS. THERE IS AN ELEVATED POTENTIAL FOR AN ATMOSPHERIC RIVER EVENT AS
THIS SET-UP EVOLVES, ESPECIALLY ACROSS CALIFORNIA. THE PROBABILISTIC EXTREMES
TOOL (PET) DERIVED FROM THE EUROPEAN ENSEMBLES HAS THE MOST ROBUST WET SIGNAL,
WITH ODDS EXCEEDING 60 PERCENT FOR PRECIPITATION TOTALS IN THE HIGHEST 15TH
PERCENTILE CLIMATOLOGICALLY THROUGHOUT CALIFORNIA, MUCH OF NEVADA, AND THE
WESTERN HALF OF THE FOUR CORNERS REGION DURING THE FIRST THREE DAYS OF THE
PERIOD (JAN 31 - FEB 2). FROM COASTAL SOUTHWESTERN CALIFORNIA INTO NORTHWESTERN
ARIZONA, THE EUROPEAN-DERIVED PET SHOWS MORE THAN AN 80 PERCENT CHANCE FOR
PRECIPITATION TOTALS IN THE TOP 15TH PERCENTILE.THE PET BASED ON THE CANADIAN
ENSEMBLES IS ALSO ROBUST, SHOWING ODDS OF 60 TO 80 PERCENT FOR THIS
PRECIPITATION THRESHOLD OVER THE SOUTHERN HALF OF CALIFORNIA, THE CENTRAL AND
SOUTHERN GREAT BASIN, AND THE WESTERN HALF OF ARIZONA. THE GEFS PET IS SLIGHTLY
LESS EXTREME, BUT ITS SIGNAL HAS INCREASED FROM YESTERDAY. THE EUROPEAN-BASED
PET SHOWS A 20 TO 40 PERCENT CHANCE THAT PRECIPITATION WILL EQUAL OR EXCEED 3
INCHES THROUGH FEB 2 OVER MANY COASTAL AND HIGHER-ELEVATION LOCATIONS IN
CALIFORNIA, INCLUDING SOME SITES OVER AND NEAR LOS ANGELES, COMING INTO
AGREEMENT WITH YESTERDAY’S CANADIAN-BASED PETS. IN ADDITION, THERE IS GOOD
CONSENSUS ACROSS MULTIPLE MODELS INDICATING A SOUTHWESTWARD EXTENSION OF THE
AREA MOST AT RISK OF HEAVY PRECIPITATION, THUS THE HIGH RISK FOR HEAVY
PRECIPITATION IS EXTENDED SOUTHWARD TO THE MEXICAN BORDER AND EASTWARD ACROSS
ARIZONA. THE MODERATE RISK AREA HAS ALSO BEEN EXPANDED IN ACCORDANCE WITH THE
ENSEMBLE MEANS AND PETS, EXTENDING THROUGH MUCH OF THE SOUTHWEST, SOUTHERN AND
CENTRAL UTAH, AND PORTIONS OF THE GREAT BASIN IN ADDITION TO CALIFORNIA.
FURTHERMORE, EXPERIMENTAL TOOLS AND MOST OF THE MODELS SHOW A HIGH LIKELIHOOD
FOR ENHANCED INTEGRATED VAPOR TRANSPORT (IVT) VALUES CONDUCIVE TO A STRONG
ATMOSPHERIC RIVER EVENT. THE TIMING AND EXACT LOCATION OF THE MOST
SEVERELY-AFFECTED AREAS ARE STILL SOMEWHAT UNCERTAIN, BUT PORTIONS OF CENTRAL
AND SOUTHERN CALIFORNIA ARE EXPECTED TO BE AT GREATEST RISK.
HEAVY PRECIPITATION ACROSS THESE REGIONS IN THE WEST MEANS HEAVY
HIGHER-ELEVATIONS SNOWFALL IS ALSO FAVORED, PARTICULARLY IN THE SIERRA NEVADA,
SOUTHERN CASCADES, AND NORTHERN COASTAL RANGES OF CALIFORNIA DURING THE FIRST
3-5 DAYS OF WEEK-2. A MODERATE RISK FOR HEAVY SNOWFALL HAS BEEN EXPANDED
EASTWARD IN AGREEMENT WITH THE INCREASED PRECIPITATION THREATS AND ELEVATED
CHANCES FOR HIGH SNOW WATER CONTENT IN THE GEFS PET, NOW REACHING INTO THE
GREAT BASIN AND THE HIGHER ELEVATIONS OF ARIZONA, SOUTHERN UTAH, AND PARTS OF
NEW MEXICO.
MEANWHILE, HIGH LIKELIHOODS FOR STRONG WINDS ARE ALSO INDICATED PARTICULARLY IN
THE EUROPEAN AND CANADIAN ENSEMBLES, AND THEIR DERIVED PETS. THE GREATEST ODDS
FOR HIGH WINDS EXTEND FROM SOUTHERN CALIFORNIA TO THE PACIFIC NORTHWEST, WHICH
IS CONSISTENT WITH THE AREAS WHERE THE ENSEMBLE MEANS FORECAST THE STRONGEST
PRESSURE GRADIENT. ACROSS SOUTHERN CALIFORNIA, THE SLIGHT SOUTHWARD SHIFT IN
THE OVERALL FORECAST PATTERN RELATIVE TO YESTERDAY HAS BROUGHT TODAY’S PET
TOOLS IN LINE WITH YESTERDAY’S THINKING, AND IN FACT BRINGS THE MODERATE HIGH
WIND RISK EVEN FARTHER SOUTH TO THE MEXICAN BORDER. IN ADDITION, THE PETS HAVE
EXPANDED ELEVATED RISKS FOR HIGH WINDS FARTHER EAST THAN YESTERDAY, INTO THE
CENTRAL GREAT BASIN, RESULTING IN THE EXPANSION OF THE MODERATE RISK AREA FOR
HIGH WINDS.
THE AMPLIFIED MID-LEVEL TROUGH ACROSS THE WEST IS PREDICTED TO EXTEND EASTWARD,
RESULTING IN A BROAD AREA OF CYCLONIC MID-LEVEL CIRCULATION ACROSS THE WEST,
WITH A FAIRLY STRONG MID-LEVEL JET PUSHING EASTWARD TOWARD THE GULF COAST
REGION. THE GUIDANCE IS NOT AS CONSISTENT ACROSS THE INTERIOR WEST AS IT IS
FURTHER WEST; HOWEVER, THE PREDICTED PATTERN WOULD SLIGHTLY ELEVATE THE RISKS
FOR HAZARDOUS WEATHER ACROSS PARTS OF THE INTERIOR WEST AND CENTRAL AND
SOUTHERN PLAINS THROUGHOUT WEEK-2, ESPECIALLY THE LATTER HALF OF THE PERIOD.
CONSISTENT WITH THESE INDICATORS, SLIGHT RISKS FOR PERIODS OF HEAVY
PRECIPITATION AND HIGH WINDS ARE POSTED FOR A LARGE PART OF THE WESTERN HALF OF
THE CONUS, WITH A SLIGHT RISK OF HEAVY SNOW AT HIGHER ELEVATIONS. THIS BROAD
AREA IS NOT EXPECTED TO BE AFFECTED BY HAZARDOUS CONDITIONS THROUGHOUT WEEK-2,
AND MAY BE RELATIVELY LOCALIZED.
THERE IS GOOD MODEL AGREEMENT AMONG ENSEMBLE MEANS SHOWING THE WESTERN CONUS
MID-LEVEL TROUGH EXTENDING EASTWARD LATE WEEK-2, REACHING INTO THE SOUTHEAST
TOWARD THE END OF THE PERIOD. THIS WILL RESULT IN A LONG STRETCH OF SUBNORMAL
500-HPA HEIGHTS EXTENDING FROM THE NORTH PACIFIC OCEAN INTO THE SOUTH-CENTRAL
CONUS, WITH A STRONG MID-LEVEL JET JUST TO THE SOUTH. THIS PUTS THE SOUTHEAST
IN AN AREA OF MID-LEVEL CYCLONICALLY-CURVED FLOW JUST TO THE EAST OF SURFACE
LOW PRESSURE, WHICH WOULD TAP INTO GULF OF MEXICO MOISTURE. THIS FLOW SUPPORTS
A SLIGHT RISK OF HEAVY PRECIPITATION ACROSS THE SOUTHEASTERN CONUS DURING THE
LAST HALF OF WEEK-2 (FEB 3-6). THE PET TOOLS ARE NOT ROBUST WITH THIS SIGNAL,
BUT CONSISTENCY HAS INCREASED RELATIVE TO YESTERDAY.
WEEK-2 IS FAVORED TO START WITH A STRONG MID-LEVEL TROUGH OVER ALASKA,
ACCOMPANIED BY MUCH BELOW NORMAL TEMPERATURES EARLY IN THE PERIOD. GUIDANCE IS
MORE CONSISTENT TODAY IN FOCUSING THE GREATEST RISK FOR MUCH BELOW NORMAL
TEMPERATURES ACROSS THE SOUTHWESTERN QUARTER OF THE STATE, THUS A MODERATE RISK
FOR MUCH BELOW NORMAL TEMPERATURES IS POSTED FOR THIS REGION EARLY IN THE
PERIOD (JAN 31 - FEB 1). PET TOOLS FROM GEFS, CANADIAN ENSEMBLE, AND EUROPEAN
ENSEMBLE ALL SHOW ODDS OF AT LEAST 40 PERCENT OF TEMPERATURES FALLING TO THE
COLDEST 15 PERCENT OF THE CLIMATOLOGICAL DISTRIBUTION ON THOSE DAYS. A SLIGHT
RISK COVERS A LARGER AREA STRETCHING INTO THE VALLEYS TO SOUTH OF THE BROOKS
RANGE, WHERE PETS SHOW A 30 TO 50 PERCENT CHANCE FOR TEMPERATURES DROPPING
BELOW -40 DEG F FOR THE FIRST FEW DAYS OF WEEK-2. TEMPERATURES ARE EXPECTED TO
REBOUND AS THE TROUGH WEAKENS TOWARD MID-WEEK, DECREASING THE THREAT FOR
HAZARDOUSLY COLD CONDITIONS. MEANWHILE, A PRESSURE GRADIENT BETWEEN LOW SURFACE
PRESSURE IN THE GULF OF ALASKA AND THE COLD SURFACE HIGH PRESSURE SYSTEM
FARTHER NORTH OVER THE MAINLAND IS EXPECTED TO LEAD TO HIGH WINDS ACROSS VALLEY
GAPS ON KODIAK ISLAND, THE SOUTHWESTERN MAINLAND, AND THE ALEUTIANS NORTHEAST
OF COLD BAY, SO A SLIGHT RISK OF HIGH WINDS HAS BEEN POSTED FOR THESE REGIONS.
THE THREAT SHOULD EASE AS THE MID-LEVEL TROUGH WEAKENS AROUND THE MIDDLE OF
WEEK-2.
FORECASTER: RICH TINKER
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