453
FXUS21 KWNC 242016
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST JANUARY 24 2024
SYNOPSIS: A VERY STORMY PERIOD IS EXPECTED FOR PORTIONS OF THE WESTERN
CONTIGUOUS U.S., PARTICULARLY ACROSS CALIFORNIA AND ARIZONA. HEAVY
PRECIPITATION, HIGHER-ELEVATION HEAVY SNOWFALL, AND ELEVATED FLOODING POTENTIAL
ARE STRONGLY INDICATED IN MODEL GUIDANCE, ALONG WITH HIGH WINDS NEAR THE WEST
COAST AND IN THE GREAT BASIN. AS THE SYSTEM SPREADS EASTWARD, THERE IS AT LEAST
A SLIGHT RISK OF HEAVY PRECIPITATION, HIGH WINDS, AND HEAVY HIGH-ELEVATIONS
SNOWFALL FOR MANY AREAS FROM THE HIGH PLAINS TO THE PACIFIC OCEAN THROUGHOUT
WEEK-2. THIS SYSTEM EXPANDS EASTWARD LATER IN THE PERIOD, TRIGGERING A MODERATE
RISK OF HEAVY RAIN IN THE LOWER MISSISSIPPI VALLEY. SOILS ARE ALREADY SATURATED
THERE, INCREASING THE RISK OF FLOODING. MUCH BELOW NORMAL TEMPERATURES ARE
POSSIBLE OVER PORTIONS OF MAINLAND ALASKA EARLY IN THE PERIOD, WITH HIGH WINDS
POSSIBLE AT THE SAME TIME IN FAR SOUTHWESTERN PARTS OF THE STATE AND MUCH OF
THE ALEUTIANS.
HAZARDS
HIGH RISK OF HEAVY PRECIPITATION FOR MUCH OF CALIFORNIA AND ARIZONA, AND SOME
ADJACENT LOCATIONS OF NEVADA AND NEW MEXICO, THU-SUN, FEB 1-4.
HIGH RISK OF HEAVY SNOW FOR MOST OF THE SIERRA NEVADA, SOUTHERN CASCADES, AND
NORTHERN COASTAL RANGES OF CALIFORNIA, THU-SUN, FEB 1-4.
MODERATE RISK OF HIGH WINDS ALONG THE WEST COAST, IN THE GREAT BASIN, AND
ACROSS THE SOUTHERN ROCKIES AND HIGH PLAINS, THU-SUN, FEB 1-4.
MODERATE RISK OF HEAVY PRECIPITATION FOR CALIFORNIA, ARIZONA, MOST OF THE GREAT
BASIN, AND PORTIONS OF THE FOUR CORNERS REGION AND SOUTHERN OREGON, THU-MON,
FEB 1-5.
MODERATE RISK OF HEAVY PRECIPITATION FOR THE LOWER MISSISSIPPI VALLEY AND SOME
ADJACENT LOCALES, SAT-MON, FEB 3-5.
MODERATE RISK OF HEAVY SNOW FOR THE SIERRA NEVADA, 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,
THU-MON, FEB 1-5.
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR MUCH OF THE CONUS FROM THE
ROCKIES WESTWARD, THE SOUTHERN PLAINS, THE LOWER MISSISSIPPI VALLEY, AND
PORTIONS OF THE SOUTHEAST, THU-WED, FEB 1-7.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WESTERN HALF OF THE CONUS, THU-WED,
FEB 1-7.
SLIGHT RISK OF PERIODS OF HEAVY SNOW FOR MANY OF THE HIGHER ELEVATIONS ACROSS
THE INTERIOR WEST AND THE CENTRAL HIGH PLAINS, THU-WED, FEB 1-7.
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR SOUTHWESTERN MAINLAND
ALASKA, THU, FEB 1.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR MUCH OF CENTRAL AND
SOUTHWESTERN MAINLAND ALASKA, THU-FRI, FEB 1-2.
SLIGHT RISK OF HIGH WINDS FOR KODIAK ISLAND, SOUTHWESTERN MAINLAND ALASKA, AND
PARTS OF THE ALEUTIANS, THU-FRI, FEB 1-2.
POSSIBLE FLOODING FOR MUCH OF ARIZONA AND ADJACENT NEW MEXICO.
POSSIBLE FLOODING FOR WESTERN CALIFORNIA, AND ADJACENT OREGON.
POSSIBLE FLOODING FOR THE LOWER MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR SATURDAY JANUARY 27 - WEDNESDAY JANUARY 31:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY FEBRUARY 01 - WEDNESDAY FEBRUARY 07: MULTIPLE MODELS STRONGLY
FAVOR A STORMY PERIOD FOR PORTIONS OF THE SOUTHWESTERN QUARTER OF THE CONUS,
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 THE WEST COAST DURING THE FIRST
HALF OF WEEK-2. TOOL CONSENSUS ON THE PLACEMENT OF METEOROLOGICAL FEATURES AND
RESULTANT HAZARDS HAS AGAIN DRIFTED TO THE SOUTH-SOUTHEAST FOR THE SECOND DAY
IN A ROW.
MODEL DIFFERENCES IN THE DETAILS OF TIMING AND EVOLUTION REMAIN, BUT THERE IS
BROAD AGREEMENT AMONG ALL MODELS SHOWING A STRONG MID-LEVEL TROUGH TRACKING
INTO THE FAR WEST, CREATING STRONG LOW-LEVEL FLOW FROM THE PACIFIC OCEAN INTO
THE WESTERN CONUS. THE GEFS-BASED PROBABILISTIC EXTREMES TOOL (PET) REMAINS
LESS ROBUST THAN THE PETS FROM THE CANADIAN AND EUROPEAN ENSEMBLES, BUT ALL
SHOW SIGNIFICANTLY ELEVATED CHANCES FOR EXCESSIVE PRECIPITATION UNTIL AT LEAST
THE MIDDLE OF WEEK-2. THERE IS ALSO AN ELEVATED POTENTIAL FOR AN ATMOSPHERIC
RIVER EVENT AS THIS SET-UP EVOLVES, ESPECIALLY ACROSS CENTRAL AND SOUTHERN
CALIFORNIA. THE PETS DERIVED FROM THE EUROPEAN AND CANADIAN ENSEMBLES SHOW
EXTREMELY ROBUST WET SIGNALS DURING THE FIRST 3 DAYS OF THE PERIOD (FEB 1-3),
WITH BOTH TOOLS BRINGING ODDS OF OVER 80 PERCENT FOR PRECIPITATION TOTALS IN
THE HIGHEST 15TH PERCENTILE CLIMATOLOGICALLY TO SOUTHEASTERN CALIFORNIA,
SOUTHERNMOST NEVADA, AND WESTERN ARIZONA, WITH THE EUROPEAN-BASED PET BRINGING
SIMILAR LIKELIHOODS FARTHER EAST TO NEAR NEW MEXICO. ODDS FOR EXTREME
PRECIPITATION DECLINE IN THE PETS AS WEEK-2 PROGRESSES, AND NOWHERE DOES THE
GEFS-BSED PET DOES NOT SHOW ODDS FOR EXCESSIVE PRECIPITATION REACHING 40
PERCENT FEB 5-7, BUT IN THE EUROPEAN- AND CANADIAN-DERIVED PETS, SOME AREAS IN
CENTRAL CALIFORNIA AND THE SOUTHWEST MAINTAIN RELATIVELY HIGH CHANCES FOR
EXCESSIVE PRECIPITATION UNTIL NEAR THE END OF WEEK-2. DURING FEB 1-3, ODDS FOR
2 OR MORE INCHES OF PRECIPITATION EXCEED 40 PERCENT BETWEEN LOS ANGELES AND SAN
DIEGO IN THE EUROPEAN- AND CANADIAN-DERIVED PETS. GIVEN THESE FACTORS, THE
MODERATE AND HIGH RISK AREAS FOR EXCESSIVE PRECIPITATION HAVE BEEN TRIMMED BACK
ON THE NORTH SIDE - IN NORTHERN CALIFORNIA AND ADJACENT OREGON - BUT EXTENDED
SLIGHTLY FARTHER EAST ALONG THE SOUTHERN TIER OF THE COUNTRY. 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
3-4 DAYS OF WEEK-2, UNCHANGED FROM YESTERDAY. THE AREA AT MODERATE RISK FOR
HEAVY SNOWFALL IS ALSO UNCHANGED FROM YESTERDAY, REACHING INTO THE GREAT BASIN
AND THE HIGHER ELEVATIONS OF ARIZONA, SOUTHERN UTAH, AND PARTS OF NEW MEXICO,
CONSISTENT WITH SIGNALS FROM THE GEFS SNOW WATER EQUIVALENT (SWE) PET. WITH THE
PREPONDERANCE OF GUIDANCE FOCUSING EXTREME CONDITIONS SLIGHTLY FARTHER
SOUTH-SOUTHEAST THAN YESTERDAY, SLIGHT RISKS FOR EXCESSIVE PRECIPITATION AND
HEAVY SNOW HAVE BEEN REMOVED FROM MUCH OF THE PACIFIC NORTHWEST.
MEANWHILE, HIGH LIKELIHOODS FOR STRONG WINDS ARE INDICATED, PARTICULARLY IN THE
EUROPEAN AND CANADIAN ENSEMBLES, AND THEIR DERIVED PETS. THE GREATEST ODDS FOR
HIGH WINDS HAVE EXPANDED SOUTHEASTWARD, IN ACCORD WITH THE SLIGHT SHIFT IN THE
OVERALL PATTERN. A MODERATE RISK FOR HIGH WINDS EARLY WEEK-2 EXTENDS ALONG THE
LENGTH OF THE WEST COAST, ACROSS THE GREAT BASIN, AND IN THE SOUTHWESTERN HALF
OF THE FOUR CORNERS REGION.
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 EXTREMES 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 LOWER
MISSISSIPPI VALLEY 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 RISK OF HEAVY PRECIPITATION ACROSS THE SOUTHEASTERN CONUS
DURING MOST OF THE LAST HALF OF WEEK-2 (FEB 3-6). RAW PRECIPITATION OUTPUT FROM
THE ENSEMBLE MEANS AND ANTECEDENT CONDITIONS FEATURING SATURATED SOILS AND
ELEVATED RIVER LEVELS SUPPORT A MODERATE RISK OF HEAVY PRECIPITATION IN THE
LOWER MISSISSIPPI VALLEY FEB 3-5.
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
FOCUSES 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 THERE FOR FEB 1. PET TOOLS FROM GEFS, CANADIAN ENSEMBLE,
AND EUROPEAN ENSEMBLE ALL SHOW ODDS OF AT LEAST 40 PERCENT OF TEMPERATURES
FALLING INTO THE COLDEST 15 PERCENT OF THE CLIMATOLOGICAL DISTRIBUTION THAT
DAY. A SLIGHT RISK COVERS A LARGER AREA STRETCHING INTO THE VALLEYS TO SOUTH OF
THE CENTRAL AND WESTERN PORTIONS OF THE BROOKS RANGE, WHERE PETS SHOW A 30 TO
50 PERCENT CHANCE FOR TEMPERATURES DROPPING BELOW -40 DEG F FOR THE FIRST TWO
DAYS OF WEEK-2. TEMPERATURES ARE EXPECTED TO REBOUND AS THE TROUGH QUICKLY
WEAKENS TOWARD MID-WEEK, ENDING 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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