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FXUS21 KWNC 201931
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST FEBRUARY 20 2024
SYNOPSIS: THERE IS GENERALLY POOR AGREEMENT AMONG MODEL GUIDANCE TODAY, BUT
SLIGHTLY BETTER THAN PRIOR FORECASTS, ACROSS MUCH OF THE CONTIGUOUS UNITED
STATES (CONUS) DURING THE WEEK-2 PERIOD. DEPENDING ON ITS EVOLUTION, AN AREA OF
MID-LEVEL LOW PRESSURE IN THE GULF OF ALASKA COULD INTRODUCE A PERIOD OF HEAVY
PRECIPITATION, SNOW, AND HIGH WINDS TO PORTIONS OF THE NORTHWESTERN CONUS.
MEANWHILE, IN THE EASTERN CONUS AN AREA OF SURFACE LOW PRESSURE IS LIKELY TO
DEVELOP AND BRING A PERIOD OF HEAVY PRECIPITATION AND WINDY CONDITIONS TO PARTS
OF THE REGION, ALTHOUGH TEMPERATURES WILL LIKELY BE TOO WARM TO SUPPORT MUCH
RISK FOR HEAVY SNOW. IN ALASKA, ARCTIC HIGH PRESSURE OVER THE NORTHERN PARTS OF
THE STATE MAY HELP TO PROMOTE MUCH BELOW NORMAL TEMPERATURES AND GAP WINDS
ACROSS THE SOUTHERN MAINLAND.
HAZARDS
SLIGHT RISK OF PERIODS OF HEAVY SNOW FOR THE SIERRA NEVADA, KLAMATH, AND
CASCADE MOUNTAINS, WED-SUN, FEBRUARY 28-MARCH 3.
SLIGHT RISK OF PERIODS OF HEAVY SNOW FOR PARTS OF THE NORTHERN ROCKIES,
WED-SUN, FEBRUARY 28-MARCH 3.
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR MUCH OF CALIFORNIA AND THE
PACIFIC NORTHWEST, WED-SUN, FEBRUARY 28-MARCH 3.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR MUCH OF THE WESTERN CONUS, WED-SUN,
FEBRUARY 28-MARCH 3.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE NORTHEAST, MID-ATLANTIC, OHIO AND
TENNESSEE RIVER VALLEYS, AND SOUTHERN APPALACHIANS, WED-THU, FEBRUARY 28-29.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR PORTIONS OF THE EASTERN CONUS, WED-THU,
FEBRUARY 28-29.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF SOUTHERN ALASKA,
WED-FRI, FEBRUARY 28-MARCH 1.
SLIGHT RISK FOR PERIODS OF HIGH WINDS FOR SOUTHERN COASTAL PORTIONS OF ALASKA,
WED-SAT, FEBRUARY 28-MARCH 2.
DETAILED SUMMARY
FOR FRIDAY FEBRUARY 23 - TUESDAY FEBRUARY 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY FEBRUARY 28 - TUESDAY MARCH 05: MULTIPLE DYNAMICAL MODEL ENSEMBLE
MEANS ARE IN FAIRLY LARGE DISAGREEMENT TODAY REGARDING THE EVOLUTION OF THE
WEEK-2 500-HPA HEIGHT PATTERN ACROSS MUCH OF THE U.S. THE ECENS MAINTAINS A
MORE AMPLIFIED PATTERN ACROSS THE DOMAIN WITH STRONG NEGATIVE 500-HPA HEIGHTS
ACROSS NORTHWESTERN NORTH AMERICA AND STRONG POSITIVE 500-HPA HEIGHT ANOMALIES
OVER THE NORTH PACIFIC AND EASTERN NORTH AMERICA. HOWEVER, THE GEFS IS MUCH
WEAKER WITH NEGATIVE 500-HPA HEIGHT ANOMALIES IN THE GULF OF ALASKA AND BROAD
RIDGING ACROSS MOST OF NORTH-CENTRAL NORTH AMERICA. THIS LEADS TO A
LOW-CONFIDENCE FORECAST, PARTICULARLY ACROSS THE WEST WHERE THE LARGEST
DISCREPANCIES BETWEEN THE GEFS AND ECENS PRECIPITATION PATTERNS ARE FOUND.
THE ECENS RAW OUTPUT AND PROBABILISTIC EXTREMES TOOL (PET) INDICATE INCREASED
CHANCES FOR HEAVY PRECIPITATION TO PARTS OF THE WESTERN CONUS. THE GREATEST
PROBABILITIES (>40%) OF 3-DAY PRECIPITATION AMOUNTS EXCEEDING THE 85TH
CLIMATOLOGICAL PERCENTILE IN THE PET ARE FOUND ACROSS NORTHERN CALIFORNIA
PARTICULARLY IN THE SOUTHERN CASCADES AND NORTHERN SIERRA NEVADA. THE GEFS IS
MORE SUPPORTIVE OF THIS HEAVY PRECIPITATION POTENTIAL TODAY RELATIVE TO
YESTERDAY, PARTICULARLY DURING THE MIDDLE OF WEEK-2. THIS IS ASSOCIATED WITH A
RELOADING TROUGH OVER THE EAST PACIFIC WHERE THE ECENS IS FORECASTING A TROUGH.
HOWEVER, DUE TO THE EVOLUTION DETAILS OF THE MID-LEVEL PATTERN BEING VERY
DIVERGENT, CONFIDENCE IS LOW REGARDING THE FORECAST OUTCOME. THEREFORE, A BROAD
AREA IS POSTED WITH A SLIGHT RISK OF HEAVY PRECIPITATION FOR THE ENTIRE WEST
COAST FROM FEBRUARY 28-MARCH 3. AN ASSOCIATED HEAVY SNOW HAZARD IS POSTED FOR
THE HIGHER ELEVATIONS OF THE SIERRA NEVADA, KLAMATH AND CASCADE MOUNTAINS FOR
THE SAME TIME PERIOD. THE EVOLUTION OF THIS STORM LOOKS LIKELY TO BRING
SLIGHTLY COOLER THAN NORMAL TEMPERATURES TO THE REGION WHICH MAY BRING
SNOW-LEVELS FURTHER DOWN THAN EARLIER THIS MONTH. FURTHER INLAND, RAW AND
CALIBRATED GUIDANCE INDICATES INCREASED CHANCES FOR SOME HEAVY SNOW AT THE
HIGHER ELEVATIONS OF THE NORTHERN ROCKIES SOUTH THROUGH THE NORTHERN WASATCH
RANGE OF UTAH. FINALLY, THERE IS BROAD SUPPORT AMONG THE TOOLS FOR A SLIGHT
CHANCE OF HIGH WINDS FOR MUCH OF THE WESTERN CONUS DURING MUCH OF WEEK-2 AS
THIS MID-LEVEL TROUGH MOVES INLAND.
IN THE EASTERN CONUS, CONFIDENCE IS FAIRLY HIGH EARLY IN THE PERIOD FOR A
FORECAST SHORTWAVE MID-LEVEL TROUGH AND ASSOCIATED SURFACE LOW-PRESSURE
EJECTING OUT OF THE CENTRAL ROCKIES. THIS FEATURE WOULD BRING INCREASED
LIKELIHOOD FOR HEAVY PRECIPITATION AND HIGH WINDS TO MUCH OF THE EASTERN CONUS
EARLY IN THE PERIOD. THE ECENS AND GEFS PETS ARE IN GOOD AGREEMENT SHOWING A
LARGE PORTION OF THE EASTERN CONUS HAVING A GREATER THAN 20% CHANCE OF 3-DAY
PRECIPITATION TOTALS EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE. RAW TOOLS
ARE SUPPORTIVE OF THESE TOTALS REACHING NEAR AN INCH ACROSS PORTIONS OF THE
REGION. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS FORECAST FOR
FEBRUARY 28-29 FOR THE NORTHEAST, MID-ATLANTIC, OHIO AND TENNESSEE RIVER
VALLEYS, AND SOUTHERN APPALACIANS. THIS SYSTEM ALSO SUPPORTS A SLIGHT RISK OF
HIGH WINDS FOR LARGELY THE SAME AREA FOR FEBRUARY 28-29 WITH ENSEMBLE GUIDANCE
INDICATING SURFACE LOW-PRESSURE POTENTIALLY FALLINGL BELOW 990MB AND SUPPORT
FROM THE GEFS AND ECENS PETS. THIS SYSTEM ACROSS THE EAST IS LIKELY TO BE
ASSOCIATED WITH VERY WARM TEMPERATURES AS INDICATED BY THE NATIONAL BLEND OF
MODELS (NBM) HIGHLIGHTING AN EXTENSIVE AREA OF RECORD HIGH MINIMUM TEMPERATURES
FOR SEVERAL DAYS AT THE END OF WEEK-1 AND BEGINNING OF WEEK-2. LATER IN THE
PERIOD, THE ECENS PET AND RAW MODEL TOOLS SHOW INCREASING CHANCES FOR A PERIOD
OF HEAVY PRECIPITATION ALONG THE GULF COAST. THE GEFS IS NOT YET SUPPORTIVE OF
THESE CHANCES BUT WILL BE MONITORED GOING FORWARD.
IN ALASKA, AN AREA OF ARCTIC HIGH PRESSURE IS FORECAST ACROSS THE NORTHERN
PARTS OF THE STATE AND THE YUKON, WITH SURFACE LOW-PRESSURE OVER THE GULF OF
ALASKA. THIS PATTERN FAVORS INCREASED CHANCES OF GAP WINDS TO MUCH OF THE
SOUTHERN ALASKA COASTLINE DURING MUCH OF THE WEEK-2 PERIOD. THE DETERMINISTIC
GFS AND ECMWF ARE IN GOOD AGREEMENT FOR THIS HAZARD POTENTIAL, PARTICULARLY
ACROSS THE ALASKA PENINSULA AND SOUTHWEST MAINLAND ALASKA. THUS, A SLIGHT RISK
OF HIGH WINDS IS POSTED FOR FEBRUARY 28-MARCH 2 ACROSS THE AREA. MEANWHILE,
TOOLS ARE ALSO STRONGLY SUPPORTIVE OF MUCH BELOW NORMAL TEMPERATURES ACROSS
MUCH OF SOUTHERN MAINLAND ALASKA DURING THE PERIOD. STRONG NORTHERLY FLOW IS
FAVORED ACROSS THE MID-LEVELS AND PETS ARE INDICATING AT LEAST A 20% CHANCE OF
TEMPERATURES FALLING BELOW THE LOWEST 5TH PERCENTILE ACROSS MUCH OF SOUTHERN
MAINLAND ALASKA WITH NEGATIVE TEMPERATURE ANOMALIES EXCEEDING 15 DEG C.
THEREFORE, A SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IS FORECAST FOR
FEBRUARY 28-MARCH 1 IN THIS REGION.
FORECASTER: RYAN BOLT
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