358  
FXUS21 KWNC 212037  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST FEBRUARY 21 2024  
 
SYNOPSIS: MODEL GUIDANCE FAVORS A MORE AMPLIFIED MID-LEVEL LOW PRESSURE OVER  
THE NORTH PACIFIC COMPARED TO YESTERDAY, SUPPORTING INCREASED LIKELIHOOD OF  
HEAVY PRECIPITATION TO THE WEST COAST. AN INCREASED POTENTIAL FOR HEAVY SNOW IN  
HIGHER ELEVATIONS OF THE NORTHERN ROCKIES, AND HIGH WINDS CONTINUES ACROSS MUCH  
OF THE WESTERN CONTIGUOUS U.S. (CONUS). THERE IS DECREASING CONFIDENCE IN THE  
HAZARDS OUTLOOK BY THE MIDDLE OF WEEK-2 DUE TO INCREASING MODEL DIVERGENCE. A  
SERIES OF SURFACE LOWS TRACKING ACROSS THE NORTHEASTERN CONUS MAY SUPPORT  
LOCALIZED HIGH WINDS AND ENHANCED PRECIPITATION AT THE BEGINNING OF THE PERIOD,  
ALTHOUGH THERE IS SIGNIFICANT UNCERTAINTY REGARDING THESE POSSIBLE STORMS. OVER  
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  
 
MODERATE RISK OF HEAVY PRECIPITATION FOR PERIODS OF HEAVY PRECIPITATION FOR THE  
NORTHERN HALF OF CALIFORNIA, THU-FRI, FEB 29-MAR 1.  
 
SLIGHT RISK OF PERIODS OF HEAVY PRECIPITATION FOR MUCH OF CALIFORNIA AND THE  
PACIFIC NORTHWEST, THU-MON, FEB 29-MAR 4.  
 
MODERATE RISK OF HEAVY SNOW FOR THE KLAMATH AND PORTIONS OF THE SIERRA NEVADA  
MOUNTAINS, FEB 29-MAR 1.  
 
SLIGHT RISK OF PERIODS OF HEAVY SNOW FOR THE SIERRA NEVADA, KLAMATH, AND  
CASCADE MOUNTAINS, THU-MON, FEB 29-MAR 4.  
 
SLIGHT RISK OF EPISODIC HIGH WINDS FOR MUCH OF THE WESTERN CONUS, THU-MON, FEB  
29-MAR 4.  
 
SLIGHT RISK OF PERIODS OF HEAVY SNOW FOR PARTS OF THE NORTHERN ROCKIES,  
WED-SUN, THU-MON, FEB 29-MAR 4.  
 
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE NORTHEASTERN CONUS, THU-FRI, FEB  
29-MAR 1.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF SOUTHERN ALASKA,  
THU-FRI, FEB 29-MAR 1.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF SOUTHERN ALASKA,  
THU-SAT, FEB 29-MAR 2.  
 
SLIGHT RISK FOR PERIODS OF HIGH WINDS FOR SOUTHERN COASTAL PORTIONS OF ALASKA,  
THU-MON, FEB 29-MAR 4.  
 
POSSIBLE FLOODING FOR PARTS OF THE NORTHERN HALF OF CALIFORNIA.  
 
DETAILED SUMMARY  
 
FOR SATURDAY FEBRUARY 24 - WEDNESDAY FEBRUARY 28:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
FOR THURSDAY FEBRUARY 29 - WEDNESDAY MARCH 06: MULTIPLE DYNAMICAL MODEL  
ENSEMBLE MEANS SHOW A MORE AMPLIFIED MEAN WEEK-2 500-HPA HEIGHT PATTERN ACROSS  
MUCH OF THE U.S. COMPARED TO YESTERDAY, BUT CONTINUE TO BE IN FAIRLY LARGE  
DISAGREEMENT. THE ECENS INDICATES A MORE AMPLIFIED MID-LEVEL TROUGH OVER THE  
NORTH PACIFIC COMPARED TO THE GEFS AT THE BEGINNING OF THE PERIOD. BY THE  
MIDDLE OF THE PERIOD,, THERE ARE INCREASING DIFFERENCES AMONG THE MODELS  
REGARDING THE EVOLUTION OF THIS FEATURE. THE GEFS MAINTAINS THIS FEATURE NEAR  
THE WEST COAST UNTIL THE END OF WEEK-2, WITH MID-LEVEL SHORTWAVE TROUGHS MOVING  
ACROSS THE CENTRAL CONUS WHEREAS THE ECENS INDICATES THE NORTH PACIFIC  
MID-LEVEL TROUGH SHIFTING EASTWARD TO THE CENTRAL CONUS, WEAKENING THROUGHOUT  
WEEK-2. THESE MODEL DIFFERENCES TRANSLATE TO DECREASING CONFIDENCE IN  
ASSOCIATED HAZARDS BY THE MIDDLE OF THE PERIOD.  
 
THE INCREASED AMPLIFICATION OF THE MID-LEVEL TROUGH OVER THE NORTH PACIFIC  
TRANSLATES TO INCREASED HEAVY PRECIPITATION SIGNALS FOR THE WEST COAST,  
ESPECIALLY AT THE BEGINNING OF WEEK-2. A MODERATE RISK (AT LEAST A 40% CHANCE)  
OF HEAVY PRECIPITATION IS POSTED ACROSS PARTS OF THE NORTHERN OF CALIFORNIA,  
FEB 29-MAR 1, BASED ON INCREASING ENHANCED INTEGRATED VAPOR TRANSPORT (IVT)  
SIGNALS IN THE GEFS, AND THE ECENS (GEFS) PROBABILISTIC EXTREMES TOOL (PET)  
WHICH SHOW AT LEAST A 40% (30%) CHANCE OF 3-DAY LIQUID EQUIVALENT TOTALS  
EXCEEDING THE 85TH PERCENTILE CLIMATOLOGICALLY AND ONE INCH IN THIS AREA. AN  
ASSOCIATED MODERATE RISK OF HIGH ELEVATION SNOW IS DESIGNATED FOR THE KLAMATH  
AND PORTIONS OF THE SIERRA NEVADA MOUNTAINS, FEB 29-MAR 1. A BROADER AREA OF  
SLIGHT RISK (>20% CHANCE) IS CONTINUED FOR PERIODS OF HEAVY PRECIPITATION FOR  
MUCH OF CALIFORNIA AND THE PACIFIC NORTHWEST WITH A SLIGHT RISK OF HEAVY SNOW  
FOR THE HIGHER ELEVATIONS OF THE SIERRA NEVADA, KLAMATH AND CASCADE MOUNTAINS,  
FEB 29- MAR 4. SHALLOW LANDSLIDES AND ROCK FALLS ARE ALWAYS POSSIBLE IN  
CALIFORNIA DURING PERIODS OF HEAVY RAINFALL IN WINTER.  
 
AS THIS MID-LEVEL TROUGH MOVES INLAND, RAW AND CALIBRATED GUIDANCE SUPPORTS A  
SLIGHT RISK OF PERIODS OF HEAVY SNOW ACROSS THE HIGHER ELEVATIONS OF THE  
NORTHERN ROCKIES SOUTH THROUGH THE NORTHERN WASATCH RANGE OF UTAH, FEB 29-MAR  
4. A SLIGHT CHANCE OF HIGH WINDS FOR MUCH OF THE WESTERN CONUS, FEB 28-MAR 3,  
IS EXPANDED TO INCLUDE SOUTHERN CALIFORNIA AND MORE OF THE SOUTHWEST COMPARED  
TO YESTERDAY ASSOCIATED WITH THE INCREASED DEEPENING OF THE MID-LEVEL TROUGH  
FAVORED IN THE NORTH PACIFIC.  
 
A SERIES OF SURFACE LOWS ARE PREDICTED TO TRACK ACROSS THE NORTHEASTERN CONUS  
AT THE BEGINNING OF THE PERIOD. HOWEVER, THERE IS SIGNIFICANT MODEL UNCERTAINTY  
REGARDING THE EVOLUTION OF THESE POTENTIAL STORMS AND ASSOCIATED IMPACTS. THERE  
MAY BE INCREASED POTENTIAL FOR LOCALIZED HEAVY SNOW ACROSS PARTS OF THE GREAT  
LAKES REGION, OHIO VALLEY, APPALACHIANS, AND NORTHEAST, ALTHOUGH THERE IS TOO  
MUCH UNCERTAINTY AT THIS TIME TO DESIGNATE AN ASSOCIATED HAZARD AT THIS TIME. A  
SLIGHT RISK OF HIGH WINDS IS HIGHLIGHTED FOR PARTS OF THE NORTHEASTERN CONUS,  
FEB 29-MAR 1, BASED ON THE POTENTIAL FOR TIGHT PRESSURE GRADIENT ASSOCIATED  
WITH THESE STORMS, AND SUPPORT FROM THE PETS INDICATING AT LEAST A 20% CHANCE  
OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 20 MPH.  
 
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 OVER MUCH OF THE  
SOUTHERN ALASKA COASTLINE THROUGHOUT THE WEEK-2 PERIOD. THUS, A SLIGHT RISK OF  
HIGH WINDS IS MAINTAINED FOR FEB 29-MAR 2 ACROSS THE AREA. THE PETS SHOW  
NOTICEABLY INCREASED PROBABILITIES FOR MUCH BELOW NORMAL TEMPERATURES RELATIVE  
TO PREVIOUS GUIDANCE, AND INDICATE AT LEAST A 40% CHANCE OF MINIMUM  
TEMPERATURES FALLING TO THE LOWEST 5TH PERCENTILE CLIMATOLOGICALLY ACROSS THE  
SOUTHWESTERN MAINLAND AND ALASKA PENINSULA ON DAY 8 (FEB 29). A MODERATE RISK  
OF MUCH BELOW NORMAL TEMPERATURES IS DESIGNATED FOR PARTS OF SOUTHERN ALASKA  
SOUTH OF THE INTERIOR BASIN, FEB 29-MAR 1. A BROADER AREA OF SLIGHT RISK IS  
HIGHLIGHTED ACROSS SOUTHERN ALASKA, FEB 29-MAR 4. HIGH WINDS ACROSS THE  
SOUTHERN COAST OF ALASKA COULD CONTRIBUTE TO ANOMALOUSLY LOW WIND CHILL VALUES.  
 
FORECASTER: MELISSA OU  
 

 
 
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