052
FXUS21 KWNC 161942
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 16 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE OVER ALASKA AND LOW PRESSURE OVER THE WEST
COAST SETS UP A PUSH-PULL EFFECT, USHERING IN COLDER AIR INTO THE WESTERN
CONTIGUOUS U.S. (CONUS). MOISTURE FROM MULTIPLE SOURCES IS FAVORED TO BRING
WETTER CONDITIONS FOR MUCH OF THE WEST, INCLUDING THE POTENTIAL FOR HEAVY SNOW
IN THE NORTHERN ROCKIES. MOIST FLOW OFF THE GULF OF MEXICO COUPLED WITH SURFACE
LOW PRESSURE OVER THE GREAT PLAINS MAY LEAD TO PERIODS OF HEAVY RAIN AND STRONG
WINDS FOR MUCH OF THE CENTRAL CONUS. LINGERING COLD AIR OVER THE NORTHEASTERN
U.S. BRINGS A CHANCE FOR FREEZE CONDITIONS BEFORE QUICKLY EXITING THE REGION.
HAZARDS
SLIGHT CHANCE FOR MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF CALIFORNIA AND
THE DESERT SOUTHWEST, TUE-FRI, OCT 24-27.
SLIGHT CHANCE FOR MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE
NORTHEASTERN U.S., TUE, OCT 24.
SLIGHT CHANCE FOR HEAVY SNOW FOR HIGHER ELEVATIONS OF THE NORTHERN ROCKIES,
TUE-FRI, OCT 24-27.
SLIGHT CHANCE FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS, AND THE LOWER AND MIDDLE MISSISSIPPI VALLEYS, TUE-SAT, OCT 24-28.
SLIGHT CHANCE FOR HIGH WINDS FOR MUCH OF THE PLAINS, TUE-SAT, OCT 24-28.
DETAILED SUMMARY
FOR THURSDAY OCTOBER 19 - MONDAY OCTOBER 23:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY OCTOBER 24 - MONDAY OCTOBER 30: THE SYNOPTIC PATTERN FOR THE WEEK-2
FORECAST PERIOD AS DEPICTED BY 500-HPA HEIGHT ANOMALIES FEATURES CONTINUED
RIDGING OVER ALASKA AND A DEEPENING TROUGH OVER THE WEST COAST. HIGH PRESSURE
OVER THE EASTERN CONUS SETS UP MOIST RETURN FLOW OFF THE GULF OF MEXICO INTO
THE GREAT PLAINS AND MISSISSIPPI VALLEY. MODEL SOLUTIONS ALSO FAVOR A TROPICAL
SYSTEM MOVING OFF THE EASTERN PACIFIC INLAND INTO MEXICO, PROVIDING ANOTHER
SOURCE OF MOISTURE BOTH TO THE PLAINS AND MORE BROADLY TO THE WESTERN CONUS.
THIS PATTERN RESULTS IN UNSETTLED AND POTENTIALLY HAZARDOUS WEATHER FOR THE
WESTERN HALF OF THE U.S. AND GENERALLY QUIETER CONDITIONS FOR THE EASTERN
SEABOARD.
RIDGING OVER ALASKA AND TROUGHING OVER THE WESTERN CONUS HELPS TO MOVE A COLD
AIRMASS OUT OF CANADA AND SOUTHWARD ALONG THE ROCKIES. THE GEFS AND ECMWF
PROBABILISTIC EXTREMES TOOLS (PETS) BOTH INDICATE AT LEAST A 20% CHANCE FOR
MINIMUM TEMPERATURES TO FALL BELOW THE 15TH PERCENTILE AND BELOW FREEZING FOR
MUCH OF THE WESTERN CONUS, WITH THE GEFS PUSHING THIS COLD SIGNAL AS FAR SOUTH
AS NORTHERN ARIZONA. THE ECMWF TENDS TO KEEP THE COLDEST AIR FURTHER NORTH AND
ALSO SPREADS IT FURTHER EASTWARD THAN THE GEFS. A SLIGHT CHANCE FOR MUCH
BELOW-NORMAL TEMPERATURES IS POSTED FOR PORTIONS OF CALIFORNIA AND THE DESERT
SOUTHWEST WHERE FREEZES HAVE NOT YET OCCURRED OR WHERE HIGHER VEGETATION
VULNERABILITY EXISTS, COVERING OCT 24-27. A SLIGHT CHANCE FOR MUCH BELOW-NORMAL
TEMPERATURES IS ALSO POSTED FOR PORTIONS OF THE NORTHEASTERN U.S. FOR OCT 24
WHERE THE PETS INDICATE A 20% CHANCE OF LOW TEMPERATURES FALLING BELOW
FREEZING, WHERE TEMPERATURES HAVE BEEN MILD LATELY AND SOME VEGETATION
VULNERABILITY TO COLD REMAINS.
TROUGHING OVER THE WEST COAST IS FAVORED TO BRING ENHANCED MOISTURE FLOW INTO
THE INTERMOUNTAIN WEST, LEADING TO THE POTENTIAL FOR HEAVY SNOW IN HIGHER
ELEVATIONS. THE INTEGRATED WATER VAPOR TRANSPORT (IVT) TOOL INDICATES A MODEST
INFLUX (>150 KG/(MS)) OF MOISTURE INTO NORTHERN CALIFORNIA. WITH THE SURGE OF
COLD AIR, THIS SHOULD BE SUFFICIENT TO GENERATE PERIODS OF POTENTIALLY HEAVY
SNOW IN HIGHER ELEVATIONS. THE GEFS PET FOR SNOW WATER EQUIVALENT (SWE)
INDICATES A 20% CHANCE OF SNOWFALL EXCEEDING THE 85TH PERCENTILE AND AT LEAST
0.5 INCHES OF SWE FOR THE FIRST HALF OF WEEK-2 OVER THE NORTHERN ROCKIES.
THEREFORE, A SLIGHT RISK FOR HEAVY SNOW IS POSTED FOR OCT 24-27.
THE TROUGHING OVER THE WESTERN CONUS ALONG WITH POSITIVE 500-HPA ANOMALIES OVER
THE EAST LEADS TO A GOOD ENVIRONMENT FOR CYCLOGENESIS IN THE LEE OF THE
ROCKIES. THIS, WHEN COUPLED WITH POTENTIAL MOISTURE SOURCES FROM BOTH THE GULF
OF MEXICO DUE TO RETURN FLOW AROUND SURFACE HIGH PRESSURE OVER THE EASTERN
CONUS, AND FROM THE EASTERN PACIFIC DUE TO TROPICAL CYCLONE ACTIVITY, LEADS TO
THE POTENTIAL FOR HEAVY PRECIPITATION OVER THE GREAT PLAINS. THE ECMWF, GEFS,
AND CMCE PETS ALL INDICATE AT LEAST A 20% PROBABILITY OF 3-DAY PRECIPITATION
TOTALS EXCEEDING THE 85TH PERCENTILE AND AT LEAST 1 INCH FOR PORTIONS OF THE
SOUTHERN AND CENTRAL PLAINS AND EXTENDING EASTWARD INTO THE MISSISSIPPI VALLEY
FOR OCT 24-28, THEREFORE A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR
THE REGIONS AND TIME PERIOD INDICATED. ADDITIONALLY, THE RESULTING STRONG
PRESSURE GRADIENT OVER THE PLAINS ENHANCES PROBABILITIES FOR HIGH WINDS FOR THE
REGION. THIS IS WELL-INDICATED BY THE PETS, PARTICULARLY EARLY IN WEEK-2.
THEREFORE A SLIGHT RISK FOR HIGH WINDS IS POSTED FOR MOST OF THE GREAT PLAINS
FOR OCT 24-28.
FORECASTER: DANNY BARANDIARAN
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