241
FXUS21 KWNC 171817
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 17 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 NORTHERN
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.
HAZARDS
SLIGHT CHANCE FOR MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN
AND CENTRAL PLAINS AND THE UPPER MISSISSIPPI VALLEY, THU-SAT, OCT 26-28.
SLIGHT CHANCE FOR HEAVY SNOW FOR HIGHER ELEVATIONS OF THE NORTHERN ROCKIES, AND
NORTHERN PLAINS, WED-FRI, OCT 25-27.
SLIGHT CHANCE FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS, AND THE LOWER AND MIDDLE MISSISSIPPI VALLEYS, WED-FRI, OCT 25-27.
SLIGHT CHANCE FOR HIGH WINDS FOR MUCH OF THE PLAINS, WED-FRI, OCT 25-27.
DETAILED SUMMARY
FOR FRIDAY OCTOBER 20 - TUESDAY OCTOBER 24:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY OCTOBER 25 - TUESDAY OCTOBER 31: 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
SURFACE 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
AIR MASS 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 10TH PERCENTILE AND BELOW 20 DEG F FOR
PORTIONS OF THE NORTHERN CONUS, WITH THE GEFS PUSHING THIS COLD SIGNAL AS FAR
SOUTH AS NORTHERN ARIZONA. THIS SIGNAL FOR THE NORTHERN CONUS IS MORE COHERENT
AND COLDER THAN YESTERDAY, THEREFORE A SLIGHT RISK FOR MUCH BELOW-NORMAL
TEMPERATURES IS POSTED FOR PORTIONS OF THE NORTHERN AND CENTRAL PLAINS AND THE
UPPER MISSISSIPPI VALLEY, VALID FOR OCT 25-27. THE SOUTHERN EXTENSION OF COLD
AIR INTO CALIFORNIA AND THE DESERT SOUTHWEST AS DEPICTED BY THE GEFS IS ALSO
CONSISTENT RELATIVE TO YESTERDAY BUT HAS LESS SUPPORT FROM OTHER TOOLS, SO THE
ASSOCIATED HAZARD HAS BEEN DISCONTINUED.
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 AND NORTHERN PLAINS. 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 AND EXTENDING INTO EASTERN MONTANA. THEREFORE, A SLIGHT RISK
FOR HEAVY SNOW IS POSTED FOR OCT 25-27.
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 FAVORED 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 25-27, 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, A FEATURE THAT IS WELL-INDICATED
BY THE PETS. THEREFORE A SLIGHT RISK FOR HIGH WINDS IS POSTED FOR MOST OF THE
GREAT PLAINS FOR OCT 25-27.
FORECASTER: DANNY BARANDIARAN
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page