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FXUS21 KWNC 261819
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 26 2023
SYNOPSIS: DURING THE WEEK-2 PERIOD, MID-LEVEL TROUGHS ARE PREDICTED OVER THE
WESTERN AND SOUTHEASTERN CONTIGUOUS U.S. (CONUS), AND MID-LEVEL RIDGING IS
FORECAST FROM THE VICINITY OF THE LOWER MISSISSIPPI VALLEY NORTHEASTWARD ACROSS
APPROXIMATELY THE NORTHEASTERN QUARTER OF THE CONUS, AND OVER ALASKA. A COASTAL
STORM SYSTEM IS FAVORED OFF THE SOUTHEAST COAST DURING AT LEAST THE FIRST HALF
OF WEEK-2, WHICH MAY BRING HEAVY PRECIPITATION AMOUNTS. TOWARDS THE END OF THE
WEEK-2 FORECAST PERIOD, THERE ARE MODEL INDICATIONS OF INCREASING ONSHORE FLOW
AND MOISTURE FOR PORTIONS OF THE WEST COAST.
HAZARDS
SLIGHT CHANCE OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE NORTHWESTERN
QUARTER OF THE CONUS, FRI-MON, OCT 6-9.
SLIGHT CHANCE OF MUCH BELOW-NORMAL TEMPERATURES FOR SOUTH-CENTRAL AND MOST OF
SOUTHEAST ALASKA, WED-FRI, OCT 4-6.
SLIGHT CHANCE OF HEAVY PRECIPITATION FOR THE SOUTHERN PLAINS AND NEIGHBORING
PORTIONS OF THE LOWER MISSISSIPPI VALLEY, SAT-TUE, OCT 7-10.
SLIGHT CHANCE OF HEAVY PRECIPITATION ALONG THE SOUTHEAST AND MID-ATLANTIC
COAST, WED-FRI, OCT 4-6.
RAPID ONSET DROUGHT (ROD) RISK ACROSS THE VICINITY OF SOUTH-CENTRAL TENNESSEE
AND MOST OF ALABAMA.
DETAILED SUMMARY
FOR FRIDAY SEPTEMBER 29 - TUESDAY OCTOBER 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY OCTOBER 04 - TUESDAY OCTOBER 10: AN AMPLIFIED RIDGE AND WELL
ABOVE-NORMAL 500-HPA HEIGHTS SUPPORTS A STRENGTHENING SURFACE HIGH AND AN
ASSOCIATED SLIGHT RISK FOR MUCH BELOW-NORMAL TEMPERATURES OVER SOUTH-CENTRAL
AND MOST OF SOUTHEAST ALASKA, OCT 4-6. THIS MEANS TEMPERATURES ARE EXPECTED TO
FALL TO (OR BELOW) THE 15TH CLIMATOLOGICAL PERCENTILE, AND OVERNIGHT
TEMPERATURES ARE FORECAST TO DROP TO (OR BELOW) 32 DEG F. THIS RIDGE OVER
ALASKA IS CONSISTENT WITH RENEWED TROUGHING AND THE ESTABLISHMENT OF
ANOMALOUSLY COLD TEMPERATURES OVER THE WESTERN AND NORTH-CENTRAL SECTIONS OF
THE LOWER 48 STATES. ACCORDINGLY, A SLIGHT CHANCE FOR MUCH BELOW-NORMAL
TEMPERATURES IS POSTED FOR INTERIOR SECTIONS OF WASHINGTON AND OREGON, NORTHERN
PARTS OF CALIFORNIA, NORTHERN AND MUCH OF THE CENTRAL INTERMOUNTAIN REGION,
NORTHERN ROCKIES, AND THE NORTHERN HIGH PLAINS, OCT 6-9. THE LOWLANDS OF
WESTERN WASHINGTON, AND THE WILLAMETTE VALLEY OF WESTERN OREGON ARE EXPECTED TO
REMAIN SUBSTANTIALLY ABOVE FREEZING DURING THIS PERIOD, SO NO COLD HAZARD IS
POSTED FOR THESE AREAS.
A SLIGHT RISK OF HEAVY PRECIPITATION IS INDICATED FOR THE SOUTHERN GREAT PLAINS
AND ADJACENT PORTIONS OF THE LOWER MISSISSIPPI VALLEY, OCT 7-10, IN ADVANCE OF
A PREDICTED MID-LEVEL TROUGH. THIS MEANS AT LEAST A 20% CHANCE THAT EXPECTED
PRECIPITATION AMOUNTS WILL REACH OR EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE,
AND AT LEAST 1-INCH OF PRECIPITATION IS FORECAST TO FALL DURING A 3-DAY PERIOD.
ALTHOUGH THIS HIGHLIGHTED AREA OF HEAVY PRECIPITATION IS SUPPORTED BY THE
VARIOUS PRECIPITATION TOOLS, ITS GREATEST SUPPORT COMES FROM THE ECMWF ENSEMBLE
PROBABILISTIC EXTREMES TOOL (PET). A MID-LEVEL TROUGH AND SURFACE LOW PRESSURE
SYSTEM ARE PREDICTED NEAR THE SOUTHEAST COAST, DURING AT LEAST THE FIRST HALF
OF WEEK-2. A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR THIS AREA, OCT
4-6. WITH THE POTENTIAL STORM ANTICIPATED SO CLOSE TO THE SOUTHEAST COAST, IT
IS UNCLEAR AS TO HOW MUCH PRECIPITATION MAY AFFECT COASTAL AREAS OR REMAIN JUST
OFFSHORE, THOUGH PROJECTED AMOUNTS ARE CLOSE TO 1 INCH. THE ANTICIPATED
COMBINATION OF SURFACE HIGH PRESSURE OVER THE NORTHEAST CONUS AND THE STORM
ALONG THE SOUTHEAST COAST IS EXPECTED TO LEAD TO SEVERAL DAYS OF SUSTAINED
EAST-NORTHEAST FLOW FOR ABOUT THE SOUTHERN HALF OF THE ATLANTIC COAST. MINOR
BEACH EROSION AND RIP CURRENTS ARE POSSIBLE WITH THIS SETUP. THESE COASTAL
STORMS ARE OFTEN ACCOMPANIED BY GUSTY WINDS, BUT AT THIS TIME, THE
PROBABILISTIC EXTREMES WIND TOOL DOES NOT SHOW A SPECIFIC WIND HAZARD.
THIRTY-DAY PRECIPITATION DEFICITS, LITTLE TO NO PRECIPITATION FAVORED DURING
THE NEXT WEEK, AND ABOVE NORMAL TEMPERATURES AND NEAR TO BELOW NORMAL
PRECIPITATION FAVORED DURING WEEK-2 CONTINUE TO SUPPORT THE POSSIBILITY OF
RAPID ONSET DROUGHT (ROD) ACROSS SOUTH-CENTRAL TENNESSEE AND MOST OF ALABAMA.
TOWARDS THE END OF THE WEEK-2 FORECAST PERIOD, THERE IS AN INCREASED SIGNAL IN
THE MODEL GUIDANCE FOR ENHANCED ONSHORE FLOW ALONG THE WEST COAST. THE
POTENTIAL FOR HEAVY PRECIPITATION BEYOND THE WEEK-2 PERIOD WILL BE MONITORED IN
THE DAYS AHEAD.
FORECASTER: ANTHONY ARTUSA
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