578
FXUS21 KWNC 271815
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 27 2023
SYNOPSIS: DURING THE WEEK-2 PERIOD, MID-LEVEL TROUGHS ARE PREDICTED OVER THE
WESTERN CONTIGUOUS U.S. (CONUS), AND JUST OFF THE SOUTHEAST COAST, 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 NORTHERN PORTIONS OF THE WEST COAST.
HAZARDS
SLIGHT CHANCE OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE NORTHWESTERN
QUARTER OF THE CONUS, THU-SUN, OCT 5-8.
SLIGHT CHANCE OF MUCH BELOW-NORMAL TEMPERATURES FOR SOUTH-CENTRAL AND MOST OF
SOUTHEAST ALASKA, THU-SAT, OCT 5-7.
SLIGHT CHANCE OF HEAVY PRECIPITATION ALONG THE SOUTHEAST COAST, THU-SAT, OCT
5-7.
SLIGHT CHANCE OF HEAVY PRECIPITATION FOR THE SOUTHERN PLAINS AND NEIGHBORING
PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THU-WED, OCT 5-11.
RAPID ONSET DROUGHT (ROD) RISK ACROSS THE VICINITY OF SOUTH-CENTRAL TENNESSEE
AND MOST OF ALABAMA.
DETAILED SUMMARY
FOR SATURDAY SEPTEMBER 30 - WEDNESDAY OCTOBER 04:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY OCTOBER 05 - WEDNESDAY OCTOBER 11: 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 5-8. 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 5-7. 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 5-11, 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.
THIS HIGHLIGHTED AREA OF HEAVY PRECIPITATION IS SUPPORTED PRIMARILY BY 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 5-7. IT IS UNCLEAR AS TO HOW MUCH PRECIPITATION MAY AFFECT
THE IMMEDIATE COAST OF THE CAROLINAS 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 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 AND PRECIPITATION ALONG THE
NORTHERN HALF OF THE WEST COAST. TODAY’S PRECIPITATION PET AND THE ATMOSPHERIC
RIVER (AR) TOOL FAVOR INCREASED PRECIPITATION AMOUNTS FOR THIS REGION COMPARED
TO YESTERDAY, THOUGH PREDICTED AMOUNTS FALL SHORT OF HAZARDOUS CRITERIA. THE
INTENSITY AND REGIONAL EXTENT OF THIS POTENTIAL HEAVY PRECIPITATION EVENT WILL
BE MONITORED IN THE DAYS AHEAD.
FORECASTER: ANTHONY ARTUSA
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