823
FXUS21 KWNC 141820
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 14 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS PREDICTED FOR THE NORTHEASTERN QUADRANT OF
THE CONTIGUOUS U.S. (CONUS). UPSTREAM, MID-LEVEL LOW PRESSURE IS FORECAST FOR
THE WESTERN TWO-THIRDS OF THE CONUS, WHICH MAY SUPPORT A SERIES OF SURFACE LOW
PRESSURE SYSTEMS ACROSS THE CENTRAL CONUS AND RESULTANT INCREASED LIKELIHOOD
FOR HEAVY PRECIPITATION AT THE BEGINNING OF WEEK-2. A SERIES OF STORMS OVER THE
NORTH PACIFIC OCEAN MAY BRING WET AND BREEZY CONDITIONS TO SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA, BUT CONDITIONS ARE NOT EXPECTED TO REACH HAZARDS
THRESHOLDS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE GREAT PLAINS AND
MISSISSIPPI VALLEY, FRI-SUN, SEP 22-24.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF THE GREAT PLAINS, FRI-MON, SEP 22-25.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE LOWER MISSISSIPPI VALLEY AND
SOUTHEAST.
DETAILED SUMMARY
FOR SUNDAY SEPTEMBER 17 - THURSDAY SEPTEMBER 21:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY SEPTEMBER 22 - THURSDAY SEPTEMBER 28: MODELS ARE IN RELATIVELY GOOD
AGREEMENT REGARDING THE MEAN PATTERN FOR WEEK-2, WITH THE 0Z GEFS, ECMWF, AND
CANADIAN ENSEMBLE MEANS INDICATING MID-LEVEL RIDGING OVER THE NORTHEASTERN
QUADRANT OF THE CONUS AND A SERIES OF MID-LEVEL LOWS PROPAGATING ACROSS THE
WESTERN TWO-THIRDS OF THE CONUS. ABOVE-NORMAL TEMPERATURES ARE FAVORED FOR THE
CONUS EAST OF THE ROCKIES, WITH NEAR TO BELOW NORMAL TEMPERATURES ACROSS THE
WEST. THE WARMTH IS NOT EXPECTED TO REACH THE DANGEROUS, EXCESSIVE LEVELS
PERIODICALLY SEEN THIS PAST SUMMER, SO NO HEAT HAZARDS ARE POSTED.
A SERIES OF MID-LEVEL TROUGH SHORTWAVES ARE ANTICIPATED TO TRACK ACROSS THE
CENTRAL CONUS FROM THE BEGINNING TO MIDDLE OF WEEK-2, SUPPORTING DEVELOPMENT OF
SURFACE LOWS ACROSS THE REGION. THESE DISTURBANCES HAVE THE POTENTIAL TO
SUPPORT THUNDERSTORMS AND HEAVY RAINFALL. ALTHOUGH THIS RAIN MAY BE BENEFICIAL
FOR MANY AREAS AFFECTED BY DROUGHT, IT COULD ALSO LEAD TO FLASH FLOODING.
RELATIVE TO YESTERDAY, THE ECMWF PROBABILISTIC EXTREMES TOOL (PET) HAS GREATER
SPATIAL COVERAGE EXTENDING ACROSS MUCH OF THE GREAT PLAINS AND THE MISSISSIPPI
VALLEY OF AT LEAST A 20% CHANCE OF 3-DAY RAINFALL TOTALS EXCEEDING THE 85TH
PERCENTILE, CLIMATOLOGICALLY, AND ONE INCH. THE GEFS COUNTERPART HAS
SIGNIFICANTLY LESS COVERAGE IN THIS SIGNAL, WHICH IS LIMITED TO THE CENTRAL AND
SOUTHERN PLAINS AND MIDDLE AND LOWER MISSISSIPPI VALLEY FOR PRECIPITATION
REACHING THESE THRESHOLDS. MEANWHILE, THE CANADIAN PET DOES NOT INDICATE THESE
WET SIGNALS. DESPITE THESE MODEL DIFFERENCES, A BROAD AREA OF SLIGHT RISK OF
HEAVY PRECIPITATION IS POSTED FOR THE GREAT PLAINS AND MISSISSIPPI VALLEY, SEP
22-24.
SURFACE LOWS PREDICTED OVER THE CENTRAL CONUS IN ADDITION TO SURFACE HIGH
PRESSURE OVER THE CENTRAL GREAT BASIN MAY SUPPORT INCREASED CHANCES FOR HIGH
WINDS IN THE LEE OF THE ROCKIES. A SLIGHT RISK OF HIGH WINDS IS HIGHLIGHTED FOR
PARTS OF THE GREAT PLAINS, SEP 22-25. THE ECMWF PET SHOWS AT LEAST A 20% CHANCE
OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 20 MPH IN THE DESIGNATED RISK
AREA.
TOWARDS THE END OF THE WEEK, MID-LEVEL RIDGING MAY BUILD ACROSS THE CENTRAL
GULF COAST REGION, SUPPORTING MAXIMUM TEMPERATURES EXCEEDING THE 85TH
PERCENTILE AND 90 DEG F ACROSS THE AREA. POTENTIAL WARM TEMPERATURES COMBINED
WITH LITTLE TO NO PRECIPITATION FORECAST DURING WEEK-1 AND WEEK-2, AND
ANTECEDENT DRY CONDITIONS (4 INCHES BELOW NORMAL IN THE PAST 30 DAYS) SUPPORTS
AN INCREASED RISK OF RAPID ONSET DROUGHT (ROD) ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY AND CENTRAL GULF COAST REGION. THERE IS SLIGHTLY LESS
COVERAGE DUE TO SOME AREAS ALREADY CURRENTLY EXPERIENCING DROUGHT. EXTREME TO
EXCESSIVE DROUGHT ALREADY EXISTS JUST WEST OF THIS AREA AT RISK, FROM CENTRAL
TEXAS EASTWARD ACROSS MOST OF LOUISIANA AND SOUTHWESTERN MISSISSIPPI.
ANOMALOUSLY HIGH 500 HPA HEIGHTS ARE EXPECTED SOUTH OF THE ALEUTIANS. TO THE
NORTH, 500-HPA HEIGHTS WILL BE CLOSER TO NORMAL, RESULTING IN AN ANOMALOUSLY
STRONG MID-LEVEL JET OVER THE NORTHERN NORTH PACIFIC. A SERIES OF SURFACE LOWS
ARE POSSIBLE OVER THE BERING SEA AND GULF OF ALASKA DURING WEEK-2, LEADING TO
INCREASED CHANCES FOR PERIODS OF ENHANCED PRECIPITATION AND STRONG MARITIME
WINDS ACROSS COASTAL PORTIONS OF SOUTHWESTERN, SOUTHERN, AND SOUTHEASTERN
ALASKA. THIS MAY OCCUR FOLLOWING A VERY WET WEEK-1, POTENTIALLY EXACERBATING
IMPACTS FROM PRECIPITATION DURING WEEK-2. AT THIS TIME, HOWEVER, GIVEN HIGH
SEPTEMBER NORMALS OF 8 TO LOCALLY 20 INCHES OF PRECIPITATION, THE WEEK-2
PRECIPITATION TOTALS ARE ANTICIPATED TO REMAIN BELOW HAZARDS THRESHOLDS, THUS
NO HAZARDS ARE POSTED ANYWHERE IN ALASKA.
FORECASTER: MELISSA OU
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