326
FXUS21 KWNC 211916
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 21 2023
SYNOPSIS: AREAS OF MID-LEVEL LOW PRESSURE ARE PREDICTED NEAR THE WEST COAST OF
THE CONTIGUOUS U.S. (CONUS), AND THE EASTERN STATES, WITH AN AREA OF MID-LEVEL
HIGH PRESSURE FORECAST OVER MUCH OF THE INTERIOR WEST AND CENTRAL CONUS DURING
WEEK-2. THE EXCESSIVE HEAT AND DRYNESS THAT HAS AFFECTED A LARGE PORTION OF THE
SOUTHWESTERN, CENTRAL, AND SOUTHEASTERN STATES IN RECENT WEEKS IS FORECAST TO
CONSOLIDATE OVER THE SOUTHERN GREAT PLAINS, LOWER MISSISSIPPI VALLEY, AND
SOUTHEAST. THESE LATTER AREAS DEFINE THE CORE OF THIS SUMMER’S EXCESSIVE HEAT,
DRYNESS/DROUGHT, AND LOSS OF SOIL MOISTURE THROUGH EVAPOTRANSPIRATION. AREAS
FARTHER NORTH HAVE EXPERIENCED A BREAK IN THE HIGH HEAT AND HUMIDITY, BUT THIS
IS NOT THE CASE FOR THE CORE DROUGHT/HEAT REGION IN THE SOUTH. THE EXTENDED
PERIOD OF EXCESSIVE HEAT AND DRYNESS INCREASES THE CHANCES FOR RAPID ONSET
DROUGHT (ROD) FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY
DURING WEEK-2.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR EASTERN PORTIONS OF THE SOUTHERN PLAINS AND
THE LOWER MISSISSIPPI VALLEY, TUE-FRI, AUG 29-SEP 1.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE NORTHERN HIGH PLAINS, TUE-WED, AUG 29-30.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF NEW MEXICO, THE SOUTHERN GREAT
PLAINS, THE LOWER MISSISSIPPI VALLEY, AND PARTS OF THE SOUTHEAST, TUE, AUG
29-MON, SEP 4.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR THURSDAY AUGUST 24 - MONDAY AUGUST 28:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY AUGUST 29 - MONDAY SEPTEMBER 04: THE ENSEMBLE MEAN MODEL SOLUTIONS
ARE IN GOOD AGREEMENT ON THE EXPECTED WEEK-2 MID-LEVEL HEIGHT PATTERN ACROSS
THE CONUS AND ALASKA. MEAN TROUGHS ARE PREDICTED OVER THE BERING SEA/WESTERN
ALASKA, NEAR THE WEST COAST OF THE CONUS, AND OVER THE EASTERN CONUS, WITH A
MEAN RIDGE FORECAST OVER THE CENTRAL AND WEST-CENTRAL CONUS. THE PROLONGED
PERIOD OF EXCESSIVE HEAT AND DRYNESS IS PREDICTED TO EASE OVER THE NORTHERN AND
CENTRAL CONUS, BUT CONTINUE LARGELY UNABATED ACROSS THE SOUTHERN STATES. A
SLIGHT RISK OF EXCESSIVE HEAT IS DEPICTED FOR PORTIONS OF NEW MEXICO, THE
SOUTHERN GREAT PLAINS, THE LOWER MISSISSIPPI VALLEY, AND PARTS OF THE
SOUTHEAST, TUE, AUG 29-MON, SEP 4. WITHIN THE SLIGHT RISK AREA, THERE IS A
MODERATE RISK OF EXCESSIVE HEAT FOR EASTERN PORTIONS OF THE SOUTHERN PLAINS AND
PARTS OF THE LOWER MISSISSIPPI VALLEY, TUE-FRI, AUG 29-SEP 1. THIS IS SUPPORTED
PRIMARILY BY THE ECMWF ENSEMBLE PROBABILISTIC EXTREMES TOOL (PET) AND THE
CALIBRATED HEAT TOOL. THESE SHAPES WERE ALSO GUIDED BY THE NATIONAL BLEND OF
MODELS (NBM). THE NBM SHOWS A RAPID DROP-OFF IN THE NUMBER OF POTENTIAL
RECORD-BREAKING HIGH TEMPERATURES ACROSS THE SOUTH NEAR THE WEEK-1/WEEK-2
INTERFACE. THE GEFS AND CANADIAN ENSEMBLE PET TOOLS WERE ALSO CONSIDERED BUT TO
A LESSER DEGREE. THE DAILY FORECAST 500-HPA HEIGHT MAPS FROM THE VARIOUS
ENSEMBLE MEANS SHOW THE ANTICIPATED GRADUAL SOUTHWARD MOVEMENT OF THE RIDGE
OVER THE SOUTHWEST CONUS, WITH THE AREA OF PREDICTED MAXIMUM 500-HPA HEIGHTS
MIGRATING FROM NEAR FOUR CORNERS TO THE INTERNATIONAL BORDER BETWEEN MEXICO AND
NEW MEXICO. THIS SOUTHWARD SHIFT IN MAXIMUM 500-HPA HEIGHTS IS ALSO CONSISTENT
WITH OBJECTIVE GUIDANCE THAT DEPICTS MONSOONAL PRECIPITATION OVERSPREADING THE
SOUTHWEST EARLY IN WEEK-2, FOLLOWED BY INCREASINGLY UNFAVORABLE CONDITIONS FOR
THE MONSOON BY THE END OF THE FORECAST PERIOD.
DURING THE FIRST FEW DAYS OF WEEK-2, A SLIGHT RISK OF EXCESSIVE HEAT IS
DELINEATED FOR THE NORTHERN HIGH PLAINS. THIS IS BASED ON THE GFS AND ECMWF
ENSEMBLE MEAN PETS, AND CONSISTENT WITH WPC’S DAY 7 TEMPERATURE GUIDANCE, WHICH
PREDICTS TEMPERATURES AND HEAT INDICES NEAR 95 DEG F. THIS MAY ALSO BE
ASSOCIATED WITH COMPRESSIONAL HEATING DUE TO DOWNSLOPE WINDS EAST OF THE
NORTHERN ROCKIES.
A RAPID ONSET DROUGHT (ROD) RISK REMAINS POSTED ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY AND TEXAS DUE TO THE COMBINATION OF INCREASED 30-DAY
PRECIPITATION DEFICITS, LITTLE TO NO RAINFALL FAVORED IN THE NEXT TWO WEEKS,
AND HIGH EVAPOTRANSPIRATION RATES ASSOCIATED WITH THE ABOVE-NORMAL
TEMPERATURES. THE ROD AREA WAS EXPANDED A BIT NORTHWARD LATE LAST WEEK TO ALIGN
WITH THE LATEST U.S. DROUGHT MONITOR MAP.
OVER ALASKA, NO HAZARDS ARE POSTED. MID-LEVEL TROUGHING FAVORED OVER THE BERING
SEA AND THE WESTERN MAINLAND IS EXPECTED TO BRING PRECIPITATION TO
SOUTH-CENTRAL AND SOUTHEASTERN PORTIONS OF THE MAINLAND, THOUGH TOTALS ARE NOT
EXPECTED TO REACH HAZARDOUS THRESHOLDS.
FORECASTER: ANTHONY ARTUSA
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