345
FXUS21 KWNC 201929
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MAY 20 2024
SYNOPSIS: EXCESSIVE HEAT IS POSSIBLE FOR THE FIRST HALF OF WEEK-2 IN CENTRAL
AND SOUTHERN PORTIONS OF BOTH TEXAS AND THE FLORIDA PENINSULA. PARTS OF THESE
AREAS HAVE BEEN UNUSUALLY DRY FOR AT LEAST SEVERAL WEEKS, AND WITH SUBNORMAL
RAINFALL POTENTIALLY ACCOMPANYING THE HEAT, THE COMBINATION OF CONDITIONS
INCREASES THE THREAT FOR RAPID-ONSET DROUGHT. MEANWHILE, A FRONTAL SYSTEM
TRAILING FROM SURFACE LOW PRESSURE TRACKING NEAR THE ST. LAWRENCE SEAWAY WILL
BRING A SLIGHT RISK OF HEAVY PRECIPITATION TO THE NORTHEAST EARLY WEEK-2. THERE
IS ALSO A SLIGHT RISK FOR HEAVY PRECIPITATION AROUND THE MIDDLE OF THE PERIOD
IN PARTS OF THE CENTRAL CONTIGUOUS UNITED STATES (CONUS).
HAZARDS
SLIGHT RISK FOR EXCESSIVE HEAT ACROSS PORTIONS OF CENTRAL AND SOUTHERN TEXAS,
TUE-THU, MAY 28-30.
SLIGHT RISK FOR EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL AND SOUTHERN FLORIDA
PENINSULA, TUE-FRI, MAY 28-31.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR MUCH OF THE NORTHEAST, TUE-THU, MAY
28-30.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL AND
SOUTH-CENTRAL GREAT PLAINS, THU-SAT, MAY 30-JUN 1.
RAPID ONSET DROUGHT RISK ACROSS THE SOUTHERN FLORIDA PENINSULA AND SOUTHERN
TEXAS.
DETAILED SUMMARY
FOR THURSDAY MAY 23 - MONDAY MAY 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY MAY 28 - MONDAY JUNE 03: THE GEFS MEAN, ECMWF MEAN, AND CANADIAN
ENSEMBLE MEAN ALL GENERALLY AGREE THAT A MID-LEVEL RIDGE WILL EXTEND FROM THE
INTERMOUNTAIN WEST INTO THE SOUTHERN GREAT PLAINS AS WEEK-2 GETS UNDERWAY, WITH
ANTICYCLONICALLY-CURVED MID-LEVEL FLOW DOWNSTREAM, SOUTH OF A MODERATELY STRONG
MID-LEVEL TROUGH CENTERED NEAR THE GREAT LAKES. THIS KEEPS MUCH OF CENTRAL AND
SOUTHERN TEXAS AND THE FLORIDA PENINSULA IN AN AREA FAVORABLE FOR WELL
ABOVE-NORMAL TEMPERATURES, WITH HIGH HEAT INDICES OVER FLORIDA AND SOUTHEASTERN
TEXAS WHERE HUMIDITY WILL BE SEASONABLY HIGH. THIS CREATES A SLIGHT RISK FOR
EXCESSIVE HEAT IN THESE AREAS DURING ROUGHLY THE FIRST HALF OF WEEK-2. THE
PROBABILISTIC EXTREMES TOOL (PET) FROM THE CANADIAN ENSEMBLES IS THE MOST
ROBUST WITH THE HEAT IN SOUTHERN TEXAS, SHOWING A 40 PERCENT CHANCE FOR MAXIMUM
TEMPERATURES ABOVE THE 85TH PERCENTILE ON DAY 8 (MAY 28). FARTHER EAST, THE
GEFS PET SHOWS THE STRONGEST POTENTIAL FOR EXCESSIVE HEAT IN SOUTHERN FLORIDA,
WITH A 30 TO 40 PERCENT CHANCE FOR TEMPERATURES ABOVE THE 85TH PERCENTILE ON
DAYS 8 AND 9 (MAY 28-29). THE MID-LEVEL RIDGE IS EXPECTED TO DRIFT
EAST-NORTHEASTWARD AND SLOWLY WEAKEN WITH TIME, ALLOWING MID-LEVEL HEIGHTS TO
DROP TO NEAR NORMAL LEVELS BY MID-WEEK, AND FLATTENING THE ANTICYCLONIC
CURVATURE OF THE MID-LEVEL FLOW OVER THE GULF OF MEXICO AND FLORIDA, BRINGING
AN END TO THE EXCESSIVE HEAT THREAT.
MEANWHILE, FARTHER NORTH, SURFACE LOW PRESSURE IS FORECAST BY MOST GUIDANCE TO
TRACK FROM THE GREAT LAKES NORTHEASTWARD ALONG THE ST. LAWRENCE SEAWAY EARLY
WEEK-2 BEFORE PUSHING AWAY FROM THE CONUS. A FRONTAL SYSTEM TRAILING SOUTHWARD
FROM THE SURFACE LOW PRESSURE WILL BE PULLED THROUGH THE NORTHEASTERN CONUS,
ENHANCING THE ODDS FOR HEAVY RAIN AND COPIOUS THUNDERSTORM ACTIVITY DURING THE
FIRST FEW DAYS OF WEEK-2. NONE OF THE PETS SHOW STRONG ODDS FOR EXCESSIVE
PRECIPITATION, BUT MOST GUIDANCE BRINGS ABOVE-NORMAL RAINFALL TOTALS TO THE
REGION WHICH COULD REASONABLY REACH HAZARDS THRESHOLDS, SO A SLIGHT RISK OF
HEAVY PRECIPITATION IS POSTED FOR EARLY WEEK-2 BEFORE THE SURFACE LOW PRESSURE
AND FRONTAL SYSTEM MOVE AWAY FROM THE NORTHEASTERN CONUS.
SURFACE HIGH PRESSURE ASSOCIATED WITH THE MID-LEVEL RIDGE AXIS ALONG THE
INTERMOUNTAIN WEST WHEN WEEK-2 GETS UNDERWAY WILL DRIFT EASTWARD, PULLING
SURFACE HIGH PRESSURE EAST OF THE PLAINS STATES WITH IT AROUND MID-WEEK.
MEANWHILE, A MID-LEVEL TROUGH FARTHER WEST WILL INDUCE SURFACE LOW PRESSURE
OVER THE INTERIOR WESTERN CONUS. MOIST, CONFLUENT FLOW WILL BE INDUCED ACROSS
THE CENTRAL GREAT PLAINS BETWEEN THE SURFACE HIGH PRESSURE TO THE EAST AND THE
LOWER SURFACE PRESSURES FARTHER WEST, INCREASING THE ODDS FOR HEAVY
PRECIPITATION AND FREQUENT THUNDERSTORMS AROUND THE MIDDLE OF WEEK-2. THERE IS
SIGNIFICANT MODEL UNCERTAINTY REGARDING TIMING AND LOCATION OF THE GREATEST
RISK OF EXCESSIVE PRECIPITATION, BUT THE BEST ODDS FOR AMOUNTS EXCEEDING
HAZARDS LEVELS SEEM TO BE CENTERED NEAR THE CENTRAL AND SOUTH-CENTRAL GREAT
PLAINS AROUND THE MIDDLE OF WEEK-2. THE ECMWF UNCALIBRATED TOOLS SHOW THIS
REGION TO HAVE THE GREATEST CHANCE FOR TOTALS EXCEEDING AN INCH AROUND THE
MIDDLE OF THE PERIOD, SIMILAR TO THE PET DERIVED FROM THE CANADIAN ENSEMBLES.
THE GEFS MEAN ALSO DROPS MODERATE PRECIPITATION HERE DURING THE SAME TIME
PERIOD. FOR THESE REGIONS, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR
PART OF THE CENTRAL CONUS AROUND THE MIDDLE OF WEEK-2 BEFORE MID-LEVEL
CIRCULATION FEATURES BECOME LESS FAVORABLE FOR SIGNIFICANT PRECIPITATION.
THE MID-LEVEL PATTERN FARTHER WEST FAVORS ABOVE-NORMAL PRECIPITATION FOR MOST
OF ALASKA, WITH MODERATELY STORMY WEATHER POSSIBLE AT TIMES ACROSS
SOUTH-CENTRAL AND SOUTHEASTERN PORTIONS OF THE STATE. HOWEVER, NEITHER
PRECIPITATION NOR WIND CONDITIONS ARE EXPECTED TO MEET HAZARDS CRITERIA.
DERIVED TOOLS ARE INCONSISTENT REGARDING TEMPERATURE FORECASTS ACROSS THE
STATE, BUT THERE ARE NO INDICATIONS THAT READINGS WILL BE EXCEPTIONALLY ABOVE
OR BELOW NORMAL.
FORECASTER: RICH TINKER
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