117
FXUS21 KWNC 251807
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT APRIL 25 2024
SYNOPSIS: EARLY IN WEEK-2, HEAVY PRECIPITATION REMAINS A CONCERN ACROSS THE
CENTRAL CONTIGUOUS U.S. (CONUS) WITH MID-LEVEL LOW PRESSURE FORECAST ACROSS THE
WEST AND MID-LEVEL HIGH PRESSURE LIKELY ACROSS THE EASTERN CONUS. THIS WILL
ALLOW FOR A CONTINUED ACTIVE PATTERN LEADING TO CHANCES FOR HEAVY RAIN AND
THUNDERSTORMS ACROSS THE PLAINS AND MISSISSIPPI VALLEY. HOWEVER, THE STRONGEST
CHANCES HAVE DIMINISHED SLIGHTLY TODAY AND DYNAMICAL MODEL TOOLS SHOW
CONSIDERABLE UNCERTAINTY. HEAVY RAIN IS ALSO EXPECTED IN WEEK-1, AND ADDITIONAL
PRECIPITATION IN WEEK-2 COULD CAUSE LOCALIZED FLOODING OVER PORTIONS OF THE
PLAINS, MISSISSIPPI VALLEY, AND WESTERN GREAT LAKES. ASSOCIATED WITH MID-LEVEL
LOW PRESSURE OVER THE WEST, CHANCES FOR PERIODIC HIGH WINDS ARE POSSIBLE FOR
MUCH OF WEEK-2 OVER MUCH OF THE SOUTHWESTERN CONUS, ROCKIES, AND PLAINS. BY THE
MIDDLE OF THE PERIOD THE LONGWAVE HEIGHT PATTERN MAY BREAK DOWN AS MORE ZONAL
FLOW IS FORECAST, REDUCING RISKS FOR HAZARDOUS WEATHER. RAPID ONSET DROUGHT MAY
BECOME A CONCERN IN PARTS OF THE FLORIDA PENINSULA OVER THE NEXT FEW WEEKS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE NORTHERN ROCKIES,
PLAINS, MISSISSIPPI VALLEY, AND WESTERN GREAT LAKES, FRI-SUN, MAY 3-5.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE SOUTHWEST, ROCKIES, AND GREAT PLAINS,
FRI-SUN, MAY 3-5.
FLOODING POSSIBLE FOR PARTS OF THE EASTERN CENTRAL AND SOUTHERN PLAINS,
MISSISSIPPI VALLEY, AND PARTS OF SOUTHWESTERN GREAT LAKES.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF CENTRAL FLORIDA.
DETAILED SUMMARY
FOR SUNDAY APRIL 28 - THURSDAY MAY 02:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY MAY 03 - THURSDAY MAY 09: THE GEFS AND ECMWF ENSEMBLE MEANS ARE IN
GOOD AGREEMENT INDICATING A FAIRLY STAGNANT PATTERN HEADING INTO EARLY WEEK-2,
FEATURING A MODERATELY-AMPLIFIED MEAN 500-HPA LONG-WAVE TROUGH OVER OR NEAR
WESTERN NORTH AMERICA, AND A DOWNSTREAM MID-LEVEL RIDGE WITH AN AXIS OVER THE
EASTERN CONUS. THE WESTERN TROUGH LOOKS LIKELY TO WEAKEN AND DIMINISH BY THE
MIDDLE OF THE WEEK-2 PERIOD WITH MORE ZONAL FLOW PATTERN TAKING HOLD ACROSS THE
CONUS FOR A PERIOD OF TIME. HOWEVER, A TROUGH ACROSS ALASKA MAY HELP TO
REESTABLISH NEGATIVE ANOMALIES ACROSS THE EASTERN PACIFIC OCEAN AT THE END OF
THE PERIOD.
THE PERSISTENT MID-LEVEL TROUGH IN THE WEST FAVORS SOUTHERLY SURFACE FLOW
BRINGING UNUSUALLY MOIST AIR NORTHWARD INTO THE CENTRAL CONUS, WHERE
CYCLONICALLY-CURVED DIVERGENT FLOW ALOFT IS EXPECTED. THIS COMBINATION PUTS A
LARGE PART OF THE CENTRAL CONUS AT INCREASED RISK FOR ONE OR MORE EPISODES OF
HEAVY PRECIPITATION AND LOCALIZED THUNDERSTORMS. THIS QUASI-STATIONARY PATTERN
IS EXPECTED TO PERSIST THROUGH THE EARLY PART OF WEEK-2 BEFORE WEAKENING LATER
IN THE PERIOD, PROMPTING A SLIGHT RISK OF HEAVY PRECIPITATION IN PLACE THROUGH
THE EARLY PART OF THE PERIOD, MAY 3-5. PROBABILISTIC EXTREMES TOOLS (PETS) FROM
THE GEFS AND THE ECENS ARE IN LESS AGREEMENT RELATIVE TO YESTERDAY. THE GEFS
HAS LOWER PRECIPITATION AMOUNTS RELATIVE TO THE ECENS AND THIS INCREASES THE
UNCERTAINTY. RAW TOOLS FROM THE GEFS AND ECENS ARE ALSO IN MORE DISAGREEMENT
WITH THE ECENS REMAINING SLIGHTLY MORE ROBUST IN ITS PROBABILITIES BUT THE GEFS
HAS FURTHER REDUCED PROBABILITIES. THEREFORE, THE MODERATE RISK OF HEAVY
PRECIPITATION HAS BEEN DISCONTINUED TODAY.
THE HEAVY PRECIPITATION AND THUNDERSTORM ACTIVITY ANTICIPATED DURING WEEK-2 IS
NOT EXPECTED TO BE AS INTENSE AS CONDITIONS IN THE SHORT-TERM, BUT WILL
EXACERBATE IMPACTS RELATED TO EXCESSIVE PRECIPITATION IN WEEK-1. THE COMBINED
EFFECTS OF TWO WEEKS OF EXCESSIVE PRECIPITATION SUPPORT A FLOODING POSSIBLE
RISK NEAR AND DOWNSTREAM FROM AREAS WHERE THE GREATEST RAINFALL TOTALS ARE
EXPECTED INCLUDING EASTERN PORTIONS OF KANSAS AND OKLAHOMA AND MUCH OF THE
MISSISSIPPI VALLEY ACCORDING TO THE GEFS AND ECMWF ENSEMBLE MEANS. RUNOFF FROM
HEAVY RAINFALL IS EXPECTED TO ENHANCE THE FLOOD RISK FARTHER TO THE SOUTH AND
EAST (DOWNSTREAM) ACROSS THE LOWER MISSISSIPPI VALLEY.
THE ANTICIPATED LONG-WAVE PATTERN ALSO FAVORS CYCLOGENESIS NEAR OR TO THE LEE
OF THE ROCKIES, WITH HIGHER SURFACE PRESSURES FORECAST FARTHER EAST AND WEST.
THE TIMING AND STRENGTH OF ANY SURFACE LOW PRESSURE SYSTEM THAT FORMS IS
UNCERTAIN, SO A LARGE AREA FROM THE SOUTHWEST AND THE ROCKIES EASTWARD THROUGH
THE GREAT PLAINS HAS A SLIGHT RISK FOR ONE OR MORE EPISODES OF HIGH WINDS FOR
MAY 3-5 UNTIL THE MID-LEVEL TROUGH ACROSS THE WEST WEAKENS BY THE END OF WEEK-2.
IN THE SOUTHEAST, ABOVE-NORMAL TEMPERATURES AND NEAR- TO BELOW-NORMAL
PRECIPITATION IS FORECAST DURING WEEKS-1 & 2. IN PARTS OF THE CENTRAL FLORIDA
PENINSULA AND THE NORTH CAROLINA PIEDMONT SOIL MOISTURE LEVELS ARE DECLINING
DUE TO LIMITED PRECIPITATION IN RECENT WEEKS AND MONTHS. RECENT WEEKS HAVE SEEN
AREAS OF ABNORMAL DRYNESS (D0) DEVELOPING AND EXPANDING ACROSS BOTH OF THESE
REGIONS. AS WE APPROACH THE MIDDLE OF MAY, INCREASING SUN ANGLES AND
TEMPERATURES IN THE 80’S TO 90’S DEG F. COULD LEAD TO RAPID ONSET DROUGHT (ROD)
ACROSS THESE REGIONS. THEREFORE, AN AREA OF ROD HAS BEEN ADDED TO PARTS OF
CENTRAL FLORIDA. HOWEVER, IN NORTH CAROLINA, NEAR-NORMAL PRECIPITATION IS
FAVORED IN THE WEEK-2 FORECAST, THEREFORE, NO ROD HAZARD HAS BEEN POSTED FOR
THIS REGION AT THIS TIME BUT INTERESTS SHOULD REMAIN VIGILANT AND A ROD RISK
HAZARD MAY BE ADDED AT OUR NEXT UPDATE OPPORTUNITY ON MONDAY IF CONFIDENCE
GROWS FOR BELOW-NORMAL PRECIPITATION IN WEEK-2.
FARTHER NORTH, MODELS GENERALLY FAVOR BELOW NORMAL 500-HPA HEIGHTS ACROSS
ALASKA, WITH A TROUGH AXIS NEAR OR WEST OF THE MAINLAND THAT FAVORS STORMY
WEATHER NEAR THE COAST OF SOUTH-CENTRAL AND SOUTHEASTERN ALASKA. THIS PATTERN
MAY SUPPORT ONE OR MORE PERIODS OF ENHANCED PRECIPITATION AND WINDS, BUT
CONDITIONS ARE NOT EXPECTED TO REACH HAZARDOUS CRITERIA PRECLUDING ASSOCIATED
HAZARDS FROM BEING DESIGNATED.
FORECASTER: RYAN BOLT
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