033
FXUS21 KWNC 111838
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 11 2024
SYNOPSIS: A SUBTROPICAL LOW PRESSURE SYSTEM OR TROPICAL CYCLONE MAY DEVELOP
NEAR THE SOUTHEAST OR MID-ATLANTIC COAST EARLY NEXT WEEK. MID-LEVEL LOW
PRESSURE OVER THE WEST IS FORECAST TO RESULT IN SURFACE LOW DEVELOPMENT ACROSS
THE CENTRAL HIGH PLAINS ON SEPTEMBER 19. THIS LOW PRESSURE SYSTEM IS THEN
EXPECTED TO TRACK NORTHEASTWARD TO THE UPPER MISSISSIPPI VALLEY. MID-LEVEL LOW
PRESSURE IS EXPECTED TO PERSIST OVER ALASKA WITH ENHANCED, ONSHORE FLOW
AFFECTING SOUTHEASTERN ALASKA.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC AND
SOUTHEAST, THU-SAT, SEP 19-21.
SLIGHT RISK OF HIGH WINDS FOR THE COASTAL MID-ATLANTIC AND SOUTHEAST, THU-SAT,
SEP 19-21.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GREAT PLAINS AND
MISSISSIPPI VALLEY, THU-FRI, SEP 19-20.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE SOUTHWEST, ROCKIES, AND GREAT PLAINS,
THU-FRI, SEP 19-20.
SLIGHT RISK OF HEAVY PRECIPITATION FOR SOUTHEASTERN ALASKA, THU-MON, SEP 19-23.
DETAILED SUMMARY
FOR SATURDAY SEPTEMBER 14 - WEDNESDAY SEPTEMBER 18:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY SEPTEMBER 19 - WEDNESDAY SEPTEMBER 25: A MID-LEVEL TROUGH MAY
RESULT IN THE DEVELOPMENT OF EITHER A SUBTROPICAL LOW PRESSURE SYSTEM OR
TROPICAL CYCLONE (TC) NEAR THE COASTAL SOUTHEAST OR MID-ATLANTIC BY EARLY NEXT
WEEK. AS OF 2PM EDT ON SEPTEMBER 11, THE NATIONAL HURRICANE CENTER STATES THAT
THERE IS A 30 PERCENT CHANCE OF A NON-TROPICAL LOW TO FORM AND BECOME A TC
ACROSS THE WESTERN ATLANTIC. THE LATEST DETERMINISTIC GFS AND ECMWF MODELS HAVE
TRENDED TOWARDS FASTER DEVELOPMENT OF THIS LOW PRESSURE SYSTEM, PERHAPS AS
EARLY AS SEPTEMBER 15, WITH A TRACK INLAND PRIOR TO WEEK-2. HOWEVER, A NUMBER
OF GFS AND ECMWF ENSEMBLE MEMBERS ARE SLOWER AND DEPICT THIS POTENTIAL LOW
PRESSURE SYSTEM REMAINING NEAR THE EAST COAST EARLY IN WEEK-2. DUE TO TIMING
UNCERTAINTY, A SLIGHT RISK OF HEAVY PRECIPITATION AND HIGH WINDS IS MAINTAINED
FOR PORTIONS OF THE MID-ATLANTIC AND SOUTHEAST THROUGH SEPTEMBER 21. THE
UNCALIBRATED ECMWF MODEL AND ITS PROBABILISTIC EXTREMES TOOL (PET) SUPPORT A 20
TO 40 PERCENT CHANCE OF HEAVY PRECIPITATION FOR THAT REGION. IN ADDITION,
SEVERAL ENSEMBLE MEANS DEPICT A SECOND LOW PRESSURE SYSTEM FORMING NEAR THE
SOUTHEAST COAST LATER IN WEEK-2 DUE TO THE PERSISTENT MID-LEVEL TROUGH.
THE GEFS AND ECMWF ENSEMBLE MEANS ARE IN GOOD AGREEMENT AND REMAIN CONSISTENT
THAT AN AMPLIFIED 500-HPA TROUGH BECOMES ESTABLISHED OVER THE WEST DURING
MID-SEPTEMBER. THIS LONGWAVE TROUGH ALONG WITH LEESIDE SURFACE CYCLOGENESIS
ACROSS THE CENTRAL HIGH PLAINS SUPPORTS A BROAD SLIGHT RISK OF HIGH WINDS FOR
MUCH OF THE SOUTHWEST, ROCKIES, AND GREAT PLAINS THROUGH SEPTEMBER 20. MODEL
GUIDANCE CONTINUES TO DEPICT A LOW PRESSURE SYSTEM AND TRAILING FRONT
PROGRESSING EASTWARD ACROSS THE GREAT PLAINS AND MISSISSIPPI VALLEY ON
SEPTEMBER 19 AND 20. BASED ON THE GEFS PET, THE SLIGHT RISK OF HEAVY
PRECIPITATION (LOCALLY MORE THAN 1 INCH) WAS EXPANDED SOUTHWARD FROM YESTERDAY
TO INCLUDE EASTERN KANSAS, WESTERN MISSOURI, AND NORTHEASTERN OKLAHOMA. GIVEN
THE ENHANCED LOW-LEVEL MOISTURE AND INSTABILITY, THE COLD FRONT COULD INITIATE
THUNDERSTORMS WITHIN THE SPECIFIED HEAVY PRECIPITATION HAZARD.
AN ANOMALOUS 500-HPA TROUGH IS LIKELY TO PROMOTE ENHANCED, ONSHORE FLOW ACROSS
SOUTHEASTERN ALASKA. THE GEFS AND ECMWF ENSEMBLE MEANS DEPICT A SURFACE LOW
CENTERED NEAR THE KENAI PENINSULA THROUGH THE EARLY TO MIDDLE PART OF WEEK-2. A
SLIGHT RISK OF HEAVY PRECIPITATION (VALID SEPTEMBER 19-23) IS POSTED FOR
SOUTHEASTERN ALASKA WHERE THE GEFS AND ECMWF PETS DEPICT THAT THERE IS MORE
THAN A 20 PERCENT CHANCE THAT 3-DAY PRECIPITATION AMOUNTS EXCEED THE 85TH
PERCENTILE AND NEAR 3 INCHES. A HIGH WIND HAZARD IS NOT POSTED AT THIS TIME
SINCE THE CONSENSUS AMONG THE GEFS AND ECMWF ENSEMBLE MEMBERS IS FOR A LOW
PRESSURE SYSTEM OF MODERATE STRENGTH.
FORECASTER: BRAD PUGH
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