589
FXUS21 KWNC 041820
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 04 2023
SYNOPSIS: CONFIDENCE IS INCREASING REGARDING AN ACTIVE SOUTHERN STREAM EARLY IN
WEEK-2, WHICH FAVORS ENHANCED PRECIPITATION CHANCES ACROSS PORTIONS OF THE
SOUTHEAST, PARTICULARLY FLORIDA. TODAY’S MODELS ARE NOT DEPICTING AS MUCH OF A
NORTHWARD COMPONENT COMPARED TO YESTERDAY RESULTING IN RELATIVELY LOWER
PRECIPITATION AMOUNTS INLAND ACROSS THE TENNESSEE VALLEY, ALLOWING THE RAPID
ONSET DROUGHT (ROD) RISK TO REMAIN IN PLACE. TOWARD THE MIDDLE OF WEEK-2,
INTERACTION WITH NORTHERN STREAM ENERGY MAY LEAD TO THE DEVELOPMENT OF A
SURFACE LOW PRESSURE SYSTEM NEAR THE NORTHEAST BRINGING ENHANCED CHANCES FOR
HEAVY PRECIPITATION UP THE EASTERN SEABOARD. WHILE INCREASED PRECIPITATION
CHANCES ARE STILL LIKELY ACROSS THE PACIFIC NORTHWEST THROUGHOUT WEEK-2 DUE TO
MID-LEVEL LOW PRESSURE OVER THE NORTHEAST PACIFIC, DAILY PRECIPITATION TOTALS
ARE NOT FORECAST TO REACH HAZARDS THRESHOLDS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE CENTRAL GULF OF
MEXICO COAST, FLORIDA, THE SOUTHEAST, AND THE SOUTHERN MID-ATLANTIC, THU-SAT,
OCT 12-14.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE MID-ATLANTIC AND
NORTHEAST, FRI-SUN, OCT 13-15.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF WESTERN
MAINLAND ALASKA AND THE ALASKA PENINSULA, THU-SAT, OCT 12-14.
RAPID ONSET DROUGHT (ROD) RISK OVER PARTS OF THE LOWER MISSISSIPPI AND
TENNESSEE VALLEYS, AND SOUTHERN APPALACHIANS.
DETAILED SUMMARY
FOR SATURDAY OCTOBER 07 - WEDNESDAY OCTOBER 11:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY OCTOBER 12 - WEDNESDAY OCTOBER 18: TODAY’S DYNAMICAL MODELS ARE
DEPICTING A MORE AMPLIFIED 500-HPA HEIGHT PATTERN DURING WEEK-2 COMPARED TO
YESTERDAY, WITH TROUGHING FAVORED ACROSS THE EASTERN CONUS, RIDGING OVER THE
WESTERN CONUS, AND ANOTHER TROUGH OVER THE EASTERN PACIFIC AND ALASKA. THE
TREND TOWARD MORE TROUGHING IN THE EAST LEADS TO INCREASING CONFIDENCE FOR
HEAVY PRECIPITATION. ADDITIONALLY AN ACTIVE SOUTHERN STREAM IS FORECAST, WITH
MOISTURE FROM TROPICAL SYSTEMS IN THE EASTERN PACIFIC BEING EJECTED EASTWARD
TOWARD THE GULF OF MEXICO AND SOUTHEAST BY THE START OF WEEK-2. BY THE MIDDLE
OF THE PERIOD, INTERACTION WITH THE TROUGH OVER THE EAST MAY PULL SOME OF THIS
MOISTURE NORTHWARD, WITH THE 0Z ECMWF ENSEMBLE FAVORING SURFACE LOW PRESSURE TO
DEVELOP ACROSS THE NORTHEAST AROUND OCT 14 BRINGING A SUBSTANTIAL PRECIPITATION
EVENT TO PARTS OF THE REGION. THE 0Z GEFS IS FURTHER OFFSHORE, AND WOULD SPARE
THE NORTHEASTERN U.S. FROM THE HEAVIEST PRECIPITATION. THE ECMWF AND GEFS
PROBABILISTIC EXTREMES TOOLS (PETS) INDICATE AT LEAST A 20 PERCENT CHANCE 3-DAY
PRECIPITATION TOTALS EXCEED THE 85TH PERCENTILE AND 1-INCH EXTENDING FROM THE
SOUTHEAST UP THROUGH PARTS OF THE NORTHEAST, WITH HIGHER PROBABILITIES IN THE
ECMWF PET GIVEN THE HIGHER PRECIPITATION AMOUNTS FORECAST, PARTICULARLY ACROSS
FLORIDA AND THE NORTHEAST. GIVEN THE UNCERTAINTY REGARDING MULTIPLE INTERACTING
FEATURES, ONLY SLIGHT RISKS OF HEAVY PRECIPITATION ARE POSTED ACROSS THE
EASTERN SEABOARD. FURTHER, AROUND THE NEW YORK METROPOLITAN AREA AND SOUTHERN
NEW ENGLAND HEAVY PRECIPITATION AND FLOODING IN THE PAST WEEK ALONG WITH
ADDITIONAL PRECIPITATION FORECAST DURING WEEK-1 FAVOR A SENSITIVE AREA FOR
ADDITIONAL PRECIPITATION IN WEEK-2. TWO SEPARATE AREAS ARE HIGHLIGHTED TO
ADDRESS THE FAVORED TEMPORAL PROGRESSION. THE FIRST IS ACROSS THE CENTRAL GULF
OF MEXICO COAST, SOUTHEAST, AND SOUTHERN MID-ATLANTIC FOR OCT 12-14, AND THE
SECOND EXTENDS NORTHWARD THROUGH THE REMAINDER OF THE MID-ATLANTIC AND
NORTHEAST FOR OCT 13-15.
THE POTENTIAL SYSTEM ACROSS THE SOUTHEAST FAVORS CUTTING BACK THE RAPID ONSET
DROUGHT (ROD) RISK ACROSS THE SOUTHEAST CLOSE TO THE GULF OF MEXICO COAST.
HOWEVER, BOTH THE ECMWF AND GEFS ENSEMBLES DO NOT BRING MUCH PRECIPITATION
NORTHWARD INTO THE TENNESSEE VALLEY, INSTEAD SLIDING MOST OF THE MOISTURE
EASTWARD ACROSS THE SOUTHEAST AND FLORIDA, AND THEN POTENTIALLY UP TO THE
NORTHEAST. THEREFORE, THE TENNESSEE VALLEY IS NOT FORECAST TO HAVE AS MUCH
PRECIPITATION AS POINTS FARTHER SOUTH AND EAST, ALLOWING THE ROD RISK TO REMAIN
OVER THIS REGION.
PERSISTENT MID-LEVEL TROUGHING IS FORECAST OVER THE NORTHEAST PACIFIC, WHICH
FAVORS ELEVATED CHANCES FOR ROUNDS OF PRECIPITATION ACROSS THE PACIFIC
NORTHWEST THROUGHOUT WEEK-2. THE ECMWF PET HAS BACKED OFF ITS ELEVATED
PROBABILITIES FOR 3-DAY PRECIPITATION REACHING THE 85TH CLIMATOLOGICAL
PERCENTILE EARLY IN THE PERIOD, AND WHILE PROBABILITIES IN THE GEFS PET REMAIN
ABOVE 20 PERCENT, PRECIPITATION TOTALS IN THE UNCALIBRATED GUIDANCE ARE NOT
PARTICULARLY NOTEWORTHY, AND THE STRONGEST ATMOSPHERIC RIVER SIGNAL BASED ON
THE GEFS AND ECMWF INTEGRATED VAPOR TRANSPORT TOOL OCCURS DURING WEEK-1. DUE TO
THESE DECREASING SIGNALS, THE SLIGHT RISKS FOR HEAVY PRECIPITATION AND HIGH
WINDS ARE DISCONTINUED ACROSS THE PACIFIC NORTHWEST. ALTHOUGH GENERALLY WET
CONDITIONS ARE FAVORED DUE TO THE ONSHORE FLOW PATTERN, PARTICULARLY ACROSS
COASTAL WASHINGTON, IT IS LESS LIKELY DAILY TOTALS IN WEEK-2 REACH HAZARDS
CRITERIA.
PERSISTENT MID-LEVEL TROUGHING FORECAST ACROSS ALASKA FAVORS BELOW-NORMAL
TEMPERATURES ACROSS MUCH OF THE STATE. THE ECMWF AND GEFS PETS CONTINUE TO
INDICATE AT LEAST A 20 PERCENT CHANCE OF MINIMUM TEMPERATURES FALLING BELOW THE
15TH CLIMATOLOGICAL PERCENTILE AND 20 DEG F ACROSS MUCH OF WESTERN MAINLAND
ALASKA AND THE ALASKA PENINSULA, SUPPORTING A SLIGHT RISK OF MUCH BELOW NORMAL
TEMPERATURES, OCT 12-14. THIS COULD LEAD TO INCREASING FREEZE-UP OF RIVERS AND
LAKES. AS THIS TROUGH RETROGRADES LATER IN WEEK-2, CHANCES FOR HEAVY
PRECIPITATION ARE LIKELY TO INCREASE ACROSS SOUTHEAST ALASKA. HOWEVER, HAZARDS
CRITERIA IS NOT FORECAST TO BE REACHED.
FORECASTER: THOMAS COLLOW
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