502
FXUS21 KWNC 061813
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 06 2023
SYNOPSIS: A WEAK MID-LEVEL TROUGH ACROSS PORTIONS OF THE EASTERN CONTIGUOUS
U.S. (CONUS) IS FAVORED TO INCREASE CHANCES FOR HEAVY PRECIPITATION ACROSS
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS EARLY IN THE WEEK-2 PERIOD. A
SECOND AREA OF CONCERN ASSOCIATED WITH THIS TROUGHING FEATURE IS ALONG THE
EASTERN SEABOARD DURING THE PERIOD. BY THE MIDDLE OF THE PERIOD, FORECAST
HURRICANE LEE COULD BE OFF SHORE OF THE NORTHEAST AND BRING THE POTENTIAL FOR
HIGH WINDS TO PARTS OF THE AREA. LOW PRESSURE IN THE GULF OF ALASKA MAY BRING
HEAVY PRECIPITATION TO SOUTHEAST ALASKA AND THE SOUTHERN ALASKAN MAINLAND.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, THU-SAT, SEP 14-16
SLIGHT RISK OF HEAVY PRECIPITATION FOR MUCH OF THE EASTERN SEABOARD, THU-MON,
SEP 14-18.
SLIGHT RISK OF HIGH WINDS FOR COASTAL PORTIONS OF NEW ENGLAND, FRI-MON, SEP
15-18.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF SOUTHEASTERN MAINLAND AND
SOUTHEAST ALASKA, THU-SAT, SEP 14-16.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE LOWER MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR SATURDAY SEPTEMBER 09 - WEDNESDAY SEPTEMBER 13:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY SEPTEMBER 14 - WEDNESDAY SEPTEMBER 20: THE MID-LEVEL HEIGHT
PATTERN ACROSS THE CONUS DURING THE PERIOD CONTINUES TO BECOME SLIGHTLY MORE
AMPLIFIED RELATIVE TO YESTERDAY. NEGATIVE 500-HPA HEIGHT ANOMALIES AND
TROUGHING IS FORECAST ACROSS THE EASTERN CONUS AND POSITIVE 500-HPA HEIGHT
ANOMALIES AND SLIGHT RIDGING IS FAVORED ACROSS THE WEST. IN ALASKA, A STRONG
TROUGH AND NEGATIVE 500-HPA HEIGHTS ARE FAVORED ACROSS THE WESTERN PARTS OF THE
STATE, LEADING TO STRONG ONSHORE FLOW.
ACROSS THE SOUTHERN TIER OF THE CONUS, TEMPERATURES ARE FAVORED TO BE
ABOVE-NORMAL BUT ARE NOT EXPECTED TO BE HAZARDOUS. THEREFORE, THERE ARE NO
EXCESSIVE HEAT HAZARDS POSTED TODAY.
IN THE EASTERN CONUS, A BROAD TROUGH IS FAVORED TO BRING BELOW-NORMAL
TEMPERATURES TO PARTS OF THE REGION. ACROSS PARTS OF THE UPPER MIDWEST, THE
ECMWF PROBABILISTIC EXTREMES TOOL (PET) INDICATES THE POTENTIAL FOR
TEMPERATURES TO FALL BELOW 40 DEG F INTRODUCING CHANCES FOR AN EARLY FROST TO
THE REGION. HOWEVER, THE GEFS PET IS NOT AS SUPPORTIVE TODAY AND RAW MODEL
GUIDANCE DOES NOT INDICATE TEMPERATURES FALLING BELOW 40 DEG F. AS SUCH, THERE
IS NO CORRESPONDING MUCH BELOW NORMAL TEMPERATURE HAZARD POSTED BUT VULNERABLE
AREAS SHOULD REMAIN COGNIZANT OF THIS RISK.
THE PETS AND RAW MODEL GUIDANCE CONTINUE TO INDICATE INCREASED CHANCES OF HEAVY
PRECIPITATION ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS. THE AREA OF
HIGHEST CONCERN HAS SHIFTED FURTHER SOUTH RELATIVE TO YESTERDAY WITH THE ECMWF
PET IN PARTICULAR HIGHLIGHTING AN AREA OF GREATER THAN 30% CHANCE OF 3 DAY
PRECIPITATION AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1 INCH. THE GEFS IS IN
ROUGH AGREEMENT WITH THE ECMWF, HOWEVER, WITH LOWER PRECIPITATION AMOUNTS. RAW
MODEL GUIDANCE IS ALSO IN GOOD AGREEMENT WITH THE STRONGEST SIGNAL FURTHER
SOUTH ACROSS PORTIONS OF TEXAS AND OKLAHOMA. THUS, A SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR PARTS OF THE CENTRAL AND SOUTHERN PLAINS FOR SEP
14-16.
IN THE EASTERN CONUS AHEAD OF A MID-LEVEL TROUGH OVER THE GREAT LAKES THERE IS
A RISK OF HEAVY PRECIPITATION FOCUSED ALONG THE EASTERN SEABOARD. THE ECMWF PET
IS SUPPORTIVE OF A RISK FOR 3-DAY PRECIPITATION AMOUNTS TO EXCEED THE 85TH
PERCENTILE AND 1 INCH. WHILE THE GEFS PET IS NOT AS SUPPORTIVE WITH A LESS THAN
20% CHANCE OF PRECIPITATION AMOUNTS GREATER THAN 85TH PERCENTILE THE GUIDANCE
INDICATES AT LEAST A 20% CHANCE OF OVER 3/4 AN INCH. RAW MODEL GUIDANCE FROM
THE GEFS AND ECMWF ARE IN GOOD AGREEMENT WITH THEIR RESPECTIVE PETS AS WELL.
THE DIFFERENCES MAY RELY ON THE STRENGTH OF THE NEGATIVE 500-HPA HEIGHT
ANOMALIES WITH A STRONG FEATURE IN THE GEFS THAT MAY PUSH THE HEAVIEST
PRECIPITATION OFF THE EAST COAST. THE ECMWF HAS A WEAKER TROUGH, IN LINE WITH
THE CANADIAN, THAT WOULD ALLOW THE PRECIPITATION TO DEVELOP NEARER TO THE
COAST. A SECOND CONCERN FOR THIS AREA IS POTENTIAL IMPACTS FROM FORECAST
HURRICANE LEE THAT MAY COME NEAR TO THE EAST COAST AND ADD ADDITIONAL MOISTURE
TO THIS BOUNDARY INTO THE MIDDLE OF THE PERIOD. RELATIVE TO YESTERDAY, THE
ENVELOPE OF POSSIBLE SOLUTIONS HAS SHIFTED SLIGHTLY WEST INCREASING CHANCES FOR
POTENTIALLY HEAVY PRECIPITATION AND HIGH WIND TO PARTS OF THE NORTHEAST. PLEASE
REFER TO THE NATIONAL HURRICANE CENTER FOR MORE INFORMATION ON TROPICAL STORM
LEE. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR SEP 14-18
FROM THE DELMARVA THROUGH THE NORTHEAST AND A SLIGHT RISK OF HIGH WINDS IS
POSTED FOR COASTAL AREAS FROM LONG ISLAND TO THE CANADIAN BORDER FOR SEP 15-18.
AS PREVIOUSLY MENTIONED, THERE IS AN INCREASED RISK OF HEAVY PRECIPITATION
ACROSS THE CENTRAL AND SOUTHERN PLAINS, OVERLAPPING WITH PREVIOUS RAPID ONSET
DROUGHT (ROD) RISKS AREAS. THESE AREAS ARE NOW FAVORED TO SEE AT LEAST SOME
PRECIPITATION IN WEEK-1 AND EARLY IN THE WEEK-2 PERIOD. THEREFORE, THE ROD RISK
WAS REDUCED YESTERDAY TO AREAS FURTHER EAST IN THE LOWER MISSISSIPPI VALLEY
WHERE LESS RAINFALL IS FAVORED DURING THE NEXT TWO WEEKS AND INCREASED 30 DAY
PRECIPITATION DEFICITS AND HIGH EVAPOTRANSPIRATION RATES ASSOCIATED WITH
ABOVE-NORMAL TEMPERATURES.
IN ALASKA, AN AREA OR MULTIPLE AREAS OF SURFACE LOW PRESSURE APPEAR LIKELY TO
DEVELOP IN THE GULF OF ALASKA THAT COULD BRING INCREASED CHANCES FOR HEAVY
PRECIPITATION AND HIGH WINDS TO PARTS OF THE SOUTHERN MAINLAND AND SOUTHEAST.
THERE IS GOOD AGREEMENT BETWEEN THE GEFS AND ECMWF PETS ALONG WITH THE RAW
DYNAMICAL TOOLS INDICATING 3-DAY PRECIPITATION AMOUNTS EXCEEDING THE 85TH
PERCENTILE AND APPROACHING 3 INCHES FOR DAYS 8-10. THUS, A SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR PORTIONS OF THE SOUTHERN MAINLAND AND MUCH OF
SOUTHEAST ALASKA FOR SEP 14-16. ALSO, THE ECMWF PET AND TO SOME EXTENT THE GEFS
HAVE ELEVATED CHANCES FOR HIGH WINDS INTO MUCH OF THE GULF OF ALASKA. THESE
WINDS ARE LIKELY TO BE MOSTLY A MARITIME HAZARD SO NO CORRESPONDING WIND HAZARD
IS POSTED.
FORECASTER: RYAN BOLT
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