961
FXUS02 KWBC 020700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT SAT SEP 02 2023
VALID 12Z TUE SEP 05 2023 - 12Z SAT SEP 09 2023
...SUMMER HEAT NEXT WEEK TO SPREAD TO THE PLAINS/MIDWEST/EAST
BEFORE SHIFTING TO THE SOUTH/SOUTHWEST...
..OVERVIEW
AN ENERGETIC UPPER TROUGH OVER THE WEST WILL LIFT OUT THROUGH THE
NORTHERN ROCKIES TO THE NORTH-CENTRAL U.S. EARLY-MID NEXT WEEK AS
KICKED BY ADDITIONAL UPPER ENERGIES FEEDING INLAND FROM THE
PACIFIC. HEIGHT FALLS AND POOLED MOISTURE AND INSTABILITY NEAR AN
ASSOCIATED FRONT WILL FUEL A SWATH OF SHOWERS AND THUNDERSTORMS
THAT COULD LEAD TO LOCALIZED AREAS OF EXCESSIVE RAINFALL AND
FLOODING CONCERNS, PARTICULARLY ACROSS THE NORTHERN HIGH
PLAINS/ROCKIES. DOWNSTREAM, YET ANOTHER HOT SUMMERTIME UPPER RIDGE
OVER THE CENTRAL U.S. WILL GRADUALLY SHIFT EASTWARD THROUGH NEXT
WEEK. THIS PATTERN WILL SUPPORT WELL ABOVE SEASONAL NORMAL
TEMPERATURES ACROSS THE PLAINS AND UPPER MIDWEST BEFORE REACHING
THE EAST AND ALSO BACK INTO THE SOUTHWEST. MEANWHILE, SCATTERED
SHOWERS AND STORMS COULD PERSIST ACROSS THE LOWER MS/TN VALLEYS
AND GULF COAST REGION BACK INTO FLORIDA NEXT WEEK WITH A LINGERING
AND SLOW MOVING SHORTWAVE AND FRONT.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE SOLUTIONS ARE GENERALLY WELL CLUSTERED OVER
MUCH OF THE LOWER 48 NEXT WEEK IN A PATTERN WITH SEEMINGLY ABOVE
NORMAL PREDICTABILITY. THERE ARE SOME GREATER DIFFERENCES NOTABLY
WITH PACIFIC ENERGIES WORKING INLAND INTO THE WEST, ALBEIT WITH
LIMITED RAINFALL, BUT IN PARTICULAR WITH THE EVENTUAL TRACK OF
IDALIA AND THE PROXIMITY AND AFFECT TO THE EAST COAST FROM
ADDITIONAL WESTERN ATLANTIC IMPULSES/UPPER TROUGHS. THERE REMAINS
SOME SUGGESTION (THOUGH LOWERING POTENTIAL) IN SOME GUIDANCE THAT
IDALIA COULD TURN BACK TO THE CANADIAN MARITIMES AND THIS
POTENTIAL RELIES HEAVILY ON DETAILS OF ENERGIES DIGGING TO THE LEE
OF THE AMPLIPIED BUILDING RIDGE IN THE EAST. PREFER THE BROAD
MODEL AND ENSEMBLE BLEND FOR THE WEST TO MINIMIZE SMALLER SCALE
VARIANCE. FOR THE WESTERN ATLANTIC IT SEEMED PRUDENT TO EXCLUDE
THE 12 UTC ECMWF FROM THE BROAD BLEND FOR IDALIA THROUGH NEXT
MIDWEEK TO BEST MATCH THE LATEST GUIDANCE FROM NHC THAT REMAINS
SIGNIFICANTLY FARTHER TO THE EAST.
..WEATHER/HAZARDS HIGHLIGHTS
AS A MAIN UPPER TROUGH EJECTS FROM THE WEST EARLY NEXT WEEK, LEAD
PRECIPITATION SHOULD WORK DOWNSTREAM THROUGH THE NORTHERN
ROCKIES/PLAINS AS INITIALLY FUELED BY CHANNELED MONSOONAL MOISTURE
WITH ABOVE NORMAL PRECIPITABLE WATER VALUES. RAIN CHANCES
GENERALLY SPREAD EAST TUESDAY-WEDNESDAY, BUT SOME LINGERING
MOISTURE ACROSS THE NORTHERN HIGH PLAINS AND INTO THE UPPER
MIDWEST SEEMS TO OFFER SOME MARGINAL RISK FOR HEAVY LOCAL
CONVECTIVE RAINS FOR DAY 4/5 TUESDAY/WEDNESDAYAS THE UPPER TROUGH
AND COLD FRONT MOVE EASTWARD. FARTHER SOUTH, A SHORTWAVE IS
FORECAST TO HOVER OVER THE LOWER MISSISSIPPI VALLEY, WHICH IN
COMBINATION WITH A FRONTAL BOUNDARY WILL PROVIDE SUPPORT FOR
SCATTERED SHOWERS AND STORMS. SIMILARLY, SOME SHOWERS ARE POSSIBLE
ACROSS ESPECIALLY THE SOUTHERN FLORIDA PENINSULA.
HEAT IS FORECAST TO BUILD ACROSS PARTS OF THE CENTRAL TO EASTERN
U.S. NEXT WEEK UNDERNEATH UPPER RIDGING. TEMPERATURES 15 TO 25
DEGREES ABOVE SEASONAL AVERAGE ARE EXPECTED ACROSS THE
NORTH-CENTRAL STATES AND RECORD WARM MAXIMUM AND MINIMUM
TEMPERATURES COULD BE WIDESPREAD. HIGHS WILL BE WELL INTO THE 90S
IF NOT POSSIBLY EVEN HITTING THE 100F MARK THERE, WITH LOWS
POTENTIALLY STAYING IN THE MID-70S WITH LIMITED OVERNIGHT RELIEF.
THE NORTH-CENTRAL U.S. SHOULD SEE SOME RELIEF WITH COOLER
TEMPERATURES PUSHING WEST TO EAST BY TUESDAY-THURSDAY AS AN UPPER
TROUGH AND SURFACE COLD FRONT MOVE THROUGH. BUT THIS WILL PUSH
ABOVE NORMAL TEMPERATURES INTO THE OHIO VALLEY AND GREAT LAKES
REGION AND THE MID-ATLANTIC AND NORTHEAST, WITH ANOMALIES AROUND
+10-15 DEGREES BEFORE MODERATING LATE NEXT WEEK. FARTHER SOUTH,
TEMPERATURES GENERALLY 10-15 DEGREES ABOVE AVERAGE (AROUND 100F
FOR HIGHS) WILL EXTEND SUMMER FOR THE SOUTHERN HALF OF THE PLAINS
THROUGH NEXT WEEK. THE WESTERN U.S. ON THE OTHER HAND LOOKS TO BE
ON THE COOL SIDE ESPECIALLY FOR HIGH TEMPERATURES PARTICULARLY
EARLY IN THE WEEK, WITH SOME MODERATION BY MIDWEEK LEADING INTO A
RENEWED RE-BUILDING OF HIGH HEAT FROM THE SOUTHERN PLAINS TO THE
SOUTHWEST AND SOUTHERN GREAT BASIN/ROCKIES THROUGH LATER NEXT WEEK.
SCHICHTEL
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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