550
FXUS02 KWBC 021845
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 PM EDT SAT SEP 02 2023
VALID 12Z TUE SEP 05 2023 - 12Z SAT SEP 09 2023
...SUMMER HEAT INTIALLY ACROSS 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 AND FLORIDA NEXT WEEK WITH A LINGERING AND
SLOW MOVING SHORTWAVE AND FRONT.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
ON THE LARGE SCALE, MODEL AND ENSEMBLE SOLUTIONS ARE MOSTLY WELL
CLUSTERED OVER THE LOWER 48 DURING THE MEDIUM RANGE PERIOD. THERE
ARE SOME NOTABLE DIFFERENCES IN THE DETAILS/TIMING OF ENERGY
EXITING THE WEST MOVING ACROSS THE UPPER MIDWEST, ROUNDING THE TOP
OF THE CENTRAL-EASTERN U.S. UPPER RIDGE. EVENTUAL DOWNSTREAM
DETAILS ARE HEAVILY RELIENT ON PERISTANT TROUGHING OFF THE EAST
COAST, WHICH MAY PLAY A ROLE IN STEERING OF CURRENTLY
POST-TROPICAL CYCLONE IDALIA, WITH POTENTIAL FOR SOME IMPACTS TO
PARTS OF THE CANADIAN MARITIMES. SHORTWAVES INTO THE NORTHEAST
SHOULD ALSO EVENTUALLY SUPPRESS THE UPPER RIDGE BACK TO THE SOUTH,
AIDED BY ADDITIONAL SHORTWAVE ENERGY MOVING THROUGH SOUTHERN
CANADA LATER NEXT WEEK. UPPER RIDGE ACROSS THE SOUTH SHOULD
STRENGTHEN AND BECOME BETTER ESTABLISHED AS THE OVERALL PATTERN
AMPLIFIES SOMEWHAT BY NEXT WEEKEND. WPCS BLEND TODAY RELIED MOSTLY
ON A BLEND OF THE DETERMINISTIC MODEL SOLUTIONS DAY 3-5, WITH
ADDITIONAL INCLUSION OF THE ENSEMBLE MEANS LATE PERIOD TO SMOOTH
OUT THE HARDER TO RESOLVE LATE PERIOD DETAIL DIFFERENCES. DID NOT
USE THE 00Z CMC AFTER DAY 4 AS IT LOOKED SLIGHTLY TOO STRONG AND
SLOW WITH THE INITIAL SHORTWAVE THROUGH THE GREAT LAKES INTO THE
NORTHEAST. THIS MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS WPC
FORECAST AS WELL.
..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/WEDNESDAY AS 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. ABOVE NORMAL
TEMPERATURES WILL ALSO EXTEND 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 THE UPPER RIDGE FROM THE SOUTHERN PLAINS TO
THE SOUTHWEST AND SOUTHERN GREAT BASIN/ROCKIES THROUGH LATER NEXT
WEEK.
SANTORELLI/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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