316
FXUS02 KWBC 010700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT FRI SEP 01 2023
VALID 12Z MON SEP 04 2023 - 12Z FRI SEP 08 2023
...IDALIA TO LINGER OVER THE WESTERN ATLANTIC NEXT WEEK ..
...SUMMER HEAT TO SPREAD SLOWLY ACROSS THE PLAINS AND MIDWEST
TOWARD THE EAST NEXT WEEK...
...WET PATTERN TO WORK FROM THE INTERMOUNTAIN WEST TO THE NORTHERN
ROCKIES/PLAINS EARLY NEXT WEEK...
..OVERVIEW
AN AMPLIFIED UPPER TROUGH OVER THE WEST WILL LIFT OUT THROUGH THE
NORTH-CENTRAL INTERMOUNTAIN WEST/ROCKIES AND 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 AREAS OF LOCALLY
EXCESSIVE RAINFALL AND LOCALIZED FLOODING CONCERNS. DOWNSTREAM,
YET ANOTHER HOT SUMMERTIME UPPER RIDGE OVER THE CENTRAL U.S. WILL
GRADUALLY SHIFT EASTWARD THROUGH NEXT NEEK. THIS PATTERN WILL
SUPPORT WELL ABOVE SEASONAL NORMAL TEMPERATURES ACROSS THE PLAINS,
UPPER MIDWEST BEFORE APPROACHING THE EAST AND ALSO BACK AGAIN INTO
THE SOUTHWEST. MEANWHILE, SCATTERED SHOWERS AND STORMS COULD
PERSIST ACROSS THE GULF COAST REGION INTO FLORIDA NEXT WEEK WITH A
LINGERING AND SLOW MOVING SHORTWAVE TROUGH AND FRONTAL BOUNDARY.
THE ULTIMATE EASTWARD PROGRESSION OF THE AFOREMENTIONED UPPER
RIDGE AND ROUNDING IMPUSLES MAY PROVE CRITICAL WITH RESPECT TO THE
LATER NEXT WEEK TRACK OF RESILIENT IDALIA OVER THE WESTERN
ATLANTIC.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
COMPOSITE OF REASONABLE CLUSTERED MID-LARGER SCALE GUIDANCE OF THE
GFS/ECMWF/UKMET/CANADIAN FOR EARLY NEXT WEEK FOR MUCH OF THE LOWER
48. SIGNIFICANT EMERGING DIFFERENCES WITH THE MID-LATER NEXT WEEK
HANDLING OF FLOW INTERACTIONS OVER THE LOWER 48 AND IDALIA OVER
THE WESTERN ATLANTIC PROMPTED A SWITCH TO THE ECMWF ENSEMBLE MEAN
AND ESPECIALLY THE GEFS ENSEMBLE MEAN FOR THESE LONGER TIME
PERIODS TO BEST MAINTAIN CONTINUITY AND TO AVOID INDIVIDUAL MODEL
VARIANCES FROM THE NHC FORECAST FOR IDALIA AS SOME RECENT RUNS OF
THE ECMWF AND CANADIAN OFFER MORE OF A TURN TOWARD THE
NORTHEAST/CANADIAN MARITIMES THAN THE GFS. THE 00 UTC ECMWF AND
CANADIAN HAVE TRENDED WAY FROM THAT POTENTIAL.
..WEATHER/HAZARDS HIGHLIGHTS
AS A MAIN UPPER TROUGH LIFTS FROM THE WEST EARLY NEXT WEEK,
PRECIPITATION SHOULD EXPAND/PUSH THROUGH THE NORTHERN
ROCKIES/PLAINS WHILE LINGERING OVER PARTS OF THE INTERMOUNTAIN
WEST. THIS IS LIKELY AS FLOW TO THE EAST OF THE TROUGH AXIS OFFERS
INSTABILITY AND CHANNELED MONSOONAL MOISTURE WITH PRECIPITABLE
WATER VALUES WELL ABOVE NORMAL. A MARGINAL RISK REMAINS IN PLACE
FOR MONDAY ACROSS THE NORTHERN ROCKIES/HIGH PLAINS AND INTO
CENTRAL UTAH AS MOISTURE LEVELS REMAIN ABOVE NORMAL. RAIN CHANCES
ARE EXPECTED TO SPREAD EAST INTO THE MIDWEST BY 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 FOR 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. 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.
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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