336
FXUS02 KWBC 011856
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 PM EDT FRI SEP 01 2023
VALID 12Z MON SEP 04 2023 - 12Z FRI SEP 08 2023
...SUMMER-LIKE 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 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, 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
IMPULSES MAY PROVE CRITICAL WITH RESPECT TO THE LATER NEXT WEEK
TRACK OF RESILIENT IDALIA OVER THE WESTERN ATLANTIC.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THERE REMAIN SOME STRENGTH/TIMING DIFFERENCES IN THE DETAILS, BUT
ON THE LARGE SCALE, THERE WAS GOOD ENOUGH AGREEMENT THE FIRST HALF
OF THE PERIOD FOR A GENERAL DETERMINISTIC MODEL BLEND, WITH SLIGHT
PREFERENCE TOWARDS THE MORE CONSISTENT ECMWF. AFTER DAY 5, THERE
ARE SOME GREATER DIFFERENCES WHICH EMERGE INVOLVING FLOW
INTERACTIONS ACROSS THE LOWER 48, AND EVENTUAL TRACK OF IDALIA
OVER THE WESTERN ATLANTIC. THERE REMAINS SOME SUGGESTION (THOUGH
LOWERING POTENTIAL) IN THE GUIDANCE THAT IDALIA COULD MAKE A TURN
BACK TOWARDS THE CANADIAN MARITIMES/NORTHEAST, AND THIS POTENTIAL
RELIES HEAVILY ON DETAILS OF ENERGIES OVER THE BUILDING RIDGE IN
THE EAST. AS SUCH, IT SEEMED PRUDENT TO SWITCH TO A MOSTLY
ENSEMBLE MEAN BLEND FOR THE LATE PERIODS.
..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. GIVEN THE FAVORABLE SET-UP AND
INCREASING QPF WITH LATER MODEL RUNS, OPTED TO ADD A SLIGHT RISK
TO THE DAY 4/MONDAY EXCESSIVE RAINFALL OUTLOOK FROM FAR EASTERN
IDAHO INTO NORTHWEST WYOMING/SOUTHEAST MONTANA. RAIN CHANCES
GENERALLY SPREAD EAST TUESDAY-WEDNESDAY, BUT SOME LINGERING
MOISTURE ACROSS THE NORTHERN HIGH PLAINS IN CONJUNCTION WITH PRIOR
DAY RAINFALL, ALLOWED FOR THE INCLUSION OF A MARGINAL RISK FOR DAY
5/TUESDAY. RAIN WILL EVENTUALLY SPREAD EAST INTO THE MIDWEST
MID-WEEK 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. 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.
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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