756
FXUS02 KWBC 031811
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
210 PM EDT SUN SEP 03 2023
VALID 12Z WED SEP 06 2023 - 12Z SUN SEP 10 2023
...IMPRESSIVE HEAT TO SHIFT FROM THE EAST/SOUTH PAST MIDWEEK BACK
TO THE SOUTH-CENTRAL U.S AND SOUTHWEST LATER WEEK/WEEKEND...
...PATTERN OVERVIEW AND GUIDANCE EVALUATION/PREDICTABILITY
ASSESSMENT...
UPPER RIDGING ACROSS THE EAST EARLY IN THE PERIOD SHOULD BE
SUPPRESSED BY LATE WEEK AS A COUPLE OF SHORTWAVES MOVE IN, WITH
AMPLIFIED TROUGHING NEXT WEEKEND ANCHORED BY AN UPPER LOW OVER
HUDSON BAY. WEAKER ENERGY LOOKS TO RIDGE OVER THE TOP OF THE RIDGE
AS IT STRENGTHENS OVER THE SOUTH/SOUTHWEST THROUGH THE PERIOD.
INTO NEXT WEEKEND, THE GUIDANCE MOSTLY OFFERS GOOD AGREEMENT ON
THIS PART OF THE FORECAST, WITH THE EXCEPTION OF THE 00Z UKMET
WHICH WAS A LITTLE SLOWER/STRONGER WITH INITIAL TROUGHING THROUGH
THE GREAT LAKES INTO THE NORTHEAST LATER THIS WEEK. THE NEXT
SYSTEM DROPS SOUTH OUT OF THE GULF OF ALASKA AROUND SATURDAY WITH
POTENTIAL FOR A CLOSED LOW INTO FAR SOUTHWEST CANADA/THE PACIFIC
NORTHWEST. THE 06Z GFS SOLUTION WAS NOTABLY FASTER THAN THE
ECMWF/CMC/ENSEMBLE MEANS AND WAS NOT INCLUDED IN THE LATE PERIOD
FORECAST BLEND FOR TODAY. THE NEW 12Z RUN (AVAILABLE AFTER
FORECAST GENERATION TIME) WAS MUCH SLOWER AND MORE IN LINE WITH
THE CONSENSUS/WPC FORECAST.
THE WPC MEDIUM RANGE PRODUCT SUITE WAS DERIVED FROM A COMPOSITE
BLEND OF THE 00Z ECMWF, 00Z CMC, AND 06Z GFS FOR THE
WEDNESDAY-FRIDAY/DAY 3-5 PERIOD. AFTER THIS, REPLACED THE GFS WITH
ENSEMBLE MEANS TO HELP MITIGATE SOME ADDITIONAL DIFFERENCES IN THE
DETAILS OF BROADER FLOW DOWNSTREAM ACROSS THE NORTHERN CONUS. THIS
APPROACH ALSO MAINTAINS GOOD WPC CONTINUITY.
..WEATHER/HAZARDS HIGHLIGHTS
HOT LATE SUMMER TEMPERATURES LINGERING ACROSS THE EAST AND SOUTH
PAST MIDWEEK WILL THEN REFOCUS TO THE SOUTH-CENTRAL U.S. AND THE
SOUTHWEST LATER WEEK INTO NEXT WEEKEND WITH RE-DIRECTION/BUILDING
OF A MAIN SUPPORTING/AMPLIFIED UPPER RIDGE. TEMPERATURE ANOMALIES
IN THE 10-15 DEGREES ABOVE NORMAL RANGE OFFERS POTENTIAL FOR
WIDESPREAD RECORD VALUES (BOTH DAILY RECORDS AND POSSIBLY SOME
MONTHLY RECORDS) IN WHAT HAS PROVEN TO BE A SWELTERING SUMMER.
THE STEADY DOWNSTREAM EJECTION OF A MAIN UPPER TROUGH AND
ENTRAINING LEAD IMPULSES FROM THE NORTHERN PLAINS THROUGH THE
NORTHEAST MIDWEEK INTO NEXT WEEKEND WILL SUPPORT A SWATH OF
PRECIPITATION ADDITIONALLY FUELED BY SOME POOLING MOISTURE AND
INSTABILITY INTO A LEADING SURFACE LOW/FRONTAL SYSTEM. SOME
LOCALIZED HEAVY CONVECTIVE DOWNPOURS WILL ALSO OCCUR IN SCATTERED
CONVECTION BACK ACROSS THE EASTERN TO CENTRAL STATES NEAR A
TRAILING FRONT IN A PATTERN WITH FAVORABLE UPPER DIFFLUENCE AND
DIGGING IMPULSES. WHILE NO WPC EXCESSIVE RAINFALL AREAS HAVE BEEN
ISSUED FOR THE DAY 4/5 PERIOD WED/THU AT THIS TIME GIVEN
UNCERTAINTIES AT THESE LONGER TIME FRAMES FOR SUMMER CONVECTION,
THERE IS A BUILDING GUIDANCE SIGNAL THAT A FEW SLOWER CELLS ALONG
WITH TRAINING COULD PRODUCE SOME RUNOFF ISSUES OVER THE MID-SOUTH
AND VICINITY. A SERIES OF ADDITIONAL SHORTWAVES WILL ALSO
UNCERTAINLY WORK FROM THE PACIFIC THROUGH THE WEST/NORTHWEST AND
INLAND ACROSS THE INTERMOUNTAIN WEST/ROCKIES, ALBEIT IN A PATTERN
WITH LIMITED PRECIPITATION BUT LOCALIZED CONVECTION THAT MAY
BECOME BEST ORGANIZED LATER WEEK ACROSS THE NORTHERN ROCKIES AND
EVENTUALLY DOWNSTREAM INTO THE NORTHERN PLAINS.
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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