276
FXUS02 KWBC 050651
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 AM EDT TUE SEP 05 2023
VALID 12Z FRI SEP 08 2023 - 12Z TUE SEP 12 2023
...HEATWAVE TO MODERATE IN THE EAST LATE WEEK, BUT PERSIST IN
EARNEST ACROSS THE SOUTH-CENTRAL U.S AND SOUTHWEST...
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE GUIDANCE OVERALL CONTINUES TO SHOW GOOD
AGREEMENT WITH THE MID-LARGE SCALE PATTERN CONSISTING OF MEAN
TROUGHING ACROSS THE EAST, AN UPPER HIGH/RIDGE REORIENTING ITSELF
A BIT WESTWARD WITH TIME FROM THE SOUTH-CENTRAL U.S. INTO THE
SOUTHWESTERN U.S., AND IMPULSES COMING INTO THE NORTHWEST AND
TRACKING EASTWARD TO THE NORTH OF THE RIDGE. MEANWHILE THERE
REMAIN SOME DIFFERENCES IN THE DETAILS OF SHORTWAVE AND FRONTAL
POSITIONS THAT ARE CERTAINLY WITHIN TYPICAL SPREAD FOR THE MEDIUM
RANGE PERIOD. THE LARGEST DIFFERENCES ARISE WITH TIMING AND
PLACEMENT OF AN UPPER TROUGH OR LOW OVER THE EASTERN PACIFIC INTO
THE WEST BY EARLY NEXT WEEK THAT WILL TAKE ADDITIONAL TIME TO
RESOLVE, BUT IN GENERAL THE 18 UTC GFS AND 12 UTC
ECMWF/UKMET/CANADIAN SOLUTIONS SEEM MOSTLY COMPATIBLE OVER THE
LOWER 48 AND VICINITY FRIDAY AND SATURDAY WHERE A COMPOSITE SEEMS
TO OFFER A GOOD FORECAST BASIS WELL SUPPORTED BY ENSEMBLES, THE 01
UTC NATIONAL BLEND OF MODELS (NBM) AND WPC CONTINUITY. 12 UTC
ECMWF DETAIL WAS A BIT BETTER MATCH WITH GEFS/NAEFS/ECMWF ENSEMBLE
MEANS AND NBM SUNDAY TO TUESDAY, SO THAT BLEND WAS USED, BUT THE
LATEST 00 UTC ECMWF SHOWS LESS THAN STELLAR RUN TO RUN CONTINUITY
AT THESE LONGER TIME FRAMES.
..WEATHER/HAZARDS HIGHLIGHTS
THE EMERGENCE OF AN AMPLIFIED UPPER TROUGH THROUGH THE
MIDWEST/OHIO VALLEY WILL ACT TO SUPPRESS UPPER RIDGING AND HIGH
HEAT ACROSS THE EAST BY FRIDAY. UPPER TROUGHING WILL SETTLE OVER
THE EAST THROUGH THE WEEKEND INTO EARLY NEXT WEEK AS ANCHORED BY
AN UPPER LOW OVER HUDSON BAY AND AS A SERIES OF WEAKER IMPULSES
RIDE OVER THE TOP THEN TO THE LEE OF THE TRANSITIONING UPPER RIDGE
AS IT STRENGTHENS OVER THE SOUTH AND EXPANDS WESTWARD INTO THE
SOUTHWEST. WITH THIS RIDGE IN PLACE, HOT LATE SUMMER TEMPERATURES
WILL LINGER ACROSS THE SOUTH-CENTRAL U.S. AND THE SOUTHWEST.
TEMPERATURE ANOMALIES MAY BE STRONGEST THROUGH LATE WEEK WITH SOME
TEMPERATURES 15-20 DEGREES ABOVE NORMAL IN THE SOUTHERN PLAINS,
WELL INTO THE 100S. HIGH DEWPOINTS AND HUMIDITY ESPECIALLY NEAR
THE WESTERN GULF COAST WILL LEAD TO DANGEROUS HEAT INDICES. ABOVE
NORMAL TEMPERATURES BY ABOUT 10-15 DEGREES SHOULD PERSIST INTO THE
WEEKEND AND EARLY NEXT WEEK ACROSS THE SOUTH-CENTRAL U.S. AND INTO
THE SOUTHWEST. WIDESPREAD DAILY RECORD HIGH MINIMUM AND MAXIMUM
TEMPERATURES ARE LIKELY TO BE SET, WITH PERHAPS EVEN A FEW MONTHLY
RECORDS, IN WHAT HAS PROVEN TO BE A SWELTERING SUMMER.
MEANWHILE IN THIS PATTERN, THE EAST OFFERS A MAIN AREA FOR
PRECIPITATION TO FOCUS, GIVEN MOISTURE (HIGHER PRECIPITABLE WATER
VALUES THAN AVERAGE IN THE NORTHEAST AT LEAST) AND INSTABILITY
POOLING AHEAD OF THE TROUGH AND FRONTAL SYSTEM. WHILE RAIN AMOUNTS
SHOULD BE MAINLY MODERATE, THE INGREDIENTS WILL BE IN PLACE FOR
LOCALIZED HEAVIER RAIN TOTALS ESPECIALLY BECAUSE STORMS MAY BE
SLOW-MOVING. THE WPC DAY 4/5 EXCESSIVE RAINFALL OUTLOOKS (EROS)
DENOTE "MARGINAL" RISK AREAS FOR FRIDAY AND SATURDAY FROM THE
NORTHERN MID-ATLANTIC INTO THE NORTHEAST AS CONVECTION LOOKS TO
HAVE A RELATIVELY BETTER FOCUS NEAR/AHEAD OF THE FRONT AND
FAVORABLE RIGHT ENTRANCE REGION UPPER JET SUPPORT. THE MARGINAL
RISK ENCOMPASSES LOWER FFGS FROM PENNSYLVANIA INTO THE NORTHEAST
AND INCLUDES FAVORED TERRAIN OF THE POCONOS AND CATSKILLS TO THE
ADIRONDACKS AND GREEN MOUNTAINS. RAIN CHANCES SHOULD GRADUALLY
DECREASE INTO NEXT WEEK ALONG THE EASTERN SEABOARD AS THE FRONTS
PUSH EAST.
FARTHER WEST, SCATTERED CONVECTION IS ALSO LIKELY NEAR A WAVY
TRAILING FRONT ACROSS THE LOWER MISSISSIPPI VALLEY AND VICINITY
THROUGH LATE WEEK, THOUGH THE PLACEMENT OF HEAVIER RAINFALL TOTALS
REMAINS UNCERTAIN. ADDITIONALLY TO THE NORTH, A SERIES OF
SHORTWAVES LOOKS TO WORK FROM THE PACIFIC THROUGH THE
WEST/NORTHWEST AND INLAND ACROSS THE INTERMOUNTAIN WEST/ROCKIES
THROUGH THE PERIOD, ALBEIT IN A PATTERN WITH LIMITED PRECIPITATION
INITIALLY. BUT BY THE WEEKEND INTO EARLY NEXT WEEK, CONVECTION MAY
START TO BECOME MORE WIDESPREAD AND BETTER ORGANIZED IN THE
NORTHERN ROCKIES BEFORE WORKING DOWN THROUGH THE PLAINS, WHICH
WILL CONTINUE TO BE MONITORED FOR SOME POTENTIALLY HEAVY TOTALS.
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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