144
FXUS02 KWBC 071802
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EDT THU SEP 07 2023
VALID 12Z SUN SEP 10 2023 - 12Z THU SEP 14 2023
...HAZARDOUS HEAT FROM THE SOUTH-CENTRAL U.S TO THE SOUTHWEST TO
MODERATE NEXT WEEK...
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
ON THE LARGE SCALE, THE GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT
ON THE OVERALL PATTERN ACROSS THE U.S. WHICH FEATURES UPPER
RIDGING OVER THE SOUTH AND WEST GETTING SUPPRESSED BY A COUPLE OF
SYSTEMS MOVING THROUGH THE NORTHERN U.S. A SHORTWAVE INTO THE
GREAT LAKES EARLY PERIOD MAY BECOME A CLOSED LOW AROUND MID-NEXT
WEEK. THE GFS AND ECMWF ARE FAIRLY CONSISTENT WITH EACH OTHER AND
THE ENSEMBLES, BUT THE CMC IS DISPLACED NOTICEABLY TO THE NORTH
AND WAS NOT INCLUDED IN THE LATE PERIOD BLEND TODAY. THIS SYSTEM
SHOULD AMPLIFY TROUGHING OVER THE EAST LATER NEXT WEEK, ALSO
ALLOWING SOME RIDGING TO BUILD BACK IN ACROSS THE WEST AS A COUPLE
WEAKER SHORTWAVES MOVE THROUGH WELL NORTH IN CANADA.
THE WPC MEDIUM RANGE SUITE FOR TODAY USED A COMPOSITE BLEND OF THE
DETERMINISTIC MODELS DAYS 3-5/SUNDAY-TUESDAY. AFTER TUESDAY,
INCREASED USAGE OF THE ENSEMBLE MEANS EVENTUALLY REACHING A 50/50
BLEND WITH THE GFS AND ECMWF DUE TO GREATER UNCERTAINTIES IN THE
LATER PERIODS. THIS APPROACH MAINTAINS GOOD CONTINUITY WITH THE
PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
THE WPC DAY 4/5 EXCESSIVE RAINFALL OUTLOOKS (EROS) DENOTE MARGINAL
RISK AREAS FROM THE NORTHERN MID-ATLANTIC ACROSS NORTHERN NEW
ENGLAND SUNDAY INTO MONDAY AS CONVECTION LOOKS TO HAVE A
RELATIVELY BETTER FOCUS ALONG A FRONT AND FAVORABLE RIGHT ENTRANCE
REGION UPPER JET SUPPORT. GUIDANCE HAS ALSO TRENDED TO A MORE
ORGANIZED MAIN FRONTAL WAVE TO WRAP IN ATLANTIC MOISTURE. THE
"MARGINAL" RISKS ENCOMPASS RELATIVELY LOWER FFGS AND INCLUDES
FAVORED TERRAIN FROM THE POCONOS AND CATSKILLS TO THE ADIRONDACKS
AND THE GREEN/WHITE MOUNTAINS, HOWEVER MUCH OF THE NORTHEAST HAS
BEEN VERY DRY RECENTLY WHICH MAY LIMIT THE OVERALL FLOOD/FLASH
FLOOD THREAT. RAIN CHANCES SHOULD GRADUALLY DECREASE AFTER MONDAY
ALONG THE EASTERN SEABOARD AS THE WAVY FRONTS PUSH EAST OFF THE
COAST BUT THE NEXT SYSTEM TO MOVE IN COULD BRING ANOTHER THREAT
FOR HEAVY RAINFALL, THOUGH STILL WITH PLENTY OF UNCERTAINTY
SURROUNDING THE DETAILS.
UPSTREAM, AN AMPLIFIED SYSTEM WILL SKIRT THE PACIFIC NORTHWEST
SUNDAY TO SUPPORT MODEST COASTAL SHOWERS. UNDERNEATH, A SERIES OF
LESS DEFINED SOUTHERN STREAM SHORTWAVES WILL WORK INLAND ACROSS
THE WEST COAST AND INTERMOUNTAIN WEST IN A PATTERN WITH LIMITED
PRECIPITATION THIS WEEKEND AND NEXT WEEK. THIS ENERGY WILL WORK
DOWNSTREAM TO THE NORTH-CENTRAL ROCKIES AND DIG INTO THE PLAINS TO
SUPPORT MORE WIDESPREAD AND LOCALLY STRONG TO SEVERE CONVECTION,
WHERE SOME HEAVY RAIN TOTALS ARE LIKELY UNDER FAVORABLE UPPER
DIFLUENCE AND POTENTIAL CELL TRAINING. THE WPC DAY 4/SUNDAY AND
DAY 5/MONDAY EROS DENOTE MARGINAL RISK AREAS SPREAD FROM THE
CENTRAL TO SOUTHERN PLAINS. ANTECEDENT CONDITIONS ARE VERY DRY
ACROSS THIS REGION, AND THIS PRECLUDES AN EMBEDDED SLIGHT RISK AT
THIS TIME, DESPITE SOME FAIRLY DECENT MODEL QPFS.
HAZARDOUS LATE SUMMER HEAT WILL LINGER ACROSS THE SOUTH-CENTRAL
U.S. AND THE SOUTHWEST UNDER A POTENT UPPER RIDGE INTO MONDAY.
HIGH DEWPOINTS AND HUMIDITY ESPECIALLY NEAR THE WESTERN GULF COAST
WILL LEAD TO DANGEROUS HEAT INDICES AS HIGH AS 115 DEGREES WITH
TEMPERATURES ELEVATED AT 10-15 DEGREES ABOVE NORMAL. EXPECT
WIDESPREAD RECORD HIGH MINIMUM AND MAXIMUM TEMPERATURES WILL BE
SET. UPPER-LEVEL ENERGY TRENDING SOUTHWARD WILL ACT TO REDUCE
RIDGE STRENGTH AND BEGIN TO BRING TEMPERATURES TO STILL HOT BUT
MORE REASONABLE/NORMAL LEVELS ONWARD NEXT WEEK.
SANTORELLI
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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