498
FXUS02 KWBC 052113
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
513 PM EDT MON AUG 5 2024
VALID 12Z THU AUG 08 2024 - 12Z MON AUG 12 2024
...HEAVY RAIN AND FLASH FLOODING THREAT ASSOCIATED WITH DEBBY EXPECTED
TO SPREAD UP THE EAST COAST TOWARD NEW ENGLAND LATE THIS WEEK...
...EXCESSIVE HEAT CONTINUES FOR PORTIONS OF TEXAS AND CENTRAL GULF
COAST THURSDAY INTO THIS WEEKEND...
..OVERVIEW
THE NATIONAL HURRICANE CENTER FORECAST TRACK FOR DEBBY TAKES IT UP
THE EASTERN SEABOARD THURSDAY INTO THIS WEEKEND WHERE THERE IS THE
THREAT FOR HEAVY RAINFALL ALONG WITH GUSTY WINDS. LATEST MODEL
GUIDANCE HAS TRENDED TOWARD GREATER FRONTAL INTERACTION OF
TROPICAL MOISTURE ASSOCIATED WITH DEBBY LEADING TO INCREASING
HEAVY RAIN POTENTIALS UP TOWARD NEW ENGLAND. UPPER RIDGING
CENTERED NEAR THE FOUR CORNERS WILL MAINTAIN MONSOONAL FLOW OVER
THE SOUTHWEST THROUGH THIS WEEKEND WITH HEAT CONCERNS SHIFTING
SOUTH AHEAD OF THE RIDGE, OVER TEXAS TO THE CENTRAL GULF COAST
(AREAS WEST OF DEBBY'S CLOUD COVER).
..GUIDANCE/PREDICTABILITY ASSESSMENT
WITH DEBBY COMING ONSHORE AND FORECAST TO MEANDER NEAR/OVER THE
SOUTHEAST U.S., HEAVY RAINFALL WILL OBVIOUSLY BE THE MAJOR FOCUS
DURING THE MEDIUM-RANGE PERIOD. A KEY QUESTION REGARDING HOW FAR
NORTH THE HEAVY RAINFALL WILL SURGE UP THE EAST COAST WILL BE HOW
MUCH INTERACTION OF AN UPPER TROUGH DIPPING INTO THE NORTHERN
PLAINS WILL CAUSE THE TROPICAL MOISTURE ASSOCIATED WITH DEBBY TO
LIFT NORTHWARD. RECENT MODEL AND ENSEMBLE CONSENSUS HAVE CONTINUED
TO INDICATE A NOTICEABLY QUICKER MOTION OF THE NORTHERN PLAINS
UPPER TROUGH TOWARD THE EASTERN U.S. THIS SETUP WOULD RESULT IN A
MORE ROBUST INTERACTION BETWEEN THE UPPER TROUGH AND THE
CIRCULATION OF DEBBY DURING THE MEDIUM-RANGE PERIOD, LEADING TO A
QUICKER NORTHWARD EXPANSION OF THE HEAVY RAIN UP THE EAST COAST
LATE THIS WEEK TOWARD/INTO NEW ENGLAND BY THE WEEKEND. THIS SETUP
IS BEARING RESEMBLANCE TO COLD SEASON EAST COAST CYCLOGENESIS OUT
OF A TRIPLE-POINT LOW, EXCEPT THAT DEBBY IS ACTING AS THE TRIPLE-
POINT LOW WITH TROPICAL MOISTURE BEING LIFTED AND OVERRUN A COASTAL
FRONT AS WELL AS ANOTHER FRONTAL BOUNDARY FARTHER INLAND.
ELSEWHERE, MODEL SOLUTIONS AGREE RATHER WELL EVEN INTO DAY 7. THE
WPC MEDIUM-RANGE FORECASTS WERE DERIVED BASED ON 40% FROM THE 06Z
GFS/GEFS, 40% FROM THE 00Z EC/EC MEAN, AND 20% FROM THE 00Z CMC/CMC
MEAN, WHILE LEANING TOWARD THE CONSENSUS OF THE ENSEMBLE MEANS.
THE QPF FROM THE 06Z GFS WAS MINIMIZED ACROSS GEORGIA ON DAY 4 DUE
TO GFS'S TRACK OF DEBBY BEING TOO FAR TO THE WEST.
..WEATHER/HAZARDS HIGHLIGHTS
GIVEN THE TREND OF A MORE ROBUST INTERACTION OF THE NORTHERN STREAM
TROUGH WITH DEBBY, DAY 4 MODERATE RISK FOR EXCESSIVE RAINFALL HAS
BEEN EXPANDED NORTHWARD INTO SOUTHERN VIRGINIA, AND WESTWARD TOWARD
THE FOOTHILLS OF THE APPALACHIANS, WITH A CORRESPONDING EXPANSION
OF THE SLIGHT RISK. WITH THE NORTHWARD TREND OF THE HEAVY RAINFALL
CONTINUES INTO DAY 5, THE SLIGHT RISK ERO HAS BEEN EXPANDED FROM
THE MID-ATLANTIC THROUGH NEW ENGLAND. A MODERATE RISK OF ERO HAS
BEEN HELD OFF IN ORDER TO ACCOMMODATE LOCAL OFFICE'S IDSS
CONSTRAITS AS WELL AS INHERENT FORECAST UNCERTAINTY. HOWEVER, A
MODERATE RISK WITHIN THE SLIGHT RISK AREA APPEARS WARRANTED IN
FUTURE ERO UPDATES.
MONSOONAL MOISTURE ON THE WESTERN SIDE OF THE RIDGE WILL KEEP A
WET AND UNSETTLED PATTERN IN PLACE FROM THE FOUR CORNERS REGION
NORTHWARD INTO THE ROCKIES/HIGH PLAINS THROUGH MUCH OF THE EXTENDED
PERIOD. MARGINAL RISKS FOR EXCESSIVE RAIN ARE IN EFFECT FOR PARTS
OF THE SOUTHWEST/FOUR CORNERS (ESPECIALLY THE SENSITIVE SLOT
CANYONS IN SOUTHERN UTAH) THROUGH THE NORTHERN HIGH PLAINS THURSDAY
WITH A SLIGHT RISK MAINTAINED FOR DAY 4 OVER NORTHERN NM/SOUTHERN
CO WHERE HIGHER QPF IS NOTED. A SLIGHT RISK HAS BEEN INTRODUCED ON
DAY 5 FROM THE FOOTFILLS OF THE CENTRAL ROCKIES TO THE ADJACENT
HIGH PLAINS.
ABOVE SEASONAL NORMAL TEMPERATURES ACROSS THE SOUTHWEST AND
SOUTHERN PLAINS ON WEDNESDAY ARE FORECAST TO TREND TOWARD NORMAL
INTO THE WEEKEND AS THE RIDGE SUPPRESSES SOUTH UNDER TROUGHING
ALONG THE CANADIAN BORDER. HAZARDOUS HEAT IS LIKELY FOR TEXAS AND
LOWER MISSISSIPPI VALLEY/CENTRAL GULF COAST LATE THIS WEEK INTO THE
WEEKEND. EXPERIMENTAL HEATRISK VALUES ARE GENERALLY MAJOR FOR MUCH
OF THIS REGION WITH EXTREME FOR THE CENTRAL GULF COAST AREA. MUCH
OF THE CENTRAL U.S. WILL COOL OFF IN THE WAKE OF A COLD FRONT
MIDWEEK.
KONG/JACKSON
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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