340
FXUS02 KWBC 040707
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
307 AM EDT SUN AUG 4 2024
VALID 12Z WED AUG 07 2024 - 12Z SUN AUG 11 2024
...HEAVY RAIN AND FLASH FLOODING INCREASINGLY LIKELY TO CONTINUE FOR
AREAS OF THE SOUTHEAST IN THE MIDDLE TO LATE PARTS OF THE WEEK
FROM DEBBY...
...EXCESSIVE HEAT/MAJOR HEATRISK FOR THE SOUTHERN PLAINS TO
CENTRAL GULF COAST WEDNESDAY THROUGH FRIDAY...
..OVERVIEW
THE NATIONAL HURRICANE CENTER FORECAST FOR DEBBY REMAINS SLOW ALONG
THE SOUTHEAST COAST INTO THE CAROLINAS WED/THUR, INCREASING THE
THREAT OF VERY HEAVY RAINFALL OVER PORTIONS OF AT LEAST THE
COASTAL SOUTHEAST ALONG WITH GUSTY WINDS. UNCERTAINTY REMAINS WITH
THE TRACK FORECAST AND THE ASSOCIATED HEAVY RAINS, SO PLEASE STAY
ALERT TO FORECAST UPDATES.
UPPER RIDGING CENTERED NEAR THE FOUR CORNERS THROUGH AT LEAST
THURSDAY NIGHT WILL MAINTAIN MONSOONAL FLOW OVER THE SOUTHWEST WITH HEAT
CONCERNS SHIFTING SOUTH AHEAD OF THE RIDGE, OVER THE SOUTHERN
PLAINS TO THE CENTRAL GULF COAST (AREAS WEST OF DEBBY).
..GUIDANCE/PREDICTABILITY ASSESSMENT
VERY STRONG RIDGING OVER NORTHWESTERN CANADA PERSISTS THROUGH AT
LEAST THURSDAY WITH BROAD RIDGING OVER THE FOUR CORNERS REGION,
FAVORING ELONGATED (E-W) TROUGHING ACROSS MUCH OF SOUTHERN CANADA
LATER IN THE WEEK. WITH ADDITIONAL UPPER RIDGING OVER THE CENTRAL
ATLANTIC, THIS LEAVES TROUGHING OVER THE EAST COAST, ALLOWING
DEBBY TO DRIFT NORTHWARD LATER IN THE WEEK. THE LATEST NHC TRACK
FAVORS THE 12Z ECMWF FOR THE DAYS 4/5 TRACK THAT IS OVER THE
CAROLINAS, THOUGH THERE IS CONSIDERABLE SPREAD AMONG GLOBAL
GUIDANCE, SO EXPECT CHANGES TO THE FORECAST TRACK WHICH WILL HAVE
SIGNIFICANT IMPLICATIONS FOR THE RATHER HEAVY QPF GIVEN THE SLOW
MOTION. THE 12Z ECMWF WAS FAVORED FOR QPF DAYS 4/5 GIVEN ITS
SIMILARITY TO THE TRACK FORECAST, BUT THE 00Z ECWMF HAS COME IN
MORE PROGRESSIVE TO THE NORTH AFTER WEDNESDAY WHILE THE GFS RETAINS
A MUCH FARTHER INLAND TRACK OVER GA.
ELSEWHERE, UPPER RIDGING CENTERED NEAR THE FOUR CORNERS SUPPRESSING
SOUTH A BIT, THEN DRIFTING EAST TO THE SOUTHERN PLAINS WITH TIME
IS AGREEABLE IN THE GUIDANCE. TROUGHING OVER CANADA WILL STILL
SUPPORT AN EASTWARD- MOVING COLD FRONT THAT WILL EVENTUALLY MEET UP
WITH ANOTHER FRONTAL BOUNDARY HUNG UP NEAR THE EAST COAST ATOP
DEBBY.
..WEATHER/HAZARDS HIGHLIGHTS
SLOW MOTION TO DEBBY RAISES THE THREAT FOR VERY HEAVY RAIN IN THE
SOUTHEAST. A MODERATE RISK FOR EXCESSIVE RAINFALL IS NOTED FOR THE
COAST OF SOUTH CAROLINA INTO THE GA COAST WEDNESDAY AND THURSDAY
AROUND THE TRACK FOR THE CENTER OF THE SYSTEM WHICH IS FORECAST TO
BE JUST OFF THE SOUTHEAST COAST FOR WEDNESDAY BEFORE TURNING NORTH
THURSDAY. THE DAY 4 AREA IS QUITE SIMILAR TO THE PREVIOUS DAY 5
WITH EXPANSION OF THE MODERATE RISK AROUND SAVANNAH. FARTHER
NORTH, THE APPROACHING FRONT WILL LIKELY STALL AND LINGER TO THE
NORTH OF DEBBY, FAVORING A PRE SETUP WITH ADDITIONAL RAINFALL
STRETCHED NORTHEASTWARD ACROSS THE MID-ATLANTIC BY LATER IN THE
WEEK. THE NEW DAY 5 ERO FEATURES A SLIGHT UP THROUGH SOUTH-CENTRAL
VA FOR SUCH FRONTAL CONVERGENCE PRECIP. EXPECT FURTHER ADJUSTMENTS
AS THE FORECAST EVOLVES, ESPECIALLY GIVEN THE BROAD TRACK SOLUTIONS
AMONG THE 00Z GLOBAL GUIDANCE.
MONSOONAL MOISTURE ON THE WESTERN SIDE OF THE RIDGE SHOULD 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) WEDNESDAY AND THURSDAY WITH A SLIGHT RISK
RAISED FOR THURSDAY/DAY 5 OVER NORTHERN NM/SOUTHERN CO WHERE
HIGHER QPF IS NOTED..
ABOVE SEASONAL NORMAL TEMPERATURES ACROSS THE SOUTHWEST AND
SOUTHERN PLAINS ON WEDNESDAY ARE FORECAST TO TREND TOWARD NORMAL
THROUGH FRIDAY AS THE RIDGE SUPPRESSES SOUTH UNDER TROUGHING ALONG
THE CANADIAN BORDER. HAZARDOUS HEAT IS LIKELY FOR THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY THROUGH MIDWEEK, THEN SUPPRESS
SOUTH TO THE CENTRAL GULF COAST. 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.
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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