165
FXUS02 KWBC 041900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SUN AUG 4 2024
VALID 12Z WED AUG 7 2024 - 12Z SUN AUG 11 2024
...HEAVY RAIN AND MAJOR FLASH FLOODING INCREASINGLY LIKELY TO
CONTINUE FOR AREAS OF THE SOUTHEAST INTO THE MIDDLE TO LATE PARTS
OF THE WEEK FROM DEBBY...
...EXCESSIVE HEAT CONTINUES 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
THE 12Z MODEL GUIDANCE SUITE MAINTAINS GOOD OVERALL AGREEMENT ON
THE SYNOPTIC SCALE ACROSS THE CENTRAL AND WESTERN U.S. FOR THE
MIDDLE OF THE WEEK, BUT THE GREATEST UNCERTAINTY EXISTS WITH THE
EVENTUAL TRACK OF DEBBY NEAR THE COASTAL CAROLINAS FOR THE SECOND
HALF OF THE WORK WEEK. THE LATEST NHC TRACK FAVORS A SCENARIO
BETWEEN THE ECMWF AND THE EC MEAN, AND THIS WAS USED AS A BASELINE
FOR THE UPDATED QPF FORECAST. WITH A COL IN PLACE ACROSS THE
SOUTHEAST U.S. IN THE WAKE OF THE DEPARTING TROUGH ACROSS THE
NORTHEAST, STEERING FLOW ALOFT WILL BE RATHER WEAK AND
DISORGANIZED, RESULTING IN A SEVERE SLOW DOWN FOR THE TROPICAL
CYCLONE AND MODEL GUIDANCE TYPICALLY STRUGGLES IN THESE TYPES OF
SITUATIONS. THE CMC HAS SPED UP CONSIDERABLY COMPARED TO ITS 12Z
RUN, WHEREAS THE UKMET IS MUCH LESS PROGRESSIVE COMPARED TO ITS
PRIOR RUN. MEANWHILE, THE GFS CONTINUES THE IDEA OF BRINGING THE
WEAKENING STORM INLAND ACROSS SOUTHERN ALABAMA AND GEORGIA, BUT
THIS SOLUTION DOES NOT HAVE AS MUCH MACHINE LEARNING OR ENSEMBLE
SUPPORT AS THE ECMWF SOLUTION. IN FACT, SOME OF THE MACHINE
LEARNING MODELS TAKE THE LOW CLOSER TO THE SOUTHERN APPALACHIANS,
WHERE THE OPERATIONAL ECMWF/CMC/UKMET FAVOR A TRACK OVER THE
COASTAL PLAIN OF THE MID-ATLANTIC WHILE STEADILY WEAKENING.
THEREFORE, THE MODEL PREFERENCE WAS HEDGED MORE IN THE DIRECTION OF
THE ECMWF/EC MEAN ALONG WITH SOME OF THE GFS/CMC EARLIER IN THE
FORECAST PERIOD. SOME PREVIOUS WPC CONTINUITY WAS ALSO INCLUDED.
..WEATHER/HAZARDS HIGHLIGHTS
SLOW MOTION TO DEBBY RAISES THE THREAT FOR EXTREME RAINFALL IN THE
SOUTHEAST. A MODERATE RISK FOR EXCESSIVE RAINFALL IS NOTED FOR THE
COAST OF SOUTH CAROLINA INTO THE GA COAST WEDNESDAY AND THURSDAY
IN VICINITY OF THE LOW CENTER, WHICH IS FORECAST TO BE NEAR THE
CENTRAL SOUTH CAROLINA COAST FOR WEDNESDAY NIGHT BEFORE TURNING
SLOWLY NORTHEAST ON THURSDAY. THE DAY 4 AREA IS QUITE SIMILAR TO
THE PREVIOUS DAY 5 WITH EXPANSION OF THE MODERATE RISK AROUND
SAVANNAH. FOR THE UPDATED DAY 5 ERO, THE MODERATE RISK AREA WAS
REDUCED IN SIZE NEAR EASTERN SOUTH CAROLINA TO ACCOUNT FOR LOWER
QPF TRENDS DURING THIS TIME. 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 DAY 5 ERO ALSO FEATURES A
SLIGHT UP THROUGH SOUTH-CENTRAL VA FOR SUCH FRONTAL CONVERGENCE
PRECIP. IT IS POSSIBLE A SLIGHT MAY EVENTUALLY BE NEEDED FOR
PORTIONS OF SOUTHERN NEW ENGLAND GIVEN A STRONGER QPF SIGNAL IN THE
ECMWF AND UKMET GUIDANCE WITH THE POTENTIAL PRE EVENT.
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.
HAMRICK/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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