220
FXUS02 KWBC 031902
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
302 PM EDT SAT AUG 3 2024
VALID 12Z TUE AUG 06 2024 - 12Z SAT AUG 10 2024
...HEAVY RAIN AND FLASH FLOODING INCREASINGLY LIKELY FOR AREAS OF
THE SOUTHEAST NEXT WEEK FROM TROPICAL CYCLONE FOUR...
...EXCESSIVE HEAT/MAJOR HEATRISK FOR THE SOUTHWEST AND INTO THE
PLAINS...
..OVERVIEW
THE NATIONAL HURRICANE CENTER CONTINUES TO FORECAST TROPICAL
CYCLONE FOUR TO TRACK INTO THE FLORIDA PANHANDLE BEFORE TURNING
EASTWARD INTO THE ATLANTIC JUST OFF THE GA/SC COAST AT THE START OF
THE PERIOD. THE FORECAST THEREAFTER CONTINUES TO TREND SLOWER,
INCREASING THE THREAT OF VERY HEAVY RAINFALL OVER PARTS OF AT LEAST
THE COASTAL SOUTHEAST NEXT WEEK ALONG WITH GUSTY WINDS.
FARTHER WEST, UPPER RIDGING CENTERED NEAR THE FOUR CORNERS WILL
MAINTAIN HEAT CONCERNS ACROSS THE WEST THROUGH PART OF NEXT WEEK.
THE RIDGING SHOULD GET SUPPRESSED BY SHORTWAVES IN THE NORTHWEST
BUT EXPAND EASTWARD TO FOCUS POTENTIALLY HAZARDOUS HEAT IN THE
SOUTH-CENTRAL U.S. MID- TO LATE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
UPPER PATTERN OVER NORTH AMERICA WILL FEATURE VERY STRONG RIDGING
OVER NORTHWESTERN CANADA WITH MODEST RIDGING OVER THE FOUR CORNERS
REGION, FAVORING ELONGATED (E-W) TROUGHING ACROSS MUCH OF SOUTHERN
CANADA. WITH ADDITIONAL UPPER RIDGING OVER THE CENTRAL ATLANTIC,
THIS LEAVES TROUGHING OVER THE EAST COAST, ALLOWING TROPICAL
CYCLONE FOUR A GATEWAY NORTHWARD THEN EASTWARD NEXT WEEK. THE
FORECAST HINGES ON THE CANADIAN RIDGING, AND WHETHER OR NOT IT WILL
DIP FAR ENOUGH SOUTH TO TUG OR PICK UP T.C. FOUR. THE TREND HAS
BEEN FOR WEAKER TROUGHING AND THUS A SLOWER MOVEMENT OF T.C. FOUR
NEAR THE SOUTHEAST COAST WITH THE POTENTIAL TO SLOWLY MOVE INLAND
BEFORE POSSIBLY THEN BEING PICKED UP LATER IN THE WEEK. THE LATEST
NHC TRACK FAVORS A SLOWING SOLUTION BUT BY NEXT FRI/SAT THERE IS A
LARGE DEGREE OF SPREAD FROM SW TO NE ANYWHERE OVER THE SOUTHEAST TO
ATLANTIC CANADA. FAVORED THE ENSEMBLE TREND (ALONG WITH THE
ECMWF/GFS) WITH A SLOWER EXODUS OF T.C. FOUR BUT SEE THE LATEST NHC
FORECAST FOR THE MOST UP-TO- DATE THINKING.
ELSEWHERE, UPPER RIDGING CENTERED NEAR THE FOUR CORNERS WEAKENING
A BIT WITH TIME IS AGREEABLE IN THE GUIDANCE. A BIT WEAKER
TROUGHING OVER CANADA WILL STILL SUPPORT AN EASTWARD-MOVING COLD
FRONT THAT WILL EVENTUALLY MEET UP WITH ANOTHER FRONTAL BOUNDARY
HUNG UP ALONG THE EAST COAST ATOP T.C. FOUR.
..WEATHER/HAZARDS HIGHLIGHTS
WITH A SLOWER TREND FOR T.C. FOUR, THE THREAT FOR VERY HEAVY RAIN
IN THE SOUTHEAST HAS INCREASED. A MODERATE RISK FOR EXCESSIVE
RAINFALL IS NOTED FOR THE COAST OF SOUTH CAROLINA BOTH TUESDAY AND
WEDNESDAY NEAR WHERE THE CENTER OF THE SYSTEM IS EXPECTED TO TURN
BACK TOWARD THE COAST. A BROADER SLIGHT RISK WAS DRAWN BEYOND THIS
AREA TO ACCOUNT FOR UNCERTAINTY IN THE TRACK/QPF. TOTAL RAINFALL
MAY WELL EXCEED TEN INCHES IN PLACES BUT WILL BE DEPENDENT ON
SEVERAL FACTORS. FARTHER NORTH, THE APPROACHING FRONT WILL LIKELY
STALL AND LINGER TO THE NORTH OF T.C. FOUR, FAVORING A PRE SETUP
WITH ADDITIONAL RAINFALL STRETCHED NORTHEASTWARD ACROSS THE MID-
ATLANTIC BY LATER IN THE WEEK. EXPECT FURTHER ADJUSTMENTS AS THE
FORECAST EVOLVES.
MODELS CONTINUE TO SHOW A POTENTIAL MESOSCALE CONVECTIVE SYSTEM
RIDING THE TOP OF THE RIDGE INTO THE UPPER MIDWEST/UPPER GREAT
LAKES ON MONDAY, AND THE MOISTURE WILL LIKELY CONTINUE EASTWARD ON
TUESDAY. A MARGINAL RISK FOR EXCESSIVE RAINFALL IS SHOWN IN THIS
REGION FOR NOW GIVEN THE UNCERTAINTY IN UPSTREAM EVOLUTION.
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) TUESDAY AND WEDNESDAY.
ABOVE SEASONAL NORMAL TEMPERATURES ACROSS THE WEST ARE ANTICIPATED
TO GRADUALLY LOWER THROUGH THE EXTENDED PERIOD. THE SOUTHWEST
SHOULD SEE THE LONGEST-LASTING HEAT CONCERNS, WITH DAYTIME HIGHS
EXCEEDING 100-110F LIKELY, BUT THIS IS ONLY A FEW DEGREES ABOVE
AVERAGE. HAZARDOUS HEAT WILL BE LIKELY FOR THE CENTRAL/SOUTHERN
PLAINS AND MIDDLE/LOWER MISSISSIPPI VALLEY EARLY IN THE WEEK. MUCH
OF THE CENTRAL U.S. WILL COOL OFF IN THE WAKE OF A COLD FRONT
MIDWEEK; HOWEVER, EXCESSIVE HEAT WILL THEN FOCUS ACROSS THE
SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND PERHAPS BACK INTO
THE SOUTHEAST ASSUMING T.C. FOUR LEAVES THE AREA. EXPERIMENTAL
HEATRISK VALUES ARE GENERALLY MAJOR FOR MUCH OF THIS REGION TO EVEN
EXTREME FOR THE CENTRAL GULF COAST AREA. THE NORTH- CENTRAL U.S.
SHOULD REMAIN NEAR TO BELOW NORMAL THROUGH THE PERIOD AS THE WEAK
COLD FRONT MOVES THROUGH.
FRACASSO/CAMPBELL/TATE
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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