719
FXUS02 KWBC 021918
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
318 PM EDT FRI AUG 2 2024
VALID 12Z MON AUG 05 2024 - 12Z FRI AUG 09 2024
...POTENTIAL TROPICAL CYCLONE FOUR WILL THREATEN PARTS OF FLORIDA
INTO THE COASTAL SOUTHEAST INTO NEXT WEEK...
...HAZARDOUS HEAT PERSISTS ACROSS THE SOUTHWEST EARLY NEXT WEEK AS
HEAT INTENSIFIES OVER THE SOUTH-CENTRAL U.S. AS THE WEEK PROGRESSES...
..OVERVIEW
THE NATIONAL HURRICANE CENTER HAS DESIGNATED POTENTIAL TROPICAL
CYCLONE FOUR, WHICH BY THE START OF THE MEDIUM RANGE PERIOD MONDAY
IS FORECAST TO HAVE CROSSED FLORIDA AND BE MAKING ITS WAY INTO THE
FAR WESTERN ATLANTIC NEAR THE SOUTHEAST COAST. THIS TROPICAL SYSTEM
WILL SPREAD HEAVY RAIN AND FLASH FLOODING AS WELL AS GUSTY WINDS
LINGERING IN FLORIDA AND PUSHING INTO THE COASTAL SOUTHEAST FOR THE
FIRST PART OF THE WEEK, WITH UNCERTAINTY IN THE TIMING AND HOW FAR
INLAND THE IMPACTS GET. FARTHER WEST, UPPER RIDGING CENTERED NEAR
THE FOUR CORNERS WILL MAINTAIN HEAT CONCERNS ACROSS THE WEST
THROUGH PARTS OF NEXT WEEK. THE RIDGING SHOULD GET SUPPRESSED BY
SHORTWAVES IN THE NORTHWEST BUT EXPAND EAST TO FOCUS POTENTIALLY
HAZARDOUS HEAT IN THE SOUTH-CENTRAL U.S. MID- TO LATE NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE FIRST MODEL DIAGNOSTICS CONCERN IS WITH THE TRACK, TIMING, AND
STRENGTH OF WHAT IS CURRENTLY POTENTIAL TROPICAL CYCLONE FOUR.
EVEN BY THE START OF THE PERIOD EARLY MONDAY, CONSIDERABLE
DIFFERENCES WERE EVIDENT IN THE MODEL GUIDANCE. AT LEAST IN
GENERAL, RECENT MODELS ARE MORE AGREEABLE IN SHOWING A TRACK FROM
THE FAR NORTHEASTERN GULF OF MEXICO CROSSING NORTHERN
FLORIDA/POSSIBLY SOUTHEASTERN GEORGIA INTO THE FAR WESTERN ATLANTIC
EARLY NEXT WEEK. GFS RUNS HAVE BEEN ON THE FASTER SIDE AND
STRONGEST WITH THE CYCLONE TAKING THIS TRACK. HOWEVER, THE 00Z CMC
WAS EVEN FASTER IN TRACKING THE LOW NORTHEAST, BUT THE NEWER 12Z
CMC WAS SLOWER BUT ALSO MORE INLAND. UKMET RUNS HAVE ALSO BEEN SLOW
AND INLAND. THE ECMWF SEEMED TO BE THE MOST REASONABLE MIDDLE
GROUND IN POSITION EARLY IN THE PERIOD, BUT INITIALLY ON THE WEAKER
SIDE. BY TUESDAY-WEDNESDAY THE GFS AND ECMWF ARE NOT TOO DIFFERENT
IN POSITION, AND THE AI/MACHINE LEARNING MODELS TENDED TO BE IN
BETWEEN. THIS TYPE OF MIDDLE GROUND SOLUTION MATCHED PRETTY WELL
WITH THE NHC FORECAST. HOW CLOSE TO LAND/INLAND THAT THE STORM
TRACKS WILL BE THE PRIMARY DRIVER OF QPF, ALONG WITH THE SPEED OF
THE SYSTEM. THEN AS THE WEEK PROGRESSES, THE POSSIBLE EJECTION OF
THE STORM NORTHEASTWARD IS UNCERTAIN AS WELL, DEPENDING ON IF AN
UPPER TROUGH STEERS IT NORTHEAST. THE 00Z ECMWF WAS GENERALLY ALONE
IN TAKING THE LOW NORTHWESTWARD TOWARD THE MID-ATLANTIC, AND NOW
THE NEW 12Z RUN RETROGRADES IT INTO THE TENNESSEE VALLEY. THE EC
SOLUTIONS APPEAR LESS LIKELY CONSIDERING THE FULL SUITE OF
GUIDANCE, BUT COULD OCCUR IF THE SYSTEM COMPLETELY MISSES THE
NORTHERN STREAM FLOW. ENSEMBLE MEMBERS ALSO ALSO SHOW AMPLE SPREAD.
FURTHER FORECAST ADJUSTMENTS WILL BE NEEDED AND SEE NHC FOR THE
OFFICIAL TRACK.
ELSEWHERE, UPPER RIDGING CENTERED NEAR THE FOUR CORNERS WEAKENING
A BIT WITH TIME IS AGREEABLE IN THE GUIDANCE, WHILE THE NORTHERN
STREAM SHORTWAVES ROUNDING THIS RIDGE AND MAKING THEIR WAY INTO THE
NORTHEASTERN U.S. SHOW MORE VARIABILITY. FRONTAL AND QPF
POSITIONING IN THE MIDWEST TO NORTHEAST VARIES BECAUSE OF THIS. A
BLEND OF MODELS/ENSEMBLES SEEMED REASONABLE THOUGH.
THE WPC FORECAST FAVORED THE 00Z ECMWF EARLY ON GIVEN ITS
INITIALLY FAVORABLE TRACK WITH POTENTIAL TC FOUR, WHILE EXCLUDING
THE SLOW 00Z UKMET AND THE FAST 00Z CMC. THIS ALSO WORKED FOR OTHER
AREAS. HOWEVER, RAMPED UP THE PROPORTION OF ENSEMBLE MEANS TO MORE
THAN HALF BY DAY 7 AS MODEL SPREAD INCREASED.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAIN IS LIKELY ALONG THE PATH OF POTENTIAL TC FOUR, BUT WITH
PLENTY OF UNCERTAINTY WITH HOW MUCH FALLS ONSHORE VERSUS OFFSHORE
DEPENDING ON THE SYSTEM'S EXACT TRACK. A SLIGHT RISK LINGERS INTO
MONDAY ACROSS NORTHERN FLORIDA WITH ANY FEEDER BANDS BEHIND THE
STORM, AND IS ALSO IN PLACE NORTHWARD INTO SOUTHEASTERN GEORGIA AND
EASTERN SOUTH CAROLINA FOR MONDAY/DAY 4. A SLIGHT RISK WAS
INTRODUCED FOR DAY 5/TUESDAY FOR MUCH OF THE COASTAL CAROLINAS AS
THE SYSTEM SLOWLY MOVES NORTHEAST. THESE RISK AREAS ATTEMPT TO
FOLLOW THE CURRENT FORECAST TRACK OF POTENTIAL TC 4, I.E. OFFSHORE
BUT NEAR ENOUGH TO LAND TO SPREAD HEAVY RAIN AMOUNTS THAT MAY CAUSE
FLASH FLOODING INLAND. EXPECT FURTHER ADJUSTMENTS AS THE FORECAST
EVOLVES.
FARTHER NORTH, MODELS SHOW A POTENTIAL MESOSCALE CONVECTIVE SYSTEM
RIDING THE TOP OF THE RIDGE INTO THE UPPER MIDWEST/UPPER GREAT
LAKES ON MONDAY. FOR THIS ACTIVITY, A MARGINAL RISK ON THE DAY 4
ERO STRETCHES FROM THE NORTHERN HIGH PLAINS TO THE LOWER GREAT
LAKES REGION WITH AN EMBEDDED SLIGHT RISK ACROSS PARTS OF SOUTHEAST
MINNESOTA AND SOUTHERN WISCONSIN GIVEN AMPLE MOISTURE,
INSTABILITY, AND SOME SOIL SENSITIVITY. WHILE RAINFALL AMOUNTS ARE
MORE UNCERTAIN FARTHER EAST, SOME GUIDANCE SHOWING 1-2 INCHES OF
RAIN ACROSS NORTHERN NEW ENGLAND IN AN UNSTABLE ENVIRONMENT FRONT
SEEMED TO WARRANT A MARGINAL RISK THERE. THEN BY DAY 5/TUESDAY,
MOISTURE STREAMS COULD COMBINE IN THE LOWER GREAT LAKES TO
NORTHEAST TO FOCUS RAIN NEAR THE FRONT IN WHAT MIGHT BE
CONSIDERED A PREDECESSOR RAIN EVENT (PRE). LACK OF MODEL
CONSISTENCY IN PLACEMENT OF RAIN AMOUNTS PRECLUDED ANY EMBEDDED
SLIGHT RISK WITHIN THE LARGER MARGINAL AT THIS TIME.
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 FOR MONDAY AND TUESDAY,
WITH SOME EXPANSION OF THE RISK AREA WEST ON TUESDAY WITH THE
MEANDERING MOISTURE PLUME AND TO COVER THE SENSITIVE SLOT CANYONS
IN SOUTHERN UTAH.
THE WEST CAN EXPECT ABOVE NORMAL TEMPERATURES INTO NEXT WEEK THAT
GRADUALLY REDUCE IN MAGNITUDE. THE SOUTHWEST SHOULD SEE THE
LONGEST-LASTING HEAT CONCERNS, WITH DAYTIME HIGHS EXCEEDING 110F
LIKELY, BUT THIS IS ONLY A FEW DEGREES ABOVE AVERAGE. MEANWHILE,
HAZARDOUS HEAT WILL BE LIKELY FOR THE CENTRAL/SOUTHERN PLAINS AND
MIDDLE/LOWER MISSISSIPPI VALLEY EARLY IN THE WEEK. AFTER A COLD
FRONT PASSES SOUTHWARD THROUGH THE CENTRAL U.S. TUESDAY-WEDNESDAY,
EXCESSIVE HEAT WILL THEN FOCUS ACROSS THE SOUTHERN PLAINS, LOWER
MISSISSIPPI VALLEY, AND SOUTHEAST. 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 WEAK SHORTWAVE ENERGIES MOVE
THROUGH.
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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