980
FXUS02 KWNH 180639
PREEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 AM EDT FRI JUL 18 2025
VALID 12Z MON JUL 21 2025 - 12Z FRI JUL 25 2025
***MAJOR HEAT WAVE BUILDING FROM THE SOUTHEAST INTO PARTS OF THE
CENTRAL U.S. NEXT WEEK AND BEYOND***
..OVERVIEW
THE OVERALL WEATHER PATTERN NEXT WEEK WILL BE DOMINATED BY A
BUILDING UPPER LEVEL RIDGE THAT WILL BE SITUATED OVER THE DEEP
SOUTH AND EXTENDING NORTH TO THE TENNESSEE AND OHIO RIVER VALLEYS.
HEAT AND HUMIDITY BUILD TO DANGEROUS LEVELS ACROSS MUCH OF THE
CENTRAL U.S. AND EXTENDING TO THE SOUTHEAST STATES. AN ACTIVE FLOW
PATTERN WILL BE IN PLACE TO THE NORTH OF THIS HIGH AS MULTIPLE
SHORTWAVE IMPULSES TRACK EASTWARD OVER THE NORTHERN TIER STATES AND
THEN REACH NEW ENGLAND. A COLD FRONT PROVIDES SOME RELIEF FROM THE
RECENT HEAT AND HUMIDITY FROM THE MID-ATLANTIC TO THE NORTHEAST TO
START THE WEEK. MEANWHILE, AN UPPER LEVEL TROUGH LIKELY DEVELOPS
NEAR THE WEST COAST GOING INTO EARLY NEXT WEEK, WITH SOME POTENTIAL
FOR AN UPPER LOW TO DEVELOP.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 12Z MODEL GUIDANCE SUITE HAS A GOOD DEPICTION OF THE GENERAL
WEATHER PATTERN TO START NEXT WEEK, AND THUS A DETERMINISTIC MODEL
BLEND WORKS VERY WELL AS A STARTING POINT. BY THE MIDDLE OF THE
WEEK, THE GUIDANCE CONTINUES TO AGREE WELL REGARDING THE LARGE
UPPER HIGH CENTERED OVER THE MID-SOUTH, BUT VARIES MORE WITH JET
STREAM FLOW AND SHORTWAVE PASSAGES/FRONTS ACROSS THE NORTHERN TIER
STATES, WITH THE GFS A LITTLE STRONGER WITH A SHORTWAVE APPROACHING
THE NORTHERN GREAT LAKES BY THURSDAY, AND THE CMC A LITTLE SLOWER
IN BRINGING A TROUGH NEAR MONTANA. THERE REMAIN SOME PLACEMENT
DIFFERENCES WITH THE POTENTIAL UPPER LOW THAT DEVELOPS OFF THE
CALIFORNIA COAST LATE IN THE WEEK, BUT IT DOES NOT CURRENTLY APPEAR
TO HAVE A MAJOR EFFECT ON THE OVERALL FORECAST. THE ENSEMBLE MEANS
WERE GRADUALLY INCREASED TO ABOUT 40% BY FRIDAY.
..WEATHER/HAZARDS HIGHLIGHTS
IT REMAINS THE CASE THAT A CORRIDOR OF UNSETTLED WEATHER WILL
REMAIN IN PLACE FROM THE UPPER MIDWEST TO THE SOUTHEAST COAST FOR
THE BEGINNING OF THE WEEK. THUNDERSTORM COMPLEXES TRAVELING AROUND
THE NORTHERN PERIPHERY OF THE BIG UPPER HIGH WILL LIKELY PRODUCE
LOCALIZED AREAS OF HEAVY RAINFALL, POTENTIALLY EXCEEDING AN INCH
PER HOUR OR MORE. THEREFORE, A BROAD MARGINAL RISK AREA EXTENDS
FROM THE EASTERN DAKOTAS, THROUGH THE OHIO VALLEY, AND TO NORTHERN
FLORIDA AND THE COASTAL CAROLINAS FOR BOTH DAYS 4 AND 5 (MONDAY AND
TUESDAY). A SLIGHT RISK AREA HAS BEEN INTRODUCED FROM EASTERN IOWA
TO WEST-CENTRAL INDIANA ON MONDAY/DAY 4 WHERE THE GUIDANCE AND NBM
HAS A MORE CONCENTRATED QPF SIGNAL, WITH A HIGH CAPE AND HIGH PW
ENVIRONMENT IN PLACE, AND THIS IS ALSO ACROSS AREAS THAT ARE
EXPECTED TO HAVE NOTEWORTHY RAINFALL IN THE DAYS LEADING UP TO
THIS, WITH SOILS LIKELY TO BE QUITE SATURATED IN MANY CASES.
HEAT WILL ONCE AGAIN MAKE WEATHER HEADLINES FOR MUCH OF NEXT WEEK
ACROSS A LARGE PORTION OF THE SOUTHERN AND CENTRAL U.S. WITH A
LARGE UPPER HIGH BECOMING ANCHORED OVER THE MID-SOUTH. WIDESPREAD
MAJOR IMPACTS ON THE HEAT RISK SCALE ARE EXPECTED FROM THE CENTRAL
PLAINS TO THE SOUTHEAST STATES EARLY IN THE WEEK, AND THESE HIGHER
IMPACTS THEN REACH THE MIDWEST AND OHIO VALLEY BY MID TO LATE WEEK.
THIS WILL BE DUE TO WIDESPREAD HIGHS IN THE MIDDLE 90S TO LOW 100S
FOR MANY OF THESE AREAS, IN COMBINATION WITH DEWPOINTS WELL INTO
THE 70S, AND OVERNIGHT LOWS REMAINING UNCOMFORTABLY WARM. THIS WILL
LIKELY HAVE SOME STAYING POWER BEYOND THIS FORECAST PERIOD BASED
ON THE LATEST WEEK TWO OUTLOOK FROM THE CLIMATE PREDICTION CENTER
FROM THE CENTRAL PLAINS TO THE DEEP SOUTH.
ELSEWHERE ACROSS THE NATION, THERE SHOULD BE JUST ENOUGH MONSOONAL
MOISTURE IN PLACE ACROSS EASTERN ARIZONA AND MUCH OF NEW MEXICO,
AND PROBABLY EXTENDING INTO SOUTHERN PORTIONS OF COLORADO, AND
GIVEN THE POTENTIAL FOR SOME ISOLATED SLOW MOVING STORMS, A
MARGINAL RISK IS IN PLACE FOR BOTH MONDAY AND TUESDAY. ACROSS THE
EAST COAST REGION, A COLD FRONT IS FORECAST TO CLEAR THE NORTHEAST
AND THE MID-ATLANTIC REGION, AND BRINGING A HIGHER QUALITY AIRMASS
AFTER ALL OF THE HEAT AND OPPRESSIVE HUMIDITY LATELY AND LOWER RAIN
CHANCES. HOWEVER, THE HEAT WILL LIKELY RETURN TOWARDS THE END OF
THE WEEK AS THE CANADIAN SURFACE HIGH MOVES OFFSHORE AND A MORE
SOUTHERLY FLOW COMMENCES.
HAMRICK
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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