268
FXUS02 KWBC 251947
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
347 PM EDT THU JUN 25 2026
VALID 12Z SUN JUN 28 2026 - 12Z THU JUL 02 2026
***SIGNIFICANT, DANGEROUS HEAT WAVE BEGINS SUNDAY ACROSS MUCH OF
THE CENTRAL TO EASTERN U.S.***
..PATTERN OVERVIEW
AN ANOMALOUS UPPER LOW DIGGING INTO THE NORTHWESTERN STATES WILL
PUT AN END TO THE HEAT WAVE ACROSS THE SOUTHWEST AND EVEN LEAD TO
SOME HIGHER ELEVATION SNOW FOR THE MONTANA AND IDAHO ROCKIES. THIS
TROUGH WILL SPUR SURFACE CYCLOGENESIS ACROSS THE PLAINS WITH AN
OCCLUDED LOW LIFTING NORTH ACROSS SOUTH-CENTRAL CANADA. IN
CONTRAST, A BUILDING DOWNSTREAM UPPER RIDGE ACROSS THE EAST-CENTRAL
U.S. WILL RESULT IN INCREASINGLY DANGEROUS HEAT AND HUMIDITY GOING
INTO MUCH OF NEXT WEEK WITH WIDESPREAD 90S ACROSS THE EASTERN HALF
OF THE COUNTRY. SHOWERS AND THUNDERSTORMS WILL BE MOST LIKELY
ACROSS THE GULF COAST REGION, THE SOUTHERN ROCKIES, AND THE UPPER
MIDWEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST 00/12 UTC MODEL GUIDANCE IS FAIRLY AGREEABLE ON THE
OVERALL PATTERN THROUGH THE FIRST PART OF THE PERIOD. GUIDANCE
INDICATES THE UPPER-FLOW WILL AMPLIFY FURTHER AS AN UPPER-TROUGH
THAT WILL BE DIGGING SOUTHWARD OVER THE WESTERN U.S. EARLY THIS
WEEKEND IS THEN COMPLEMENTED BY AN UPPER-HIGH BUILDING OVER THE
MISSISSIPPI VALLEY TO SOUTHEAST LATE WEEKEND AND INTO EARLY NEXT
WEEK. THE GUIDANCE IS ALSO NOW WELL CLUSTERED DEPICTING AN INITIAL
UPPER-LEVEL SHORTWAVE ROUNDING THE TROUGH AND LIFTING NORTHWARD ON
THE WESTERN SIDE OF THE RIDGE, LEADING TO DEEP LEE CYCLOGENESIS
OVER THE NORTHERN/CENTRAL PLAINS. GUIDANCE AGREES THE PROGRESS OF
THIS SYSTEM WILL GENERALLY BE RATHER SLOW GIVEN THE POTENT UPPER-
HIGH/RIDGE TO THE EAST THROUGH EARLY NEXT WEEK. THE GUIDANCE THEN
NOTABLY DIVERGES INTO THE LATER PART OF THE PERIOD WITH THE
EVOLUTION OF THIS SYSTEM AS THE 00Z ECMWF (AND ECMWF AIFS) SHOWS
THE UPPER-ENERGY/SURFACE LOW LIFTING NORTHWARD WHILE THE 12Z
GFS/CMC PROGRESS EASTWARD AND GENERALLY SHEAR OUT WHILE ROUNDING
THE TOP OF THE UPPER-RIDGE, THE GFS FIRST THEN THE CMC. DETAILS ARE
NOT SURPRISINGLY LESS CLEAR IN THE ENSEMBLE MEANS THOUGH THEY DO
TEND TO SUPPORT A MIDDLE GROUND SIMILAR TO THE GFS AS OPPOSED TO
THE OTHER DETERMINISTIC GUIDANCE. THE CMC HAS ALSO TENDED TO TREND
WEAKER WITH THE UPPER-HIGH EXPANDING OVER THE MISS/OHIO VALLEYS AND
SOUTHEAST COMPARED TO THE OTHER GUIDANCE AND THE MEANS. THE
UPDATED WPC FORECAST INITIALLY USED A COMPOSITE BLEND OF THE 00Z
ECMWF/ECMWF AIFS/UKMET AND 12Z GFS/CMC GIVEN THE GOOD OVERALL
AGREEMENT. THE CONTRIBUTION FROM THE DETERMINISTIC GUIDANCE WAS
SIGNIFICANTLY REDUCED ASIDE FROM THE GFS FOR THE LATTER HALF OF THE
PERIOD AND REPLACED BY A CONTRIBUTION FROM THE GEFS/ECENS/CMC
MEANS GIVEN THE NOTED DIVERGING SOLUTIONS FROM THE ECMWF/ECMWF
AIFS/CMC.
..WEATHER/HAZARDS HIGHLIGHTS
THERE SHOULD BE AN OVERALL DECREASE IN RAINFALL COVERAGE GOING
INTO SUNDAY ACROSS MOST OF THE COUNTRY COMPARED TO THE SHORT RANGE
FORECAST PERIOD. THERE WILL LIKELY BE SOME SHOWERS AND STORMS NEAR
THE COASTAL CAROLINAS AS A WEAK WAVE OF LOW PRESSURE DEVELOPS
OFFSHORE. RAIN AND MOUNTAIN SNOW OVER CENTRAL AND WESTERN MONTANA
SHOULD STILL BE ONGOING, WITH SEVERAL INCHES OF SNOW ACCUMULATION
POSSIBLE FOR THE HIGHEST MOUNTAIN RANGES. LOOKING AHEAD TO
MONDAY/TUESDAY, A CORRIDOR OF SHOWERS AND STORMS, SOME OF WHICH
COULD BE HEAVY, ARE FORECAST TO DEVELOP FROM NEBRASKA TO THE UPPER
PENINSULA OF MICHIGAN AHEAD OF THE COLD FRONT CROSSING THE UPPER
MIDWEST.
ELSEWHERE ACROSS THE COUNTRY, SOME THUNDERSTORMS ARE LIKELY TO
DEVELOP IN THE VICINITY OF THE DRYLINE ACROSS WESTERN TEXAS AND
EASTERN NEW MEXICO FOR THE FIRST HALF OF THE WEEK, WITH A HIGHER
TREND COMPARED TO PREVIOUS FORECASTS. SCATTERED SHOWERS AND
THUNDERSTORMS ARE EXPECTED FROM THE CENTRAL GULF COAST TO THE
FLORIDA PENINSULA WITH MOISTURE INCREASING SOUTH OF THE UPPER
RIDGE, WITH MOST OF THESE HAPPENING DURING THE AFTERNOON AND
EVENING HOURS.
A TEMPERATURE DICHOTOMY WILL EXIST ACROSS THE COUNTRY STARTING
THIS WEEKEND AS THE DEEP UPPER TROUGH HERALDS THE ARRIVAL OF MUCH
COOLER CONDITIONS STARTING ACROSS THE PACIFIC NORTHWEST AND
NORTHERN ROCKIES, WITH HIGHS RUNNING ON THE ORDER OF 15-25 DEGREES
BELOW LATE JUNE AVERAGES. THIS WILL LIKELY BE COLD ENOUGH TO COME
CLOSE TO SOME NEW DAILY RECORD LOW TEMPERATURES. THE OPPOSITE WILL
HOLD TRUE ACROSS MUCH OF THE PLAINS, MIDWEST, SOUTHEAST, AND MID-
ATLANTIC AS THE BUILDING UPPER-RIDGE BRINGS A SIGNIFICANT,
DANGEROUS HEAT WAVE BEGINNING SUNDAY. HIGHS IN THE 90S ARE EXPECTED
AS FAR NORTH AS THE GREAT LAKES AND MINNESOTA, AND 100S FOR MUCH
OF TEXAS. SOME 100+ DEGREE READINGS ARE ALSO POSSIBLE FOR PORTIONS
OF THE SOUTHEAST BY THURSDAY. HEAT INDICES APPROACHING 110-115
DEGREES ARE POSSIBLE FROM THE MID-SOUTH TO THE CENTRAL GULF COAST
WHERE THE COMBINATION OF HEAT AND HIGH DEWPOINTS WILL BE GREATEST.
OVERNIGHT LOWS WILL ALSO BE QUITE WARM, WITH SOME RECORD HIGH
MINIMUMS POSSIBLE, BRINGING LITTLE TO KNOW RELIEF FROM THE HEAT.
PUTNAM/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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY MESSAGES
ARE AT:
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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