556
FXUS02 KWBC 221958
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
358 PM EDT MON JUN 22 2026
VALID 12Z THU JUN 25 2026 - 12Z MON JUN 29 2026
***ADDITIONAL HEAVY RAIN FOR THE CENTRAL PLAINS AND VERY HOT
CONDITIONS FOR THE DESERT SOUTHWEST THROUGH FRIDAY***
***HAZARDOUS HEAT TO DEVELOP THIS WEEKEND ACROSS THE SOUTH***
..GENERAL OVERVIEW
A RELATIVELY ZONAL UPPER LEVEL FLOW PATTERN IS EXPECTED TO BE IN
PLACE FOR THE BEGINNING OF THE FORECAST PERIOD THURSDAY, AND THE
UPPER RIDGE OVER THE SOUTHWEST STATES WEAKENS AFTER FRIDAY. THIS
WILL BE DUE TO AN AMPLIFYING TROUGH OVER THE NORTHWESTERN QUADRANT
OF THE COUNTRY OVER THE WEEKEND, BRINGING A WELCOMED COOL DOWN
AFTER A HOT WEEK. THIS STRONG TROUGH WILL SUPPORT AN ORGANIZED LOW
PRESSURE SYSTEM THAT WILL EMERGE FROM THE ROCKIES TO THE
CENTRAL/NORTHERN PLAINS WITH A RELATIVELY POTENT COLD FRONT
CROSSING THE PACIFIC NORTHWEST AND INTERMOUNTAIN WEST. THIS WILL
LIKELY RESULT IN A DOWNSTREAM UPPER RIDGE DEVELOPING OVER THE EAST-
CENTRAL U.S. TOWARDS EARLY NEXT WEEK WITH A BUILDING HEATWAVE OVER
THE SOUTH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST OF THE LATEST 00/06Z UTC GUIDANCE REMAINS WELL-CLUSTERED ON
THE GENERAL PATTERN THROUGH THE MEDIUM RANGE PERIOD LATE THIS WEEK,
THROUGH THE WEEKEND, AND INTO EARLY NEXT WEEK. GUIDANCE INDICATES
THE PATTERN WILL BEGIN TO SHIFT FROM MORE ZONAL TO AMPLIFIED FLOW
FIRST AS A BROAD UPPER-TROUGH BEGINS TO DIG OVER THE WESTERN U.S.
AND THEN AS AN UPPER-HIGH DEVELOPS OVER THE SOUTHEASTERN U.S.
VARIABLE UPPER-WAVE TIMING IN THE FLOW NOT SURPRISINGLY LEADS TO A
BIT MORE UNCERTAINTY ON TEMPERATURES AND PRECIPITATION,
PARTICULARLY LATER IN THE PERIOD AS THE MEAN UPPER-FLOW BEGINS TO
SHIFT NORTHWARD OVER FROM THE ROCKIES EASTWARD, THOUGH THE NBM
LOOKED LIKE A GOOD STARTING POINT OVERALL THROUGH AT LEAST THE LATE
WEEK. THE GUIDANCE BEGINS TO DIVERGE A BIT MORE INTO THE WEEKEND
PARTICULARLY AS ONE UPPER-WAVE ROUNDS THE TROUGH AND THEN EJECTS
EASTWARD ONTO THE NORTHERN PLAINS, LEADING TO DEEP LEE CYCLOGENESIS
AND SYSTEM DEVELOPMENT. THE 00Z CMC IS MUCH FASTER/MORE SOUTHERLY
COMPARED TO THE 00Z/06Z GFS AND THEN 00Z ECMWF WHICH IS THE
SLOWEST. HEAVIER PRECIPITATION OVER THE NORTHERN ROCKIES/PLAINS AND
THROUGHOUT THE MIDWEST INTO THE OHIO/TENNESSEE VALLEYS LOOKS
LIKELIER COMPARED TO THE DRIER NBM, THOUGH DIFFERENCES WITH THE
TIMING/PROGRESSION OF UPPER-WAVES/SURFACE SYSTEM REFLECTION LEAD TO
GREATER UNCERTAINTY ON COVERAGE AND GENERAL LOCATION. THE UPDATED
WPC FORECAST WAS BASED ON AN INITIAL COMPOSITE BLEND OF THE 00Z
ECMWF/ECMWF AIFS/CMC/UKMET AND 06Z GFS GIVEN THE GOOD AGREEMENT ON
THE MAIN FEATURES. THE CMC WAS REMOVED MID- TO LATE PERIOD (UKMET
IS ALSO TIME-LIMITED) AND REPLACED BY A CONTRIBUTION FROM THE
ECENS/GEFS MEANS GIVEN THE NOTED DIVERGENCE IN THE SOLUTIONS AND
THE MORE OUTLIER NATURE OF THE CMC WITH THIS GUIDANCE CYCLE.
..WEATHER/HAZARDS HIGHLIGHTS
MULTIPLE MESOSCALE CONVECTIVE SYSTEMS ARE LIKELY TO AFFECT MUCH OF
THE CENTRAL PLAINS AND EXTENDING EASTWARD TO INCLUDE THE OHIO
VALLEY THROUGH THE END OF THE WEEK AND INTO THE WEEKEND, WITH SOME
AREAS GETTING AN ADDITIONAL 2-4 INCHES OF RAIN OVER ALREADY
SATURATED GROUNDS FROM RECENT HEAVY RAINFALL. A LINGERING FRONTAL
BOUNDARY WITH SHORTWAVE ENERGY ALOFT AND STRONG MOISTURE
CONVERGENCE WILL PROVIDE ENOUGH INSTABILITY AND LIFT TO SUSTAIN
THESE THUNDERSTORM COMPLEXES, AND SOME OF THESE STORMS COULD
PRODUCE FLASH FLOODING. A DAY 4/THURSDAY SLIGHT RISK ERO STRETCHES
FROM THE CENTRAL PLAINS TO THE OZARKS WITH A DAY 5/FRIDAY MARGINAL
ERO FROM THE OZARKS VICINITY EAST IN TO THE OHIO/TENNESSEE VALLEYS
TO COVER THIS THREAT. SOME STRONG TO SEVERE THUNDERSTORMS ARE ALSO
A DISTINCT POSSIBILITY, PARTICULARLY ACROSS THE WESTERN HIGH PLAINS
ON THURSDAY. AT LEAST SCATTERED THUNDERSTORM CHANCES LOOK TO
CONTINUE THROUGH THE MIDWEST INTO THE OHIO/TENNESSEE VALLEYS INTO
THE WEEKEND AS A FRONTAL BOUNDARY LINGERS AND THEN LIFTS NORTHWARD
THROUGH THE REGION.
ELSEWHERE ACROSS THE NATION, RAINFALL INCREASES FOR WASHINGTON AND
OREGON TO CLOSE OUT THE WORK WEEK WITH THE STORM SYSTEM MOVING
THROUGH THE REGION, AND A LARGER AREA OF HEAVIER RAINFALL DEVELOPS
ACROSS THE DAKOTAS AS THE MAIN SURFACE LOW EJECTS EASTWARD OVER THE
NORTHERN PLAINS BY THE WEEKEND. HEAVY PRECIPITATION IS LOOKING
MORE LIKELY ALONG THE NORTHERN ROCKIES ON THE BACK SIDE OF THE
SYSTEM WHILE HEAVY RAIN AND A POSSIBLE RISK FOR FLASH FLOODING IS
ALSO LOOKING MORE LIKELY ACROSS PORTIONS OF THE NORTHERN PLAINS
SUNDAY. SCATTERED SHOWERS AND THUNDERSTORMS ARE ALSO EXPECTED FOR
THE EAST COAST THROUGH SATURDAY WITH INCREASING LOW LEVEL MOISTURE
IN PLACE.
THE WIDESPREAD ABOVE AVERAGE HEAT LEVELS ACROSS THE WESTERN THIRD
OF THE NATION ARE LIKELY TO CONTINUE GOING INTO THURSDAY, WITH 110S
LIKELY FOR THE LOWER ELEVATIONS OF THE DESERT SOUTHWEST, AND 90S
EXTENDING AS FAR NORTH AS SOUTHERN IDAHO. A STRONG COLD FRONT
BRINGS RELIEF FROM THE HEAT STARTING FRIDAY AND BECOMING EVEN MORE
NOTICEABLE GOING INTO THE WEEKEND AS HIGHS RETURN TO BELOW AVERAGE
BY LATE JUNE STANDARDS, WHEREAS OVERNIGHT LOWS SHOULD BE LESS
ANOMALOUS. THE OPPOSITE HOLDS TRUE FURTHER EAST AS THE UPPER-HIGH
BEGINS TO DOMINATE THE WEATHER PATTERN. HIGHS ACROSS THE SOUTHERN
HIGH PLAINS ARE LIKELY TO INCREASE INTO THE 100S WHILE A
COMBINATION OF HIGHS IN THE 90S AND HIGH HUMIDITY WITH BRING HEAT
INDICES INTO THE 100-105 DEGREE RANGE (LOCALLY UP TO 110) ACROSS
THE SOUTH. THIS LEVEL OF HEAT WILL BE MORE LIKELY TO BE A DANGER TO
ANYONE WITHOUT ADEQUATE COOLING OR HYDRATION, PARTICULARLY
OUTDOORS. UNFORTUNATELY, THIS LOOKS TO BE A PROLONGED HEAT WAVE
LASTING INTO NEXT WEEK AND LIKELY EXPANDING FURTHER NORTH IN
COVERAGE.
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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