336
FXUS02 KWNH 170659
PREEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT TUE JUN 17 2025
VALID 12Z THU JUN 19 2025 - 12Z MON JUN 23 2025
...FIRST SIGNIFICANT, DANGEROUS HEAT WAVE OF THE SEASON EXPECTED
ACROSS MUCH OF THE CENTRAL/EASTERN U.S. BEGINNING LATE THIS
WEEK/WEEKEND...
..GENERAL OVERVIEW
A SIGNIFICANT, DANGEROUS HEAT WAVE IS EXPECTED TO START THE SUMMER
ACROSS MUCH OF THE CENTRAL/EASTERN U.S. LATE THIS WEEK, THROUGH
THE WEEKEND, AND INTO NEXT WEEK AS A STRONG UPPER-LEVEL RIDGE
BEGINS TO BUILD IN. STORM TRACK NORTH OF THE RIDGE MAY BRING MCS
ACTIVITY AND HEAVY RAINFALL/FLASH FLOODING FROM THE UPPER
MIDWEST/GREAT LAKES TO THE INTERIOR NORTHEAST FRIDAY-SATURDAY. A
DEEP-UPPER TROUGH OVER THE WEST WILL BRING COOLER, BELOW AVERAGE
TEMPERATURES, WITH EVENTUAL LEAD FRONTAL SYSTEM DEVELOPMENT OVER
THE PLAINS BRINGING A RENEWED CHANCE FOR THUNDERSTORMS AND
POTENTIAL HEAVY RAINFALL/SEVERE WEATHER THREAT TO THE
CENTRAL/NORTHERN PLAINS AND MIDWEST EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT WITH THE DEPICTION
OF THE LARGE SCALE PATTERN THROUGH THE MEDIUM RANGE PERIOD. A
QAUSI-ZONAL 500MB FLOW PATTERN LATE THIS WEEK INTO THE FIRST HALF
OF THE WEEKEND IS FORECAST TO BECOME INCREASINGLY AMPLIFIED THROUGH
EARLY NEXT WEEK, SETTING THE STAGE FOR A HIGH CONFIDENCE,
SIGNIFICANT HEAT WAVE FROM THE PLAINS TO THE MID-ATLANTIC. MOST
GUIDANCE REMAINS WELL CLUSTERED DEPICTING THE LAST IN A SERIES OF
UPPER-WAVES IN THE ZONAL PATTERN WITH LEADING FRONTAL SYSTEM
PUSHING EAST OFF THE EAST COAST AND INTO THE ATLANTIC FRIDAY. THE
LATEST 12Z CMC IS MUCH FASTER AND THE 18Z GFS A BIT SLOWER COMPARED
TO THE 12Z GFS/ECMWF/UKMET, WHICH ARE ALSO SUPPORTED BY THE ECMWF
AIFS/GRAPHCAST, GFS GRAPHCAST, AND ENSEMBLE MEANS. THEN, ALL
GUIDANCE SHOWS THAT THE PATTERN WILL BEGIN TO AMPLIFY, WITH AN
UPPER-RIDGE INITIALLY OVER THE SOUTHWESTERN U.S. PROGRESSIVELY
BUILDING/EXPANDING NORTH AND EASTWARD THROUGH THE WEEKEND AND INTO
NEXT WEEK. MEANWHILE, AN UPPER-LOW ANCHORED OVER THE NORTHEASTERN
PACIFIC WILL DROP SOUTHWARD, WITH DEEPENING UPPER-TROUGHING
OVERSPREADING THE WESTERN U.S. MOST OF THE UNCERTAINTY IS WITH
REGARDS TO UPPER-LEVEL SHORTWAVE(S) AND LEADING SURFACE FRONTAL
SYSTEM DEVELOPMENT OVER THE PLAINS AS THE UPPER-TROUGH MAKES SLOW
EASTWARD PROGRESSION THROUGH THE WEEKEND, WITH AT LEAST A COUPLE
ROUNDS OF CYCLOGENESIS OVER THE PLAINS POSSIBLE. THE ECMWF,
GRAPHCAST GFS, AND MEANS FAVOR ONE MAIN SURFACE LOW, WHILE THE
LATEST 12Z RUNS OF THE GFS, CMC, AND ECMWF AIFS/GRAPHCAST,
ESPECIALLY THE 18Z GFS, SUGGEST AT LEAST ONE INITIAL UPPER WAVE
WILL LIFT A SYSTEM NORTHWARD AHEAD OF THE MAIN DEVELOPMENT FOCUSED
OVER THE PLAINS. OTHER THAN THESE SPECIFICS THOUGH, GUIDANCE SHOWS
THE MAIN, LARGER- SCALE FEATURES OF THE PATTERN WITH UPPER-RIDGING
IN THE EASTERN U.S. AND UPPER-TROUGHING IN THE WESTERN U.S. WILL
REMAIN THROUGH THE PERIOD INTO EARLY NEXT WEEK, THOUGH EXPECT A
GENERAL WEAKENING OF THE UPPER-TROUGH WITH TIME.
THE UPDATED WPC FORECAST USES A BLEND OF THE 12Z ECMWF/UKMET AS
WELL AS THE 12Z/18Z GFS BUT NOT THE CMC GIVEN THE OTHER GUIDANCE IS
GENERALLY WELL CLUSTERED. THE 12Z GFS IS EVENTUALLY FAVORED OVER
THE 18Z AS ITS DEPICTION OF LEADING WAVE ENERGY AHEAD OF THE UPPER-
TROUGH IS MORE SIMILAR TO OTHER AVAILABLE GUIDANCE WHILE THE 18Z
GFS IS SIGNIFICANTLY MORE AGGRESSIVE IN DEEPENING A LIFTING SURFACE
LOW. A CONTRIBUTION FROM THE MEANS IS STEADILY ADDED UP TO 45% OF
THE BLEND AS UNCERTAINTIES WITH THESE SMALLER
-SCALE DETAILS OVER THE CENTRAL U.S. GROW.
..WEATHER/HAZARDS HIGHLIGHTS
LATE WEEK/WEEKEND WILL BRING A PATTERN CHANGE AS AN AMPLIFYING
UPPER-LEVEL RIDGE OVER THE CENTRAL/EASTERN U.S. SHIFTS THE STORM
TRACK NORTHWARD AND BRINGS A PERIOD OF DRIER CONDITIONS TO MANY
AFTER UNSETTLED WEATHER MUCH OF THE WEEK. EMBEDDED IMPULSES WITHIN
THE UPPER-RIDGE WILL TRIGGER CONVECTION, POTENTIALLY ORGANIZED,
ACROSS THE UPPER MIDWEST/GREAT LAKES FRIDAY (DAY 4) AND GREAT
LAKES/INTERIOR NORTHEAST SATURDAY (DAY 5). A MARGINAL RISK ERO IS
IN PLACE FOR BOTH DAYS AS A STRONG LOW LEVEL JET AND HIGH
PRECIPITABLE WATER VALUES (UP TO 2 STANDARD DEVIATIONS ABOVE THE
MEAN) SUPPORT THE THREAT OF HEAVY RAINFALL AND AT LEAST ISOLATED
FLASH FLOODING. AN EMBEDDED SLIGHT RISK LOOKS POSSIBLE BASED ON
FORECAST QPF VALUES WITH MORE CONFIDENCE IN AREAL PLACEMENT OF THIS
ORGANIZED CONVECTION. DAILY SHOWERS AND THUNDERSTORMS ARE ALSO
EXPECTED IN VICINITY OF THE GULF COAST AS A FRONTAL BOUNDARY
LINGERS IN THE REGION AND WITH POSSIBLE INFLUENCE OF TROPICAL
MOISTURE FOR THE WESTERN GULF COAST/SOUTH TEXAS. THIS INFLUX OF
MOISTURE ALSO LOOKS TO BRING PRECIPITATION CHANCES FURTHER
NORTHWEST INTO WESTERN TEXAS AND THE SOUTHERN HIGH PLAINS BY LATE
WEEKEND/EARLY NEXT WEEK. UPSTREAM, THE ENERGETIC APPROACH OF A DEEP
UPPER- TROUGH/PACIFIC SYSTEM AND NORTHERN STREAM INTO THE WEST
WILL BRING INCREASING PRECIPITATION CHANCES TO THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES/PLAINS FRIDAY THROUGH THE WEEKEND IN
UNSETTLED FLOW WITH MODERATE TO HEAVY RAINFALL POTENTIAL. A
MARGINAL RISK ERO HAS BEEN ADDED FOR FRIDAY (DAY 4) FOR PORTIONS OF
NORTH-CENTRAL MONTANA GIVEN THE PRESENCE OF STRONG, VERY MOIST
UPSLOPE FLOW TO SUPPORT HEAVY RAINFALL. EVENTUAL LEAD FRONTAL
SYSTEM DEVELOPMENT OVER THE PLAINS WILL BRING A RETURN OF
THUNDERSTORM CHANCES TO PORTIONS OF THE NORTHERN/CENTRAL PLAINS AND
MIDWEST SUNDAY AND PARTICULARLY MONDAY- TUESDAY, WITH POTENTIAL
FOR MORE HEAVY RAINFALL/FLASH FLOODING AS WELL AS SEVERE WEATHER.
THE FIRST SIGNIFICANT HEAT WAVE OF THE SEASON IS EXPECTED ACROSS
THE CENTRAL PLAINS BY FRIDAY, THE MIDDLE/UPPER MISSISSIPPI VALLEY
BY SATURDAY, AND THE LOWER GREAT LAKES/OHIO VALLEY/MID-ATLANTIC BY
SUNDAY THANKS TO ANOMALOUS UPPER-LEVEL RIDGING BUILDING OVERHEAD.
SUMMER HEAT WILL ALSO BEGIN TO INTENSIFY ACROSS THE LOWER
MISSISSIPPI VALLEY AND SOUTHEAST AS THE RIDGE EXPANDS EASTWARD.
WIDESPREAD MAJOR TO EXTREME HEAT RISK (LEVELS 3 AND 4/4) IS
FORECAST, INDICATING AN INTENSITY OF HEAT THAT IS DANGEROUS TO
ANYONE WITHOUT ADEQUATE COOLING OR HYDRATION, AS HEAT INDICES CLIMB
INTO THE 100-110 DEGREE RANGE, POTENTIALLY HIGHER. IN ADDITION,
MUGGY OVERNIGHT LOWS IN THE MID- TO UPPER 70S WILL BRING LITTLE
OVERNIGHT RELIEF FROM THE HEAT. UNFORTUNATELY, THIS HEAT WAVE LOOKS
TO PERSIST THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. HIGHS WILL
BEGIN TO TREND COOLER AND BELOW AVERAGE BY AS MUCH AS 10-20 DEGREES
ACROSS PORTIONS OF THE PACIFIC NORTHWEST BY FRIDAY AND EXPAND INTO
THE GREAT BASIN AND NORTHERN ROCKIES/HIGH PLAINS BY THE WEEKEND AS
AN UPPER LEVEL TROUGH AND ASSOCIATED SURFACE COLD FRONT FROM THE
NORTHEAST PACIFIC BEGIN TO OVERSPREAD THE REGION.
PUTNAM
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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