576
FXUS02 KWBC 270555
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
155 AM EDT SAT JUN 27 2026
VALID 12Z TUE JUN 30 2026 - 12Z SAT JUL 04 2026
...SIGNIFICANT, DANGEROUS HEAT WAVE EXPECTED NEXT WEEK FOR THE
CENTRAL TO EASTERN U.S...
..PATTERN OVERVIEW
THE PATTERN DURING THE UPCOMING MEDIUM RANGE LOOKS TO BE HIGHLY
AMPLIFIED MOST OF THE PERIOD WITH A STRONG UPPER HIGH/RIDGE OVER
THE EASTERN HALF OF THE U.S. AND A DEEP TROUGH OVER THE WEST. THIS
TROUGH WILL BE REINFORCED THROUGH THE PERIOD BY A SERIES OF
SHORTWAVES, WITH SOME ENERGY POSSIBLY ACTING TO SUPPRESS THE
EASTERN RIDGE SLIGHTLY BY NEXT WEEKEND. IN THE EAST, A SPRAWLING
UPPER HIGH WILL RESULT IN INCREASINGLY DANGEROUS HEAT AND HUMIDITY
THROUGH MUCH OF NEXT WEEK (AND POSSIBLY BEYOND INTO THE JULY 4TH
HOLIDAY WEEKEND). SHOWERS AND THUNDERSTORMS WILL BE MOST LIKELY
ACROSS THE GULF COAST/FLORIDA REGION, THE SOUTHERN ROCKIES, AND THE
UPPER MIDWEST TO GREAT LAKES/NORTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE MAINTAINS GOOD AGREEMENT WITH ITS DEPICTION OF
THE LARGE SCALE PATTERN THROUGH MOST OF THE MEDIUM RANGE PERIOD.
CONFIDENCE AND PREDICTABILITY REMAINS HIGH FOR A LARGE UPPER RIDGE
INITIALLY CENTERED OVER THE MID-MISSISSIPPI VALLEY EARLY IN THE
PERIOD BEFORE SLOWLY SHIFTING EASTWARD AND WEAKENING SLIGHTLY BY
THE END OF THE WEEK. OUT WEST, SHORTWAVES WILL ACT TO REINFORCE
TROUGHING ACROSS THE REGION MUCH OF THE PERIOD. UNCERTAINTY
INCREASES BY MID WEEK WITH PLACEMENT AND TRACK OF AN UPPER LOW INTO
THE NORTHWEST. THE GFS SEEMS MOST AGGRESSIVE WITH THIS FEATURE AND
WAS NOT PREFERRED. BY LATE WEEK, THERE IS SOME CONSENSUS FOR
WESTERN U.S. ENERGY TO RIDE OVER THE TOP OF THE EASTERN RIDGE,
WHICH MAY ACT TO SUPPRESS IT SLIGHTLY. THE ECMWF SEEMS LESS
ENTHUSED WITH THIS SCENARIO, HANGING ONTO A STRONGER RIDGE INTO THE
WEEKEND. THE WPC FORECAST FOR TONIGHT USED A BLEND OF THE
DETERMINISTIC GUIDANCE EARLY ON, TRANSITIONING TO A 50/50 BLEND OF
THE ECMWF/ECAIFS/CMC WITH THE ENSEMBLE MEANS. OVERALL, MAINTAINED
GOOD AGREEMENT WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
THE MOST IMPACTFUL WEATHER HAZARD DURING THE MEDIUM RANGE PERIOD
WILL BE A LONG LASTING HEAT WAVE AFFECTING MUCH OF THE CENTRAL TO
EASTERN U.S. BEGINNING DURING THE SHORT RANGE PERIOD AND LASTING
THROUGH THE MEDIUM RANGE PERIOD. WIDESPREAD TEMPERATURES INTO THE
90S TO LOW 100S, COMBINED WITH HIGH HUMIDITY, WILL RESULT IN HEAT
INDICES APPROACHING OR EXCEEDING 105-110 IN MANY PLACES. THIS
EQUATES TO WIDESPREAD MAJOR TO EXTREME HEATRISK FROM THE MIDWEST/MS
VALLEY EASTWARD TO THE EAST COAST. OVERNIGHT LOWS WILL ALSO BE
QUITE WARM, WITH SOME RECORD HIGH MINIMUMS POSSIBLE, BRINGING
LITTLE TO NO RELIEF FROM THE HEAT IN THE NIGHTTIME HOURS.
RAIN AND THUNDERSTORMS WILL DEVELOP ASSOCIATED WITH A FRONTAL
SYSTEM ACROSS PARTS OF THE UPPER MIDWEST AND GREAT LAKES TUESDAY-
WEDNESDAY. SOME OF THIS ACTIVITY WILL LIKELY MAKE ITS WAY INTO
PARTS OF THE NORTHEAST AS WELL AS IT ROUNDS THE NORTHERN PERIPHERY
OF THE MID/UPPER LEVEL RIDGE. WHILE MUCH OF THIS SHOULD BE FAIRLY
PROGRESSIVE, MOISTURE ANOMALIES AND INSTABILITY MAY SUPPORT A
LOCALIZED FLASH FLOOD THREAT. WPC CONTINUES TO HIGHLIGHT PARTS OF
THE UPPER MIDWEST AND THE INTERIOR NORTHEAST WITH MARGINAL RISKS ON
BOTH THE DAY 4/TUESDAY AND DAY 5/WEDNESDAY EXCESSIVE RAINFALL
OUTLOOK.
ELSEWHERE, MOISTURE FUNNELING BETWEEN THE WESTERN TROUGH AND THE
EASTERN RIDGE SHOULD SUPPORT SHOWERS AND THUNDERSTORMS ACROSS PARTS
OF THE SOUTHERN ROCKIES AND SOUTHERN HIGH PLAINS FOR AT LEAST THE
EARLY PART OF THE WEEK. A MARGINAL RISK ERO REMAINS FOR DAY
4/TUESDAY. DIURNALLY DRIVEN SHOWERS AND STORMS ARE ALSO EXPECTED
FROM THE CENTRAL GULF COAST TO FLORIDA WITH MOISTURE INCREASING
SOUTH OF THE UPPER RIDGE. SHOWERS MAY INCREASE ACROSS PARTS OF THE
OHIO VALLEY AND EAST LATE WEEK/NEXT WEEKEND AS THE UPPER RIDGE
SLIGHTLY WEAKENS AND UPPER LEVEL ENERGY TRIES TO INTRUDE INTO THE
REGION.
SANTORELLI
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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