367
FXUS02 KWBC 301856
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT TUE JUN 30 2026
VALID 12Z FRI JUL 03 2026 - 12Z TUE JUL 07 2026
...SIGNIFICANT, DANGEROUS, AND RECORD BREAKING HEAT WAVE EXPECTED
TO SHIFT/LAST INTO THE WEEKEND FOR THE CENTRAL TO EASTERN U.S...
..PATTERN OVERVIEW
IT GENERALLLY REMAINS THE SAME THAT THIS MEDIUM-RANGE FORECAST
PERIOD BEGINS WITH A STRONG RIDGE ANCHORED OVER THE EASTERN HALF
OF THE COUNTRY, CONTINUING TO SUPPORT A SIGNIFICANT AND DANGEROUS
HEAT WAVE WHICH WILL BEGIN DURING THE SHORT RANGE PERIOD. ENERGY
OUT WEST SHOULD EVENTUALLY MAKE ITS WAY INTO THE NORTHERN PLAINS
AND GREAT LAKES, WORKING TO SUPPRESS THE RIDGE, BRINGING AN END TO
THE BROAD HEAT WAVE FOR MOST PLACES BY NEXT WEEK. HOWEVER, RIDGING
MAY BUILD BACK INTO THE SOUTHWEST U.S. REGION FOR LATER IN THE
PERIOD. SHOWERS AND STORMS INITIALLY ACROSS THE NORTHERN TIER WILL
EVENTUALLY EXPAND ACROSS THE OHIO VALLEY AND THE SOUTH/EAST NEXT
WEEKEND AS THE RIDGE GRADUALLY WEAKENS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT WITH THE SYNOPTIC SCALE
PATTERN, BUT UNCERTAINTY REMAINS WITH THE DETAILS/EVOLUTION OF
ENERGY TRAVERSING THE FLOW IN THE WEST AND THE TIMING OF RIDGE
BREAK DOWN OVER THE EAST. MOST OF THE GUIDANCE SHOW THE HEAT WAVE
PEAKING IN THE THURSDAY-FRIDAY TIME FRAME, AND BY THE WEEKEND
CONFIDENCE IS INCREASING THAT ENERGY FROM THE WEST SHOULD WORK INTO
THE MIMDWEST/GREAT LAKES WEAKENING THE RIDGE AND OVERALL
OPPRESSIVE HEAT. HOW QUICKLY AND HOW MUCH THE RIDGE IS SUPPRESSED
IS STILL IN QUESTION. THE AMPLITUDE OF THE SHORTWAVE FEATURE
REMAINS UNCERTAIN, BUT THERE SEEMS TO BE SOME TREND TOWARDS
SLIGHTLY LESS AMPLIFIED FLOW BY EARLY NEXT WEEK.
ACCORDINGLY, THE WPC FRONTS/PRESSURES PROGS WAS BASED ON A
BROAD BLEND OF COMPATIBLE MODEL AND ENSEMBLE MEAN GUIDANCE ALONG
WITH SOME MACHINE LEARNING GUIDANCE INPUT. THIS GENERALLY
MAINTAINED GOOD AGREEMENT WITH THE PREVIOUS WPC FORECAST AND THE
NBM, ALBEIT WITH SENSIBLE WEATHER ADJUSTMENTS TO THE NBM FOCUSED
PRIMARILY FOR MAX T AND AFTERNOON DEWPOINTS UNDERNEATH THE RIDGE.
..WEATHER/HAZARDS HIGHLIGHTS
A SIGNIFICANT AND MAJOR HEAT WAVE SET TO BEGIN BY THE MIDDLE OF
THIS WEEK WILL PEAK AT THE START OF THE MEDIUM RANGE PERIOD OVER
MUCH OF THE CENTRAL TO EASTERN U.S.. WIDESPREAD AND DAILY RECORD
BREAKING MAXIMUM TEMPERATURES INTO THE 90S TO LOW 100S, COMBINED
WITH HIGH HUMIDITY, WILL RESULT IN HEAT INDICES APPROACHING OR
EXCEEDING 105-110 IN MANY PLACES. SOME OF THESE VALUES MAY BREAK
ALL TIME RECORDS AS WELL. THIS EQUATES TO WIDESPREAD MAJOR TO
EXTREME HEATRISK FROM THE MIDWEST/MISSISSIPPI VALLEY EASTWARD TO
THE EAST COAST. OVERNIGHT LOWS WILL LINGER AND ALSO BE QUITE WARM,
WITH NUMEROUS RECORD HIGH MINIMUMS POSSIBLE, BRINGING LITTLE TO NO
RELIEF FROM THE HEAT IN THE NIGHTTIME HOURS. AFTERNOON HEAT MAY
FINALLY BEGIN TO ABATE FROM WEST TO EAST THIS WEEKEND, WITH UPPER
TEMPERATURE LIMITS POSSIBLY RESTRICTED BY INCREASING
CLOUDS/CONVECTION AS RIDGE BREAKDOWN BEGINS. ABOVE NORMAL
TEMPERATURES SHOULD EXPAND WESTWARD INTO THE SOUTHERN AND CENTRAL
PLAINS AS WELL, WITH TEMPERATURES OUT WEST NEAR TO BELOW NORMAL
UNDERNEATH OF GENERAL/WEAKENED TROUGHING.
RAIN AND THUNDERSTORMS ASSOCIATED WITH A SLOW MOVING AND WAVY FRONTAL
BOUNDARY OVER THE NORTHERN TIER OF THE NATION WILL IMPACT PARTS OF
THE NORTHERN PLAINS TO UPPER MIDWEST AND GREAT LAKES INTO NEXT
WEEKEND AND INTO EARLY NEXT WEEK. MOISTURE ANOMALIES AND
INSTABILITY WITHIN FAIRLY WEAK FLOW MAY SUPPORT AT LEAST A
LOCALIZED FLASH FLOOD THREAT. WPC HIGHLIGHTS MUCH OF THIS REGION
WITHIN A MARGINAL RISK FOR THE DAY 4/FRIDAY AND DAY 5/SATURDAY
EXCESSIVE RAINFALL OUTLOOKS. STORM CHANCES WILL EXPAND THIS WEEKEND
AND EARLY NEXT WEEK ACROSS MUCH OF THE OHIO/TENNESSEE VALLEYS AND
EAST AND ALSO SPREAD SOME TO THE SOUTH AS THE UPPER RIDGE WEAKENS,
BUT STILL WARM TEMPERATURES SUPPORT A MOIST AND UNSTABLE
ENVIRONMENT FOR AFTERNOON CONVECTION AHEAD OF A FRONTAL SYSTEM.
THIS REGION IS ALSO INCLUDED IN THE DAY 5 MARGINAL ERO.
ELSEWHERE, DIURNALLY DRIVEN SHOWERS AND STORMS ARE EXPECTED FROM
PARTS OF THE CENTRAL GULF COAST TO FLORIDA MOST OF THE PERIOD WITH
MOISTURE INCREASING SOUTH OF THE UPPER RIDGE. SHOWERS MAY REFIRE
AGAIN LATER IN THE PERIOD FOR PARTS OF THE SOUTHERN/CENTRAL ROCKIES
AND HIGH PLAINS, AS WELL AS THE NORTHERN TIER AHEAD OF ADDITIONAL
SHORTWAVE ENERGY.
SANTORELLI/SCHICHTEL
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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