121
FXUS02 KWBC 300618
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
218 AM 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 LAST INTO NEXT WEEKEND FOR THE CENTRAL TO EASTERN U.S...
..PATTERN OVERVIEW
THE 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 HEAT WAVE BY AROUND SUNDAY FOR MOST PLACES. THIS SHOULD
ALSO ALLOW RIDGING TO BUILD BACK INTO THE SOUTHWEST REGION FOR
LATER IN THE PERIOD. SHOWERS AND STORMS INITIALLY ACROSS THE
NORTHERN TIER WILL EVENTUALLY EXPAND INTO THE OHIO VALLEY AND THE
EAST NEXT WEEKEND AS THE RIDGE WEAKENS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST 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 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. THERE ARE NOT REALLY ANY
CLEAR OUTLIERS IN THE LATEST MODEL CYCLE, SO THE WPC
FRONTS/PRESSURES FORECAST WAS BASED ON A GENERAL MODEL BLEND OF THE
DETERMINISTIC GUIDANCE FOR THE FIRST HALF OF THE PERIOD, GRADUALLY
INCREASING WEIGHTING OF THE ENSEMBLE MEANS TO JUST OVER HALF OF
THE BLEND BY THE LATTER HALF. THIS GENERALLY MAINTAINED GOOD
AGREEMENT WITH THE PREVIOUS WPC FORECAST, 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 ALSO BE QUITE WARM, WITH
NUMEROUS RECORD HIGH MINIMUMS POSSIBLE, BRINGING LITTLE TO NO
RELIEF FROM THE HEAT IN THE NIGHTTIME HOURS. 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 TROUGHING.
RAIN AND THUNDERSTORMS ASSOCIATED WITH A SLOW MOVING FRONTAL
BOUNDARY WILL IMPACT PARTS OF THE NORTHERN PLAINS TO UPPER MIDWEST
AND GREAT LAKES INTO NEXT WEEKEND. 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 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
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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