035
FXUS02 KWBC 290621
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 AM EDT MON JUN 29 2026
VALID 12Z THU JUL 02 2026 - 12Z MON JUL 06 2026
...SIGNIFICANT, DANGEROUS, AND RECORD BREAKING HEAT WAVE EXPECTED
NEXT WEEK FOR THE CENTRAL TO EASTERN U.S...
..PATTERN OVERVIEW
THE PERIOD BEGINS THURSDAY WITH A STRONG RIDGE ANCHORED OVER THE
EASTERN HALF OF THE COUNTRY, SUPPORTING A SIGNIFICANT AND DANGEROUS
HEAT WAVE. MEANWHILE AN AMPLIFIED TROUGH WILL BE OVER THE WEST TO
START THE PERIOD, WITH SOME ENERGY WORKING TO SUPPRESS THE EASTERN
RIDGE SLIGHTLY BY NEXT WEEKEND AS A SHORTWAVE SLIDES INTO THE GREAT
LAKES. RIDGING MAY BUILD BACK ACROSS THE SOUTH-CENTRAL PLAINS BY
LATER IN THE PERIOD AS WELL. SHOWERS AND THUNDERSTORMS WILL BE MOST
LIKELY OVER THE UPPER MIDWEST/GREAT LAKES, THE GULF COAST, AND
EVENTUALLY ACROSS THE EAST NEXT WEEKEND AND EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GOOD AGREEMENT CONTINUES AMONGST THE LATEST GUIDANCE FOR AT LEAST
THE LARGE SCALE PATTERN, BUT THE DETAILS REMAIN UNCERTAIN ACROSS
THE WEST AND SPECIFICALLY THE EVOLUTION OF ENERGY AS IT PROGRESSES
NORTHEASTWARD AND FINALLY BREAKS DOWN THE EASTERN RIDGE. CONFIDENCE
AND PREDICTABILITY IS HIGH FOR THE LARGE UPPER RIDGE CENTERED OVER
THE EAST TO START THE PERIOD, WITH BASICALLY ALL GUIDANCE SHOWING
A CLOSED 594DM CONTOUR THAT PERSISTS THROUGH AT LEAST FRIDAY. OUT
WEST, A SHORTWAVE OVER THE NORTHWEST BY THURSDAY WILL DRIFT
EASTWARD WITH TIME, EVENTUALLY WORKING TO BREAK DOWN THE RIDGE OVER
THE EAST. SOME OF THE GUIDANCE SHOWS GRADUAL AMPLIFICATION OF THIS
FEATURE AS WELL WHICH SHOULD ALLOW FOR RIDGING TO BUILD BACK
UPSTREAM OVER THE SOUTH-CENTRAL AND SOUTHWEST U.S.. CONFIDENCE IS
INCREASING THAT THE RIDGE SHOULD WEAKEN BY THE END OF THE PERIOD,
BUT THE TIMING OF WHEN THIS BEGINS IS STILL QUITE UNCERTAIN. THE
GUIDANCE IS MIXED ON HOW STRONG THIS SHORTWAVE WILL BE AS IT MOVES
INTO THE GREAT LAKES/MIDWEST EARLY NEXT WEEK. THERE IS ALSO SOME
TIMING UNCERTAINTIES ON ANOTHER TROUGH ENTERING THE NORTHWEST LATE
PERIOD AS WELL.
THE WPC FRONTS/PRESSURES FORECAST FOR TONIGHT USED A BLEND OF THE
DETERMINISTIC GUIDANCE FOR THE FIRST HALF OF THE PERIOD, GRADUALLY
INCREASING WEIGHTING OF THE ENSEMBLE MEANS TO 60 PERCENT OF THE
BLEND BY THE LATTER HALF. GENERALLY MAINTAINED GOOD AGREEMENT WITH
THE PREVIOUS WPC FORECAST, WITH SENSIBLE WEATHER ADJUSTMENTS TO THE
NBM NEEDED PRIMARILY FOR MAX T AND AFTERNOON DEWPOINTS.
..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. SPANNING THE SHORT TO MEDIUM RANGE PERIOD, PEAKING
AROUND THURSDAY OR FRIDAY OF THIS WEEK. 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/MS 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 CLOUDS/CONVECTION. ABOVE NORMAL TEMPERATURES SHOULD
EXPAND WESTWARD INTO THE SOUTHERN AND CENTRAL PLAINS AS WELL, WITH
TEMPERATURES OUT WEST NEAR TO BELOW NORMAL UNDERNEATH OF THE UPPER
TROUGH.
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 BOTH THE DAY 4/THURSDAY AND DAY 5/FRIDAY
EXCESSIVE RAINFALL OUTLOOKS. 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.
ELSEWHERE, DIURNALLY DRIVEN SHOWERS AND STORMS ARE 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 BY NEXT WEEKEND AS THE UPPER RIDGE SLIGHTLY WEAKENS
AND UPPER LEVEL ENERGY INTRUDES 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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page