139
FXUS02 KWBC 261907
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
307 PM EDT FRI JUN 26 2026
VALID 12Z MON JUN 29 2026 - 12Z FRI JUL 03 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 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 SNOW
POSSIBLE AT THE HIGHEST ELEVATIONS OF THE NORTHERN ROCKIES
ASSOCIATED WITH ONE COMPACT UPPER LOW EARLY IN THE PERIOD. 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.
THE FEATURE THAT WILL CONTINUE TO HAVE THE MOST PREDICTABILITY IS
THE LARGE AND SPRAWLING 594+DM MID/UPPER LEVEL RIDGE THAT WILL
INITIALLY BE CENTERED OVER THE MID-MISSISSIPPI VALLEY EARLY IN THE
PERIOD BEFORE SLOWLY SHIFTING EASTWARD INTO THE CENTRAL
APPALACHIANS BY THE END OF NEXT WEEK. UPSTREAM OF THIS RIDGE, A
MEAN MID/UPPER LEVEL TROUGH WILL DRIVE THE PATTERN ACROSS THE
WESTERN U.S., WITH A SERIES OF RELATIVELY LOWER PREDICTABILITY
SHORTWAVES REINFORCING THE TROUGH THROUGH MOST OF NEXT WEEK. GIVEN
THE ABOVE, THE WPC FORECAST WAS DERIVED USING A BLEND OF MOSTLY
DETERMINISTIC AND MACHINE LEARNING GUIDANCE THROUGH DAY 5 BEFORE
SHIFTING MORE WEIGHT (60/40 SPLIT) TO THE EC AND GEFS ENSEMBLE
MEANS FOR DAYS 6 AND 7. THIS APPROACH LIMITED THE IMPACTS OF
SMALLER SCALE SPATIAL AND TEMPORAL DIFFERENCES (MAINLY WITH
TROUGHING IN THE WESTERN U.S.) LATER IN THE PERIOD WHILE
MAINTAINING CONTINUITY 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 THIS WEEKEND AND LASTING THROUGH NEXT WEEK,
AND LIKELY INTO THE JULY 4TH HOLIDAY WEEKEND AS WELL. 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 HEATRISK ACROSS THE
ENTIRE REGION, WITH AREAS OF EXTREME HEATRISK IN PARTS OF THE
MIDWEST AND OHIO VALLEY UNDERNEATH THE CORE OF THE UPPER HIGH.
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 MOUNTAIN SNOW WILL BE ONGOING INTO MONDAY FOR MUCH OF THE
NORTHERN ROCKIES, WITH SEVERAL INCHES OF SNOW ACCUMULATION FOR THE
HIGHEST MOUNTAIN RANGES. AHEAD OF THIS, RAIN AND THUNDERSTORMS MAY
DEVELOP ACROSS PARTS OF THE UPPER MIDWEST AND GREAT LAKES INTO
TUESDAY AHEAD/NORTH OF A LIFTING WARM FRONT THROUGH THE REGION.
SOME OF THIS ACTIVITY WILL LIKELY MAKE ITS WAY INTO PARTS OF THE
NORTHEAST BY MIDWEEK 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
THE DAY 5/TUESDAY 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 HAS BEEN INTRODUCED FOR
DAY 4/MONDAY AND MAINTAINED FOR DAY 5/TUESDAY TO ACCOUNT FOR ANY
LOCALIZED FLASH FLOODING CONCERNS. DIURNALLY DRIVEN SHOWERS AND
STORMS ARE ALSO EXPECTED FROM THE CENTRAL GULF COAST TO FLORIDA
WITH MOISTURE INCREASING SOUTH OF THE UPPER RIDGE.
SANTORELLI/MILLER
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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