536
FXUS02 KWBC 271850
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 PM EDT SUN JUL 27 2025
...DANGEROUS HEAT WAVE PERSISTS IN THE SOUTHEAST THROUGH MIDWEEK
WITH GRADUAL RELIEF LATER IN THE WEEK...
...HEAVY RAIN AND FLASH FLOODING POTENTIAL IN THE CENTRAL PLAINS
FOR MULTIPLE DAYS...
..OVERVIEW
BY THE START OF THE MEDIUM RANGE PERIOD MIDWEEK, THE SPRAWLING
UPPER HIGH ATOP MUCH OF THE U.S. EARLY THIS WEEK WILL BE WEAKENING
SOMEWHAT AND BE PRESSED SOUTH BY A NORTHERN STREAM UPPER TROUGH.
DANGEROUS HEAT IS POSSIBLE ACROSS THE LOWER OHIO/TENNESSEE VALLEYS
AND MID-ATLANTIC WEDNESDAY BEFORE A COLD FRONT (TIED TO THE UPPER
TROUGH) MOVES THROUGH. THE SOUTHEAST IS FORECAST TO SEE THE HEAT
CONTINUE INTO LATE WEEK BUT GRADUALLY SHRINK IN SCOPE. COMPLEXES OF
SHOWERS AND STORMS ARE LIKELY NEAR AND AHEAD OF THE FRONTAL SYSTEM
STRETCHING FROM THE HIGH PLAINS EASTWARD ACROSS THE CENTRAL
PLAINS/MID-MISSISSIPPI VALLEY INTO THE NORTHEAST WEDNESDAY. THE
FRONT IS LIKELY TO STALL NEAR THE CENTRAL PLAINS AND LEAD TO
MULTIPLE DAYS OF STORMS WITH HEAVY RAIN THAT COULD CAUSE FLASH
FLOODING. FARTHER EAST THE COLD FRONT SHOULD BE MORE PROGRESSIVE,
MAKING ITS WAY SOUTHWARD ACROSS THE MID-ATLANTIC AND SOUTHEAST BUT
CREATING AN ENVIRONMENT FOR POSSIBLY HEAVY RAIN EACH DAY AS IT
MOVES. MEANWHILE, SOUTHERLY FLOW WILL BRING MONSOONAL MOISTURE INTO
PARTS OF THE SOUTHWEST STATES FOR POSSIBLY HEAVY RAIN.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT IS EXCELLENT FOR THE OVERALL PATTERN THROUGH LATE
THIS WEEK. MODELS HAVE BEEN PERSISTENT IN SHOWING THE EXPANSIVE
UPPER HIGH SHRINKING IN SCOPE BY WEDNESDAY AND BECOMING CENTERED
OVER THE SOUTHERN PLAINS LATE WEEK, WITH PERHAPS ANOTHER
SUBTROPICAL HIGH MOVING ACROSS FLORIDA. MEANWHILE THE RIDGE AXIS
WILL STRETCH NORTHWARD ACROSS THE NORTHERN ROCKIES INTO WESTERN
CANADA STARTING TUESDAY, COINCIDENT WITH THE UPPER TROUGH EDGING
INTO THE NORTH-CENTRAL TO NORTHEASTERN U.S. ANCHORED BY A LARGE
HUDSON BAY TO EASTERN CANADA UPPER LOW. SINCE MODEL DIFFERENCES
WERE MOSTLY NEGLIGIBLE THROUGH LATE WEEK, USED A DETERMINISTIC
BLEND OF THE LATEST 00Z/06Z GUIDANCE FOR THE FIRST HALF OF THE
FORECAST PERIOD. REGARDLESS OF THE LARGE SCALE AGREEMENT,
SHORTWAVES RIDING AROUND THE RIDGE WILL CAUSE MORE DIFFERENCES IN
SENSIBLE WEATHER LIKE FRONTAL PLACEMENT, AND CONVECTION WILL HAVE
FURTHER UNCERTAINTIES DUE TO SMALL BOUNDARIES LIKE OUTFLOWS
INTERACTING. THESE TEND NOT TO BECOME CLEARER UNTIL THE SHORT RANGE
OR NEAR TERM, SO THE DETAILS OF QPF REMAIN UNCERTAIN, BUT AT LEAST
THE OVERALL PATTERN SEEMS SET.
BY NEXT WEEKEND, MODEL DIFFERENCES START TO INCREASE AS THE
PATTERN BECOMES MORE QUASI-ZONAL AND UNCERTAIN SHORTWAVES BECOME
MORE DOMINANT. ONE LARGER SCALE MODEL DIFFERENCE WAS THE PATTERN IN
THE NORTHWEST ESPECIALLY BY NEXT SUNDAY. THIS WILL BE INFLUENCED
BY A LARGE NORTHEAST PACIFIC UPPER LOW WITH SOMEWHAT UNCERTAIN
PLACEMENT. THE MODELS HAVE WAVERED ON HOW MUCH AND HOW QUICKLY TO
LOWER HEIGHTS INTO THE NORTHWEST/ROCKIES WITH NO CLEAR CONSENSUS.
THE AI/ML MODELS INDICATED A BIT MORE TROUGHING EAST OF 120W THAN
THE DYNAMICAL ENSEMBLES, BUT THAT IS STILL LIKELY WITHIN THE
NOISE/SPREAD. BALANCE THE DAY 6-7 FORECAST WITH A BLEND OF SOME
ENSEMBLE MEAN WEIGHTING ALONG WITH CONTINUITY. THIS RESULTED IN FEW
CHANGES OVERALL FROM THE PREVIOUS FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
ANOTHER HOT DAY IS FORECAST FROM THE SOUTH-CENTRAL U.S. INTO THE
SOUTHEAST, TENNESSEE AND OHIO VALLEYS, AND MUCH OF THE EASTERN
SEABOARD ON WEDNESDAY UNDERNEATH THE (ALBEIT SHRINKING) UPPER HIGH.
HEATRISK IS MAINLY IN THE MAJOR (LEVEL 3/4) CATEGORY WITH SOME
EMBEDDED EXTREME (LEVEL 4/4) AREAS WITH HIGHS GENERALLY IN THE 90S
TO NEAR/EXCEEDING 100 WITH HIGHER HEAT INDICES (NEARING 110F),
WHILE MORNING LOWS WELL INTO THE 70S AND NEARING 80 WILL NOT
PROVIDE MUCH RELIEF. A FEW MORE DAILY RECORDS FOR TEMPERATURES
COULD BE SET INTO WEDNESDAY. ON THURSDAY, THE COLD FRONT WILL PASS
THROUGH THE OHIO VALLEY TO MID-ATLANTIC AND BRING NEAR TO BELOW
NORMAL TEMPERATURES, WITH THE HEAT WAVE BECOMING MORE LIMITED TO
THE SOUTHEAST/CAROLINAS. THE GRADUAL MOVEMENT OF THE FRONT
SOUTHWARD SHOULD FINALLY LEAD TO HEAT RELIEF IN THE SOUTHEAST
FRIDAY-SATURDAY, THOUGH FLORIDA COULD STILL BE HOT. COOLER THAN
AVERAGE TEMPERATURES (ESPECIALLY HIGHS) ARE LIKELY IN THE
NORTHERN/CENTRAL PLAINS ON THE COOL SIDE OF THE FRONT AND WITH THE
CLOUDS AND RAIN CHANCES -- SOME LOCATIONS MAY EVEN CHALLENGE RECORD
COOL MAXES FOR THE DAY (LOW 70S).
RAIN AND THUNDERSTORMS ARE FORECAST TO FOCUS ON THE PERIPHERY OF
THE RIDGE, ENHANCED BY A FRONTAL BOUNDARY ACROSS THE NORTHERN
ROCKIES INTO THE NORTH-CENTRAL PLAINS AND MISSISSIPPI VALLEY. SOME
SHORTWAVE FORCING AND ABOVE NORMAL MOISTURE AND INSTABILITY SHOULD
LEAD TO MULTIPLE ROUNDS OF CONVECTION WITH HIGH RAIN RATES, AND
SOME AREAS COULD SEE REPEATING ROUNDS OF STORMS WITH THE FRONT
STALLING. THUS, THE DAY 4/WEDNESDAY AND DAY 5/THURSDAY EROS SHOW
SLIGHT RISKS OVER THE CENTRAL PLAINS FOR THE POSSIBILITY OF FLASH
FLOODING. ON DAY 4/WEDNESDAY, ALSO HAVE THE SLIGHT RISK LOOPING
EAST INTO THE MIDDLE MISSISSIPPI VALLEY WHERE MODELS SHOW MCS
POTENTIAL AND ANTECEDENT CONDITIONS ARE GENERALLY WET. MARGINAL
RISKS STRETCH NORTHWARD INTO THE NORTHERN ROCKIES/HIGH PLAINS NEAR
THE BACK END OF THE FRONT AS MUCH HIGHER THAN AVERAGE INSTABILITY
(PER THE EXTREME FORECAST INDEX) IS IN PLACE. MEANWHILE THE FRONT
EXTENDS FARTHER EAST ACROSS THE OHIO VALLEY AND NORTHEAST ON
WEDNESDAY, PROMOTING POTENTIALLY HEAVIER RAIN IN A MOISTURE-LADEN
PRE-FRONTAL ENVIRONMENT COINCIDENT WITH AREAS THAT HAVE SEEN WELL
ABOVE NORMAL RAINFALL THE PAST SEVERAL WEEKS, ALLOWING FOR A
MARGINAL RISK IN THE DAY 4/WED ERO. BY THURSDAY, THE FRONT WILL
GRADUALLY MOVE SOUTH AND LEAD TO POOLING MOISTURE AND INSTABILITY
IN THE MID-ATLANTIC ALONG WITH INCREASING DYNAMICAL SUPPORT IN THE
FORM OF THE RIGHT ENTRANCE REGION OF THE UPPER JET. A SLIGHT RISK
IS NOTED IN THE DAY 5/THU ERO FOR THIS ACTIVITY. ENHANCED RAIN IS
POSSIBLE IN THE CAROLINAS BY FRIDAY AND SATURDAY NEAR THIS FRONT.
TO THE WEST OF THE RIDGE, MONSOONAL MOISTURE (WITH PRECIPITABLE
WATER VALUES GENERALLY IN THE 75TH-90TH PERCENTILE) WILL BE PRESENT
OVER THE SOUTHWEST WITH SOME INSTABILITY. MARGINAL RISKS ARE IN
PLACE IN THE DAYS 4 AND 5 EROS FOR PARTS OF THE SOUTHWEST AND
REACHING INTO THE CENTRAL ROCKIES/HIGH PLAINS AS THE MONSOONAL
MOISTURE MEETS THE FRONTAL SYSTEM TO THE NORTH.
ELSEWHERE, MOISTURE AND INSTABILITY COULD LEAD TO SCATTERED
THUNDERSTORMS IN THE SOUTHEASTERN U.S. FROM DAY TO DAY. THERE MAY
BE SOME FOCUS FOR STORMS NEAR THE CENTRAL GULF COAST IN PARTICULAR
WITH WEAK LOW LEVEL TROUGHS/LOWS IN THE VICINITY. MARGINAL RISKS OF
FLASH FLOODING ARE IN PLACE FOR THE CENTRAL GULF COAST AND PARTS
OF THE SOUTHEAST DUE TO HIGH RAIN RATES THAT MAY OVERCOME THE HIGH
FLASH FLOOD GUIDANCE AND/OR FALL ATOP URBAN AREAS.
FRACASSO/TATE
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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