023
FXUS02 KWBC 231832
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT MON JUN 23 2025
VALID 12Z THU JUN 26 2025 - 12Z MON JUN 30 2025
...RECORD HEAT IS LESS LIKELY BY LATER WEEK, BUT DANGEROUS HEAT
CONTINUES FOR THE OHIO/TENNESSEE VALLEYS AND MID-ATLANTIC/SOUTHEAST...
...HEAVY RAIN AND FLASH FLOODING POSSIBLE IN THE UPPER
MIDWEST/GREAT LAKES LATE WEEK...
..OVERVIEW
INTO THE LATTER PART OF THE THE WEEK, THE PEAK OF THE SIGNIFICANT
AND EXTREMELY DANGEROUS HEAT WAVE WILL HAVE WANED. HOWEVER,
TEMPERATURES WILL REMAIN QUITE HOT ACROSS THE OHIO AND TENNESSEE
VALLEYS INTO THE MID-ATLANTIC AND SOUTHEAST, AND THE LONG DURATION
OF THE HEAT WAVE COULD CAUSE EXACERBATED IMPACTS, MAINTAINING MAJOR
TO EXTREME HEATRISK IN SOME AREAS INTO LATE WEEK. TROPICAL AND
SUBTROPICAL MOISTURE WILL ADVECT NORTH ACROSS NEW MEXICO AND THEN
EAST AROUND THE SOUTHEASTERN U.S. UPPER RIDGE IN A "RING OF FIRE"
SETUP. THE MOISTURE SHOULD INTERACT WITH A WAVY FRONTAL BOUNDARY
AND PROMOTE POTENTIALLY HEAVY RAIN AND FLASH FLOODING IN THE
MIDWEST AND GREAT LAKES REGIONS LATE WEEK. ADDITIONAL ROUNDS OF
SCATTERED THUNDERSTORMS ARE POSSIBLE ACROSS MUCH OF THE CENTRAL AND
EASTERN U.S. INTO THE WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN VERY GOOD OVERALL AGREEMENT WITH THE
DEPICTION OF THE LARGE SCALE PATTERN THROUGH THE MEDIUM RANGE
PERIOD. MODELS CONTINUE TO ADVERTISE THE LARGE AND EXPANSIVE RIDGE,
WHICH IS BRINGING RECORD-SETTING AND DANGEROUS HEAT TO MUCH OF THE
EASTERN HALF OF THE COUNTRY THIS WEEK, BREAKING DOWN AND WEAKENING
HEADING INTO THE WEEKEND. COMBINED WITH WEAKENING TROUGHING ACROSS
THE WESTERN U.S., THE SYNOPTIC PATTERN IS PROGGED TO BECOME MUCH
MORE ZONAL THROUGH AT LEAST SUNDAY BEFORE SHOWING SIGNS OF
AMPLIFYING AGAIN DURING THE FIRST HALF OF NEXT WEEK. A FASTER AND
MORE ZONAL PATTERN PUTS MUCH MORE EMPHASIS ON THE SPEED, DEPTH, AND
EVOLUTION OF INDIVIDUAL SHORTWAVES, WHICH CAN BE MORE DIFFICULT TO
NAIL DOWN AT EXTENDED TIME RANGES. FOR THE MOST PART, MODELS
GENERALLY AGREED WITH THE SMALLER SCALE WAVELENGTHS AND THEIR
SURFACE FEATURES, EVEN FOR THE LATTER HALF OF THE FORECAST PERIOD.
HOWEVER, SIMILAR TO LAST NIGHT'S PACKAGE, THE 00Z AND 06Z RUNS OF
THE GFS DIFFERED ENOUGH WITH THEIR HANDLING OF MULTIPLE WAVES
ACROSS SOUTHERN CANADA, THE NORTH-CENTRAL U.S. AND THE GREAT LAKES
REGION (COMPARED TO THE EC, CMC, AND UKMET) THAT THEIR
CONTRIBUTIONS TO THE OVERALL COMPOSITE FORECAST BLEND WERE
SIGNIFICANTLY REDUCED BY DAY 5 AND BEYOND.
THE LATEST WPC FORECAST WAS INITIALLY BASED ON A COMPOSITE BLEND
OF THE DETERMINISTIC GUIDANCE, FAVORING THE NON-NCEP MODELS OVER
THE GFS. ADDITIONALLY, BEYOND DAY 5, INTRODUCED AND GRADUALLY
INCREASED THE PROPORTION OF THE EC AND GEFS ENSEMBLE MEANS TO HALF
TO LESSEN THE INFLUENCE OF INDIVIDUAL MODEL VARIABILITY WHILE STILL
MAINTAINING CONTINUITY.
..WEATHER/HAZARDS HIGHLIGHTS
ON THURSDAY, SOME ANOMALOUSLY HIGH TROPICAL AND SUBTROPICAL
MOISTURE SHOULD STILL BE FILTERING INTO NEW MEXICO. HOWEVER, WITH
THE UPPER TROUGH IN THE INTERIOR WEST WEAKENING, THERE WILL BE LESS
UPPER LEVEL SUPPORT FOR WIDESPREAD CONVECTION COMPARED TO THE
SHORT RANGE PERIOD. REGARDLESS, HEAVY RAIN COULD STILL BE A CONCERN
IN NEW MEXICO, ESPECIALLY CONSIDERING THE WET ANTECEDENT
CONDITIONS BY THEN. WILL MAINTAIN MARGINAL RISKS IN THE DAYS 4/5
(THURSDAY/FRIDAY) EROS WITH A PARTICULAR FOCUS ON THE SACRAMENTO
MOUNTAINS, WHERE OROGRAPHIC SUPPORT COULD ENHANCE RAINFALL TOTALS
AND WHERE BURN SCARS AND STEEP TERRAIN MAKE THE AREA SENSITIVE TO
HEAVY RAIN. SOME SHOWERS AND STORMS ARE POSSIBLE THERE INTO THE
WEEKEND.
THE PLUME OF MOISTURE WILL ARC NORTHEASTWARD INTO THE UPPER
MIDWEST/GREAT LAKES REGION, WHERE THE ADDITIONAL LIFT AROUND A WEAK
SURFACE LOW AND FRONTAL BOUNDARY IN THE VICINITY AND POTENTIAL
TRAINING WILL FAVOR AREAS OF HEAVIER RAINFALL AND SOME FLASH
FLOODING POTENTIAL. FOR THE DAY 4/THURSDAY ERO, CONTINUE TO SHOW A
SLIGHT RISK ACROSS THE UPPER MIDWEST/MUCH OF WISCONSIN AND THE U.P.
OF MICHIGAN, GIVEN POTENTIAL FOR 2 TO 4 INCHES TO ACCUMULATE
DESPITE CONTINUED SPREAD IN THE EXACT POSITIONING. SOME CONVECTION
WITH LOCALLY HEAVY RAIN COULD TRAVERSE THE NORTHERN SIDE OF THE
RIDGE FARTHER EAST INTO NEW YORK STATE AND THE NORTHERN MID-
ATLANTIC, AND HAVE CAPTURED THESE AREAS WITHIN THE MARGINAL RISK ON
THURSDAY. BY FRIDAY THE SURFACE LOW/FRONTAL SYSTEM WILL CONTINUE
TO TRACK EAST, BRINGING SOME POTENTIALLY ENHANCED RAIN AMOUNTS TO
THE LOWER GREAT LAKES REGION AND INTERIOR NORTHEAST. THERE STILL
REMAINS SOME UNCERTAINTY WITH THE POSITIONING OF THE HEAVIEST QPF,
INCLUDING SOME MODELS SHOWING THE HEAVIEST RAIN STAYING IN CANADA,
SO WILL MAINTAIN A MARGINAL RISK IN THE DAY 5/FRIDAY ERO RATHER
THAN INTRODUCING A SLIGHT RISK FOR THIS CYCLE. THAT BEING SAID, WILL
CONTINUE TO MONITOR TRENDS SINCE SOME OF THE HIGHER TERRAIN THERE
CAN BE SENSITIVE TO HEAVY RAINFALL. MEANWHILE, ANOTHER SHORTWAVE
MAY MOVE THROUGH THE NORTH-CENTRAL U.S. WHILE INSTABILITY IS
LIKELY TO BE HIGH (MUCAPE OF 3000-5000 J/KG ALREADY SHOWN BY THE
GLOBAL MODELS). HAVE A MARGINAL RISK DELINEATED IN PARTS OF THE
DAKOTAS TO MINNESOTA SINCE LOCALLY HEAVY RAIN RATES ARE LIKELY IN
THIS UNSTABLE ATMOSPHERE.
SCATTERED SHOWERS AND THUNDERSTORMS WILL BECOME MORE WIDESPREAD
ACROSS MUCH OF THE EASTERN THIRD OF THE COUNTRY THROUGH THE PERIOD.
A WEAK UPPER LOW MAY TRACK ACROSS FLORIDA AND VICINITY ON
THURSDAY-FRIDAY AND PROVIDE ADDITIONAL SUPPORT FOR CONVECTION.
WILL CONTINUE TO HOLD OFF ON INTRODUCING ANY ERO RISK AREAS FOR
THE TIME BEING GIVEN LOWER END QPF WITH RELATIVELY HIGH FLASH
FLOOD GUIDANCE. SCATTERED CONVECTION IS ALSO LIKELY ACROSS THE
APPALACHIANS AND INTO THE EASTERN SEABOARD EACH DAY AS THE HEAT
CREATES AN UNSTABLE AIRMASS.
THE STRONG UPPER HIGH/RIDGE STRETCHING ACROSS THE SOUTH-CENTRAL TO
EASTERN U.S. WILL WEAKEN SOMEWHAT INTO LATE WEEK, BUT REMAIN
GENERALLY IN PLACE, MAINTAINING HOT TEMPERATURES ALBEIT SLIGHTLY
MODERATED FROM THE SHORT RANGE PERIOD AND LESS LIKELY TO BREAK
RECORDS. NEVERTHELESS, TEMPERATURES WILL BE WELL INTO THE 90S IN
MANY CENTRAL AND EASTERN AREAS, WHILE DEWPOINTS IN THE 70S WILL
RAISE HEAT INDICES INTO THE 100S. OVERNIGHT LOWS WILL ONLY DROP
INTO THE LOW/MID 70S FOR MANY AREAS, BRINGING LITTLE RELIEF FROM
THE HEAT AND EXACERBATING POTENTIAL IMPACTS. ESPECIALLY AFTER THE
EXTREME HEAT IN THE SHORT RANGE, THROUGH LATE WEEK HEATRISK VALUES
WILL BE MAJOR TO EXTREME FOR PORTIONS OF THE MIDWEST AND OHIO
VALLEY TO EASTERN STATES -- LEVELS 3 AND 4 ON A SCALE FROM 1 TO 4
(4 BEING EXTREME). THIS INDICATES AN INTENSITY AND DURATION OF HEAT
THAT IS EXTREMELY DANGEROUS TO ANYONE WITHOUT ADEQUATE COOLING OR
HYDRATION. EXTREME HEAT IS THE NUMBER 1 WEATHER-RELATED KILLER --
PLEASE TAKE PRECAUTIONS IF YOU ARE OUTSIDE DURING THE HOTTEST PART
OF THE DAY AND SEEK COOLING IF YOU ARE WITHOUT ADEQUATE MEANS.
TEMPERATURES MAY CONTINUE TO SLOWLY MODERATE INTO THE WEEKEND FOR
CLOSER TO NORMAL SUMMER HEAT. ELSEWHERE, THE NORTHEAST SHOULD SEE
RELIEF FROM THE HEAT BY THE MEDIUM RANGE PERIOD BEHIND A BACKDOOR
FRONT. THE NORTH-CENTRAL U.S. CAN EXPECT WARMER THAN AVERAGE
TEMPERATURES BY 5 TO 10 DEGREES AROUND FRIDAY-SATURDAY AND THEN
COOL BEHIND A COLD FRONT. TEMPERATURES IN THE NORTHWEST WILL WARM
BY EARLY NEXT WEEK UNDER AN UPPER RIDGE. THE DESERT SOUTHWEST CAN
EXPECT TYPICAL SUMMER HEAT WITH TEMPERATURES IN THE 100S AND 110S.
MILLER/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page