661
FXUS02 KWBC 230659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM 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/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 AGREEMENT IS RATHER GOOD AT THE START OF THE MEDIUM RANGE
PERIOD, WITH GUIDANCE SHOWING FOR MULTIPLE DAYS THAT THE UPPER HIGH
WILL BE WEAKENING BY THURSDAY. A TROUGH ACROSS THE INTERIOR WEST
WILL ALSO BE DECAYING AT THAT POINT, WHILE MODELS ARE NOW SHOWING
AN UPPER LOW COMING ACROSS FLORIDA WHILE WEAKENING AS WELL. OVERALL
THE PATTERN WILL BECOME MORE ZONAL BY LATE WEEK INTO THE WEEKEND.
THIS IS SHOWN WELL BY THE MODELS, BUT AS A RESULT SHORTWAVES ARE
THE PRIMARY DRIVER OF SENSIBLE WEATHER LIKE FRONTAL POSITIONS, AND
THESE SMALLER SCALE FEATURES ARE MORE UNCERTAIN. THE FIRST
SHORTWAVE IN A NORTHERN STREAM WAVE TRAIN WILL CROSS THE GREAT
LAKES/SOUTHERN CANADA THURSDAY-FRIDAY AND SUPPORT A SURFACE
LOW/FRONTAL SYSTEM AND THE POTENTIALLY HEAVY QPF. THERE IS SOME
SPREAD IN THE DEPTH AND TIMING OF THIS SHORTWAVE AND THUS THE
SURFACE FEATURES. THE 18Z GFS WAS UNFAVORABLE WITH A STRONGER
SURFACE LOW FARTHER NORTH OF THE BETTER CONSENSUS. BEHIND THIS A
BROADER, BUT NOT VERY AMPLIFIED, TROUGH IS FORECAST TO MOVE THROUGH
THE NORTHWEST FRIDAY AND CONTINUE ACROSS THE NORTH-CENTRAL U.S.
OVER THE WEEKEND AND THE GREAT LAKES BY NEXT MONDAY. THE 12Z GFS
WAS ON THE SLOWER SIDE WITH THIS TROUGH, BUT OTHER MODELS LINED UP
WELL. THERE IS GOOD AGREEMENT FOR A RIDGE BEHIND THAT TROUGH, AND
THEN WILL MONITOR A NORTHEAST PACIFIC UPPER LOW TO POTENTIALLY
IMPACT THE PATTERN EARLY NEXT WEEK, WHILE SOME WEAK SOUTHERN STREAM
TROUGHING SETS UP NEAR THE WEST COAST.
THE WPC FORECAST WAS BASED ON A MULTI-MODEL BLEND EARLY IN THE
MEDIUM RANGE, AND INTRODUCED AND GRADUALLY INCREASED THE GEFS AND
EC ENSEMBLE MEANS TO HALF BY DAY 7 TO LESSEN THE INFLUENCE OF
INDIVIDUAL MODEL VARIABILITY.
..WEATHER/HAZARDS HIGHLIGHTS
ON THURSDAY, SOME ANOMALOUSLY HIGH TROPICAL/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 IS SOME
SPREAD IN THE MODELS' POSITIONING OF THE HEAVIEST QPF, INCLUDING
SOME MODELS SHOWING THE HEAVIEST RAIN STAYING IN CANADA, SO WILL
START WITH A MARGINAL RISK IN THE DAY 5/FRIDAY ERO RATHER THAN
SHOWING A SLIGHT RISK AT THIS POINT. BUT WILL CONTINUE TO MONITOR
TRENDS ESPECIALLY BECAUSE SOME AREAS LIKE THE 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.
PLAN TO WAIT AND SEE IF MODEL AGREEMENT GETS BETTER FOR HEAVY
AMOUNTS AND THEIR PLACEMENT BEFORE SHOWING ANY ERO RISKS. 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.
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