503
FOUS30 KWBC 262018
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
418 PM EDT THU JUN 26 2025
DAY 1
VALID 16Z THU JUN 26 2025 - 12Z FRI JUN 27 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE CENTRAL PLAINS, UPPER MIDWEST, AND UPPER GREAT LAKES, ALONG
WITH NORTHERN PORTIONS OF THE MID ATLANTIC...
..CENTRAL PLAINS INTO THE UPPER GREAT LAKES
16Z UPDATE... THE WESTERN BOUNDS OF THE MARGINAL RISK AREA WAS
EXPANDED WESTWARD TO NOW INCLUDE MORE OF EASTERN NEBRASKA. CELLS
ARE OBSERVED FIRING UP NEAR THE HEAVY RAIN AXIS FROM YESTERDAY AND
ARE EXPECTED TO PERSIST FOR A FEW MORE HOURS. THE LATEST CAM
GUIDANCE SHOW A FAIRLY PROGRESSIVE LINE TRACKING THROUGH THE REGION
WITH RAIN RATES OF 1 TO 3 INCHES/HOUR WITH MAXIMUM 24-HOUR
ACCUMULATIONS OF 3 TO 5 INCHES. ELSEWHERE THE MARGINAL AND SLIGHT
RISK AREAS WERE MAINTAINED WITH NO ADJUSTMENTS.
CAMPBELL
UPPER SHORTWAVE TROUGH ACROSS THE NORTHERN PLAINS EARLY THU WILL
PIVOT EASTWARD ACROSS THE UPPER MS VALLEY AND UPPER GREAT LAKES
REGION LATER THU AND THU NIGHT. ENHANCING THE DEEP-LAYER FORCING
WILL BE THE CURVED 90KT UPPER LEVEL JET STREAK THAT WILL BE
SKIRTING THE U.S.-CANADIAN BORDER. AHEAD OF THE UPPER SHORTWAVE
TROUGH/SURFACE FRONT -- 850-700 MB MOISTURE FLUX ANOMALIES ARE
NOTEWORTHY (1.5-2.0 STANDARD DEVIATIONS ABOVE NORMAL), AS IS THE
0-6KM BULK SHEAR VALUES (35-45+ KTS). THIS WILL LIKELY SUPPORT MORE
WIDESPREAD, ORGANIZED CONVECTIVE LINE SEGMENTS LATER THIS
AFTERNOON/EVENING AND INTO THE OVERNIGHT ACROSS THE ELONGATED
SLIGHT RISK AREA. COMPARED TO YESTERDAY'S DAY 2 ERO, BASED ON THE
LATEST GUIDANCE TRENDS WE DID NUDGE THE SLIGHT SLIGHTLY FARTHER
EAST ACROSS NORTHWEST MO AND SOUTHEAST IA. THE 00Z CAMS SHOW 24HR
MAX QPF GENERALLY IN THE 3-5" RANGE WITHIN THE SLIGHT RISK AREA,
WHICH IS SUPPORTED BY THE HREF AND RRFS 24HR QPF PROBABILITIES.
MULTIPLE CAMS (INCLUDING THE 00Z RRFS) SHOW ISOLATED TOTALS
EXCEEDING 5" ACROSS EASTERN KS.
..MID ATLANTIC
MOST OF THE CAMS SHOW MORE WIDESPREAD SLOW-MOVING CONVECTIVE
CLUSTERS WITHIN A NEWLY-HOISTED SLIGHT AREA, INITIATING ALONG THE
LEE-SIDE TROUGH AND QUASI-STATIONARY, BACKDOOR FRONT. RELATIVELY LIGHT
(GENERALLY 20KT OR LESS) DEEP-LAYER SHEAR WOULD SUGGEST PULSE-
TYPE DURATIONS FOR THE HEAVIEST RAINS, BUT NEVERTHELESS BOTH THE
HREF AND RRFS DO SHOW POCKETS OF ELEVATED PROBABILITIES WITH >2"/HR
RAINFALL RATES BY MID-LATE AFTERNOON INTO THU EVENING. THEREFORE
GIVEN THE FAVORABLE THERMODYNAMIC PROFILE (1.75-2.00" PWS AND MAX
CAPES 2000-3000 J/KG), THE LIKELIHOOD OF SLOW CELL MOTIONS WITH THE
POTENTIAL FOR REPETITIVE CONVECTION ALONG THESE BOUNDARIES WOULD
SUPPORT A LOW-END SLIGHT RISK ACROSS THE NORTHERN MID ATLANTIC
(NORTHERN VA INTO EASTERN MD AND EASTERN PA), DESPITE THE LACK OF
STRONG SYNOPTIC/ KINEMATIC SUPPORT.
..PARTS OF THE LOWER MS VALLEY, TN VALLEY, AND SOUTHEAST
SCATTERED TO WIDELY SCATTERED THUNDERSTORMS OVER MUCH OF THE
SOUTH-CENTRAL TO SOUTHEASTERN CONUS WILL YIELD SOME HEAVY RAINFALL
PROSPECTS DURING THE DAY THURSDAY WITH A DECAY IN COVERAGE ONCE WE
LOSE DIURNAL HEATING. THE MAIN AREAS OF INTEREST WILL LIE ALONG
THE TERRAIN IN THE SOUTHERN APPALACHIANS AND ALONG THE GULF COAST
WHERE THE REMNANTS OF A MIGRATING TUTT CELL WILL MAINTAIN A FOCAL
POINT FOR HEAVY CONVECTIVE PROSPECTS DURING THE PERIOD. BEST THREAT
FOR ANY FLASH FLOODING WILL BE TIED TO THE COMPLEX TOPOGRAPHY AND
URBAN SETTINGS WHERE RUNOFF CAPABILITIES ARE HIGHEST. RELATIVELY
MODEST HREF PROBS FOR >3" (40-60%) WERE NOTED ACROSS PORTIONS OF
MS/LA AND ESPECIALLY ALONG THE WEST COAST OF THE FL PENINSULA. FOR
NOW THE RISK APPEARS TO BE A 'HIGH END' MARGINAL, I.E. MAINLY AN
ISOLATED FLASH FLOOD RISK, LARGELY DUE TO THE PULSE/SHORT-FUSED
NATURE OF THE MORE INTENSE RAINFALL RATES AND RELATIVELY HIGH FFG
VALUES.
..NEW MEXICO
ISOLATED TO SCATTERED THUNDERSTORMS ACROSS THE SACRAMENTO'S AND
ADJACENT DESERT WILL MAINTAIN AT LEAST SOME THREAT FOR FLASH
FLOODING GIVEN WET ANTECEDENT CONDITIONS FOLLOWING PREVIOUS MULTI-
DAY CONVECTIVE IMPACT IN PRIOR PERIODS. COVERAGE AND INTENSITY OF
CONVECTION WILL BE LESS THAN PREVIOUS DAYS AS WE LOSE THE BENEFIT
OF THE RER JET DYNAMICS THAT HAVE ASSISTED IN THE RECENT DAYS.
STILL, REMNANT ELEVATED MOISTURE AND SUFFICIENT BUOYANCY WITHIN
THE CONFINES OF FAR WEST TX UP THROUGH SOUTHERN AND EASTERN NM WILL
MAINTAIN A POSTURE OF DIURNALLY DRIVEN THUNDERSTORMS WITH LOCALLY
HEAVY RAINFALL ACROSS THE ABOVE AREAS. HEAVIEST THUNDERSTORMS WILL
BE CAPABLE OF 1-2" WITH THE PEAK QPF MAX PROBABLY CLOSER TO 3" AS
NOTED BY MODEST HREF NEIGHBORHOOD PROBABILITIES FOR >3" WITH A
DECLINE TO 0% FOR >5". THE PREVIOUS MRGL RISK WAS MAINTAINED.
HURLEY
DAY 2
VALID 12Z FRI JUN 27 2025 - 12Z SAT JUN 28 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NORTHERN NEW YORK AND NORTHERN NEW ENGLAND...
..NORTHERN NY-NEW ENGLAND
21Z UPDATE... THE LATEST GUIDANCE MAINTAINS THE SCENARIO DESCRIBED
BELOW WITH SIMILIAR QPF AMOUNTS, PARTICULARLY FROM NORTHEAST NEW
YORK TO NORTHERN VERMONT, THEREFORE THE MARGINAL AND SLIGHT RISK
AREAS WERE MAINTAINED AS IS.
CAMPBELL
THE FORECAST FOR A FOCUSED CORRIDOR OF HEAVY RAINFALL ASSOCIATED
WITH AN MCS AND TRAILING CONVECTION CROSSING FROM SOUTHEASTERN
CANADA INTO PORTIONS OF UPDATE NEW YORK/NORTHERN NEW ENGLAND
REMAINS ON TRACK. WHILE THERE ARE EXPECTEDLY SOME VARIANCES ON THE
POSSIBLE MCS PATH WHICH ADD SOME EAST-WEST UNCERTAINTY, ALL
GUIDANCE IS STILL IN GOOD AGREEMENT THAT THE TRACK WILL CLIP AREAS
SOUTH OF THE INTERNATIONAL BORDER BRINGING AN ATTENDANT FLASH FLOOD
THREAT. DETERMINISTIC GUIDANCE INDICATES THE POTENTIAL OF RAINFALL
TOTALS BETWEEN 1-3", WITH ENSEMBLE PROBABILITIES OF 2"+ BETWEEN
15-25%. A SMALL EASTWARD ADJUSTMENT OF THE SLIGHT RISK AREA WAS
ADDED BASED ON THESE LATEST ENSEMBLE PROBABILITIES. ELSEWHERE,
PRIOR FORECAST HAS REMAINED CONSISTENT.
..NORTHERN PLAINS
21Z UPDATE... THE PROGRESSIVE NATURE OF THE EXPECTED SHORTWAVE WILL
HELP LIMIT THE SEVERITY OF ANY LOCAL FLOODING THAT ARISES. THE
MARGINAL RISK CURRENTLY IN PLACE REMAINS WITHOUT ANY CHANGES AT
THIS TIME.
CAMPBELL
A QUICK MOVING SHORTWAVE ACROSS THE NORTH-CENTRAL TIER OF THE CONUS
WILL LEAD TO SCATTERED THUNDERSTORM ACTIVITY CAPABLE OF LOCALLY
HEAVY RAINFALL AND FLASH FLOOD PROSPECTS. THE BEST THREAT WILL BE
OVER NORTHERN ND INTO THE RED RIVER AREA WHERE SOME URBANIZED ZONES
WILL HAVE A GREATER THREAT FOR FLASH FLOODING. A QUICK 1-3+" IS
LIKELY ANYWHERE OVER CENTRAL ND INTO NORTHWEST MN. THIS THREAT IS
WITHIN THE LOWER END OF THE MRGL RISK THRESHOLD AND WILL BE
MONITORED CLOSELY TO SEE IF THE RISK IS WARRANTED, OR NEEDS ANY
EXPANSION.
..WEST TEXAS INTO NEW MEXICO
21Z UPDATE... THE THREAT FOR LOCALIZED HEAVY RAINFALL REMAINS
SPOTTY ACROSS THE AREA GIVEN THE PATTERN. THE MARGINAL RISK AREA
CONTINUES TO HIGHLIGHT THE LOCATIONS THAT MAY HAVE LOCAL FLASH
FLOODING DURING THIS PERIOD.
CAMPBELL
CONTINUED THREAT OF WIDELY SCATTERED THUNDERSTORMS ACROSS FAR WEST
TX INTO NM WILL ALLOW FOR ISOLATED FLASH FLOOD CONCERNS OVER AREAS
THAT WILL HAVE SEEN SEVERAL DAYS OF HEAVY CONVECTIVE IMPACTS WITH
COMPROMISED FFG'S. LOCAL 1-2" IS POSSIBLE IN THE PERIOD WITH THE
HIGHEST THREAT LIKELY OVER THE SACRAMENTO'S DOWN THROUGH THE
GUADALUPE MTNS. AND ADJACENT VALLEYS. A MRGL RISK WAS MAINTAINED TO
COVER FOR THE THREAT.
DAY 3
VALID 12Z SAT JUN 28 2025 - 12Z SUN JUN 29 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHERN PLAINS AND UPPER MIDWEST, THE NORTHEAST, AND
SOUTH-CENTRAL NEW MEXICO...
..NORTHERN PLAINS AND UPPER MIDWEST
21Z UPDATE... THE LATEST GUIDANCE CONTINUES TO SIGNAL THE HIGHEST
QPF AMOUNTS TO BE OVER CENTRAL MINNESOTA INTO WESTERN/NORTHERN
WISCONSIN WITH AREAL AVERAGES OF 1 TO 3 INCHES WITH LOCALLY HIGHER
AMOUNTS STILL POSSIBLE. THE ENVIRONMENT LOOKS TO REMAIN FAVORABLE
FOR REPEATING CELLS, THUS MAINTAINING AN ELEVATED THREAT FOR
LOCALIZED FLASH FLOODING.
CAMPBELL
NEXT APPROACHING UPPER SHORTWAVE TROUGH, WITH A 90KT UPPER LEVEL
JET STREAK ON THE LEE SIDE, WILL GENERATE A COMPACT AREA OF FAIRLY
ROBUST, TRANSIENT DEEP-LAYER FORCING OVER THE OUTLOOK AREA LATER IN
THE PERIOD (ESPECIALLY SAT NIGHT). MUCAPES ARE EXPECTED TO SOAR
WITHIN THE WARM SECTOR PRIOR TO THE SURFACE COLD FRONTAL PASSAGE --
I.E. AOA 4,000 J/KG PER THE GFS. THIS ALONG WITH PWS GETTING NEAR
1.75" WILL LEAD TO MORE ORGANIZED, WIDESPREAD CONVECTION BY
SATURDAY NIGHT AS THE ACTIVITY LIKELY GROWS UPSCALE WITH THE
INCREASING PRE-FRONTAL LOW-LEVEL INFLOW (30-40KTS AT 850 MB). THE
00Z GUIDANCE INDICATES SIGNIFICANT LATITUDINAL SPREAD IN THE
HEAVIER QPF, AND AS A RESULT, HAVE MAINTAINED THE MARGINAL RISK
FROM YESTERDAY'S DAY 4 ERO. HOWEVER, THE POTENTIAL FOR AN UPGRADE
TO SLIGHT IS CERTAINLY PLAUSIBLE GIVEN THE KINEMATIC AND
THERMODYNAMIC PROFILE, ESPECIALLY AFTER 00Z SUN WHEN THE CORFIDI
VECTORS DECREASE TO 10KT OR LESS (THEREBY ENHANCING THE RISK FOR
CELL TRAINING).
..NORTHEAST
21Z UPDATE... THERE IS AN INCREASING POTENTIAL FOR HEAVY RAINFALL
TO DEVELOP ACROSS WESTERN PENNSLYVANIA AND SURROUNDING AREAS AS
THE FRONTAL BOUNDARY SAGS SOUTHWARD AND TAPS INTO THE POOLED PW
VALUES OF 1.5-2". THE LATEST MODEL GUIDANCE ARE SHOWING LOCAL
MAXIMUMS UPWARDS OF 2 INCHES POSSIBLE AND THE ERO FIRST GUESS
SUPPORTS EXPANDING THE MARGINAL RISK FROM EASTERN PENNSYLVANIA
FURTHER WEST INTO EASTERN OHIO, WEST VIRGINIA AND WESTERN MARYLAND.
CAMPBELL
UPPER SHORTWAVE TROUGH PUSHES ACROSS THE NORTHEAST BY LATE SAT,
THEN OFF THE COAST SUN MORNING. THE BULK OF THE RAINFALL WILL FALL
DURING THE FIRST HALF OF THE PERIOD (DURING THE DAY SAT),
COINCIDING WITH THE MOST FAVORABLE PRE-FRONTAL DEEP-LAYER
INSTABILITY AND MOISTURE (PWS 1.75-2.00+ INCHES). THE 00Z GUIDANCE
SHOWS CONSIDERABLE SPREAD WITH THE HEAVIEST QPF, THOUGH ARE FAIRLY
SIMILAR WITH THE MAX TOTALS (1.5-3.0"). GIVEN THE SPREAD IN THE
MODEL QPFS, ALONG WITH THE PROGRESSION OF THE FRONT AND FAIRLY
QUICK DIMINISHMENT IN INSTABILITY AFTER 00Z SUN, FOR NOW WILL
MAINTAIN THE MARGINAL RISK.
..NEW MEXICO
21Z UPDATE... NO CHANGES WERE MADE TO THE MARGINAL RISK AREA.
CAMPBELL
MAINTAINED A TARGETED MARGINAL RISK AREA OVER/NEAR THE SACRAMENTO
MTNS, PARTICULARLY THE BURN SCAR AREAS FROM THE 2024 FIRES (BLUE 2,
SOUTH FORK, AND SALT BURN SCARS). QPF TRENDS (COVERAGE, INTENSITY)
ARE SIMILAR TO DAY 2, WITH THE MOIST S-SE LOW-LEVEL UPSLOPE FLOW
LIKELY RESULTING IN A CONCENTRATED AREA OF HEAVIER RAINFALL ACROSS
THE SACRAMENTO MTNS AND EASTERN FOOTHILLS. THE FLASH FLOOD
POTENTIAL IS EXPECTED TO REMAIN ISOLATED/LOCALIZED.
HURLEY
DAY 1 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT
DAY 2 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT
DAY 3 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT
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