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

