FOUS30 KWBC 040830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Thu Jun 4 2026

Day 1
Valid 12Z Thu Jun 04 2026 - 12Z Fri Jun 05 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
THE UPPER MIDWEST...

Circulation around a broad area of high pressure over the 
Northeast US and the Mid-Atlantic Region will keep an easterly flow
of deep moisture over Florida and and anticyclonic flow from the 
Texas and Louisiana Gulf coast that becomes southwesterly from 
parts of the Central Plains/Upper Midwest through much of the 
period. An upper low over northern Mexico will help draw some of 
that moisture westward to support the risk of locally heavy 
rainfall there.

...Gulf Coast to Upper Midwest/Northern Plains...
With a persistent fetch of an airmass from the Gulf Coast region
into the Upper Midwest...precipitable water values increase
throughout the day...exceeding 2 inches along the Texas Gulf coast
to the ARKLATEX while increasing to 1.5 inches or more in a plume
extending into parts of Minnesota and Wisconsin. The highest
probability of heaviest rain was shown in both the operational
models and the ensembles across parts of Iowa into portions of
nearby Nebraska and Kansas as mid level height falls make their way
out of the High Plains and as surface pressures fall. Rainfall
rates of 1-2 inches per hour are possible. The 00Z runs of the HREF
and the RRFS show neighborhood probabilities of 10 to 20 percent
occurrence for 2 inch amounts in 3 hours for the 24 hour period
ending at 12Z Friday morning. Those rates could be enough to
overcome initially dry soils in parts of the area as well as be
problematic in urban areas.

Elsewhere along that corridor...there is sufficient CAPE to drive
locally intense downpours from any convection that forms. The big
problem is the relatively weak shortwave energy within the flow
will be difficult to time with much lead-time. As such...left the
Marginal Risk area pretty much in place with the expectation that
some area may well stay rain-free.

...West Texas to Eastern New Mexico...

An upper level system over Mexico will help draw some of the deeper
Gulf moisture westward...keeping a risk of locally heavy rainfall
and isolated instances of flash flooding. As previously
mentioned...the overall organization of the convection is expected
to be on the lower side, but the precipitable water anomalies and
the subtle increase in the upper level difluence near the
international border support potential for locally intense rain 
rates and the Marginal Risk.

...South Florida...
Frontal boundary stalling in the vicinity of the area will remain
the focus for scattered to numerous showers and thunderstorms
capable of producing intense rain rates and locally heavy rainfall
over the highly urbanized corridor. The risk shifts a bit farther 
south across South Florida compared with yesterday...mainly 
centering across the Miami metro.

Bann


Day 2
Valid 12Z Fri Jun 05 2026 - 12Z Sat Jun 06 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER MIDWEST/NORTHERN PLAINS ON FRIDAY...

...21Z Outlook Update...
The ongoing forecast remainder largely on track. The main change
was the introduction of a Slight Risk across portions of Iowa to 
parts of nearby Wisconsin and Illinois as areas of moderate to 
heavy rainfall lingers in the area. Elsewhere...there were only 
minimal changes needed to the Marginal Risk areas across the 
central Gulf Coast to New Mexico...southern Louisiana and the 
southern Florida peninsula.

Upper Midwest...
Additional scattered thunderstorm activity is expected once again 
ahead of a front making its way from Iowa into Wisconsin and 
vicinity, spreading 1-2 inches of rain with local amounts reaching 
4 inches. Storms in that area should be progressive in nature due 
to 20-30 knot mid/upper level flow, though localized backbuilding 
and mergers may increase totals locally. 

The Marginal Risk surrounding the Slight Risk was largely
unchanged...although some of the territory was removed from the
northern part of Michigan now that timing of the boundary and low 
level moisture fields have become handled better by the 
models/ensembles.

Texas into New Mexico...
Weak mid/upper troughing across the southern Rockies and Texas 
will promote another round of thunderstorm activity across a large 
part of Texas and southern New Mexico, with attendant flash 
flooding expected due to slow storm motions and abundant moisture. 

Coastal Louisiana...
A trough of low pressure interacting with the higher moisture in 
place will bring a higher coverage of thunderstorms with the 
potential for intense rain rates and localized heavy rainfall.
Spaghetti plots show more ARW core members than NMMB...suggesting
that there could still be shifts in placement or QPF amounts
between now and the time the outlook verifies.

South Florida...
A stalled frontal boundary over the southern Florida peninsula 
will continue to focus scattered to numerous afternoon and evening 
showers and thunderstorms. Given the instability...intense rain 
rates and locally heavy rainfall over the highly urbanized 
corridor.

Bann


Day 3
Valid 12Z Sat Jun 06 2026 - 12Z Sun Jun 07 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE GREAT LAKES/OHIO VALLEY AND ACROSS THE MIDDLE GULF COAST INTO
THE SOUTHERN PLAINS...

Great Lakes/Ohio Valley...
Maintained a Marginal Risk area over portions of Ohio Valley and
nearby southern Great Lakes as a front become oriented along an
east to west axis and flow aloft is weakly forced to lift
isentropically. Maximum areal average rainfall after the start of 
the period at 12Z Saturday generally looks to be little more than
an inch. The cumulative effect of rainfall on Days 2 and 3
suggested it was too early to entirely remove the Marginal.

Texas northward into the Southern Plains...
Little change in the overall synoptic pattern is expected with
southerly flow of moisture continuing to be drawn into parts of the
Southern Plains. Some stronger/better defined shortwave energy
within the flow aloft will promote yet another round of 
thunderstorm activity across a large part of Texas and southern New
Mexico and extending as far north as parts of Oklahoma/Arkansas and
Kansas by late Saturday night/early Sunday morning, with attendant
flash flooding expected due to slow storm motions and abundant 
moisture.

Bann
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