Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
845 PM EDT Fri Jul 31 2026
Day 1
Valid 01Z Sat Aug 01 2026 - 12Z Sat Aug 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MIDWEST & UPPER PENINSULA OF MICHIGAN...

...Central US system...
An extremely anomalous mid- level low exists for late July across
IA. An impressively deep system overlapping late July thermodynamics
is a clear indicator of excessive rainfall potential.  Near the
occluded cyclone in IA (and farther downstream warm sector) PWs
range from 1.75 to 2.00 inches, with ML CAPE of 500-3000 J/kg at
the writing of this discussion. Effective bulk shear of 25-35 kts
should continue convective organization. This environment supports
hourly rain amounts to 2.5", with the 18z HREF/12z REFS supporting
additional local totals to 5" this evening/tonight. The three
hourly flash flood guidance values have lowered due to earlier
rainfall. Overall, the risk levels from continuity appear
reasonable but areas were reshaped based on recent convective
evolution and the 18z HREF/12z REFS guidance.


...Upper Peninsula of Michigan...
Increased deformation between 700-500mb pivoting into the Upper
Peninsula this aftn/eve along with lake breeze circulations have
led to convection across eastern portion of the UP of MI. PWs are
as high as 1.8 inches. Along with ML CAPE of 500+ J/kg, hourly rain
amounts up to 2.5" remain possible in the short term. This would
exceed the 3-hr FFG, suggesting at least scattered instances of
flash flooding are possible. The Slight Risk remains intact to deal
with convective development here over the next several hours.


...Northern Florida through the Central Gulf Coast...
Robust late-July thermodynamics characterized by PWs of 2-2.25
inches and MUCAPE above 2000 J/kg will spread across the area today
and tonight ahead of a quasi-stationary front. Afternoon and
evening thunderstorms are presently on the wane, but a secondary
signal exists early Saturday morning, especially across the
Florida Panhandle and into the Big Bend area. A slow moving
shortwave moving within an area of thickness diffluence leads to a
longer period of enhanced synoptic lift aided by modest jet- level
diffluence. Low-level inflow backs subtly more to the WSW from W
as the front approaches, drawing even more impressive PWs along the
coast and instability from the Gulf. During this time, Corfidi
vectors are progged to collapse to 5 kts or less and become
increasingly anti- parallel to the mean wind suggesting some
greater backbuilding/training potential with rain rates potentially
reaching 3"/hr if everything aligns perfectly prior to 12z. The
18z HREF/12z REFS indicate the potential for local 2-4" by 12z,
with the HREF less bullish. Left the Marginal Risk intact but
Slight Risk impacts can't be ruled out.


...Southern-Central High Plains...
The monsoon ridge gets suppressed to the south and west in
response to the potent system moving through the Plains/Midwest,
with a secondary piece of vorticity energy dropping across the
southern High Plains into the Texas Panhandle. This will help push
a cold front through the Southern Plains and bank against the
terrain of New Mexico later this evening. The overlapping ascent
from the cold front and shortwave will act upon favorable
thermodynamics as a ribbon of PWs above 1.5 inches and pooled
MUCAPE of 1000-1500 J/kg get drawn westward ahead of the front.
Radar reflectivity trends show some clustering of thunderstorms in
eastern NM which could merge into preceding activity across
northwest TX in the short term. Activity should be on the wane
midnight or so. Left the Marginal Risk level but resculpted the
area to reflect recent radar reflectivity and 18z HREF/12z REFS
guidance.

Roth


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt