FOUS30 KWBC 150809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Tue Jul 15 2025

Day 1
Valid 12Z Tue Jul 15 2025 - 12Z Wed Jul 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA 
PENINSULA, PARTS OF THE MID-ATLANTIC, THE UPPER MIDWEST, SOUTHEAST 
ARIZONA, AND CENTRAL TEXAS...

...Florida... 
Potent and intensifying mid-level trough positioned just east of 
the FL peninsula tonight will translate slowly westward beneath a 
ridge positioned to its north. As this feature tracks back over the
Gulf on Tuesday, a surface reflection is likely to develop (even 
if not Tuesday, eventually, and NHC has a 40% chance of 
development) which will enhance ascent. This feature will be 
accompanied by a pool of exceptional PWs of 2.25 to 2.5 inches, 
approaching +3 standard deviations above the climo mean, and 
elevated MUCAPE of 1000-2000 J/kg. As this tracks across the 
peninsula Tuesday, convection is expected both in the vicinity of 
the mid-level center, but also along any convergence bands that 
occur within the pivoting 850mb inflow. Due to the robust 
thermodynamics, rainfall rates of 2-3"/hr are expected (50-70% 
chance of 2+"/hr according to HREF neighborhood probabilities), 
which through generally slow and chaotic storm motions will result 
in axes of 3-5" of rain, highest along the western coast or beneath
the core of the mid-level center. This rain will occur atop areas 
that are more vulnerable due to heavy rainfall on Monday, and the 
SLGT risk remains with only modest cosmetic adjustments.

...Northern Rockies through the Upper Midwest... 
Expanding trough digging across the Northern Rockies and Northern 
Plains will drop steadily southward Tuesday in response to a potent
shortwave digging out of Alberta, Canada. As this impulse gets 
embedded into the more pinched westerlies downstream, it will shed 
spokes of vorticity across the region to help enhance ascent 
already intensifying through height falls. This evolutions will 
also drag a cold front southward, but this front will oscillate 
north and south through D1 in response to the aforementioned
shortwaves/vorticity spokes interacting with its baroclinic 
gradient. In fact, the latest guidance suggests that two distinct 
waves of low pressure will develop along this front and track 
eastward, leading to more focused heavy rain from convection within
otherwise scattered thunderstorms.

Although the broad MRGL risk remains, there appears to be two 
focused areas for heavier rainfall. The first is in a SW to NE 
oriented axis from Nebraska through the Arrowhead of Minnesota. 
Here, southerly 850mb inflow will surge out of the Central Plains at 
20-25 kts and impinge into the front itself. This will additionally 
draw impressive thermodynamics (MUCAPE above 2000 J/kg and PWs above 
1.75 inches, or the 97th percentile according to NAEFS) northward 
into the front. Where the maximum ascent occurs atop these 
thermodynamics, widespread convection with heavy rainfall rates of 1-
2"/hr are expected, and these storms have a high potential to train 
SW to NE along the front due to 0-6km mean winds that are 
progressive at 10-20 kts, but parallel to the boundary. Where these 
elements train, HREF 3-hr FFG exceedance probabilities peak above 
40%, and the inherited SLGT risk remains.

A second region of heavier rainfall is expected across MT. Here, 
persistent westerly mid-level flow atop the front combined with 
sloped frontogenesis will drive nearly continuous periods of 
rainfall. PWs in the region will be elevated above the 90th 
percentile according to NAEFS (0.75 to 1 inch), but accompanying 
instability is minimal. This suggests that most of the rainfall 
rates should be 0.5"/hr or less, so despite the impressive ECMWF EFI 
signal for heavy rain (EFI > 0.9), the excessive rainfall risk 
remains MRGL even if a few locations approach 3 inches of total rainfall.

...Mid-Atlantic and Southeast... 
Broad mid-level ridging centered off the Carolinas will continue 
to extend back to the west as far as the Southern Plains. This will
persist the moist and unstable environment that has been plaguing 
much of the east for several days now, resulting in another day of 
scattered to numerous thunderstorms. On Tuesday, the focus for 
convection will likely be along the decaying front which will drag 
slowly southeast as it wanes, reaching from the Ozarks to the Mid-
Atlantic states, although with some oscillation north-south 
expected at times. Along this boundary, generally SW flow emerging 
from the Southern Plains will drive periodic impulses northeast, 
interacting with the front and providing locally enhanced focused 
ascent for convection. With PWs consistently above 2-2.25 inches 
and MUCAPE 1000-2000+ J/kg, storms that develop will be capable of 
producing efficient rain rates in excess of 2"/hr pretty much 
anywhere across the region. 

In general, coverage should be scattered and not support more than a 
MRGL risk of excessive rainfall. However, some locally focused 
convection beneath an impulse and aided by upslope 850mb inflow 
could produce heavier rainfall from the Central Appalachians into 
the Mid-Atlantic states. The guidance has continued to trend just a 
bit south overnight with the axis of heaviest rainfall, but with the 
front wavering through the day, and a general noted northward bias 
in the convection on Monday (compared to progs), changes to the 
inherited SLGT risk were modest and focused over more vulnerable 
areas from recent heavy rainfall.

...Southwest... 
The monsoon will become more active today as the elongated mid-
level ridge over the Desert Southwest weakens in response to a 
potent vorticity maxima/shortwave drifting around its periphery. 
This feature will traverse westward beneath the ridge, crossing 
from the High Plains of NM through southern Arizona, and act upon 
an increasingly moist and unstable environment. PWs are progged to 
surge to as high as 1.25-1.5 inches, highest in southern AZ, 
coincident with a ribbon of MUCAPE of 1000 J/kg lifting northward 
as low-level flow surges out of the Rio Grande Valley and Mexico. 

The high-res CAMs are generally modest with convective coverage on 
Tuesday, but the recent HRRR and RRFS are much more aggressive with 
simulated reflectivity, and are likely the better solutions 
conceptually for the environment. As storms develop, generally in 
the higher terrain first, they will be slow movers with rain rates 
of 0.5-1"/hr. However, during peak instability, storms will congeal 
and feature at least subtle organization beneath the shortwave as 
bulk shear rises to 20-25 kts and storms coming off the terrain will 
move generally west-southwest and feature rain rates that may 
briefly exceed 1"/hr. The inherited SLGT risk is maintained and 
adjusted subtly.

...Central Texas... 
850mb LLJ surging to 20-25 kts from the south and up through the 
Rio Grande Valley will again support overnight convection 
persisting into the new D1 period (after 12Z Tuesday). This will be
accompanied by a shortwave/vorticity maxima lifting northward and 
favorable instability of more than 1000 J/kg to support at least 
scattered thunderstorms. The high-res CAMs are not aggressive with 
convective coverage after 12Z Tuesday, but even isolated activity 
will contain rain rates that could exceed 2"/hr, and Corfidi 
vectors that are aligned anti-parallel to the mean wind, combined 
with favorable upslope into the Hill Country on southerly winds 
could result in backbuilding/nearly stationary storms at times. 
With the area remaining extremely vulnerable due to repeated rounds
of heavy rain in the past week, (FFG as low as 0.25"/3hrs) the 
SLGT risk was tailored but continued into Tuesday.

...Mid-Mississippi Valley... 
Weak impulses/MCVs embedded within the mean SW to NE mid-level 
flow will lift out of Texas and interact with a weakening 
stationary front over the Mid-Mississippi Valley. ALthough in 
general, forcing for ascent will be modest, it will be locally 
enhanced where these impulses move atop the surface convergence 
associated with the front itself. Intense thermodynamics will 
remain across the area reflected by PWs approaching or exceeding 2 
inches collocated with MUCAPE above 1000 J/kg to support rainfall 
rates of 1-2"/hr in convection. Mean winds of 10-15 kts suggest 
individual storms will be progressive, but some weak organization 
and some training along the front could enhance the duration of 
heavy rainfall. This appears most likely in the vicinity of 
southern IN where moisture confluence maximizes, creating a locally
greater excessive rain risk, but the MRGL risk remains for 
isolated impacts today.

Weiss
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