Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 PM EDT Thu Oct 16 2025

Day 1
Valid 16Z Thu Oct 16 2025 - 12Z Fri Oct 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHERN HIGH PLAINS...

16z update: Forecast remains on track and no sizable adjustments
were required.

A line of scattered thunderstorms along a stationary front with
possible short-term training from SSW to NNE exists across the
Central High Plains of NW KS into the Sand Hills of NEB. Localized
1-2" totals are possible given 500-750 J/kg of CAPE and flux
confluence of 30-40kts of 1-1.25" total Pwats. However, rates will
generally be around .75-1"/hr and given soil conditions, rains are
likely to be mainly beneficial rains than hazardous. As such, there
is a non-zero risk of isolated flooding, but remains at a sub-
Marginal Risk category.

Gallina


~~~~~Prior Discussion~~~~~
Strengthening mid-latitude cyclone will traverse the Northern High
Plains by Thursday afternoon and beyond with a developing closed
mid-level vorticity center propagating over eastern MT to the MT/ND
border later Thursday night. The subsequent evolution will lead to
a period of moderate to heavy rainfall across the above areas with
a prominent deformation axis (deepening TROWAL zone) anticipated
to setup along the MT/ND border. At this juncture, instability will
be lacking from a thermodynamic sense, however the dynamical
forcing and prolonged period of enhancement with the axis of
deformation will likely spur a widespread area of moderate to heavy
rainfall capable of low-end flash flood concerns. These concerns
will be suited mainly over those urbanized zones and any low-water
crossing. Totals area expected to be a widespread 1-2" of rainfall
with some localized totals >2", likely over parts of eastern MT
into western and northwestern ND, as the heaviest rain will hang on
there given the proxy of the surface low progression and
positioning of the axis of deformation. A MRGL risk was maintained
with a small expansion south and east to account for the latest QPF
trends.

Hurley


Day 2
Valid 12Z Fri Oct 17 2025 - 12Z Sat Oct 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Gallina


Day 3
Valid 12Z Sat Oct 18 2025 - 12Z Sun Oct 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHERN 
ARKANSAS TO NORTHERN INDIANA...

21z update: 
12z guidance trends depict a tightening of the two phasing
shortwave features; with the northern stream digging a tad faster
and the southern stream slowing and lifting northward. As such the
initial rounding jet streak appears to be broadening and increasing
overall diffluence across the Central MS Valley; further enhancing
low level confluent flow toward 45-50kts and generally supporting
of increased duration of enhanced flux within the training
convective environment from the eastern Ozark Plateau across
central IL toward L.P. of MI. The higher flux, slightly higher
CAPEs to 500-1500 J/kg, and solid right entrance ascent and general
diffluence while maintaining a parallel mean cell motion to the
mean wind supporting SSW to NNE training along and downstream of
the surface wave. As such, guidance has seen an increase in overall
totals toward 2-3" though localized totals to 4"+. Instability
reduces fairly quickly through the late afternoon, but the dynamics
remain strong to have enhanced rainfall totals into the central
Great Lakes. 

South of the base of the northern stream trof, cold front should be
more progressive, dropping southeast. Deeper moisture pool and
instability of 1000-2000 J/kg will allow for stronger/broader
updrafts with higher rainfall intensity, but steering should
limit duration with only exception to any right moving rotating
updrafts that could locally reduce forward speed while increasing
moisture flux convergence in speed and directional confluence. As
such, narrower streets of enhanced rainfall totals are more likely
than in the deformation zone further north. Along with higher FFG
values, a broader Marginal Risk is preferred at this time/cycle. 

Gallina

~~~~Prior Discussion~~~~
By the beginning of Day 3 (12Z Sat), the southern stream shortwave
traversing the Southern Plains will begin to merge with the 
northern stream shortwave digging into the Central Plains. As this 
occurs, by the end of the period (12Z Sun) there will be a 
strengthening upper level jet streak rounding the trough base, with
a fairly vigorous and sizable accompanying vort center across the 
Lower MO and Mid MS Valley. As the upper shortwaves phase, the 
guidance remains consistent with the uptick in low-level moisture 
transport across the Mid South into the Lower OH Valley (confluence
of the MS and OH Rivers). The 00Z GEFS in fact shows 850 mb 
moisture flux between 3-3.5 standard deviations above normal over 
the Slight Risk area, along an axis of TPW values between 1.7-1.9".

Meanwhile, deep-layer instability, while not overly robust (MUCAPEs
500-1000 J/Kg per the 00Z GFS), will be sufficient for intense
short-term rainfall rates considering the degree of synoptic
forcing and available deep moisture. The main inhibitor to the
excessive rainfall threat is the likelihood that the upper trough
and associated surface cold front will become more progressive with
time later in the period (Sunday night). Nevertheless, the setup
continues to align with the expectations of a low-end Slight ERO
Risk, as supported by the latest CSU ERO first-guess fields (UFVS
verified) over an area where the current 3 hourly FFG is 2-2.5
inches.

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