FOUS30 KWBC 240808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Tue Jun 24 2025

Day 1
Valid 12Z Tue Jun 24 2025 - 12Z Wed Jun 25 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
CENTRAL AND SOUTHERN NEW MEXICO...

...New Mexico...

A massive 597dm ridge centered over the Ohio Valley and Mid
Atlantic will flex further as we head into Tuesday with the higher
heights on the western fringes pushing back west beyond the 
eastern portions NM. A steady north- south progression within the 
mid and upper levels will send numerous smaller shortwave 
perturbations poleward with anticipated motions into the 
Sacramento's, eventually north into the Sangre de Cristos by the
late-afternoon and evening period today. Anomalous moisture ranking
in the 99th percentile via NAEFS and ECENS Climatological
percentiles will remain parked over the region the next 24-36 hrs 
and will couple with the focused ascent and narrow upslope proxy 
within the Sacramento Mtns. This will translate to a corridor of 
heavy convection remaining situated in- of the terrain beginning 
late this morning and carrying through peak diurnal instability. 
Consensus within all deterministic and relevant ensembles agree 
that local topographic effects within this pattern will yield some 
significant rainfall potential over areas that are prone to flash 
flooding, especially with the burn scars still present near Ruidoso
creating higher runoff capabilities. 00z HREF neighborhood
probabilities were elevated for the >3" (60-80%) and >5" (30-60%)
prospects within the Sacramento's for the period. The biggest
difference is the increased probs for those similar thresholds for
areas west of the Sacramento's, encroaching on places northeast of
the Bootheel into Southern NM. 

The difference the past 24 hrs. has been the expected influence of
the approaching trough out west providing a reinforcement of the 
trailing upper jet with the amplitude of the pattern creating more 
room further west for large scale ascent, and moisture advection 
back into the western half of NM, even sneaking into Southeast AZ. 
The entire evolution will likely spur scattered to widespread 
thunderstorm activity over the aforementioned regions with cold 
pool mergers from storms likely to produce some upscale growth in 
the evening as the convergence of cold pools will act to spawn more
multi-cell modes. A lot of the deterministic now has locally 2-4" 
across places like the San Mateo Mtns. and adjacent deserts 
stemming from the convective clusters propagating eastward over the
second half of the forecast cycle. These areas are prone to any 
type of heavy rainfall, and given the highly anomalous environment,
1-2"/hr rates are certainly in the cards. This threat will linger
through the overnight time frame before finally settling closer to
Wednesday AM.  

Further north, the signal for heavy rainfall continues into the 
Sangre de Cristos where the afternoon and evening time frames call 
for widespread heavy thunderstorm activity aligned with the ridges 
of the southern Rockies. These areas also have burn scar prevalence
that could exacerbate flash flood risks as runoff capabilities are
maximized. 24hr 100yr ARI exceedance probabilities are highest
across Central and Southern NM, but a small axis of >20% probs
remains parked over the Sangre de Cristos north of Santa Fe. 10yr
ARI exceedance probs are between 60-80% for the same area (90+%
over the Sacramento's), so the threat is within the upper echelon
of the prob fields leading to a higher chance of significant
impacts over the complex terrain and remnant burn scars. 

The previous MDT risk was expanded westward to include those areas
that could see locally as much as 2-4" in any storm impacts this
afternoon and evening lasting into early Wednesday. A high-end MDT
is forecast for the Sacramento and Sangre de Cristo Mtns. in NM.
High end SLGT risk is forecast for El Paso proper and surrounding
suburbs. There's a chance the threat for El Paso trends more
impactful, so be sure to check in with the latest updates in the
next forecast package for a potential upgrade over the urban center.

...Central Plains to Midwest...

Current radar/sat composite shows an extensive line of convection
extending from southwest to northeast out of KS to as far north as
Central WI. The setup for the convective pattern lies within the
northern periphery of a ridge and along a quasi-stationary front
bisecting the areas above. Smaller shortwaves rounding the western
flank of the ridge will continue riding over top the front 
creating focused areas of showers and thunderstorms through the 
first 6hrs of the period with some areas over far Northeast KS into
Northwest MO and Southern IA seeing a continuation of locally 
heavy rainfall bleeding into the new D1. This area is the focus 
initially for flash flood impacts with saturated grounds likely to 
struggle to withstand the initial batch of storms that push 
through. Thankfully, there will be a small "break" in the 
persistence of the convective pattern moving into the late-morning
and afternoon, but still some scattered shower/storm development 
will be forecast during the prime destabilization period, so the 
threat for isolated flash flooding will carry through the daytime. 

By the evening, the focus of the convective pattern shifts back
west and southwest with an ejection of a potent shortwave out of
the Southern High Plains and Front Range of the Rockies. With ample
instability presence across the Central Plains into the Midwest
along the quasi-stationary front, a second convective onslaught is
forecast to materialize likely beginning between 20-00z, carrying
east and northeast through the remainder of the forecast. At the
same juncture, a strong 700-900 kg/ms IVT pulse will be advecting
northeastward into the Central Plains and Midwest during the time 
frame of interest (00-12z Wednesday), so the heavy rain threat with
2-3"/hr rates will certainly have potential for basically anywhere
in the Central Plains/Midwest domain. There's a growing consensus 
on the area positioned over Southern SD, much of NE, and parts of 
KS being the initial beneficiary of the convective development 
which could lead to scattered flash flood prospects within a 6hr 
window upon initiation. As we move into the evening, nocturnal LLJ 
will spawn in-of the High Plains arcing northeast into parts of the
Midwest allowing the stationary front to begin lifting north in 
the form of a warm front. The mean layer flow will begin to orient 
more parallel to the front itself creating an environment capable 
for cells to mature and begin training over areas within proxy to 
the boundary. Guidance has been subject to bouncing around on 
exactly where this may occur, but 00z CAMs have come into a 
reasonable agreement on an axis extending over Eastern NE, 
including the Omaha metro, through Western IA. This is correlated 
with the higher neighborhood probs for >2" (50-70%) aligned over 
the area with the >3" signal pretty respectable (40-60%) over the 
same area. The highest probs and overlap of heavy precip within the
CAMs is surprisingly directly over Omaha and surrounding areas. 
This depicting likely stems from the nose of the LLJ being forecast
to right over the general vicinity, a synoptic representation that
typically denotes a greater likelihood of where the heavier precip
could occur. It will be something to monitor in the next 
succession of CAMs output, but with such a solid signal, was 
inclined to mention as a higher end SLGT will be forecast within 
that Eastern NE through Western IA region. 

Further north, a complex of storms will originate over Southern SD
from another shortwave progression moving through the Northern
Plains. This area could see the benefit of cell mergers somewhere
in the proxy of Southeast SD into Southwest MN as depicted within
multiple deterministic. Considering this area levying higher FFG's
compared to areas further south, the threat for significant flash
flooding is lower, but still generally within the SLGT risk
threshold considering the airmass in place. The SLGT risk is
positioned as far back as Northeast CO into Southern NE and as far
east as Northern IL and Southern WI thanks to multiple periods of
heavy convection impacting the region. 

Kleebauer

Day 2
Valid 12Z Wed Jun 25 2025 - 12Z Thu Jun 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NEW MEXICO, CENTRAL PLAINS AND MIDWEST...

...New Mexico...

Despite a smaller areal coverage anticipated for convection across
New Mexico for Wednesday, scattered thunderstorms will still 
cause problems during afternoon initiation as ample heating during
the prime destabilization window (16-21z) will yield another 
threat of heavy rainfall across the terrain and adjacent valleys in
Central and Southern NM. Current signals are nowhere near as 
robust as the D1 time frame, but with forecasted significant 
impacts the period prior, there's a greater threat of truly 
compromised FFG's leading in, allowing for the bar to be very low 
for flash flooding over areas that will see significant rainfall in
the areas referenced above. Hi-res ensemble blended mean QPF is now
solidly within the 1-2" range with locally higher totals across the
Sacramento's. Areal average 0.5-1" of rainfall is forecast over
much of South-Central NM and over the Sangre de Cristos with totals
potentially up to 2" in stronger convective cores. The overlap with
the previous period allows for at least a SLGT risk with a higher
end SLGT progged over the Sacramento's where convective initiation
is likely. A targeted upgrade is plausible within the two main
mountain areas in the state, especially when you factor in the
antecedent conditions for the period in question. If CAMs come in
more robust, or impacts during the D1 are severe enough to fully
compromise soils to where any convective threat could be deemed significant.

...Central Plains to Midwest...

Convective pattern across the Plains and Midwest at the end of the
D1 will translate northward into the Upper Mississippi Valley with
organized convection over NE/IA and SD/MN converging along the
propagating warm front leading to a swath of heavy rainfall across
much of the Southern 1/3rd of MN. All guidance is in agreement on a
pretty significant QPF shield moving through the area encompassing
Southern MN up through Northwest WI with some back-building
potential along the front as it migrates north and begins to slow
its momentum. Areal average of 1-2" with locally up to 4" totals 
are forecast across that portion of the Upper Midwest, reflected 
well within the NBM 90th percentile QPF signature, as well as 
within the 12-00z time frame covered by the end of the 00z HREF 
blended mean. This is just round 1 of what will be yet another
secondary convective initiation come Wednesday evening when another
strong shortwave and attendant IVT pulse comes pushing back over
Eastern NE, Western IA and points north. Additional heavy rainfall
will intersect many areas that will have seen significant totals
earlier in the period and the second half of the D1. The
compounding impacts will lead to scattered to widespread flash
flood instances as FFG's will be notably lower comparatively to 
the before the previous rounds. Ensemble bias corrected mean is now
between 3-4" over a large area encompassing Southern MN into 
Northwest WI with 2-3" positioned just to the southwest of MN. EC 
AIFS output is in agreement with the positioning of the QPF maxima
anticipated, something that has not been the case over the past few
days, so we seem to be moving into a greater consensus. As a 
result, there is a large high-end SLGT risk positioned from 
Northeast NE up through MN into the western portion of WI. An 
upgrade within anywhere in that zone is plausible in the coming 
updates as multi-day impacts could spur some locally significant 
flash flood prospects. 

Kleebauer
$$
--- SBBSecho 3.20-Linux
 * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1)