Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Mon Oct 12 2026
Day 2
Valid 12Z Tue Oct 13 2026 - 12Z Wed Oct 14 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE GREAT BASIN, ALONG WITH THE CENTRAL AND SOUTHERN PLAINS...

...Great Basin...

Upper low across NV will shift slowly eastward into the interior
west with sights on UT and surrounds leading to an isolated flash
flood threat continuing directly underneath the low itself. As of
now, the probabilities for >1" are relatively benign in terms of
coverage for >50%. That said, the max probability of 50-80% is
centered over the valley between Provo up to Logan which is right
in the population center for the state, and coincides with more
urbanization factors that could promote run off potential. The area
has seen several inches of rainfall with this setup leading into
Tuesday, so antecedent conditions are more favorable for these
isolated flash flood prospects compared to normal. Considering the
setup has not really wavered in terms of its evolution, felt it was
a case to maintain continuity in the forecast with a small MRGL
risk placed over the western and north-central portion of the state
with the centroid over the valley of northern UT.

...Central and Southern Plains...

Longwave pattern across the Central and Southern U.S. will
materialize in such that a broad convective evolution is
increasingly favorable for late-Tuesday afternoon, carrying into
Wednesday morning. The western ULL will slowly pivot eastward into
UT by Tuesday with increasingly diffluent flow positioned across
the Central Plains and portions of the Southern High Plains as we
move into the second half of the D2. A broad upper jet alignment
will arc over the the northern tier of the CONUS leading to a well
placed RER jet core centered over the Central U.S. with the ascent
maximized likely south of a latitude of I-80. The current progs are
for lee cyclogenesis to begin the period prior, but exhibit very
little forward propagation from its initiation point as the pattern
evolution out west motions very slowly. Additional input of energy
streaming poleward out of the Eastern Pacific, up through Mexico,
and into the High Plains will occur in tandem with the overall
longwave evolution as energy on the northern edge of Hurricane
Simon will advance north-northeast into the region around the
western periphery of a broad ridge centered over the Lower
Mississippi Valley. The ample ascent provided by both mid-level
vorticity advection and improving large scale jet dynamics within
deep layer moisture presence over the Plains will aid in the
production of convection as we step into the peak diurnal
instability hours, and beyond.

The setup also calls for an integration of a LLJ development
around 00z Wednesday which will only act as a convergent piece of
this puzzle as the addition of low- level southerly enhancement
will only act to assist the convective pattern as increasing low-
level shear and maintenance of general buoyancy across the Plains
will allow for a maturation of area convection over the Central
Plains and Mid-Mississippi Valley. Model consensus indicates a
blossoming of convective coverage across KS/MO/OK by nightfall on
Tuesday with an expected initiation of convection over west TX
thanks to the LLJ interaction with the streaming mid- level energy
ejecting out of Mexico. Generally slow cell motions and potential
for repeating convection are anticipated over the entire stretch
from southwest TX up through the Central Plains with the latest
forecast soundings across the South-Central U.S. indicative of
weakening mean winds and backing of the low-level flow that would
support some back-building potential of precipitation in-of OK/KS
into western MO. As of this time, the relative FFG's in the area
would support at least the initial threat of heavy rainfall as
current QPF means hover between 1-2" over a broad area from the
Permian Basin up into eastern KS and adjacent western MO.
Deterministic outputs do signal some local totals >3" across
portions of the aforementioned area which would place them near the
3 and 6hr FFG thresholds in place across these particular areas.
We are still at the very end of the HREF output for this setup
meaning we are missing the key final 12hrs of the period to see how
the CAMs handle the magnitude of the convection for this time
frame. At first glance, there may be enough of a signal for a SLGT
risk somewhere across the High Plains extending northeast, so stay
tuned over the next few forecast cycles for possible upgrades for
the period. For now, the previous MRGL risk from the Big Bend up
through the southern tier of the Midwest remains consistent with
this evening's guidance.

Kleebauer


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt