Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
447 AM EDT Sat Sep 30 2023

Day 1
Valid 12Z Sat Sep 30 2023 - 12Z Sun Oct 01 2023

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE GREAT BASIN, NEW MEXICO AND FAR WEST TEXAS, UPPER MIDWEST, AND
FLORIDA...

...Great Basin/Nevada...

A deep upper-trough will transport a plume of moisture (1-2 PWAT
stndv) into the West today. A cold front associated with a
deepening low pressure system will act as a focus for convection
over the Great Basin, in particular. There's been some
consolidation and better agreement between the hi-res and global
guidance with respect to the location of the axis of heaviest
precipitation. Some parts of central Nevada, southeastern Oregon
and southwestern Idaho could see rainfall rates around 0.25"/hr
with isolated higher amounts. Ample forcing over elevated terrain
could lead to more efficient/enhanced rain rates. Between 1-3" of
rainfall is expected through tonight.

...New Mexico/west Texas...

Convection supported by a deep upper trough to the West and
leading shortwave energy will support another localized flash
flood threat over parts of eastern New Mexico and into west Texas.
Decent instability (1000J/kg+), modest moisture flux and a
favorable low level jet may produce bursts of heavy rainfall over
our marginal risk area. Urban areas and dry washes are most
vulnerable of flash flooding.

...Upper Midwest...

An embedded shortwave within an omega ridge will continue driving
convection through this afternoon. The heaviest rainfall may
already be occurring over parts of eastern Minnesota and
northwestern Wisconsin. That being said, impressive forcing,
instability (1000J/Kg+) and moisture (2-3 PWAT stndv) could still
generate excessive rainfall leading to isolated instances of flash
flooding.

...Florida...

A slow moving shortwave trough will allow for the continuation of
scattered to isolated thunderstorms across the central/southern
peninsula today. Some cells may produce localized heavy rainfall
within the marginal risk area. Antecedent conditions will also
contribute to the sensitivity to any isolated heavy rainfall
threats.


Kebede


Day 2
Valid 12Z Sun Oct 01 2023 - 12Z Mon Oct 02 2023

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
FLORIDA AND THE SOUTHERN HIGH PLAINS OF NEW MEXICO AND TEXAS...

...Southern High Plains of New Mexico/Texas...

The deep diffluent pattern over the Great Plains will continue to
generate convection in the Southern Plains on Sunday. Instability
around 1000J/Kg and PWATs of over 1" could support some instances
o flash flooding Sunday afternoon and evening. The global models
appear to be well clustered over the Southern High Plains as well,
however the past couple of GFS runs appear to suggest that the
heaviest rainfall will occur on the southern edge of the marginal
risk area so an upgrade is not necessary at this time. Ensemble
mean exceedence probabilities of 1" in 24 hours including the 00z
GEFS are well clustered over the northeastern New Mexico and the
Texas panhandle.

...Florida...

Shortwave energy present across the state of Florida will support
isolated flash flooding concerns on Sunday. Scattered to isolated
thunderstorms will continue to develop along a quasi-stationary
front draped across the southern peninsula. There will be plenty
of instability in place so there's always the risk of some cells
over performing current forecasts with efficient rainfall rates
that exceed flash flood guidance.


Kebede

Day 3
Valid 12Z Mon Oct 02 2023 - 12Z Tue Oct 03 2023

,...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS
OF THE SOUTHERN HIGH PLAINS OF NEW MEXICO AND TEXAS...

...Southern High Plains...

The Southern High Plains will be under the influence of deep
diffluent flow from a potent upper trough propagating through the
West on Monday. This will be coupled with the arrival of a strong
upper jet aloft and favorable low level jet dynamics. Cape values
in the 1000-1500J/Kg range and moisture anomalies well over 2
standard deviations (1-1.5in") should support thunderstorm
activity with excessive rainfall potential. The latest guidance
has certainly trended wetter and is well clustered over the
Southern High Plains region for the location of heaviest rainfall
potential. The ensemble mean excellence probabilities are in good
agreement for 1 and 2" within the drawn marginal risk area.
Mitigating factors for an upgrade at this time include relatively
dry soils and high flash flood guidance. Potential severe
thunderstorms could overcome the mitigating factors by producing
higher rain rates, but there is still some uncertainty around the
severe weather threat at this time.


Kebede


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt