FOUS30 KWBC 020814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
414 AM EDT Sat Nov 2 2024

Day 1
Valid 12Z Sat Nov 02 2024 - 12Z Sun Nov 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE SOUTHERN PLAINS...

A deep but slow-moving longwave trough will move across the Desert
Southwest through tonight. Multiple shortwaves of upper level 
energy will move through the jet stream rounding the base of the 
trough. As those shortwaves eject over the high Plains of Texas and
Oklahoma, they will meet up with increasing Gulf moisture tracking
northward across Texas. At the surface, the trough-ridge interface
will feature a slow-moving cold front which will also add to the
forcing in the area. PWATs will increase above 1.75 inches across
much of the Slight Risk area.

The combination of the increasing moisture and ample low and upper
level forcing will be multiple rounds of training thunderstorms
initiating over northwest Texas and the Panhandle, then quickly
organize into segments which will slowly track east as embedded
heavier cells track northeastward and roughly parallel to the
lines. This will support training convection which in addition to 2
inch per hour rates, could mean any particular location in the 
Slight Risk area could see multiple rounds of heavy rainfall.

In contrast to the heavy rains, mitigating the flood risk has been
multiple weeks of very little rain across the middle of the
country. The dry streams and creekbeds will easily be able to
handle most of the rain that falls, but should training of multiple
storms occur, especially over any urban areas such as Oklahoma
City, then flash flooding impacts could quickly arise. Since the
storms will be slow moving, this will support widely scattered
flooding impacts, especially from Wichita Falls, TX through
Oklahoma City. 

Wegman


Day 2
Valid 12Z Sun Nov 03 2024 - 12Z Mon Nov 04 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM CENTRAL AND
NORTHEASTERN OKLAHOMA AND ALONG THE KANSAS/MISSOURI BORDER...

Storms from the overnight period Saturday night will diminish with
daytime heating and the typical daytime weakening of the LLJ.
However, throughout the day the atmosphere will recharge such that
by Sunday night the passage of another shortwave will result in a
refiring of the storms across central and eastern Oklahoma, which
will grow and train upscale into far eastern Kansas, Missouri, and
eventually Iowa and far western Illinois. The Moderate Risk was
largely unchanged, with a small northward expansion. This is
primarily the portion of the region which is expected to get some
rain tonight, which will prime the soils for the heavier rains for
most of eastern Oklahoma and points north and east by Sunday night.
This expected overlap of rainfall is what will push the flash
flooding impact and coverage potential into the Moderate Risk
category, albeit the lower end of the category. Obviously this will
largely depend on how much rain is seen in the Moderate Risk area
Saturday night before the start of the period.

Once again the LLJ off the Gulf will supply a stream of ample
moisture to the slow-moving storms, so the flooding impact
potential, especially in areas where Sunday is the first
significant rains seen in the area in weeks, will be dependent on
the upper level energy tracking along the surface front keeping
storms moving over the same areas. The ERO risk areas were
conservative on the north and east sides and more liberal on the
south and west sides due to expected prior rainfall (or lack
thereof) on Saturday. The lack of prior rainfall has gotten river
levels to very low conditions, making plenty of room for the water
from heavy rain. This will greatly diminish the flooding threat
broadly. Had there been recent rains in this area, then a more
expansive Moderate Risk may have been needed. From Day 2 onward the
flooding potential across the middle of the country will be highly
dependent on how well previous days rains were able to result in
flooding, as amounts in the highest rainfall risk areas will be
largely the same day to day, so overlap with previous' days will be
critical. Of course, urban and low-lying/flood prone areas will be
at greater risk of flash flooding through Sunday night.

Wegman


Day 3
Valid 12Z Mon Nov 04 2024 - 12Z Tue Nov 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST
TEXAS THROUGH THE CHICAGOLAND AREA...

The slow moving cold front that will have brought rains to areas
west of the Mississippi this weekend will move a little faster to
the east Monday and Monday night. Additional lines of storms are
expected again on Monday, but mostly for areas not expected to get
too much rain this weekend. Thus, the Slight Risk remains good as
the flooding from heavy rain is offset by the dry soil conditions.
By this point we should have a good idea as to how much flooding
will be seen as both Saturday and Sunday's forecast rains will be
on repeat over the Slight Risk area again on Monday. No significant
changes were made or needed from the inherited Day 4 forecast.

Wegman
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