Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
856 PM EDT Fri May 3 2024
Day 2
Valid 12Z Sat May 04 2024 - 12Z Sun May 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF
CENTRAL AND NORTH TEXAS...

...2030Z Update...

...Southern Plains...

Model guidance has shifted south quite a bit with the most recent
updates. The general consensus now is for storms to form along the
dry line in West Texas, then develop upscale and towards the east
in central Texas. As the storms develop, there will be cell mergers
and other interactions, as well as possible training that could
lead to local rainfall totals to 5 inches. Further, soils in this
area have been saturated due to rainfall from thunderstorms as
recently as yesterday. Thus, the Slight Risk area was expanded
south to include much of central Texas. The surrounding Marginal
was expanded further south to account for likely guidance changes
prior to the event. Most of the flash flood producing rainfall is
expected overnight Saturday night, continuing into Sunday morning.

On the northern side of the Slight, what happens further south will
be critical as to how much rain falls along the Red River. Since
this area too has nearly saturated soils, the northern side of the
Slight was trimmed less on the north side than it was expanded on
the south. Nonetheless, the northern side of the Slight has more
uncertainty.

...Sacramento Valley of California...

The inherited Marginal was shifted a few miles west to move the
area off of the higher elevations of the Sierras. Unseasonably cold
air associated with an upper level low will keep most of the
precipitation at the higher elevations and passes through the
Sierras as snow. Any rainfall at the lower elevations will be
confined to the valley. The event is a strong one for this time of
year, and so abundance of moisture still keeps the area as a low
end flash flooding threat.

Wegman

...Previous Discussion...

Height falls aloft ejecting eastward from the Southern Rockies and
the presence of a dryline over West Texas will foster an
environment for thunderstorms capable of producing heavy rainfall
by later in the day on Saturday that persists into Saturday
night/early Sunday morning. Precipitable water values will have
increased to nearly 1,5 inches...some 2 to 2.5 standardized
anomalies greater than climatology...over portions of central and
west central Texas by 00Z Sunday in response to a period of
southeasterly flow off of the Gulf of Mexico. Consensus of model
guidance QPF in the range of 1 to 3 inches seems
reasonable...although the UKMET was a notable outlier.

...Northern Sierra Nevada Foothills...

A fairly robust IVT pulse will slide down the west coast with
southwesterly flow aimed orthogonally to the northern and central
Sierra's by Saturday. Higher elevations will be greeted with more
snow, but the adjacent foothills will remain warm enough to benefit
from all rainfall. Rates will be borderline overall, but the
prospects for over 1" of precip has grown in the past succession
of runs with the ensemble bias corrected guidance now upwards of 2"
now forecast within the elevations below 8000' MSL, falling mainly
in a span of 8-12 hours. The threat is on the lower end of MRGL. Maintained
continuity from previous forecast and will assess whether it needs
adjusting, or removal pending future trends in guidance.

Bann