Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
754 PM EST Thu Feb 6 2025
Day 1
Valid 01Z Fri Feb 07 2025 - 12Z Fri Feb 07 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF CALIFORNIA AND THE OHIO VALLEY...
...California...
A compact, dynamic system with a vigorous mid level shortwave and
strong left exit region upper level jet forcing should support a
short duration period of enhanced rainfall rates, although the
quick forward motion of the system will limit overall rainfall
magnitudes. Given the low-level ageostrophic response ahead of the
upper level jet streak, the latest (00Z) GEFS output shows a quick
uptick in southwesterly 850-700 mb moisture transport, peaking
between 3-4 standard deviations above normal across the central 2/3
of CA Thursday afternoon and evening. Recent model runs continue
to show 1-2+ inches falling mostly within 12 hours, with localized
amounts of 3+ inches over the coastal ranges and Sierra foothills
per the latest high-res guidance. Given the saturated conditions
and brief potential for higher rates (0.35+ in/hr) beginning around
21Z along the coast and by 00Z farther inland, this may result in
localized runoff issues, especially over burn scars across Santa
Barbara, Ventura, and Los Angeles counties.
Gallina/Hurley
...TN Valley into the Southern Appalachians...
A round of locally heavy rain is in progress across portions of
KY, TN, WV and southwest VA near and ahead of an approaching cold
front and near the base of a broad shortwave transiting the Great
Lakes. While precipitable water values are run of the mill --
0.75-1.25" -- the coolness of the atmosphere is leading to
significant saturation, which is aiding precipitation efficiency.
ML CAPE of 500-1000 J/Kg is being tapped by increasingly surface
based convection closer to the front. Thus far, hourly rain totals
have maximized in the 0.5-1" range. Given the ingredients above,
hourly rain totals to 1.5" and local amounts of 3" remain
possible over the next several hours. The decreasing size of the
rainfall pattern with time suggests a decline in the risk as we
move through the overnight hours. Some of this region (the
northeast portion of the Marginal Risk) is more sensitive than
normal to additional heavy rainfall given the 2-4" that fell over
the past 24 hours. Overall, an isolated to widely scattered flash
flood risk appears to exist now that the convective pattern is
narrowing and showing increasing progression. The overall excessive
rainfall risk is expected to end during the early morning hours of
Friday across northern GA, roughly 07z-08z based on the 18z HREF
probabilities of 0.5"+ in an hour.
Roth
Day 2
Valid 12Z Fri Feb 07 2025 - 12Z Sat Feb 08 2025
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.
Pereira
Day 3
Valid 12Z Sat Feb 08 2025 - 12Z Sun Feb 09 2025
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.
Pereira
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