FOUS30 KWBC 260830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Sun Jan 26 2025

Day 1
Valid 12Z Sun Jan 26 2025 - 12Z Mon Jan 27 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN AND AROUND THE
PALISADES, EATON, AND HURST BURN SCARS, GENERALLY JUST NORTH AND 
WEST OF THE CENTER OF LOS ANGELES, CALIFORNIA...

...Southern California...

Shower coverage is becoming more numerous to widespread early this
morning across much of the Southern California coastline and 
adjacent inland areas, as a deep layer closed low churns near the
central California coast. As the low gradually slides southward
along the coastline today, localized moderate to heavy downpours
will become more likely along upslope portions of the Transverse 
and Peninsular Ranges (and to a lesser extent the adjacent Los 
Angeles Basin and coastal areas). While falling snow levels should
help to mitigate runoff issues at higher elevations, there are
increasing concerns for potentially significant localized impacts
for more sensitive localities, chiefly for recent burn scars where
runoff concerns are highest. While an additional 0.5" to 1.0 of
areal average QPF is expected for the region, some hi-res CAM
solutions (including the HRRR) indicate highly localized totals of
1"+. Most concerningly, these localized totals are possible in and
around the Palisades, Eaton, and Hurst burn scars. The CAMs also
indicate the potential for sub-hourly (15-min) rainfall rates of 
0.25"+, which would drive an elevated threat for mudslides and 
debris flows in and around burn scars. While the bulk of the 
rainfall should be largely beneficial for the region, the
heightened risk for significant flash flood impacts in association
with these burn scars has necessitated an upgrade to Slight risk
for a target region (generally encompassing the aforementioned burn scars).


...Texas Gulf Coast into Lower Mississippi Valley...

Moist southerly low-level flow from the western Gulf has returned
to much of the western Gulf Coast, spreading northeastward into
portions of the Lower Mississippi Valley. This return flow will
combine with a wave of low pressure and associated surface frontal
zone which will likely result in embedded moderate to heavy 
showers by late morning to midday, gradually driven southeastward 
towards the coastline with the progression of the front. While
hourly rates will generally be capped near 1", 24-hr totals could 
add up to be locally as high as 3-4" (per 00z HREF 40-km 
neighborhood probabilities for 3" exceedance of 20-30%). While 
instability will be somewhat limited, MU CAPE up to 1000 J/kg 
(maximized primarily in and between Corpus Christi to Houston) 
could support a period of localized 1-2"/hr rainfall rates (which 
adds a bit to the threat, especially within urbanized terrain). 
While models are in relatively good agreement concerning the 
magnitude of QPF (localized 3-4" totals), there is still a good bit
of uncertainty with regard to the placement of these higher totals
(with the ECMWF the most consistent in indicating these amounts in
and around Houston, while the latest HRRR-EXT run indicates totals
nearly this high as far southwest as Corpus Christi). Overall, the
CAM consensus is clustered farther southwest than much of the 
coarser global guidance has been over the past several days, and 
convection tends to verify farther southwest than expected (giving 
credence to the HRRR solution, which resulted in an expansion of 
the Marginal risk area farther southwest). A targeted upgrade to a 
Slight risk remains possible with subsequent updates, which would 
be most likely across portions of TX (where instability and the 
potential for 1-2"/hr rainfall rates is expected to be maximized). 

Churchill


Day 2
Valid 12Z Mon Jan 27 2025 - 12Z Tue Jan 28 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE TRANSVERSE/PENINSULAR RANGES, LOS ANGELES BASIN, AND INLAND
EMPIRE OF SOUTHERN CALIFORNIA...

Shower activity in association with the deep closed low looks to
continue into Monday morning over portions of Southern California,
before the low pivots inland and brings an end to the potential for
sub-hourly (15-min) rainfall rates of 0.25"+. This will continue
the Marginal risk for excessive rainfall into Day 2 for both
coastal and more inland low elevation areas (with particular
concern for any lingering shower activity over aforementioned burn
scars). The threat is expected to last for only the first half of
Day 2 (prior to 00z Tuesday). 

Churchill


Day 3
Valid 12Z Tue Jan 28 2025 - 12Z Wed Jan 29 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Churchill
$$
--- SBBSecho 3.20-Linux
 * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1)