FOUS30 KWBC 060754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
254 AM EST Thu Mar 6 2025

Day 1
Valid 12Z Thu Mar 06 2025 - 12Z Fri Mar 07 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA...

Trailing vorticity maxima analyzed off the coast of CA will rotate
around the backside of the mean trough ejecting into the
Southwestern U.S. A slight void in precipitation, outside some
lingering showers will transpire this morning as the primary ascent
focuses further inland. A trailing mid-level shortwave will motion
east-southeastward into the southern portion of CA later this
afternoon and evening with one last enhancement for scattered to
widespread convection as the energy accompanies a more focused
850-700mb moisture flux as progged. The heaviest precip time frame
will likely occur as the nose of the 700mb jet moves ashore near
San Diego with the streaming westerlies working inland with low-
level ascent maximized over the southern end of the Transverse
Range down through the Peninsular Range just east of San Diego proper.

Latest CAMs output is pretty consistent with the areal max hovering
between 1-2" across the above locations with the highest situated 
closer to the Baja border just east of the SD metro. This is mainly
due to the forecast orientation of the 700mb jet co-located within
this small zone, a consistency among most of the deterministic 
suite this evening. PWATs will be generally near to just above 
seasonal for the anomalies (0.6-0.9", but considering the previous
period of rainfall with remnant burn scars being impacted 
currently, the continued rainfall will only maintain the potential 
for low-end flash flood exceedance. With the 00z HREF 
EAS/neighborhood probs nestled between 70-90% for at least 1" over 
the hardest hit locations in the Peninsular/Transverse domain, a 
continuation of the MRGL risk was still relevant given the 
characteristics above. 

Kleebauer


Day 2
Valid 12Z Fri Mar 07 2025 - 12Z Sat Mar 08 2025

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

Kleebauer


Day 3
Valid 12Z Sat Mar 08 2025 - 12Z Sun Mar 09 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
CENTRAL GULF COAST...

A fairly robust upper-low over the Southwestern U.S will pivot
eastward into the Southern Plains with multiple shortwave ejections
crossing out of the Gulf with steady motion through the Gulf coast.
The proxy of the dynamic upper pattern will help initiate surface
cyclogenesis in-of the Gulf coast with most deterministic now
developing a surface low just south of LA by the end of the D3 time
frame. Southerly flow ahead of the mean trough will lead to the
advection of more warm, moist air northward with the northern
fringe notated by a developing warm front that is depicted when
assessing the sfc-850mb wind field showing convergent flow in-of
the boundary. Guidance is becoming more focused along the Gulf
coast for the proxy of the boundary which will be key in
determining the northern extent of the instability field which will
be situated south of the aforementioned front. 

Trends within most of the deterministic and ensembles have now
shifted further south with the heaviest QPF footprint, aligning
with the ML guidance over the past 24 hrs that place the more
significant theta_E tongue within the proximity of the Gulf coast
area extending from southeastern LA over into the FL Panhandle.
PWAT anomalies are pushing towards the +2 deviation marker, a
threshold typically necessary this time of year to attain any flash
flood threat due to the locally elevated FFG's within this area of
the CONUS. Ensemble output of 1-3" is focused within the corridor
extending from the Southeastern most Parishes of LA through the
I-10 corridor, including places like Mobile, Pensacola, Panama 
City to as far east as Tallahassee. The ECMWF has been the most
consistent with this forecast over the past several runs with the
other global deterministic slowly shifting south with the primary
axis of heavier QPF. Considering the better instability gradient
closer to the Gulf coast, the best chance for heavier convection
will likely lie in that warm sector south of the warm front, and
within the convergent axis just inland within the bounds of the
front placement. Steering flow is likely to align parallel to the
front as the west-east placement will create a funneling affect for
moisture within that zone of expected impact. 

The previous MRGL risk was trimmed on the northern and western
extent and now encompasses a smaller region along the Central Gulf
Coast, including the cities referenced above. This was also agreed
upon by the local MOB/TAE WFO's representing the areas in question.
Will assess the trends closely in the coming days, but the
prospects flash flooding remain in reason to maintain some
continuity. 

Kleebauer

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