FOUS30 KWBC 180756
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
256 AM EST Mon Nov 18 2024

Day 1
Valid 12Z Mon Nov 18 2024 - 12Z Tue Nov 19 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST
LOUISIANA INTO FAR SOUTHWEST MISSISSIPPI...


An axis of much above average tropical PW values expected to be
drawn rapidly northeastward from the remnants of Sara, across the
central Gulf of Mexico and into the Central Gulf coast ahead of 
the negatively tilted closed low ejecting northeastward from the 
Southern Plains into the Upper Mississippi Valley day 1. These 
anomalous tropical PW values, 3 to 4+ standard deviations above the
mean will enhance convection along and ahead of the cold front 
pushing eastward across the Gulf coast, primarily during the second
half of day 1 from southeast Louisiana into southern Mississippi. 
A slight risk area was maintained where the latest HREF 
neighborhood probabilities are highest for 2 and 3"+ amounts. The 
simulated hi res radars are in good agreement in showing potential 
for a period of training of cells in this anomalous PW axis in the 
0000-1200 UTC Tuesday time period across the slight risk area of 
southeast LA into southern MS. In areas of training, hourly 
rainfall amounts of 1-2"+ possible, resulting in flash flooding, 
especially in the urbanized areas of New Orleans. 

Across the Southern to Central Plains toward the Upper MS Valley...there
is fairly good agreement on an axis of heavy rain from northern 
OK, across much of KS, eastern NE, northwest MO, southeast SD, much
of IA, southern MN into southwest WI in a region of strong
isentropic lift ahead of the deepening surface low moving quickly
northeastward across these areas. While widespread heavy amounts
are likely, hourly rates will are mostly depicted as .25-50"+ in
the latest hi res guidance. This should keep the threat of any
runoff issues at marginal. The previous marginal risk area was
trimmed on the eastern end, taking out much of IA, MO and eastern
OK. The current marginal risk coincides well with the axis of the
highest HREF 2"+ day 1 probabilities.

Oravec

Day 2
Valid 12Z Tue Nov 19 2024 - 12Z Wed Nov 20 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEAST
LOUISIANA, ACROSS FAR SOUTHERN MISSISSIPPI, FAR SOUTHERN ALABAMA
INTO THE WESTERN FLORIDA PANHANDLE...

The convection that is expected to enhance along the Central Gulf 
coast late day 1, will continue into day 2 as the surface front 
continues to push east along the Gulf Coast. The tropical PW 
values entrained ahead of this front day 1, will continue to push 
across central to eastern Gulf coast day 2. Training of cells in a 
southwest to northeasterly direction likely to continue Tuesday 
morning from southeast LA into far southern MS, far southern AL and
the western FL Panhandle. There is some timing differences as to 
whether heavy rains will continue in the vicinity of New Orleans 
early Tuesday, or have pressed just to the east. The New Orleans 
metro area was kept in the slight risk given potential for an 
overlap of day 1 and day 2 heavy rain areas. The latest HREF 12 
hour neighborhood probabilities ending 00Z Wed show the highest 
probabilities for 2 and 3"+ amounts remaining across far southeast 
LA, far southern MS, far southern AL and the western FL Panhandle. 
This was the region depicted in a slight risk for day 2, with the 
previous risk area trimmed on the northern end across south central
AL after collaboration with WFO MOB. The slight risk area 
corresponds with the hi res consensus for the greatest hourly 
totals of 1-2"+ in regions of training.

...Coastal Washington, Oregon and far northwest California...

Models are in good agreement with the rapid cyclogenesis event
across the northeast Pacific off the Pacific Northwest coast. The
low level southerly flow along and ahead of the associated cold
front will become very anomalous Tuesday night into early
Wednesday, with 850-700 mb moisture flux anomalies of 3-4 standard
deviations above the mean impacting the Pac NW/far northwest CA
coast. A well defined area of frontal precip likely to push inland
across coastal Pac NW/far northwest CA after 0000 UTC. Hourly
rainfall rates in the .25-50"+ range possible, especially across
southwest Oregon into far northwest CA where the strong southerly
low level flow will have a better upslope component. For areas of
northwest California into far southwest Oregon, this will be the
beginning of a multi day Atmospheric River event. No changes made 
to the marginal risk area from the previous issuance.

Oravec


Day 3
Valid 12Z Wed Nov 20 2024 - 12Z Thu Nov 21 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS FAR 
Southwest OREGON INTO NORTHWEST CALIFORNIA...

The multi day atmospheric river event the began late day 2 for far
southwest Oregon into northwest California will continue day 3. The
rapidly deepening day 2 low over the northeast Pacific will anchor
a nearly stationary upper vortex off the Pac NW coast day 3. Strong
persistent deep layered west southwest flow on the south side of
this vortex will impact northwest California into far southwest
Oregon day 3. with IVT values of 500-800 km/m-1 s-2. and 850-700 mb
moisture flux anomalies of 2-4 standard deviations above the mean.
There is fairly good model agreement with heavy precip totals of 
3-5" primarily over northwest California, with isolated totals of 
6-8" possible. No significant changes made to the previous slight risk area.

Oravec

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