FOUS30 KWBC 220809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Wed May 22 2024

Day 1
Valid 12Z Wed May 22 2024 - 12Z Thu May 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST 
TEXAS/SOUTHEAST OKLAHOMA, INTO SOUTHERN ARKANSAS AND NORTHERN
LOUISIANA...

The southern portion of the frontal boundary emanating from the 
low moving from the Upper Mississippi Valley into southern Ontario
this morning will slow significantly from the Southern Plains into
the Lower Arkansas and Mid Mississippi Valley during the upcoming day
1 period, becoming aligned more parallel to the southwest flow 
aloft. Additional convection likely to form in the axis of PW 
values 2+ standard deviations above the mean as shortwave energy 
moves east northeastward across the Southern Plains and along this
slowing frontal zone. There has been a significant southward shift
in nearly all of the models with the forecast axis of heaviest 
precip along this front. The individual hi res runs and the HREF 
mean are the farthest south now, with global models to the north of
the HREF mean, closer to the 18Z axis of the RRFS and 06Z May 21 
axis of the RRFSMEAN. The 00Z EC is the farthest south global
model, closer to the hi res and HREF mean axis.  WPC has followed 
the southward trend in our latest qpf and we will also trend 
farther to the south with the Excessive Rainfall probabilities. 
Training of cells parallel to the boundary is a concern for heavy 
to locally excessive rainfall totals day 1, although confidence is 
not great with placement given the spread and significant changes 
run to run. With respect to the previous outlook for this period, 
there has been approximately a 60-80 mile southward adjustment to 
the marginal and slight risk areas, extending them farther south 
into northeast Texas and northern Louisiana and reducing the risk 
from the OH/MS river confluence into northern Arkansas. 


Day 2
Valid 12Z Thu May 23 2024 - 12Z Fri May 24 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM FAR NORTHEAST
TEXAS/ FAR SOUTHEAST OKLAHOMA, ACROSS SOUTHERN ARKANSAS INTO
NORTHERN MISSISSIPPI...

Similar to the day 1 time period, a stationary frontal boundary 
expected to remain stretched in a west southwest to east 
northeasterly direction across northeast Texas/southeast Oklahoma 
into Arkansas, although this front will be weakening with time. PW 
values expected to remain 1.5 to 2 standard deviations above the 
mean along this weakening front during day 2. Additional shortwave
energy moving west to east across the Southern Plains will support
additional convection in this high PW axis and potential for 
additional heavy rains from northeast Texas/southeast Oklahoma, 
east across the Lower Arkansas Valley into the Lower Mississippi 
Valley. Given the low confidence with how convection will develop 
day 1 and whether there will be an outflow boundary still in tact 
for the day 2 convection, confidence does remain low on qpf 
placement. Models do seem to support a farther northward axis day 2
compared to day 1 as the stationary front weakens and southerly low
level flow pushes the high PW values farther to the north.  There 
still is potential for overlap of day 1 heavy rains with day 2, but
with low confidence in the day 1 axis, confidence is low as to
where this overlap will be. The new day 2 Excessive Rainfall
Outlook did trend southward from the previous issuance for this
period by approximately 50 miles to better match the latest WPC 
and model qpf consensus.

...Eastern portions of the Northern to Central Plains into the 
Upper Mississippi Valley...

No significant changes made to the marginal risk area across 
eastern portions of the Northern to Central Plains into the Upper 
Mississippi Valley. Additional convection likely ahead of the next
strong area of height falls rotating from the Northern Rockies 
into the Northern and Central Plains day 2. This region has seen heavy
rainfall amounts over the past 24 hours, keeping stream flows high
prior to the potential day 2 mounts. There is a lot of spread with
qpf details, leading to low confidence in any one solution. 
However, with the strong upper trof, and associated strengthening 
low level southerly flow and increasing PW values, there will be 
potential for localized heavy rainfall amounts that may fall across
areas that received heavy totals over the past 24 hours.


Oravec

Day 3
Valid 12Z Fri May 24 2024 - 12Z Sat May 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE UPPER MISSISSIPPI VALLEY INTO THE UPPER GREAT LAKES AND FROM
THE LOWER ARKANSAS/LOWER MISSISSIPPI VALLEYS INTO THE TENNESSEE
VALLEY AND SOUTHERN TO CENTRAL APPALACHIANS...

...Upper Mississippi Valley into the Upper Great Lakes...

The next strong area of height falls moving into the Northern High
Plains at the end of day 2 will continue to push eastward through
the Northern Plains and into the Upper Mississippi Valley during
day 3. The overall favorable large scale conditions ahead of these
height falls day 2 will continue into day 3 along the associated
front where strong frontal convergence in an axis of PW values 1 to
1.5 standard deviations above the mean will support potential for
moderate to locally heavy rainfall totals. This front does look 
very progressive day 3, which may limit very heavy amounts. The 
marginal risk was drawn to where there may be overlap of locally 
heavy rains day 3 with heavy rains that have fallen over the past 
24 hours.

...Lower Arkansas/Lower Mississippi Valley, Tennessee Valley into
the Southern to Central Appalachians...

A broad marginal risk area was maintained from the Lower 
Arkansas/Lower Mississippi Valley region, east northeast across the  
Tennessee Valley and into the Southern to Central Appalachians. PW
values across these regions will remain above average for the day 3
period, with additional shortwave energy moving west to east
supporting scattered convection and locally heavy rainfall 
amounts. Not a lot of confidence in where the scattered convection 
will become more organized, with a fairly large spread in model qpf
details.

Oravec

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