350
FOUS30 KWBC 060058
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Sun May 5 2024

Day 1
Valid 01Z Mon May 06 2024 - 12Z Mon May 06 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE LOWER-MID MISSISSIPPI VALLEY INTO THE TENNESSEE AND LOWER OHIO
VALLEY...FOR SOUTHEAST TEXAS TODAY...

...0100 UTC Update...
Significant changes were made to the Day 1 ERO, most notably the
removal of all risk areas (including Moderate) across TX, along
with the Slight Risk across eastern OK and much of AR, given the
dissipation of organized convection behind the upper shortwave and
with negative dMUCAPE/dt trends. Meanwhile, have expanded the
Marginal Risk into southern IN, central KY-TN, and northern AL into
far northwest GA, ahead of the aforementioned shortwave, based on
the current mesoanalysis and observational trends. MUCAPEs peaking
between 1000-1500 J/Kg, along with PWs of 1.5-1.7" in an area of
more favorable forcing (divergence aloft/deep-layer ascent) will
foster more numerous showers/tstms, with some of the more intense
clusters capable of producing 1.5-2.0"/hr rainfall rates based on
the latest (18Z) HREF neighborhood probabilities. The HREF also
indicates isolated higher probabilities (35-40%) of total overnight
rainfall exceeding 3", particularly over far western KY-TN.

Hurley


Day 2
Valid 12Z Mon May 06 2024 - 12Z Tue May 07 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL AND NORTHERN PLAINS...

21Z update... The setup continues to look favorable for areas of
heavy rainfall and localized flooding across the Northern and
Central Plains. Only minor adjustments were needed to reflect the
latest trends and WPC forecast.

Campbell

Central Plains...
A negative tilted trough will make its way out of the Rockie and
out over the central and northern plains. A corresponding area of
surface low pressure will organize over the Northern High Plains.
This results in strengthening low level flow that draws deepening
moisture and instability over the nation`s mid-section. Storms that
form farther west will encounter the increasingly moist and
unstable airmass resulting in increasing potential for downpours
and for embedded higher amounts within a broader region of 1 to 2
inch areal average amounts. Given the amount of instability to
support downpours..the alignment of the flow aloft does set up the
possibility of repeat convection and excessive rainfall. Expanded
the western boundary of the Marginal a bit westward base on
guidance but the overall forecast reasoning has changed little.

Northern portion of the Western High Plains...
Model signal continued to strengthen with respect to rainfall
amounts and the potential for a soaking to potentially excessive
rain. Much of this region has nearly saturated soils which has
reduced the 3-hr FFG to as low as 1 inch. Rainfall is only one side
of the worry given because the rainfall will be falling into
lingering snowpack. Areas of local flash flooding will be
possible.

Bann

Day 3
Valid 12Z Tue May 07 2024 - 12Z Wed May 08 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN UNITED STATES...

21Z update... The latest trends supported a complete westward
shift of Marginal Risk area covering the Upper Great lakes and
Midwest region. Small westward adjustments were made across north-
central Montana were the QPF increased and was not in the area of
snow forecast by WPC.


Campbell

Great Lakes Region...
A cold front associated with what had been the highly dynamic
system on Monday will shift westward into the western Great Lakes
region on Tuesday. The front should encounter some lingering
moisture that propagated downstream on Monday but the overall
moisture pattern is getting stretched. The GFS showed precipitable
water values...though...are either side of 1.5 inches on Tuesday
morning from parts of Wisconsin south and eastward. Values that
high tend to be pushing 2 standardized anomalies greater than
climatology for this time of year...so some locally enhanced
rainfall rates are possible.

Northern portion of the Western High Plains...
With the mid/upper low moving little since Monday...continuation of
rainfall at the lower elevations should continue into Tuesday, Only
change from the previous outlook was to minimize the overlap
between the Marginal Risk area and area where snowfall is forecast
by the WPC Winter Weather Desk.

Bann


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt