290
FOUS30 KWBC 010048
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
848 PM EDT Fri May 31 2024

Day 1
Valid 01Z Sat Jun 01 2024 - 12Z Sat Jun 01 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE UPPER MIDWEST AND SOUTHEAST U.S. INTO THE LOWER/MID
MISSISSIPPI VALLEY...

...01Z Update...
With the 0100 UTC update, included a targeted Slight Risk area
across portions of central-southcentral TX, including much of the
Austin and San Antonio metros and Hill Country, owing to the
expanding cluster of convection moving into an area of untapped
deep-layer instability (mixed-layer CAPEs 2000-2500 J/Kg).
Moreover, recent heavy rainfall has significantly lowered FFGs in
this region, with 1hr FFG as low as 1-1.5". For further details,
please refer to the latest Mesoscale Precipitation Discussion or
MPD #361, which can be accessed at
www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd.php.


...20Z Update...
Based on the latest observational and mesoanalysis trends, have updated
the Day 1 ERO to (a) add a Slight Risk area across northeast NE-
Southeast SD into northwest IA and much of southern MN, and (b)
pare much of the Slight risk west of AR-LA. Despite the earlier
heavy rainfall/antecedent wet soils, shortwave ridging is limiting
the converage of any renewed convection, despite the airmass
recovery (destabilization) this afternoon. Per the latest high-res
CAMs (HRRRs and 18Z HREF), less-organized or spottier convection
later this afternoon and evening may result in additional localized
instances of flash flooding, though mainly south of where the
heaviest rainfall had occurred over the past 24hrs.

Hurley


Day 2
Valid 12Z Sat Jun 01 2024 - 12Z Sun Jun 02 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST US INTO THE LOWER MISSISSIPPI VALLEY...

21Z update... Minor reduction of the Marginal Risk near the Sand
Hills where FFG is notably higher than surrounding locations and
along the northern bounds across southern Michigan. Otherwise the
area highlighted by the Marginal Risk remains in good order. There
was a notable increase of QPF along part of the central Gulf Coast
and into western Florida where the latest guidance is suggesting
heavy rain to materialize a bit further east than previous cycles.
The Slight Risk area as a whole was translated a bit east/south
and expanded coverage from southeast Louisiana to western Florida.
In turn the Marginal was adjusted east as well across Florida and
toward the Georgia state line. There are hints that the Pensacola
vicinity could have downpours yielding upwards of 3 inches locally.

Campbell

The shortwave that started lifting northeastward into the Mid-
Mississippi Valley will continue to focus and support convection
capable of producing heavy rainfall mainly across parts of
Mississippi. Guidance continues to show the potential for isolated
3 to 5 inch amounts within the Slight Risk area. Concern in the
western portion of the Slight Risk area where flash flood guidance
has been lowered by recent bouts of rainfall while areas on the
eastern side of the Slight Risk area should be in a better position
to receive higher rainfall rates given a persistent axis of
precipitable water values at or above 1.75 inches across Alabama.
This is roughly coincident with the low-end probabilities for 3
inches of rainfall in an hour as shown by the HREF probabilities.
Farther west...the still expect convection over the western High
Plains from southwest Nebraska southward into western
Oklahoma/Texas panhandle and extending nearly as far south as the
Rio Grande. Spaghetti plots showed moisture beginning to return as
low level winds backed during the afternoon.

Bann

Day 3
Valid 12Z Sun Jun 02 2024 - 12Z Mon Jun 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS AND UPPER MISSISSIPPI VALLEY...

21Z update... Although there is spread amongst the guidance on
where areas of moderate/heavy rain will be there is a growing
signal from far northeast Kansas north/northeastward to
central/northern Minnesota and western Wisconsin. Parts of this
region has had recent rains to raise soil saturation which has
lowered the threshold needed for flooding concerns to arise. Areal
averages of 1 to 3 inches are forecast with local maximums of 4+
inches possible. A Slight Risk area was raised for this period
covering northeast Kansas/northwest Missouri to central
Minnesota/western Wisconsin.

Campbell

Surface low pressure forming over eastern Montana/eastern Wyoming
and the western Dakotas Saturday evening will increase moisture
transport east of the Rockies as a fast moving/low amplitude trough
emerges out over the northern and central plains on Sunday. The
surface low and an attached cold front will help focus and support
convection capable of producing locally heavy rainfall. Moisture
flux anomalies increase to more than 3 standardized anomalies above
climatology ahead of the approaching cold front...which allows
precipitable water values to approach 1.5 inches in the northern
Plains. Farther south...isolated thunderstorms are also expected
later in the day and in the evening in confluent flow along the dry
line which also has the potential for locally intense rainfall and
isolated flooding.

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