701
FOUS30 KWBC 310827
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
427 AM EDT Fri May 31 2024

Day 1
Valid 01Z Fri May 31 2024 - 12Z Fri May 31 2024

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

Multiple clusters of convection in rather close proximity to each
other during the overnight hours preceding the start of the Day 1
period prevented any one storm from becoming dominant...but the
multiple boundaries left behind has muddled the picture of what
will be on-going as of 31/12Z. And how the models have struggled
certainly has not helped. As a result...the Day 1 Excessive
Rainfall Outlook depicts a broader and more diffuse picture than is
normally preferred early on. As the day progresses...trends in the
guidance suggests that the convection should be more progressive
than what occurred on Thursday...but that does not preclude the
possibility of additional rain falling on areas that received heavy
rainfall in recent days (especially over portions of Louisiana and
Mississippi) before mid-level energy begins to shift northeastward
and spread any associated rainfall into parts of the Mid-
Mississippi Valley by 12Z Saturday. The option for an upgrade to a
Moderate remains but not done at this time with the
uncertainty...but clearly even a brief period of intense rainfall
in areas already waterlogged could exacerbate any on-going
flooding. Maintained the Marginal Risk over the Colorado High
Plains and adjacent areas introduced on Thursday given the
potential for isolated convection capable of producing brief
downpours.

Bann

Day 2
Valid 12Z Fri May 31 2024 - 12Z Sat Jun 01 2024

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

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 Sat Jun 01 2024 - 12Z Sun Jun 02 2024

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

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