151
FOUS30 KWBC 010831
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Mon Jul 1 2024

Day 1
Valid 12Z Mon Jul 01 2024 - 12Z Tue Jul 02 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOW COUNTRY OF SOUTH CAROLINA AND THE NORTH GEORGIA COAST...

...09Z Issuance...

...Southeast US...

Anomalous moisture with PWATs exceeding 2.25" along the Southeast
Coast to N Florida (around 2.5 sigma above normal) is in place
ahead of a slow moving cold front. Ongoing heavy thunderstorms over
eastern NC and southeast VA will continue working south ahead of
the cold front through today with activity lingering near the
front which should stall along the GA/SC coasts this evening.
Continued confidence for heavy rain with rates exceeding 3" in 3hrs
(per the 00Z HREF) along the SC coast this afternoon warrants
maintenance of the Moderate Risk along the coast that includes
Charleston, SC and Savannah, GA. Pre-frontal thunderstorms farther
south to the FL border warrants maintenance of the Slight Risk over
southeast GA.


...Northern Plains to Upper Midwest...

A trough over the northern Rockies early this morning shifts east
over the northern Plains through tonight. Gulf-sourced moisture
surging up the Plains and over a developing warm front that shifts
east over the central Plains today/tonight. Increased confidence in
two main swaths of rainfall, from eastern Neb through western WI
including much of IA and southern MN warrants a high end Slight
Risk considering ongoing main-stem flooding from heavy rains a week
ago. The second areas is ahead of the upper trough in a stripe from
north-central SD through northern MN. The Slight Risk here was
expanded into northern SD given the 00Z consensus for 1.5" or so
over areas with 3hr FFG of 2" or less.

In between these areas, a corridor of less rainfall depicted in the
00Z consensus QPF warrants some removal of Slight Risk areas in
north-Central MN.

...Southwest US...

Monsoonal moisture lingers over the Four Corners states today to west
of a ridge axis over the southern Plains and below an upper trough
over the Intermountain West. PW anomalies of 2 to 3 sigma above
normal will allow for diurnal development, primarily along terrain.
Expanded the Marginal Risk over the central NM terrain given the
isolated to widely scattered thunderstorm potential there that
includes particularly sensitive areas in the Sacramento Mtns per
the 00Z CAM consensus.

Jackson


Day 2 Valid 12Z Tue Jul 02 2024 - 12Z Wed Jul 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST TO CENTRAL GREAT PLAINS...

...09Z Issuance...

...Upper Midwest through Central Great Plains...

A reinforcing shortwave trough rounding the upper trough that will
be over the Dakotas Tuesday morning crosses the Neb/SD border
through the day. Right entrance jet streak dynamics warrants
maintenance of ongoing activity over the central Plains, IA, and
central WI that then drifts south/southeast through the day that
spreads No big changes were made with this update. Concerns remain
from the KC metro and northeast over an expansive area to western
IL and up through much of WI as gulf-sourced moisture (PWs 2 to 2.5
sigma above normal) with deep layer SW flow allowing training
thunderstorm concerns. A Moderate Risk may be needed somewhere
between KC and Madison WI, but for now consider this a higher end
Slight Risk.

...Southeast...

A Marginal Risk is maintained over the Florida Panhandle and
southern GA. This will be a continuation of the convection from
Monday night ahead of a slow moving cold front. Rainfall still
expected to be lower than on Monday, but the plentiful Gulf
moisture allows for the potential for very high rainfall rates.

...Southwest...

Again maintained a Marginal over eastern AZ/western NM with a
suppressed Monsoonal flow day as troughing to the north shunts the
ridge axis farther east to the lower Miss Valley. Elevated moisture
is limited to the southern portions of those states and remnant
stratus from Monday night activity may further suppress Tuesday
activity.

Jackson


Day 3
Valid 12Z Wed Jul 03 2024 - 12Z Thu Jul 04 2024

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

...Midwest to Great Plains...

A cold front from a passing trough over the northern tier of states
stalls over KS/MO by Wednesday morning, providing continued focus
for heavy thunderstorm development from eastern KS through southern
IL where a Slight Risk is maintained.

The frontal zone extends east over the rest of the Midwest to the
eastern Great Lakes where a Marginal Risk is maintained with some
areas of the Northeast trimmed with the 00Z QPF consensus being
farther west.

Over the northern Plains, the next trough axis enters the northern
High Plains Wednesday night with activity over the Dakotas
warranting a Marginal Risk.


...Southwest...

A trough axis from the next reinforcing wave allows anomalous
moisture over AZ/NM to spread northeast to the southern High Plains
on Wednesday which warrants maintenance of the Marginal Risk with
some trimming based on the 00Z consensus.


Jackson


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