741
FXUS63 KPAH 162027
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
327 PM CDT Thu May 16 2024

.KEY MESSAGES...

- A few strong to severe thunderstorms are possible late this
  afternoon and this evening mainly over southeast Missouri and
  adjacent portions of southern Illinois and west Kentucky.
  Large hail and damaging winds will be the primary threats.

- A Flood Watch for flash flooding is in effect from 7 PM
  tonight through 7 PM Friday over southern portions of
  southeast Missouri, the southern tip of Illinois and the
  Purchase Area of west Kentucky

- Very warm conditions will return Sunday through Tuesday with
  daily high temperatures in the upper 80s. A few 90 degree
  readings will be possible.

- A cold front will bring a good chance of thunderstorms to the
  region Tuesday night into Wednesday. At this time locally
  heavy rainfall and lightning are the primary hazards.

&&

.DISCUSSION...
Issued at 327 PM CDT Thu May 16 2024

SPC mesoanalysis indicates that there is 1000 J/kg of mixed-
layer CAPE over western portions of southeast Missouri as of
19Z. This could spread farther east with additional heating late
this afternoon. Effective bulk shear of 30-35kts could support
multicell thunderstorms with mainly a damaging wind risk. Mid-
level lapse rates are weak, but low-level lapse rates are
pushing 8C/km. The steep low-level lapse rates, coupled with
downdraft CAPE approaching a 1000 J/kg certainly supports a
damaging wind threat.

A Flood Watch for flash flooding has been issued for southern
portions of southeast Missouri, the southern tip of Illinois,
and the Purchase Area of west Kentucky for tonight and Friday.
Please consult the hydrology section of this discussion for
details.

An upper trough over the southern Rockies today will push
gradually eastward to the southeast states by Sunday.
Disturbances will lift northeast over the Quad State tonight
through Friday, leading to the heavy rainfall concern. As the
main trough passes to the south of the area Saturday, more
showers and even some thunderstorm may linger over the eastern
half of the region. The GFS even hints at some showers lingering
into Sunday in the southeast.

The upper trough will be stubborn over the southeast, and that
will eventually result in a pesky upper ridge over the Quad
State. The ridge will hold overhead into Tuesday, effectively
deflecting disturbances northeast from the Plains to the upper
Mississippi Valley early next week. Eventually a disturbance is
expected to push more to the east and bring a weak cold front
through the Quad State along with a good chance of more showers
and storms Tuesday night into Wednesday. At this time, the best
lift and wind fields look to be to our west, so for now will
just advertise locally heavy rainfall and lightning with this
event.

With zonal flow developing aloft, there is potential for the
front and associated convection to linger in our vicinity into
next Thursday.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1247 PM CDT Thu May 16 2024

Limited the mention of thunderstorms to the vicinity of KCGI
and KPAH, mainly this evening. Scattered showers and isolated
storms will stream east across the area this evening with some
MVFR conditions possible. There should be a few hours break
before another area of showers streams mainly over southern
portions of the area after 12Z. MVFR and even IFR conditions
will be possible.

&&

.HYDROLOGY...
Issued at 327 PM CDT Thu May 16 2024

It is pretty simple sometimes. The convection from early this
weak resulted in a couple of swaths of very heavy rainfall. One
from near the OH/MS confluence northeast along the Ohio to the
Evansville/Henderson areas, and the another along the TN/KY
border from the Lakes eastward. In southern Illinois yesterday,
creeks were at bankfull and there remained considerable field
flooding.

WPC QPF has 2-3" of rainfall forecast from late this afternoon
through Friday. Most of this will fall in two waves, one
through this evening and another from pre-dawn through Friday
morning. The footprint of this expected heavy rainfall overlaps
much of the previous heavy rainfall, and it is in those water-
logged areas where we have the greatest concern for renewed
flash flooding.

Instability is not great, but will be maximized in the Watch
area. Precipitable water values will be near the 90th
percentile, so efficient rains are a good bet. If we had better
instability and a better defined surface boundary to focus
convection, confidence would be higher, but with the antecedent
rainfall, there was little reason not to issue the watch this
afternoon

There is potential for the heavy rains to spread farther east
across the Quad State and that could lead to an expansion of the
Flood Watch at some point tonight or Friday morning. Stay
tuned.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch from 7 PM CDT this evening through Friday evening
     for ILZ088>090-092>094.
MO...Flood Watch from 7 PM CDT this evening through Friday evening
     for MOZ108>112-114.
IN...None.
KY...Flood Watch from 7 PM CDT this evening through Friday evening
     for KYZ001>009.

&&

$$

DISCUSSION...DRS
AVIATION...DRS
HYDROLOGY...DWS