Flash Flood and Damaging Winds in Illinois, May 24, 2020

Area Forecast Discussion
National Weather Service Paducah KY
1232 PM CDT Sun May 24 2020

.UPDATE...
Issued at 1232 PM CDT Sun May 24 2020

Updated aviation section for the 18Z TAF issuance.

&&

.SHORT TERM...(Today through Tuesday night)
Issued at 310 AM CDT Sun May 24 2020

A weak upper-level disturbance in the vicinity of the Missouri
Bootheel early this morning has kept some scattered showers going
for much of the night. The associated mid and high clouds may hold
down heating and thus surface destabilization today, but the
associated lift will likely overcome the lack of heating. There is
a good signal for deep convection to develop possibly by Noon
over southeast Missouri. It should develop northeast into the
early afternoon and build eastward through the late afternoon and
early evening.

The 00Z NAM develops over 3000J/kg of SBCAPE throughout the
region, but struggles to generate convection despite there being
no cap to deal with. Its SBCAPE is likely overdone, given the
expected early start to diurnal convection. Wind fields are weak
through the column, so these should be pulsy storms. However,
given the amount of instability, and rather steep mid and low-
level lapse rates, we cannot completely rule out an isolated
strong storm producing damaging winds. Locally heavy rainfall and
lightning will be the primary concerns today.

A few storms may linger into the evening over the eastern half of
the region. There is some potential that southeast Missouri and
southwest Illinois may keep enough moisture around 850mb to
support isolated elevated convection overnight tonight.

Guidance indicates that there should be more sunshine on Monday,
Memorial Day. With rather steep mid-level lapse rates and no cap,
we should have no problem developing diurnal convection perhaps as
early as Noon in some locations. Once again there will be no
shear, so we would expect the same threats as today. Given the
amount of instability, this could be one of those days where
storms bounce around all day on outflows, until all of the SBCAPE
has been chewed up. If for whatever reason, storms do not
proliferate Monday, it will be quite hot and humid with heat
indices likely reaching at least 90 over most of the region.

Cloud cover is expected to hold down temperatures Tuesday, but
there are signs of another mid/upper-level disturbance in our
vicinity. Similar to today, the lift is likely to overcome the
relative lack of heating to support a decent coverage of diurnal
convection. Our PoPs seem a bit high, but we cannot argue with
them too much. With the disturbance lingering in the area some
convection could linger well into the Tuesday night period.

With no surface boundaries or wind shear to organize the
convection today through Tuesday, heavy rainfall is likely to be
rather isolated across the region. However, with decent coverage
of convection expected each afternoon, some at least isolated
flooding could develop in areas that get hit with heavy rainfall
on successive days.

.LONG TERM...(Wednesday through Saturday)
Issued at 310 AM CDT Sun May 24 2020

By the middle of the week, a cut-off low will be stranded over the
southern Plains, while an Omega block sets up along the Eastern
Seaboard. Weak disturbances rotating around the southern Plains low
will provide a source of lift for convection, and the Omega block
will funnel warm, moist, and moderately unstable air from the Gulf
of Mexico into the forecast area. With the jet stream displaced to
the north across southern Canada, this synoptic configuration will
be slow to change. The end result will be a daily chance of
thunderstorms, mainly during the heat of the day.

Tried to taper the NBM POPs to reflect this diurnal TSRA trend. This
resulted in high chance/likely POPs during the daytime hours
Wednesday through Friday, and isolated to low chance POPs overnight.
By Friday into Saturday, a cold front will try to clear the forecast
area, although it may stall along the AR/TN border through next
weekend. Therefore, accepted the NBM solution of low chance POPs for
next Saturday and Sunday.

Temperatures will be seasonably warm for late spring, with highs in
the lower to middle 80s and overnight lows in the middle to upper
60s. Dew point temperatures will be seasonable muggy as well, with
values generally in the middle to upper 60s.

&&

.AVIATION...
Issued at 1232 PM CDT Sun May 24 2020

Isolated to scattered TSRA possible across the region through 02z.
Included VCTS this afternoon through 00z-02z at all TAF sites.
Cigs and vsbys will be VFR, with brief MVFR cigs and vsbys
possible in or near storms. After 02z, VFR conditions expected
overnight into tomorrow morning. Winds will be from the south at 5
to 10 kts through the TAF period, with a few gusts to around 15
kts through 01z.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

SHORT TERM...DRS
LONG TERM...DWS
AVIATION...RST

Hazardous Weather Outlook
National Weather Service Paducah KY
331 AM CDT Sun May 24 2020

ILZ075>078-080>094-INZ081-082-085>088-KYZ001>022-MOZ076-086-087-
100-107>112-114-251000-
Jefferson-Wayne IL-Edwards-Wabash-Perry IL-Franklin-Hamilton-
White-Jackson-Williamson-Saline-Gallatin-Union-Johnson-Pope-
Hardin-Alexander-Pulaski-Massac-Gibson-Pike-Posey-Vanderburgh-
Warrick-Spencer-Fulton-Hickman-Carlisle-Ballard-McCracken-Graves-
Livingston-Marshall-Calloway-Crittenden-Lyon-Trigg-Caldwell-
Union KY-Webster-Hopkins-Christian-Henderson-Daviess-McLean-
Muhlenberg-Todd-Perry MO-Bollinger-Cape Girardeau-Wayne MO-Carter-
Ripley-Butler-Stoddard-Scott-Mississippi-New Madrid-
331 AM CDT Sun May 24 2020

This Hazardous Weather Outlook is for portions of southern
Illinois, southwest Indiana, western Kentucky, and southeast
Missouri.

.DAY ONE...Today and Tonight

Scattered thunderstorms are expected throughout the region this
afternoon. A few storms may linger through the night mainly over
southeast Missouri and southern Illinois. Locally heavy rainfall
and lightning will be the primary concerns, but a stray strong
storm could produce some isolated damaging winds in the heat of
the day.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Scattered to numerous thunderstorms are expected each afternoon
through the week. Locally heavy rainfall and lightning will be the
primary concerns, but an isolated strong storm could produce
damaging winds.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

DRS/DWS

Special Weather Statement
National Weather Service Paducah KY
136 PM CDT Sun May 24 2020

ILZ075-081-241900-
Franklin IL-Jefferson IL-
136 PM CDT Sun May 24 2020

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHERN JEFFERSON AND NORTHERN
FRANKLIN COUNTIES UNTIL 200 PM CDT...

At 136 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from Rend Lake Area to near Valier to Christopher.
Movement was northeast at 35 mph.

Nickel size hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Benton, Christopher, Rend Lake Area, Sesser, Valier, West City, Ina,
North City, Buckner, Bonnie, Ewing and Nason.

LAT...LON 3824 8879 3802 8877 3791 8915 3795 8915
      3795 8918 3797 8915 3802 8914 3804 8914
      3806 8912 3810 8912 3810 8914 3818 8909
TIME...MOT...LOC 1836Z 225DEG 29KT 3810 8896 3805 8904 3797 8906

07