Flash Flood Warning 7, NWS Lincoln, IL

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
644 PM CDT Sun May 7 2023

.SYNOPSIS...
Issued at 644 PM CDT Sun May 7 2023

Strong to severe thunderstorms this afternoon are expected to
gradually weaken this evening. Additional rounds of storms are
anticipated overnight into Monday morning, and potentially Monday
evening. Quieter weather is forecast for Tuesday and Wednesday.
Precipitation chances return from Thursday into the weekend.

&&

.MESOSCALE DISCUSSION...
Issued at 510 PM CDT Sun May 7 2023

A line of scattered thunderstorms continues from roughly Vermont,
IL southeast across the Springfield area to south of
Taylorville. Outflow is expanding from these clusters of storms,
but satellite imagery reveals that updrafts remain vigorous,
though may be becoming slightly elevated with time as mid level
southwest flow overruns the shallow outflow. Stronger storms
continue to have the potential for very large hail with normalized
CAPE values still high, in the 0.25 to 0.30 range (albeit
slightly lower from a couple hours ago). While deep layer shear
continues to support the potential for a few supercells, weak low
level shear and negligible low level helicity are limiting
factors in terms of any tornado potential. Finally, while storm
motions will continue to be east around 20 mph or so (southeast
for deviant right moving supercells), there has been some backward
propagation resulting in very slow to near stationary speeds.
There remains a threat for flash flooding under these storms.

Deubelbeiss

&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 218 PM CDT Sun May 7 2023

As warm and humid air advects into central Illinois from the
west, a remnant outflow boundary from morning convection has moved
to a position from just west of Peoria, to just west of
Springfield, passing just east of the St. Louis Metro and curving
toward Paducah KY. Expect this feature to the the focus for
convective initiation this afternoon/evening. With MLCAPE near
3000 J/kg in the vicinity of this boundary and cloud layer shear
in excess of 40 knots, both large hail and severe wind gusts will
be threats from these cells. As a short wave trough moving through
northern Arkansas approaches, additional forcing for ascent along
with some degree of mid-level cooling will likely lead to fairly
broad multicell storm coverage near the outflow boundary, though
even in this situation stronger updrafts may be capable of large
hail. The expected coverage will likely lead to a growing cold
pool and another southward push of the outflow boundary this
evening, with the severity of this round of thunderstorms waning
by around 8-9 pm.

CAMs depict a second round of convection during the early morning
hours on Monday, with an organized bowing complex of thunderstorms
approaching from southern IA/northern MO. The extent of
afternoon/evening convection across central Illinois will likely
play a large role in the evolution of this complex, with the most
likely outcome at this point being a weakening complex as it moves
into central Illinois after midnight, and/or the complex following
the instability gradient to the southeast with the wind threat
remaining farther west. Even so, the potential for strong to severe
wind gusts in association with this complex will need to be watched,
especially if little convection occurs with the first round across
northern parts of the ILX forecast area. In addition, there is
potential for flash flooding with both rounds of convection,
especially where training storms occur and/or where large amounts of
rain fell early this morning.

In the wake of the early morning convective activity, expect a
fairly quiet period for at least part of the late morning/early
afternoon on Monday before thunderstorms again develop on a cold
front/the remnant outflow boundary from morning convection. MLCAPE
will be closer to 1000 J/kg, with cloud layer shear decreasing to
around 25-30 kt. Though those values are less than today, there will
still be a risk of storms producing large hail and/or severe wind
gusts Monday afternoon/evening. Expect the storms to move out of the
southeast corner of the ILX forecast area by around 9-10pm with the
cold front, with light northeast winds and relatively quiet
conditions for the rest of the overnight hours.

AAT

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 218 PM CDT Sun May 7 2023

Key Messages:

1) Much quieter weather is forecast for Tuesday and Wednesday.

2) Precipitation chances increase once again from Thursday into the
weekend.

A mid-level ridge will amplify over the Midwest from Tuesday into
Wednesday, with minimal precipitation chances and high temperatures
falling back into the mid to upper 70s. Precipitation chances begin
to return on Thursday in association with a closed low moving from
the northern/central Rockies into the upper Midwest. Cluster
analysis shows ensemble member differences regarding the depth and
speed/track of this low, which will eventually affect where and how
much precipitation falls. Even so, this period doesn't look terribly
high-impact at this point, with NBM probability of rainfall > 1" in
the entire Friday-Sunday period only in the 20-30% range. However,
we'll need to keep an eye out for substantial rainfall accumulations
where soils are becoming more saturated. Additionally, the grand
ensemble (GEFS/EC/CMC) mean CAPE in the Fri/Sun period does poke up
between 500-1000 J/kg during the afternoons.

AAT

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 644 PM CDT Sun May 7 2023

Thunderstorms this evening along a line from KMQB-KSPI-KTAZ are
forecast to gradually weaken over the next couple of hours, but
could bring brief MVFR ceilings or visibilities to KSPI and
points east such as KPIA as well. The next round of storms late
tonight into early Monday morning will bring a shot at variable
gusty winds, TSRA, and MVFR ceilings/visibility, with some
uncertainty regarding the exact track/evolution of a thunderstorm
complex coming from Iowa. Following exit of the early morning
activity, MVFR ceilings may occur into the morning, scattering out
by early afternoon. Redevelopment of TSRA along a cold
front/outflow boundary may occur prior to 00Z Monday evening, but
these cells will likely be southeast of TAF sites.

AAT

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

WFO ILX

Hazardous Weather Outlook
National Weather Service Lincoln IL
312 PM CDT Sun May 7 2023

ILZ027>031-036>038-040>057-061>063-066>068-071>073-081645-
Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-McLean-Schuyler-
Mason-Logan-De Witt-Piatt-Champaign-Vermilion-Cass-Menard-Scott-
Morgan-Sangamon-Christian-Macon-Moultrie-Douglas-Coles-Edgar-Shelby-
Cumberland-Clark-Effingham-Jasper-Crawford-Clay-Richland-Lawrence-
312 PM CDT Sun May 7 2023

This Hazardous Weather Outlook is for central Illinois, east
central Illinois, southeast Illinois and west central Illinois.

.DAY ONE...This afternoon and tonight.

Scattered thunderstorms are expected to develop this afternoon and
persist into early evening, focused along an outflow boundary from
near Springfield to just west of Peoria. Storms this evening should
develop near this boundary, then move east-northeast at around 20 to
30 mph. Tonight, a line of storms will likely develop and push
southeast across central IL after midnight. Both rounds of
thunderstorms could be severe with damaging winds and large hail
being the primary hazards. An isolated flash flood risk may develop
if thunderstorms repeatedly affect the same location.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Periods of thunderstorms are expected ahead of a cold front on
Monday. Severe storms will again be possible. Damaging wind gusts
and large hail are the primary hazards. An isolated flash flood risk
may develop if thunderstorms repeatedly affect the same location.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and tonight.

25/AAT

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
703 PM CDT SUN MAY 7 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0700 PM     HAIL             MARIETTA                40.50N 90.39W
05/07/2023  M1.75 INCH       FULTON             IL   TRAINED SPOTTER

            GOLF BALL SIZE HAIL RELAYED BY EMA.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
705 PM CDT SUN MAY 7 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0700 PM     HAIL             2 N MARIETTA            40.50N 90.39W
05/07/2023  M1.75 INCH       FULTON             IL   TRAINED SPOTTER

            CORRECTS PREVIOUS HAIL REPORT FROM MARIETTA.
            GOLF BALL SIZE HAIL RELAYED BY EMA.

&&

07

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
709 PM CDT SUN MAY 7 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0705 PM     HAIL             CHATHAM                 39.68N 89.70W
05/07/2023  M1.75 INCH       SANGAMON           IL   TRAINED SPOTTER

            GOLF BALL SIZE HAIL.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
722 PM CDT SUN MAY 7 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0629 PM     HAIL             2 E CHATHAM             39.67N 89.67W
05/07/2023  U0.75 INCH       SANGAMON           IL   PUBLIC

            REPORT FROM MPING: DIME (0.75 IN.).

0622 PM     HAIL             1 E CHATHAM             39.67N 89.68W
05/07/2023  U1.25 INCH       SANGAMON           IL   PUBLIC

            REPORT FROM MPING: HALF DOLLAR (1.25 IN.).

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
726 PM CDT SUN MAY 7 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0456 PM     HAIL             2 E CHATHAM             39.67N 89.67W
05/07/2023  U1.00 INCH       SANGAMON           IL   PUBLIC

            REPORT FROM MPING: QUARTER (1.00 IN.).

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
755 PM CDT SUN MAY 7 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0700 PM     HAIL             4 S ELLISVILLE          40.57N 90.31W
05/07/2023  M1.00 INCH       FULTON             IL   MESONET

            QUARTER SIZE HAIL 2 MILES WEST OF BLYTON.
            SOCIAL MEDIA REPORT WITH PHOTO ON TWITTER.

&&