Severe Thunderstorm Warning 171, NWS Lincoln, IL

Area Forecast Discussion
National Weather Service Lincoln IL
310 AM CDT Mon Jul 29 2024

.KEY MESSAGES...

- Daily chances for showers and storms continue through the week,
  with the potential for severe storms at times.

- Hot and humid conditions build in today with with heat indices
  approaching 100 west of the Illinois River this afternoon. Heat
  indices between 100-110 will be seen areawide Tuesday through
  Thursday.

- Drier and seasonable condtions return this weekend into early
  next week.

&&

.DISCUSSION...
Issued at 310 AM CDT Mon Jul 29 2024

Radar imagery early this morning shows a cluster of thunderstorms
from eastern Iowa into northwest Illinois, along the nose of a 40-45
kt 850 mb jet. This activity will work into central parts of the
state over the next several hours as the LLJ veers into Illinois
closer to sunrise. Some of these storms could be strong, posing a
threat for gusty winds, though storm coverage should wane some as
the LLJ recedes later this morning. Heavy rainfall is the main
threat with the latest RAP analysis showing PWATs of around 2 inches
noted near the complex. Rainfall rates of 1 to 2 inches per hour are
a possibility underneath the heaviest storms, posing a threat for
flooding especially in urban and low-lying areas. Because of this
potential, a Flood Watch has been added for a handful of counties in
western Illinois through late morning.

Thunderstorms will push into Indiana by late morning or early
afternoon, turning things mostly dry for a few hours this afternoon.
Another round of storms may develop this evening along a remnant
outflow boundary from the morning MCS, with convective allowing
models starting to hone in on an area near or south of I-72.
Destabilization after morning storms won't be an issue with moisture-
rich air sending CAPE values toward 3000+ J/kg. Moderate mid-level
flow of 35-45 kts will be sufficient for storm organization,
posing a threat for severe storms mainly capable of damaging
winds. A slight risk (level 2 of 5) has been introduced by SPC
near/south of I-70.

West-northwest flow aloft will continue to support daily
thunderstorm chances the next few days as upper ridging remains over
the central CONUS. An upper trough will work to deamplify the ridge
some by the end of the week, pushing a cold front through the area
later Thursday into Friday. Severe storm chances will also exist
each day through at least Thursday due to favorable environmental
parameters, though exact timing of any thunderstorm activity
remains uncertain.

The heat ramps up this week with seasonably warm temperatures and
oppressive dewpoints sending heat indices into hazardous
territory. Daytime highs will range from the middle 80s to low 90s
today, climbing into the low to mid 90s Tuesday through Thursday.
Heat indices could begin to approach 100 today in far western
Illinois, with values of 100-110 becoming common areawide Tuesday
through Thursday. Heat headlines will likely be needed each of
these days, especially if timing of storms doesn't interfere with
temperatures each afternoon.

High pressure will settle southward this weekend into early next
week, turning things drier and seasonable.

NMA

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1144 PM CDT Sun Jul 28 2024

Thunderstorms continue to organize across central/eastern Iowa
late this evening...with 00z CAMs suggesting a storm complex
tracking east-southeastward into central Illinois late tonight
into Monday morning. Based on radar trends and latest HRRR/RAP,
have introduced thunder at KPIA by 09z...then further east to KCMI
by 13z. Once the storms pass east of the terminals by 16z, a
period of lingering low VFR or MVFR ceilings will be observed
through midday before skies partially clear. There may be a
potential for scattered convection re-developing across parts of
central Illinois by late afternoon/evening: however, confidence
in the location, timing, and exact areal coverage remains too low
to include in the TAFs at this time.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 10 AM CDT this morning for ILZ027>029-036-037-
040-041.

&&

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