Severe Thunderstorm Warning 172, NWS Lincoln, IL

Area Forecast Discussion
National Weather Service Lincoln IL
343 AM CDT Tue Jul 30 2024

.KEY MESSAGES...

- A Dense Fog Advisory remains in effect for portions of central
  Illinois until 8 am.

- A slight risk (level 2 of 5) for severe storms exists across
  most of the area for this afternoon into evening, with
  additional chances for severe storms on both Wednesday and
  Thursday.

- Heat and humidity continues across the area through Thursday
  with daily heat indices ranging from 100-110 each day.

&&

.DISCUSSION...
Issued at 343 AM CDT Tue Jul 30 2024

Light winds, recent rain, and clear skies have resulted in patchy
fog across the area early this morning. HREF probabilities for one-
quarter mile visibility or less are highest from roughly Beardstown
to near Champaign, which is roughly where the lowest visibilities
are as of 3 am. A Dense Fog Advisory is in effect for these areas
until 8 am.

594 dm mid-level ridge remains positioned over the Plains states
with northwest flow in place further east over the Midwest states.
This will open the door for several mid-level shortwaves/mesoscale
features to slide southeast across the area the next several days,
bringing daily chances for storms. There remains quite a bit of
uncertainty in storm timing for today, but the general idea is for a
remnant boundary or MCV from storms over central Iowa to be the
trigger for new development sometime later today. Very warm/humid
conditions will bring strong instability in excess of 2500 J/kg by
this afternoon paired with moderately strong mid-level flow, which
will be more than enough to support storm organization. Primary
hazards with storms will be damaging winds gusts, with SPC
introducing a hatched area for the potential of significant wind
gusts (75 mph). Orthogonal shear vectors to the orientation of the
thunderstorm complex could bring a low threat for a few tornadoes as
well. Heavy rain will also be a threat with PWATs of 1.77 to 2
inches aiding in high rainfall rates.

Heat and humidity ramp up today and persist through Thursday. High
temperatures today will climb into the upper 80s to low 90s with
heat indices of 100 to 105. However, if storms develop earlier in
the day, cloud cover and precipitation will hold these values down.
Since the potential for dangerous heat indices does exist, elected
to issue a Heat Advisory for counties along and south of a
Beardstown to Robinson line. Heat indices ranging from 105 to 110
will are likely across the entire area on both Wednesday and
Thursday, but once again storm timing will drive the need for heat
headlines in coming days.

Additional chances for storms, including severe storms, will be seen
on both Wednesday and Thursday with the higher threat (slight risk)
being on Thursday as a stronger mid-level wave brings better
forcing. Wednesday morning could start out stormy with CAMs
suggesting activity blossoming on the nose of a 40 kt LLJ over
eastern Iowa and spilling east-southeastward into Illinois.
Additional clusters could move through both late Wednesday night
into Thursday morning and Thursday evening. Some storms may fester
into Friday until the upper low pushes east of here, but the
severe threat should be minimal by that time.

High pressure settles into the Midwest states by the weekend,
bringing a period of mostly dry and more seasonable temperatures.
Oppressive dewpoints will be slow to retreat back southward until
a secondary cold front brings some relief from that early next
week.

NMA

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1140 PM CDT Mon Jul 29 2024

Scattered convection has dropped well south of the terminals and
skies have cleared across central Illinois late this evening.
Given clear skies, nearly calm winds, and ample boundary layer
moisture with surface dewpoints in the lower to middle 70s, the
stage is set for overnight fog. Some minor reductions in visby
have already occurred at KSPI/KCMI and think this trend will
continue through dawn. CAMs suggest widespread visbys less than 3
miles, with pockets of 1/4 mile visbys in dense fog. Will need to
carefully monitor obs over the next few hours, but for the 06z
TAF issuance have reduced visbys to 1/2 to 1 mile at all sites
between 09z and 13z. After the morning fog dissipates, attention
will turn to convection chances later in the day. Several models
suggest an upstream storm complex currently over southeast South
Dakota will weaken later tonight as it crosses Iowa...then re-generate
as the atmosphere destabilizes further east into Illinois by late
morning. Based on approximate 00z HRRR timing, have introduced a
period of VCTS at KPIA between 18z and 22z...then further east to
KCMI between 21z and 01z.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 8 AM CDT this morning for ILZ029-031-
036>038-040>053.

Heat Advisory from 1 PM this afternoon to 8 PM CDT this evening
for ILZ040-047>052-061-066>068-071>073.

&&

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Preliminary Local Storm Report
National Weather Service Lincoln IL
1236 AM CDT Tue Jul 30 2024

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

0933 PM     Tstm Wnd Gst     3 W Xenia               38.63N 88.70W
07/29/2024  E60 MPH          Clay               IL   Fire Dept/Rescue

            Along highway 50 near the Marion County
            line.

&&

Geelhart