Hail and Damaging Winds in Illinois, May 2, 2024

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1223 PM CDT Thu May 2 2024

.KEY MESSAGES...

- Level 1 (marginal) risk of severe weather continues from mid
  afternoon into mid evening from McLean, DeWitt, Logan and
  Sangamon counties west.

- Warm, more humid and breezy today with highs in the mid 80s,
  except closer to 80F by Galesburg. This will be the warmest day
  since Apr 14th over much of central IL.

- Numerous chances for showers and thunderstorms through
  Wednesday, though brief drier periods expected Friday night and
  Saturday morning and overnight Saturday night and Sunday
  morning.

&&

.UPDATE...
Issued at 952 AM CDT Thu May 2 2024

Earlier convection has lifted northeast into northern Indiana,
with a large part of the forecast area now mostly sunny. A large
band of showers and embedded thunderstorms extends from western
Wisconsin to south of Kansas City, though cloud tops have steadily
been warming with this activity. Early look at the morning high-
res models has slowed some of the eastward progression of this
activity, though a few still pop up a few showers/storms east of
I-57 before late afternoon. However, they're in better agreement
with an uptick in activity west of the Illinois River before mid
afternoon. Afternoon PoP's above 60% are generally limited to this
area, with scattered showers/storms elsewhere, though areas south
of I-70 may stay dry the entire time.

Geelhart

&&

.DISCUSSION...
Issued at 400 AM CDT Thu May 2 2024

Predawn surface map shows 1002 mb low pressure over southeast
Nebraska with a warm front extending eastward over central MO and
into sw IL. Very small/isolated shower and thunderstorm over
eastern Shelby county and nw Macon county lifting ne ahead of warm
front and along an old outflow boundary originating from
convection that was near St Louis area Wed evening. Temps were in
the mid 50s to lower 60s over central IL with mid 60s along and
south of highway 50. Drier dewpoints in the low to mid 40s from
Macomb to Rantoul north while more moist dewpoints in the lower
60s over Clay, Richland and Lawrence counties.

Latest CAMs show warm front lifting northward over central IL
during this morning and only isolated convection possible as it
moves through with much of morning being dry over the area. Breezy
south winds by afternoon to bring warmer highs in the mid 80s over
much of area, with Galesburg closer to 80F. Getting more humid too
as dewpoints rise into the low to mid 60s across the area by
midday and afternoon. Air mass gets more unstable during this
afternoon as CAPES peak from 1000-1500 j/kg by mid afternoon with
wind shear values of 15-25 kts, highest over western CWA. SPC day1
outlook has marginal risk of severe storms from McLean, DeWitt,
Logan and Sangamon counties west from mid to late afternoon into
mid evening where wind shear values will be higher than in
eastern IL. Isolated convection early this afternoon to become
more scattered over the IL river valley by late afternoon. Higher
chance of showers and thunderstorms spreads eastward during
tonight as cold front moves thru central IL overnight. Lows
overnight mostly in the lower 60s over central IL, but range from
upper 50s nw of the IL river to near 65F se of I-70.

Best chances of convection will be over eastern IL on Friday
especially Fri morning. Models have trended faster with pushing
convection eastward during Friday afternoon and much of CWA should
be dry by sunset Friday with just isolated showers near the Wabash
river early Fri evening. We are not in any outlook for severe wx
on Friday as wind shear and instability is weak. Cooler highs
Friday in the low to mid 70s and becoming partly to mostly sunny
over the IL river valley during Fri afternoon as drier air moves
in behind the cold front.

A brief period of dry weather expected over most of area Friday
night and Sat morning. Then a disturbances ejects eastward from
the central plains and returns chance of showers and thunderstorms
Sat afternoon/evening. A bit more instability develops Saturday
afternoon especially sw CWA with CAPES around 500 j/kg and still
rather weak wind shear values 15-25 kts. A few stronger storms
possible from mid Sat afternoon into early Sat evening mainly sw
CWA. Highs Saturday in the upper 70s in central IL and near 80F in
southeast IL. More humid again as dewpoints elevate into the lower
60s as day progresses.

Drier conditions expected overnight Sat night and Sunday morning
though can not completed rule out an isolated shower or
thunderstorm south of I-72. Diurnal heating could develop isolated
to scattered convection late Sunday afternoon especially southern
CWA, then convection chances increase northward during Sunday
night into Monday as short wave moves into the mid MS river
valley. Highs Sunday in the low to mid 70s in central IL and upper
70s southeast of I-70. CAPES increase to 500-800 j/kg Monday
afternoon with wind shear values around 25 kts, so a few stronger
thunderstorms possible Mon afternoon.

Stronger mid/upper level trof develops over the Rockies Sunday and
ejects strong low pressure system into western ND by Tue morning.
Models agree on a swath of convection moving into IL later Monday
night and Tuesday. CSU machine learning and CIPS analogs shows
risk of severe storm on Tuesday into Wednesday over IL and will
need to monitor this period. Highs Monday in the upper 70s and
80-85F Tue/Wed.

The Climate Prediction Center (CPC) 6-10 Day outlook for May
7-11th shows 60-70% chance of above normal temperatures over
central IL with 40-45% chance of above normal precipitation. The
8-14 day outlook for May 9-15th also trending toward wetter
conditions. So the mild and active wx pattern looks to continue
next two weeks.

07

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1223 PM CDT Thu May 2 2024

Main concern in the shorter term will be with timing of convective
development. Initial development is expected along the IL/IA
border toward 20-21Z with storms moving east, though some
weakening will take place after 00Z. While some of the heavier
storms may produce some brief MVFR visibility or ceilings,
confidence levels are not high enough yet to introduce a TEMPO
period.

Later on, a more sustained period of ceilings below 3,000 feet
will accompany the cold front following the rain. This should be
moving into KPIA as early as 06-07Z, though not reaching KCMI
until closer to 11-12Z. Morning HREF guidance suggests a 2-3 hour
period of IFR conditions isn't out of the question (30-50%
probability), so this will need to be monitored.

Geelhart

&&

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

Hazardous Weather Outlook
National Weather Service Lincoln IL
500 AM CDT Thu May 2 2024

ILZ027>031-036>038-040>043-047>051-031100-
Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-McLean-Schuyler-
Mason-Logan-De Witt-Cass-Menard-Scott-Morgan-Sangamon-
500 AM CDT Thu May 2 2024

This Hazardous Weather Outlook is for central Illinois and west
central Illinois.

.DAY ONE...Today and tonight.

Scattered thunderstorms are possible this afternoon and evening, some
of which may become strong to severe with hail and strong gusty
winds. Additionally, these storms will bring potential for locally
heavy rainfall. Scattered thunderstorms will likely continue
overnight, but are not expected to remain severe.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Occasional thunderstorms are possible over the weekend and early next
week. The probability for severe weather is low over the weekend, but
it is too early to determine the threat for severe weather next week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed from around 3 to 9 PM.

Expected storm motion is toward the northeast around 30 mph.

ILZ044>046-052>057-061>063-066>068-071>073-031100-
Piatt-Champaign-Vermilion-Christian-Macon-Moultrie-Douglas-Coles-
Edgar-Shelby-Cumberland-Clark-Effingham-Jasper-Crawford-Clay-
Richland-Lawrence-
500 AM CDT Thu May 2 2024

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

.DAY ONE...Today and tonight.

Scattered thunderstorms are expected to develop by tonight. The
probability for severe storms is low, but these storms will bring
potential for locally heavy rainfall and dangerous cloud-to-ground
lightning.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Occasional thunderstorms are possible over the weekend and early next
week. The probability for severe weather is low over the weekend, but
it is too early to determine the threat for severe weather next week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated through tonight.

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