875
FXUS63 KILX 041757
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1257 PM CDT Tue Jun 4 2024

.KEY MESSAGES...

- 2 rounds of storms and showers this afternoon into the overnight
  hours ahead of a passing cold front with another low threat for
  strong-to-severe storms.

- A brief dry period settles in before the potential for rain
  arrives again for the weekend (10-20% chance).

&&

.DISCUSSION...
Issued at 250 AM CDT Tue Jun 4 2024

As a MCV passes through again today, more showers and thunderstorms
could pop up. Today, the shear looks healthier (25-35kts) than
yesterday. This could mean that the storms that do fire up could
live slightly longer. There is a threat of severe weather this
afternoon, with the main hazards being marginally severe hail and
locally damaging winds, but most storms will be of the typical
summer-time pop up storm genre. MCVs are known to be tricky and
could increase the severe threat. There is a 40-60% chance of
showers and thunderstorms this afternoon starting after 18z.
Coverage will be of the scattered nature for areas along and north
of I-70. SBCAPE values of 1500-2500 J/kg support the development of
these storms. The PWAT values this afternoon are 1.6-1.8, which
support that these showers/storms could produce locally heavy
downpours.

The first and second rounds appear to blend together around midnight
as the cold front enters the CWA from the west. The line of showers
and thunderstorms along the front will move through from 05z to 15z
tomorrow. Thunderstorm activity with this round may be limited due
to the convection earlier in the day, if the afternoon convection
pans out like the CAMs (NAM 3km, HRRR, ARW) are depicting. The
potential for a worked over environment to be in place could mean
that along the front there would only be stronger showers without
the presence of thunderstorms. As the line moves across central
Illinois, it breaks up as it passes the I-55 corridor. Many
locations east of I-57 could see no rain out of the overnight system
as it become more scattered.

Behind the cold front, we will see a short period of dry weather as
a high pressure builds over the region. Surface high temperatures
cool slightly but remain around the upper 70s. By Sunday, highs warm
back up to near or just above 80 degrees. There is a very small
chance for rain this weekend (saturday and Sunday), with POPs of 10-
20%, as MCSs are passing to our far south. There is the small chance
that one could drift just far enough north-northeast to affect
central and southeastern Illinois.

Copple

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1257 PM CDT Tue Jun 4 2024

The primary aviation forecast challenge will be predicting the
areal coverage and timing of convection later today. 1730z/1230pm
visible satellite imagery is showing Cu blossoming along/southwest
of a KGBG to KDEC line and this will be the area to watch for
thunderstorm development over the next 2-4 hours. Most CAMs
indicate the highest concentration of storms will be focused
along/west of I-55, so have hit the thunder forecast hardest
across this area. Based on satellite trends and the latest
RAP/HRRR forecast, have mentioned thunder at all sites between 21z
and 04z, but have opted to go TEMPO thunder at KPIA/KSPI/KBMI due
to higher confidence in greater areal coverage there. Once the
late afternoon and early evening convection lifts northward, a
lull in precip chances will be observed before an approaching cold
front brings a broken line of showers/storms well after midnight.
Once the front passes, the showers will come to an end and winds
will veer to W/NW by Wednesday morning. MVFR ceilings will be
observed at KSPI/KPIA for the next couple of hours before cloud
bases diurnally rise to low VFR by around 20z. After that, VFR
will generally prevail until after FROPA when models suggest a
band of MVFR ceilings will form.

Barnes

&&

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

$$