845
FXUS63 KILX 160201
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
901 PM CDT Wed May 15 2024

.KEY MESSAGES...

- It will be dry tonight, but occasional precip chances exist
  throughout much of the extended forecast.

- The severe weather potential is low Thursday-Friday, but an
  isolated strong to severe storm can`t be ruled out south of I-70
  Thursday afternoon.

- A gradual warming trend is expected this weekend, with highs
  likely (greater than 75% chance) in the 80s across much of the
  area Saturday through Tuesday.

&&

.UPDATE...
Issued at 901 PM CDT Wed May 15 2024

Clouds are advecting into the CWA as forecast and will continue
the rest of the night. HiRes models continue to forecast precip
arriving into central IL tomorrow morning and the current forecast
has a good handle on this. Therefore, no update planned for the
forecast at this time.

Auten

&&

.DISCUSSION...
Issued at 228 PM CDT Wed May 15 2024

2024 has been a tricky planting season across Illinois. Total
precip over the last month has ranged from 75% of normal east of
I-57 to 150-200% of normal west of I-55. It`s not just the precip
amounts that have made things challenging, but also the frequency.
For example, 15 of the last 30 days have had measurable precip in
Lincoln. A recent USDA report showed that about 40% of corn and
soybeans have been planted in Illinois so far, as opposed to
70-80% by this time last year.

This pattern of frequent rain chances is set to continue, with
little in the way of high confidence dry time over the next week.
While there will certainly be breaks in the precip, and some
locations may miss out on rain from any given wave, the only
periods over the next week that we can confidently say look void
of precip anywhere in the ILX CWA is tonight into Thurs AM, and
late Saturday through the daytime hours on Sunday.

Through the remainder of the work week, there are two waves to
monitor, the first of which will provided scattered showers/storm
chances on Thurs, the other on Fri (and perhaps lingering into
Sat). For Thurs, there are two forcing mechanisms in play, an
upper trough and its associated sfc low over the northern
Plains/upper Midwest, and a shortwave emerging from the south-
central Plains. This south- central Plains shortwave is expected
to produce convective activity across KS/OK/TX tonight - and CAMs
depict this activity eventually lifting northeast into central IL
after 12z/7am Thurs.

Dealing with the evolution of overnight convection comes with
plenty of uncertainty, which is evident in varying CAM solutions.
HREF probs highlight a 40-60% chance of precip west of a Peoria-
Springfield line by midday Thurs, spreading northeast during the
afternoon. The CAPE/shear parameter space doesn`t look
particularly intriguing for Thurs. Modest instability (500-1000
J/kg) is progged to develop by mid-afternoon, but it`s a
relatively skinny CAPE profile with mid-level lapse rates around 7
degC/km at best. Bulk shear could also be described as marginal,
at best, with values around 25-35 knots, increasing with southward
extent. Can`t rule out isolated hail if an updraft or two
overperforms, but organized severe thunderstorms look unlikely
Thurs.

On Friday, an upper trough lifts from OK toward the OH River
Valley. Deterministic models continue to have a fairly large
spread regarding the evolution of this wave, with the GFS
depicting a deeper, closer upper low, which subsequent moves much
slower and keeps precip chances around into Saturday. The Euro is
weaker and faster, with no precip on Sat. In both cases, the track
of the upper low results in increasing precip chances with SE
extent, a trend that is matched by the few CAMs that go out that
far. While the blended guidance did trend PoPs lower north of
I-72, did not think it went low enough and adjustments were made
to lower them further. CAM coverage is quite sparse for Fri, so
further PoP reductions are possible if guidance comes into better
agreement regarding the strength of that wave. With the ILX CWA on
the north side of the upper low track, severe wx is not expected
Friday.

While it remains to be seen how long, if at, precip lingers into
Saturday, dry conditions are eventually expected to prevail as
upper level height rises occur by Sat afternoon. That will result
in dry weather Saturday evening through at least the day on
Sunday, a welcome reprieve from the repeated rain chances. This
reprieve will be short-lived, however, as upper ridging develops
over Mexico/the deep southern Plains. This upper pattern will be
favorable for one or more disturbances to track towards the
Midwest next week. The exact timing of these disturbances remains
vague at this range, but with southerly flow advecting gulf
moisture northward, the prospects of severe weather are set to
increase for early next week, at least relative to our Thurs and
Fri disturbances.

In terms of temperatures, a gradual warming trend is expected this
weekend into next week, with highs likely (>75% chance) climbing
into the 80s. Exactly how warm the temperatures climb will depend
on the strength of the ridging and how precip/cloud cover from
storms next week unfold.

Erwin

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 654 PM CDT Wed May 15 2024

VFR conditions will prevail at all TAF sites next 24hrs. CU is
quickly dissipating, but high cirrus is moving over the sites and
will continue into the evening. Just after midnight, AC will move
over the sites, in advance of the precip that should move into the
area tomorrow morning. During the morning hours, clouds will
become broken around 5kft. Based on HiRes models, showers should
begin at each site in the late morning to early afternoon and
continue, on and off, through the afternoon. Cigs will remain VFR
but at around 3.5kft. Winds will be light this evening into the
overnight hours, but become more southeast. Southerly winds are
expected late morning through the afternoon with speeds around
10kts.

Auten

&&

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

$$