796
FXUS63 KILX 131956
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
256 PM CDT Tue Aug 13 2024

.KEY MESSAGES...

- A couple periods of thunderstorms are expected later this week,
  one Thursday morning and the other in the evening/nighttime
  hours of Thursday. The latter one has the better chances for any
  strong to severe storms.

- The storms also have some potential to produce heavy rainfall
  amounts, though details on exact placement are a bit murky at
  the moment.

- After a short period of more typical mid-August temperatures,
  late week and early next week will see a modest cooldown.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 256 PM CDT Tue Aug 13 2024

Latest surface map shows high pressure centered near northern Lake
Michigan. Some diurnal cumulus has formed across the forecast
area, with some delay where the earlier mid-level clouds had hung
on the longest. The MCS continues to roll across southern Missouri
but has been weakening, and a bit of thinning of the high clouds
has occurred along its periphery. A general decrease in cloud
cover will begin in earnest after sunset, and skies over our area
should be mostly clear by mid evening.

Morning high-res models trended slower with the eastward
progression of the line of showers/storms that is expected to form
over the central Plains overnight, and most show the line fizzling
as it comes into western Illinois. PoP`s have been trimmed back
some and generally limited to the far western CWA. Otherwise, a
general increase in clouds is expected tomorrow, though a fair
amount of sunshine is expected. While temperatures will be
comparable to today, southeast winds will result in a general
uptick in dew points and make it feel a bit more uncomfortable.

Geelhart


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 256 PM CDT Tue Aug 13 2024

Wednesday Night-Friday:
-----------------------

Main focus in this period will be with a pair of convective
clusters moving across the region. Morning models continue to show
the first cluster developing across the mid-Missouri Valley
Wednesday evening, moving southeast. HREF guidance has trended
more southeast with its movement overnight, with several of the
individual members bringing the line into the Illinois River
Valley toward 5-6 am Thursday. The highest PoP`s have been
reoriented as a result, favoring the 4 am to noon period.
Precipitable water values are forecast to increase to 2+ inches
during this period, with NBM probabilities of rainfall amounts
over an inch increasing around 60% near/north of I-72 by mid
morning Thursday. While a few stronger wind gusts can`t be ruled
out as the line arrives around sunrise, it should generally be in
a weaker state as it passes through.

Some model discrepancies were noted with the second round late
afternoon and evening, notably the NAM focusing the west-east band
of heavier rain south of I-72. Only a handful of GFS ensemble
members come close to the amount of rain shown by the NAM, but
focus it more northwest, and the European ensembles are generally
lighter. This will probably be one of those situations where
guidance fluctuates until better mesoscale details (not available
this far out) start to get incorporated. In terms of the severe
threat, surface based CAPE`s over 3000 J/kg will be favorable for
convection as it refires later in the afternoon, though shear
levels ahead of the line will be a bit more marginal. Damaging
winds appear to be the main threat.

On Friday, much of the activity will be out of the area. However,
as an upper low swings across the Great Lakes, some wraparound
showers can`t be ruled out, primarily near and north of I-74.


Saturday-Tuesday:
-----------------

Longer range appears to be relatively quiet at this point. The
departure of the upper low over the Great Lakes may be slowed a
tad late week, depending on tropical activity across the western
Atlantic. In general, the upper ridge will amplify again across
the Rockies, with broad troughing setting up over the eastern U.S.
This will keep us in more of a northwest flow, with temperatures a
few degrees below seasonal normals, and humidity levels not
expected to be oppressive.

Geelhart

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1204 PM CDT Tue Aug 13 2024

VFR conditions expected through the period. Ceilings this
afternoon will generally in be in the 5000-8000 foot range, though
skies clear for a good portion of the night. Any lowering ceilings
on Wednesday morning will likely stay west of KSPI.

East/southeast winds this afternoon should only be in the 4-7 knot
range, but a more sustained increase to 8-10 knots is expected
by late Wednesday morning.

Geelhart

&&

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

$$