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FXUS63 KILX 020453
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1153 PM CDT Mon Jul 1 2024

.KEY MESSAGES...

- A couple periods of heavier rain potential exist, one Tuesday
  night west of I-55 and the other Wednesday night into Thursday
  night.

- There will be some strong to severe thunderstorm potential west
  of the Illinois River Tuesday night, and south of I-70 on
  Wednesday.

- Independence Day will be a bit cooler than normal, though that
  will be offset by muggy 70s dew points. While a dry period
  exists by afternoon, rain chances increase enough during the
  evening to complicate fireworks planning.

&&

.UPDATE...
Issued at 840 PM CDT Mon Jul 1 2024

High cloud cover continues to stream over the top of an upper
level ridge into central IL, while extremely dry air is located in
a layer just above 850 mb with over 50 deg C dewpoint depression
for an absence of any lower level cloud. A couple of upper level
shortwaves will skirt the forecast area to the north through
Tuesday morning, first this evening which should keep any
precipitation to the north given the very dry layer. In the
morning, another wave currently over eastern NE will clip northern
IL, with a slight chance of showers and thunderstorms into Knox
and Stark Counties and portions of adjacent counties, however
models produce varying degrees of moistening of the dry layer, and
most maintain precipitation just north of the area. At this point
the afternoon package does not look to need any modifications in
this regard. Lows from around 60 in east central IL to the mid 60s
in west central IL look on track.

37

&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 303 PM CDT Mon Jul 1 2024

High clouds continue to stream across the area, overtop of an
upper level high pressure ridge extending from eastern Texas into
western Wisconsin. A weak wave is tracking across Iowa and
northern Missouri, though surface obs continue to highlight the
dry airmass (a few rain reports from cloud bases around 11,000
feet). For the most part, will keep the forecast dry through this
period, though some of the high-res models suggest some light
showers skimming by the northern edge of the forecast area after
sunrise. Forecast soundings in this area are still dry in the
lower levels, though with some increase in moisture down to around
5,000 feet. Will mainly address this with some 20% PoP`s around
Galesburg.

Winds continue to turn more southeasterly tonight, as the high
pressure pulls further east away from the area. This will keep
temperatures warmer than last night, though areas near/east of
I-57 are still likely to drop into the 50s as dew points remain
lower in this area. Tuesday will feel a bit more likely early July
as temperatures approach 90 degrees west of I-55, though with
dew points staying near or below 60 in a good part of the forecast
area, heat index will be about the same as the temperatures.

Geelhart

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 303 PM CDT Mon Jul 1 2024

The longer range forecast will be highlighted by some heavier
rainfall at times from Tuesday through Thursday night, along with
a few potentials for strong to severe thunderstorms.


Tuesday night through Thursday night:

Moisture levels begin to quickly increase from the west on
Tuesday, with HREF precipitable water values near 2 inches around
Galesburg by mid evening and reaching I-55 shortly after midnight.
Main convective initiation takes place Tuesday afternoon along the
cold front in Iowa and northwest Missouri, with general consensus
of the CAM`s bringing a line of thunderstorms to the
Iowa/Illinois border by early evening. Low-level jet out of the
southwest suggests potential for some training echoes as the
overall line moves east-southeast. Though the brunt of the
heaviest rain will be focused just to our west, HREF probabilities
of over 1 inch of rain are around 30-40% west of the Illinois
River. Main severe weather threat will also be just to our west,
though latest SPC Day2 outlook maintains a marginal (level 1) risk
west of the Illinois River and the main threat further into west
central Illinois.

The cold front is progged to reach the I-72/I-70 vicinity on
Wednesday, before getting hung up in the southwest upper flow.
Area south of I-70 is in a level 2 severe risk which seems
reasonable, though the level 1 risk as far back as Springfield and
Rantoul may be a little generous. Focus for heavy rain potential
then shifts into this region Wednesday night, where high (>2 inch)
precipitable water values persist. GFS and European deterministic
models lift the front back north Thursday afternoon, before a
final cold front surge Thursday night. QPF guidance from WPC
suggests potential for another inch of rain along and west of the
Illinois River Thursday evening, though this seems to be driven by
the deterministic GFS as only a handful of its ensemble members
have this level of rain included. In any event, probably enough of
a rain threat to throw a wrench into fireworks plans for the
evening.

Temperature-wise, cloud cover from the leftover thunderstorm
complexes make highs a challenge at times, though areas south of
I-70 stand the best chance of exceeding 90 degrees on Wednesday.
Independence Day will be near or a little below normal for highs,
but that will be offset by muggy dew points in the 70s.


Friday through Monday:

By Friday morning, longer range models are in good agreement with
a cutoff low over southern Minnesota, tracking it to eastern
Lake Superior by Saturday morning. While a dry slot prevails over
a good portion of the forecast area, some wraparound showers
can`t be ruled out.

Upper level ridging builds along the West Coast over the weekend,
putting us in more of a northwest flow into early next week. An
upper wave in this flow arrives later in the weekend, bringing
another chance of showers and a few storms. Temperatures will be
below normal for the first weekend of July, with highs only in the
lower 80s over most of the forecast area.

Geelhart

&&

.AVIATION...  
-- Changed Discussion --
(For the 06z TAFs through 06z Tuesday Night)
Issued at 1053 PM CDT Mon Jul 1 2024

High and mid clouds will continue to stream across the central IL
terminals, although conditions will remain VFR until at least 03Z.
A line of thunderstorms will approach from the west late in the
period, potentially reaching KPIA as early as 03Z, but likely
arriving after 06Z for the remainder of the central IL terminals.
Brief MVFR cigs/vsbys possible with thunderstorms, as well as
strong gusty winds. Otherwise, winds SE around 10 kts overnight,
becoming S 10-15 kts with gusts 20-25 kts by 14Z.

37
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&&

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

$$