814
FXUS63 KLOT 041902
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
202 PM CDT Thu Jul 4 2024

.KEY MESSAGES...

- Lingering showers, possibly an isolated storm, this afternoon
  with diminishing coverage through this evening. Additional
  storm chances arrive after midnight tonight.

- Mostly dry conditions for the weekend, but there will be increasing
  rain chances late Sunday through Monday.

- Seasonable temperatures will continue through next week.

&&

.DISCUSSION...
Issued at 202 PM CDT Thu Jul 4 2024

Through Friday night:

The earlier cohesive/widespread light-moderate rain has
diminished. With several vorticity maxima and embedded jet
streaks still in the vicinity, however, additional isolated to
scattered showers will likely continue this afternoon. Locally
greater coverage appears plausible 1) near/north of the WI state
line in the vicinity of the lake breeze, 2) near the I-39
corridor and points west where a bit more instability resides,
and 3) well south of I-80 where broad warm advection remains
north of a modest 25 knot southwesterly 850 mb LLJ in the
vicinity of a subtle surface boundary. While we can`t rule out
a few lightning strikes, forecast soundings depict gradually-
warming and drying mid-levels through the rest of the
afternoon, likely in response to developing subsidence on the
backside of the departing parent shortwave. Localized downpours
will be possible owing to very slow cell motions. Finally, while
not an overly-conducive setup, we`ve received several funnel
cloud reports from central Illinois. Based on radar motions,
there`s clearly a subtle boundary that showers are tied to,
providing a little low-level vorticity/spin boost, so this
potential will continue until showers diminish.

Through the 5-7 PM timeframe, it looks like most if not all of
our forecast area will trend precipitation-free as subsidence
shifts across the region yielding favorable conditions for
firework displays.

Overnight (likely after midnight), shower and storm chances will
increase as the shortwave currently pinwheeling into western
Minnesota scoots east across Iowa. Have delayed the arrival
time of precip chances based on latest guidance which generally
matches current upstream conditions well. Suspect the greatest
storm coverage will focus north of I-88 in closer proximity to
large scale forcing, but sufficient MUCAPE exists for isolated
to widely scattered storms to "zipper" farther south ahead of
the incoming front/trough. While mid and upper winds are strong,
shallow effective inflow depths and equilibrium levels should
curtail storm organization. Can`t rule out a stronger cell with
some small hail/gusty winds, however.

Activity will push east of the region through Friday morning. By
midday and into the afternoon, scattered showers will develop in
the deeply mixed cold advection regime with coverage increasing
the farther north of I-80 you go. Continue to advertised isolated
thunder chances (20%), but guidance does depict a region of mid-
level warming which may tend to inhibit more widespread
electrification. Activity will tend to gradually diminish through
the evening hours.

Carlaw


Saturday through Thursday:

To be issued shortly.


&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1247 PM CDT Thu Jul 4 2024

The primary aviation weather concerns for the 18Z TAF period
include:

* On and off pockets of non-impactful rain throughout the period

* The likelihood of MVFR cigs beginning early Friday morning

Intermittent periods of light rain or sprinkles will continue
through this afternoon and into this evening with no related impacts
expected. Additional pockets of light rain will be possible
overnight, although perhaps the most appreciable chance comes ahead
of an impending cold front in the roughly 08-12Z timeframe. At RFD,
this potential will arrive closer to 06Z and a light thunderstorm
cannot be ruled out up that way tonight either. Confidence is rather
high in a several hour period of MVFR cigs beginning predawn on
Friday and lasting through the bulk of the morning. Most models
suggest the MVFR should clear away by noon but will likely return
during the latter part of the afternoon as more pockets of rain look
to move in. There is also a signal that the cigs refuse to budge
during the afternoon and we remain MVFR throughout the day.

Meanwhile, light southeasterlies will persist into this evening.
Confidence on wind direction takes a tumble for the overnight
period, but best guess is SSW while magnitude should remain below
10 kt. It`s very possible winds even go variable for several hours
overnight. Winds will build through the morning on Friday as they
establish a WSW direction and get gusting to around 20 kt by late
morning.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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