Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/13/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 652 PM CDT Mon Sep 12 2022

.SHORT TERM...
Issued at 310 PM CDT Mon Sep 12 2022

Through Tuesday night...

Forecast concerns in the short term are focused on the ending time
of the pesky drizzle and scattered showers, as well as cloud
departure time.

A plethora of vorticity centers of different scales noted on
satellite, with the primary synoptic scale one in the mid-levels
centered over southern Lake Michigan and northwest Indiana.
Pinwheeling immediately around this center is an easing moist
conveyor belt, but still providing deep enough moisture in tandem
with the system`s ascent for scattered showers. This is amidst
areas of drizzle seen fairly well on radar, some of which earlier
brought MDW down to 3/4 mile visibility (i.e. heavy drizzle).
Aircraft soundings cloud depths around 5,000 ft over/near Chicago
right now, though there is a finger of clearing associated with a
wraparound dry slot that will likely diminish that depth some
over Chicago late today. Forecast soundings though indicate enough
depth, low-level wind profiles and some ascent are favorable for
continued collision and coalescence for drizzle. Also, the shower
potential may actually uptick over northeast Illinois mid to late
evening as another moisture corridor pinwheels overhead within
residual deformation. Overall, low QPF expected especially
compared to the last 36 hours, so no flood threat expected.

Also to note, there is a threat of waterspout potential over the
far southern part of Lake Michigan where an overlap exists of
low-level convergence, lake induced instability, and weaker deep
layer shear. This has supported nearly stationary showers rooted
on convergence zones near the Indiana nearshore where low-level
stretching is favored with the lake-induced lapse rates. The
motions are very slow and are not favored to move onto shore.
Cannot rule out a lightning strike or two in far northwest Indiana
though, with lake induced equilibrium levels around 25 kt (<-20C).

The back edge of the synoptic cloud shield stretches from
northern/western Wisconsin through eastern Iowa. This has been
slow to move so far today but should actually start to move some
tonight as the synoptic scale system begins to pick up haste
eastward. A majority of guidance shows a pretty quick clearing
trend overnight into early Tuesday morning, and this almost seems
too rapid given the cyclonic flow and depth of low-level
moisture. So have trended slightly slower with clearing.
Confidence though is low, especially west of the Fox River
Valley. If clearing were to occur in the far western CWA where
winds are lighter, there may be some fog but likely a little too
much wind for a dense threat.

As skies clear Tuesday morning, temperatures will be able to leap
from what they were today. Highs are likely to reach mid 70s.

MTF

&&

.LONG TERM...
Issued at 159 PM CDT Mon Sep 12 2022

Wednesday through Monday...

Much of the long term period looks quiet and dry as a surface high
pressure system slides overhead. Southerly flow will become
reestablished toward the end of the workweek leading to a gradual
warming trend with highs back in the 80s by this weekend. Ensemble
mean 500mb heights depict building heights and perhaps zonal flow
becoming established toward the end of the weekend and into next
week, which would provide increasing chances for thunderstorms. At
this point, blended NBM guidance provides low-end chance (20-30%)
PoPs as early as Saturday evening. However, a quick glimpse at
ensemble meteograms plots suggests chances for thunderstorms may
hold off until the next workweek.

Borchardt

&&

.AVIATION...
For the 00Z TAFs...

Aviation weather concerns are centered around this evening and
tonight and consist of:

* Likelihood of northwest winds returning at ORD/MDW this evening;
  expected to be light.

* Quick re-development of low-MVFR and IFR cigs and a period of
  shradz tonight.

* Timing of scattering low stratus and return to VFR into Tuesday
  morning and afternoon.

Northeast winds prevail at ORD/MDW at this time, but a switch to
the northwest is anticipated over the next 1-2 hours. Winds will
be light when this occurs, however, likely less than 7 kts, which
should allow some leeway in determining any runway configuration
changes.

Low-MVFR and IFR cigs are sharply re-developing across northwest
Illinois at this hour, and these will slosh back across the
Chicago-area sites later this evening. A period of showers or
drizzle is expected to accompany these lower cigs, but this
activity will likely be fairly brief as drier air will arrive on
increasing northwesterly winds. While confidence in timing the
cessation of IFR is fairly high at this time, it is lower for
timing the end of MVFR cigs, with it possible these persist
through much of the morning at ORD and MDW. Eventually, however,
VFR conditions will return to all the regional terminals into
Tuesday afternoon with northwest to west winds.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Beach Hazards Statement...INZ002...7 AM Tuesday to 7 PM Tuesday.

LM...None.
&&

$$

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