Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/17/23

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 544 PM CST Thu Nov 16 2023

.SHORT TERM...
Issued at 235 PM CST Thu Nov 16 2023

Through Friday night...

KEY MESSAGES:

* Gusty SW winds through this evening

* Scattered showers tonight into early Friday morning

* Much cooler conditions than late beginning Friday

Comfortably mild conditions grace the CWA today with temperatures
early this afternoon sitting in the 60s underneath increasing
cloud cover. Unfortunately, the unseasonably warm weather will
come to an end following a cold frontal passage tonight. As of
2PM, the boundary is just beginning to approach northwest Iowa and
is making steady progress as it marches into the Midwest. We`ll
continue to see our cloud cover thicken up through the afternoon
in anticipation of the front.

Meanwhile, a ripping low level jet sits on the leeward side of the
pre-frontal trough. The bulk of the jet is up to our north but
its tail end is moving over the area and we`ve had no problem
regularly pulling 25 to 35 mph gusts down to the surface for the
past few hours. With the jet expected to ramp up a bit later today
before ejecting to the east, gusts could approach 40 mph at times
during the late afternoon and through much of the evening. Winds
should come down quite a bit just ahead of the front but remain
somewhat breezy tonight and will continue to step down through the
day tomorrow.

No rain is currently falling in the vicinity of the front. Scattered
showers are expected to begin developing along the boundary this
evening as the front collides with a low level moisture plume that`s
being fed into northern Illinois this afternoon. Guidance seems to
be trending toward the idea that we could see some light pre-frontal
activity late this evening given the added moisture and modest
isentropic upglide. The front will begin pushing a broken line of
showers into the northwestern CWA late in the evening and will
progress across the area through the night and into early Friday.

Rain coverage along the front is anticipated to build with eastward
extent with the better moisture leading to greater low level
instability and models resolving an uptick in synoptic forcing
later in the night tied to that departing upper jet max. By
daybreak on Friday, the rain should be mostly confined to parts of
northwest Indiana. The entire CWA is expected to be rain-free by
mid to late morning. High pressure quickly builds in behind the
front which should keep any post-frontal activity at bay and clear
things up nicely for Friday. However, the cooler airmass will
keep temperatures for the better part of the day stuck in the 40s
with sub-freezing temperatures forecast for Friday night into
early Saturday.

Doom

&&

.LONG TERM...
Issued at 235 PM CST Thu Nov 16 2023

Saturday through Thursday...

KEY MESSAGES:

* Dry and near to above normal temperatures this weekend

* Rainy and breezy later Monday into Tuesday (70-80%+ chance)

* Much colder Tuesday night through Thanksgiving and beyond

Following a seasonably chilly start to Saturday, high temperatures
will reach the lower 50s, which is a few to several degrees above
normal for the date. A weak pressure gradient Saturday night will
support favorable radiational cooling of the dry air mass,
yielding lows in the upper 20s to lower 30s outside of Chicago and
mid-upper 30s in and near the city. Slight warming at 850-925 mb
on Sunday should add a couple degrees to the highs (low-mid 50s),
which will be the last mild and dry day for the foreseeable
future. Mid and high level cloud cover will stream in from the
west toward and after sunset.

For Monday PM into Tuesday, the signal for a period of wet
weather has increased. There are certainly some complexities
evident in terms of evolution of various features associated with
the Monday-Tuesday system that will affect smaller scale details
and forecast specifics. However, in a broad sense, a short-wave
trough will emerge into the central and southern Plains on Sunday,
supporting surface cyclogenesis. The surface low will then track
east-northeast at a steady or weakening state, reaching the
eastern Great Lakes on Tuesday. Chances of meaningful phasing with
an incoming deep northern stream short-wave trough and a higher
impact system affecting our area appear to have gone down over the
past few days. The phasing currently is more likely to occur
later and result in a deeper system well to our north-northeast
Tuesday night into Wednesday.

As the system approaches on Monday, a tightening pressure gradient
between the low pressure and expansive high pressure to the
northeast will result in breezy easterly winds. Eventually, rain
will spread northward during the afternoon, with some uncertainty
on onset, so chance PoPs Monday afternoon appear reasonable. Given
increasing model agreement and good ensemble support, felt comfortable
with the high likely to categorical PoPs (70-80%+ as referenced in
key messages) Monday night. Lighter rain should continue Tuesday
morning (~60+% chance), with the precip then winding down for the
most part prior to the arrival of much colder air aloft Tuesday PM.
We`re showing some lower end PoPs (20-40%) into Tuesday evening
in the form of rain-snow mention, but at this time, expectation is
for most of if not all of the appreciable precip Monday PM into
Tuesday to be in the form of rain.

For the busy Wednesday holiday travel day, Thanksgiving Day, and
at least several days beyond, confidence has increased in a
period of winter-like temperatures. Amplified western North
American ridging will carve out deep eastern troughing and plunge
by far the coldest air mass of the season to this point southward
into the region. At this time, both Wednesday and Thursday appear
they will be dry but cold with blustery westerly winds (strongest
on Wednesday). Forecast highs are in the lower to locally mid 30s
on Wednesday and only upper 20s to lower 30s on Thanksgiving, with
highs in the teens to around 20F. The main issue to contend with
for holiday travelers will be cold wind chills, as low as the
teens on Wednesday and single digits Thursday morning.

Castro

&&

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

Concerns in this TAF period include:
 - SSW gusts in excess of 30 knots this evening
 - Scattered SHRA and MVFR ceilings overnight
 - NNW wind shift with a cold front late tonight

A developing 50 knot LLJ per recent VWP and MDW ACARS data will
gradually lower this evening, allowing sporadic 30 knot gusts or
higher to become more frequent by mid-evening. WAA ahead of an
approaching cold front will support increasing coverage of light
showers and MVFR ceilings late this evening through much of the
overnight hours as winds begin to diminish. The cold front will
bring a NNW wind shift in the 10-12Z window with gusts in excess
of 20 knots persisting into the afternoon. Wind direction may
settle due north or even briefly east of north (010 degrees)
during the afternoon, but expectations are for the overall
direction to remain slightly west of north (350 degrees).

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...IL nearshore waters until 4 PM Friday.

     Small Craft Advisory...IN nearshore waters until 10 PM Friday.

&&

$$

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