Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/29/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 831 PM CDT Fri Oct 28 2022

.UPDATE...
Issued at 831 PM CDT Fri Oct 28 2022

The forecast is in good shape with few changes needed this evening.

A recent hand analysis of the surface pressure, dew point, and wind
fields reveals a stout 1030+mb surface high pressure system centered
in the northeastern United States with a westward surface ridge
extension through the Great Lakes. Full sunshine earlier this
afternoon facilitated the development of a late-season lake breeze,
which has since "washed out" across the Chicago metropolitan area.
What`s left behind is a shallow (~200-300 ft deep per AMDAR
soundings) localized pool of marine moisture characterized by
surface dew points in the lower 40s extending more or less along and
east of Interstate 355 and a few miles south of Interstate 80.

With clear skies, calm winds, and subsidence all being provided by
the surface ridge over the Great Lakes, ideal radiational cooling
conditions will allow for temperatures to (continue) nosediving
through the overnight hours with lows likely to hit the low to mid
30s everywhere outside the urban core of Chicago. Considering low
temperatures are poised to fall below where dew point temperatures
were this afternoon (mid to upper 30s; the so-called "cross-over"
temperatures), areas of fog appear all but certain to develop
tonight with the densest likely within the aforementioned marine
airmass across the Chicago metropolitan area. Visibility at
Waukegan National Airport is already below 2 miles, giving
confidence in such a forecast scenario. For this reason, opted to
"bump" up wording of fog but held short of an explicit mention of
anything dense as even the most favorable or obvious set-ups
sometimes fail to produce.

Updated products will be sent shortly.

Borchardt

&&

.SHORT TERM...
Issued at 226 PM CDT Fri Oct 28 2022

Through Saturday night...

An expansive area of high pressure will remain the dominant
weather feature across the Great Lakes tonight into Saturday.
Mainly clear skies and light winds in this regime will generally
result in mild daytime highs (both this afternoon and again
Saturday afternoon) and cool overnight lows (in the 30s tonight).

The only potential weather concern through the period is the
threat for fog late tonight into early Saturday morning,
especially outside the city. We will have a fairly good set up
for good radiative cooling tonight as winds remain light under
clear skies. Accordingly, we should see temperatures cool back
into the low to mid 30s for lows tonight. With this afternoon`s
cross over temperature likely to be similar to the current dew
points (in the upper 30s), at least patchy fog development looks
to be a good bet late tonight for must areas outside the city.

The fog will burn off by mid morning Saturday, and once it does
we will be in store for another very nice weather day across the
area. Mainly sunny skies and a warming lower level airmass will
allow temperatures to rebound nicely during the day, with highs
likely to reach into the low to mid 60s.

Cloud cover will begin to increase from south to north across the
area into Saturday evening as a slow moving weather system begins
to shift northeastward into the Ozarks. This weather system will
move close enough to our area to result in a decent chance of
showers for at least southeastern sections of the area, but
likely not until after daybreak Sunday. For this reason, we have
a dry forecast continuing across the whole area Saturday night.

KJB

&&

.LONG TERM...
Issued at 146 PM CDT Fri Oct 28 2022

Sunday through Friday...

By Sunday morning the surface high will have shifted further east as
the upper/surface low over south-central CONUS continues it`s
northeastern trek. Skies will remain mostly cloudy due to the
approaching system, keeping low temperatures a bit warmer but high
temperatures a bit lower, compared to the previous day. Rain showers
will begin to move in from the south, with areas south of I-80
having a slight chance for a shower or two Sunday morning, but best
chances will be Sunday afternoon, especially south and east of I-57.
Chances for precipitation will decrease the further north and west
you go, with areas towards Rockford and towards the IL/WI state
border possibly seeing no rain at all. There still remains a bit of
a variation on the exact low track, with some models bringing the
actual low center over the eastern portion of our forecast area,
although most deterministic models have it just skimming us to our
south and east. Models continue to show PWATS of 1.20+ inches, which
as indicated in previous discussions is above the 90th percentile.
Most locations that receive any rain will see around a tenth of an
inch, although locations to the far southeast (Ford County, IL
northeast towards Jasper County, IN) could see a quarter inch of
total rainfall.

The low will move east of us by Monday morning, although there is a
chance for a few lingering showers along and east of I-57. Skies
will begin clearing west to east by mid Monday morning, with all
locations seeing mostly clear skies by Monday evening. 850 mb
temperatures will not change much during this period, so decreasing
cloud cover Monday will lead to high temperatures in the low to mid
60s west, with highs a few degrees lower in the east due to the
cloud cover departing later. Easterly winds on Sunday will back to
the west by Monday afternoon, but will remain light. High pressure
will ridge in from the south in the wake of the low, transitioning
to our east by Wednesday morning, and providing mostly clear skies
for the first half of the week. As the high moves to our east, flow
will become southerly, allowing our temperatures to climb once again
to above normal for early November, with lows in the lower 40s, and
highs in the mid to upper 60s by Wednesday. Otherwise models show
our next chance for rain will be towards next weekend.

BKL

&&

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

The only aviation forecast concern for the current TAF period is
the potential for fog (possibly dense) overnight into early Saturday
morning.

High pressure spanning the Great Lakes will yield very light/calm
winds and clear skies tonight, which will afford the possibility
of fog forming overnight and persisting for up to a few hours
beyond daybreak Saturday morning. There are still mixed signals
over where exactly fog may develop and the overall spatial extent
of it, but there has been a persistent signal in most guidance
that fog will develop at or in the vicinity of most or all of our
TAF sites overnight, so opted to not stray from the inherited fog
mentions and associated visibility reductions from the previous
TAFs. Any fog that does develop will have the potential to become
at least somewhat dense, with IFR or LIFR criteria being reached
being very much within the realm of possibilities at each of our
TAF sites.

Any fog that develops overnight should dissipate by mid-morning.
Light winds and mostly clear skies are then expected to prevail
through the remainder of the day on Saturday.

Ogorek

&&

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

$$

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