Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/07/23

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 628 PM CDT Thu Jul 6 2023

.SHORT TERM...
Issued at 246 PM CDT Thu Jul 6 2023

Through Friday night...

Surface convergence continues to tighten along an inland-advancing
lake breeze early this afternoon. Dewpoints both ahead of and
behind this boundary remain in the mid and even upper 60s, and
recent objective analysis indicates MLCIN has completely eroded.
Seeing a bit more vertical growth to the cumulus field along the
boundary along with a few spits/sprinkles. AMDAR observations
generally corroborate forecast soundings, suggesting that
lingering mid-level warming will continue to limit overall
instability magnitudes/Equilibrium levels, and suspect that any
electrification potential will be extremely limited. Any lingering
isolated activity early this evening will wane with the loss of
heating.

Outside of some very shallow/patchy fog tonight, looking pretty
quiet in the weather department.

The next feature of interest will be a shortwave disturbance
(presently embedded within a stream of cyclonic shear vorticity
across Wyoming) which will traverse the region into Friday night.
To some degree, this shortwave will be convectively- augmented,
but suspect not quite the degree depicted by the 12z NAM. In fact,
most other guidance depicts a much lower amplitude wave and
associated muted low-level mass response, and continue to lean
this way in the forecast. While some thickening of the cloud deck
will take place through Friday afternoon, it looks like most of
the daytime hours may remain precip-free, with sub-cloud dry air a
bit too deep even for a sprinkle mention. Loosely-
organized/transient bands of f-gen will develop across the region
through Friday evening and overnight, yielding some increase in
shower and isolated thunderstorm coverage. At this time, seems
like the highest coverage may set up near/south of I-88. Some
signal that west-east oriented clusters of showers/embedded storms
may set up through the night which does suggest a potential for a
little training/backbuilding. The parameter space for this,
however, isn`t high end at all, with a very modest southwesterly
LLJ (generally 20 kts or less), but we`ll continue to monitor
trends for a very localized heavy rain threat Friday night.

Carlaw

&&

.LONG TERM...
Issued at 300 PM CDT Thu Jul 6 2023

Saturday through Thursday...

Key Forecast Messages:

* Weekend: For areas seeing rain/embedded t-storms past daybreak
  Saturday, likely drying out thereafter and mainly dry Sunday

* Chance for showers and storms returns Tuesday PM as a cold front
  sags south and potentially stalls for a time Wednesday, which
  may yield a heavy rain/flooding threat

Regarding Friday night/overnight`s parent short-wave and surface
reflection, global guidance consensus is for a notably more
southerly trajectory than this morning`s (12z) NAM12 and 3km
NAMnest runs. With this is mind, suspect that trend will be
steadily drying north/northwest to south/southeast as drier air
builds in from the surface to the mid-levels. To wit, even the
(possibly) convective feedback modulated NAM12, along with the 12z
ECMWF and Canadian are dry for a lion`s share of the CWA during
the afternoon, with the exception of our far south/southeast.
Curtailed PoPs more quickly than the NBM init, along with thunder
chances, which would primarily be in the early-mid AM south of
I-80. If clouds clear more quickly, we may see temps creep up
above the upper 70s inland currently advertised, with low 70s
forecast lakeside.

Lack of forcing and very dry mid-levels, plus dew points at peak
heating probably prone to mix out closer to projections of better
verifying guidance such as the ECMWF, suggests little/no threat
for precip. in the Sunday-Monday timeframe. Temperatures will warm
to the low-mid 80s Sunday afternoon away from the lake (mid 70s
lakeside) and then further to the mid-upper 80s on Monday when
southwest winds may be strong enough to bring the warmth to the
lakefront for a change.

Tuesday will probably start out dry as the roughly west-east
oriented front starts to make southward movement from the upper MS
Valley and northern Great Lakes. Should be another warm day in the
mid-upper 80s. Moisture pooling along the front and convergence,
plus possibly modest large scale ascent could kick off scattered
storms Tuesday afternoon and evening, with deep shear potentially
enough for organization. Wednesday- Wednesday evening looks
"interesting" from a heavy rain/flooding threat signal, though
obviously several days out to assess this. The front should then
make headway south on Thursday.

Castro

&&

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

628 PM...Forecast concerns include...

Fog potential early Friday morning.
Wind shift/lake breeze to easterly Friday.
Chance for showers Friday evening.

A lake breeze continues to slowly move inland early this evening
and will likely push through DPA before dissipating. Few/sct cu
should dissipate through the evening with current high level cloud
cover also shifting east, leaving generally skc overnight.
Combined with light/calm winds, some fog is possible by early
Friday morning. Much of the guidance has the best potential south
and southeast of the terminals. Overall confidence for fog is
fairly low and maintained fog mention at RFD/DPA/GYY. Any fog that
does form should dissipate quickly after sunrise.

While light, prevailing wind directions overnight will likely be
northwest and at some point Friday morning, will shift easterly.
This may occur ahead of a possible lake breeze and confidence is
low. Further inland, winds may become southeast or even southerly
at RFD and wind adjustments can be expected with later forecasts.

A mid deck is expected later Friday afternoon which is expected to
lower some into Friday evening. Some showers are possible in the
evening, across all of northern IL though low confidence for
coverage. Opted to include vicinity mention for the 30 hour
ORD/MDW tafs and if trends continued, some tempo or prevailing
shower/light rain may be needed with later forecasts. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Beach Hazards Statement...INZ001-INZ002 until 10 PM Thursday.

LM...None.
&&

$$

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