Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/15/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 919 PM EST Sat Jan 14 2023

.Forecast Update...
Issued at 918 PM EST Sat Jan 14 2023

- Partly Cloudy and Cold Overnight

Surface analysis this evening shows a large area of high pressure in
place over western Ohio, stretching northeast into southern Ontario
and southwest toward the lower Mississippi valley.  Low clouds
across central Indiana have dissipated, leaving just some high
invading clouds from the west. Water Vapor imagery shows ridging in
place across the plains states with a ridge axis west of Indiana.
Northwest flow was in place across Indiana with high clouds spilling
over the top of the ridge into Indiana.  Temperatures had fallen
into the middle 20s across Central Indiana.

Dry weather is expected to persist overnight as the ridging aloft to
the west slowly builds eastward. Thin high clouds, as seen on
GOES16, will continue to stream across Indiana, providing partly
cloudy skies. Forecast soundings and time heights continue to reveal
a very dry column in the mid and lower levels overnight, indicative
of subsidence. Thus will aim for just partly cloudy skies and lows
in the lower 20s. Overall, little change to the ongoing forecast.

&&

.Short Term...(This evening through Sunday)
Issued at 237 PM EST Sat Jan 14 2023

A pronounced subsident inversion is evident in ACARS soundings early
this afternoon, with low-level moisture restricted from
substantial vertical mixing and confined within a shallow PBL.
Stratus has persisted and been thickest per satellite trends
downstream of the long fetch of Lake Michigan. It has eroded across
east-central Indiana, and partially eroded across western Indiana. A
general decrease is expected to continue with modest surface
diabatic heating/mixing through the end of the diurnal cycle, and
especially this evening as surface ridge axis moves in resulting in
drier trajectory given upstream air mass to the south.

Southerly winds later tonight will be light, but should be
sufficient to provide enough mechanical mixing to prevent a
significant radiative cooling event. So, our forecast is slightly
cooler that previous forecasts owing to trends in cloud cover, but
now as low as the lowest end of the model suite. There is a very
minor signal for fog, but given upstream moisture magnitude and
mostly neutral advection, we think any meaningful visibility
reductions are unlikely tonight.

For Sunday, mean ridging placement should support at least a 10
degree warm-up compared to today, and there`s an argument to be
made for even warmer. At least low 40s seem achievable, but we have
nudged the forecast closer to the higher percentile blended and
statistical model guidance which handles these situations fairly
well, typically. This would place roughly the southwest two-thirds
of the area in the mid 40s for maximum temperatures. Cirrus will
increase at the downstream/ascending end of deeper moisture plume
with the next upstream trough.

&&

.Long Term...(Sunday night through Saturday)
Issued at 237 PM EST Sat Jan 14 2023

Sunday Night Through Tuesday.

The transition into an active pattern will really pick up Sunday
night into Monday as a rapidly deepening upper level trough tracks
from northern Kansas through Iowa into Wisconsin during the daytime
hours Monday into Monday night. Run to run model consistency remains
high which brings relatively high confidence in both the track and
strength of the low and resulting impacts.

Locally we expect periods of moderate rain Monday, especially during
the afternoon hours.  A few rumbles of thunder are possible, but
think that coverage would be minimal with only minimal amounts of
elevated instability.  Rain amounts of around a half inch are likely
with locally higher amounts possible. This system then exits Monday
night with the potential for drizzle hanging around into Tuesday as
the backside of the system passes through.

Wednesday Through Saturday.

The active pattern will continue into the latter portions of the
work week as another deepening low pressure system exits the lee of
the Rockies and pushes northeast.  Model ensembles have a much
weaker handle on this system with a more significant spread in both
track and strength.

That being said, there has been a gradual trend for this system to
deepen further than earlier expected and a more potent core of cold
air that brings the snow potential down as far as the northwestern
counties.  Rain is the much more likely scenario, but will have to
continue to monitor these trends going into next week.

There may be a few lingering impacts late Friday into Saturday, but
overall think that the best chances will be Wednesday night into
Thursday.  Temperatures will generally be above average with highs
in the 40s and lows in the 30s.

&&

.Aviation...(00Z TAF Issuance)
Issued at 531 PM EST Sat Jan 14 2023

Impacts:

* Brief MVFR ceilings at IND improving to VFR quickly
* Mainly VFR conditions this TAf period.

Discussion:

GOES16 continues to show a band of low cloud stretching from
northern Indiana toward Indianapolis, although these clouds appear
to be showing a dissipating trend. This is expected to continue the
next few hours as dry air and subsidence continues to build across
the area. Satellite also shows high cloud middle Mississippi valley
advancing toward Indiana. These clouds will be the main feature
during this TAF period, invading from the west and resulting in high
and thin VFR ceilings. Forecast soundings are on board with this,
showing some saturation well aloft, but dry air within the mid
and low levels.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Update...Puma
Short Term...BRB
Long Term...White
Aviation...Puma



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 541 PM CST Sat Jan 14 2023

.SHORT TERM...
Issued at 151 PM CST Sat Jan 14 2023

Through Sunday evening...

Our stubborn stratus deck, which has become extremely thin (less
than 500 feet thick per aircraft soundings), has cleared out
nicely across lake-adjacent locales in northeast Illinois and
continues to try to scatter elsewhere. Will probably see these
trends continue through the afternoon. Low level warm advection is
increasing off to our west and will move into the forecast area
this evening and overnight. As a result, it`s possible that the
stratus deck will begin to re-develop overnight. At the same
time, a thickening cirrus canopy will spread out of Iowa as
surface winds gradually increase. All of this suggests another
night of muted temperature falls.

Tomorrow`s primary forecast challenge revolves around temperature
trends which will be tied to the longevity of stratus in our
area. If we start the day with a thinner-than-expected deck, some
insolation through incoming high cloud cover suggest mid 40 degree
highs would be attainable. Currently, however, favoring a
lingering low stratus layer across most of the area which should
eventually erode through the morning and afternoon. In addition, a
formidable subsidence inversion (which has been acting to keep
this stratus deck stuck in our region) will likely limit how
deeply we`re able to mix (and thus warm). For now, have slightly
nudged highs down to either side of 40 degrees across most of the
forecast area, with low to mid 40s closer to central Illinois.

Carlaw

&&

.LONG TERM...
Issued at 300 PM CST Sat Jan 14 2023

Early Monday through Saturday...

Main forecast highlights and concerns:

* Showers with isolated thunderstorms possible on Monday

* Increasing threat for accumulating wet snow in parts of the area
  Wednesday night and Thursday

Late Sunday night through Monday, a neutrally tilted 500 mb
short-wave trough and associated surface low will eject northeast
from the southern/central High Plains to the upper Mississippi
Valley, and across southern Wisconsin Monday evening. Increasing
warm and moist advection and large scale ascent will foster
increasing shower coverage pre-dawn Monday through the day,
peaking in the morning through mid day/early afternoon. Well above
normal PWATs advecting northward may yield brief heavier rain
rates in more robust showers. Gusty south-southeast winds will
result in gradually climbing temps, particularly as the system
warm front lifts north, favoring late day into the evening highs
from the mid 40s to low 50s (coolest north and mildest south).

Out ahead of the dry slot in the late afternoon and early
evening, cold 500 mb temps (-20 to-25C) with the trough will
steepen mid-level lapse rates enough for minor MUCAPE and a threat
for a few embedded thunderstorms in the late afternoon and early
evening along with the more widespread showers. Once again
maintained slight chance thunder mention in the grids roughly
along and south of I-90. Latest thinking continues to be that
instability is likely to be too meager for any stronger t-storm
risk. If there is a trend for notably higher dew points than upper
40s to around 50F in the southern CWA late day- Monday evening, a
marginal or conditional threat for stronger thunderstorms may
evolve given the otherwise favorable synoptic pattern. Have not
yet seen signs of dew points well into the 50s in any guidance and
for that reason, current worst case scenario would be instances
of hail (if MUCAPE trends higher) given steep mid-level lapse
rates and the low freezing level.

Muted cold advection and cyclonic flow aloft in the wake of the
system should keep a few spotty showers or sprinkles/drizzle
going late Monday night into Tuesday, primarily near and north of
I-80. It will otherwise be a cloudy and mild day on Tuesday in
the offing as highs reach the 40s once again. Tuesday night
through the daytime hours on Wednesday will then be mostly cloudy
and continued mild for January. The next notable trough ejection
from the southwest will occur on Wednesday with broad low pressure
(or eventual double barreled low pressure) consolidating and this
stronger low pressure center then tracking northeastward or
north- northeastward through Thursday. This may bring the first
appreciable accumulating snow of this exceptionally mild January.

While this system is at a range (around day 5) in which fairly
large run to run variability is common, the 12z 1/14 global
operational models were in pretty good agreement in the big
picture details of the synoptic pattern and the entire area seeing
precipitation starting Wednesday night into early Thursday. Since
a distinct majority of ensemble members also indicate a favorable
storm track to spread precip. across the area, continue to feel
comfortable with the likely PoPs offered by the NBM.

A strong enough synoptic system (which is currently favored at
this vantage point), in addition to good large scale ascent, can
be expected to draw a plume of well above normal PWATs northward.
Thus regardless of precipitation type, a solid precip. producer
for this time of year remains in the offing. The antecedent air
mass will be marginally but sufficiently cold for wet snow,
particularly for locales near and north of I-80. The exact track
and strength of the low will determine how much of the area will
see accumulating snow, with overall probabilities higher the farther
north you go per most recent model and ensemble member and mean
progs. The high PWATs and mixing ratios, plus the aforementioned
strong large scale forcing are a concern for moderate to heavy
snow rates.

In summary, the threat for impactful winter weather in the form
of heavy/wet accumulating snow for at least portions of the area
has continued to tick upward, again with important caveats of this
being about 5 days out. Stay tuned to later forecast updates for
the Wednesday night-Thursday period. A colder (though not
exceptionally cold for late January) and active pattern looks to
continue heading into late January per solid ensemble consistency
out in the medium-long range.

Castro

&&

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

Some patches of MVFR CIGS linger west of Chicago terminals and
east of RFD. Forecast model guidance generally does not suggest
this stratus will expand tonight, however recent ACARS soundings
from ORD and MDW both show a saturated layer at the top of the
boundary layer. As diurnal cooling of the boundary layer commences
this evening, it is quite plausible that there will be an
expansion and redevelopment of MVFR CIGS. Previous TAFS included
the redevelopment of MVFR stratus, so opted to maintain that in
the forecast and monitor trends this evening. If MVFR CIGS
redevelop, anticipate they will scatter out Sunday morning with
VFR conditions expected.

Otherwise, look for light south winds tonight to increase Sunday
morning and likely attain some gustiness later Sunday morning into
the afternoon.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...9 AM Sunday to 6
     PM Monday.

     Small Craft Advisory...LMZ743-LMZ744-LMZ745...2 PM Sunday to 6
     PM Monday.

&&

$$

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