Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/24/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 1008 PM EST Mon Jan 23 2023

.Forecast Update...
Issued at 1002 PM EST Mon Jan 23 2023

No changes to the short term forecast for this evening`s update.

Current surface analysis shows high pressure centered over Northern
Alabama with a diffuse frontal boundary pushing into NW Indiana. This
front has little to no forcing with it as the parent low is well to
the north in Quebec. Skies have cleared out across the region
earlier this evening; however expect thin, high clouds to stream in
overnight as the weak frontal boundary passes by to the north.

Forecast remains on track for the expected winter storm beginning
early Wednesday morning. Next update on that will be around 4 AM
with the morning forecast package.

&&

.Short Term...(This evening through Tuesday)
Issued at 228 PM EST Mon Jan 23 2023

- Mostly Cloudy and Cold Tonight
- More Clouds but warmer on Tuesday

Surface analysis early this afternoon shows cold high pressure in
place over Arkansas, Louisiana/OK and E TX.  The strong high was
providing cold northwest surface flow across the western Great Lakes
and into Indiana. GOES16 shows extensive cloudiness across Indiana
within this flow extending well northwest through the upper midwest.
Aloft, water vapor showed a trough of low pressure stretching from
New England to West Virginia, exiting east, while a ridging aloft
was found across the Great Lakes. Again this was resulting in
northerly flow aloft over Indiana on the lee side of the ridge axis.
Of note, water vapor shows a deep upper low over the American
southwest, which will become quite important in the Ohio Valley by
mid week, providing our mid week storm.

Tonight...

Upper ridging over the Great Lakes is expected to flatten and become
more zonal tonight as the deep upper low begins to move east across
the American southwest. Little in the way of forcing dynamics is
seen and the mid and upper levels remain dry with subsidence.
Surface high pressure looks to continue to progress southwest of
Indiana, keeping weak westerly lower level flow in place.

Cloud cover remains extensive across the region, including Central
Indiana. The moisture with these low stratus clouds remain trapped
within the lower levels as ACARS soundings across the area continue
to show a steep inversion above the saturation. GOES16 is finally
showing some erosion of the cloud deck from the southwest, over
Central IL, as well as a few holes over southern Central Indiana.
With only a few more hours of heating and mixing left in the day,
confidence for full clearing is low and some clouds are expected to
linger overnight.  Thus will trend toward a mostly cloudy sky along
with lows in the upper 20s.

Tuesday...

Upper ridging is suggested to remain across Central Indiana and the
Ohio Valley on Tuesday as the deep low moves through Texas. This
sets up the development of SW flow aloft as the day progresses.
Models suggest some upper forcing being ejected into this SW flow
pushing toward the Ohio Valley, but with a lack of moisture across
the area, this will only result in the invasion of high clouds as
the system from the southwest approaches. Forecast soundings on
Tuesday on dry low and mid levels with a top down saturation
developing as the day progresses. Thus a few breaks of sunshine will
be possible mid day as the stratus deck may dissolve, but high
clouds are expected to quickly move in on Tuesday afternoon in
advance of the arriving storm system. Given the ongoing warm air
advection in advance of the system, will trend highs to around 40.

&&

.Long Term...(Tuesday night through Monday)
Issued at 228 PM EST Mon Jan 23 2023

*************
Highlights:
*************

WINTER STORM WATCH across most of central Indiana from Late Tuesday
Night Through Wednesday Afternoon

- Heavy snow, 3-7 inches expected.
- Highest snow amounts along north and west of Indianapolis
- Warm ground temperatures and rain mixing in will limit the overall
snow depth by the end of the event

*****************
Synoptic Pattern:
*****************

Confidence continues to increase in a deepening low pressure system
tracking from northern Texas into the Midwest with that will
continue to go cyclogenesis as it tracks to the northeast.  Morning
ensemble runs have a tight cluster for the low that passes along the
Ohio River during the daytime hours on Wednesday. The trend has been
a slightly further south track which may move the deformation axis
of higher snow a bit further southeast. The exact strength of the
low remains somewhat uncertain with a wider model spread on the
strength.

The biggest uncertainty with this system will be how the warm air
ahead of the system is eroded and where the rain/snow line sets up.
Model surface temperatures are right around the 32 degree point with
a steady state temperature spread from late Tuesday night through
Wednesday.  Temperatures aloft will be subfreezing with ice
nucleation present and keep precipitation type just rain and snow.

Much of the snow Tuesday night into early Wednesday will form
outside of the dendritic growth layer which will cut snow ratios
before colder air arrives Wednesday morning.  Will gradually
increase the snow ratios from around 8:1 during the overnight hours
to 10:1 by mid morning on Wednesday.

The precipitation will likely set up in two different waves.  The
initial wave will be focused south and east of Indianapolis with the
main nose of warmer air.  Snow will be the more likely precipitation
type with some rain mixed in, especially further southeast but with
low snow ratios.  The deformation band with slightly higher snow
ratios will then settle in after daybreak with the focus for higher
snow amounts across the northwestern counties.

***********
Impacts:
***********

The period of most intense impacts currently looks to be the morning
hours Wednesday as colder air arrives in the mid levels and brings
the dendritic growth zone into play. Snow will be falling on roads
that will be generally in the low to mid 30 degree range which will
allow for some melting as it falls and limit the overall snow depth
even if 6-8 inches of snow falls.  Intense rates are likely at times
Wednesday which will help to overcome the warmer temperatures, but
think that the axis of heavier snow will be in the 4-6 inch range
when it is all said and done with 3-5 inches in the areas outside of
the axis.  Areas further to the south where the snow will be earlier
in the morning and mixed with rain are likely to see closer to 1-3
inches

***********
Conclusion:
***********

A deepening low pressure system is expected to progress through the
Ohio Valley Tuesday night through Wednesday. This will provide
widespread precipitation over central Indiana.  Rain is likely to
mix in with snow south of Indianapolis with better confidence for
snow to the north. The highest snow accumulations currently look to
be along the I-69 corridor north of Indianapolis, but relatively
warm temperatures and the rain mix will limit the final snow depth
even with impressive accumulations.  Snow amounts of 4-7 inches are
possible in the heaviest axis with 3-5 inches outside of that area.
Areas south of Indianapolis may only see 1-3 inches.

Regarding headlines; plan on maintaining the Winter Storm Watch with
no major changes for now.  When confidence increases in the
rain/snow line and axis of higher snow, Winter Storm
Warnings/Advisories will be issued accordingly.

Thursday through Monday.

Snow will likely continue Thursday into Friday as the system exits
and backend forcing squeezes out any remaining moisture.  Amounts up
to an inch are possible through the day Thursday. Surface flow will
return to the south Friday into the weekend which will lead to
melting of the mid week snow.

The next system then looks to arrive Saturday night into Sunday
with another potential shot for rain/snow across the area.  This
system has a more northerly origin, but looks to tap into some Gulf
moisture as it arrives.  There remains a large amount of uncertainty
as to precipitation type and amounts, but confidence is higher than
it will not be as impactful as the midweek system.

&&

.Aviation...(00Z TAF Issuance)
Issued at 646 PM EST Mon Jan 23 2023

Impacts:

* Mainly VFR Ceilings are expected this TAF period.

* SW winds under 10 kts through the period

Discussion:

Current satellite imagery shows clearing skies across much of
Central Indiana this evening. BKN ceilings around 2,000 ft are
quickly clearing from west to east with all TAF sites expected to be
mainly clear by 03z. With high pressure remaining south of the
region, expect winds to remain under 10 kts and out of the southwest
through tomorrow. Winds will eventually go calm and become
southeasterly tomorrow evening ahead of the next approaching weather
system. For now, expect VFR conditions to persist over the next 24
hours.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from late Tuesday night through Wednesday
afternoon for INZ021-028>031-035>049-051>057-060>063-067.

&&

$$

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