Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/14/24

Area Forecast Discussion

National Weather Service Indianapolis IN

 944 PM EST Tue Feb 13 2024

.Key Messages...

- A band or two of snow over central Indiana could lead to
  accumulating snow fall

- Rain chances Wednesday night into Thursday morning

- Breezy conditions on Thursday with gusts of 30 to 40 mph

- Potential for light snow Friday night with cooler temps for
  the weekend

&&

.Mesoscale Update...
Issued at 944 PM EST Tue Feb 13 2024

Mid level clouds remain prevalent across much of the forecast area
this evening...extending northwest to southeast. This has kept temps
from falling as quickly as they would with still many locations in
the lower 40s as of 02Z. Where they has been less cloud cover though
across far northeast portions of central Indiana...temperatures were
already down in the lower and middle 30s.

Despite the variation in temperatures...the forecast remains on
track for overnight with the chance for a band or two of light snow
developing within a zone of frontogenetical forcing associated with
a subtle wave aloft. The one main adjustment though is a southward
shift in the area where the band(s) are most likely to align based
on observational trends to our W/NW over the last few hours.

An increase in flow at the 850mb level from the W/SW is beginning to
interact with the zone of frontogenesis across western Illinois and
eastern Iowa and have seen some enhancement to cloud tops in that
area since 00Z. Radar returns have also organized over western
Illinois as well...although not seeing any obs or reports of precip
reaching the ground yet. A glance back at ACARS soundings from KSTL
and KPIA show a lack of saturation through the dendritic growth zone
which supports the idea that the returns are not reaching the ground
at this point.

As the night progresses however...increased saturation will occur as
the low level jet strengthens and interacts with the axis of
frontogenesis. With the wet bulb temps currently in the mid 30s...as
soon as dynamic cooling commences should see that drop back to just
below freezing. So once precip starts reaching the ground...it will
be in the form of snow. Expect to see chances for snow increase over
the Wabash Valley by 06Z then expand southeast quickly with snow
shifting east near daybreak.

There still remains uncertainty on how much banding occurs and how
well the best forcing and moisture align...but there are hints that
the dendritic growth zone may become fully saturated for an hour or
two. The axis where the best chance for any banding is increasingly
likely to set up a bit further south than originally thought closer
to the I-74 corridor. This is the likely zone where the best chance
to see light accums of a few tenths will exist but the uncertainty
in the alignment between the forcing and moisture means banding and
rates are likely to be non-uniform. Slick spots may develop wherever
snow can persist as temps fall back into the upper 20s by daybreak.

Zone and grid updates out.

&&

.Short Term...(This evening through Wednesday)
Issued at 254 PM EST Tue Feb 13 2024

Rest of Today...

As of 19Z, the PBL mixing depth has begun to tap into higher winds
aloft, leading to modest gusts of 20-25MPH along and north of I-70.
This will subside around dusk as a diurnal inversion develops.

Temperatures are running slightly above forecasted values, likely
due to the abnormally dry surface layer leading to more efficient
diurnal warming. A mid level cloud deck has developed over IL, and
is progressing into IN. This should stop any additional warming with
most locations topping out in the upper 40s to low 50s.

Tonight...

Latest high resolution models have picked up on a region of
marginal, but enhanced 800-700mb forcing in the entrance region of
the LLJ. This will lead to moistening with regions of ascent and
eventually the development of snow bands. This will likely occur
between 06-12Z tonight corresponding to typical diurnal LLJ
intensification. Overall, antecedent dry air and a shallow layer of
ascent should keep general QPF values low, but in areas of more
intense banding, higher snowfall is possible.

A few uncertainties still remain for tonight. First is the location
of ascent. Model soundings vary on the depth of saturation, of which
could play a significant role is amount of snow. A shallower depth
of saturation could misalign with the greatest region of ascent
leading to minimal QPF, whereas better alignment could lead to more
prolonged moderate snow rates. Second, is where the banding will be
located. Current expectation is anywhere between Martinsville and
Kokomo. Steep gradients on the edge of bands could lead to many
locations receiving no snowfall. Lastly, with temperatures well
above freezing, ground/road temps may be delayed to reach freezing
leading to snow initially melting and lowering snow amounts.

Overall, the expectation is for a few snow bands to develop over
central Indiana. Locations within banding should receive around 0.5"
with isolated areas up to 1" of snow. With that said, most areas
will receive less than 0.2" of snow.

Tomorrow...

After the passage of the LLJ, flow over central Indiana will begin
to veer towards S/SW. This will create light and variable winds over
the area. The airmass for tomorrow will generally be similar with
temperatures reaching the upper 40s to low 50s across the region.
The only exception would be if any locations received higher end
snowfall, and initial evaporative cooling could lead to slightly
lower afternoon highs.

&&

.Long Term...(Wednesday night through Tuesday)
Issued at 254 PM EST Tue Feb 13 2024

Wednesday night into Thursday...

An upper level trough will bring some lift to the area. A surface
low will move to the northwest of central Indiana, keeping the area
in the warm sector. With no good flow from the Gulf, moisture looks
to be confined to stronger part of the system to the north of the
area.

Will go with mainly chance PoPs across the area, mainly Thursday
morning when the best forcing moves through. Precipitation type will
be rain with the area in the warm sector.

Stronger winds will mix down with this system, producing gusts in
the 30 to 40 mph range, mainly Thursday morning.

Friday and Friday night...

A stronger upper trough will move in during this period. This trough
will create a surface low that will move across the southern USA.
Models differ though on how far north the surface low will get, with
the GFS and it ensembles farther north. The path of the low will
have an impact on precipitation types and amounts.

Given the uncertainties, will keep PoPs no higher than the chance
category. Will also keep a rain/snow mixture as precipitation type
until details become clearer.

If everything were to come together, there is some potential for
light accumulating snow in the forecast area. Will continue to
monitor.

Saturday...

A shot of colder air will follow behind Friday`s system. High
pressure will keep Saturday dry but cold. Lows will be around 20,
with highs in the upper 20s to lower 30s. Winds will keep wind
chills in the teens for much of the day.

Sunday and beyond...

The coldest air will quickly retreat, allowing temperatures to
return into the upper 30s into the 40s for Sunday`s highs. As the
upper flow generally flattens out into next week, temperatures will
continue to moderate, with highs around 50 most areas by Tuesday.

An upper wave quickly moving through could bring some light
precipitation around Monday night, but details in the timing and
strength of the wave remain uncertain this far out. Will just have
some slight chance PoPs Monday night with low confidence.

&&

.Aviation...(00Z TAF Issuance)
Issued at 533 PM EST Tue Feb 13 2024

Impacts:

- Winds diminishing to light and variable by late evening
- Short period of light snow may possibly impact KIND and KLAF
during the predawn hours with brief restrictions
- Clearing Wednesday morning

Discussion: Axis of mid level clouds had overspread the terminals
late this afternoon and will likely linger through the evening and
early overnight. W/NW winds at 10-15kts currently will fall back to
light and variable later this evening.

Overnight...focus shifts to a weak surface wave developing along a
boundary and tracking from northern Missouri E/SE across the region.
The development of a low level jet will coincide with moistening
through the boundary layer and localized ascent supporting the
development of one or two snow bands in a NW to SE orientation.
While the specifics remain unsettled...there is potential for the
bands to drift across KIND and KLAF between 07Z and 11Z with the
possibility for very brief MVFR restrictions should the rates
intensify. At this point...appear both KBMG and KHUF will remain
south of any snow bands.

High pressure returns quickly Wednesday morning with skies clearing.
Expect a light E/SE flow through the day with just scattered clouds
from mid morning on.

&&

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

&&

$$

Mesoscale...Ryan
Short Term...Updike
Long Term...50
Aviation...Ryan