Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/26/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 1042 PM EST Wed Jan 25 2023

.Forecast Update...
Issued at 1042 PM EST Wed Jan 25 2023

Snow showers are expected to continue over the next 24 hours across
Central Indiana as cyclonic flow remains in place under a broad
upper trough with multiple vort maxes rotating through the region.
Current Nighttime Microphysics satellite imagery depicts the
incoming wave well across Iowa and Southern Minnesota with surface
observations reporting snow and reduced visibilities. ACARS
soundings from up there show deep saturation from the surface up to
around 700mb, including the dendritic growth zone, indicating
sufficient moisture for snow showers. Even the IND ACARS sounding
still show deep saturation through the DGZ this evening, so P-type
is no concern through tomorrow as RAP forecast soundings and cross
sections keep deep saturation through the region. Forcing comes in
the way of upper level vort maxes swinging through the region and
areas of low level frontogenetical forcing allowing for scattered to
numerous snow shower development. Best chance for snow showers
across the region appears to be earlier in the day from the early
morning hours through early afternoon, tapering off during the
evening. Forcing and saturation within the DGZ wane later in the
evening tomorrow indicating snow showers may taper off to light
flurries and areas of drizzle before precipitation fully shuts off.
So would not be surprised to see slick spots tomorrow night as
temperatures plummet into the lower 20s.

As far as accumulations, snow amounts will very across short
distances due to the showery nature of the precipitation. Heaviest
snow showers will likely be along and north of I-70 where upwards of
an inch to possibly 2 inches could fall in some spots. Lighter
amounts expected across the southern half of Indiana. Because these
are showers, some areas could be missed entirely with just flurries
and cloudy skies tomorrow... hence the wording "scattered" snow
showers.

Low and mid level lapse rates steepen somewhat as cold air advection
continues to filter in aloft tomorrow. This combined with winds
around 20-30 kts just above the surface may lead to a few stronger
gusts to 25-30 kts mixing down to the surface, especially in
stronger snow showers. This could reduce visibility at times.

&&

.Short Term...(This evening through Thursday)
Issued at 309 PM EST Wed Jan 25 2023

* Snow rapidly tapering off across north central Indiana.

* Additional flurries possible this evening, with snow showers
  possible later tonight into Thursday. Light accumulations possible
  in some areas.

As the primary low pressure system that brought wet snowfall to the
area today rapidly departs to the northeast, focus for the short
term will shift to potential for additional light snow showers at
times, primarily late tonight through Thursday.

With the snow rapidly coming to an end, and significant melting
leading to primarily wet roads, have cancelled the remaining
headlines across the northern portion of the area.

Some modest midlevel drying noted on forecast soundings is causing
some changeover from light snow to drizzle on the southern end of
the departing snow shield. Temperatures should remain above freezing
across the majority of the area into this evening and limit any
impact due to this.

The initial weakening shortwave accompanying today`s snowfall will
be followed by weak subsidence during the evening hours, which will
very likely prevent any additional measurable precipitation during
the early part of the night, with flurries or drizzle remaining
possible. Late tonight into Thursday, additional subtle upper level
disturbances in the broader cyclonic flow will impinge upon the
region and produce potential for additional snow showers.
Additionally, low level flow configuration may allow some lake
enhancement to this activity across our north/northeastern forecast
area, and will carry the highest pops in these areas.

Very light QPF is expected, likely around 0.05" or less in most
areas, but with the onset of cold advection, snow ratios will
increase well above the 3-5 to 1 observed today to near
climatological average of around 11 or 12 to 1. This will result in
amounts of around a half inch with isolated 1 inch amounts. This
will likely not be uniform as activity will be a bit more showery in
nature.

Despite the onset of cold advection, widespread cloud cover will
significantly limit diurnal range through Thursday, with lows
tonight likely remaining no cooler than the upper 20s to low 30s and
highs tomorrow barely budging into the low 30s.

&&

.Long Term...(Thursday night through Wednesday)
Issued at 309 PM EST Wed Jan 25 2023

The long term period will see multiple chances for precipitation.
For Thursday night through Sunday, there is not a lot of
variation between models which show a positively tilted trough
stretching from north central Canada towards the Rockies. This
trough will persist into the middle of next week as well with some
forward progression, but there is less agreement amongst models
for the end of the period. Multiple short waves will ride along
the leading edge of the trough which is where the numerous precip
chances will arrive from.

The first shortwave in the long term will come Friday afternoon as
the associated surface low tracks just north of the Great Lakes.
Best chances for precipitation will be mainly across the northern
half of the forecast area and will likely be light. Temperatures
will be flirting with the freezing line as afternoon highs are
expected to range from the mid 30s to near 40 so expect a mix of
rain and snow for the ptype. Up to half an inch of snow accumulation
would be possible but could see it not sticking around for very long
given the temperatures. At the low to mid levels, a broad jet will
set up aloft which should mix down some breezy winds to the surface.
Could see wind gusts up to around 35 mph Friday.

After a shot of drier air, another short wave, with a better
moisture content than the first wave, will bring PoPs and light
precipitation from late in the day Saturday through the day Sunday.
Again a mixture of precip type will be likely with this system but
in this case will be due to warmer temperatures of upper 30s to low
40s to start out with late Saturday followed by colder air slowly
pushing southeast through the night and into the day Sunday. The
transition to snow could begin in the far NW as early as prior to
daybreak. Will need to watch for freezing precipitation that could
mix in during the day Sunday, but confidence is not high enough for
a day 5 forecast to include in the grids at this time.

A surface high will then move through Monday providing another break
in PoPs for the start of the work week but we could see another
chance of precipitation for the end of the period. There is quite a
bit of variability in the solutions so many details are yet to be
seen but could again see a mix of precip type with this late period
system as well.

Temperatures through the period will start out slightly above normal
for the first half of the period and then become slightly below
normal for the latter half.

&&

.Aviation...(00Z TAF Issuance)
Issued at 635 PM EST Wed Jan 25 2023

Impacts:

* IFR ceilings likely through most of the period

* Scattered light snow showers will develop late tonight and
  continue on Thursday

Discussion:

Last of the light returns on the back side of this system are moving
out as we speak early this evening. Generally...this has fallen as
pockets of drizzle over the last few hours. Expect dry weather for
much of the evening into the early overnight as weak ridging aloft
shifts across the area. With deep moisture lingering throughout the
low levels...IFR ceilings will persist through the evening with
W/NW winds at 10-15kt.

As an upper level disturbance pivots across the region Thursday
morning...expect scattered snow showers to expand during the predawn
hours and continue for much of the day Thursday. Visibilities will
be variable as snow showers pass the terminals but IFR stratus will
persist all day before lifting to MVFR late day. Winds will back
through the day to W/SW and may sporadically gust at times to near
20kts.


&&

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

$$

Update...CM
Short Term...Nield
Long Term...KH
Aviation...Ryan