Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/30/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 1015 PM EDT Sun Oct 29 2023

.Forecast Update...
Issued at 1014 PM EDT Sun Oct 29 2023

* Widespread rainfall continuing into the overnight hours
* Coldest air of the season so far arrives Monday

The forecast for tonight remains on track as rain has overspread the
entire region from the southwest. Latest IND ACARS sounding shows
deep saturation from the surface to around 300mb with strong
southwest flow in the mid and upper levels continuing to advect in
ample moisture. The most widespread rainfall should persist over the
next 3 to 5 hours as the region remains in an area of strong lift
within the right entrance region of a 150+ kt jet streak. Short term
guidance shows the best forcing and moisture beginning to push off
to the south and east later tonight and towards sunrise. The
heaviest rainfall is expected to gradually taper off from NW to SE
through the morning hours with a few hours of sprinkles/drizzle
possible on the backside of the rain through mid to late morning
before much colder and drier air filters in.

Observations and IND ACARS sounding already shows a colder airmass
pushing into the region in the lowest 1 km agl with a strong warm
nose just above 850mb. Surface temperatures have already fallen into
the mid to upper 40s at this hour and will continue to drop into the
30s by sunrise as much colder advects in at the surface and aloft.
With such a strong push of cold air, it is possible precipitation
may end with a few flurries in portions of Northwest and North
Central Indiana, but confidence in this occurring widespread is low,
so have kept it out of the official forecast. Typically in these
scenarios, the dendritic growth zone dries out too fast for any
significant wintry precipitation to occur. No worries for wintry
precipitation... for Monday at least! (See the Long Term Discussion
for more information on snow chances later this week). The rest of
the day Monday will feature the coldest temperatures of the season
so far with afternoon temperatures only in the 40s and breezy
conditions resulting in wind chills remaining in the 30s!

&&

.Short Term...(This Evening through Monday)
Issued at 246 PM EDT Sun Oct 29 2023

* More rain through tonight
* Cooler and drier Monday

Rest of This Afternoon into Early Evening...

An initial round of upper energy is bringing some rain to parts of
central Indiana early this afternoon. Will have some mainly chance
PoPs to cover this. Later this afternoon, more potent upper energy
along with a surface wave riding a cold front to the south will
provide enough lift for widespread rain to move in from the
southwest. Will ramp up PoPs then.

Tonight...

The aforementioned forcing mechanisms will continue to produce rain
across the forecast area. Will go high PoPs all areas. Although
there will be some frontogenetical forcing added to the mix in a
baroclinic zone over the area, highest moisture content remains to
the south. Thus, not expecting heavy rain locally, but an additional
three quarter of an inch is possible south.

Rain will diminish from northwest to southeast overnight as forcing
exits.

Colder air will work in behind the surface wave, allowing
temperatures to dip into the 30s to lower 40s. The precipitation
should be gone by the time temperatures get cold enough for snow in
the northwest.

Monday...

Surface high pressure will build in from the northwest. This will
eventually break up the clouds, allowing some sunshine by afternoon.
Before it does, some lingering rain may still be in the southeast
part of the forecast area Monday morning. Will keep some low PoPs
there early.

Even with the sunshine, temperatures will only peak in the 40s.

&&

.Long Term...(Monday Night through Sunday)
Issued at 246 PM EDT Sun Oct 29 2023

The main focus for the extended is the coldest air of the season so
far expanding into the Ohio Valley through midweek with a growing
potential for the first snowflakes of the season for some as well
Tuesday afternoon and evening. Dry and cool conditions that set up
for most of the rest of the extended.

Monday Night through Tuesday Night...

A progressively deepening and meridional upper level trough will
pivot across the eastern half of the country for the first half of
the week as the frontal boundary currently aiding in the rain
expected tonight and early Monday shifts away to the southeast. The
upper trough is the strongest we have seen to this point in the
autumn...and it will get an assist on Tuesday as another piece of
energy carves out an even sharper trough with a closed low to boot.

The primary impact from this feature will be the much colder
temperatures as initially on Monday night and Tuesday morning...the
region will be under the influence of a broad high pressure ridge.
With clear skies...high confidence exists in the first hard freeze
of the season for central Indiana late Monday night and Tuesday
morning as lows should plummet into the mid 20s in spots. Will
continue with the current Freeze Watch headlines for Monday night
after collaboration with surrounding WFOs...but almost certainly
expect an upgrade to Freeze Warning on the midnight shift tonight.
Temperatures on Tuesday will hold only in the low to mid 40s with a
stiff wind from the W/SW then shifting to northwest with the passage
of a cold front in the afternoon.

That cold front is associated with the closed upper low diving into
the trough discussed above. Besides bringing a reinforcing shot of
colder air late Tuesday...it will also likely generate scattered
light snow showers and flurries as well despite limited low level
moisture. Model soundings continue to advertise weak instability
within the boundary layer and steepening lapse rates that should be
able to overcome the limited moisture available. THe focus for
precipitation will largely be across the northeast half of the
forecast area during the afternoon and evening but could see
flurries further to the southwest as well. May see a few rain drops
mix in initially and perhaps even some graupel in heavier showers...
but snow will become the predominant precip type. Potential is there
for localized very light accums but no issues are anticipated with
the ground well above freezing. The biggest impact in all reality
will be to aid with the cold temperatures and wind to make it feel
that much colder and miserable for the trick or treaters.

Wednesday through Sunday...

Any lingering flurries will diminish late Tuesday night as strong
high pressure reestablishes quickly by Wednesday. The high will
slowly track from the southern Plains into the Mid Atlantic by the
end of the work week...maintaining dry conditions and mainly clear
skies while enabling temperatures to slowly warm. After another day
in the 40s Wednesday...expect highs to return to near normal levels
at 55 to 60 by Friday and Saturday courtesy of southwest winds. A
weak wave aloft will move into the Great Lakes Saturday night and
Sunday and could bring a few light showers to the region for the
second half of the weekend.

Extended model guidance continues to waffle in the 7-10 day period
on the potential for a strong surface low developing over the
central Plains and shifting into the Great Lakes early next week.
This will be something to monitor over the coming several days as
this sort of a setup would be supportive of a more widespread threat
of precipitation and perhaps convection for the Ohio Valley

&&

.Aviation...(00Z TAF Issuance)
Issued at 727 PM EDT Sun Oct 29 2023

Impacts:

* Widespread IFR conditions to persist through the overnight hours
* Improving ceilings and vis towards sunrise Monday
* Gusty northwest winds to 20 kts beginning after 09z

Discussion:

Latest satellite and radar imagery shows widespread rainfall and low
clouds across all of Central Indiana this evening. Observations
indicate ceilings bouncing between 600ft and 1200ft at times with
vis from 2 to 6sm. While conditions will bounce from MVFR to IFR at
times , expect mainly IFR ceilings and vis through at least around
09z when rainfall begins to taper off. Expect gradually improving
ceilings and vis from NW to SE around sunrise through mid morning
with all locations having VFR conditions by 15z.

Stronger northwest winds develop behind the front and continue
through Monday afternoon. Light northwest winds increase this
evening gradually increasing through the night becoming sustained
around 10-15 kts. Gusts upwards of 20 kts expected at times.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from Monday evening through Tuesday morning for
INZ021-028>031-035>049-051>057-060>065-067>072.

&&

$$

Update...CM
Short Term...50
Long Term...Ryan
Aviation...CM