288
FXUS63 KIND 050352
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1052 PM EST Wed Dec 4 2024

.KEY MESSAGES...

- Windy through tonight, particularly this evening with passage of
  an Arctic front, which will produce a flash freeze

- Snow showers expected, with localized snow squalls possible; minor
  accumulations possible

- Subzero wind chills as low as -10 late tonight into early Thursday
  morning

&&

.MESOSCALE UPDATE...
Issued at 1049 PM EST Wed Dec 4 2024

Observations and DOT cameras over the past couple hours have
indicated the rain-to-snow showers stretched across the I-69
corridor NE of Indianapolis, and south of I-70 to the WSW...
become intense enough in areas to changeover to a burst of wet
snow...with the larger-scale 32F isotherm generally accompanying
the shower`s back edge where precipitation tapers to -SN/flurries.
Snow will continue accumulating under steadier/heavier, yet
generally short-lived snow.

Winds are the overnight`s other concern following marginally-severe
gusts observed at both Danville and Lafayette when the boundary was
passing these locations just before 900 PM EST...and more recently
54KT at KIND...so Wind Advisory has been expanded farther south and
extended to 700 AM Thursday.

&&

.SHORT TERM (This evening through Thursday)...
Issued at 240 PM EST Wed Dec 4 2024

A busy night is expected across central Indiana with the imminent
passage of an Arctic front, which will produce rapidly plummeting
temperatures/a flash freeze, strong gusty winds as high as 40-50
MPH, snow showers and potential snow squalls, and subzero wind
chills as low as -10 by late tonight into daybreak Thursday.

Some virga associated with a weak prefrontal trough is currently
noted on area radar mosaic passing through the northern half of the
area, which will help to erode some lingering dry low level air. The
primary Arctic front is further northwest at this time, stretching
from the UP of Michigan southwest into eastern Iowa and northwest
Missouri - this front will rapidly sweep through the area later this
evening into tonight, with potential for scattered to numerous
showers, beginning as rain ahead of the boundary and transitioning
rapidly to snow as very potent cold air advection ramps up first in
the wake of the prefrontal trough and then especially as the Arctic
front itself rapidly pushes through the area.

While not a classic snow squall pattern, due at least in part to the
later diurnal timing, the rapidly falling temperatures, strong,
gusty winds, and scattered snow showers, which may become briefly
intense, will certainly have the potential to produce localized
impacts on roadways - variable visibility, localized slick spots,
and impacts to drivers from gusty winds, particularly those in high
profile vehicles.

Minor accumulations will certainly be possible, but may be quite
variable given the showery nature of the precipitation. Anywhere
from a light dusting up to an inch will be possible.

Wind advisory will be left in place in the areas it is currently
valid for - BUFKIT profiles suggest frequent gusts around 40 MPH
tonight with occasional gusts in the 40-50 MPH range. Even areas
outside the advisory will likely see a few gusts to around 40 MPH.
Conditions will remain breezy but winds will weaken late tonight as
the surface pressure gradient relaxes somewhat - but gusty winds
will remain an issue into Thursday, though more in the 20-30 MPH
range.

Again, temperatures will drop rapidly overnight, from the mid 30s to
mid 40s by 00Z to the low to mid teens by daybreak Thursday. This
will produce subzero wind chill values as low as -10F late tonight
into daybreak Thursday - the coldest conditions experienced thus far
this season.

Thursday will be quite a bit quieter, if quite cool - highs are
likely to struggle to get out of the low to mid 20s, and continued
breezy conditions will keep wind chills largely in the teens
throughout the day. A few lake-effect flurries may sneak into far
northern/northeastern portions of the area, but should be of little
to no impact.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 240 PM EST Wed Dec 4 2024

Thursday Night Through Monday.

Another very cold night is expected for Thursday night with
temperatures in the low teens, but winds will be closer to calm
which will keep wind chills above zero.  Upper level flow will
remain northwesterly going into the weekend but surface ridging over
the Southern Appalachians will help to pivot the surface flow to a
more southerly direction which will allow for gradual warming Friday
into Saturday with highs approaching 50 by Sunday.

Focus then shifts to a low pressure system exiting the southern Four
Corners Region and tracking rain chances as it moves to the
northeast. There isn`t very strong surface cyclogenesis with this
system, but there will be a rapidly strengthening LLJ that will
advect large amounts of Gulf Moisture and bring PWATs well into the
90th-95th percentile of climatology. Ensembles have good agreement
in rain amounts in excess of a half inch with decent probabilities
of greater than an inch of rain.  Will have to track the potential
for thunderstorms and potentially a strong to severe storm, but
those chances look much higher down into the southern Ohio Valley
which lines up with the low CSU probabilities for severe weather
that highlights Tennessee into the Gulf states.

There then is a potential for a secondary to to develop on the
backend which could keep precipitation around into Monday, but
confidence is low as ensembles show that solution remains to be the
outlier vs most likely outcome.

Tuesday Through Wednesday.

Cooler weather then is expected Tuesday into Wednesday but overall
confidence in the forecast is low beyond that.  The 06Z showed an
impactful winter system Wednesday into Thursday with a TROWAL axis
of heavy across the Wabash River Valley, but there is very little
support in this within the GFS ensembles or other deterministic
models outside of the Canadian which keeps the impacts isolated to
the East Coast.  Will continue to monitor trends, but at this point
there isn`t even enough confidence for anything more than Slight
Chance POPs.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 633 PM EST Wed Dec 4 2024

Impacts:

- Strong wind gusts throughout the period, approaching 40-45KT at
  times depending upon the site

- Snow showers advancing from NW to SE along polar frontal
  zone...within 01Z-04Z this evening...with possible snow squalls,
  especially at KLAF/KIND

- WSW winds veering quickly to northwest with frontal
  passage...when gusts may briefly exceed 40KT this evening

Discussion:

Potent polar cold front will pass the terminals this evening,
quickly veering robust WSW winds to gusty northwesterly...which will
be sustained at 18-25KT, and gust to 36-40KT...before slowly
diminishing from pre-dawn to midday Thursday.  Gusts may briefly
exceed 40KT following the boundary.

Numerous snow showers are expected with possibly a few snow squalls
this evening...which may actually start as a brief period of rain as
temperatures fall quickly below freezing.  At least brief MVFR/worse
ceilings/visibilities are on the table.

High confidence in strong NW winds impacting KIND during the
critical evening push period...with chances for lingering snow
showers also early in this period.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 AM EST Thursday for INZ021-028>031-035>049-
051>057.

Wind Advisory from 4 AM to 7 AM EST Thursday for INZ060>065-
067>072.

&&

$$

MESOSCALE...AGM
SHORT TERM...Nield
LONG TERM...White
AVIATION...AGM