399
FXUS63 KIND 220323
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1023 PM EST Tue Jan 21 2025

.KEY MESSAGES...

- Cold Weather Advisory in effect through Wednesday morning

- Frequent wind chills of 10 below with brief periods as low as 20
  below expected through Wednesday

- Scattered flurries with a few snow showers this morning into the
  early afternoon hours.

- Potential for more flurries or light snow showers Thursday into
  Thursday night

- Another shot of cooler air will move in around Friday, then
  temperatures will return to closer to average

&&

.FORECAST UPDATE...
Issued at 1023 PM EST Tue Jan 21 2025

An arctic air continues to plague much of the United States
resulting in an extended period of temperatures near or below zero
and wind chill values as low as -20F locally! Surface high pressure
is currently centered over the lower Ohio Valley and will slowly
push eastward into tomorrow. With the center of the high close to
the region, optimal conditions for radiational cooling have resulted
in temperatures already in the 0 to -6 degree range so early in the
evening. Temperatures in wind sheltered areas and lower lying
locations/valleys will make a run for -10F during the overnight
hours tonight. Surface high pressure slides eastward by the morning
with winds becoming southerly by sunrise, potentially resulting in
temperatures bottoming out within the 3am-6am timeframe and already
on the rise by the time the sun comes up. A tightening southerly
pressure gradient and increasing low level jet should lead to
southerly winds of 10-15 mph with gusts 20-25 mph for much of the
day tomorrow. Breezy conditions should help keep the shallow
boundary layer well mixed and help temperatures rise at least into
the teens and lower 20s. While temperatures slightly moderate
tomorrow, breezy conditions may keep wind chill values in the single
digits.

&&

.SHORT TERM (This Evening through Wednesday)...
Issued at 214 PM EST Tue Jan 21 2025

Getting filtered sunshine between stratocu and scattered flurries
this afternoon but this is doing nothing to help the temperatures.
Temps have been largely steady state since earlier this morning once
the front passed through. With strong cold advection...much of the
area is in the 0 to 5 degree range at 19Z. A brisk westerly wind is
adding to the misery with subzero wind chills ongoing and some
locations as low as -20.

The main focus for the short term is the start of the process that
will eventually pull the region out of the brutally cold air mass
that has enveloped much of the country east of the Rockies. It will
be slow but the transition to warm advection as high pressure passes
by overnight will jumpstart the temp rises which will culminate with
readings finally rising above freezing by Saturday. Winds will
become more of a factor Wednesday as well keeping the chilly feel to
the air even as temperatures recover.

An upper wave continues to slowly pivot through the region and
flurries will linger until it shifts east by late afternoon. Once it
does pass and as we approach sunset...the approach of the strong
surface high will enable skies to clear this evening and set the
stage for potentially the coldest night yet for parts of the
forecast area. Winds will lighten quickly into the evening with an
ideal radiational cooling setup into the predawn hours before mid
level clouds arrive from the northwest and warm advection commences.

Considering where current reading are and with the expectation of
little to no further rise this afternoon...temps will pull back to
subzero levels through the first half of the night for most if not
all of the forecast area. Nudged lows a couple degrees below the
model blend as a result. Obviously...the Cold Weather Advisory will
continue through Wednesday morning. Wind chills in the -20 to -10
degree range will remain common through much of the night.

A cold front will quickly move into the upper Midwest on Wednesday
and should progress into the western Great Lakes south into Missouri
by Wednesday evening. The approach of the boundary will tighten the
surface pressure gradient with the strong high pressure moving to
the East Coast. This will result in southwest winds becoming gusty
on Wednesday with peak gusts up to 35mph possible for the afternoon.
Mid level clouds will remain largely prevalent over much of the
forecast area with the best chance to see sunshine over south
central Indiana. Highs will range from the upper teens northwest to
mid 20s in the lower Wabash Valley. Wind chills will still be
unpleasant but should rise into the single digits for the afternoon.

&&

.LONG TERM (Wednesday Night through Tuesday)...
Issued at 214 PM EST Tue Jan 21 2025

The deep upper trough that has covered much of the country the last
few days will finally relax through the end of the week with the
bitterly cold air retreating to the north. A quasi-zonal split flow
regime will replace the deep trough by the weekend leading to a
moderation in temperatures with no major storm system concerns for
the region. The expansion of another surge of Arctic air by early
next week will provide a glancing blow to the Ohio Valley before
milder air arrives by the middle of next week.

Wednesday Night through Friday

Even as the broad longwave trough retreats...its influence will
linger through the end of the week with a series of waves traversing
the back side of the trough. The first of these is the stronger
one...moving through the lower Great Lakes late Wednesday night into
Thursday in tandem with a cold front...bringing flurries and perhaps
a few light snow showers focused over the northern half of the
forecast area. Could see a tenth or two of snow in a couple
locations.
n
High pressure will return by Thursday night with a brief reinforcing
shot of cold that will serve to delay the upcoming warmup by about
36 hours. A second weaker upper wave will swing through the region
Friday but with model soundings showing little moisture available...
anticipate just a brief increase in clouds as it passes. Highs both
Thursday and Friday will remain below freezing but much warmer than
current readings. Expect highs in the 20s both days with lows mainly
in the teens.

Friday Night through Tuesday

The aforementioned transition to a more quasi-zonal split flow aloft
will commence heading into the weekend...with a more progressive
pattern developing. A frontal boundary will elongate back west
across the region in the wake of a surface low tracking into the
Canadian Maritimes over the weekend...slowly sliding south through
Sunday. This will be key as the position of the boundary will likely
serve to suppress moisture associated with a surface low tracking
out of Texas...keeping precipitation largely south of the forecast
area Sunday and Sunday night. Will hang onto low pops through this
period with lower than desired confidence here but overall signals
continue to focus main area of precip over the Tennessee and lower
Ohio Valleys and points south. Highs over the weekend will rise
above freezing finally with the potential for low 40s over the
southern half of the forecast area.

The region will catch a passing glance from a storm system passing
well to the northeast early next week and will pull temps back
slightly on Monday before warming resumes by the middle of next week
as quasi-zonal flow return. Looking further out next week...the
transition away from the deep and extended cold of the last week or
so will continue. There is likely to be another surge of Arctic air
into the eastern part of the country late next week but the duration
and intensity will be minimized with an increasingly transient
pattern developing in early February marked by alternating periods
of warmer and colder air.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 648 PM EST Tue Jan 21 2025

Impacts:

- Southerly gusts peaking at around 25kts Wednesday

Discussion:

High pressure will move across the Ohio Valley tonight into
Wednesday with VFR conditions expected throughout the forecast
period. Westerly winds under 10 kts persist at all TAF sites as of
00z, however expect winds to drop to near calm briefly before
becoming southerly (170-190 deg) during the overnight hours. A
tightening pressure gradient and increasing LLJ winds should result
in surface winds increasing to 10-15 kts after sunrise Wednesday
with gusts 20-25 kts likely after 15z and through the afternoon
hours.

Clear skies are expected for most of tonight with a mid level deck
expanding across the area from the predawn hours through sunrise.
Cigs should remain mainly VFR as the cloud deck remains in the mid
and upper levels.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Cold Weather Advisory until 10 AM EST Wednesday for INZ021-
028>031-035>049-051>057-060>065-067>072.

&&

$$

UPDATE...CM
SHORT TERM...Ryan
LONG TERM...Ryan
AVIATION...CM