Cold in Indiana, January 20 to 22, 2025

Area Forecast Discussion
National Weather Service Indianapolis IN
1200 AM EST Mon Jan 20 2025

.KEY MESSAGES...

- Cold Weather Advisory in effect tonight through Wednesday morning

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

- Moderating temperatures Wednesday onward, though still below
  normal

&&

.FORECAST UPDATE...
Issued at 1044 PM EST Sun Jan 19 2025

Not too much to update this evening as the well forecasted arctic
blast has already made its way into Indiana today. A strong area of
high pressure stretches down the front range of the Canadian Rockies
southeastward into the Central Plains with cold air advection
bringing arctic air all the way down to the Gulf Coast.
Northwesterly flow extends from the Canadian prairies into Indiana
with latest IND ACARs soundings observing -25C at 850mb! An arctic
airmass this deep is more typical of midwinter in Central Alaska
rather than Central Indiana, but what current differentiates this
airmass from what is normal in Alaska is the steep low level lapse
rates and lack of surface inversion... keeping surface temperatures
a tad "warmer." Forecast soundings this evening indicate steep lapse
rates in the lowest 1 km agl as extremely cold air advection pushes
in aloft with 850mb temperatures nearing -25C and surface
temperatures around -15C/5F. These steep lapse rates have kept windy
conditions persisting after sunset as winds within the low level jet
continue to mix down to the surface with gusts upwards of 20 mph at
times. Expect surface winds out of the WNW to continue into the
overnight hours remaining around 8 to 12 mph resulting in wind chill
values in the -10F to -20F range with actual lows in the -5 to +2
range. In fact, wind chills may remain below zero for much of the
day Monday, especially along and north of the I-70 corridor and any
location that still has snow on the ground. Despite the frigid
temperatures and wind chills, these numbers still are not near
record cold temperatures as record lows for this time of winter are
some of the lowest of the year, much lower than what is currently
forecasted.

&&

.SHORT TERM (This evening through Monday)...
Issued at 149 PM EST Sun Jan 19 2025

Rest of Today into Tonight.

Clouds continue to gradually clear from west to east as the upper
level trough that brought snow to Kentucky and southern Indiana
continues to push eastwards while the fetch from Lake Michigan that
helped to enhance the snow becomes more northwesterly and primarily
impacts the areas north and east of central Indiana. Expect that by
the late afternoon that snow will have ended with temperatures
dropping as strong CAA continues.

Sub-zero wind chills look likely around or slightly before sunset
with the 15-25 mph winds and temperatures dropping into the single
digits. Skies should be clear by midnight which will allow for a
combination of radiational cooling along with the continued
advection-based cooling that has been ongoing. There remains some
uncertainty as to how cold temperatures fall, but confidence is high
that most areas should drop at or below zero with wind chills
between -10 and -20.

Monday.

Winds will gradually become more westerly into the daytime hours
tomorrow which will help to limit the advection of cold air and
allow for temperatures to rise into the low to mid teens with plenty
of sun expected. Winds will remain in the 10-15 mph range which will
keep wind chills in the 0 to -10 range with some spots in the south
briefly rising above zero. Although typical Cold Weather Advisory
criteria won't be met during much of the mid to late afternoon,
opted to have the Advisory continue through the day as those low
temperatures return during the overnight to help keep the messaging
simple.

&&

.LONG TERM (Monday night through Sunday)...
Issued at 149 PM EST Sun Jan 19 2025

Similar thinking with regards to the long term and little change was
needed. We'll add a few points to the midnight shift's forecast,
based on the latest data:

We have a little higher confidence on clouds Monday night given a
trend toward a more amplified/sharper shortwave trough, within the
broad highly anomalous trough. Although the Arctic air mass will
feature negative precipitable water anomalies, modest ascent ahead
of the trough amid minor amounts of moisture relative to the
temperature should result in some clouds disrupting the radiative
process.

We have added low probabilities for snow late Thursday into Thursday
night with deepening trough overhead. Despite modest moisture,
steepening low level lapse rates may result in some light snow
showers during this period.

Although the MSLP high center will probably result in calm winds for
most of the area Tuesday night, mid-high clouds are expected to move
in late ahead of the next shortwave trough. Light southerly flow and
associated warm advection and mechanical mixing of shallow nocturnal
inversion could start across western/northern portions of the area
before sunrise as well, disrupting the opportunity for currently
forecasted lows to be realized. Therefore, we don't have a reason to
go below the 50th percentile and statistical/MOS guidance supports
the idea of temperatures as high as the 75th percentile. What we did
do with this update is sharpen the nocturnal temperature drop early
in the night and then level it off.

No change to the Cold Weather Advisory with wind chills expected in
the -10 to -20 range still at times during its valid period.

There's a good signal for modest moisture return preceding an
upstream wave by Sunday, but differences in where the forcing exists
across the region precludes high precipitation probabilities at this
time. Several ensemble members are more suppressed with
moisture/forcing, keeping it south of the Ohio River.

Previous discussion sent at 243 AM Sunday:

Anomalously deep troughing over almost the entirety of North America
will lead to very cold weather for the next several days. Ensembles
are in excellent agreement showing 850mb temps as low as -25 to -30
C over portions of the Midwest early this week. Surface temperatures
below zero degrees are expected for multiple nights, with wind chill
readings occasionally reaching -15 to -20 degrees F.

Some clouds should overspread the southern half of our area Monday
night, which may prevent low temps from being as cold as they could
be. We bumped low temperatures up a bit across our southern counties
while keeping temperatures north of I-70 slightly below guidance.
Radiational cooling will be maximized in areas that see clearing,
effects of which can be washed out in lower-resolution guidance.
Tuesday night looks to have the best radiational cooling potential
as surface high pressure is directly overhead. Light winds and clear
skies along with a patchy snowpack should lead to temperatures as
low as -10 F in places. There remains some spread within guidance,
however, as some members show warm air advection beginning halfway
through the night as the high slides eastward. We will lean towards
the colder solutions for now, as a sharp boundary layer inversion
should help limit any southerly winds that begin to develop. Diurnal
mixing could lead to a nice southerly breeze (gusts up to 25kt)
during the day on Wednesday, however, which should help temperatures
rebound quickly into the 20s.

We will maintain a Cold Weather Advisory with this update, as a
majority of locations will experience wind chill values between -10
and -19 degrees F...with only isolated readings exceeding -20 F.
Confidence is very high for -10 degree or lower wind chills Sunday
night into Monday as the combination of wind and cold is maximized.
Thereafter, winds diminish leading to less frequent periods of -10
to -19 degree wind chills, but still frequent enough to warrant the
Cold Weather Advisory through Wednesday morning.

Ensemble guidance depicts the trough flattening somewhat by
Wednesday, with modest warm air advection taking hold. Temperatures
at the surface moderate but are expected to remain below normal
through the coming week. Above-freezing high temps are looking
increasingly likely by the weekend. Longer term ensemble guidance
retains mean troughing over the eastern US so below-average
temperature are favored through the remainder of January.

With the polar jet displaced well to our south...precipitations
chances look quite minimal through the next 7 days or so. There may
be a weak upper-level impulse / clipper system passing through late
this week with scattered snow showers or flurries but that's about
it. Some of the global models bring about a more active weather
pattern towards the end of the month but no coherent signal exists
within the ensembles as of yet.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1200 AM EST Mon Jan 20 2025

Impacts:

- Northwest winds diminishing overnight
- MVFR ceilings may persist at KBMG early in the period

Discussion:

Cloud bands will gradually shift south and east overnight. KIND
should be just scattered by valid time, but MVFR ceilings may linger
at KBMG early. Otherwise, VFR conditions with mostly clear skies
will continue much of Monday. Mid cloud will move in later on Monday
into Monday night.

Winds may gust to over 20kt early in the period, but a diminishing
trend will occur overnight.

&&

.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...White
LONG TERM...BRB/Eckhoff
AVIATION...50

Hazardous Weather Outlook
National Weather Service Indianapolis IN
148 PM EST Sun Jan 19 2025

INZ021-028>031-035>049-051>057-060>065-067>072-201900-
Carroll-Warren-Tippecanoe-Clinton-Howard-Fountain-Montgomery-Boone-
Tipton-Hamilton-Madison-Delaware-Randolph-Vermillion-Parke-Putnam-
Hendricks-Marion-Hancock-Henry-Vigo-Clay-Owen-Morgan-Johnson-Shelby-
Rush-Sullivan-Greene-Monroe-Brown-Bartholomew-Decatur-Knox-Daviess-
Martin-Lawrence-Jackson-Jennings-
148 PM EST Sun Jan 19 2025

This hazardous weather outlook is for central Indiana.

.DAY ONE...Through Tonight.

Very cold temperatures are expected with wind chills up to 20 below
zero.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Bitter cold conditions, including low temperatures below zero, and
wind chills well below zero are likely at times through Wednesday
morning.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

&&

More information, along with other weather, hydrological and climate
information can be found at http://weather.gov/ind