Indiana’s Weather For Sunday

Here comes the big storm, centered in the south and heading east.

HEADLINES
– WINTER STORM Warning in effect across much of central IN for a significant winter storm expected to impact the region later today and tomorrow.
– Winter Weather Advisory in effect for far N/NW portions of central Indiana where lower snowfall totals and overall impacts are expected.
– Below normal temperatures are expected through at least next Sunday. The coldest temperatures look to be Wednesday night with overnight lows in the single digits.

TECHNICAL DISCUSSION VIA NWS INDIANAPOLIS

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OVERVIEW -

1) WINTER STORM WARNING across much of central Indiana for a winter
storm expected today through Monday, with potential for significant
to major impacts, in the form of heavy snow, sleet/ice
accumulations, and gusty winds/blowing and drifting. A WINTER
WEATHER ADVISORY is in effect for far N/NW portions of central
Indiana where lower snow amounts are expected.

2) Bitterly cold conditions arriving in the wake of the winter
storm, likely persisting well into the week 2 period before
improvement.

WINTER STORM TODAY INTO MONDAY...

A significant winter storm will impact the Ohio Valley today with
impacts expected through Monday. Models have continued to converge
on solutions providing relatively good confidence in the evolution
of this system, but there are still some slight uncertainties in the
forecast.

Current surface analysis shows the impending winter storm is getting
its act together across the Plains. Expect the system to continue
organizing as it pushes eastward towards our neck of the woods.
Anomalous deep moisture streaming northward within a strong LLJ and
increasing dynamics will promote widespread wintry precipitation
overspreading the area from SW to NE during the day. Precipitation
is expected to begin across the southwest around 8-10am and reach
the I-70 corridor by early-mid afternoon. Look for precipitation to
begin as all snow with increasing warm air advection from the strong
LLJ then leading to sleet or freezing rain mixing in for south-
central during the afternoon and evening.

Forecast soundings generally support sleet being the more dominant
precipitation type where this transition occurs initially. The
reason for this is the warm nose remains only a degree or two above
the 0C isotherm near south-central IN with a sufficient sub-freezing
surface layer for sleet. Most guidance shows a significant dry slot
moving in aloft this evening and overnight resulting in an
unsaturated DGZ and no ice nuclei. This will likely lead to
widespread freezing drizzle for areas south of the I-70 corridor.
At this time, thermal profiles north of I-70 suggest precipitation
type remains snow. There is still some slight uncertainty in how far
north freezing drizzle mixes in as guidance differs on the dry slots
northward progress overnight so this will be monitored closely.

The strongest large scale ascent and frontogenetical forcing is
expected to move across the area late Sunday in tandem with the
transition of wintry precipitation. Thus, the heaviest snowfall
rates are likely to occur in this period as well. Dynamic cooling
will eventually transition precipitation back to all snow by late
overnight. By this point, high resolution models show another round
of higher SLR snow moving through as a TROWAL develops. Given the
high SLRs and narrow banding potential with this portion of the
storm, a wide range in 6hour snowfall amounts is possible between
09Z and 15Z Monday.

The winter storm will shift east during the day Monday allowing snow
to eventually taper off as drier air filters in. Most guidance shows
snow diminishing by mid-late afternoon.

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Summary of Winter Storm:

Given the strong forcing, plentiful moisture, and long duration of
the event due to the orientation and motion of the primary
precipitation band with the system, probabilities are still high for
warning criteria of 5 inches, especially for areas along and south
of I70. For this reason a Winter Storm Warming remains in effect for
a majority of central Indiana. NW portions of central Indiana, there
exhibits greater uncertainty with a sharp northward gradient in
snowfall totals expected in these areas.

Greatest snowfall amounts are likely to remain near or south of the
I-70 corridor. The current forecast is for snowfall totals as high
as 12 inches. Areas that see any mixing of sleet or freezing rain
will likely see some decrease in snowfall totals, but impacts could
still be just as bad due to ice accretion. Winds will also be a
concern, particularly tonight into Monday, with blowing and drifting
likely becoming at least a moderate concern in areas that did not
receive freezing drizzle Sunday night. Winds gusts between 30-40 mph
are expected with a low chance for isolated higher gusts.

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.LONG TERM (Monday through Saturday)...
Issued at 304 AM EST Sun Jan 5 2025

Bitter cold temperatures will be featured in the long term as
broad Arctic high pressure slowly builds in from the Plains.
Wednesday night looks to see coldest temperatures as the high moves
overhead. Meanwhile, temperatures will moderate slightly this
weekend as another one low pressure system moves in from the Great
Lakes and another lifts northeast from the Gulf to the southern
states. In addition to the moderating temperatures, more snowfall
will be possible. That said, models and ensembles are having
temporal and spacial differences tracking these systems, this far
out. So, confidence on coverage and timing is low.

A big caveat regarding temperatures will be how much snow cover we
receive with this first looming Winter system. This will have a big
say in how cold it gets and especially Wednesday night, when
substantial clearing is possible per model soundings. Because of
that unknown, confidence in precise temperatures is low. However,
current projections are temperatures Wednesday and Thursday will
have a hard time hitting 20 degrees for highs. Otherwise,
temperatures should reach the 20s Tuesday and 20s again this
weekend. The coldest night will likely be Wednesday night, when near
zero temperatures and below zero wind chills will be possible.
Normal highs and lows for early January are in the 30s and lower 20s
respectively.

NWS CHARTS FOR TODAY/TONIGHT