IND issues Area Forecast Discussion (AFD) at Dec 11, 11:48 PM EST
075
FXUS63 KIND 120448
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1148 PM EST Wed Dec 11 2024
.KEY MESSAGES...
- Mostly Clear and Colder Overnight
- Sub-zero wind chills tonight into Thursday morning
- Light snow possible Thursday afternoon and evening along and north
of I-70
- Rain chances and near normal temperatures return for this weekend
&&
.FORECAST UPDATE...
Issued at 929 PM EST Wed Dec 11 2024
Surface analysis this evening shows deep low pressure in place
over Quebec. Arctic high pressure was found over the northern
plains stretching south toward the lower Mississippi Valley. A
sharp, cyclonic pressure gradient was found across Central
Indiana. Radar shows the wave associated with the arrival of the
arctic air and afternoon snow showers has exited east of Central
Indiana. GOES16 shows limited cloud cover across Central Indiana
in the wake of the wave. Mostly clear skies were found upstream
across Illinois, and had already worked into the Wabash Valley.
Much colder air, in the 20s, has arrived across Central Indiana.
Upstream, dew points in the single digits were found amid arriving
subsidence.
Overnight, the cold air advection is expected to continue as high
pressure builds across Central Indiana from the west. Forecast
soundings and time heights both show a dry column through the night,
suggesting mostly clear skies. Models suggest the moderate pressure
gradient in place across the area causing the gusty winds will
lessen overnight. This will lead to gradually decreasing winds. HRRR
suggests low falling to the lower teens and single digits in the
northwest parts of Central Indiana. Given the dew points upstream,
this seems quite reasonable.
&&
.SHORT TERM (This evening through Thursday)...
Issued at 306 PM EST Wed Dec 11 2024
Two rounds of snow are expected through the short term, with one
arriving this afternoon and another arriving Thursday afternoon. The
two rounds of snow will be quite different from one another as well.
Today's snowfall looks to be more scattered in nature with a few
squalls possible. Thursday's snow looks to be more stratiform in
nature with a light but steady area of snowfall. Each will be
discussed below.
Today
As mentioned above, today's snow will be scattered in nature due to
an environment characterized by steep low-level lapse rates and
instability. An approaching arctic front will provide the lift
necessary for widespread snow showers, some of which may be heavy
leading to snow squall conditions. ACARS soundings out of IND
already show increasing low-level lapse rates, despite widespread
stratus, and some areas of clearing are filling in with cumulus
indicative of the rapidly destabilizing air mass.
Further upstream, radar shows snow showers already entering into
Indiana. Deeper into Illinois, radar echoes take on a more cellular
appearance hinting at further destabilization upstream. As the
increasingly unstable air mass advects east-southeastward into
Indiana, these heavier snow showers are expected to spread into the
area as well. Snow showers may retain this cellular appearance and
not that of a typical linear snow squall, mainly due to the lack of
a sharp front and PV anomaly aloft.
Temperatures across the region are generally in the low to mid 30s.
Dew point temperatures are in the low 20s with wetbulb temperatures
below freezing. This sets the stage for potential "flash-freezes"
where initial snow melts on contact with the road but then quickly
refreezes as temperatures wetbulb down to below freezing. Combined
with reduced visibility in heavy snow, treacherous driving
conditions are possible this afternoon and evening.
Additionally, winds along and behind the front will increase
substantially. Gusts up to 40mph are possible which could further
impact driving conditions within heavy snow showers or squalls.
Tonight
Snow showers and squalls should diminish by midnight, leaving us
with clearing skies and bitterly cold temperatures. Lows are
expected to drop quickly into the teens, and combined with the gusty
winds, could lead to wind chills below zero in portions of our CWA.
Thursday
The day should start off mostly sunny with dry cold advection
ongoing behind tonight's front. Clouds quickly increase after
sunrise as a mid-level wave approaches from the west. Guidance is
coming into better agreement on an area of steady light snow on the
northern edge of this system, which could track west to east across
central Indiana.
There remains some model uncertainty regarding the exact placement
of where this corridor of snow may fall, but the overall consensus
is generally along or just to the north of I-70. There has been a
slight shift southward within guidance over the past 12 to 18 hours.
Timing looks to be mid to late afternoon continuing into the
overnight hours.
In terms of amounts, guidance only has a couple hundredths of an
inch liquid, on average, with at most an inch of snow in the more
robust model solutions. Model soundings show deep saturation around
the -10C isotherm, hinting at the potential for optimal dendritic
growth. This could lead to an "over-achiever" scenario should
forcing be a bit more than initially modeled. One particular HRRR
run had upwards of 2-3 inches of snow in a narrow band across the
area. This would represent a good reasonable worse case scenario.
&&
.LONG TERM (Thursday night through Wednesday)...
Issued at 306 PM EST Wed Dec 11 2024
In a very similar fashion to last week, after a brief period of
winter weather, a warming trend arrives just in time for the
weekend! In addition to warmer temperatures comes multiple
chances for rainfall this weekend and into next week.
A warmer, wetter, and more progressive weather pattern sets up for
the next week or so across the Great Lakes region as the persistent
trough overhead is kicked out and numerous smaller systems pass
through the region. With the jet stream lifting northward, the main
P-type in the extended range should be mainly rain through early
next week, limiting the overall impacts expected. Long range signals
for indicate a return of cooler, more winter-like conditions mid to
late next week.
The systems to focus on arrive Saturday into Sunday, Monday into
Tuesday, then again mid to late next week.
.This weekend...
An upper low approaches the Great Lakes region from the west this
weekend with ridging building out ahead of it. This should lead to
drier and relatively "warmer" conditions Friday. Surface low tracks
from Northern MO to near Chicago Saturday into Sunday morning
spreading rainfall across all of Indiana midday Saturday. Latest
guidance has slowed down the onset of the precipitation some;
however Saturday still looks mostly wet for the second half of the
day. Brief ridging builds in Sunday as the region will be in between
the departing low to the northeast and the next incoming system to
the southwest. Expect widespread clouds to persist; however
southerly flow and weak warm air advection aloft will keep
temperatures above average in the 40s and low 50s.
.Next week...
The next system follows a slightly more northerly track from the
previous one, keeping Central Indiana within the "warm" sector of
the system. Above average temperatures persist into the beginning of
next week with rain likely much of the day on Monday. Tuesday will
likely be colder and dreary on the backside of that system as
cyclonic flow through the region will support a low chance for
showers within the cold air advection regime.
There is a little more discrepancy in the overall pattern for mid
to late next week; however confidence is high that the active
pattern will continue. Ensembles to indicate a switch back to a
colder weather pattern with more chances for snow.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1148 PM EST Wed Dec 11 2024
Impacts:
- Wind gusts diminishing late tonight
- A second round of snow possible Thursday afternoon and evening
focused at KIND and KLAF
Discussion:
Skies have cleared quickly this evening within the wake of the snow
showers from earlier. Skies will remain clear for most of the night
with mid level clouds returning in the predawn hours then
overspreading the region after daybreak. Westerly winds remain gusty
but those winds will gradually diminish over the next several hours
as the pressure gradient relaxes.
A mid level wave will pivot through the region on Thursday afternoon
with an area of light snow impacting northern portions of central
Indiana and especially KIND and KLAF. Reduced visibilities are
likely within the light snow and ceilings may dip to MVFR levels for
a period of time as well. Scattered snow showers and flurries will
linger into Thursday evening before ending. Westerly winds will
persist at 5-10kts throughout the day then veer to northerly
Thursday night.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
UPDATE...Puma
SHORT TERM...Eckhoff
LONG TERM...CM
AVIATION...Ryan
Source: IND issues Area Forecast Discussion (AFD) at Dec 11, 11:48 PM EST (https://mesonet.agron.iastate.edu/p.php?pid=202412120448-KIND-FXUS63-AFDIND)
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