420 
FXUS63 KIND 062013
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
313 PM EST Sat Jan 6 2024

.Key Messages...

- Drizzle/patchy fog through the rest of the afternoon.

- A weak system tonight will bring additional light snow with 
amounts up to an inch north of Indianapolis.

- Few changes to forecast with storm system Monday night into early 
Wednesday; primarily rain and gusty winds expected much of the 
event, with a brief burst of light snow accumulations possible at 
the onset and ending Monday night and Tuesday night. Impacts to the 
Wednesday morning commute possible.

- Yet another strong winter storm is possible in the Midwest late 
next week into the weekend. Much too early for details but continue 
to watch for possible impacts.

&&

.Short Term...(This evening through Sunday)
Issued at 312 PM EST Sat Jan 6 2024

Rest of Today.

Lingering low clouds and abundant near surface moisture has led to 
occasional drizzle with lowered visibilities across central Indiana. 
Temperatures at Indianapolis have only varied by 3 degrees between 
31 and 34 since midnight and with sunset approaching, not expecting 
any more than a 1 degree increase through the rest of the day.  With 
surface temperatures just above freezing, there haven't been any 
impacts from the drizzle but will continue to monitor this ahead of 
the loss of the minimal daytime sun. ACARs soundings combined with 
IR satellite show that the top of the cloud layer lacks ice which is 
leading to the drizzle vs snow as seen earlier.

Tonight.

This cloud layer will begin to deepen later into the evening and 
overnight hours with ice nucleation expected to begin around 7-8PM 
which will coincide with a weak wave that is expected to move across 
the northern counties to bring another quick hitting snow. There is 
little to no vorticity with this system with snow being driven more 
by lift within the 600mb to 850mb layer which is much less 
substantial than what was seen during the overnight hours last night.

This snow should generally remain isolated to points along and north 
of I-70 with amounts no greater than an inch for most spots with 
most areas seeing closer to 0.50". Temperatures tonight will remain 
near steady state with lows in the low 30s with westerly winds 
beginning to strengthen as pressure gradients briefly tighten across 
the forecast area.

Sunday.

Similar weather is expected for tomorrow with some lingering low 
clouds in the morning with drier air gradually working in.  Non-zero 
instability will arrive by the afternoon with dry adiabatic lapse 
rates up to the top of the boundary layer at around 3kft with drier 
air above it. This could have led to some brief convective snow 
showers/light rain if the top of the cloud layer had been a bit 
cooler combined with a weaker cap at the top of the boundary layer, 
but with those limitations expect just a few areas of heavier 
sprinkles or perhaps light snow mid to late afternoon with much of 
the precipitation ending by noon.

&&

.Long Term...(Sunday night through Saturday)
Issued at 312 PM EST Sat Jan 6 2024

Very active long term period across central Indiana, with at least a 
couple of impactful systems likely for the region.

The first round of the week comes Monday night into early Wednesday. 
A very strong low pressure system will pull quickly northeast out of 
the Texas Panhandle into central Illinois and northwest Indiana late 
Monday into Tuesday evening. Ensemble guidance is very well 
clustered with a low track near or just northwest of the northwest 
corner of the forecast area, which will keep central Indiana in the 
warm sector and all rain for the bulk of the event.

However, Monday night presents an opportunity for a quick burst of 
accumulating snow on the leading edge of the precipitation, despite 
borderline near surface temperatures - forecast profiles show a deep 
near-isothermal layer near or just below 0C, and with the onset of 
strong frontogenetic forcing at the nose of the low level jet Monday 
night, dynamic cooling may offset midlevel warm advection for a few 
hours either side of midnight and allow for a burst of briefly heavy 
snow to accumulate, potentially up to an inch or two, primarily from 
Indy northward.

However, strong low and midlevel warm advection as we approach 
daybreak Tuesday will rapidly produce a changeover to rain, with 
rain continuing through the day on Tuesday. Precipitable water 
values continue to exceed climatological 90th percentile much of the 
event, with probabilistic guidance showing rainfall amounts in 
excess of a half inch a virtual certainty (90%) and in excess of an 
inch a significant likelihood (50-60+%), which may put a slight dent 
in the longer term drought conditions. Some minimal upright 
instability is present in some forecast profiles, and given the 
strong dynamics present throughout the depth of the troposphere, 
some elevated convection/embedded thunder cannot be ruled out, but 
remain uncertain and will not include for now.

As the low continues to wrap up and move rapidly northeast into the 
central Great Lakes, onset of cold advection Tuesday night will 
promote a potentially rapid changeover back to a mix or all snow, 
with potential for another brief burst of accumulations in the 
plentiful wraparound moisture before precipitation tapers off late 
Tuesday night into Wednesday morning as the column dries from aloft. 
Will have to monitor for possible impacts to the Wednesday morning 
commute.

Some of the guidance suite produces a weak clipper-type system 
moving through the Great Lakes late Thursday into Friday, with 
additional potential for light snow or a mix across portions of the 
area, particularly north.

Models then show another strong low somewhere in the region Friday 
night into Saturday, but extremely large ensemble spread and model-
to-model inconsistencies give very low confidence on precipitation 
types and amounts - but another round of impactful precipitation is 
on the table.

It remains very important to avoid keying in on one model, one run, 
or one cherry-picked extreme solution, particularly for the late 
week system, and to instead monitor trends and updates from trusted 
sources as the week wears on.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1219 PM EST Sat Jan 6 2024

Impacts:

-IFR to LIFR cigs through much of TAF period
-Vsbys generally MVFR through the evening, becoming IFR with snow 
tonight
-Wind shift from 000 to 270 after 04Z.

Discussion:

Lingering low visibilities will continue through the afternoon with 
cigs generally IFR. LIFR cigs and IFR to LIFR vsbys return after 04Z 
with additional snow expected through 10Z. Highest confidence in the 
more severe conditions will be at LAF and IND with lower confidence 
at HUF and BMG.  Winds will shift westerly after 04Z and generally 
remain between 7 and 12 kts.

&&

.IND WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Short Term...White
Long Term...Nield
Aviation...White