566 
FXUS63 KIND 190824
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
324 AM EST Fri Jan 19 2024

.Key Messages...

- Winter Weather Advisory continues thru 10 AM

- Total snow accumulations ranging from 1-3 inches along the I-70 
corridors, with 2-4 inches for North Central Indiana and Eastern 
Indiana

- Lows near or below zero tonight and Saturday night with wind 
chills below -15F.

- Warmer with multiple rounds of rain mid next week. Watching 
out for river flooding and ice jams going into the weekend.

&&

.Mesoscale Update...
Issued at 323 AM EST Fri Jan 19 2024

Area of snow continues to fall across Central Indiana early this 
morning. Best reflectivity showing up on WSR-88D KIND along and 
southwest of Indy Metro from an area of stronger snow showers 
sliding east. This area is associated with a zone where some 
increased vertical ascent to moist parcels is occurring, and is 
easily reaching the dendritic growth layer where an abundance of 
omega still resides and helping to further enhance the larger 
aggregates that are falling. The presence of additional moisture 
here is also evident with the higher reflectance. The frontal 
boundary is still displaced west of the area, but steadily 
approaching Indiana. Across Illinois temperatures have already 
fallen into the lower teens with winds gusting to around 25-30 mph 
from the northwest. This will reach Central Indiana within the next 
couple of hours, and when coupled with the fresh powder snow should 
easily create some blowing snow and at times reduced visibilities.

&&

.Short Term...(Today and tonight)
Issued at 208 AM EST Fri Jan 19 2024

Through this afternoon...
No changes to current winter weather advisory will remain in place 
for the remainder of the early morning hours. Still anticipate 
snowfall values of 1 to 3 inches, with the highest values in the 
northern portions. Closer to the Indy metro and along the I-74 
corridor still forecasting between 1 to 2 inches. 

Steady moistening through the lowest layer of the atmosphere has 
finally occurred as this shortwave trough arrives from the west. 
Reflectivity has steadily increased over Central Indiana, with 
latest aircraft soundings depicting only a minor dry layer 
remaining. But the bigger storyline early this morning is the 
increased omega or vertical component to moistening parcels reaching 
the dendritic growth zone. The combination of these moist parcels 
and a tightening isallobaric gradient is helping to develop a narrow 
channel of better snowfall between Crawfordsville to Frankfort to 
Kokomo, but should drift south/southeast over the pre-dawn hours. 
Satellite imagery is showing some agitated clouds just upstream in 
Illinois, which is just ahead of the sharp frontal boundary, and is 
likely going to further enhance the omega fields over Central 
Indiana. 

The presence of ice through the profile will further help dendritic 
production with larger aggregates progged between the 8-10Z 
timeframe which also matches up well with the aforementioned 
stronger ascending parcels in Illinois ahead of the frontal 
boundary. Confidence remains high that despite the temperatures at 
onset of upper 20s, the SLR ratios will generally be increasing to 
the upper teens and likely around 20:1 by daybreak as the snowfall 
begins to dwindle and deeper moisture peels east. 

With the broad trough axis covering the Great Lakes/Ohio River, the 
850mb shortwave will be marching east into Ohio allowing the steady 
eastward push of the sharp cold front this morning, which will 
likely cause the high temps to be early in the day with steady to 
falling temps in the afternoon into the lower teens to in some 
locations the high single digits. Mixed layer still will be a 
concern while the favored DGZ becomes less optimal late morning. The 
mixing will still be pulling to the surface winds along and behind 
the boundary into the 20-30kt range, likely generating frequent 
gusts into the 20-25 mph range. Leading to apparent temps in the 
single digits below zero by early afternoon. 

Evening through Overnight... Broad trough will continue to linger 
across the Great Lakes region, but it is going to be coupled with a 
modest surface ridge nudging east this evening. The leading edge 
still appears to paint a tight isallobaric gradient over Indiana, 
which will likely favor continued breezy conditions. The combination 
of clearing sky cover this evening, fresh snowpack, and temperatures 
easily falling to around zero or a few degrees below will set the 
stage for wind chill values between -12 to -18 deg. Have continued 
the already issued wind chill advisory and expanded to include the 
southern counties. There is some concern that perhaps the surface 
ridge will inhibit the mixing in the lower layers sooner, and thus 
produce lighter surface winds and bring apparent temps back a touch 
below criteria. But based on ensembles and the current setup, have 
maintained the going headlines.

&&

.Long Term...(Saturday through Thursday)
Issued at 208 AM EST Fri Jan 19 2024

Saturday Through Sunday.

By Saturday morning the surface and near surface flow will have 
enough of a westerly vs northerly component to bring an end to any 
lake enhanced snow showers across the northeastern counties. High 
pressure will quickly begin to develop across the Central Plains and 
drift eastwards towards the Midwest Saturday night.  There is good 
model agreement in a surface high centered over southern Illinois 
around 1040mb late Saturday night with models showing a dry column 
and little to no surface winds.  This should allow for extremely 
efficient radiational cooling with overnight lows falling below most 
model guidance.  Will continue trending the forecast towards the 
lowest model guidance which would allow for lows around -5.  To get 
this low wind speeds will need to be near calm which should limit 
the wind chill threat.

Temperatures will remain chilly through the daytime hours on Sunday 
before a major pattern shift which will bring a return to warmer 
temperatures and rain chances.  Surface flow will regain a southerly 
component during the daytime hours, but with cold temperatures deep 
into the Tennessee Valley, WAA will take a while to begin to make a 
dent in the cold across the region.

Monday Through Thursday.

An upper level trough will exit the Four Corners region Monday and 
track to the northeast Monday night into Tuesday which will further 
enhance the southerly flow across central Indiana with a saturated 
column with much higher available moisture than normal for this time 
of the year by mid week. The first wave will see greatest impacts 
Tuesday evening into Wednesday with widespread light to moderate 
rain.  Model ensembles are clustering on two different solutions for 
the speed of progression of the aforementioned low, but both show 
similar strengths and resulting rain amounts with the main question 
being whether the heaviest precipitation falls Tuesday evening or 
Wednesday morning.

Two additional waves will impact the area Thursday but with a lot of 
feedback within the models on how things evolve from the Tuesday 
system, confidence quickly drops off into Thursday on forecast 
details, but above normal temperatures and wetter than normal 
conditions look likely to finish the work week into the weekend.  If 
some of the higher end QPF scenarios play out, will have to keep an 
eye on the potential for flooding due to the warming causing a break 
up of the ice along various rivers.  MMEFS river ensemble members 
generally show rises back to near action stage by next weekend with 
the potential for minor flooding along the Wabash River.

&&

.Aviation...(06Z TAF Issuance)
Issued at 105 AM EST Fri Jan 19 2024

Impacts:

- Snow will bring IFR conditions thru daybreak
- Gusty NW winds up to around 25 knots

Discussion:

Snow has arrived over airfields across Central Indiana, and expected 
to persist through midday. Conditions will fall to MVFR near the 
start time of snow then quickly fall to IFR as snow intensifies. 
Snow intensity will diminish from west to east toward 12Z, allowing 
some improvement.

Colder air moving in behind the main push of snow will bring 
northwest winds gusting up to around 25kt, and these winds will 
continue through the daylight hours today. Questions remain on how 
much blowing snow will occur, but the potential exists for some 
reduction in visibility through daybreak, especially at the northern 
sites.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 10 AM EST this morning for INZ021-
028>031-035>049-054>057-062>065-070>072.

Wind Chill Advisory from 7 PM this evening to 10 AM EST Saturday 
for INZ021-028>031-035>049-051>057-060>065-067>072.

&&

$$

Mesoscale...Beach
Short Term...Beach
Long Term...White
Aviation...Beach