IWX issues Area Forecast Discussion (AFD) at Feb 20, 1:15 AM EST702
FXUS63 KIWX 200615
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
115 AM EST Thu Feb 20 2025
.KEY MESSAGES...
- A period of light snow expected this evening into early
Thursday. Light accumulations up to 1" expected.
- Wind chills as low as -10 Thursday morning, coldest along and
south of US 30 in Indiana.
- Periods of heavy lake effect snow late tonight into Thursday
in northwest flow prone areas downwind of Lake Michigan.
Reduced visibilities and difficult travel expected, mainly in
areas under a Winter Weather Advisory.
&&
.DISCUSSION...
Issued at 238 PM EST Wed Feb 19 2025
Main focus remains on light system snow this evening into the early
overnight, transitioning to pure lake effect snow for our nw flow
snow belts later tonight through Thursday evening.
Shortwave and deeper moisture, currently over eastern IA, will
translate east through the area tonight as a weak closed low.
Associated modest deep layer ascent over steepening low level
lapse rates (within a portion of the DGZ) to promote this light
snow, particularly along and southeast of US 24 near the nose of
a 70 kt mid level jet. Light snow accums of a half inch to inch
should tend to stick on untreated roads given lingering cold
sfc temps.
Attention then turns to lake effect/enhanced snow, most organized in
the 06-18z window on Thursday when 0-2km theta-e lapse rate values
trend negative within a developing long lake axis thermal trough.
Model soundings/x-sections also continue to suggest omega and
saturation with respect to ice maximized within a portion of the DGZ
with signs of seeding on the backside of the exiting upper wave.
This long axis fetch, and supportive thermodynamic parameters,
suggest a decent potential for 1"/hr rates (12z HREF 10-30%
probs) and locally heavy snow totals (HREF max totals exceed 8"
in Berrien Ct) within any banded elements. Potential failure
points could be embedded disrupting mesolows and/or an earlier
breakdown of the lake aggregate trough.
There should be a trend toward less organized, cellular, multibands
Thursday afternoon into Thursday evening as trajectories slightly
back with the convergent lake plume eventually releasing from the
eastern Lake MI shoreline. The only change in headlines for this
package was to add Elkhart Ct into the Winter Weather Advisory.
Considered upgrading Berrien Ct to a Winter Storm Warning
(criteria is >8"), but opted to hold off for now with probabilistic
data favoring totals more in the 4-6" range overall in the
county. Did issue a SPS for the rest of area to cover more of a
nuisance impact to travel and wind chills as cold as -10 by
daybreak Thursday.
Friday through early next week will feature a moderating trend as
return wsw flow sets up under a lower amplitude flow regime aloft. A
few mid level shortwaves will take aim on the Great Lakes next week
with low periodic chances for precipitation. As expected, there are
sizable differences within the ensemble global systems regarding
track and timing of these mid level features resulting in low
predictability in daily rain/snow chances.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 115 AM EST Thu Feb 20 2025
System and lake effect snow continues across northern Indiana
early this morning. Strongest synoptic ascent should exit
northeast Indiana after 09Z with diminishment in coverage of
snow. However, lake effect snow will continue through much of
this period. A dominant bands have tried to form over southeast
part of Lake Michigan the past few hours, but this remains more
cellular and broken in nature. Near term guidance with some
support from observational trends suggests mesolow development
on tail end of this synoptic upper trough shifting southward
across eastern half of Lake Michigan into mid morning Thursday.
A more dominant single band could affect KSBN in wake of this
mesolow in the 14-19Z timeframe with the best potential of 1/2SM
or less vsbys. Lake induced troughing may be stubborn to break
down into early Thursday evening, although lake induced
instability should begin to diminishing during the mid-late
afternoon hours as inversion heights lower. Will continue with
prevailing snow showers at KFWA (IFR vsbys) during the afternoon
hours on Thursday as low level flow trajectories look
supportive.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 7 PM EST /6 PM CST/ this evening
for INZ005-103-104-204.
OH...None.
MI...Winter Weather Advisory until 7 PM EST this evening for MIZ078-
177-277.
MARINE...Small Craft Advisory from 4 AM early this morning to 4 AM EST
Friday for LMZ043-046.
&&
$$
DISCUSSION...Steinwedel
AVIATION...Marsili
Source:
IWX issues Area Forecast Discussion (AFD) at Feb 20, 1:15 AM EST---------------
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