IWX issues Area Forecast Discussion (AFD) at Jan 23, 12:26 AM EST656
FXUS63 KIWX 230526
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1226 AM EST Thu Jan 23 2025
.KEY MESSAGES...
- A period of lake enhanced snow (1-4") late tonight into Thursday
in sw MI and nw IN. Slippery travel expected at times.
- Mainly dry and milder (near normal) by this weekend and early
next week.
&&
.UPDATE...
Issued at 922 PM EST Wed Jan 22 2025
Broad isentropic ascent has had a difficult time overcoming dry
subcloud layer evident on ACARS data in lowest 4k feet for much
of the evening. Over the past hour, starting to get some
reports of light snow into northwest Indiana as large scale
synoptic lift increases over next few hours downstream of
leading edge of positive vorticity advection lifting out of
central Illinois. Near term guidance suggests lowest
condensation pressure deficits overnight, generally along and
north of the US 6 corridor which still stands best location for
light snow accumulations during the late evening and overnight
hours. No major changes needed to previous forecast grids, and
no changes anticipated to the Winter Weather Advisory for
Berrien/Cass MI.
&&
.DISCUSSION...
Issued at 205 PM EST Wed Jan 22 2025
Chances for light snow is the primary forecast concern tonight
into Thursday as an upper trough and cold front swing through. A
lead, low amplitude, shortwave moving through the southern
Great Lakes as of this writing has failed to produce anything
more than a few light snow showers locally given dry low levels
and weak ascent. This feature exits east late this afternoon
with most locations remaining dry through mid evening. The main
upper trough and cold front look to reach nw IN and sw MI later
this evening into the overnight, and through the rest of the
forecast area Thursday morning/early afternoon. Synoptically
speaking, this system does't have a lot going for it thanks to a
dearth of moisture and disjointed forcing. This favors holding
with chance PoPs and only light snow accums for most, though a
relatively deep pre-frontal dendritic growth zone (DGZ) could
support accums up to a half inch in spots. The exception will be
closer to the lake where enhancement is expected immediately
along and behind the cold front. 850 mb delta T's nearing 20C,
inversion heights to 7-8 kft, and the cloud layer clearly within
the DGZ are supportive of lake enhancement in the morning,
transitioning to pure lake effect by Thursday aftn/eve in our nw
flow snow belts. Have snow totals in the 1-2" range in the
South Bend/Elkhart area, with amounts up into the 2-4" range in
Cass/Berrien MI, with the bulk of this likely falling during the
morning and early afternoon thanks to the synoptic support and
seeding. Coverage likely falls off a bit mid afternoon into the
evening hours as incoming dry/subsident air begins to take its
toll on inversion heights. Made no changes to the counties in a
Winter Weather Advisory in Cass/Berrien MI (for blowing snow
into this evening, accumulating snow overnight into Thursday),
but did extend through 00z Friday. A SPS may be needed for the
surrounding counties for slippery travel on Thursday.
A stretch of mainly dry wx and seasonable temps is expected for the
remainder of the period thanks to lower amplitude, quasi-zonal,
flow aloft.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1222 AM EST Thu Jan 23 2025
Wrn flank of departing ridge slow to saturate ahead of leading
upper disturbance seen over wrn IL attm. Better saturation invof
KSBN yielding a band of warm advection induced snow which looks
to struggle ewd in time. Better prospects seen this aftn ahead
of more potent shortwave digging through lower MI which will
also veer low level flow back nwrly to afford some lake
enhancement invof KSBN with vigorous snow showers expected.
Expect these will reach into the KFWA vcnty late day with
transient IFR conditions.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...Winter Weather Advisory until 7 PM EST this evening for MIZ078-
177-277.
MARINE...None.
&&
$$
UPDATE...Marsili
DISCUSSION...Steinwedel
AVIATION...T
Source:
IWX issues Area Forecast Discussion (AFD) at Jan 23, 12:26 AM EST---------------
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