IWX issues Area Forecast Discussion (AFD) at Feb 20, 2:32 AM EST
113
FXUS63 KIWX 200732
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
232 AM EST Thu Feb 20 2025
.KEY MESSAGES...
- The Winter Weather Advisory has been extended until 1 AM EST
Friday for Berrien, Cass, St Joseph (IN), and northern La
Porte counties. Additional lake effect snow accumulations
between 2 to 6 inches possible, with the highest totals in
Berrien County. Difficult travel is likely throughout the day
with areas of blowing snow expected.
- A dry stretch ensues for the weekend, with temperatures
finally climbing back above freezing by Sunday.
- Mild with highs in the 40s next week with chances for rain and
snow midweek.
&&
.DISCUSSION...
Issued at 230 AM EST Thu Feb 20 2025
Light system snow is making its way out of the area early this
morning, with observed amounts between 0.5" to 1". This has allowed
for roads, bridges, and overpasses to become snow-covered and slick
so take it slow for the morning commute! Secondary and untreated
roads will be especially slick this morning with potential for black
ice to develop where cars have driven over the snow and compacted it.
We continue to monitor lake effect snow along and downwind of Lake
Michigan. Current radar imagery shows two ongoing lake effect snow
bands across Berrien County and into Cass and St Joseph (IN)
counties. A mesolow can also be seen on radar over Lake Michigan
offshore of Ludington, which will continue to move southward and
potentially impact our forecast area later this morning into early
afternoon. We've had a few lake effect snow bands visible on radar
overnight, but we are still expecting a dominant single band of lake
effect snow to set up later this morning (with potential enhancement
from the aforementioned mesolow). Favorable parameters include
pronounced low level convergence, a Lake Michigan to Lake
Superior connection given the long northerly fetch, inversion
heights around 6-8 kft, Delta-Ts of -15C, and negative theta e
lapse rates. Forecast soundings depict increasing lift and
saturation as inversion heights rise this morning. Latest hi res
model guidance, particularly the HRRR, suggests SW Berrien, NW
St Joseph (IN), and NE La Porte counties will be the bullseye
for this single band of lake effect. However, forecasting a
single, strong lake effect snow band can be quite tricky as
small wobbles in its track can have implications on snow
amounts. The lake effect snow band is likely to only be 20 to 30
miles wide, with a sharp gradient in snow amounts on either
side. Additional snow accumulations from now into Friday morning
are highest in Berrien County with up to 6", with the rest of
the Advisory area expected to see anywhere between 2-5" with a
sharp cutoff in totals. Higher amounts are definitely possible,
especially given the highly variable nature of lake effect snow.
The lake effect snow in northwest Indiana and southwest Lower
Michigan will result in difficult travel conditions this morning and
afternoon, especially along the I-94 and parts of the Toll Road (I-
80/I-90). Be prepared for impacts to the Thursday morning and
evening commutes. Rapid changes in the visibility over a few miles
are possible within the single dominant lake effect snow band.
Northwesterly wind gusts will increase this afternoon to 20-25
mph, which will yield areas of blowing snow in the NW flow lake
effect zones. N-S roads and rural, open areas will be the most
impacted. To account for these impacts (and the likelihood that
the lake effect snow persists into early Friday morning), have
opted to extend the Winter Weather Advisory until 1 AM EST
Friday.
Lake effect ends and a dry stretch ensues for Friday and into the
weekend as high pressure builds across the eastern CONUS.
Temperatures finally climb above freezing by the end of the
weekend and into the 40s by the middle of next week. An active
pattern returns next week with chances for rain and snow.
&&
.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 1 AM EST /midnight CST/ Friday
for INZ005-103-104-204.
OH...None.
MI...Winter Weather Advisory until 1 AM EST Friday for MIZ078-177-
277.
MARINE...Small Craft Advisory until 4 AM EST Friday for LMZ043-046.
&&
$$
DISCUSSION...Johnson
AVIATION...Marsili
Source: IWX issues Area Forecast Discussion (AFD) at Feb 20, 2:32 AM EST (https://mesonet.agron.iastate.edu/p.php?pid=202502200732-KIWX-FXUS63-AFDIWX)
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