IWX issues Area Forecast Discussion (AFD) at Feb 19, 12:36 PM EST358
FXUS63 KIWX 191736
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1236 PM EST Wed Feb 19 2025
.KEY MESSAGES...
- A period of light system snow expected tonight into early
Thursday morning. Accumulations up to 0.5" possible. Lake
effect snow expected late tonight into Thursday in northwest
flow prone areas downwind of Lake Michigan.
- A Winter Weather Advisory has been issued from 4 PM EST today
until 7 PM EST Thursday for Berrien, Cass, St Joseph (IN), and
northern La Porte counties. Lake effect snow accumulations
between 2-7" possible, with the highest totals in Berrien
County. Difficult travel is likely through Thursday. Areas of
blowing snow are expected on Thursday.
- A dry stretch ensues for the weekend, with temperatures
finally climbing back above freezing by Sunday.
&&
.DISCUSSION...
Issued at 250 AM EST Wed Feb 19 2025
Another cold day is ahead with increasing chances for snow, thanks
to an upper level low pivoting through the Great Lakes. As the
aforementioned low moves through later today with an attendant 500
mb shortwave, this will allow for some light system snow to
overspread the area and illicit a lake effect response tonight as
winds become northwesterly. For the system snow, increasing low
level lapse rates will create some lift to generate light snow
showers across the area, mainly this evening into the early
overnight hours. Minor accumulations up to a half inch are
possible, which could create some slick spots on roadways this
evening.
The more concerning timeframe is tonight into Thursday morning
as a dominant single band of lake effect snow quickly ramps up
downwind of Lake Michigan. With northwesterly winds, any
location in northwest Indiana and southwest Lower Michigan could
see some lake effect snow. Favorable parameters include
pronounced low level convergence, a Lake Michigan to Lake
Superior connection given the northerly fetch, inversion heights
around 7-8 kft, Delta-Ts of -15C, and negative theta e lapse
rates. Forecast soundings depict increasing lift and saturation
as inversion heights rise after sunset tonight. Lake effect snow
will ramp up this evening and into the overnight hours. Hi res
model guidance does not yet have a consensus on exactly where
this band sets up and how far inland it persists; forecasting a
single, strong lake effect snow band can be quite tricky as
small wobbles in its track can have implications on snow
amounts. For now, have issued a Winter Weather Advisory from 4
PM EST this afternoon to 7 PM Thursday for Berrien, Cass, St
Joseph IN, and northern La Porte counties. Will punt to the next
shift as to whether they want to add any counties and/or
upgrade Berrien County to a Winter Storm Warning. At this time,
these 4 counties in the Advisory are the ones I have highest
confidence in that will likely see several inches of snowfall
out of this band. It is possible the lake effect snow band sets
up as far west as Lake or Porter counties in Indiana or as far
east as Kalamazoo and Three Rivers in Lower Michigan. Snow
totals are highest in Berrien County with 4-7", with the rest of
the Advisory 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.
Did not have enough confidence to go for a Winter Storm Warning
in Berrien County as the warning criteria there is 8", but
could certainly see the next shift upgrading them to a Warning
if confidence increases.
The lake effect snow in northwest Indiana and southwest Lower
Michigan will result in difficult travel conditions, especially
along the I-94 and parts of the Toll Road (I-80/I-90). Be prepared
for impacts to the Wednesday evening and Thursday morning 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 on Thursday 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.
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 early next week. The next chance for rain/snow
arrives on Monday.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1235 PM EST Wed Feb 19 2025
As an upper low pressure system moves through during this taf
period, system and lake effect snow across the area will keep
flight conditions in MVFR for a good portion of the time with
snow falling and from CIGs. After an initial trough moved
through the area this morning and invigorated lake effect snow
with small flakes bringing VISBYs down to around 2 miles, a
weakening in lake effect snow becomes possible after around 21z.
It is then expected to return around 6z with more MVFR flight
conditions possible. SBN could also drop into IFR VISBY during
that time frame. Expect winds to be out of the west northwest
and gusts may approach 20 kts during the midday and afternoon
Thursday, but that is just at the tail end of this taf period so
will wait for the next issuance to include it. This appears to
be caused by a trough that moves down the lake and may enhance
snow and bring lower flight conditions as a result.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory from 4 PM EST /3 PM CST/ this
afternoon to 7 PM EST /6 PM CST/ Thursday for INZ103-104-
204.
OH...None.
MI...Winter Weather Advisory from 4 PM this afternoon to 7 PM EST
Thursday for MIZ078-177-277.
MARINE...None.
&&
$$
DISCUSSION...Johnson
AVIATION...Roller
Source:
IWX issues Area Forecast Discussion (AFD) at Feb 19, 12:36 PM EST---------------
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