IWX issues Area Forecast Discussion (AFD) at Dec 3, 3:09 PM EST004
FXUS63 KIWX 032009
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
309 PM EST Tue Dec 3 2024
.KEY MESSAGES...
- Lake effect snow, gusty winds, and lowered visibility are
expected Wednesday evening overnight into early Thursday. A
winter storm watch has been issued for Berrien, Cass, and St
Joseph, MI with lowered visibility possible in the snow,
especially closer to Lake MI. Winds could gust between 30 and
40 mph with 45 mph possible near Lake MI. Lake effect snow
continues, but slowly wanes through the day Thursday.
Hazardous travel is possible in these areas.
- The cold air is expected to last through Friday with highs
Thursday and Friday in the mid 20s to around 30 degrees. Lows
are expected to be in the teens to around 20 degrees. Apparent
temperatures drop below zero south of US-30 Wednesday night.
- Our next chance for precipitation is expected to occur Sunday
night/Monday.
&&
.DISCUSSION...
Issued at 253 PM EST Tue Dec 3 2024
Low level southwesterly trajectories continue to take the remaining
lake effect snow clouds east away from the area as surface high
pressure pushes into the Tennessee River Valley. Those trajectories
do look to bring in warmer air near the low levels and this is
expected to keep the area warmer than it was last night with low to
mid 20s as opposed to areas seeing teens creep into areas south of
US-30. This should also allow temperatures to creep back into the
30s and above freezing on Wednesday.
Then, another clipper system approaches from the northwest. Moisture
appears to struggle, as is usual with these systems. However, when
the cold front moves through, temperatures do appear conducive to
more rain than snow. Initially, could also see some graupel mix in
as strong low level lapse begin to form. Additionally, strong gusty
winds 25 to 40 mph will be across the area ahead of the cold front.
Gusts could briefly exceed 40 mph along the cold front Wednesday
evening and then as the colder begins to come in behind the cold
front, areas down wind of Lake MI (Berrien and Cass in Michigan and
N Laporte and St Joseph in Indiana) could see winds surpass 40 mph
overnight. Expect to see lake effect snow take shape during the
evening and early overnight hours as a strong vigorous
shortwave/secondary cold front approaches Lake MI. Delta T values
approach 30 degrees with inversion heights up to 3 km/700 mb and
lift through the DGZ. Those inversion heights do drop after 2am or
so though to 2 to 2.5 km. Low level wind convergence becomes
northwesterly with good RH through the layer. With strong gusty
winds continuing overnight, the snow flakes could be ripped apart,
which limits SLR/snow totals, but may act to arbitrarily lower
visibility as is often the case with smaller snow flakes. Given the
combination of moderate to heavy snow and the strong gusty winds
leading to lower visibility, have decided to go with an impact-based
winter storm watch for Berrien, Cass, and St Joseph. With the
falling temperatures, there could be a refreeze problem in areas
that roadways become wet. However, there's also the possibility that
roadways stay dry with these clipper systems having the dry lower
levels allowing for evaporation.
Lake enhancement continues on Thursday as surface high pressure
nudges in. Despite continued northwest trajectories, low level
moisture begins to dry out, but it'll take its time. It likely
continues at a light to moderate pace Thursday with temperatures at
a similar magnitude to this morning, in the teens and low 20s.
Continued northwest flow does look to keep high temperatures below
freezing though. It may take until Thursday evening/night to finally
shut off lake effect snow, though clouds may linger as northwest
flow still continues.
Another clipper system comes through Friday night and Saturday and
that mainly looks to increase winds, but a dry airmass in place
should keep the area devoid of precipitation. Then, with high
pressure setting up across the Gulf of Mexico, it initially
looks like the next system coming in Monday will be rain.
&&
.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1229 PM EST Tue Dec 3 2024
Stayed close to the existing TAFs amid clearing skies and few
near-term weather concerns. However, a low will deepen over the
northern Great Lakes late in the TAF period. This will bring
increasing wind gusts and perhaps a LLWS concern. Precipitation
is delayed until just outside this period, though some MVFR
ceilings could arrive at the terminals late. Higher confidence
in that occuring at KSBN as KFWA could be just east of these
ceilings.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...Winter Storm Watch from Wednesday evening through late
Thursday night for MIZ078-079-177-277.
MARINE...Small Craft Advisory until 4 PM EST Wednesday for LMZ043-046.
Gale Warning from 4 PM Wednesday to 1 PM EST Thursday for
LMZ043-046.
&&
$$
DISCUSSION...Roller
AVIATION...Brown/Skipper
Source:
IWX issues Area Forecast Discussion (AFD) at Dec 3, 3:09 PM EST---------------
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