IWX issues Area Forecast Discussion (AFD) at Dec 11, 3:51 AM EST651
FXUS63 KIWX 110851
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
351 AM EST Wed Dec 11 2024
.KEY MESSAGES...
- A reinforcing cold front will result in steady to slowly
falling temperatures this afternoon along with enhancement to
lake effect snow showers later this afternoon into tonight. A
Winter Weather Advisory remains in effect for Berrien, Cass,
and St. Joseph Counties Michigan.
- Wind chills drop into the 0 to 10 degree below zero range tonight
into early Thursday morning.
- Warming temperatures with chances of rain showers for the
weekend.
&&
.DISCUSSION...
Issued at 350 AM EST Wed Dec 11 2024
Only change to winter weather headlines this morning was to push
back onset time of Winter Weather Advisory for Berrien, Cass, and
St. Joseph Counties to 16Z this afternoon. Otherwise, no changes
made to end time and counties included.
Bulk of lake effect snow showers this morning have remained across
west central Lower Michigan. The initial low level baroclinic zone
associated with yesterday's frontal passage is yielding some low and
mid level fgen forcing across far northeast Indiana/northwest Ohio.
Some seeder-feeder process could be enough for a few flurries, but
nothing of consequence is expected with this lagging frontal
forcing. Turning attention upstream, a pair of upper level waves and
an accompanying reinforcing cold front will be the features of
interest heading into this afternoon and evening. A pocket of snow
showers is already accompanying this forcing at the leading edge of
a stronger mid level cold pool. Chances for snow showers will
increase this afternoon as these forcing mechanisms push east.
Some concern that good frontal mixing and mid level forcing and
low level fgen could be enough to generate some gusty snow
showers with rapid drop offs in vsbys this afternoon. However,
this setup is missing a few ingredients from squall setup last
week including strength of fgen forcing, a sharp isallobaric
couplet, and a stronger flash freeze component. Dry mid level
air and also modest nature to fgen forcing could turn this into
a cellular setup also this afternoon into this evening. Perhaps
best chance of snow squall could be across far northeast
Indiana/south central Lower MI/far northwest Ohio late this
afternoon into early this evening (~22Z-02Z timeframe) in closer
proximity to southern fringe of stronger mid level short wave
forcing. Some signal for this period of higher snowfall rates
also shows up in HREF probabilistic guidance. A secondary area
of potential more concentrated snow showers could be across far
southern locations this afternoon/early evening in association
with what could be a slightly more pronounced axis of low level
fgen.
Lake effect snow showers are expected to increase in coverage later
today, especially in wake of the second cold front this afternoon.
Fetch should remain west-northwest throughout the duration of this
event. Coupling this fetch with a background dry mid level airmass,
could yield some challenges in more efficient snow accumulation.
There does appear to be a window of more impressive lake effect
snow shower parameters from 22Z to 06Z this evening as
inversion heights rise sharply with stronger low level vertical
motions nicely aligned with DGZ. 850/750 mb delta Ts also are
also on the order of 20 and 30 degrees respectively during this
period. Inversion heights begin to lower overnight into Thursday
morning, but impacts to the Thursday morning commute across
southwest Lower Michigan still appear likely due to combination
of lingering lake effect snow showers and gusty west winds with
patchy blowing/drifting snow. Perhaps the best thing going for
this event in terms of snow accumulation is just the duration,
which should help to yield 2 to 4 inch accumulations across
southern Lower Michigan (locally higher amounts possible). Of
lower confidence is extent of accumulations south south of IN/MI
stateline. West-northwest fetch would support accumulations to
Toll Road vicinity, but extent of dry air entrainment may limit
these accumulations with southward extent. Will continue to
carry the Winter Weather Advisory from 16Z this morning to 18Z
Thursday.
The other big story with this system will be the transition to much
colder temperatures this afternoon/tonight. The combination of
prevailing west winds 15 to 25 mph and air temps falling into
the teens tonight should yield min wind chills in the 0 to 10
degree below range late tonight into early Thursday AM. Will
issue an SPS this morning to address the cold and afternoon snow
shower potential.
Lake effect snow showers should continue to wind down on Thursday as
lake induced instability wanes and winds exhibit subtle backing in
the afternoon. A highly sheared upper level short wave is
expected to eject east of the Rockies Thursday afternoon with
onset of some low level WAA/fgen forcing due to pre-existing
strong baroclinic zone across the region. Low and mid level
thermal profiles should also "warm" into the DGZ in this warm
advection pattern which could support a band of snow from
central Illinois into west central/northwest Indiana later
Thursday afternoon/night. Moisture quality/depth could be a
limitation, but some light snow accumulations are possible with
what could be a narrow band of snow. Otherwise, it will be quite
cold Thursday with afternoon highs only in the upper teens to
mid 20s.
Upper pattern to become more progressive for late work week into the
weekend. The weekend looks warmer, with indications of another
amplified upper trough approaching with a couple of systems to
bring more precip chances this weekend into early next week. The
first system has exhibited a bit of a slower trend from
previous several guidance iterations and have cut back on
blended PoPs as a result for Friday night, but did maintain
likely/categorical PoPs on Saturday. Can't rule out a brief
period of some mixed precip or light snow at precip onset
Saturday AM, but profiles should quickly transition to
supporting liquid after daybreak Saturday. While a wet period
looks likely first part of weekend, it does appear warmer for
Sat/Sun. Another amplified trough may bring additional rain
chances Monday, but timing of this second trough is of lower
confidence. After the warmer weekend, temps should trend more
seasonable to begin next work week.
&&
.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1256 AM EST Wed Dec 11 2024
Persistent MVFR stratocu deck with lift somewhat as slightly
drier air arrives in advance of the arctic front. Although cloud
cover will persist through the period behind the front, very dry
nature of the airmass is likely to keep cigs in the VFR range
for both sites with the main item being stronger wind gusts. A
lot of uncertainty exists as to impacts along the arctic front
with widely scattered snow showers and briefly reduced vsbys.
Have opted to carry a few hour period at both sites with a
prob30 for lowered vsby. Thereafter, mainly lake effect
snowshowers are expected to kick in, but overall flow suggest
the bulk of the more impactful -shsn will reside north of the
airport. As a result has kept an unrestricted flurry mention for
now.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...Winter Weather Advisory from 11 AM this morning to 1 PM EST
Thursday for MIZ078-079-177-277.
MARINE...Gale Warning from 4 PM this afternoon to 4 PM EST Thursday for
LMZ043-046.
Heavy Freezing Spray Warning from 10 PM this evening to 10 AM
EST Thursday for LMZ043-046.
&&
$$
DISCUSSION...Marsili
AVIATION...Fisher
Source:
IWX issues Area Forecast Discussion (AFD) at Dec 11, 3:51 AM EST---------------
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