IWX issues Area Forecast Discussion (AFD) at Nov 25, 1:53 PM EST539
FXUS63 KIWX 251853
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
153 PM EST Mon Nov 25 2024
.KEY MESSAGES...
- A few showers will be possible this evening as a cold front
arrives, but those should depart quickly.
- Cooler air arrives Tuesday, Wednesday, and Thursday with highs
either side of 40 degrees, but even cooler air arrives for
Friday and the weekend with highs struggling to reach 30
degrees.
- Lake effect snow will be possible starting Thursday night
through Friday night and then again Sunday into next week.
&&
.DISCUSSION...
Issued at 149 PM EST Mon Nov 25 2024
A low pressure system is swinging through the area. Cloudy skies and
isolated to scattered showers were observed this morning as low
ceilings and shallow moisture depths limited rainfall amounts and
coverage. As the cold front swings through this evening, expect an
increase to chance PoPs as moisture depths increase and a broad area
of large scale ascent exists associated with the low pressure
center. However, limited instability and relatively dry low to mid
level dew points are expected to limit QPF.
Dry advection takes over behind the cold front and surface high
pressure follows allowing for a dry period between tonight and the
first portion of Wednesday. Clouds are expected to clear out Tuesday
as well. Today's highs in the 50s will be cooler by the time we get
to Tuesday and Wednesday with highs in the upper 30s to low 40s as
cold advection ensues tonight.
Cloud cover returns Tuesday night into Wednesday as a warm front
situates itself across the lower Great Lakes. There is some
uncertainty with how strong the associated low pressure system gets
and therefore how much cold air it is able to wrap into itself
between Wednesday and Thursday. The GFS is suppressed and much
farther south, than the stronger ECMWF solution, with its warm front
as a result. The GFS has been trending northward with its last two
runs and the NAM came in similar to the ECMWF's solution, which
hasn't changed a whole lot over the last couple of runs. As such, am
more inclined to lean towards the ECMWF's handling of the low
pressure system and its sensible weather. However, will lean towards
a low snowfall amount to start here given the marginal
temperature profile. The amount of cold air that wraps in on
the backside also depends on the strength of the initial low
with the ECMWF much colder on its backside. This would also
impact the intensity of cold air for the lake effect signal
starting later Thursday night into the rest of the week
including Thanksgiving.
There is a vort max that dives down across Lake MI Thursday night
and continues to remain in that area in some capacity into Friday
night. This appears to be the best time for lake effect snow with
the highest snow ratios. Even on the more suppressed GFS
soundings, there appears to be mixing up to around 850 mb/1.5 km
and delta T values around 20C, which usually amounts to a low
end lake effect snowfall event.
High pressure cuts off precipitation Friday night. Then, there has
been some signal of a clipper system diving south from the Northern
Plains. Today's 12z runs took that out of the area, but will retain
some slight chance PoPs in case it does bounce back next run. Later
Saturday night into early next week may bring our next lake effect
chance. Plan to use a model blend to handle the PoPs for this
system.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1222 PM EST Mon Nov 25 2024
Little rain to speak of thus far given poor forcing and a
shallow moisture profile. However, an upper-level jet is
forecast to amplify over the state late this afternoon which
ought to improve the chance for rain and subsequent low
ceilings in the wake of an approaching cold front. Increasing
winds behind a cold front, currently located over extreme
eastern Illinois. Cross sections show shallow moisture pooling
beyond daybreak tomorrow giving me some concern that MVFR ceilings
could linger through the day.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 7 PM EST Tuesday for LMZ043-046.
&&
$$
DISCUSSION...Roller
AVIATION...Brown
Source:
IWX issues Area Forecast Discussion (AFD) at Nov 25, 1:53 PM EST---------------
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