Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 171741

Area Forecast Discussion
National Weather Service Northern Indiana
1241 PM EST Wed Jan 17 2018

Issued at 352 AM EST Wed Jan 17 2018

Drier and warmer conditions will dominate the remainder of the
week into Saturday, before rain chances return. Afternoon highs
today will reach the upper teens to lower 20s. Highs by the
weekend will climb into the 40s.


.SHORT TERM...(Today and Tonight)
Issued at 352 AM EST Wed Jan 17 2018

Lake effect snow showers are ongoing this morning across eastern La
Porte, western Berrien, and western St. Joseph IN counties. A
positively tilted upper level trough from the eastern Great Lakes to
the Ohio Valley will continue to push eastward this morning with
ensuing mid level height rises across the western Great Lakes.
Backing low level winds on northeast periphery of low level
anticyclone across the Plains has also allowed for better dry air
entrainment early this morning. Lessening fetch and intrusion of
drier low/mid level air should result in continued diminishing
intensity of the lake effect snow showers, with just an inch or
two of additional accumulation through 14Z. Will drop Starke
county from the advisory, and may be able to drop the winter
weather advisories before the 12Z expiration for Berrien/La Porte.
Otherwise, remnant lake effect stratocu/light snow showers likely
to drift across northern Indiana/southern Lower Michigan this
morning with a band of mid level cloud then expected to drop
southeast across the region this afternoon. Temperatures somewhat
tricky today with uncertainties in mixed layer depth given snow
cover/shallow arctic air/inversion. Modest gradient should be
maintained today with onset of low level warm advection, that
should allow temperatures to crack the 20 degree mark most
locations, although if poorer mixing does materialize, could be
capped in the upper teens for highs.

Low level height gradient will strengthen a bit tonight as low
level anticyclone sags southeast across the Lower MS Valley. This
gradient combined with continued low level warm advection should
keep lows in the teens tonight, although steady west-southwest
winds of 10 to 20 mph will produce wind chills right around zero.


.LONG TERM...(Thursday through Tuesday)
Issued at 352 AM EST Wed Jan 17 2018

A more notable warm up in store for Thursday as strong westerly
low/mid level flow in lee of Rockies allows west-east oriented low
level thermal ridge to nose across the southern Great Lakes. Low
level inversion will be sharpened with this warm advection, which
will of course limit extent of surface warming, but upper 20s should
be attainable for Thursday afternoon with mainly sunny skies. Short
wave mid/upper ridging to migrate eastward across the Great Lakes
region through the end of work week, keeping quiet/dry weather in
place with continuation of moderating temperature trend through the

The main feature to monitor for the long term period will be
amplified southern stream trough emerging across southwest CONUS in
split flow eastern Pacific pattern. Warm/moist advection to become
more dramatic for the Saturday night-Sunday period as a strong low
level jet allows pronounced low/mid level theta-e ridge to work
across Ohio Valley/southern Great Lakes. With limited moisture depth
initially Saturday evening, precip may be more drizzly in nature.
Sfc/near sfc wet bulbs should remain just warm enough even at precip
onset for liquid on Saturday night, and at this time not
anticipating any p-type issues of consequence given strength of
advective fields. Could have some patchy fog issues to contend with
as this air mass overspreads lingering snowpack across the area, but
still some question as to how much snowmelt will occur before this

Large scale upper support increases more dramatically for the Sunday
night/early Monday period as southern stream trough lifts northeast.
Guidance overall in fairly good agreement in this scenario with
expected subtle timing/strength differences. Rain/categorical PoPs
still look reasonable for this period. Fortunately, the progression
of the forcing should be enough to limit rainfall amounts.
Temperatures to become mild this weekend in advance of this trough,
with mid-upper 40s highs by Sunday. Some phasing of this southern
stream with south central Canadian trough should slow this negative
upper height anomaly across northern Great Lakes/Ontario for
Monday night/Tuesday, with broad wrap-around precip region likely
persisting across the region. Some light snow accumulations
possible with broad deformation area/TROWAL lingering into Monday
night. Monday could end up being a fairly windy day depending on
track/strength of associated sfc reflection as sfc cold advection
commences in occluded portion of cyclone. Did keep in some low
snow shower PoPs Tue-Wed next week with some indications of
additional lower amplitude waves interacting with baroclinic zone
across the region, but confidence quite low at this forecast
distance given smaller scale of these waves.


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 1237 PM EST Wed Jan 17 2018

High pressure will dominate conditions through the period with
little more than some passing high clouds. Southwesterly winds
will persist and may become gusty late in the period through after
18Z Thurs.




SHORT TERM...Marsili
LONG TERM...Marsili

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