Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 051740

Area Forecast Discussion
National Weather Service Northern Indiana
1240 PM EST Mon Dec 5 2016

Issued at 1235 PM EST Mon Dec 5 2016

Clouds will linger through tonight with areas of fog possibly
developing tonight in areas where snow remains. A weather system
will spread some rain across the area Tuesday, with the greatest
coverage expected along and east of the Interstate 69 corridor. A
brief period of some light snow is possible at onset on Tuesday,
but little or no snow accumulation is expected. Much colder air
will spread over the area Thursday with lake effect snow
developing. Highs will be in the 30s through Wednesday, then in
the 20s Thursday and Friday. Lows will be around 30 tonight then
falling into the teens later this week.


Issued at 1053 AM EST Mon Dec 5 2016

Near term challenges will continue to center on temp trends and
fog potential. Downward trends in vsbys have been noted west of
the forecast area across much of northwest and north central
Illinois in association with better snowpack. As low level
anticyclone progresses eastward this afternoon, some concern that
fog could spread eastward, particularly across far northwest
portions of the area. Currently not expecting any dense fog at
this time and may need to add mention of patchy fog with late
morning update. Perhaps better potential of fog for particularly
northwest half of the area for tonight as slightly better near sfc
moisture wraps into the area on northwest periphery of this
anticyclone, with some effects from lingering snowpack. Otherwise,
a very strong low level inversion should persist through the day
keeping low clouds in place. Temps not likely to recover much,
especially across snow covered areas where highs at or just above
freezing are more likely. May need to make a slight downward
adjustment in temps for a few spots, but otherwise trends from
previous forecast remain intact.


.SHORT TERM...(Today and Tonight)
Issued at 422 AM EST Mon Dec 5 2016

Have maintained a mention of some fog today over west areas,
mainly west of highway 31 given some of the high resolution/WPC
models and upstream fog development over western Illinois. Given
abundant cloud cover and some fog, have cut high temps a few
degrees over these areas. Otherwise, the cloud cover will linger
through tonight. Some light precipitation is possible late tonight
over southern areas ahead of the next system. It looks like any
travel issues through tonight should be at a minimum given
temperatures holding near freezing tonight.


.LONG TERM...(Tuesday through Sunday)
Issued at 422 AM EST Mon Dec 5 2016

A number of weather systems this period are expected to produce a
variety of weather across the forecast area through this week.
An upper low will eject northeast Tuesday. This system will become
more of an open wave then earlier expected and track farther
southeast than earlier expected. This will limit precipitation
Tuesday. Given this track, and thermal profiles, continued to
trend back snow accumulations. The limited upper motion and a warm
layer will also limit snowfall. At this point, some light wet snow
accumulations are possible over mainly grassy areas Tuesday.

Much colder weather will follow Thursday. The ECMWF continues a
weakening of the wave and subsequent snow Wednesday night. Kept a
small chance of snow with this system before much colder air arrives
Thursday. Lake effect snow will develop Thursday as much colder air
spreads over the relatively warm waters of Lake Michigan.  Delta T
values over 20C at 850 mb with a northwest flow will favor snow
accumulations over far southwest Lower Michigan into northwest
Indiana. Lake effect snow will diminish from late Friday into early
Saturday as winds back to the southwest.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 1229 PM EST Mon Dec 5 2016

Satellite/obs trends show stratus will likely hold strong with
limited hope of at least partial clearing. A few of the high res
models have been persistent on cigs lowering somewhat tonight, but
more with visibilities dropping to LIFR at KSBN and more MVFR at KFWA.
Other models show little or no impact, likely from mixing below
the inversion. Will be a tough call how this unfolds with winds in
the 5 to 8 kt range not normally the most conducive to fog
development. After coordination will introduce fog tonight,
dropping to 3/4SM at KSBN at times to start a trend and more
conservative 3 miles at KFWA.

Next system will be arriving on Tuesday, keeping clouds in place
with some precip chances at mainly KFWA. For now have left any
mention out.




SHORT TERM...Skipper
LONG TERM...Skipper

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