Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 170542

Area Forecast Discussion
National Weather Service Northern Indiana
1242 AM EST Sun Feb 17 2019

Issued at 645 PM EST Sat Feb 16 2019

Cloudy skies will persist tonight with low temperatures into the
20 to 25 degree range. An upper level system will bring light
snow Sunday with amounts from an inch to around 3 inches. Highs
Sunday will be near 25 to 30. Monday and Tuesday should be mainly
dry with highs from the upper 20s to middle 30s.


Issued at 901 PM EST Sat Feb 16 2019

Just minor tweaks for the evening update for tonight. Latest
flight data indicates relatively thin but stubborn saturated layer
across northeast Illinois/northwest Indiana persisting. Gradual
veering of low level winds overnight to the southeast may tend to
erode this deck from south to north, but the window of any
clearing looks to be short-lived if at all in most locations as
stronger low level moisture advection works in overnight. Thus,
have increased sky cover tonight. Some increasing signals in
guidance of conditional symmetric instability for Sunday that
could yield an interesting evolution to snow, and some potential
for banded snow. No change with respect to tomorrow`s accumulating
snow and will continue to mention 1-3" accumulations. Primary
forcing mechanisms are progressive with eventual dry slot
intrusion late afternoon/evening. May have to watch for narrow
window for enhanced snow rates with some banding potential,
particularly within the 16Z-22Z window that could yield some
rather non-uniform distributions to total snow accumulations by


.SHORT TERM...(This Evening through Sunday)
Issued at 324 PM EST Sat Feb 16 2019

An upper level trof will eject out of a very large upper level low
over western North America and move across the Upper Midwest. This
system will bring a chance for snow to the forecast area. There
was still a fairly large range among models in handling this system,
especially precipitation amounts. Isentropic moisture per 295K
surface was impressive with adequate mixing ratios around 3 g/kg.
Given a very strong 200+ knot upper level jet with favorable jet
dynamics, have raised snow amounts up to around 3 inches,
especially over far northern Indiana into Lower Michigan in the
vicinity of the left exit of the jet. Otherwise, snow will end
Sunday night with lows dropping to around 20.


.LONG TERM...(Sunday Night through Saturday)
Issued at 324 PM EST Sat Feb 16 2019

The upper air pattern depicted by the bulk of the models for this
upcoming week has been consistent during the past 48 hours
indicating a persistent trof along the west North American coast
and ridging along the Gulf Coast. Smaller scale upper trofs will
eject out of the large dominant upper trof and may be able to tap
some moisture for snow by the middle of the week. Thermal profiles
will moderate allowing a rain/snow mix Wednesday north of the
Ohio river reaching north from near Marion to Portland. However,
by far, the bulk of the rain with this system should stay well
south of the region where flooding rains are eventually likely.
Timing of this next system looks favorable from late Tuesday into
Wednesday night. Heavy snow is not expected with this system at
this time.


.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
Issued at 1242 AM EST Sun Feb 17 2019

Models continue to have a poor handle on thin stratus deck
blanketing the area. Forecast soundings suggest some thinning may
be possible later this morning but confidence is low and suspect
fuel alternate ceilings will persist through much of the period.
Light snow will spread over the area by the afternoon with
previous timing still in good shape. IFR visibilities likely
during the afternoon and IFR ceilings are also possible during the
evening and overnight. A period of freezing drizzle is also
possible during the evening but will hold off on any mention in
the TAF`s for now.




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

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