Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 212319

Area Forecast Discussion
National Weather Service Northern Indiana
619 PM EST Mon Jan 21 2019

Issued at 405 PM EST Mon Jan 21 2019

Very cold conditions will start the night but temperatures will
become steady or slowly rise overnight. Gusty south winds will
bring warmer air north on Tuesday. An approaching storm system
will bring a wintry mix Tuesday afternoon into early Tuesday
evening before precipitation changes to rain Tuesday night as
temperatures warm above freezing. Some patchy drizzle and
freezing drizzle will continue into Wednesday as colder air begins
to build back in. Another intrusion of very cold arctic air is
expected by Thursday and Friday with additional chances of snow
and lake effect snow showers.


.SHORT TERM...(This Evening through Tuesday)
Issued at 405 PM EST Mon Jan 21 2019

Main concerns for the short term period will continue to be
retreat of arctic air mass tonight into early Tuesday followed
by potential of wintry mix later Tuesday afternoon into Tuesday

Arctic high pressure centered across the Great Lakes/Ohio Valley
this afternoon will continue to slide off to the east tonight with
strengthening gradient from west to east. Temperatures have
struggled this afternoon despite good deal of sun due to snow
cover and very poor mixing. Big question this evening will be
magnitude of temperature drops this evening, particularly eastern
half of the area where the gradient will be weaker for the longest
duration. By late evening into the overnight, high clouds will
increase from the west which should also couple with the stronger
gradient to level off temperatures and result in a steady or
slowly rising trend for the overnight. Current forecasted
temps/winds do have a window from early this evening through
midnight with wind chills as cold as 15 below zero, especially
along and east of Interstate 69. Given expected relatively brief
duration to wind chills to these levels, will hold off on advisory
at this time. After 06Z. air temps/wind chills should be on a
slow upward trend (with earlier onset to steady/slowly rising
trend across the west).

Attention on Tuesday shifts from bitterly cold temps to wintry mix
potential. Large scale upper level trough across western CONUS
will tend to emerge in a couple of pieces through mid week. A
neutral to slightly positively tilted upper trough will lift
across western Great Lakes Tuesday night while additional energy
digs across southern Plains. A strong southwesterly low level jet
will develop in advance of this features during the day Tuesday.
Strong positive low level theta-e advection/moisture convergence
will accompany this jet. Primary item of forecast uncertainty
remains on response to near sfc/sfc/and pavement temps as this
strong low level warm advection occurs. A period of mixed snow,
sleet, freezing rain is expected, although for a shorter duration
for southern half of the forecast area. Greatest concern for
travel impacts and slick roads should be across the north where
sfc/near sfc conditions could remain colder for a longer period
into early Tuesday evening. Have continued to play it fairly
conservative with ice accumulations. Did contemplate headlines for
late Tuesday afternoon/evening, but lower confidence in near sfc
and pavement temps/impacts have nudged toward just a continued
mention in weather stories/HWO. Winds will also be gusty on
Tuesday/Tuesday evening with southerly gusts to 25-30 mph

Milder air continues to advect northward Tuesday evening
eventually transitioning precip to all rain even across the north.
Some decent liquid equivalents are possible given good moisture
transport and strengthening frontal response in advance of
positively tilted short wave. This could cause some ponding of
water on roads into Wednesday when considered with some melting
snow. Deeper moisture shifts eastward on Wednesday with some
concerns for lingering drizzle/patchy freezing drizzle as colder
air pushes into the area.


.LONG TERM...(Tuesday Night through Monday)
Issued at 405 PM EST Mon Jan 21 2019

Not much change for the extended period with biggest weather story
transitioning to another arctic blast late in the work week.
Temps/wind chills will likely plummet to similar values observed
early this week. Lake effect snow showers will also become
increasingly likely for much Thursday through weekend period.
Pattern this weekend into early next week should also favor
potential of several clipper-type systems with low predictability
at this forecast distance.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
Issued at 611 PM EST Mon Jan 21 2019

VFR through at least mid afternoon Tuesday before conditions begin
to deteriorate. Winds will slowly increase through the night from
the southeast and become gusty Tuesday morning. Increasing
moisture ahead of next system will likely bring a mix of snow,
freezing rain and even some sleet initially late Tue afternoon,
primarily at KSBN. Pcpn likely to hold off until near or just
after 00z at KFWA so no inclusion there at this time. Pcpn should
change over to just rain as sfc temps slowly rise above freezing
but this will not be until just after the valid period of this
package Tuesday evening.


LM...Small Craft Advisory from 10 PM this evening to 5 AM EST
     Thursday for LMZ043-046.



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

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