Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 130014

Area Forecast Discussion
National Weather Service Northern Indiana
714 PM EST Thu Jan 12 2017

Issued at 712 PM EST Thu Jan 12 2017

Dry conditions are expected overnight through Friday as a ridge
of high pressure builds into the area behind a cold front. Colder
conditions will be in store through the weekend. The next
disturbance will increase chances of freezing rain late Friday
night into Saturday morning, mainly south of Route 30 where some
ice accumulation is possible. A stronger system will approach the
area Sunday night through Tuesday. Precipitation may begin as
freezing rain Sunday night into Monday morning before changing to
rain. The Monday through Wednesday period will feature above
normal temperatures.


.SHORT TERM...(This Evening through Friday)
Issued at 338 PM EST Thu Jan 12 2017

A period of quiet weather in the short term which will be
characterized by colder, more seasonable temperatures.

A surge of much drier low level air will continue to overspread the
forecast area from northwest to southeast this evening with an
eventual decrease in low cloud cover. Could still have a few
scattered flurries or patches of very light freezing drizzle over
the next few hours, mainly downwind of Lake Michigan. No
significant impacts are expected. Mid/high clouds should increase
tonight downstream of broad western CONUS. Much cooler temps for
tonight behind the front with loss of low clouds helping temp
drops. Low levels should remain relatively well mixed however, so
will maintain lows dropping into the lower to mid 20s.

Partly to mostly cloudy skies tomorrow with upstream broad western
CONUS confluence zone allowing for persistent mid clouds. A weak
reinforcing mid level trough across the Great Lakes region on Friday
will allow low level cold advection to persist limiting highs from
the upper 20s north to lower 30s south.


.LONG TERM...(Friday Night through Thursday)
Issued at 338 PM EST Thu Jan 12 2017

An active long term period still looks to be in store for the
Friday night through early next week period with potential of a
few periods of ice accumulation for the weekend, and higher
rain chances Monday-Tuesday.

Complex upper flow pattern to begin the long term period Friday
night with split flow across western CONUS. Cut-off upper low will
linger across southwest CONUS through the weekend, with a series of
northern stream waves expected to track across north central
CONUS/Great Lakes. One of these more distinct waves should eject
out of of the northern Plains Friday evening with an eventual
more veered low level flow developing across the mid MS Valley. An
upstream broad confluence zone associated with this split pattern
will continue to provide strong downstream baroclinicity, which
will allow for periodic enhancement to isentropic/frontogenesis
forcing. Indications suggest at least the potential of a swath of
freezing rain to develop from the mid MS Valley eastward across
approximately southern half of the area late Friday night into
Saturday morning. Given tight thermal packing/moisture gradient
and the fact just subtle changes in upstream forcing will modulate
isentropic/fgen fields, confidence is still somewhat on the low
side in how far north more substantial freezing rain will make it
Fri night/early Saturday. Consider going with some likely PoPs for
freezing rain across the far south for this period, but given
continued spread in guidance will keep at high chance level.
Potential does exist for ice accumulation for this period, and may
eventually need an advisory across the south.

Forecast confidence continues to be on the low side for Saturday
afternoon through Sunday afternoon with distinct possibility that
lull could develop in freezing rain chances with passage of the
initial northern stream wave on Saturday. Next higher potential
impact period still appears to be Sunday night-Monday morning as cut-
off PV anomaly across southwest CONUS begins to emerge across the TX
panhandle. A downstream ramp up of low level jet and strong
thermal/moisture advective push will accompany this evolution with
additional synoptic support via strengthening upper divergence in
western Great Lakes right entrance region of upper jet streak.
Thermal profiles should support a period of freezing rain before
transitioning to rain from southwest to northeast late Sunday night-
Monday morning.

Rain will persist through Monday-early Tuesday as the Texas upper
trough ejects northeast with another period of anomalous PWATS (in
excess of an inch) advecting into the area. Will have to watch rain
amounts this period with a potential of some renewed river rises.
Otherwise, bulk of the long term period should be above normal
temperature wise, with no immediate arctic intrusions on the horizon.


.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 711 PM EST Thu Jan 12 2017

Improving ceilings to VFR by late tonight/early Fri morning as
drier/subsident airmass continues to build into the Upper Great


LM...Small Craft Advisory until 4 PM EST Friday for LMZ043-046.



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

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