Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 112356

Area Forecast Discussion
National Weather Service Northern Indiana
656 PM EST Wed Jan 11 2017

Issued at 654 PM EST Wed Jan 11 2017

Rain showers will become more numerous overnight as a pair of
upper level disturbances begin to interact with a frontal boundary
approaching the region. Foggy conditions can also be expected
through this evening. Rain will continue into Thursday with
conditions drying out from west to east during the day.
Precipitation may end as a brief period of freezing drizzle across
southwest lower Michigan and northwest Indiana on Thursday. Dry
conditions are expected Thursday night through Friday evening.
There is still a good deal of uncertainty regarding freezing rain
chances this weekend, but the greater chances should be confined
to areas along and south of Route 24. Mild conditions can be
expected this evening in advance of the cold front as temperatures
rise through the 40s and 50s, with steady to slowly falling
temperatures for Thursday.


.SHORT TERM...(This Evening through Thursday)
Issued at 342 PM EST Wed Jan 11 2017

Primary forecast challenges for the short term will be rain/iso
thunder tonight, and fog.

Strong low level thetae advection to continue tonight with axis of
highly anomalous moisture working into the area. Low clouds and fog
have overspread approximately southwest half of the area late this
afternoon, with some concern of patchy dense fog over the next
several hours across far southwest/western portions of the area.
Will monitor trends over next few hours for the need for any

In terms of precipitation, a couple of distinct waves to bring
enhanced chances of rain. One of these waves skirting across the
Ohio Valley through early evening will bring greater coverage of
rain across far southeast sections. Another short wave across
northwest Illinois will race across southern lower Michigan this
evening also bringing an increase in rain shower chances. By mid
to late evening a larger scale upstream trough should allow for
strengthening low level frontogenesis forcing in association with
strong baroclinic zone located just northwest of the area. This
should result in an increase in rain showers and a potential of
more impressive rainfall rates late evening into the overnight
hours. Air mass advecting into the area will be characterized by
PWATS in excess of an inch, and concern persists for total
rainfall amounts in excess of an inch and possibly approaching
localized two inch amounts where stronger frontogenesis forcing
materializes. Favored area for these potential heavier rainfall
amounts still appears to be across southeast portions of the area,
roughly along and southeast of the US Route 24 corridor. Some
localized minor flooding will be possible with the corridors of
heavier rainfall, along with continued rises on some area rivers.
Will continue to carry isolated thunder mention into Thursday
morning with weak elevated instability.

Non-diurnal temp trends for this evening with temperatures rising
into the 40s and 50s, and even a chance at extreme south/southeast
making a run at the 60 degree mark for a time. Temps will drop
sharply across the northwest half overnight as frontal boundary begins
to progress through the area.

Rain will continue Thursday morning, with greatest
coverage/intensity across southeast half. One thing that will need
to be watched is the potential of a brief period of light freezing
rain/freezing drizzle across northwest portions of the forecast
area. Low levels should dry out rapidly, but enough moisture beneath
the frontal inversion and shallow cold air could promote a period of
freezing drizzle before precip ends. Temps on Thursday will be
steady to slowly falling.


.LONG TERM...(Thursday Night through Wednesday)
Issued at 342 PM EST Wed Jan 11 2017

Dry conditions will develop by Thursday evening as a very dry
low/mid level air mass advects across the southern Great Lakes
region. A strong low level baroclinic will stall out just south
of the local area as a strong 1045 mb high becomes established
across the Great Lakes.

A rather complicated upper level flow evolution will commence for
the weekend with cut-off upper PV anomaly setting up across
southwest CONUS and a series of smaller scales waves approaching
from the northern stream. Consensus of medium range model guidance
remains suppressed enough with the boundary that icing concerns with
initial warm advection ramp up may not be a big issue as far
north as local area for Friday night/Saturday, but will maintain
chance PoPs for freezing rain mainly across the south. A period of
perhaps greater concern that will need to be watched is for some
time in the Sunday/Sunday night period when a leading stronger
warm advection wing could spread across the area with a risk of
some ice accumulation. Have opted to keep just chance PoPs with
any freezing rain mention at this time given low confidence in
timing and placement of warm advection wing type forcing. Cut-off
PV anomaly to eventually lift across central CONUS early next week
with greater chances of precip for local area, but an eventual
preference to liquid precip type for Monday-Tuesday. Any heavier
rainfall during this period may cause some renewed/aggravated
hydro concerns. Milder temperatures will be in store for the early
portions of next week as this upper PV anomaly approaches.


.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 652 PM EST Wed Jan 11 2017

Gradual improvement through the forecast period as warm sector
becomes more deeply established through the evening hours. Wind
shift detail associated with cold frontal passage and will also
aid to maintain low lifting condensation levels/IFR ceilings
dominant at least until midday Thursday.




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

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