Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 152336
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
636 PM EST Sun Jan 15 2017

.SYNOPSIS...
Issued at 316 PM EST Sun Jan 15 2017

Mainly dry conditions are expected to continue overnight, but
chances of precipitation will increase across portions of
northwest and north central Indiana later tonight into Monday
morning as a warm front begins to lift northward. A brief period
of light freezing rain is possible Monday morning before
precipitation changes over to rain. Rain will become more
widespread by Monday night with even an isolated thunderstorm
possible. Rain will diminish in coverage by Tuesday as this system
begins to pull off to the east. Mild conditions will work into the
area Monday night, with slightly cooler conditions mid week before
much above normal temperatures return for next weekend along with
periodic chances of rain.

&&

.SHORT TERM...(This Evening through Monday)
Issued at 316 PM EST Sun Jan 15 2017

Potential of brief light freezing rain late tonight into Monday
morning and then more widespread rain chances from Monday
afternoon through Monday night will be the main forecast
challenges in the short term.

Forecast area remains on dry side of sharp low level moisture
gradient this afternoon which extends from west central Illinois
into west central Indiana. The broad low level anticyclone across
the Great Lakes/northeast CONUS which has been responsible for the
dry weather over past 24 hour will slide southeast to the mid
Atlantic states Monday afternoon. Southwest low level flow will
very gradually ramp up this evening as this high departs allowing
the low level thetae gradient to progress northeast, but flow
across this gradient will remain relatively weak through most of
the early overnight hours. Outside of advective forcing, mid/upper
level synoptic forcing continues to appear to be on the meager
side. AMDAR soundings/regional RAOBs from this morning indicated
very dry sub mid cloud layers which will take some time to
saturate tonight. Without that additional mid/upper level synoptic
forcing, confidence in measurable precip is low through most of
the night, although have not made substantial changes from
previous forecast in ramping up PoPs to mid chance toward morning
across the west where slightly stronger isentropic ascent is noted
on 290K surface. With overall weak low level flow, profiles
conducive for freezing rain may be of relatively short duration as
evaporative cooling results in isothermal tendencies in low/near
sfc levels toward daybreak before stronger advection occurs after
12Z Monday taking entire thermal profiles above freezing. A brief
period of light icing still appears to be a possibility but with
sfc temperatures expected to rise to close to the freezing mark
close to daybreak and anticipated very light nature to precip,
confidence remains very low if there will be any impacts. Thus,
will hold off on any headlines at this time. Will have to watch
the far northwest where stronger isentropic forcing is expected,
along with extreme northern Indiana/southern lower Michigan where
maintenance of shallow cold layer may be slightly prolonged.

Precipitation to change to rain from south to north Monday with
greatest coverage across the west, and eventual higher coverage
spreading across remainder of the forecast area Monday night as
the cut-off upper trough lifts northeast across the Mid MS Valley.
An impressive 1+ inch PWAT axis will advect across the area Monday
night aided by a 50 knot south-southwesterly low level jet. One
potential area that mix may hold on longer into Monday
afternoon/early evening is across the very extreme northeast where
some southeast trajectory to near sfc flow holds a bit longer.
Have also maintained isolated thunder mention with some weak
elevated instability. The other story Monday will be the
temperature trends, and sharply rising temps by Monday evening as
warm front advances into the area taking temps into the 50s across
the southeast. Fog may also become an issue later Monday night
across the north as very moist air mass overspreads the forecast
area.

&&

.LONG TERM...(Monday Night through Sunday)
Issued at 316 PM EST Sun Jan 15 2017

Low level thermal ridge will be shifting east of the area Tuesday
morning as sfc reflection tracks across southern lower Michigan.
Precip coverage should diminish through the morning as mid level
dry slot advects across the area. Fog may linger into Tuesday, and
could have some lingering patchy drizzle or light rain into
Tuesday afternoon. A secondary upper trough will approach from the
mid MS River valley Tuesday night which could prolong some low
coverage rain/snow chance as deeper moisture profiles may be
briefly aided by this next upper trough and mid level moisture
wrapping around departing upper trough.

Wednesday will be a transition today as low level thermal troughing
begins to depart to the east with local area becoming positioned in
upper level inflection zone. The remainder of the week will feature
a steady warming trend to much above normal temperatures by Thursday
and Friday with highs from upper 40s to lower 50s on Friday.
Periodic rain chances can be expected Friday through next weekend as
a western CONUS trough/eastern CONUS ridge longwave pattern becomes
established with a potential of several embedded waves approaching
in southwest upper flow. This flow pattern should also support very
mild temps by next weekend with highs in the 50s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
Issued at 632 PM EST Sun Jan 15 2017

Continuing with the high clouds/VFR conditions into the overnight.
With low pressure approaching from the south, precipitation chances
will be on the increase Monday morning, however think dry air will
be a problem for morning precipitation. Best time for freezing rain
would be from 12z to 16z, however, still think that dry air will be
able to eat into that. Have gone with a VCSH to cover that time
period. Thereafter, as the upper low from the southwest gets closer
to the Great Lakes during early afternoon, feel enough moisture will
be around the region for precipitation and it may be raining hard
enough to reduce VISBY some as well.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...Marsili/Roller
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...Roller


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