Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 181642

Area Forecast Discussion
National Weather Service Northern Indiana
1142 AM EST Thu Jan 18 2018

Issued at 330 AM EST Thu Jan 18 2018

Mostly sunny skies and moderating temperatures can be expected
today. High temperatures this afternoon are expected to range from
the mid 20s to lower 30s. Quiet weather will continue tonight into
Saturday, but rain chances will begin to increase Saturday night
into Sunday. Rain will become more likely for Sunday night into
Monday as a stronger system approaches the region. The moderating
temperature trend will continue into the weekend with highs on
Saturday near 40, warming to the mid and upper 40s by Monday.


.SHORT TERM...(Today and Tonight)
Issued at 330 AM EST Thu Jan 18 2018

Quiet weather for the short term period, with the main weather story
centering on moderating temperature trend, that will continue
through Monday.

In the near term, a very weak mid level wave in northwest flow
across the Great Lakes will produce some scattered high/mid clouds
across the far north but this morning, but mainly mostly sunny
skies are in store for today. A more vigorous upper level short
wave across northeast ND/southern Manitoba will maintain a track
north of the area, but west-northwest low/mid level regime will
continue for the local area as this wave tracks to the north. This
flow off high Plans terrain will enhance west-east oriented
thermal ridge as it sags east-southeast across the southern Great
Lakes later this afternoon. Snowpack and sharp low level inversion
will offset this warm advection to a large extent, but magnitude
of thermal advection alone, even with shallow mixing, should
support highs in the upper 20s to around 30. Given competing
effects, confidence in high temp forecast today a bit lower than
normal for period 1. Despite shallow mixing, fairly strong
gradient today should support southwest winds of 10 to 20 mph with
gusts to around 25 mph.

Short wave ridging pushes back across the area tonight in wake of
short wave tracking across the northern Great Lakes which will
provide continued quiet weather. Modest gradient persisting tonight
and transition to more neutral temp advection pattern will result
in limited diurnal ranges, with lows only dropping into the upper
teens to lower 20s.


.LONG TERM...(Friday through Wednesday)
Issued at 330 AM EST Thu Jan 18 2018

A ridge-riding short wave across southwest Canada will result in
subtle backing and strengthening low level southwesterlies again by
Friday allowing a continuation of moderating temperature trend.
Temps across most of the area should rise above freezing on
Friday. With this wave tracking well north of the area leaving
zonal flow behind for Saturday, associated cold frontal boundary
will stall and remain north/northwest of the local area,
providing even milder conditions for Saturday with highs
approaching 40. Rain chances creep up for Saturday night/Sunday as
advective forcing begins to increase. Profiles may be marginal for
light rain/drizzle vs light freezing rain/drizzle concern across
far north for a brief time Saturday night, but given only chance
probs and no expectation of any impacts at this time, will keep
mention as liquid.

The feature of interest that will be tracked for late weekend is a
southern stream trough that will dig across Four Corners region
late Saturday night before ejecting northeastward for later
Sunday. A strong low level jet will provide the strongest
warm/moist transport of the period for later Sunday night into
Monday. While most all areas should receive measurable rain late
weekend into Monday, subtle timing/strength discrepancies make it
a little difficult to pin down the optimal 6 hour period for
highest PoPs. EC/GEM operational runs remain a bit slower in
lifting upper height minimum northeast across the Central
Plains/Mid MS Valley Sunday night, with operational GFS appearing
to be a fast outlier. 00Z GEFS means do exhibit just a slightly
slower evolution, but not nearly as slow as GEM/EC cluster. At
this time, hedging on a compromised solution of these two camps,
with slight preference to slower solution given ensemble mean
tendencies, and historically some bias to eject these amplified
systems out too quickly. Will keep broadbrush high end likely PoPs
going for late Sunday night through Monday, and categorical PoPs
probably needed once this spread diminishes. Some decent rainfall
amounts are possible but progression of this forcing and
relatively short duration of narrow deeper moisture plume should
provide a limitation.

Strong cold advection to overspread region later Monday/Monday
evening as system occludes northwest of the area. Rain showers
should change to snow showers, with TROWAL remnants working across
Great Lakes region late Monday night into Tuesday. Some light
snow possible across the area late Monday into Tuesday as this
system departs, with best chances downwind of Lake Michigan due to
juxtaposition of wrap around moisture/lake enhancement. With deep
sfc cyclone northwest of the area, and increasing mixed layer
depths with onset of CAA Monday, may need to watch wind speeds
Monday afternoon/evening with early indications suggesting some
gusts to 30 to 40 mph a possibility depending on track/strength.
Strong subsidence/drying anticipated for later Tuesday in wake of
this trough, and remainder of the extended period will be marked
by possibility of smaller scale progressive waves affecting the
area. Moisture availability may be in issue however, and will keep
all PoPs of the low chance variety for the end of the period.
After highs in the mid-upper 40s Monday, temps will cool back to
near seasonal normal for Wed-Thu.


.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1131 AM EST Thu Jan 18 2018

VFR conditions will persist through the TAF period as a large high
pressure area drifts across the Gulf states. The pressure gradient
between this system and a developing surface low over south
central Canada will keep brisk southwest winds over northern
Indiana. Have continued a low level wind shear group given in
response to these factors.




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

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