Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 162032

Area Forecast Discussion
National Weather Service Northern Indiana
332 PM EST Fri Feb 16 2018

Issued at 331 PM EST Fri Feb 16 2018

Clearing skies expected tonight with lows in the mid teens to lower
20s for most locations. Highs tomorrow will be in the mid to upper
30s. There is a chance for light rain or snow Saturday evening but
little to no snow accumulation is expected. Much warmer and wetter
conditions then expected Monday through Wednesday. Highs will climb
into the 60s for many locations with several rounds of moderate
rain. Given recent wet conditions...this could cause additional
flooding on area rivers next week.


.SHORT TERM...(This Evening through Saturday)
Issued at 331 PM EST Fri Feb 16 2018

Tranquil weather will persist through most of the day tomorrow as
surface high pressure slides across Ohio Valley in wake of exiting
shortwave. Shortwave presently crossing MI and some marginal lake
instability generating a few flurries at times in our far NW zones.
There will be no accumulation and even flurries will taper by late
evening as winds back, dry air advection increases, and subsidence
builds. Expect a sharp drop in temps this evening with clear skies
and light winds but should level off by late tonight as ridge passes
and southerly gradient picks up a bit. Latest raw and MOS guidance
has trended slightly warmer. Did nudge lows up a bit but stayed on
the cool side with good radiational cooling potential in the
evening. Anticipate mid teens in far north to low/mid 20s in S/SE.
Highs tomorrow will be similar to today, if not a touch warmer.
Clouds will return ahead of next system though.


.LONG TERM...(Saturday Night through Friday)
Issued at 331 PM EST Fri Feb 16 2018

Next shortwave arrives late Sat afternoon and overall forecast has
not changed much. Best moisture convergence and isentropic lift will
remain locked well to our south with lead wave. Secondary wave
encounters a much drier and more stable environment across our area
with left entrance upper jet placement for most of the day. Have
therefore delayed PoPs considerably with our best and only chances
for precip with broad convergent boundary passing around 00Z.
Forecast soundings show no more than a 2-3 hour window with deep
enough saturation for measurable precip at any one point. Even that
is tenuous with weak forcing and highly limited moisture. Kept
chance PoPs but did reduce the time window on the back edge as well.
Precip types continue to be a mix of rain and snow with surface wet
bulbs right around freezing. Little/no accumulation or impact

Very brief and minor shot of CAA Sat night with strong SW flow/WAA
developing Sunday ahead of western CONUS longwave trough. Sunday
will remain dry, relatively warm, and at least partly sunny, but
real warm/moist air advection kicks in Monday. Deep southwest flow
and a long period of efficient moisture transport will send PW
values well over an inch (near 1.5 by Tue). Very good chance of rain
Mon morning with initial theta-e surge. Will probably see a bit of a
break thereafter before second main surge arrives Tue-Wed with
frontal zone slowly sagging SE. Potential for several inches of rain
over this 3-day period and river flooding is a concern given recent
rain and snowmelt. Still a lot of uncertainty regarding
timing/evolution details with slower/wetter solution still being
championed by the 12Z ECMWF. Will continue to watch this period
closely. Seasonably cool and dry immediately thereafter but
additional rain chances toward the end of next week as active W/SW
flow pattern continues.


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1220 PM EST Fri Feb 16 2018

Latest visible satellite imagery depicting persistent post frontal
strato-cu that will continue to bring MVFR cigs to KSBN this
afternoon. Leading edge also approaching KFWA so will introduce a
brief tempo group to start the TAF cycle. Large scale subsidence
associated with high pressure building into the region this evening
should scatter/clear skies overnight and NW winds will diminish to
light and variable. High clouds will begin overspreading the region
on Saturday as frontal wave moves into the TN valley. High pressure
quickly exits to the east and will back winds around the the south
but less than 10kts in presence of fairly weak gradient.





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