Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 290108

Area Forecast Discussion
National Weather Service Northern Indiana
908 PM EDT Wed Jun 28 2017

Issued at 335 PM EDT Wed Jun 28 2017

A few light showers and storms are possible across northwest Indiana
and southwest Michigan tonight but a much better chance of rain is
expected Thursday evening and Friday. Some of these storms may be
severe with damaging winds and heavy rain possible. Drier and less
humid conditions are anticipated over the weekend.


Issued at 855 PM EDT Wed Jun 28 2017

Minor changes on latest short term update. Svr bow echo movg east
across nrn IL should make a run toward far nw portion of the cwa
late this eve, but still expect a diminishing trend as convection
moves into stable airmass over IN/MI. Only sgfnt change to
previous grids was to move up timing of pops into the late evening
hours. Given bowing structure of storms and strong wind field in
place, there is a potential for some strong winds if dissipating
storms reach the nw late this eve, though svr wx still not
expected tonight.


.SHORT TERM...(This Evening through Thursday Night)
Issued at 335 PM EDT Wed Jun 28 2017

Impressive shortwave entering the western Lakes starting to dampen
and lift more ENE amid general longwave ridge building. Healthy
LLJ/theta-e surge ahead of this wave but best moisture flux
convergence focused generally NW of our area with models indicating
a relative theta-e sink across IN and OH through the evening.
Earlier convection tried to make a run at our western CWA but
withered quickly as it divorced from better convergence and
associated moisture/instability plume. A few decaying showers in our
far NW but by and large expect dry conditions through the evening.
Another chance for rain will arrive in our NW after 06Z tonight. LLJ
continues to veer and support a little better moisture in our N/NW.
Another round of decaying showers/storms possible along remnant
convergent boundary. However, moisture quality still somewhat
questionable with limited MUCAPE and lack of coherent forcing with
increasingly diffuse boundary. Maintained some low chances in north
but made further cuts based on latest hi-res CAM`s and underlying
setup. No severe threat.

Better chances for storms, potentially severe, arrive late Thursday.
Next shortwave approaches by that time with old stationary boundary
draped generally along the I-80/90 corridor and ample moisture
streaming into the region in SW flow. The synoptic picture is a
little muddled with persistent convection upstream ejecting multiple
shortwaves into our area. Assuming morning convection dissipates as
expected, tomorrow will be largely dry during the day with enough
sun (and more importantly, rising surface dewpoints) to generate
around 2K J/kg of SBCAPE. 70F dewpoints seen in raw guidance quite
possible given support from MOS guidance. Wind/shear profiles also
supportive of severe weather with 850mb flow of 30+ kts and 0-6km
shear values around 30 kts. Wind/shear profiles oriented generally
parallel to the front, indicating some bowing segments with damaging
winds possible if more sustained updraft develops. Isolated heavy
rain/flooding also a concern given orientation of the front,
potential for training, relatively low MBE velocities, and PW values
around 1.75 inches. However, confidence is still not high on
severe/flooding threat. Best chances don`t arrive until late (after
21Z and potentially as late as 03-06Z when diurnal instability is
waning) and there is a weak cap noted in both GFS and NAM soundings
around 750mb. Forcing is also a bit dubious, predicated on
convectively enhanced wave ejecting out of the High Plains with
otherwise fairly broad convergence. Track of any potential organized
convective system also uncertain with higher resolution models
offering disparate solutions regarding the finer-scale details.


.LONG TERM...(Friday through Wednesday)
Issued at 335 PM EDT Wed Jun 28 2017

Friday expected to be equally, if not more, busy. Main longwave
trough inches closer with another convective shortwave ejecting into
our area. Moisture quality remains high and could see another 2K
J/kg of SBCAPE by late afternoon with healthy wind/shear profiles.
Problem is that uncertainty with regard to Thursday night leads to
compounding uncertainty for Friday. Some solutions suggest
rain/clouds may persist through Friday morning with limited
opportunity to recover. Others suggest dry conditions during the day
with ample destabilization and healthy line of convection during the
evening. Lean toward the latter solution given approaching
trough/better synoptic forcing signal but will have to get through
Thursday first before anything definitive can be said. If severe
weather does occur, looks like it would be in the 21-03Z period with
damaging winds the main threat.

A few (non-severe) showers and storms may persist into Saturday,
especially in our east but expect a gradual drying trend as broad
trough axis passes and NW flow/negative theta-e advection slowly
ramp up. Highs will still be near 80F but do expect a significant
drop in dewpoints that will make it feel cooler. Chances for
showers/storms return around the 3rd-4th as moisture plume creeps
back north and multiple shortwaves approach. Still much too early to
nail down any timing details though.


.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 717 PM EDT Wed Jun 28 2017

Main concern is potential for tstms this taf period. Bkn line of
storms from srn WI to srn IA this eve on s-sern fringe of shrtwv
movg east across MN. This wk forcing should move across nrn IN
late tonight, but stable airmass over IN should persist through
that timeframe, so strongest storms will likely propagate south
along ern fringe of instability axis through the mid MS Valley
with just wk convection perhaps surviving into nwrn IN. Veering
LLJ should transport increased low level moisture into our area
by tomorrow morning and combined with diurnal heating result in
moderate instability in the aftn. Wk forcing/capping inversion
limiting convective potential hwvr, so no mention of tstms in tafs
for the aftn. Otrws, vfr conditions should persist with vsbys
>6sm and mainly mid/high clouds tonight and a bkn cu deck dvlpg


MI...Beach Hazards Statement through Thursday afternoon for MIZ077.

LM...Small Craft Advisory until 2 PM EDT Thursday for LMZ043-046.




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