Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 300446
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1246 AM EDT Thu Mar 30 2017

.SYNOPSIS...
Issued at 1237 AM EDT Thu Mar 30 2017

Scattered showers across the area will become more numerous
overnight and Thursday as a low pressure system approaches from
the southern plains. Thunderstorms are also possible Thursday and
Thursday night as the low moves through. There is a marginal risk
of severe storms south of Route 30...mainly Thursday afternoon
and evening. Showers will taper off from west to east Friday as
the low departs. High pressure will build into the Midwest
Saturday providing fair weather.

&&

.SHORT TERM...(This Evening through Tonight)
Issued at 330 PM EDT Wed Mar 29 2017

Quiet weather will continue through the evening as ridge axis
downstream of potent upper low folds over our area. Decaying
convection presently over Illinois will struggle to reach our CWA
given persistent E/SE flow until after 06Z tonight and very dry air
aloft noted in 12Z KDTX and KILN soundings. Radar mosaic looks
decent but ceilings are 6-10 kft. A stray sprinkle may survive into
our NW third this evening but best chances for rain will hold off
until after 09Z when nose of southwesterly LLJ and associated theta-
e surge arrive. Clouds will obviously be on the increase overnight
but late arrival of veering winds and good warm/moist air advection
should still allow overnight lows to drop into the upper 30s to low
40s. No concern for mixed precip, even in far NE counties where lows
may touch mid 30s.

&&

.LONG TERM...(Thursday Night through Wednesday)
Issued at 330 PM EDT Wed Mar 29 2017

Rain and severe weather chances tomorrow are primary story for this
forecast package. Another very moist airmass is being drawn north by
this high amplitude southern stream wave. 850mb dewpoints hover
around 10C with PW values around 1.25 inches. Meanwhile, plenty of
dynamical support for UVM with coupled upper jet streaks (for a
time), diffluence aloft, and ample midlevel CVA/height falls. 295K
isentropic fields are correspondingly impressive in the AM WAA wing
with 40kts of sharp cross-isobar flow and mixing ratios climbing
above 6 g/kg. Rain virtually assured...though likely won`t be steady
through the whole day. Suspect a brief break in heavier rain in the
early afternoon...between morning WAA/theta-e surge and evening
arrival of CVA bullseye and associated surface low/convergent
boundary. Storm total QPF anticipated to be around an inch for many
locations. Some minor/nuisance flooding may be possible in typical
low-lying areas given recent wet conditions but ground should be
able to absorb this rain without significant impacts. Latest river
forecasts holding in action stage at worst.

Severe weather threat appears low. As is typically the case in these
events, low to midlevel wind/shear values are more than adequate
with 40kt LLJ but destabilization remains highly questionable.
Latest guidance continues to hold surface warm front over our
southern CWA with ample clouds/precip earlier in the day to limit
surface-based destabilization. If there is a sufficient break after
midday precip, our far southern counties may destabilize enough to
support a few strong storms in the 21-03Z period. However,
amplified/cutoff nature of parent trough suggests a slightly later
arrival of WAA precip (possibly mid-afternoon in eastern zones) that
will leave a very narrow window for sufficient diurnal heating. Hail
would be the main threat although isolated wind and tornadoes cannot
be entirely ruled out if instability axis creeps far enough north.
Certainly worth watching for our southern counties but threat does
appear low at this point.

Sporadic rain showers will continue through Friday as vort lobe and
deformation axis move overhead. Rainfall amounts during this period
will be much lighter and more scattered. Weekend looks much more
pleasant as ridge builds over the region. Not much CAA to speak of,
so high temps will hold generally in the 50s Fri-Sun, near average
for this time of year.

Wet pattern looks to continue into next week with one chance of rain
on Monday and another Wed/Thu. Still plenty of details to iron out
but looks favorable for several chances of decent rainfall. Temps
may be a touch warmer but no significant deviations from climo
expected at this time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1237 AM EDT Thu Mar 30 2017

Strong low level theta-e advection/isent lift ahead of low
pressure system centered over ern KS resulting in sct shra
across nrn IN attm. SHRA should become more widespread overnight
and Thu as low moves ne and moisture deepens across the area.
Isolated tstms also psbl this morning as elevated instability
overspreads the area but coverage too limited to mention in tafs.
Instability will increase Thu aftn as the low moves ne and
associated warm front lift into nrn IN. This combination appears
to offer a decent chc of tstms, especially at FWA closer to the
warm front. For now will just mention vcts in tafs. Flight
conditions should grdly lower to mvfr this morning but may improve
to vfr at FWA this aftn as a pocket of drier air wraps around the
low.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory from 4 AM early this morning to 4 PM EDT
     this afternoon for LMZ043-046.

&&

$$

SYNOPSIS...JT
SHORT TERM...AGD
LONG TERM...AGD
AVIATION...JT


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