Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 252325

Area Forecast Discussion
National Weather Service Northern Indiana
725 PM EDT Sat Mar 25 2017

Issued at 325 PM EDT Sat Mar 25 2017

Scattered showers will increase in coverage overnight into Sunday
morning. A brief break in rain is expected Sunday night into Monday
but another round will arrive Monday night. A few isolated storms
and moderate rain are possible but no impacts are expected. Lows
tonight will generally be in the upper 40s to lower 50s. Highs on
Sunday will be in the low to mid 60s.


.SHORT TERM...(This Evening through Sunday)
Issued at 325 PM EDT Sat Mar 25 2017

Healthy band of 925-850mb fgen clipping our north earlier today in
right-rear quadrant of 140kt upper jet streak has largely dissipated
and shifted out of the area as jet axis pulls rapidly eastward.
Chances for a few SCT showers will continue through the evening as
upper low slowly drifts into the region with a very moist airmass
(850mb dewpoints near 10C on 12Z KILX sounding) advected into place.
However, center of upper low is still over Missouri and subtle
downstream ridging is preventing most, if not all, UVM/precip,
especially in our eastern zones. Hi-res guidance still suggests a
few SCT showers possible this evening (with minor elevated
instability possibly supporting a few isolated thunderstorms) but
much better chances look to arrive later tonight into Sunday morning
as differential CVA bullseye and midlevel deformation/fgen swing
through the CWA. Overall lackluster, moist adiabatic lapse rates but
forecast soundings indicate just enough instability based at 925mb
to refrain from pulling thunder mention altogether. Some moderate
rainfall rates possible at times with an additional half inch or so
basin-average QPF but not anticipating any impacts.

Suspect there will be a break in steadier precip from west to east
by tomorrow afternoon as center of dampening/opening upper low moves
overhead and slightly drier air wraps around. 12Z NAM appears to be
overdoing diurnal destabilization as per usual and resultant
convective QPF seems overzealous. However, sufficient residual
moisture/decreased stability and small, pinwheeling vort lobes will
maintain chance for some SCT showers through the afternoon with an
isolated storm not impossible. Should see a fairly quick end to
precip Sunday evening with lifting wave and loss of diurnal heating.
Extreme, marine layer-driven temp gradient today will be washed out
by tomorrow with highs for most of the CWA in the low to mid 60s.
Lows tonight will stay in the 50s, save for the far N/NE where
stubborn marine layer has current temps still in the 40s.


.LONG TERM...(Sunday Night through Saturday)
Issued at 325 PM EDT Sat Mar 25 2017

After a brief break early Monday, secondary southern stream wave,
currently over the southwest CONUS, will lift into the area with
another round of light/moderate rain. Footprint of this wave is much
smaller and weaker so precip will be in and out by around 12 hours
with limited total QPF of around a quarter inch. Tuesday and
Wednesday looking pleasant as midlevel ridge and Canadian surface
high settle over the Great Lakes. Will be slightly cooler but still
near/slightly above average for this time of year. Active southern
stream wavetrain continues into the end of the week but latest
models split on whether next upper low will lift into our region
(ECMWF and Canadian) or stay confined to the Tennessee Valley (GFS).
Will hold with concensus high chance PoPs for now given the time


.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 718 PM EDT Sat Mar 25 2017

Previous TAF package much too pessimistic looking at regional
observations and satellite trends. Consensus short term and hires
guidance all pointing toward VFR/MVFR with MVFR within heavier
showers through at least mid to late evening. Have trended the
latest TAFs in this direction. Scattered showers to continue off
and on at KSBN most of evening as moisture streams north around
upper low. KFWA may see an occasional pop up similar to last few
hours but models keep pcpn west of terminal until maybe 04-06z and
then only for a few hours. Main short wave rotates north toward
12z with models depicting a larger area of widespread rain lasting
most of morning Sunday with MVFR/IFR then. Dry slot expected in
afternoon but enough moisture and weak short waves to support
scattered showers and MVFR. Cannot rule out a few tsra through
the period but lightning data has shown only very isolated and
short duration activity and expect this to continue tonight making
timing/inclusion in TAFs impossible.





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