Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 271748

Area Forecast Discussion
National Weather Service Northern Indiana
148 PM EDT Thu Jul 27 2017

Issued at 126 PM EDT Thu Jul 27 2017

Isolated showers and thunderstorms will continue through the early
evening. A weak cold front will sag southward from the Great Lakes
before stalling across Central Indiana overnight. Another round of
showers is expected late Friday as another push of cooler air
settles into the Great Lakes. Following this, a period of cooler,
drier and rainfree weather is expected for the weekend into early
next week. Lows tonight will drop into the middle 60s. Highs on
Friday will be in the upper 70s. Over the weekend highs will be in
the upper 70s with overnight lows in the middle 50s.


Issued at 1040 AM EDT Thu Jul 27 2017

Minor tweaks to the grids but forecast generally in good shape for
the time being. MCV noted across NW Indiana with an agitated cu
field surrounding this feature. A few showers have now started to
pop near the Indiana Toll Road. An area of rain/showers has been
slowly expanding across portions of NE Indiana into NW Ohio closer
to the deeper moisture feed. The greatest coverage in precip will
remain in SE areas and suspect by mid afternoon much of it will be
east or south of the area. Isolated to scattered showers/few
storms will remain possible until the departure of the upper level
trough which is not in a major hurry to leave.

High temps may struggle to reach forecasted levels in a few
locations, but generally attainable with slow rises noted even
with clouds.


.SHORT TERM...(Today and Tonight)
Issued at 340 AM EDT Thu Jul 27 2017

Most of the weather of interest this forecast cycle will reside in
the short term, with convective chances today through Friday the
main concerns.

Old convective complex that moved across the area from northern
Illinois has diminished in coverage, although over past few hours
some uptick in showers/storms at leading edge of what appears to be
MCV entering northwest Indiana. Some wind gusts around 30 mph have
been noted, but primary note of interest for these showers has
been impressive rainfall rates. Weak westerly low level jet
allowed a very strong low level theta-e gradient to advect across
southwest/western portions of the forecast area resulting in PWATS
increasing to over 2 inches. Warm cloud depths in excess of 13k
feet and overall marginal instability profiles will continue to be
conducive for some brief heavier rainfall rates over the next few
hours as these showers approach portions of north central
Indiana. Lack of strong low level jet and limited upwind
development should preclude any hydro concerns early this morning.

The convectively enhanced vorticity max should track east-southeast
across the area later this morning, likely sustaining at least
scattered showers/isolated storms into portions of northeast
Indiana and possibly northwest Ohio toward daybreak. In addition to
this convectively enhanced vort, another weaker/low amplitude short
wave will continue eastward across Lower Michigan this morning
eventually allowing low level trough axis to sag southward across
the southern Great Lakes/Ohio Valley through the day. Best chance of
additional showers and thunderstorms this afternoon should generally
be along and south of the Route 24 corridor in closer proximity
to this stronger low level convergence axis (or perhaps more
likely south of the forecast area). Without a good deal of
upstream mid/upper level forcing behind convective vort through
late morning, prospects of convection re-firing across northern
half of the area on the low confidence side. Shear/instability
profiles still appear to be disjointed today for any appreciable
severe weather threat, with best shear profiles likely north of
surface boundary across southeast Lower Michigan where instability
profiles will be more marginal. If storms are able to redevelop
this afternoon across the south, some heavier rainfall rates would
be possible with 2 inch PWATS and deep warm cloud depths
persisting, but again better potential may remain south of the
forecast area across central Indiana. Otherwise for today, temps
will be somewhat tricky depending on extent of afternoon cloud
debris/precip, but if some afternoon breaks in clouds can be
sustained even shallow mixing to 900 mb could support highs into
the lower 80s.

Low level boundary to eventually sag southward this evening with
diminishing precip chances for local area, and more focused precip
potential across east central Indiana/southern Ohio. The main
feature of interest for Friday will be vigorous upper level trough
evident on water vapor imagery early this morning across southern
Manitoba. Stronger DPVA with this vort max should be felt across
northeast Indiana/south central Lower Michigan/northwest Ohio on
Friday where have maintained low to mid range chance TSRA PoPs.
Deeper moisture will remain tied more south of the area with
aforementioned low level boundary but stronger forcing with this
wave should allow isolated/scattered convection to develop. An
accompanying 40-50 knot 500 mb speed max will enhance deep layer
shear profiles, but again meager instability profiles look to be a
limiting factor for any isolated severe potential. Slightly
cooler temperatures expected for Friday with northeast flow
continuing to the north of the sfc boundary.


.LONG TERM...(Friday through Wednesday)
Issued at 340 AM EDT Thu Jul 27 2017

Upper trough that will bring shower/storm chances to eastern
locations Friday will exit on Friday evening setting up what should
be a stretch of tranquil and cooler/less humid weather through the
weekend. Slight amplification of western CONUS longwave ridge late
in the weekend will keep main short wave track across southern
Canada and prolonged period of downstream low level anticyclone
maintaining its influence on the area. Some indications in medium
range models of more substantial ridge-riding upper wave toward
end of this forecast period which could promote next notable
fropa, but at this forecast distance will cover this with just
some low chance PoPs.


.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 126 PM EDT Thu Jul 27 2017

Surface based low pressure is evident in satellite, radar and
surface observations, centered slightly southeast of the KIWX
radar. The frontal boundary extends eastward across Lake Erie and
southwest to near Saint Louis. Convective temperatures have been
reached and this has triggered isolated SHRA/TSRA along and south
of the frontal boundary. Likewise with the weak isentropic ascent
is keeping stratus well entrenched through sunset. Expect to see
isold IFR cigs and more extensive MVFR cigs, especially south of
the forecast points.

Another shortwave will dive through the Great Lakes Friday and
across the forecast area during the evening. This will lead to
another round of TSRA/SHRA beyond the 18Z end time.


IN...Beach Hazards Statement from 5 PM CDT this afternoon through
     late Friday night for INZ003.

MI...Beach Hazards Statement from 6 PM EDT this evening through late
     Friday night for MIZ077.

LM...Small Craft Advisory from 6 PM this evening to 5 AM EDT Saturday
     for LMZ043-046.



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

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