Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 222026

Area Forecast Discussion
National Weather Service Northern Indiana
426 PM EDT FRI JUL 22 2016

Issued at 418 PM EDT Fri Jul 22 2016

Dangerous heat and humidity will continue through much of the
weekend. Peak afternoon heat index values are expected to reach
around 100 on Saturday, and possibly into the 95 to 100 degree
range again on Sunday. Isolated thunderstorms are possible again
Saturday, with a better chance of showers and thunderstorms Sunday
and Sunday night as an upper level disturbance and cool front
approach. Scattered showers and thunderstorms may linger across
southern locations Monday, but cooler and less humid conditions
will overspread the area late Monday as the cold front moves
through. Low temperatures tonight will range from the upper 60s to
mid 70s. High temperatures on Saturday will be near 90, or in the
lower 90s.


.SHORT TERM...(This Evening through Saturday)
Issued at 418 PM EDT Fri Jul 22 2016

Heat and thunderstorm chances will continue to be the main forecast
items of concern for the short term.

A fairly strong instability gradient exists across the area this
afternoon with best low level moisture residing east of the
position of the old outflow boundary from last night. Latest RAP
analysis indicates MLCAPES on the order of 2000 J/kg across the
extreme southeast tapering to 500-1000 J/kg across the west,
although with lingering CIN for mixed layer parcel across the
west. Old convectively enhanced vort max appears to be exiting
across west central Ohio, and see little in the way of any
additional upstream forcing with overall preference to weak
mid/upper level downward motion through late this afternoon. Given
meager forcing and lack of appreciable surface based instability
have opted to confine iso mention to eastern locations through
the remainder of the afternoon. Heat indices should top out around
100 for most locations through the remainder of the afternoon.

For tonight, weak frontal boundary should stall across the southern
Great Lakes as weak upper short wave departs across the eastern
Great Lakes. Weak low level positive theta-e advection will begin to
work around the ridge later tonight into western portions of the
area, and cannot completely rule out an isolated storm with this
weak advective forcing. Did contemplate pulling PoPs completely for
tonight, but will maintain slight chance mention.

Low-mid level theta-e recovery to continue into Saturday, with sfc
dew points expected to be solidly in the lower to mid 70s. The
combination of this increasing moisture and highs once again around
the 90 degree mark or perhaps lower 90s, should promote heat indices
around 100 for most locations. Main exception to this will likely be
across the far north/northeast where a slightly drier low level air
mass will persist due to lingering effects from aforementioned
backdoor cool front. Not planning any changes to heat headlines at
this time with continued heat advisory for all but southern lower
Michigan counties for Saturday, but could approach near advisory
levels across portions of south central/southwest lower Michigan
Saturday afternoon. While instability should be more robust for
Saturday, the same limiting factor today should exist in terms of
lack of a coherent forcing mechanism. Given instability magnitude,
will maintain 20-30 PoPs during the afternoon, particularly across
the southwest half or southwest two-thirds.


.LONG TERM...(Saturday Night through Friday)
Issued at 418 PM EDT Fri Jul 22 2016

Thunderstorm chances to increase Saturday night as veering low level
jet brings deeper moisture axis back eastward. Could see some
remnants of an upstream MCS make it into western portions of the
area later Saturday night, but plenty of uncertainty in this
scenario so will keep low chance PoPs, mainly across the west.

Heat advisory conditions may linger into Sunday, but enough
uncertainty exists with convective evolution and impacts on temps to
not extend heat advisory for northern Indiana/northwest Ohio past
Saturday at this time. Better chance of storms may hold off until
Sunday night however due to increasing large scale forcing and
approach of sfc cold front. Overall severe risk appears to be low
at this time given lingering weak shear during the day Sunday, and
late timing of main frontal boundary/upper forcing.

Chance of showers and thunderstorms may linger across the south into
into Monday afternoon, but previous forecast trend to cooler and
less humid conditions post-Monday still appears to be reasonable.
Have maintained a dry forecast until the end of the period when
another Pacific wave may bring another chance of rain on Thursday.


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 126 PM EDT Fri Jul 22 2016

A CI shield has been moving across northern IN today due to
overnight convection dropping swd across IL today. An isolated
tstm is possible, but not enough to warrant mention in the fcst.
expect sct to bkn MVFR conds this aftn then a mid deck overnight.
NW winds around 8 to m10 kts will be light and variable overnight.


.IWX Watches/Warnings/Advisories...
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for INZ003>009-

MI...Heat Advisory until 8 PM EDT this evening for MIZ077>081.

OH...Heat Advisory until 8 PM EDT Saturday for OHZ001-002-004-005-015-



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

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