Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 171739

Area Forecast Discussion
National Weather Service Northern Indiana
139 PM EDT Sun Sep 17 2017

Issued at 348 AM EDT Sun Sep 17 2017

A weak frontal boundary will enter the region, bringing off and on
chances for showers and thunderstorms this afternoon into Tuesday
night. Highs today will reach the low to mid 80s before cooling
slightly into the upper 70s to lower 80s for Monday and Tuesday.


Issued at 1033 AM EDT Sun Sep 17 2017

Low/mid level theta-e advection will continue this afternoon as
stronger upper vort max lifts northeast across the arrowhead of
Minnesota. A few showers have attempted to develop this morning
across portions of north central Indiana in association with this
advective forcing, but have remained weak with very limited
elevated instability. Subtle confluence in association with pre-
frontal trough type feature will allow deeper moisture axis to
advect from west to east across the area later this afternoon into
this evening. Forcing will remain quite limited although weak
mid/upper level perturbations will be progressing across the
region emanating from debris from overnight upstream convection.

Previous PoPs in the 30-40 range still appear to be reasonable
following this forcing this afternoon...and then more in
association with weak frontal forcing late afternoon/evening. Sfc
based instability will be somewhat limited by marginal mid level
lapse rates, but at least isolated thunder potential can be
expected this afternoon/evening. Previous forecast is in good
shape and only minor modification was to include isolated PoPs
this morning across northeast Indiana along leading edge of
positive low/mid level theta-e advection.


.SHORT TERM...(Today and Tonight)
Issued at 348 AM EDT Sun Sep 17 2017

Low level moisture advecting into western areas was allowing for the
day starting in the mid to upper 60s (mid 50s to lower 60s east).
Little more than some cirrus from upstream, likely dying convection,
will invade the sky through the morning. Temperatures will climb
into the 80s across the area with dewpoints in the lower to middle
60s by afternoon resulting in 1000 to 2000 J/KG of surface based
CAPE. Limited convergence along a weak frontal boundary as well as
increased flux of sfc/850 mb theta-e will increase lift along the
boundary and allow widely scattered to scattered
shower/thunderstorm development. Shear is almost non existent
resulting in poorly organized storms and minimal if not zero
severe risk.

NAM12 showing some lingering forcing and sporadic showers behind the
front tonight. Can`t fully rule out with frontal boundary not that
far east of the area so will leave chc pops in and let day shift
look at model runs.


.LONG TERM...(Monday through Saturday)
Issued at 348 AM EDT Sun Sep 17 2017

After a brief lull Monday morning, the frontal boundary just to
the south will likely light up again with showers and
thunderstorms as a slightly stronger wave approaches. Models past
couple of days have attempted to bring low likely pops in western
areas as convection develops to the west and moves in mainly Mon
night into Tues. Consensus has been to nudge back to high chance
with more of a scattered coverage once again.

After Wednesday, the region looks to be sandwiched between
building upper level ridge to the east and deepening trough to the
west. This should result in a generally dry forecast and return
to above normal temperatures in the 80s. Had to remove spurious
pops added in by blend of models. Can`t rule out a wave riding the
ridge and getting close enough to western areas for a stray
shower, but no worth mention at this point.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 133 PM EDT Sun Sep 17 2017

A cold front approaches from the west allowing for a chance for
showers and a possible thunderstorm this afternoon. Shear will
be low so pulse-type thunderstorms appear most likely with heavy
rain and possibly some lightning as the main threats. The front
will stall just to the north of the region allowing the
southerly winds to become more northeasterly by Monday morning.

Especially where the rain was able to fall during the
afternoon, there may be a chance for MVFR fog/br and CIGs to
develop Monday morning. FWA appears to have favorable cross-over
temps, light to calm winds and a moist sfc layer, which all appear
favorable for MVFR fog/br. SBN will have a little stronger winds
than FWA and while conditions may approach MVFR range, feel it may
remain just above it.




LONG TERM...Fisher

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