Area Forecast Discussion
Issued by NWS Northern Indiana

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310
FXUS63 KIWX 172009
AFDIWX

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

.SYNOPSIS...
Issued at 350 PM EDT Sun Sep 17 2017

There is a chance of showers and a few thunderstorms tonight as a
cold front slowly approaches the area. Chances of rain will
diminish late tonight into Monday morning as this frontal boundary
stalls across central Indiana. An upper level disturbance will
approach the Great Lakes and Ohio Valley Monday night into Tuesday
providing another chance of showers and isolated thunderstorms.
Low temperatures tonight will range from the upper 50s northwest
to the lower to mid 60s southeast. High temperatures on Monday
will range from the mid and upper 70s across the north, to the
lower 80s south.

&&

.SHORT TERM...(This Evening through Monday)
Issued at 350 PM EDT Sun Sep 17 2017

Chances of showers and storms tonight and Monday will continue to be
the primary short term forecast concern. Isolated showers have
developed this afternoon in association with pre-frontal trough
type feature from west central Indiana into northeast Indiana.
Greater coverage of scattered showers and isolated thunderstorms
also noted over past hour or two across northeast Illinois,
roughly from Lansing to east of Bloomington in proximity of
advancing cool front. Expecting these two general areas to
continue to be focus for additional showers and thunderstorms this
afternoon with greatest coverage expected to focus across western
portions of the forecast area with approach of better pooled
moisture axis/cold front. Surface based instability in the
1000-1500 J/kg should be sufficient for at least isolated thunder
through the evening hours. Effective shear values will remain
generally below 20 knots through the evening supporting more of a
pulsey nature to any stronger cores capable of producing brief
heavier rain showers and perhaps some wind gusts to 30 mph across
the west through early evening. Did maintain slight chance of
showers across the far northwest for a time behind the front late
this evening/early overnight with some indications over earlier
HRRR runs this afternoon of some development associated with
approach of low level trough/weak convergence axis.

A lull in precip chances is expected to develop late tonight into
Monday morning as frontal boundary drops just south of the area
and stalls out. Current indications suggest a south to north
moisture gradient should set up in association with this stalling
frontal boundary. Difficult to discern a clear forcing mechanism
for precip chances with low level boundary, and will maintain just
low chance PoPs through the day, focused mainly across southern
portions of the area. Highs will be cooler on Monday ranging from
the upper 70s north to the lower 80s south.

&&

.LONG TERM...(Monday Night through Sunday)
Issued at 350 PM EDT Sun Sep 17 2017

It still appears though the best chance of showers/storms this
period will be Monday night into Tuesday as isentropic lift/WAA
ramp up in vicinity of stalled boundary as next upper level short
wave approaches from the Rockies. Local area will remain at nose
of modest low level jet through Wednesday, but mid level height
rises in wake of Tuesday system lends to much lower confidence in
precip chances Tuesday and beyond. Guidance remains in general
agreement of significant amplification of eastern CONUS ridge and
continued much above normal temperatures for the Thursday through
next weekend period. While cannot completely discount weak
perturbations in southwest flow tracking across the western Great
Lakes for late this period, tried to maintain a mainly dry
forecast for much of the Days 5-7 period given ridge amplification
and considerable uncertainty in short wave track.

&&

.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.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...Marsili
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...Roller


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