Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 162303
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
603 PM EST Thu Nov 16 2017

.SYNOPSIS...
Issued at 305 PM EST Thu Nov 16 2017

Cool and cloudy conditions will persist through Friday with lows
around 30 and highs on Friday in the mid to upper 40s. Widespread
rain is expected on Saturday. Rainfall amounts around an inch are
expected for most locations with isolated amounts up to around two
inches possible. This could cause minor flooding in low lying and
poor drainage areas. Thunderstorms are also possible but no severe
weather is expected. Some light lake effect snow will then be
possible Sunday morning but little to no accumulation is expected.
Dry and seasonable temperatures are anticipated for next week.

&&

.SHORT TERM...(This Evening through Friday)
Issued at 305 PM EST Thu Nov 16 2017

Lake effect sprinkles/flurries/drizzle will continue to dissipate
this afternoon as surface ridge axis moves overhead. Expecting a dry
and cool night. Still plenty of cloud cover to contend with but
thermal trough now directly overhead. With current temps only around
40F...suspect lows around 30F are reasonable. Similar conditions
anticipated tomorrow as well but increasing WAA will lead to warmer
afternoon highs (mid/upper 40s). Will still be cloudy and there
could be a stray sprinkle in our far NW late in the day but
primarily dry conditions will persist until the Fri night period.

&&

.LONG TERM...(Friday Night through Thursday)
Issued at 305 PM EST Thu Nov 16 2017

Main focus of forecast is on next, highly dynamic, midlevel wave
crossing the area on Sat. Coupled upper jet structure with 150+ kt
jet streak on the southern wing will support strong deformation/fgen
directly over our CWA with rapid cyclogenesis over the eastern Great
Lakes as trough deepens and self-development processes quickly ramp
up. The main story for us will be heavy rain. Ample moisture being
efficiently advected northward on 60+ kt LLJ with 850mb dewpoints
near 10C and PW values around 1.25 inches. Forecast soundings even
suggest some elevated static instability given this aggressive
moisture push that could support a few (non-severe) rumbles of
thunder. Perhaps most concerning is the orientation and location of
main baroclinic zone as well as degree of forcing. Light rain in
warm sector will begin Fri night but heaviest rain is expected
midday Sat as sharp trough axis approaches and left exit deformation
really lights up. Most locations are likely to see at least an inch
and up to around 2 inches is possible wherever the main fgen band
sets up given degree of moisture/instability and forcing. Truly
heavy rain won`t last long and most rivers are running relatively
low but do expect some minor flooding in low-lying/poor drainage
areas. Will just mention in HWO for now as impacts should remain on
the low side. Winds will also gust to around 30 mph on the backside
Sat evening.

Colder air does filter south Sat night but parent trough remains
very progressive and deep-layer moisture is stripped away much
faster than low level CAA. Expect little (if any) mixed precip until
Sun morning when lake effect ramps up with a secondary shortwave
passing. Not a great lake effect setup either though. Synoptic
support is weak and transient with inversion heights hovering around
6 kft and some dry air entrainment concerns with a NW fetch/
multiband setup. Some light snow possible 09-18Z but winds quickly
back by late Sun. Warm/wet ground will make accumulations difficult
but if a more organized band of convergence can develop...could see
snowfall rates high enough for some brief accums on grassy/elevated
surfaces north of US-30.

Rest of the long term relatively quiet with seasonable temps and no
good chances of precip noted through Thanksgiving.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 603 PM EST Thu Nov 16 2017

Upstream observations indicate MVFR ceilings will likely be the
story for the night hours. High pressure along the IL/IN state
line will gradually shift eastward overnight allowing for light
and variable winds.

Near daybreak Friday this feature is forecast to be over the
eastern Ohio River Valley and we expect southeasterly flow to
develop. Wind speeds will increase through the day, especially at
SBN, as the pressure gradient tightens in response to a pair of
low pressures; one to our northwest and one to our southwest.

As an upper-level low deepens over the Great Lakes Friday night,
850 mb winds from the southwest at 40-50 knots are possible. As
such, LLWS may need to be introduced in future TAFs.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory until 10 PM EST this evening for LMZ043-046.

&&

$$

SYNOPSIS...AGD
SHORT TERM...AGD
LONG TERM...AGD
AVIATION...Brown


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