Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 251021

Area Forecast Discussion
National Weather Service Northern Indiana
621 AM EDT Tue Oct 25 2016

Issued at 352 AM EDT Tue Oct 25 2016

Dry conditions will continue today with an increase in clouds
expected this afternoon into this evening. Rain chances will begin
to increase late tonight, mainly across far northern Indiana and
southwest lower Michigan. Rain will become more widespread by
Wednesday and Wednesday night before diminishing on Thursday. High
temperatures today will be mainly in the mid 50s with low
temperatures tonight from the upper 30s to lower 40s.


.SHORT TERM...(Today and Tonight)
Issued at 352 AM EDT Tue Oct 25 2016

Quiet weather to continue for most of today and tonight, although
rain chances will increase later tonight mainly for the far
northern Indiana and southern lower Michigan.

Day will start of on the cold side with ideal radiational cooling
conditions and temps in the lower to mid 30s. Mid level ridging
across the central/northern Plains will shift to the MS Rvr Valley
today with an increase in downstream mid level WAA and high clouds
overspreading the area. Low level anticyclone will be stubborn to
shift east today with with weak easterly flow and relatively poor
mixing. Not much advective change in low level thermal profiles over
the past 18 hours, and highs this afternoon under poorer mixing
and increasing mid cloud will likely be near or a few degrees
cooler than that of yesterday.

The main forecast challenge for tonight will be resolving potential
rain chances in warm advection wing type forcing ahead of next upper
level trough that will be tracking across the Rockies this morning.
Isentropic analyses from NAM/GFS would tend to suggest best
chance of some light rain late in the night would be across the
far north. It is possible precip onset may be delayed until closer
to or just after daybreak Wednesday given primary low level jet
axis and maturing low/mid level circulation should be west of the
area across the mid MS Valley. In reality, PoP gradient for late
tonight probably needs to be tighter with a sharper north-south
gradient although with a good deal of uncertainty will maintain
low to mid range chance PoPs ramping up across the north/northwest
in the 09Z-12Z timeframe.


.LONG TERM...(Wednesday through Monday)
Issued at 352 AM EDT Tue Oct 25 2016

The upper level short wave across the Rockies this morning will
be the primary feature of interest for Wednesday-Thursday morning.
This feature does appear to be a bit more disjointed than earlier
indications with better phasing/upper dynamics possibly not coming
into play until this wave is east of the area on Thursday.
Nevertheless, this short wave will be accompanied by strong
thermal/frontal forcing and moisture advection/convergence, and
thus have not made significant changes to likely and categorical
PoPs for the Wednesday afternoon-night period.

While details are uncertain, would suspect leading warm-advection
forced band of light rain may be skirting across northern/northeast
portions of the area early Wednesday with perhaps a brief lull until
stronger low/mid level isentropic ascent/fgen forcing shifts across
the southern Great Lakes for late morning/afternoon. Some decent
rainfall amounts are possible especially far northern
Indiana/southern lower Michigan where longer residence time of
stronger isentropic lift/fgen forcing should reside. Rainfall
amounts between half inch and an inch are possible across these
locations Wednesday-Wednesday night. Surface reflection will likely
track across northern portions of the CWA with best chance of weak
near surface based instability across the far south. Instability
progs should be more limited across the north, although with some
very weak and highly elevated instability and strong low/mid level
front in the vicinity, cannot discount an isolated storm most
locations. This system will pull of the east Thursday with some
lingering rain showers possible east of I-69 in the morning.

The Friday-Saturday period is still plagued by some dramatic run to
run inconsistency in medium range models with biggest item of
inconsistency in how to handle the phasing of additional eastern
Pacific waves with south central Canadian perturbations.
Deterministic/ensemble trends have been toward less phasing and less
southward latitudinal extent of next short wave trough for Friday
night/early Saturday, and have made some downward adjustments to
PoPs for this period. If this idea does verify, weekend may shape
up milder than previous indications. As mentioned, still a lot of
volatility and run to run differences for this period which will
need to be refined in later forecasts.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
Issued at 617 AM EDT Tue Oct 25 2016

Low level ridge axis over the region will continue to support
light winds and VFR/mainly clear conditions through the morning.
Mid-high level clouds will increase this afternoon into tonight.
VFR otherwise as lowest 7 kft remain very dry/stable. Could see
some high based light showers/sprinkles into KSBN toward the end
of the TAF period (9-12z) as elevated warm advection wing in
advance of approaching upper trough tracks in.




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

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