Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 201046

Area Forecast Discussion
National Weather Service Northern Indiana
646 AM EDT Tue Sep 20 2016

Issued at 359 AM EDT Tue Sep 20 2016

A weak cool front will continue to track across the southern Great
Lakes region early this morning with a few showers possible
across extreme northwest and north central Indiana and southwest
lower Michigan. Otherwise, mainly dry conditions are expected
today. The warm and dry weather pattern will continue through
Friday. High temperatures this afternoon will reach into the lower
to mid 80s. Low temperatures tonight will range from the upper 50s
to lower 60s.


.SHORT TERM...(Today through Wednesday night)
Issued at 359 AM EDT Tue Sep 20 2016

An overall quiet period in store for the short term with above
normal temps continuing.

Weak surface cool front is approaching northwest Indiana/southwest
lower Michigan early this morning with isolated-scattered showers
persisting immediately behind surface front. A very narrow MUCAPE
axis of 250-500 J/kg is nosing into northeast Illinois at this time
with instability magnitudes expected to lessen further as the
instability axis shifts southeast into northwest Indiana over the
next few hours. Despite strongest mid/upper level forcing confined
well north of the forecast area across the northern Great Lakes,
showers appear to be aided by modest post-sfc frontal low level fgen
forcing and weak convective vort max from earlier upstream
convection. Still believe that showers should tend to
weaken/dissipate as they shift into northwest portions of forecast
area this morning but will carry isolated shower mention through
12Z. Cannot rule out an isolated storm, but will hold off on ZFP
mention at this time.

Surface front should lose its integrity across central portions of
the area this afternoon with better near sfc convergence likely
confined to west central Illinois. There could be narrow window in
the 16-20Z timeframe for an isolated shower to develop across
southwest portions of the area in closer proximity to weak sfc based
instability axis, but with such meager forcing outside of any
exiting smaller scale convective vorts, difficult to latch onto much
for mentionable PoPs and will refrain from any isolated shower
mention at this time. Otherwise, mid level cloud deck should
continue to track across northeast/eastern portions of the area
this morning, with partly cloudy to mostly sunny skies this
afternoon. Thermal advections not particularly strong with washing
out front today, which should still support above normal highs
into the lower to mid 80s.

For tonight vort max emanating from eastern Pacific tropical system
will get ingested into southwesterlies and will lift across central
Rockies by late tonight. A strengthening low level jet downstream of
this feature should focus renewed convection across upper MS Valley
and may need to watch potential of any remnant outflow/MCV tracking
across southern Great Lakes Wednesday or Wednesday night. A good
deal of inherent uncertainty exists with this type of setup but
given expected pronounced elevated mixed layer advecting into the
area Wednesday and subsequent capping potential, will continue to
be conservative with PoPs and limited to slight mention across the
far north Wednesday night. Above to much above normal temps to
continue into Wednesday with highs once again into the low-mid


.LONG TERM...(Thursday through Monday)
Issued at 359 AM EDT Tue Sep 20 2016

Warm conditions to continue into Thursday with mid/upper
ridging remaining in place. Aformentioned vort max from southwest
CONUS may be progressing across southern Great Lakes on Thursday
but capping issues should remain in place. By Thursday night into
Friday, guidance has been somewhat consistent in south central
Canadian vort max from north central Manitoba dropping into
western Quebec on Friday. This should allow cool front to make
more southward progress during this period. Despite approach of
this front, precip chances are of low confidence at this time as
approach of the front will be quickly followed by mid level height
rises in response to large scale flow amplification. This will
result in cooler temperatures by Saturday with highs closer to
seasonable norms (although likely still a bit above normal across
the southwest).

Medium range models continue to exhibit dramatic run to run
volatility regarding evolution of larger scale western CONUS trough
for next weekend, with differences in handling the extent of
southwest CONUS cut-off troughing. Synoptic wave pattern will be
somewhat stable, and thus mid/upper ridging will be slow to progress
eastward Saturday-Sunday which should keep bulk of next weekend dry.
Despite run to run variations, 00Z deterministic solutions at least
still support idea of upper trough approaching the region Sunday
night-Monday and will maintain low to mid range chance PoPs.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
Issued at 631 AM EDT Tue Sep 20 2016

Diffuse frontal boundary was working into NW parts of the area.
Band of showers was not giving up, residing from southern Lk
Michigan NE into western Lower MI drifting mainly east. This
afternoon, whatever is left of the front may provide enough focus
for some cu development with a non-zero chance of a shower popping
up. Very low confidence in this occurring so VFR conditions will

Lots of ground fog noted upstream across Wisconsin into northern
Lower Michigan. Position of ridging and dry air should keep any
fog/stratus at bay but will still need to watch.




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

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