Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 211720

Area Forecast Discussion
National Weather Service Northern Indiana
120 PM EDT Fri Oct 21 2016

Issued at 101 PM EDT Fri Oct 21 2016

Lake effect rain showers over NE Indiana for the rest of the
afternoon into the evening and then diminish overnight. Low
temperatures tonight will drop down into the upper 30s in eastern
portions of Indiana with a possibility of patchy frost to lower
40s in NW Indiana due to increased cloud cover. A warmup is
expected this weekend with high temperatures rising into the upper
50s on Saturday to mid 60s on Sunday.


.SHORT TERM...(Today and Tonight)
Issued at 418 AM EDT Fri Oct 21 2016

A band of rain showers persists from south central lower Michigan
into central Indiana this morning, tied fairly closely to strong
upper level front and upper vort max progressing through the area.
This mid/upper level baroclinic zone/upper forcing will shift east
of the area after 12Z with downward trend in rain shower activity
especially closer to the 12Z timeframe. Otherwise, main forecast
challenge will be transition to isolated-scattered lake effect
rain showers. Orientation of low level trough axis across the Ohio
Valley is currently supporting more favorable low level
trajectories for lake effect just west of the forecast area across
northwest Indiana. Observations have suggested some thermal
convergence increasing across far southern Lake Michigan during
the overnight hours which should support better chances of lake
effect rain showers over the next several hours as low level cold
advection continues. As synoptic system pulls off to the east
this morning, lake effect rain showers should shift eastward into
far northwest portions of the forecast area. Lake induced
equilibrium heights should also be on the increase toward 12Z as
850-700 hPa thermal troughing sags across the southern Great
Lakes. Have not made substantial changes to previous grids with
scattered-like (40-50%) lake effect rain shower PoPs into this
afternoon. Outside of lake effect, skies should partially clear
today as synoptic scale subsidence becomes more established this
afternoon in wake of upper trough this morning. Decent mixing
today should allow highs to reach into the low to mid 50s most
locations despite strength of low level thermal trough.

Lake effect rain showers may linger into tonight given weaker PV
anomaly digging southward from south central Canada and maintenance
of somewhat favorable thermodynamic profiles. Lowering inversion
heights overnight and eventual eastward progression of vort filament
should bring an end to any isolated-scattered lake effect rain
showers late in the overnight hours. Some patchy frost appears to be
possible, although could be just enough low level mixing across
the northeast away from lake effect clouds to limit this
potential. Other potential patchy frost area could materialize
across the far southwest closer to the low level ridge axis. Given
above uncertainties with strength of gradient/mixing and lake
effect clouds will hold off on any headlines for these locations.


.LONG TERM...(Saturday through Thursday)
Issued at 418 AM EDT Fri Oct 21 2016

Low level thermal trough will slowly push east of the area on
Saturday with some slight moderation into the 55 to 60 degree
range. Main cloud cover of note will be eastward progression of
remnant lake effect cloudiness eventually transitioning to a
diurnally enhanced cu deck inland. Most locations should see good
deal of sun by afternoon.

The second half of the weekend will feature a more distinct
moderating trend as upstream broad upper level ridging across
central CONUS shifts eastward. Fairly strong westerly low level
flow/WAA in this setup should allow highs to reach into the 65 to 70
degree range with the warmest temps in the southwest. Models have
been consistent in advertising a progressive eastern Pacific wave
that rides this upper ridge which may eventually try to phase with
southward sagging central Canadian vort max. Better forcing should
remain confined across central/northern Great Lakes however, with
some indications of stratospheric intrusion really drying out mid
levels across the southern Great Lakes Sunday/Sunday night. Thus,
have maintained dry forecast for this period with dry frontal
passage Sunday night.

The early to mid portions of next week should be more seasonable
with region located in upper level inflection zone. Medium range
models still suggest a more active mid-late week pattern next week
as series of eastern Pacific waves suppress mean upper ridging.


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 101 PM EDT Fri Oct 21 2016

Cool northerly flow expected this afternoon into this evening in
wake of low pressure system. This cold advection over relatively
warm lake waters will keep lake effect stratocu around through
much of the period...especially this afternoon/evening at KSBN
when lake effect rain showers will be possible. Under the lake
effect bands CIGS will down between 2 kft and 3 kft. VFR outside
of the lake effect showers.


LM...Small Craft Advisory until 5 AM EDT Saturday for LMZ043-046.



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

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