Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 140501

Area Forecast Discussion
National Weather Service Northern Indiana
1201 AM EST Tue Nov 14 2017

Issued at 1149 PM EST Mon Nov 13 2017

Cloudy to Mostly cloudy skies will prevail overnight with lows
generally around 30 degrees. Areas of fog are expected, with
patches of dense fog. Expect an increasing amount of sun on
Tuesday, though some clouds will still persist into the afternoon.
Afternoon highs on Tuesday will reach the middle 40s to around
50. A frontal system will bring showers and a slight chance of
thunderstorms on Wednesday followed by another strong system and
additional showers and possible storms on Friday.


Issued at 1149 PM EST Mon Nov 13 2017

Issued an SPS highlighting the developing fog, and patches of
dense fog observed across the area. As of 445Z, most areas in the
central and west were between 2-5 miles, and suspect it may
become more like 1-3 miles towards morning if winds remain light
and cloud cover clears out a bit more. We`ve received several
reports of denser fog, with visibilities less than 1 mile. Some
observation stations are even reporting visibilities of 1/4 mile.
Given the lingering low level moisture trapped beneath the
inversion, and observed upstream conditions last night the concern
is that the more hazardous conditions could become more
widespread. However, confidence is lower in this occurring
because of the more expansive cloud cover and since winds are
forecast to strengthen slightly overnight in the west. As
mentioned in the previous short term discussion, things look to
favor more of a stratus deck developing vs. widespread fog, but
will keep a close eye on the conditions overnight. For now, just
wanted to raise awareness for some of the lower visibilities
around the region.


.SHORT TERM...(This Evening through Tuesday)
Issued at 408 PM EST Mon Nov 13 2017

Low level moisture trapped beneath subsidence inversion holding
firm, even well upstream over northern IL this afternoon. Modified
sky coverage grids significantly higher over blend with some breaks,
especially northwest CWA towards daybreak as saturated layer thins
amid persistent downward vertical motion and start of dry air
advection within return/southerly flow as centroid of ridge moves
into central OH by daybreak. Constricted patchy fog mention in
time/space to near daybreak/land areas only with best potential in
clear/partially cleared spots, though overall stratus favored per
bufkit hydrolapse rates/lightly mixed moist boundary layer.


.LONG TERM...(Tuesday Night through Monday)
Issued at 408 PM EST Mon Nov 13 2017

Slight delay with respect to Wednesday convection per good model
agreement with only low chance mention late Tue night western CWA.
Low MUCAPE on order of 100-250 j/kg sufficient for continued
inclusion of slight chance thunderstorms given strong kinematic
field/nose of low level jet riding eastward along I70 corridor, near
KSTL at 09 UTC to west central OH by about 18 UTC. Added thunder
mention with Friday mention as well given markedly deep/progressive
mid level trof passage through CONUS.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
Issued at 603 PM EST Mon Nov 13 2017

Overcast skies are gradually working their way out of the area
this evening with clearing skies being reported upstream over
portions of Illinois. Clear skies for the 23Z SBN observation may
be short lived with another batch of clouds looming. As such,
have opted to play MVFR ceilings at both terminals with this cloud
cover working its way through.

After broken and overcast skies vacate, the forecast challenge
is whether or not fog will develop overnight. As the 18Z
forecaster stated, forecast soundings suggest the lowest 2,000
feet may not be saturated. Forecast soundings continue this
thought. However, today`s inversion worked to keep recent surface
moisture in its place. So, perhaps the clearing skies will be
enough to activate some radiation fog. However, because fog
confidence is low at this time, we will hold with low-end MVFR




LONG TERM...Murphy

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