Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 171942

Area Forecast Discussion
National Weather Service Northern Indiana
242 PM EST Sat Nov 17 2018

Issued at 242 PM EST Sat Nov 17 2018

Light rain and snow is expected through Sunday morning with
accumulations around an inch possible for areas along and just north
of highway 24. Temperatures will hold in the 30s. The next chance of
light snow is Monday night but dry conditions are then expected
through Friday...along with slowly warming temperatures.


.SHORT TERM...(This Evening through Sunday)
Issued at 242 PM EST Sat Nov 17 2018

First round of light precip currently winding down as expected with
attention turning to second round expected tonight. Right entrance
region of 120+ kt upper jet will move overhead tonight with ensuing
ageostrophic adjustments lighting up a deep fgen band from roughly
800-500 mb (though dry air on the northern side of the frontal slope
will keep active portion confined to the lower levels around 700mb).
Models in general agreement on a decent yet broad region of ascent
and light precip with 700mb specific humidities near 3 g/kg. Main
limiting factor is stability. Model cross-sections of theta-e and
EPV show a very stable environment above the frontal slope that will
limit potential for a narrower, stronger mesoband. Instead, expect a
more broad and lighter response (similar to this morning) lined up
generally along and just north of the US-24 corridor. 12Z model
suite still generating around 0.25 inches QPF from 00Z this evening
through 18Z tomorrow in this area, which seems plausible given
strength of fgen/omega and decent moisture. Temps and snow ratios
will be tricky though (especially in our southeast) as better WAA
forcing also leads to slightly warmer profiles for tonight and
tomorrow. Overnight timing will favor less melting than our first
round but surface wet bulb temps expected to hold in the low/mid 30s
for much of the event with ground temps also still running in the
mid/upper 30s. Some QPF will also fall after sunrise Sunday with
more melting potential. Atmospheric factors also not favorable for
really high snow ratios. Much of the ascent is just below the DGZ
with a relatively deep layer of 0 to -10C and shallow DGZ. This
should produce final snow ratios of around 12:1 or less with
substantial melting concerns. Currently anticipate around an inch of
accumulation for most locations with isolated amounts up to 3
possible just north of US-24 where moisture remains relatively high
and temps are cold enough for more snow/higher ratios. Given low
confidence/coverage in these higher totals and overall low impacts
due to marginal road advisory necessary.


.LONG TERM...(Sunday Night through Saturday)
Issued at 242 PM EST Sat Nov 17 2018

Rest of the forecast period remains relatively quiet. Another chance
for light snow Monday night as another shortwave/cold front rotates
through the Great Lakes. Forcing is weak and broad with very limited
moisture so do not anticipate any substantial accumulation...
generally a half inch or less. Highs will remain in the 30s
through Tuesday but longwave pattern finally breaks down next week
with strong ridge pushing into eastern NOAM. This will yield an
extended period of dry weather with steadily increasing temps.
Next trough and chance of precip arrives late in the week with
temps sufficiently warm for an all-liquid forecast.


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 106 PM EST Sat Nov 17 2018

MVFR to IFR conditions will continue through the period thanks to a
decaying boundary with weak upper level forcing lingering across the
area. Light snow will continue at KSBN through late afternoon before
tapering off for a brief period. KFWA should stay MVFR until this
evening. As a surface low drifts from MO into KY/OH tonight into
Sunday afternoon, the frontal boundary will sink southeastward and
reintensify as a band of light to moderate snow. Models disagree
regarding the exact location of the boundary and how much it will
intensify, but it seems that KFWA will see IFR conditions develop
either way, with LIFR not out of the question. Lower confidence as
to whether or not KSBN will see a return of snow showers, but still
included given that conditions could once again drop to IFR later





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