Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 041723

Area Forecast Discussion
National Weather Service Northern Indiana
1223 PM EST Sun Dec 4 2016

Issued at 505 AM EST Sun Dec 4 2016

An area of snow mixed with rain will move through the region
today. Precipitation should fall as mainly snow north of a line
from Monticello to Fort Wayne to Lima with 2 to 4 inches over
northwest Indiana into far southern Lower Michigan. More wet snow
is likely Tuesday before much colder air and lake effect snow
arrive late this week.


Issued at 920 AM EST Sun Dec 4 2016

Forecast generally remains on track and minor update this morning
to adjust pcpn timing a tad based on latest hires guidance and
radar trends. Morning radar shows leading edge of pcpn into east
central IL. Bulk of returns over Indiana evaporating in initial
dry lower levels. This should be overcome by late morning to early
afternoon west and mid afternoon east as stronger lift and
moisture flux overcome the dry boundary layer. The biggest
concerns with this system are exact location of rain/snow line and
how much snow will accumulate on roads later this afternoon and
evening. Snow ratios combined with expected QPF yields 1 to 3
inches with a few spots in far NW around 3.5 inches. Ground
remains warm and Wet bulb sfc temps remain above freezing so
expect a lot of melting and compaction initially. Roads temps
currently above freezing and should remain just wet with onset
and through about 21 to 22z. we begin to lose sun and
temps drop a couple degrees late this afternoon...heaviest pcpn
rates will be over the NW areas with moderate snowfall rates
expected. Could see accumulations begin on roads early this
evening before pcpn ends mid evening. This will be watched
closely as possible short duration winter weather advisory may be
needed if we see the roads becoming snow covered given this is the
first decent snow event of season. Just too many uncertainties
right now to warrant hoisting advisory but will keep an eye on
trends this afternoon.


.SHORT TERM...(Today and Tonight)
Issued at 447 AM EST Sun Dec 4 2016

An upper level trof will move east today and bring a round of
precipitation to the area. High resolution WPC models favor a
rather intense band of snow or a rain/snow mix for 3 to 6 hours
associated with this system. BUFKIT profiles favor snow over
northwest areas mainly northwest of Warsaw with generally a
rain/snow mix over southeast areas. The dendritic growth zone will
also be favorable for snow development given impressive omega
through this layer. The 295K isentropic layer of the RAP also
supports a rather intense band of snow with 30-40 kts of lift with
3.0 to 4.0 g/kg of moisture. Therefore, have raised snow amounts
considerably especially over these northwest areas to around 3
inches. Current thinking is roads will be mainly wet given
pavement temps staying above freezing. The snow should end rather
quickly over all areas by early tonight.


.LONG TERM...(Monday through Saturday)
Issued at 447 AM EST Sun Dec 4 2016

...Wet snow Tuesday then much colder weather and lake effect snow
still on track for later this week...

A second system expected to arrive Tuesday will follow the path of
the system that moves across the area today. Favor more of a wet
snow forecast in lieu of a rain solution given the latest forecast
thermal profiles. This system will be an ejecting upper low from the
southern stream. Have trended this low and associated precipitation
farther northwest given solid support from the GFS and the ECMWF.

A third system will bring much colder air to the area late this
upcoming week. The ECMWF continues to be at odds with the GFS and
still holds onto the Wednesday night frontal wave, bringing a round
of snow ahead of a very strong cold front. There is also support
from other models for this wave. Have rejected the model blend
and kept the previous forecast given uncertainty. Lake effect snow
will develop Thursday as much colder air spreads over the mild
lake waters. Delta T values should eventually reach 25 to 30C, so
lake effect snow accumulations appear very favorable at this time.
A fourth system appears on the horizon with snow chances
increasing Saturday.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 1223 PM EST Sun Dec 4 2016

Main focus remains on impacts/ptypes from area of light-moderate
precipitation expected to move through mid afternoon through mid
evening, heaviest in 21-01z window. Pcpn still expected to fall as
mainly snow at KSBN with VFR conditions at TAF issuance quickly
deteriorating into IFR/LIFR range with snowfall.

Pcpn likely starts as a rain/snow mix at KFWA given slightly
warmer near sfc conditions. However, latest model/observation
trends suggest a quicker transition to mainly snow by 22z and then
ending toward 01z. As a result have trended toward lower visby`s
and all snow at KFWA 22-01z. Some slushy accumulations will be
possible on the pavement at both terminals (better chances at
KSBN) in times of heavier snowfall.

Winds veer westerly and drier mid-upper level will bring an end
to more widespread pcpn behind shortwave and associated sfc
trough later this evening. Low stratus in IFR to low MVFR range
then settles in under post-frontal inversion, with some patchy
drizzle possible late evening/early overnight.




SHORT TERM...Skipper
LONG TERM...Skipper

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