Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 152343

Area Forecast Discussion
National Weather Service Northern Indiana
643 PM EST Fri Dec 15 2017

Issued at 231 PM EST Fri Dec 15 2017

A weak system will pass across the Great Lakes tonight bringing
scattered to numerous snow showers north of the Toll Road. Some
light snow accumulations of an inch or two are possible tonight,
especially across southern Lower Michigan where lake effect snow
showers are expected to be more numerous. Lows tonight will not be
as cold, ranging from the mid to upper 20s. Moderating trend
will continue into the weekend with highs in the 30s and 40s for
Saturday and Sunday.


.SHORT TERM...(Tonight and Saturday)
Issued at 231 PM EST Fri Dec 15 2017

Earlier sw trough skirting through MI on the way out with light
snow/flurries ending northeast.

Attention this period focused on secondary disturbance swinging
through se ON overnight and fairly robust low level warm advection
impinging into retreating low level baroclinic zone. Upstream sat
imagery along with 12Z sounding diag show decent slug of h85-7 base
rh progged to skirt se through base of ON trough and should seed a
robust lake enhanced response through srn MI this evening. Primary
question is how far to take mentionable pops especially in light of
how far morning snow showers progressed. Given some degree of
backing in low level flow will limit to north of highway 30 yet keep
close to prior update spreading pops a bit further south. Otherwise
favorable low centered dgz should yield mod snow for a time esp
north of a cassopolis to coldwater line with 1-2 inches there.

Warm sector expands nwd Sat with sunshine returning and warmer
although snow cover across nrn/ne areas will retard more substantial
diurnal heating.


.LONG TERM...(Saturday through Thursday)
Issued at 231 PM EST Fri Dec 15 2017

Persistent neg height anomaly over se Canada finally decays this
period with significant height anomalies developing through the wrn
US for a change. Downstream height rises are substantial given where
we have been for the last week and general west-swrly flow aloft
yields fairly mild weather especially Mon-Tue with well above normal

In this transition weak srn stream sw trough minors out through the
OH valley late Sun with a decaying chance for rain. Blended pops
still appear a bit high but had trended lower and left for now given
as yet still high model based uncertainty relating to how fast this
wave shears out.

Thereafter pattern to turn colder toward next weekend as mean
troughing redevelops through Hudson Bay and potentially dicey as
perturbed srn stream flow remains through the swrn US.


.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 637 PM EST Fri Dec 15 2017

Disturbance in IL was forcing some sporadic snow showers with a
dry sfc layer (5-10 degree Td depressions). As the disturbance
moves over the lake, returns may increase across the area with
the increased sfc moisture, but best indication would be SBN will
get some snow showers and not FWA. As a result, will include a
SHSN for SBN early, but it will only be a quick pass through.

CIGs start out close to entering MVFR and appear to move towards
MVFR during the first few hours of this period at SBN as the
disturbance passes through. VFR conditions will return thereafter.

Finally, LLWS is possible, but looks too marginal for inclusion at
this point. Thereafter, the low level jet vacates the area to the
east and wind speeds will be less gusty on Saturday.


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




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