Area Forecast Discussion
Issued by NWS Northern Indiana

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890
FXUS63 KIWX 160559
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1259 AM EST Sat Dec 16 2017

.SYNOPSIS...
Issued at 1016 PM EST Fri Dec 15 2017

A weak system will pass across the Great Lakes tonight bringing
a brief period of light snow mainly 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.

&&

.UPDATE...
Issued at 1014 PM EST Fri Dec 15 2017

Changes made to grids to reflect NW to SE orientation of precip
and further north/faster trend.

Radar and surface data shows initial push of weaker isentropic
lift was used to start saturation across the northern counties.
Stronger isentropic lift rapidly arriving, allowing for a
blossoming area of returns on the radar from southern Lk MI into
NW Indiana. SE extent of this area should be somewhat limited but
will expand across areas north of the Toll Road. May see some
light accumulations still across mainly Michigan counties but
greater potential for accumulation will likely take place
near/north of Interstate 94 in Michigan as area quickly lifts
north over the next several hours.

No other changes warranted with plenty of cloud cover for the area
the remainder of the night.

&&

.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
temps.

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 06Z TAFS through 06Z Saturday Night)
Issued at 1250 AM EST Sat Dec 16 2017

South to southwest surface flow will continue over northern
Indiana through the TAF period as a high pressure system remain
southeast of the Ohio River and low pressure developing over the
Central Plains. A weak clipper type of system was tracking across
Lower Michigan at the start of the period. The best lift and all
snow should stay north of the terminals. Although the airmass was
rather dry at the onset, low level moisture will be increasing
today and will increase the chances for fog just beyond the end
of the TAF period.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory until 5 AM EST early this morning for
     LMZ043-046.

&&

$$

UPDATE...Fisher
SYNOPSIS...Marsili/T/Fisher
SHORT TERM...T
LONG TERM...T
AVIATION...Skipper


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