Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 130939
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
439 AM EST Wed Dec 13 2017

.SYNOPSIS...
Issued at 438 AM EST Wed Dec 13 2017

A clipper system will bring light to moderate snow to the area
today, with the best chances for accumulations north of US 30 and
east of US 131. Conditions may be hazardous for the evening commute
in these areas. Otherwise, expect light lake effect snow tonight
into Thursday. Highs today will be in the 20s and 30s, warmest in
the southwest. Lows tonight will drop into the single digits and
teens. It will be colder Thursday, with highs only reaching into the
upper teens and 20s. Additional light snow is expected this weekend
with another system that will move through, followed by more lake
effect.

&&

.SHORT TERM...(Today and Tonight)
Issued at 438 AM EST Wed Dec 13 2017


The primary concern for the short term is the clipper system moving
into the area today and tonight. Opted to air on the side of caution
and issue a winter weather advisory for the northeast-most portions
of our forecast area (Branch/Hillsdale, MI; Fulton, OH). If the
forecast plays out as expected, accumulations of 2 to 4 inches are
expected in the advisory area, and less than 2" elsewhere. A few
localized higher amounts up to 5" are possible north of US 12 in
Hillsdale/Branch counties, MI where the better forcing will be.
Confidence in this playing out as planned is medium, as there are
several concerns to contend with.

On the pro-higher accumulations side, we have the low pressure
system dropping down across our forecast area, with the low tracking
from southern Lake Michigan at 21z into northern Indiana by 00z, and
southeastward into Ohio by 06z tonight. Guidance shows a pretty
potent wave aloft with this system, which is confirmed by recent
water vapor imagery. With a stout 40 knot jet streak ahead of the
low, there will be at least some WAA/moisture transport into our
area starting this morning, with the best 850-500mb qvector
convergence during the 18-00z timeframe.

The thing we lack is moisture, and the worry is that dry air to our
southwest will significantly limit the amount of moisture that is
lifted into the system ahead of the low/warm front. I think we`ll
miss out largely on this initial swath of precipitation that some
models are suggesting we`ll see, as higher-res guidance has things
staying fairly dry until 18z or so, before picking up in our far
northeast for at least a few hours. However, in collaboration with
neighbors decided to start the advisory at 15z, just in the event we
see some light snow on that northern side earlier today.

So for the forecast, I cut qpf/snow amounts fairly decently, with
the maximum potentially in far northern Hillsdale/Branch counties
north of US 12. Up to 4" is expected in northern Fulton, OH. Some of
the guidance shifts the axis of heavier precipitation slightly
southward, so I wouldn`t be entirely surprised to see perhaps
Steuben, Williams, Henry, and St. Joseph get added to the advisory
later this afternoon, but confidence was not high enough to put
them in now. I think that the drier guidance has a better handle
on current conditions, thus migrated more towards those when doing
my snow forecast. Impact wise, expect periods of low visibility,
and slick snow covered roads-especially in the advisory area.
Winds won`t be gusting as much as in the previous event, but we
could see some patchy blowing snow during the peak of the event
this afternoon/evening.

Otherwise, expect lows to bottom out into the single digits tonight
as cold air filters in. This colder air will also bring decent
chances for lake effect snow in the west, with NNE winds gradually
becoming more northerly. This keeps the band largely west of our CWA
until later in the overnight, when winds shift northwestward and
bring the band inland in LaPorte/Berrien counties. Expect light
accumulations with this, mainly 0.5" or less.

&&

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 327 PM EST Tue Dec 12 2017

Another in the series of a clipper type of system will move across
the Great Lakes Region Thursday and Friday. The surface low track
with this system will be far to the north of the forecast area over
Upper Michigan. Some warm air advection type of snow is possible
mainly Friday and Friday night; and with some lake enhancement, may
be able to generate an inch or two of snow over far northern Indiana
into Lower Michigan. Milder air will spread into the area Saturday
through Monday with little if any precipitation expected.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
Issued at 128 AM EST Wed Dec 13 2017

Crashing inversion heights and slowly backing winds have eroded
lake effect snow showers. Two distinct upstream waves are being
monitored for additional snow chances later today. The better
chance of initial warm advection surge snow will likely remain
just north of terminals, but better chances of snow should arrive
after the 18Z-20Z timeframe as one of these two upstream waves
across the Northern High Plains approaches the western Great
Lakes. The secondary wave will drive a cold front southward this
evening with a period of light synoptic snow expected for most of
northern Indiana. Cigs should trend into the 1500-2500 ft range
this evening as this occurs with improvement back to VFR likely
not long after the end of this forecast valid period. In addition
to the potential of more accumulating snow today, south-southwest
winds ahead of this system will become somewhat gusty to around 20
knots late morning/afternoon before veering more north-northwest
tonight as sfc reflection tracks across the region.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...Winter Weather Advisory from 10 AM this morning to 11 PM EST
     this evening for MIZ080-081.

OH...Winter Weather Advisory from 10 AM this morning to 11 PM EST
     this evening for OHZ002.

LM...Small Craft Advisory until 10 AM EST Thursday for LMZ043-046.

&&

$$

SYNOPSIS...MCD
SHORT TERM...MCD
LONG TERM...Fisher
AVIATION...Marsili


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