Area Forecast Discussion
Issued by NWS Duluth, MN

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244
FXUS63 KDLH 081138
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
538 AM CST Thu Dec 8 2016

.UPDATE...
Issued at 532 AM CST Thu Dec 8 2016

Updated aviation section below.

&&

.SHORT TERM...(Today through Friday)
Issued at 340 AM CST Thu Dec 8 2016

Sfc low pressure that has brought persistent light snow across
the Northland will continue moving off to the northeast across
Quebec Canada. While the center of the low is well away from the
region, we remain within its cyclonic northwesterly flow. Strong
cold air advection is expected with this northwest flow, as 925
mb temperatures between -8 and -14 degrees C will move in over
the forecast area. Latest model soundings differ a little bit on
the extent of the saturation within the dendritic growth zone as
the GFS is more supportive of ice development than the NAM.
However, the NAM does keep this saturation through the Thursday
morning hours. However, soundings are hinting at a loss of
dendrites Thursday afternoon as drier air moves in. I did put in
just a slight chance of a flurry across the area as we are progged
to remain within the cyclonic flow through the day Thursday. Low
level lapse rates also look to remain steep enough to support
these flurries.

The lake effect snow event in northwestern Wisconsin is expected
to ramp up this morning as winds turn from the northwest. Winds
could remain breezy Thursday as a tight sfc pressure gradient
remains in place. The latest RAP soundings near the Apostle
Islands are indicating good delta-T values this morning/afternoon
between the lake temperature and the 850 mb temperatures, with
values between 19 and 22 degrees C - sufficient for lake
enhancement. Soundings also indicate lake induced convective
available potential energy between 300 and 500 j/kg during this
time. New snowfall amounts from 12z this morning through the day
Friday will range between 6 to 12" possible in Iron county, with
2 to 6" possible in Ashland and Bayfield counties. Thus, the Lake
Effect Snow Warning and Advisories will continue as we currently
have them.

Other than the lake effect snow in northwestern Wisconsin, most
places should dry up for Friday as slight mid-level ridging and
sfc high pressure moves in. This high pressure is expected to
bring with it a colder airmass, which will drop our temperatures
into the lower teens and single digits Friday morning, which will
only get colder by Saturday morning. Wind chill values Friday are
expected to drop into the single digits - both above and below
zero.

.LONG TERM...(Friday night through Wednesday)
Issued at 108 AM CST Thu Dec 8 2016

Friday night and early Saturday look to be relatively quiet
across the region with a ridge of high pressure building into the
area from the west. Winds will still be out of the northwest,
keeping the lake effect snow machine going for the south shore,
justifying continuing the warning until Saturday morning. Winds to
weaken and then shift around to a more easterly direction on
Saturday, cutting off the south shore snow showers. We may end up
only shifting things to the north shore then based on the
temperature differences from lake to 850mb, but it is also going
to depend on moisture availability and we will have to wait and
see on this.

Our next round of synoptic scale accumulating snow is associated
with a fairly potent shortwave that moves through the broad
troughing over the central CONUS beginning on Saturday. Models
have varied a lot in the strength of this wave, ranging from a
very potent system that develops a strong surface low and a fairly
major snowfall event, to a fast moving weaker wave that brings
lighter amounts of snow south of us. The NAM12 has been stronger
than the GFS or ECMWF on the latest runs, but the GFS was stronger
before and has been trending towards the weaker and faster ECMWF
solution as well. This wave is still off the western CONUS shore,
and do not have a lot of confidence in the forecast just yet.
Thus, have left the consensus blends alone for now and will have
to maintain the wait and see plan on this for now.

The broad troughing over the CONUS continues into next week with
some shortwaves diving through the larger scale flow to bring us
intermittent waves of accumulating snows to the area.  We will also
have another round of lake effect snow for the south shore Tuesday
into Wednesday of next week and have increased pops for this time
range.  Temperatures through the period remain on the cold side with
lows in the single digits below zero and highs in the single digits
above zero.  We should be making a lot of ice on area inland lakes,
and also cooling off Lake Superior, though it is a long ways from
being able to develop ice just yet.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 532 AM CST Thu Dec 8 2016

A surface trough over the region will keep a mixture of MVFR and
VFR ceilings and visibilities in snow showers over the area
through at least 01z, if not longer. There may be a locations that
get IFR visibilities if stronger snow showers move across. Gusty
winds to 20 knots are expected in the 15z-23z time range, but not
as strong as yesterday. MVFR ceilings expected to continue after
00z even as the snow showers diminish.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  24   8  13   1 /  50  10  10   0
INL  20   5   9  -4 /  40  10  20  10
BRD  20   7   9   0 /  60  10   0   0
HYR  25  12  16   4 /  70  20  10  10
ASX  28  15  17   8 /  90  50  40  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Lake Effect Snow Warning until 6 AM CST Saturday for WIZ004.

     Lake Effect Snow Advisory until 3 PM CST Friday for WIZ002-003.

MN...None.
LS...Small Craft Advisory until 6 AM CST Friday for LSZ121-140>148.

&&

$$

UPDATE...LE
SHORT TERM...JTS
LONG TERM...LE
AVIATION...LE



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