Area Forecast Discussion
Issued by NWS Duluth, MN

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869
FXUS63 KDLH 011720
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1120 AM CST Thu Dec 1 2016

.UPDATE...
Issued at 1118 AM CST Thu Dec 1 2016

Updated to upgrade chance for S-/ZL- to scattered coverage. There
has be continuous reports of light snow with patchy freezing
drizzle across portions of the forecast area.

UPDATE Issued at 911 AM CST Thu Dec 1 2016

Updated to add chance of freezing drizzle across areas north of
iron range and arrowhead for this morning. Have receive ed
reports of ZL- in those areas. The threat for s-/ZL- still looks
possible for the rest of the day with the low clouds and abundant
low level moisture across the area. Rest of fcst unchanged.

UPDATE Issued at 558 AM CST Thu Dec 1 2016

An updated aviation discussion is below for the 12Z TAF issuance.

UPDATE Issued at 449 AM CST Thu Dec 1 2016

Impressive gravity wave induced precipitation band has formed
this morning along the North Shore into Douglas and Pine counties
this morning. The low level flow was north from 15 to 20 knots
through 850mb per KDLH VWP. NAM BUFR soundings show a strong low
level inversion. Both the NAM and RAP show the gravity wave
continuing through much of the day. However, they also show low to
mid level moisture diminishing this morning into the afternoon
which would cause the precipitation to diminish. The intensity of
the band of precipitation has already shown some signs of
weakening but the conditions responsible for it remain. We
increased POPs quite a bit for this morning and have some snow
accumulation up to 2 inches. There is uncertainty if this band of
precipitation will maintain its strength and if so for how long.
Surface temperatures were from 32 to 36 degrees as of 11Z and a
mix of rain and snow will be more likely close to the lake with
mostly snow inland.

&&

.SHORT TERM...(Today through Friday)
Issued at 320 AM CST Thu Dec 1 2016

Low pressure centered near the Ontario and Quebec border will
move slowly east today into tonight. Cyclonic flow, low level
moisture, and colder air will support light precipitation today
over the Northland. A gravity wave feature was observed along the
North Shore into northern Douglas county as well and the RAP
suggests it will remain in some form today. Moisture was deep
enough into colder air aloft to support mostly light snow early
this morning with surface temperatures warm enough in a few spots
to support light rain or drizzle. We do expect the coverage of the
precipitation to diminish through the day over much of the
Northland. There will be a loss of mid level moisture today into
tonight over portions of the Northland which will cause the
precipitation to mix with or become freezing drizzle or drizzle
where it lingers.

Colder air flowing over Lake Superior will cause lake effect snow to
become more widespread through the day along portions of the South
Shore, continuing into tonight. There may be a mix that occurs
close to Lake Superior due to the warmer lake temperatures. The
low level flow will back this afternoon into this evening to more
northwest which will is less than ideal for lake effect snow over
the snowbelt of Ashland and Iron counties. Snowfall from 2 to 4
inches will be possible today into tonight, mainly over northern
Iron county. There could be some locally higher amounts as well.

Outside of the lake effect precipitation, we expect mainly dry
conditions over the rest of the Northland tonight into Friday. It
is possible there could be some patchy freezing drizzle/flurries
in spots but we don`t think it will be widespread enough to include
at this time.

We expect highs today in the upper twenties to mid thirties with
highs in the upper twenties to lower thirties on Friday.

.LONG TERM...(Friday night through Wednesday)
Issued at 320 AM CST Thu Dec 1 2016

The next weather system to affect the region is progged to traverse
the Upper Midwest late Saturday night and Sunday.  A broad lower
tropospheric warm advection pattern should be the primary forcing
mechanism for ascent and precip production.  There is still no true
arctic air in place this weekend, and thus, temps will be
sufficiently warm that some precip could be in the form of rain
during the day on Sunday.

Short wave ridging then builds briefly into the Upper
Midwest/Western Great Lakes region Sunday night into Monday night as
a low level Pacific-type airmass once again takes up residence over
the region. While we do not have PoPs mentioned during this time
period right now, it is entirely possible that a mention of
drizzle/freezing drizzle/flurries/fog may eventually need to be
added, as low level clouds are unlikely to clear with persistent
weak low level ascent.

Thereafter, the pattern becomes very active for the rest of next
week as the medium range models all suggest that another significant
winter storm will take shape over the middle part of the country
during the Tues-Thurs time frame.  It should be emphasized at this
point that any specific forecasts of snow/ice/blizzard conditions
for any particular area directly from deterministic model data
should be taken with a very large grain of salt, as both the
GFS/ECMWF have exhibited considerable inconsistency with timing and
placement both from run to run and between models.  With that said,
both medium range models seem to be slowly coming to the consensus
that this system will have a deep fetch of quality low level
moisture supplied by 48+ hours of southerly flow northward through
the Mississippi Valley in the warm sector, and an ample supply of
true arctic air flooding southward on the west side of the trof
axis. Typically this time of year, when an amplifying full latitude
trof has these two ingredients to work with, there is often
something quite significant that eventually results.  Therefore,
there is at least some potential for 1) significant snow
accumulations, 2) a band of wintry mixed precipitation, and 3) some
thunderstorms, followed by 4) the first true outbreak of arctic air
across the Northland by the end of next week. Details on the
strength of any potential storm, as well as timing and placement
of precipitation will come into focus over the next few days, and
it will be an excellent idea for anyone with weather interests
across the region to stay current with the latest information over
the coming days.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 558 AM CST Thu Dec 1 2016

Large upper low will continue to slowly weaken and move away from
the region today/tonight, with north/northwest winds persisting
through the period. There is sufficient wrap-around moisture for
MVFR and perhaps some short periods of IFR ceilings to persist,
along with some periods of light snow or flurries. However, precip
and fog should not limit visibility too much today or tonight.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  33  26  30  24 /  40  10  10   0
INL  30  24  29  21 /  30  10  10  10
BRD  32  25  29  21 /  30  10  10   0
HYR  34  26  31  24 /  30  10  10  10
ASX  34  29  33  26 /  40  20  10  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

UPDATE...Stewart



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