Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 171727
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1127 AM CST Sun Dec 17 2017

.UPDATE...
Issued at 1127 AM CST Sun Dec 17 2017

Updated for the latest 18Z Aviation Discussion below.



UPDATE Issued at 1034 AM CST Sun Dec 17 2017

The forecast was updated through this evening. Added light
snowfall accumulation to areas of northwest Wisconsin through
early this evening in relation to a frontogenetical band. Leaned
on the HRRR and RAP for placement and precipitation/snowfall
amounts because of good matching up with radar.

Also, the previous forecast had some clearing from the west today.
However, satellite trends and some model guidance suggest this
clearing will be delayed or not even happen. We have high cloud
cover preventing much heating of a widespread low stratus layer.
In general this is an easy time of the year to have stratus stick
around because of the lack of solar heating. The latest HRRR seems
to be doing well depicting the coverage of the low stratus, and it
has it sticking around over the Northland through tonight. The
cloud cover forecast was increased to reflect this skepticism in
any clearing, and might increase cloud cover even more soon.

&&

.SHORT TERM...(Today through Monday)
Issued at 325 AM CST Sun Dec 17 2017

A warm-up today into tomorrow with a chance for light snow across
parts of northern Minnesota on Monday.

On the synoptic scale the northwest flow pattern of recent weeks has
transitioned to a temporarily more zonal-like flow over the Upper
Midwest. A low level ridge/warm front will track east across the
region Sunday night with southwest flow at low levels overnight
leading to weak warm advection. A cold front then moves in from the
northwest bringing with it sufficient low/mid level moisture and
broad-scale lift from a stacked low over southern Canada to produce
light snow with perhaps rain mixing with snow at times due to
temperatures near or above the freezing mark Monday afternoon.
Snowfall accumulation of up to an inch is possible north of the Iron
Range. Monday may also be breezy with gusts to around 30 knots
possible due in part to the deep low tracking east across northern
Manitoba.

Highs in the mid 20s to near 30 today. Overnight lows in the mid
teens to near 20. Then warmer Monday with highs in the low to mid
30s with much of the Northland outside the interior MN Arrowhead
region expected to warm up above freezing. These highs are above our
normal highs in the low 20s, but well below record values - the
record highs for Monday are 44 (Duluth) and 40 (International
Falls). (Per Duluth climo record, a high temperature above freezing
has occured 18% of the time on Dec 18.)

.LONG TERM...(Monday night through Saturday)
Issued at 325 AM CST Sun Dec 17 2017

The focus in the extended period will be on a storm system that is
expected to start to affect the Northland Wednesday and possibly
continuing into late week, depending on the model, and on very cold
air that will move in next weekend and continue into next week.

Light snow with a possible light mix will end over northern
Minnesota Monday evening with little additional accumulation. Colder
air will move over the area Monday night knocking highs down into
the lower twenties to around thirty for Tuesday. Gusty west to
northwest winds are expected Tuesday, with gusts of 25 to 35 mph
possible. The upper flow will be quasi-zonal with a couple
shortwaves embedded in the fast flow aloft but little significant
precipitation is expected through Tuesday night.

An upper trough will be coming onto the Pacific Northwest coast late
Tuesday continuing into the Northern Rockies/Great Basin on
Wednesday. Low pressure will form downstream with a broad low
centered over the Nebraska/Wyoming/South Dakota vicinity. Increasing
warm air advection will lead to a chance for snow Wednesday. As the
low and upper trough move further east Wednesday night, snow will
continue and is expected to be widespread. The models are in very
good agreement through Wednesday night. The GFS and ECMWF start to
diverge some Thursday and that continues into Friday. The ECMWF is
slower and deeper with the surface low and lifts the surface low
into southern Wisconsin by 12Z Friday. The ECMWF solution would keep
snow going into Friday with the GFS dry or only having light
snowfall. In addition to snow from the low, the low level winds will
have an easterly component starting late Wednesday. This will lead
to lake enhanced snowfall along the North Shore, Twin Ports area,
and South Shore late Wednesday and possibly into Friday(if the ECMWF
is correct). It still appears a fairly widespread 2 to 4 inches of
snow will occur Wednesday into Thursday with the potential for some
areas of the Northland to receive heavy snowfall, especially if the
ECMWF solution ends up being correct with areas around Lake Superior
and northwest Wisconsin most likely to receive the higher amounts.

After the storm system passes late in the week, colder air will
start to move into the area with much colder air arriving Friday
night into Saturday night. Both the ECMWF and GFS show 850MB
temperatures dropping to near -30C at KINL by 12Z Sunday with 850MB
temperatures from -25C to -30C for all of the Northland by 00Z
Monday. Highs Saturday will only be in the single digits above zero
to lower teens, then struggle to climb above zero along the
International Border Sunday with single digits to around 10
elsewhere. There will also be northwest Winds Saturday through
Christmas Day creating even lower wind chill values. The cold looks
to stick around well into next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1127 AM CST Sun Dec 17 2017

Widespread LIFR/IFR conditions will likely continue through early
Monday, primarily because of low ceilings. There are also areas of
lower visibility from fog/mist. It previously looked like there
may be some clearing this afternoon and evening, but we are
increasing skeptical of that clearing. The latest HRRR model runs
have been reflecting the current low-level stratus layer well, and
the HRRR maintains this LIFR/IFR stratus through tonight. There
will be light snow in northwest Wisconsin early this afternoon,
including at KHYR.

Expect increasing southwest flow Monday morning. This will help to
lift the ceilings back into MVFR and VFR by late morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  28  17  33  23 /  10   0  30  10
INL  28  18  32  20 /  10  20  60  20
BRD  31  19  35  23 /  10   0  10  10
HYR  28  18  35  24 /  30  10  10  10
ASX  30  20  36  26 /  10   0  20  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory from 9 PM this evening to 10 PM CST Tuesday
     for LSZ146-147.

     Small Craft Advisory from 4 AM Monday to 10 PM CST Tuesday for
     LSZ141>143.

     Small Craft Advisory until 10 PM CST Tuesday for LSZ140.

&&

$$

UPDATE...Grochocinski
SHORT TERM...JJM
LONG TERM...Melde
AVIATION...Grochocinski



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