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Area Forecast Discussion (AFD)

Issued by Duluth, MN (DLH)

FXUS63 KDLH 210542

Area Forecast Discussion
National Weather Service Duluth MN
1142 PM CST Sun Jan 20 2019

.SHORT TERM...(This evening through Monday)
Issued at 400 PM CST Sun Jan 20 2019

Not as cold tonight as warmer air begins to advect in from the 
south tonight into Monday. A warm front building across the Upper 
Midwest on Monday into Monday night will be a focus for light to 
moderate snowfall developing, with a cold front then approaching 
from the west on Tuesday. Snowfall will be slow to start Monday 
afternoon from west to east, then a period of steady moderate 
snowfall rates Monday night will produce around 4 to 6 inches of 
snow across the Highway 2 corridor by daybreak Tuesday, including 
in Duluth. North of the Iron Range and south of the Highway 210 
corridor into northwest Wisconsin amounts will be less, around 2 
to 4 inches by daybreak Tuesday. Temperatures will be on a warming
trend - highs on MOnday in the low to mid teens, then lows Monday
night mild in the single digits to low teens above zero! (Normal 
lows range from around -7 to +1 for this time of year.)

On the synoptic scale a broad mid/upper level ridge over the 
Great Plains is building east followed by a deep longwave trough 
at mid/upper levels developing over the western states. This 
trough will track towards the Four Corners region on Monday into 
Monday night, with resultant southwest flow developing at mid 
levels over the Great Plains and Midwest. At low levels the arctic
high pressure that brought this weekend's frigid temperatures is 
over Lake Superior and exiting to the east with southerly flow 
developing over the Upper Mississippi River Valley in its wake 
late tonight into Monday. This will result in warmer air advecting
in at low levels, converging on a warm front boundary that lifts 
into northern Minnesota and northern Wisconsin through the day 
Monday. Broad-scale forcing from this warm air advection and a 
weak mid-level shortwave trough ejecting out of the main longwave 
trough over the southwest will result in widespread light to 
moderate snowfall rates developing. 

Guidance has been fairly consistent will this warm front
development and associated precipitation, with convection- 
allowing guidance exhibiting the usual higher amounts while the 
parameterized guidance (GFS, ECMWF, CMC-Global) having a slightly 
more conservative consensus. There have been some variations run- 
to-run and across ensembles in the north-south placement of the 
highest precip amounts, but the consensus seems to be right along
the Highway 2 corridor in northeast Minnesota, including the Twin
Ports. With the best lift across the dendritic growth zone at 
around 700-600mb, there will be a long duration for flakes to grow
and combine in a nearly isothermal layer at low levels, resulting
in large flakes and aggregates as snowfall falls Monday night. 
Confidence in snowfall amounts is fairly high, and while there 
will likely be some timing adjustments needed (snow may begin a 
little later than currently forecast, and north-south placement of
higher amounts still carry some uncertainty), we felt confident 
enough to issue a Winter Weather Advisory for snow late Monday 
into Tuesday morning due to the likely impacts to the Tuesday 
morning commute. 

.LONG TERM...(Monday night through Sunday)
Issued at 400 PM CST Sun Jan 20 2019

The main focus for the long term period continues to be chances of 
light to moderate snow during the morning hours Tuesday, with a 
return of bitterly cold temperatures and wind chills by the end of 
the week.

Tuesday morning will have widespread chances of light to moderate 
snow across much of the Northland as a mid-level shortwave trough 
phased with an upper-level longwave trough, located across the 
Intermountain West states, moves through the region. Isentropic lift 
doesn't appear to be as strong after sunrise Tuesday morning as 
opposed to Monday night, but with the bulk of the snow falling 
overnight, expect the Tuesday morning commute to be hazardous. 
Eventually, the wave and the inverted trough axis of the surface low 
associated with the parent longwave trough will shift eastward, 
bringing the snow to an end by Tuesday afternoon and evening. It 
appears the snow will take some time to end as there will be a few 
positive vorticity advection maxima translating over northwest 
Wisconsin, so expect that snow will linger there through the evening.

Eventually, surface high pressure ridging will translate through the 
Northland, which will bring chilly conditions Tuesday 
night/Wednesday morning. Expect overnight lows in the single digits, 
above and below zero, despite the possibility of low clouds 
lingering overnight. Then, a compact mid-level shortwave trough will 
sweep through the region on Thursday, which should bring chances of 
light snow. The synoptic guidance is in pretty good agreement with 
bringing a tight surface pressure gradient across the region as 
well, which will bring some gusty northwest winds. Then, 
temperatures will plummet late Thursday through Saturday morning as 
arctic high pressure builds into the region. 1000-500 mb layer 
thickness values decrease to around 480 to 490 decameters Thursday 
night/Friday morning, so some bitterly cold temperatures and wind 
chills are anticipated. Temperatures look to moderate slightly into 
next weekend from southerly return flow as the high pressure ridge 
passes to the east. There could be a few rounds of light snow 
possible, but there's quite a bit of uncertainty regarding the 
timing and areal coverage. However, confidence is higher for some 
lake effect snowfall over the Lake Superior snowbelt region through 
the day Sunday.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1142 PM CST Sun Jan 20 2019

MVFR ceilings were over northern Ashland/Iron Counties and along 
the North Shore with an arm extending toward the International 
Border. These ceilings will be mainly over the North Shore and 
Arrowhead as the night progresses as low level winds will continue
to veer to southerly. There will be some light snow showers or 
flurries as well along the North Shore. Clouds will thicken and 
lower Monday into Monday night as low pressure moves into the 
region. Snow will also develop from southwest to northeast Monday
into Monday night with IFR or lower visibilities and IFR/MVFR 

Southerly winds will increase on Monday with low level wind shear
occurring over far northern Minnesota from around 12Z through late


DLH -14  14   9  18 /  50  80 100  80 
INL -24  12   2  16 /   0  70  80  40 
BRD -21  12   8  18 /   0  90  90  70 
HYR -14  15  14  20 /   0  70  90  60 
ASX -11  18  13  21 /  40  60  90  70 


WI...Winter Weather Advisory from 6 PM Monday to noon CST Tuesday for 

     Wind Chill Advisory until 9 AM CST Monday for WIZ001.

MN...Winter Weather Advisory from 6 PM Monday to noon CST Tuesday for 

     Winter Weather Advisory from noon Monday to noon CST Tuesday for 

     Wind Chill Advisory until 9 AM CST Monday for MNZ010>012-018>021-