Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 210529
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1129 PM CST Tue Feb 20 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 308 PM CST Tue Feb 20 2018

Colder and drier air will filter into the Northland through
tonight as an area of low pressure lifts from Upper Michigan this
afternoon to Quebec overnight. An area of high pressure will be
slowly shifting east through the Northern Plains into the Upper
Midwest. The current overcast cloud cover will then and clear out
overnight. It will be a pretty clear and cold morning by dawn
Wednesday with very light winds speeds. It earlier appeared we
would have wind chills colder than 25 below zero, but this no
longer seems to be the case. The winds will be weakening through
the night even though temperatures will be dropping off. It now
appears we will have widespread wind chills of 10 to 20 below zero
by late tonight and early Wednesday.

Wednesday looks sunny with light westerly winds. The area of high
pressure will shift east into the Upper Midwest, centering itself
across southern Minnesota and into central Wisconsin.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 308 PM CST Tue Feb 20 2018

The active weather pattern will continue during the long term
with a quick shot of snow, possibly mixed with freezing drizzle,
Thursday night and Friday and another chance of snow Saturday
afternoon and evening.

High pressure will remain over the region Wednesday night into
Thursday ahead of a fast-moving shortwave trough forecast to
arrive Thursday night. At 00Z Thursday a jet streak is forecast
near the Baja and will lift quickly into the Southern Plains as it
rounds the base of the western CONUS longwave trough. The surface
ridge over the Northland will drift away from the area during the
day, with winds backing southerly ahead of the approaching
shortwave. Northward moisture transport from the Gulf of Mexico is
expected ahead of the wave, which will support clouds and light
snow. The shortwave trough and associated vort max will be located
over the Central Plains into the mid- Mississippi Valley by
Thursday evening. Precipitation is forecast to spread northward
from Nebraska, South Dakota, and Iowa, into northern Minnesota,
Upper Michigan, and northern Wisconsin during the evening. Model
thermal profiles over northwest Wisconsin suggest a potential for
freezing drizzle late Thursday night into Friday. Have opted for a
mix of light snow and freezing drizzle with this forecast since
confidence in a complete change to FZDZ is low. However, even a
light glaze of ice can create significant travel difficulties, so
definitely want to include a mention in the forecast and HWO.
Raised QPF above the consensus blend and lowered snow ratios with
this forecast. The dendritic growth area will be relatively
shallow and located well aloft in the cloud bearing layer, with
temperatures increasing below the DGZ and super-saturation
decreasing. Think small dendrites, needles, and columns will be
the dominant snow crystal habit. Higher ratios seems likely at the
start of the event, before the column warms with increasing WAA,
with 15:1 in the northwest and 13:1 in the southeast 00-06Z
Friday. The gradient in the snow ratios increases after 06Z with
interior portions of northwest Wisconsin around 11.5:1 and north-
central Minnesota around 16:1. However, with the increase in QPF,
a swath of 2-4 inches of snow exists from central Minnesota into
the Arrowhead, with lower totals in north-central Minnesota and
interior northwest Wisconsin.

The shortwave quickly exits the Northland Friday afternoon with
high pressure returning to the Upper Midwest. The longwave trough
will gradually push eastward into the center of the CONUS while
de-amplifying on Saturday. Deterministic guidance shifted
considerably for the 20.00Z and 20.12Z runs with a much better
organized system than yesterday`s guidance indicated. Another
southern stream jet streak will round the trough and move into the
mid-Mississippi Valley Saturday evening. Deterministic guidance
sill diverges in handling this feature with the GFS phasing the
southern jet streak with a northern stream feature, resulting in
the development of a well-organized storm system. The ECMWF
features less separation between the two airstreams, and less
phasing, while the GEM is more progressive. The GEM handles the
surface system as an open wave, while the GFS and ECMWF feature a
closed surface low. The trajectories of the respective low
pressure systems would support slight to likely POPs over the
Northland Saturday afternoon through the evening. The best
potential for light snow is over northwest Wisconsin, as the storm
track is well to the southeast. Confidence is low given the
diverse solutions offered by the models. A few inches of snow
accumulation are possible as of this afternoon.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1129 PM CST Tue Feb 20 2018

An upper level trof will move past the terminals with MVFR cigs
over northeast Minnesota, but should remain east of the
terminals. Otherwise, high pressure will be in the vicinity
through the forecast with VFR at all sites.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  -2  19  -1  26 /   0   0   0  10
INL  -6  17  -7  28 /   0   0   0   0
BRD  -5  19  -2  26 /   0   0   0  20
HYR  -2  20  -3  29 /   0   0   0  20
ASX   2  22   2  31 /  10   0   0  10

&&

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

$$

SHORT TERM...Grochocinski
LONG TERM...Huyck
AVIATION...GSF



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