Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 211045

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
445 AM CST Sun Jan 21 2018

.SHORT TERM...(Today through Monday Night)
Issued at 440 AM CST Sun Jan 21 2018

The storm system expected to impact our area overnight and
through tomorrow is now moving over the four corners region and
remains on track to bring heavy snow and strong winds to southern
Minnesota and western Wisconsin.

For today, widespread cloud cover will continue streaming north of
the upper trough.  We will see another warm day with highs in the
upper 30s as the warm airmass remains in place before the system
arrives. Northeast winds will begin developing across the area as
surface cyclogenesis occurs today on the lee side of the Rockies.
A band of modest frontogenesis may will saturate the lower
atmosphere this afternoon, but may not be enough to produce
anything more than lower clouds and possibly some flurry activity.

The surface low will eject eastward during the day and curl
northeast this evening, heading in our direction.  Northeast winds
will increase overnight as the system approaches, with the latest
guidance suggesting widespread precip reaches the I-90 corridor
around midnight tonight, and continues northward from there.  A warm
thermal profile initially in place along I-90 will mean a wintry mix
is likely at the onset, with some chance of freezing rain if the
surface can cool quickly enough tonight.

The snow forecast remains on track for much of southern MN and
western WI. Confidence has increased in the threat of true whiteout
conditions in a portion of south central MN west and south of
Mankato, so a Blizzard Warning has been issued. Winds gusting 35-40
MPH with heavy snow falling in this area justified upgrading to a
Blizzard Warning at this stage. With 8 to 12 inches expected,
drifting will be significant as well. East of there, the Winter
Storm Warning area will also see strong winds leading to blowing and
drifting, but the wind speeds aren`t quite as strong as farther
west.  Nonetheless, very difficult travel is expected in the Winter
Storm Warning area.

The uncertainty comes into play with the location of a snowfall
gradient that will be tighter than we can realistically forecast. As
this system lifts into Iowa, very strong frontogenesis and upper
level forcing will lift across southern MN, but it`s northern extent
will be very sharply defined, further aided by the dry northerly
flow in the low levels.  This band looks to setup over or very close
to the metro.  The current forecast calls for around 2" in the
northwest metro with 6-8" in the southeast metro.  The gradient will
likely be tighter than that and subtle shifts north or south will
make big differences in your local impacts.  Overall though, the
model suite is again trending to the south, so the main change along
the northern periphery of the watch was to tighten the gradient,
including the metro, lowering snow totals for the northern end of
the watch. Did leave the winter storm watch in place along this
gradient until we have higher confidence in where it will end up as
there are still some minor differences among the models. With the
main area of snow arriving in about 24 hours, several hi-resolution
models will start reaching far enough out time to aid in our
confidence in the placement of this band. Keep checking back for

.LONG TERM...(Tuesday through Saturday)
Issued at 440 AM CST Sun Jan 21 2018

The long-term portion of this forecast will commence with the deep
wound-up low pressure system situated over Michigan while a wavy
generalized WNW-ESE flow aloft settles down over the north-central
CONUS. This will shift the deep low into New England and southeast
Canada, essentially setting up an eastern NOAM trough while a
western ridge develops, producing dry northwest flow aloft atop weak
surface high pressure through the middle of the week. A longwave
trough will move onshore the west coast Thursday and push across the
Rockies Friday then move through the central CONUS Saturday. This
system will spawn a weakly-organized low pressure system which will
bring a mix of rain and snow to the area Friday night into Saturday.
Not expecting a lot from this system as the low pressure center is
progged to track to the north of the WFO MPX coverage area plus
moisture will not be all that impressive with the system.

As for temperatures, behind the large storm system, no arctic surges
are foreseen. In fact, temperatures look to run above normal for the
latter half of the week through the upcoming weekend.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1120 PM CST Sat Jan 20 2018

High ceilings look to remain fairly stoic through the overnight
period into much of tomorrow in advance of the potent winter storm
expected to strongly impact the region Sunday night through
Monday. The consequence of the high clouds tonight will be to
prevent fog development to a more widespread degree, despite winds
going calm and warm air resident over residual snowpack.
Additional moisture will begin to stream in from the Deep South
ahead of the storm system but while this is mainly taking the
form of the high clouds, there still will be patches of MVFR
visibility in MN with MVFR-IFR potentially at the WI TAF sites.
The high clouds will then steadily lower during the day tomorrow,
resulting in MVFR to IFR ceilings tomorrow evening. Except for
KMSP which covers 30 hours, it is still too early to mention
precipitation at this point as chances won`t increase until after
06z tomorrow night. Winds will be fairly light out of the north,
if not calm, overnight before becoming northeast 5-10 kt tomorrow.

KMSP...Will maintain VFR conditions through tomorrow afternoon as
high clouds lower to mid-levels. Cannot rule out MVFR-IFR fog
close to daybreak Sunday morning so with winds going calm, have
added a mention of MVFR visibility around 12z. Ceilings will
lower to MVFR then IFR levels tomorrow evening in advance of the
strong winter storm system. Conditions will deteriorate further
beyond 06z tomorrow evening, including the commencement of light-
moderate snow along with increasing winds, making for a difficult
Monday morning push.

Mon...IFR/LIFR with +SN/BLSN. Several inches of snow likely.
Winds N 15-25 kts gusting to 30 kts.
Tue...Mainly VFR. Winds NW 5-10 kts.
Wed...Mainly MVFR with a chance of IFR cigs. Winds 5 kts or less.


WI...Winter Storm Warning from 3 AM Monday to midnight CST Monday
     night for WIZ015-016-023>028.

     Winter Storm Watch from late tonight through Monday evening for

MN...Winter Storm Warning from 3 AM Monday to midnight CST Monday
     night for MNZ069-070-077-078.

     Winter Storm Watch from late tonight through Monday evening for

     Winter Weather Advisory from 9 PM this evening to midnight CST
     Monday night for MNZ064-065.

     Winter Storm Warning from 9 PM this evening to midnight CST
     Monday night for MNZ073-075-076-084-085-093.

     Blizzard Warning from 9 PM this evening to midnight CST Monday
     night for MNZ074-082-083-091-092.



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