Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 221142

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
642 AM CDT Thu Mar 22 2018

Issued at 637 AM CDT Thu Mar 22 2018

Updated to include 12z aviation discussion below.


.SHORT TERM...(Today and tonight)
Issued at 351 AM CDT Thu Mar 22 2018

Surface analysis early this morning shows north-south oriented
high pressure centered over the entire length of the Mississippi
River. Meanwhile, a conglomerate of weak low pressure centers
gather over eastern CO/WY in the vicinity of a frontal boundary
extending from central British Columbia province southeast through
MT/WY/NE. Aloft, a ridge axis is aligned over the lee of the
Rockies, producing NW flow over the central CONUS, while a potent
longwave trough approaches the Pacific Northwest. The ridge axis
aloft will slowly shift east, moving to the western MN border by
daybreak Friday morning. This ridge will keep the surface frontal
boundary well off to the west and south through Friday morning.
Nevertheless, a convergence of Pacific and Gulf moisture will take
place along and just to the west of the ridge axis which will
allow much deeper moisture to make its way into western and
southern MN late tonight thru early Friday morning. The slow
progression of the main low pressure area developing along the
front will help keep precipitation out of western MN through
daybreak Friday morning so will maintain a dry forecast for today
through all of tonight. That said, clouds will certainly be on the
increase, especially in the lower levels. Temperatures will
continue to run mild, especially in western MN, through tonight.
Lows will have about a 10 degree spread from western MN to western
WI both early this morning and again early Friday morning (with
the warmer readings in western MN). Highs this afternoon will
climb to the 40-45 degree range.

.LONG TERM...(Friday through Wednesday)
Issued at 351 AM CDT Thu Mar 22 2018

Wintry weather remains on track for Friday-Saturday, with the
heaviest snow still looking to occur from western MN through south
central MN. The latest guidance was pretty consistent from
yesterday and still indicates the winter storm watch area has the
highest snowfall potential with this system.

A deep low off the coast of the Pacific Northwest will encourage a
quickly amplifying ridge along the east side of the Rockies today.
Later today, shortwave energy will lift northeast through the four
corners region and by tonight strong lift out ahead of the
shortwave owing to strong theta-e advection and increasing f-gen
in a northwest to southeast oriented band will lead to snow
quickly breaking out across the Dakotas.

The baroclinic zone will setup from the central Dakotas to the
Southeast through western MN and south central MN, and will be a
focus for lift.  For tomorrow, timing still remains similar to the
previous forecast, with precip moving into western MN in the
morning and expanding somewhat eastward as strong differential
divergence becomes juxtaposed with the aforementioned baroclinic
zone. By midday tomorrow, the eastern progression of the precip
shield will slow as the main surface low begins paralleling the
orientation of the precip shield toward the southeast. Surface
temperatures in the mid 30s to near 40 ahead of the precip will
quickly cool once precipitation begins, and any rain should
changeover to snow within the first hour or two of moderate

The high pressure that will be in place across eastern Ontario and
the northern Great Lakes will provide very dry easterly flow
across western WI and eastern MN, and hence confidence in how far
east the heavy snow reaches remains modest at best. For tomorrow
night, the precip shield will begin to focus its movement to the
southeast, and halt the expansion eastward, so portions of western
Wisconsin still look to miss most (or all) of the snowfall from
this system. By Saturday morning, light snow will still linger
across south central MN as the surface low pulls away well to our

Overall, still expect 5 to 8 inches of snow in much of the watch
area (less along the periphery of the watch). Did not gain enough
confidence yet to issue a warning for this system, but if todays
guidance continues to narrow in on this solution, that will
increase our confidence. The tight gradient looks to be along a
line from St. Cloud through the Twin Cities and Cannon Falls. This
gradient will be especially tight due to the fact that system
will transition from an eastward expansion to a parallel path to
the orientation of the precip shield, and due to the very dry
easterly flow in the lowest levels of the atmosphere.

By early next week, we`ll be in a southwest flow regime as a
deeply amplified trough pushes across the western CONUS, which
will likely lead to active weather locally, however it looks
warmer so rain would be the primary p-type but certainly could see
snow mix in, especially at night.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 637 AM CDT Thu Mar 22 2018

Mainly low VFR stratus clouds this morning with a few pockets of
MVFR. These low clouds will likely linger thru late morning then
scatter out late this afternoon into this evening. High ceilings
will then move in late tonight through Friday morning in advance
of the precipitation expected to spread across MN during the day

KMSP...Ceilings expected to stay just over 3000ft thru late
morning then scatter out for this afternoon and evening. High
ceilings to develop during the day tomorrow but no precipitation
expected through this TAF cycle.

SAT...MVFR with a.m. -RA/-SN. Wind E 10-15 kts.
SUN...VFR. Wind SE 10-15 kts.
MON...MVFR with -RASN, possibly IFR. Wind SE 5-10 kts.


MN...Winter Storm Watch from Friday afternoon through Saturday
     morning for MNZ041-048-057-065-067-074-075-082>084-091>093.

     Winter Storm Watch from Friday evening through Saturday morning
     for MNZ049-058>060-066-068>070-076>078-085.

     Winter Storm Watch from Friday morning through Saturday morning
     for MNZ047-054>056-064-073.



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