Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 220852

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

.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 precipitation.

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 south-southeast.

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 06Z TAFS through 06Z Thursday night)
Issued at 1100 PM CDT Wed Mar 21 2018

MVFR conditions are expected to continue through Thursday morning
at sites west of the Interstate corridor. Areas along and to the
east of I-35 will remain VFR. Mostly skies over WI will gradually
work westward across MN sites Wednesday afternoon, with all sites
expected to be VFR by the start of the next TAF period (00z
Thursday). Winds will be light and variable to calm, and then
increase to 5-8 knots from the east on Wednesday.

The ceiling will vary between 3000 and 3500 feet overnight, be
mainly VFR on Thursday morning, then scatter out on Thursday

FRI...VFR early becoming MFVR with -RA/-SN. Wind ESE 10G15 kts.
SAT...MVFR with Chc -RA/-SN. Wind ESE 10G15 kts.
SUN...VFR. Wind SE 10G15 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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