Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 140026 AAA

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
626 PM CST Sat Jan 13 2018

.SHORT TERM...(This evening through Sunday)
Issued at 245 PM CST Sat Jan 13 2018

Forecast confidence is fairly high on snow developing across
central Minnesota after sunrise, and across southern Minnesota,
and west central Wisconsin by the afternoon. The main concern is
snowfall ratio which could be as high as 20 to 25-1 based on
the best area of lift & moisture availability. Due to the higher
snowfall ratios, any small amount of QPF could produce a light
dusting, or up to a few inches. This again is dependent on the
amount of moisture, and lift, which coincides in the dendritic
growth zone region. A general 1 to 3 inches of snow looks likely
from central, east central, southeast Minnesota, and west central
Wisconsin. Amounts taper off to a light dusting, or up to an inch
from west central to south central Minnesota. The other concern
with this system is the possibility of blowing snow. Using several
weather tools, pressure gradient increasing, and surface low
holding steady and not falling too much, it would suggest that
some blowing snow will develop in western/southern Minnesota.
However, the usual areas that are prime for blowing snow in
western/southern Minnesota, the snow depth is shallow and new
snowfall will likely be less than an inch. Therefore, I am not
anticipating blizzard conditions. The best scenario is for
patchy/areas of blowing snow, but surface visibilities should
remain above 1SM. The best forecast is to advertise the worst case
scenario in the HWO, and hold off on any headlines until more
snowfall develops, or wind speeds increase.

.LONG TERM...(Sunday night through Saturday)
Issued at 255 PM CST Sat Jan 13 2018

This system on Sunday is rather fast and will likely be out of the
area (accumulating snowfall) by Sunday evening. Other than the
possibility of blowing snow, the main concern is the subzero
temperatures returning, with wind chill values approaching or
exceeding -25F for several hours, starting Sunday evening. Wind
chill headlines will likely be issued for Sunday night/Monday
morning as wind chill values drop to -25F, to locally -40F in
portions of west central/central Minnesota by Monday morning.
Monday night and Tuesday will also be very cold and wind chill
values will likely exceed the threshold of wind chill advisory

After Tuesday, return flow develops and the Arctic air mass will
be replaced by modified Pacific/Canadian air for the ladder part
of the week.

The mean long wave trough that has been established for a good
part of late December, and early January seems to be retreating
into northern Canada in the next 1-2 week period. There is a sign
that more zonal, or progressive flow will develop after next
week. This means that the core of the coldest air will remain in
Canada, but it also means that we have a better chance of getting
more precipitation. Although a storm system is forecast to move
across the mid section of the nation the weekend of January 20th,
it is too far out to decide if it will affect our region or not.

In addition, the teleconnections (Strong Negative PNA, Weak
Positive NAO) are supporting a more active period on the west
coast late next week, and this usually means milder air
transported across the Rockies and into the Plains.

To sum things up, the Arctic air mass will retreat northward as
the more active/progressive flow develops in the mid section of
the nation late next week. This active/progressive flow could
also mean a wetter pattern for the Upper Midwest depending upon
the orientation of the storm systems moving out into the Plains.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 626 PM CST Sat Jan 13 2018

VFR conditions until Sunday morning. Cigs will lower quickly, with
light snow or flurries beginning shortly thereafter. Steady snow
will move in during the afternoon with LIFR conditions expected.
Light snow may continue into Sunday evening, especially east of
I-35. Two to three inches of accumulation are expected, except
closer to an inch across western MN.

KMSP...VFR until light snow begins mid morning. The heavier snow
will arrive early afternoon, continuing through early evening.

Mon...VFR with MVFR possible. Wind NW 15G20 kts.
Tue...VFR. Wind NW at 5-10 kts.
Wed...VFR. Wind SW at 5-10 kts.




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