Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 161757

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1157 AM CST Fri Feb 16 2018

.SHORT TERM...(Today and tonight)
Issued at 430 AM CST Fri Feb 16 2018

The short term concerns are temperatures trends and the chance of
light snow over the south later tonight.

Water vapor imagery showing the upper trough exiting to the east
this morning. Sharp clearing associated with its passage after a
period of light snow over the south and east portion of the area
last evening. High pressure building east today should provide
lighter winds into the day as the ridge moves into the state.
Temperatures should be able to warm through the upper tees to
lower 20s to the east with perhaps some mid/upper 20s in the snow
free areas of west central MN.

The ridge passes off to the southeast this evening allowing the
next short wave to move in from the Dakotas. This will spread
mid/high level clouds rapidly to the east during the first part of
the night. We will likely see temperatures become steady or
slowly rise overnight. Isentropic analysis is indicating possible
saturation occurring to mainly the southeast portion of the cwa
late tonight. We will trim PoPs some to the north but continue the
small chance PoPs into south central MN after 06z Sat.

.LONG TERM...(Saturday through Thursday)
Issued at 430 AM CST Fri Feb 16 2018

Focus continues to be on the Sunday-Tuesday period where an
impactful multi-day wintry event looks to take place over much of
the region.

Saturday will feature a few linger snow showers, along and on the
back side of a weak passing cold front, for mainly far
eastern/southern MN into western WI. The modified Pacific moisture
being shunted into the area on the western and southern periphery
of a large NOAM trough will not be particularly deep, so there may
even be some brief freezing drizzle due to low level warm air
advection in advance of the cold front. Model soundings have not
been particularly bullish on this idea so have omitted it at this
point but it is a non-zero chance. Once this front pushes through,
it looks to stall out just to the east/south of the WFO MPX
coverage area Saturday night into Sunday morning.

The front then starts to waver back north as a warm front Sunday
morning while an area of low pressure develops along the front
over the SD/NE border. In addition, upper level flow takes on a
more WSW-ENE flow, with H5 heights nudging higher just enough to
indicate a more definitive warm bubble over southern MN into SW
WI. The main question is how far north the surface front and low
level warm layer moves as this will be key in determining the
demarcation of snow and icy precipitation across the the WFO MPX
coverage area for Sunday into Monday, with Tuesday expected to be
solely snow. Moisture looks to increase over the area late Sunday
through Monday as the broad-scale flow takes a more southerly
direction, allowing Gulf of Mexico moisture to shift into the
region. While most of it will be focused southeast of the coverage
area, enough will be able to blend with the Pacific moisture
moving in from the west ahead of another longwave western trough
to nudge up QPF`s from Sunday-Tuesday to the 0.25-0.50 for much of
the coverage area. The key difference from this time yesterday is
that the models overall have shifted the front slightly further
north. What this has done is to hold off on ideal cold air
advection until later Monday plus introduce warmer air further
north, bringing a greater potential of freezing drizzle and
freezing rain into southern portions of the area, particularly
Sunday night through Monday. The mixture of precipitation will
persist Sunday into Monday with deeper colder air taking over late
Monday through Tuesday, allowing for solely snow. Because this is
such a fluid scenario in the models, it is difficult to produce
amounts this far out. Roughly speaking, the northern half of the
coverage area may be subject to 3 to 7 inches of snow Sunday
through Tuesday with less than 3 inches south of a Redwood Falls-
Twin Cities-Eau Claire line. In addition, south of a Redwood
Falls-Twin Cities-Rice Lake line may see accumulating ice, with
potentially over a tenth of an inch of ice south of a Mankato-Eau
Claire line. That is how things look at this point but, as
mentioned earlier, uncertainty looms large with this forecast so
the amounts and locations of various p-types may well change over
the next few days.

The upper trough will dig deep into the Four Corners region Monday
night while H5 heights drop on the back side of the cold front,
which looks to now be definitively southeast of the coverage area
by then. While surface features will be less intense, there will
still be a few weak upper level waves passing through the region
Monday night through Tuesday which will keep lingering light snow
going but nothing intense or heavy. High pressure will then arrive
for midweek, resulting in a break from the precipitation.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1136 AM CST Fri Feb 16 2018

We will remain on the northern edge of surface high pressure
through the remainder of the afternoon with near 10 kts winds
becoming more southerly. Cloud cover will increase from the west
overnight with ceilings lowering to near MVFR by late Saturday
morning as a weak warm front passes through. In addition, there
will be a chance for flurries associated with the warm front and
ahead of the approaching cold front. Winds will remain light and
southerly through much of the morning before the aforementioned
cold front increases wind speeds and shifts winds to out of the

KMSP...VFR conditions are forecast but the main concern will be
the near MVFR ceilings during the mid to late morning. There is
also a chance for flurries, but visibility is not expected to be

Sat night...VFR. Chc mvfr. Winds S 5 to 10 kts.
Sun...VFR. Chc MVFR -SN. Winds SE 10 kts becoming NE.
Mon...IFR/-SN Likely. Winds NE 10-20 kts.




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