Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 222008
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
308 PM CDT Sun Oct 22 2017

.SHORT TERM...(This evening through Monday)
Issued at 308 PM CDT Sun Oct 22 2017

Clouds from our system yesterday are slowly moving out of western
WI, but clouds are already rapidly approaching western MN out ahead
of our next wave, which is currently moving across the
Montana/Saskatchewan border. This wave will come at us in two waves,
this first late tonight into Monday morning, with a second wave
dropping through in the afternoon. Both waves will have associated
cold fronts, with the second one actually having cold air with it
this time around.  For precip, if we see anything it will be very
light, with the bigger issue being winds behind the second boundary.

Looking at forecast soundings and obs back in ND, this first wave
will just result in clouds moving in up around 10k ft. There are
returns on the BIS radar, though rainfall obs are lacking,
indicating it`s mainly virga.  The HRRR shows potential precip with
this wave reaching western MN around 6z. This will probably be light
rain/sprinkles and may actually not be enough to measure, but will
be moving across western WI by 12z Friday. Precip chances look
better in the afternoon with the second wave, though that is due in
part to strong CAA, which looks to create steep low level lapse and
a favorable environment for developing showers with peak daytime
heating. Coverage looks to be isolated to scattered, with amounts
being fairly light once again (under 0.05").

As for winds, it`s behind the second boundary that we will see those
pick up quickly. Pretty good deal of spread though between the GFS
and NAM with how much wind we will see, and the differences come
down to winds in the h9-h8 layer (where we will be mixed up to and
through). The NAM shows winds in this layer in the 30-40 kt range,
with the GFS out in western MN showing 40-50 kts. The heart of the
isallobaric high (with 6 hr pressure rises on the order of +10-12
mb) will be heading into northwest MN, so kept our winds more
tempered toward the NAM. We should see gusts up near 40 mph out in
west central/southwest MN. Though strong, wind advy criteria is
sustained 30 mph/gusts to 45 mph and at the moment we look to stay
just below that level, but did add the strong wind mention to the
HWO.

.LONG TERM...(Monday night through Sunday)
Issued at 308 PM CDT Sun Oct 22 2017

We will definitely see a change in the weather this week, with
things fallish and even slightly wintry across the area. The
guidance is in good agreement on the big picture, with a deep
upper trough across the east and ridging out west. Over the course
of the week we see a few shortwave features drop into our area,
resulting in brief warm advection periods followed by reinforcing
shots of colder air. The guidance has come into better agreement
with a more significant system in the Thursday/Friday time frame,
but at this point most solutions point toward it having its
greatest impacts north of our area.

We will see ridging build in from the west Monday night and
Tuesday, which will bring any lingering shower activity associated
with the upper low and low-level cyclonic flow to an end. Some
showers could linger across the east on Tuesday, with a few
snowflakes certainly possible, but with no accumulation. The next
shortwave embedded in northwest flow looks to drop southeast
through the region Tuesday night and Wednesday, but things have
trended east with this feature, keeping any rain mostly out of our
area. After that we`ll await the arrival of a more significant
upper wave that will emerge into the northern High Plains
Wednesday night, and drive a surface low east across
central/northern Minnesota during the day on Thursday. This looks
to bring decent precipitation, including the possibility of snow,
to northern Minnesota, but for our area much will depend on the
exact track of the system and how much precipitation will wrap
south in the wake of the surface low in association with the upper
trough and deformation zone. Although the guidance is in good
agreement on the larger scale pattern, there are definitely some
differences in these details. For now, mostly chance PoPs Thursday
through Friday are the wisest course of action, with the best time
frame for snow coming on the backside of the system on overnight
Thursday night into Friday. The deterministic GFS is much more
aggressive in bringing heavier precipitation (which would at least
be a mix of snow if not all snow) southward into our area in
comparison to the ECMWF and the GEFS. The GFS is essentially
outside of the envelope the GEFS in terms of precipitation across
our area, so won`t get too excited about things at this point.
However, it does appear that we should at least have a shot at
many locations see their first snow of the season, even if it
isn`t able to accumulate. Needless to say, it will be something to
keep an eye on through the week, as we will sometimes see
successive shortwaves in these patterns drop a bit farther south
than initially progged. Any lingering precipitation should exit by
Saturday with ridging looking to hold on into Sunday (although
there is quite a bit of spread in the solutions at that point).

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1244 PM CDT Sun Oct 22 2017

Main concern is timing wind shifts with a pair of cold fropas
tomorrow. We will see winds back to the SSE this evening ahead of
these boundaries. Boundary one will send the winds to the SW, with
wind shift two coming 3 or 4 hours later with the NW winds. It is
this second boundary that will see strong winds with it as well,
with the potential for some 40kt gusts out in western MN Monday.
These boundaries and associated upper waves will bring bouts of
mid-level clouds with. Each will have a small precip chance as
well, but confidence in precip even occurring is too low to have
any sort of mention in the TAFs.

KMSP...First boundary will come through in the middle of the
morning push and give us a SW cross wind for much of the push,
though with wind speeds around 10 kts. By 17z, winds will be WNW.
High end of the gust potential Monday afternoon looks to be 30-35
kts.

/OUTLOOK FOR KMSP/
Tue...VFR with MVFR possible. Wind NW at 20G30 kts.
Wed...VFR. Wind NW at 10 kts.
Thu...VFR with MVFR late. Wind S at 10 bcmg NW at 15G25 kts.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...MPG
LONG TERM...
AVIATION...MPG



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