Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 230045

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

Issued at 734 PM CDT Sun Oct 22 2017

Updated to include 00z aviation discussion below.


.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 autumn-like 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 00Z TAFS through 00Z Monday evening)
Issued at 734 PM CDT Sun Oct 22 2017

High clouds will move into the region tonight in advance of a cold
front due to pass through the region during the day tomorrow. High
ceilings will lower into the mid-levels but remain solidly in the
VFR range. A few isolated showers are possible from time to time
but nothing that should impact operations to any great degree.
Main issue will be shifting and strong/breezy winds. Winds will
shift from S to W overnight then to NW during the day tomorrow.
Speeds at the surface will remain around 10 knots while winds in
the 1-2 kft layer may climb to around 30 knots, close to LLWS
criteria but looks to be more turbulence at this point so will
leave out LLWS mention. After daybreak, deep mixing will allow the
stronger WNW winds to mix down to the surface, resulting in speeds
around 15-20G30kts.

KMSP...Pre-frontal boundary will move across the area close to
daybreak, potentially creating crosswinds on the 12/30s through
the morning push, with wind speeds around 10 knots. Winds then
will continue veering to WNW by the evening push. Gusts will
commonly run in the low 20s knots but could hit 30 knots at times.

Tue...VFR with MVFR possible. Wind NW 15-20kts gusting to 30 kts.
Wed...VFR. Wind NW 5-10 kts.
Thu...VFR with MVFR late. Wind S 5-10kts becoming NW.




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