Area Forecast Discussion
Issued by NWS Twin Cities, MN

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066
FXUS63 KMPX 201751
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1251 PM CDT Mon Mar 20 2017

.SHORT TERM...(Today and tonight)
Issued at 310 AM CDT Mon Mar 20 2017

Surface analysis early this morning shows high pressure centered
over the Appalachians with a weak low pressure center near KOMA.
Its associated cold front stretches nearly due westward into
central Wyoming with an east-west oriented area of high pressure
to the north of the cold front into southern Canada. Aloft, the
pattern is very much zonal with troughs offshore each CONUS coast.
As the day progresses today, the low pressure system over the
central Plains will shift southeast to near KSTL by midday while
the cooler high pressure to the northwest sags into the upper
Mississippi River Valley. This will result in mainly high clouds
for much of the day but also enact cold air advection to the
region. Another cold front in southern Canada will drop southeast
this evening but will contain limited moisture. The lack of upper
air support combined with deeper moisture well to the southwest of
the WFO MPX coverage area will mean that any precipitation
associated with the cold front will also remain off to the
southwest. The front will cross the coverage area during the early
morning hours Tuesday, resulting in nothing more than a
reinforcing shot of colder air which will last into midweek. While
max temperatures today attempt to climb into the lower 50s, highs
will only reach the 35-40 degree range on Tuesday.

.LONG TERM...(Tuesday through Sunday)
Issued at 310 AM CDT Mon Mar 20 2017

The mean pattern will change significantly over the next few days
as a series of storm systems move inland across the west coast.
This will lead to the weak quasi-zonal flow aloft, to a more west-
southwest flow. This change will also cause the relatively dry
weather we have been experiencing, to a more wet and active
period.

As always, models usually try to change long wave (persistent)
patterns too fast and lead to timing issues for the onset and
duration of precipitation. In addition, there remains
inconsistency on the evolution of the mean long wave trough
moving across the CONUS, and how short waves develop over the
plains. This continues today as the EC/GFS/GEM have different
scenarios of where/when the upper low moves out into the plains
late this week.

Another aspect to this pattern change is how will the influence of
an upstream upper trough in eastern Canada, and an upper ridge off
the southeast coast, play a role in the speed/evolution of this
weeks storm system. Even a blended forecast of all the
deterministic models doesn`t support the timing/speed of this
weeks system. Although once the pattern does change, a period of
wet weather is likely. As for QPF/rainfall amounts... do to the
increase surge of gulf moisture by Thursday/Thursday night, QPF
amounts could be conservative from the models, especially
considering the higher PWAT values expected above one inch.
Although there could be some light snow as the pattern changes
late Wednesday, early Thursday, anything that falls should be
little if any.

Once this system leaves the region early in the weekend, another
storm is expected to form in the plains early next week. Thermal
profiles still remain warm enough to support rain/snow mix.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1241 PM CDT Mon Mar 20 2017

Quiet weather this period with just some mid-high level cloudiness
today, decreasing cloud cover tonight and tomorrow, especially
north and east. In terms of winds, they are jumping a bit between
NNW and NNE today and that will continue but should generally stay
northerly for the most part.

KMSP...could have a few gusts tomorrow afternoon but held off on
including that in the forecast as it doesn`t look to be much above
the sustained speed.

/OUTLOOK FOR KMSP/
Wed...Mainly VFR. Chance MVFR with -RA/-SN late. Wind SE 5-10 kt.
Thu...MVFR with -RA likely in afternoon. Wind SSE 10 kt.
FRI...MVFR with -RA likely. Wind NE 5-10 kt.

&&

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

$$

SHORT TERM...JPC
LONG TERM...JLT
AVIATION...SPD



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