Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 162051

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
351 PM CDT Sat Sep 16 2017

.SHORT TERM...(This evening through Sunday)
Issued at 315 PM CDT Sat Sep 16 2017

The main forecast concern is when and/or where thunderstorms begin
to develop during the late afternoon/early evening along the
instability gradient in the southeast 1/4 of MPX forecast area.

Earlier morning convection was all elevated and the latest batch
was moving rapidly northeast across central Minnesota. Regional
radar does show a few showers in northeast Nebraska which could be
the first start of thunderstorm activity beginning to build
across the Upper Midwest. Not a lot of support upstairs as the
main upper wave was across the western Dakotas. However, as this
area of showers moves eastward into the axis of greater
instability, thunderstorms could develop. But again, these showers
have no upper level support at the current time, and most of the
higher chances of precipitation occurs once it moves into the
instability axis late tonight. Therefore, if nothing happens as
the showers move northeast, then it may be mostly dry this evening
until the main upper wave begins to move eastward and allows
greater upper level support, and hence, better shower and
thunderstorm development along this axis of instability.

Will continue highest percentages east of the Minnesota/Wisconsin
border, but later forecasters need to watch south central
Minnesota if thunderstorms develop earlier along the area of
showers moving northeast into northwest Iowa. Otherwise, Sunday
will have clearing skies with temperatures closer to normal highs
for mid September.

.LONG TERM...(Sunday night through Saturday)
Issued at 315 PM CDT Sat Sep 16 2017

A more active pattern is expected as the upcoming week progresses,
mainly due to the formation of a trough in the western CONUS with
a ridge in the eastern CONUS, putting the Upper Mississippi River
Valley region in pronounced southwest flow aloft which will allow
several organized systems to impact this region.

The first will be a weaker system for Monday, which will feature a
shortwave trough axis aloft while a low pressure center and its
associated warm front in advance of it shifts from the central
Plains into the Ohio Valley. Enough isentropic lift to the north
of the warm front plus the buckling aloft from the trough within
deep enough moisture will bring a few isolated to scattered
showers to the area.

A more organized system is expected for Tuesday night into
Wednesday but will be fairly quick-moving as the flow aloft
becomes more amplified and a potent trough aloft kicks the system
through the region. However, even with the passage of the
shortwave trough, the longwave pattern will continue to become
more amplified by the end of the week, such that nearly meridional
flow is expected by next weekend. This will result in a deep plume
of moisture being shunted into the region in advance of the next
well-developed frontal system for the end of the week. Showers and
thunderstorms already look likely with this end-of-week system.

As for temperatures, with a more southwesterly flow taking place,
this will allow for day-by-day warm air advection for the region.
Temperatures will go on a gradual warming trend back to above-
normal levels, including highs near 80 degrees by midweek.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1225 PM CDT Sat Sep 16 2017

Wind shift line/cold front has moved through most of the Twin
Cities metro area as of 12 noon. MVFR/IFR cigs had developed
behind this front, but the typical daytime LCLs are lifting, and
some of the MVFR cigs are becoming VFR, especially in southwest
Minnesota. Area web cams are also noted the partial skies clearing
in western/southwest Minnesota which may mean a better forecast of
VFR cigs compared to the current forecast. Will hold off on major
adjustments, but VFR cigs in western Minnesota may develop
earlier. Otherwise, there remains enough instability in eastern
Minnesota, western Wisconsin to continue as least VCTS for the
afternoon/evening hours. Will adjust tafs once more activity
develops this afternoon. Otherwise, VFR conditions will develop
overnight as drier air filters across the area.

KMSP...Eastern Minnesota will be on the edge of the instability
gradient which means the continuation of at least VCTS. Will hold
off on changes to current taf of initiation of VCTS by 23z, but
this could be altered to 20z based on afternoon development. Most
of the activity should be done by 1-3z with VFR conditions
developing overnight.

Mon...VFR with SHRA/MVFR possible. Winds SE 5-10 kts.
Tue...VFR. Winds SE 5-10 kts.
Wed...VFR with TSRA/MVFR possible. Winds SW 5-10 kts.




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