Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 181148

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
648 AM CDT Tue Apr 18 2017

.UPDATE...For 12z Aviation discussion below


.SHORT TERM...(Today and tonight)
Issued at 340 AM CDT Tue Apr 18 2017

The surface trough is on our doorstep this morning, while water
vapor satellite shows a well-defined shortwave trough over the
Dakotas. A look upstairs also reveals a coupled jet structure
which is facilitating rather impressive differential divergence
over western MN. These factors are combining to generate showers
from western into central MN, with embedded thunderstorms to the
west where negative best lifted indices are negative. As the
surface low central moves across central MN to Lake Superior today
the precipitation will shift eastward and winds will become gusty
from the west/northwest.

Hi-res models have trended a bit slower with the eastward exit of
the precipitation today, so have tweaked grids to reflect that. By
18z activity should be mostly over west of the Interstate 35
corridor, and out of the area by 00z Wed.

Temperatures will have the potential to warm into the 65-70 degree
range over south central MN where some sun is possible and breezy
southwest flow will yield decent mixing. For the remainder of the
area, lower 50s to lower 60s are expected. Lows tonight are not
expected to get quite down to freezing, with mid 30s to lower 40s

.LONG TERM...(Wednesday through Monday)
Issued at 340 AM CDT Tue Apr 18 2017

Slight differences in the models continue for Wednesday/Thursday
weather system, as two short waves moving out of the Rockies, begin
to interact with each other.

Although most of the sensible weather elements will remain the same
as rain is almost certain Wednesday/Wednesday night across the Upper
Midwest. The differences begin late Wednesday night/Thursday morning
as a secondary short wave moves across the Canadian Rockies, and
into the Northern Plains. The GFS/MPAS/GEM remain fixed on the
southern short wave that moves across the Plains, and into the
western Great Lakes by Thursday morning. The EC is similar, but has
more interaction with the short wave in the Northern Plains. This
creates a northern bias of the EC weather elements vs. the
GFS/MPAS/GEM. The interaction of the EC also holds onto the
precipitation longer across east central Mn and west central Wi into
Thursday afternoon/evening.

Although confidence remains high for a prolonged period of
precipitation developing Wednesday morning, and lasting through late
Wednesday night, uncertainties continue on when the precipitation
will end Thursday. Due to more consistency of the GFS over the past
several days, am leaning toward a faster solution of the
precipitation ending late Wednesday night/early Thursday morning. If
the EC is correct, the precipitation will hold on longer through
Thursday. This will also affect highs on Thursday where only the
lower 40s are forecast if the precipitation holds on longer. Even if
the GFS/GEM/MPAS is correct, highs will likely on rise to near 50
with a cool northerly wind.

As in previous discussions, frost/freezing conditions are likely in
east central Minnesota, and west central Wisconsin Friday morning as
temperatures fall into the upper 20s to lower 30s.

No changes for the upcoming weekend as a storm system dives
southeast across the Rockies, and into the Southern Plains, Lower
Mississippi River Valley by Sunday. Easterly flow from this system
to our south will keep conditions dry, but cool for late April.

The weather pattern will likely change early next week to a more
active period once again as a series of storm systems dive southeast
across an active upper trough forming along the east coast.
Therefore, the Upper Midwest will be slightly cooler than normal on
temperatures, but wetter than normal.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 649 AM CDT Tue Apr 18 2017

Showers and isolated embedded thunderstorms will affect the sites
this morning, along with a period of MVFR ceilings in the wake of
the activity. Winds will also be gusty from the south then
west/northwest as the front passes. To start the period will also
have some low level wind shear at KMSP and KRNH until about 17z,
where the directional component varies by 40-50 degrees and speeds
increase to around 60kts at 2000 feet off the ground.

Dry conditions tonight with wind speeds diminishing below 10 knots.
TAFs are potentially too optimistic with the return to VFR, but
currently expect cigs to improve to VFR this afternoon.

Low level wind shear is the first concern, with speeds increasing
to between 55-60 knots by 2000ft, and a directional change of
about 50 degrees. Showers with embedded thunder look to reach the
field between 1230z and 13z...lasting for the better part of the
morning. Expect cigs to reduce to MVFR for most of the afternoon,
with improvement this eve. Southeast winds gradually shift to the
northwest with the frontal passage and remain gusty until
around/after 00z Wed.

Wed...VFR with RA/MVFR ceilings in the aft/eve. Wind NE 10-15
Thu...MVFR Cigs possible early then VFR. Wind NE at 5-10kt.
Fri...VFR. Wind NE 5kts.




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