Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 131725

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1225 PM CDT Wed Sep 13 2017

.SHORT TERM...(Today and tonight) Issued at 347 AM CDT Wed Sep 13

Weak high pressure at the surface combined with a building ridge
axis aloft will be just enough to prevent the wavy quasi-
stationary front from the southern tip of Hudson Bay to far
northern MN to southwestern SD from making any appreciable
progress east today. The ridge from the southwestern CONUS will
keep unseasonably warm temperatures in place once again today as
highs will hit the 80s area-wide, with potentially some 90-degree
readings in far western MN. Dewpoints will also remain on the high
side for the season, reaching the mid 60s, so muggy conditions
can again be expected. The ridge will break down a bit tonight
into Thursday morning, just enough such that the surface front
will drop to near a KFAR-KDLH line in northern MN while deep
moisture increases from the west. Shower chances increase in
northern MN overnight and potentially a few isolated rain showers
may reach a few counties in the northwestern portion of the WFO
MPX coverage area. Temperatures will again run warm tonight with
lows ranging from the upper 50s to mid 60s.

.LONG TERM...(Thursday through Tuesday)
Issued at 347 AM CDT Wed Sep 13 2017

The forecast reasoning from yesterday afternoon`s discussion
remains largely intact. A large scale pattern shift will take
place Thursday with a deep trough developing across the western
U.S., and the semi-permanent western ridge of late finally
focusing over the east. Southwest flow aloft will prevail into the
weekend, with the baroclinic zone nearly stationary from the
central Rockies northeast to northern Minnesota. Multiple waves of
energy embedded in the southwest flow will bring periodic
thunderstorm chances Thursday through Saturday night. Capping will
limit the activity with eastward extent due to a dry boundary
layer, and focus it where the deeper moisture tongue will be found
across central and western MN. Generally convection that fires in
that zone through Friday night will weaken and diminish as it
heads eastward.

The highest PoPs will be Friday evening into the early overnight
hours with a quickly moving mid level wave ejecting from Colorado
that will track to the northwest of the CWA and exit northern MN
by early Saturday morning. The best overlap of forcing, moisture,
and instability will be west of I-35 where likely PoPs continue.
Convection will lose everything it has supporting it by Saturday
morning and thus quickly weaken as it approaches Wisconsin.

Another good chance of storms will come late Saturday and Saturday
night with the surface front and mid level trough axis. Robust
instability due to steep mid level lapse rates and a moistening
boundary layer may develop Saturday afternoon across MN.
Sufficient shear and forcing along the front could bring a severe
thunderstorm risk through the mid evening hours. A cooling and
stabilizing boundary layer will diminish the severe risk in
Wisconsin from late evening onward.

The biggest change to the long term were temperatures. We were
able to reach the mid 80s area wide Tuesday with 925 mb temps of
+22 to +24C. By Thursday and Friday, those will reach +24 to +28C.
Increased highs to around 90 Thursday and upper 80s Friday from
the Twin Cities southwestward away from potential convective
development. The NAM and GFS seem to be a bit overzealous with
storms Thursday night which may be impacting their temperatures
Friday. Nonetheless, held back from the full potential scenario
given this threat. An absence of convection and resultant
considerable mid/high clouds, with the presence of a well mixed
boundary layer should bring us into the low 90s easily both days.

Cooler air follows for Sunday and Monday before the trough/ridge
pattern reloads during the middle of the week. This should resume
the warm and wet pattern into late September.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1225 PM CDT Wed Sep 13 2017

High confidence in TAFs with forecast soundings supporting MPX
terminals remaining dry and VFR. AXN will remain in the region of
a stalled out boundary, so they will have light/variable winds
most of this period. Everywhere else enjoys south winds, which
will be starting to kick up late Thu morning, especially for

KMSP...No additional concerns.

Fri...VFR. Chc TSRA late. Wind S S 10G20 kts.
Sat...VFR. Chc TSRA/MVFR. Winds SW 5-10 kts.
Sun...MVFR cigs possible. Winds WNW 10G15 kts.




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