Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 152017

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
317 PM CDT Fri Sep 15 2017

.SHORT TERM...(This evening through Saturday)
Issued at 318 PM CDT Fri Sep 15 2017

Several short waves were noted across the Upper Midwest this
afternoon, which was based on the regional satellite and radar
imagery. Earlier models have a hard time with morning convection
which led to numerous updates from mainly a dry forecast this
morning. Overnight convection is the main forecast concern as models
remain uncertain on areal coverage and timing.

First, there was a significant mid level jet over eastern South
Dakota, and western Minnesota this afternoon. This, plus ample mid
level instability kept showers and thunderstorms reforming across
west central and central Minnesota this afternoon. There was another
weaker short wave noted in south central Minnesota which was related
to earlier convection in northern Iowa. This may support a few
showers or storms in far east central Minnesota and west central
Wisconsin late this afternoon/early evening.

The bulk of the shower and thunderstorm activity will be centered in
northern Minnesota this evening and this is based on the
aforementioned mid level jet and instability. Further to the south
across Nebraska, another area of elevated instability was noted on
regional radar. This area of elevated instability will likely be the
focus of late evening showers and thunderstorms in southern and
eastern Minnesota once another low level jet develops. This is also
where the higher percentages occur tonight. By morning, most of this
activity will likely be in west central Wisconsin and decreasing in
areal coverage. Saturday`s forecast is based on the main energy from
the storm system, plus the cold front sweeping across the area.

Severe weather is still possible but not likely to be widespread due
to limited wind shear in the area of highest Saturday afternoon
instability. This could change but more than likely a few strong or
severe storms will develop in the warm section in south central
Minnesota Saturday afternoon, and quickly move northeast into west
central Wisconsin.

.LONG TERM...(Saturday night through Friday)
Issued at 318 PM CDT Fri Sep 15 2017

The large scale pattern during the long term forecast period still
looks to feature a deep mid/upper trough over the western CONUS,
with resultant active weather across the central CONUS. Timing of
precipitation chances associated with embedded waves lifting out
of the trough will be the primary forecast concern.

Showers and thunderstorms will be ongoing Saturday night,
especially along/east of I-35 as the cold front passes. Sunday we
dry out behind the front, and high temperatures retreat to
slightly below normal values in the 60s.

Sunday night and Monday the stalled front lifts back north toward
the area as a warm front. Weak low level moisture transport
ensues, although with high pressure in place at the surface over
the eastern part of the area, expect it to be difficult for
activity to expand north/eastward.

Tuesday looks to be dry with temperatures moderating back into the
mid/upper 70s.

Tuesday night through Friday looks to be the most active time
frame as southwest flow aloft ushers several weak waves over the
area, and a surface frontal system eventually pushes through.
Temperatures will remain above seasonal normals as long as the
trough stays to our west.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1215 PM CDT Fri Sep 15 2017

Ongoing convection across central/southern Minnesota is the main
concern in the next 6 hours as whether current trends dictate
VCSH/VCTS for most of central/east central Minnesota for an hour
or two. Although models continue to hold off on any type of
convection this morning, in the past two runs it does show at
least holding onto the activity for an hour or two. Therefore,
kept in the VCTS/VCSH where it is warranted in Minnesota. West
central Wisconsin will likely hold off on any activity until later
tonight. As for tonights activity, believe the main convection
will be associated with a stronger disturbance moving northeast
across Nebraska today. This will lead to at least VCTS/VCSH this
evening/overnight. After tonight, IFR/MVFR cigs will likely move
eastward but timing/areal extent remains questionable.


Kept in VCSH until 20z due to proximity of SHRA in the western
Twin Cities area. Otherwise, most of the precipitation should die
off in the afternoon as an increasing cap develops. If anything
develops, it will be elevated and isolated. Kept the remainder of
the taf the same as more activity is likely overnight.


Sat...VFR. TSRA/MVFR likely late. Winds SSW 10 kts bcmg NW.
Sun...MVFR cigs possible early. Winds WNW 5-10 kts.
Mon...VFR. Slight chc TSRA/MVFR. Winds SE 10-15 kts.




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