Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 151716

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1216 PM CDT Fri Sep 15 2017

.SHORT TERM...(Today and tonight)
Issued at 335 AM CDT Fri Sep 15 2017

We have a somewhat complex weather setup across the area this
morning as we remain in zonal flow with respect to the broad upper
low across central/northern Canada, with a trough continuing to dig
across the Rockies. Broad area of isentropic lift has resulted in
some showers forming east of I-35 overnight, in what`s left of the
LLJ that brought heavy rains to the Arrowhead. There was another
area of accas with showers down over western IA and it`s associated
with the LLJ that is strengthening across KS into Neb in response to
a strong shortwave moving from Colorado into Wyoming. And ahead of
the CO/WY wave, there`s an MCV moving north across Nebraska, with a
nice cluster of storms moving up out of central Nebraska with it.
And of course at the surface, the quasi-stationary baroclinic zone
still bisects our area, from Jackson up to Willmar, then northeast
toward Hayward, WI.

First, the activity over WI will quickly move east of the MPX and
weaken as the LLJ continues to veer and weaken. The MCV over central
Nebraska will stay to our west, with that thunderstorm activity
remaining west of our area. The LLJ driving the activity over
western IA is forecast to get up to about the upper MN River Valley
mid day and eventually the Grand Forks, ND area by this evening. As
this LLJ lift north across western MN, we may see some
isolated/scattered showers. However, the EML that kept us capped and
dry Thursday, will remain over us today and expect it to have a
similar impact on precip chances in the MPX area, so really got the
eraser out for PoPs all the way out into the early evening, with
most of the activity remaining well north of the front where better
forcing is expected to reside in association with the jet across
southern Canada.

That CO/WY wave will head into ND today and the impact it will have
is shift low pressure back into the Plains, helping push the front
back west and north through the day. This will again put much of the
MPX area in a warm sector with very similar 925-850 temps that we
saw yesterday. Areas that got up around 90 Thursday look to do the
same today. The one area that has some big bust potential is up
around Alexandria. Highs Thursday went 88 (AXN), 75 (FAR), and 63
(GFK) and expect a similar gradient with highs today. Depending on
how far northwest the warm front retreats today, AXN has the
potential to see highs only in the upper 60s or punch back up into
the mid 80s. We went toward the higher end for now.

As the CO/WY wave moves through the Dakotas this afternoon, we
should see thunderstorms develop along the cold front to the west of
I-29, with a broken line of thunderstorms moving into western MN
this evening with the cold front. The NAMnest and NSSLwrf capture
the idea of what we are expecting, with a broken line of storms
weakening through the night. A slight risk for severe weather is
probably pushing it, but the SPC Day 1 outlook goes along with
NAMnest/NSSLwrf idea as well. Finally, as we are seeing tonight, the
warm sector will remain very warm tonight, with some lows staying up
in the low 70s once again, so upped lows some in the warm sector.

.LONG TERM...(Saturday through Thursday)
Issued at 335 AM CDT Fri Sep 15 2017

Much of the thunderstorm activity from Friday night will likely
dissipate by Saturday morning. There may be a few showers post
frontal across western Minnesota at the start of the period, but
chances will increase through the day with the approach of the
main mid level trough axis from the southwest. The front should be
situated near a line from Redwood Falls to Long Prairie Saturday
morning with widespread low clouds to the west. This may keep
temperatures in the 50s or low 60s for much of the day in those
areas, depending when the next round of showers and storms
develop. Anticipating a "clean" atmosphere free of convection due
to capping in the warm sector for much of Saturday, which should
allow temps to rocket back into the mid 80s. Dew point pooling
along the front beneath steep mid level lapse rates will create a
moderately unstable airmass. Thunderstorms will develop during the
afternoon, mostly post-frontal where the best upper support will
reside, but some storms may also fire along the front. It is in
that narrow corridor near the front that stands the best chance
for severe weather. The front will be east of a healthy 75 kt mid
level jet streak stretching across South Dakota into western and
northern MN, and it is a good thing it is because that streak
would produce an environment for a widespread severe event if it
overspread the warm sector. Storms should be widespread by
Saturday evening, stretching from south central to east central
MN. Increased PoPs to 80 percent for those areas before the upper
support shifts north and a stabilizing boundary layer results in
weakening convection overnight.

Cooler and drier air arrives Sunday and Monday before meridional
flow redevelops midweek. At least a couple systems will affect the
region next week, each bringing a risk for showers and
thunderstorms. Warm and humid air will return ahead of each
system, and it`s likely temperatures aren`t warm enough later
next week. Spatial and temporal differences with these airmasses
reduce confidence in exactly how warm we could get on any given
day, so stuck close to the blended guidance at this range.


.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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