Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 202043

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
343 PM CDT Tue Jun 20 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 340 PM CDT Tue Jun 20 2017

Dry and cool tonight with patchy fog possible in low lying areas,
and river valleys in west central Wisconsin.

Late tonight in far southwest Minnesota, strong theta-e advection
will commence as a storm system begins to organize across the
plains. The orientation of the theta-e ridge across Nebraska, and
elevated instability building to the north of this ridge, should
allow for showers and thunderstorms to develop. The best placement
overnight will occur in southeast South Dakota with a general
movement of the storms to the east-northeast across southwest
Minnesota toward sunrise. As the nocturnal low level jet veers to
the east during the morning, convection should diminish as the
activity moves from southwest to south central Minnesota. The best
instability is well south of Minnesota, so any thunderstorms that
develop should be non-severe. By the late morning, early
afternoon redevelopment of showers/thunderstorms will likely form
near the boundary of the earlier morning convection in southern
Minnesota. Depending upon the amount of instability that can re-
establish itself in the warm sector, will determine the severity
of the thunderstorms. The best wind shear/instability values
remain in Iowa, but these parameters can be altered based on how
the morning convection evolves.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 330 PM CDT Tue Jun 20 2017

Main concern is the baroclinic zone/frontal boundary sparking
thunderstorms tomorrow night and again Thursday night but more
likely farther south.  There are some timing differences that
account for why POPs are not higher than currently forecast for each
period, but it still looks like thunderstorm activity will be
ongoing across southern Minnesota at the start of the long term
period tomorrow evening, but some of the guidance indicates this
could evolve quickly and be primarily east of our are by 06Z
tomorrow night.  Not much has changed in terms of the environment
with plentiful CAPE progged south of the front and sufficient shear
for strong to severe storms to develop.  The SPC continues to
include most of southern Minnesota in a slight risk of severe weather
with large hail and damaging winds the main concerns into the

The front pushes down into northern Iowa by tomorrow night so while
that area has the best chance for storms, we could see some thunder
into far southern Minnesota, where a Marginal risk for severe
weather is in place.  Heavy rain could be an issue along the front
but at this time northern Iowa would also be most susceptible to
that.  However, if the front drifts back north along I-90, heavy
rain producing thunderstorms would as well.  Check back for updates
over the next few days.

For the weekend and beyond, we get into predominant northwest flow
with a longwave trough across much of North America, and the jet
sinking to our south.  This means cooler than normal weather is
expected, with rounds of showers and a few weak thunderstorms
possible under the cyclonic flow pattern.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1210 PM CDT Tue Jun 20 2017

No aviation concerns through the afternoon/evening across
central/southern Minnesota, as well as west central Wisconsin.
Cigs of 5-7k could affect west central Wisconsin early this
afternoon. Otherwise, light winds overnight could cause some fog
problems in west central Wisconsin, especially near KEAU toward
sunrise. Most of the SHRA/TSRA activity will hold off for MPX taf
sites through Wednesday morning, but a few SHRA are possible
before 18z near KRWF.


No additional aviation concerns with any convection holding off
until late Wednesday afternoon.


Thu...Mainly VFR. Slight chc -TSRA/MVFR. Wind WNW 5-10 kts.
Fri...VFR. Wind NW 10 kts.
Sat...Mainly VFR. Slight chc -TSRA/MVFR. Wind NW 5-10 kts.




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