Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 171932

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
232 PM CDT WED AUG 17 2016

.SHORT TERM...(This evening through Thursday)
Issued at 230 PM CDT Wed Aug 17 2016

The short term concern is the chance of fog developing east
tonight and the timing of incoming front/convection into Thursday.

Initially...we have some isolated -shra/-tsra over northwest
Wisconsin...which may affect the far northeast portion of the cwa
through 00z. This lake breeze induced acitivity should wane as it
sags south into more stable air.

With light winds...moist boundary layer and mainly clear
conditions...we should see areas of fog redevelop...mainly to the
east later tonight. The far west will see some high clouds and
some increase in gradient winds develop so this should limit any
significant fog issue. The threat of at least isolated convection
working into far western cwa late as waa and some mid level
moisture tries to work east into the area. The HRRR and HRRR
experimental is showing some type of complex/area working across
the dakotas and into the far west after 09z Wed.

Instability increases into Thursday as thermal ridge moves into
southwest MN. The front sags into the northwest cwa by late in the
afternoon and this should regenerate thunderstorms over the
northwest area during the day. The severe weather threat will
increase by late afternoon as well as steeper lapse rates and
35 kts deep layer shear moves into the region. PW`s increase to
around 2 inches once gain by late afternoon along the boundary.
This will yield the possibility of heavy rain by evening.
Hail...strong winds and torrential rain will be the main severe
weather threats once again.

.LONG TERM...(Thursday night through Wednesday)
Issued at 230 PM CDT Wed Aug 17 2016

The main focus of the long term period is the frontal boundary
expected to move into the area and essentially stall out tomorrow
night through much of the day Friday.  This will be followed by a
cool down to below normal temperatures as a deep longwave trough
overspreads the north central CONUS.  Temperatures will rebound
early next week as low level southwesterly flow increases, which
will again lead to chances for thunderstorms.

By tomorrow evening, the cold front will still be off to our west,
with a pool of very unstable air across the forecast area.  Storms
should not have any problems initating along the front given the low
level convergence and available buoyant energy.  In terms of severe
potential in our area, the effective deep shear is rather
unimpressive.  2,000 to 3,000 ML CAPE values combined with 25-40
knots of effective shear will lead to primarily multicellular storms
which will likely conglomerate into an MCS tomorrow night.  This
area should track east across southern/central MN through west
central WI overnight.  With the lack of deep layer shear, PWATS
increasing to ~1.75" and the front not moving much, there is
potential for a couple inches of rain to fall in south central MN
through west central WI. The pops were pretty consistent with the
previous forecast, but we did nudge them south a little. This front
will essentially stall out from southwest MN through northwest WI
through much of the day Friday and into Saturday, with continued
rounds of showers and thunderstorms possible as the main upper level
trough swings through from the west.

With a deeeper trough expected, the system looks to slow down some,
which means the cool down is still on for Saturday and Sunday, but
we will likely be dealing with the low level moisture in cyclonic
flow for a longer period of time.  Cool temps and cloudy skies with
showers possible will result on Saturday directly underneath the
trough axis.  We should see conditions drying out a bit more on
Sunday as low level flow becomes more anti-cyclonic.

For next week, we`ll see return flow and warm air advection increase
on Monday but with not much in terms of moisture to warrant pops. By
mid to lateweek, shortwave energy will move through the area with
another slow moving frontal boundary being the source of precip.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1205 pm CDT Wed Aug 17 2016

Main concern near term is possibility of isold convection over
southeast areas and then chance of fog reforming tonight. some
short term hires models indicate a small threat of isold
convection over the southeast portion of the area. Water vapor
imagery shows strong upper trough moving over eastern Wisconsin.
This should help limit overall potential so we will leave out of
eastern tafs for now. Fog should be able to reform late
tonight...mainly eastern half of the area...with light winds and
clear sky expected. SREF probs do increase from east central MN
into western WI into the night. We will mention MVFR BR in eastern
MN and go IFR into western wi...mainly after 07z-08z. Expect this
to burn off through 14z as southerly winds develop. Some mid/high
level clouds moving into western areas later tonight/Thu morning.
We will keep TAFS dry through 18z for now...although we could see
some showers work into far western mn around 12z Thu. Light winds
becoming southerly and increasing from west to east into Thu.

Main concern is fog threat later tonight. With light winds and
clear sky...we should be able to generate some fog later tonight
at kmsp. We will mention MVFR br for now...and become vfr again
through 13z Thu. We will keep this period dry for now...although
there could be some shra moving across central mn Thu morning
before dissipating.

Fri nite...Becoming MVFR with SHRA/TSRA. Winds becoming N 10 kts.
Sat...Periods of MVFR Cigs & SHRA/TSRA. Winds N 10-15 kts.
Sun...VFR. Morning MVFR Cigs Possible. Winds NW 10 kts.


.MPX Watches/Warnings/Advisories...


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