Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 171659

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1159 AM CDT WED AUG 17 2016

.SHORT TERM...(Today and tonight)
Issued at 326 AM CDT Wed Aug 17 2016

Surface analysis early this morning indicated a weak circulation
west of the Twin Cities along with mainly clear skies in
Minnesota. This weak circulation, as it moves southeastward this
morning, may generate an isolated shower or storm, but coverage
will be very limited. Several of the CAMS do support an isolated
shower across mainly west central Wisconsin/south
central/southeast Minnesota after 18z. But any activity will
quickly dissipate by sunset.

Early morning "Vis/Fog" satellite imagery did show very little in
the way of fog, but surface observation did have localized dense
fog (1/4 mile or less) near Morris and Benson in west central
Minnesota. Also some fog was reported around Hutchinson, Glencoe
and Litchfield prior to 4 am. Otherwise, most surface observations
were VFR across far southern Minnesota. Due to very weak boundary
layer winds (limited mixing) and ample moisture from Tuesday`s
rainfall, fog will likely continue to form prior to sunrise in
Minnesota and west central Wisconsin. I am not anticipating any
widespread dense fog, but something to consider if conditions
warrant for a dense fog advisory.

Tonight`s forecast will be similar to this morning as some fog
forms in the eastern `1/3 of MPX CWA, especially in west central
Wisconsin as clear skies and light winds will persist. Further to
the west, return flow and the added temperature/moisture advection
may generate a few thunderstorms in the far west toward sunrise
Thursday morning.

.LONG TERM...(Thursday through Tuesday)
Issued at 326 AM CDT Wed Aug 17 2016

Thursday through Friday...Thursday will feature a large trough
rotating through central Canada while zonal flow generally
prevails over the north-central CONUS. As Thursday progresses, the
southeastward expansion of this trough will allow H5 heights to
drop across the Dakotas into MN/WI. Meanwhile, at the surface, a
conglomeration of low pressure centers in the lee of the Rockies
will become organized and a better defined cold front will form in
advance of the Canadian upper trough. Prolonged southerly flow
will enhance warming and an increase in moisture in advance of the
front, helping set the stage for periods of showers and t-storms
from late Thursday lasting through late Friday. Although several
upper level disturbances rotating around the large Canadian trough
will spark off some storms during the first half of Thursday,
daytime heating plus the approach of both the surface and aloft
features will bring an increase in coverage and storm strength by
Thursday evening. The strong instability and the development of
increased mid-level jetting, enhancing bulk shear, will create a
severe weather threat for mainly the Thursday night period.
Showers and t-storms will last through much of Friday though storm
strength will weaken since the frontal passage is expected around
daybreak Friday, shifting winds to a northerly direction. The
upper level trough will trail the front, which will allow for the
continued precipitation, but the stronger instability and better
low-level forcing will shift off to the east. The precipitation
will steadily wind down Friday night into early Saturday morning.
But, when all is said and done, precipitation amounts reaching 1
inch will not be unreasonable throughout this event with some
localized higher amounts possible. There will be a noticeable
change in temperatures Friday into Saturday, particularly due to
the cold frontal passage. Highs on Thursday will be considerably
warm, with highs in the upper 80s to around 90 and with dewpoints
to around 70. Behind the frontal passage, highs will drop into the
lower 70s to lower 80s.

Saturday through Tuesday...Much more tranquil conditions are on
tap for the weekend into early next week as expansive high
pressure moves into the area. This will help squelch most
precipitation chances for this week. Dewpoints will lower
significantly while high temperatures drop to around 70 on Sunday.
However, temperatures will go on a slow rise during the first half
of next week as high pressure slides over the area, changing deep
flow from northerly to southerly. This will in turn allow
temperatures to increase to around 80 by Tuesday.


.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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