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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
655 PM CDT Monday Aug 31 2015

issued at 655 PM CDT Monday Aug 31 2015

Updated to include 00z aviation discussion below.


Short term...(this evening through tuesday)
issued at 358 PM CDT Monday Aug 31 2015

A cold front is now entering the northwest edge of the mpx County Warning Area...but strong moisture...and weak forcing are all conspiring
make this a dry front. With the upper wave driving this front now
heading NE along the Manitoba/Ontario not see the status
of the front being a dry one changing through the removed
what little probability of precipitation we had for tonight. Being closer to the front...we
have seen south winds increase today...which has resulted in about a
5 degree increase in both temperatures and dewpoints this afternoon.
Outside of western WI...where the stratus has held strong...temperatures
have warmed nicely into the low/middle 80s...with widespread dewpoints
in the low 70s as well now.

Of course the theme of the overnight hours since Thursday night has
been the expansion of low stratus across the area. Well...that is
not expected to be as much of an issue here tonight. One...the
prefrontal region we are in has been stratus free the last few
nights. In addition...forecast soundings from the NAM are not as
moist in the low levels and not looking as foggy/stratusy as they
have since Friday morning. Based on 950 mb relative humidity and sref probs for
ceilings under 3k feet...expect stratus to form tonight over northern
Wisconsin and try to build south into western WI. Even though we are not
expecting as much stratus Tuesday does not mean we will
be waking up to blue skies. Instead...we will be replacing the sub
1k foot clouds with middle/upper level clouds associated with the
remnants of the front moving into western Minnesota now.

As for the front...with the upper wave driving it getting farther
and farther northeast of the area...its eastward progression will
come to a halt overnight...with it washing out across the mpx area
on Tuesday. As a result...not expecting any precipitation
have removed what little probability of precipitation we had in western WI for Tuesday
afternoon. The weather for Tuesday looks very similar to today in
terms of temperature and dewpoints with only differences being some
more middle/high level clouds tomorrow and lighter south winds.

Long term...(tuesday night through monday)
issued at 358 PM CDT Monday Aug 31 2015

Little change to the long term forecast...and unfortunately no
better clarity on the timing and chances of precipitation for
Labor Day weekend. Temperatures in the middle to upper 80s with dew
points hanging around that 70 degree mark for the next several
days is likely.

The upper ridge across the center of the Continental U.S. Will remain in
place through the week...with a subtle shortwave indicated along
the Minnesota/Iowa border by both the ec and GFS on Wednesday night.
Remained consistent with slight chance probability of precipitation and some chance probability of precipitation
in extreme southern Minnesota. These probability of precipitation are there to account for the
chance a few showers and isolated thunderstorms are able to
overcome the cap. Other than vorticity advection...there is not a
lot of upper level support for much in terms of still
thinking most people will miss out on any rain...but must remain
consistent with the chance for isolated to scattered activity at
this time.

The next chance for precipitation comes again Thursday night into Friday
as wave that originates in the eastern Pacific is pulled northeast
while an impressive upper trough deepens over the Pacific
northwest. The ec/GFS/Gem all indicate this wave advancing
northeast and through the upper Midwest from Thursday through
Friday night /and possibly lingering into Saturday/. The 12z run
of the ec is interesting to say the least...with this feature
suddenly intensifying rapidly Friday as it moves from Colorado to
Minnesota. I'm not buying into this quite yet...but it has shown
run to run consistency in some sort of upper wave taking this
course. Stuck with low probability of precipitation for now as timing and placement...and
questions about the strength of this wave are all uncertain at
this point.

For the main system we have been seeing for the latter half of
Labor Day...we gained no additional clarity on expectations for
it. It will move eastward along the US/Canadian border from the
Pacific northwest...but as this feature moves further east...the
GFS and ec diverge on the handling of it...quite a bit. The ec
wants to strengthen the upper ridge across the Central
Plains...pushing the strong upper low further north as it moves
east...toward Hudson Bay...and slowing this system down quite a
bit. The GFS still takes it through the upper Midwest and is much
faster. The bottom line remains...there is quite a bit of
disagreement amongst the guidance for this weekend. So...stuck
with chance probability of precipitation that are almost certainly spread across to broad
of an area...spatially and temporally. This will change once the
guidance begins demonstrating some better agreement.


Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 655 PM CDT Monday Aug 31 2015

Should be a quiet period with mainly VFR conditions. The exception
looks like it might be some fog and stratus later tonight... but
that should mainly impact eastern sites which won't see as much
high cloud cover move in overnight. Front to the west looks to
continue to wash out as it moves east overnight and Tuesday... and
should only serve to bring some middle/high clouds and virga across
the area. Winds will remain fairly light through the period... and
generally be from the south.

Kmsp...taf reflects expectations with fairly high confidence.
Primary item of uncertainty would be the possibility of some MVFR
fog late tonight... but right now that does not appear to be much
of a concern.

/Outlook for kmsp/
Tuesday overnight...VFR. Southwest wind 5 to 10 knots.
Wednesday...VFR. South wind 10 to 20 knots.
Wednesday night...MVFR possible with a chance of shra/tsra.
Southeast wind 10 to 15 knots becoming southwest.
Thursday...VFR. South wind 15 to 20 knots.
Thursday night and Friday...MVFR possible with a chance of
shra/tsra. South wind 10 to 20 knots.


Mpx watches/warnings/advisories...


short term...mpg
long term...speed

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