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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1026 PM CDT Monday Sep 22 2014

Update...for 06z aviation discussion below

&&

Short term...(this evening through tuesday)
issued at 305 PM CDT Monday Sep 22 2014

High pressure remains in control this afternoon...but is progressing
slowly east across the Midwest. An upper level low is ejecting from
California to the northeast and is currently moving across the Rocky
Mountain region. This system will begin spreading cloud cover into
the western forecast area overnight...which combined with an increased pressure
gradient due to the high pressure center pushing farther away...will
make for at least some mixing of the boundary layer across the
west. The increasing cloud cover and mixing will help hold low
temperatures tonight in the low 50s. Further east...clear skies and
lighter winds will again allow fog to develop in prone and low lying
areas. Western WI looks to be the most vulnerable area for fog and
the coldest temperatures in the forecast area tonight. Went slightly cooler
than most guidance across the eastern County Warning Area due to the potential for
strong radiational cooling.

For Tuesday...the approaching upper low will become more or less an
open shortwave trough and wont have much of a surface reflection.
The eastern half of the forecast area will not see much of anything from this
system through the daylight hours tomorrow...with partly cloudy
skies in the forecast as cloud cover builds in to western Minnesota. The
clouds will be slow to work east from the South Dakota border
overnight to near the Twin Cities by evening. The main focus with
this system is the chance for precipitation as it moves in. This
wave will be running into a dry air mass...and forcing is limited.
However...enough forcing exists to warrant probability of precipitation across the western
half of the state tomorrow and despite the low level dry
air...saturation should occur but amounts will simply be
limited...with no more than about one tenth of an inch in the
forecast through the day. Do not expect thunder with this wave.
Best lifted indice's remain positive...and Theta-E differences from 850h-500h
indicate instability will remain to the west of the forecast area. MUCAPE
agrees and shows all instability well to the west of the
Minnesota/South Dakota border. Southerly winds will increase to
10-15 miles per hour on the back side of the departing surface high.

Long term...(tuesday night through monday)
issued at 305 PM CDT Monday Sep 22 2014

The upper low will be in the process of decaying by Tuesday night
as a portion of it becomes sheared apart by the westerlies across
central Canada. As the forcing becomes less focused and the light
showers encounter increasingly dry air with northeastward
extent...the chance for showers across eastern Minnesota and western WI are too
low to mention. By Wednesday...the entire County Warning Area should be
precipitation-free.

For the remainder of the period...ridging will build northeast
from The Rockies into the northern and Central Plains by
Thursday...be centered over the upper Midwest with heights in the
low 590s dm this weekend...then slide southeast and weaken
somewhat by early next week. This will mean several days of clear
skies and temperatures 10-15 degrees above normal. Raised highs
into the lower 80s on Friday as the warmest temperatures aloft push
in...before advertising a slow cooling trend thereafter as the
ridge breaks down a bit and focuses more on the East Coast.

&&

Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1027 PM CDT Monday Sep 22 2014

Winds remain light and variable overnight...particularly at west
central WI sites /krnh and Keau/ near the surface ridge axis. Kept
the mention of fog at WI sites given similar conditions to last
night and dewpoints around 50 degrees this evening. Western sites
will have a canopy of high clouds moving in and winds will be a
few knots stronger...so fog is less of a concern there. By 00z
Wednesday...middle level saturation occurs at western sites with a
broken-overcast deck circa 5kft expected along with a few showers. South-
southeast winds prevail on Tuesday with gusts developing at kaxn
and kstc.

Kmsp...
clear skies overnight with middle/high clouds increasing
throughout the day on Tuesday. Still expect patchy fog in nearby
valleys but not at the site. South-southeast winds at or below 10kts through
Tuesday.

/Outlook for kmsp/
Wednesday...VFR. MVFR ceilings possible overnight. Winds south-southeast 12-15g25 kts.
Thursday...VFR. Winds S 7-10 kts.
Friday...VFR. Winds south-southeast 5-10 kts.

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$



Short term...speed
long term...borghoff
aviation...ls

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