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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
614 am CDT Thursday Sep 3 2015

Updated for 12z aviation discussion...
issued at 608 am CDT Thursday Sep 3 2015

&&

Short term...(today and tonight)
issued at 415 am CDT Thursday Sep 3 2015

The upper level wave that brought efficient rainfall across
western Wisconsin yesterday was the driving force behind an area
of showers and thunderstorms that lingered across eastern
Wisconsin early this morning. Meanwhile another pv anomaly was
evident on water vapor across The Arrowhead of Minnesota. A few
showers and thunderstorms may develop ahead of this wave...but if
they do they will be south and east of the forecast area.

For central Minnesota and western WI expect another mild and muggy day.
The morning fog and stratus should quickly mix out per the
BUFKIT soundings. Afternoon highs in the middle 80s should be
widespread this afternoon. Later tonight another wave currently
over the 4-corners region will lift northeast into the Dakotas.
This will be the trigger for another mesoscale convective system...which could make it
into southwest Minnesota. A few members of the ncar ensemble show
this...as well as some of the large scale guidance. However the
NAM nest...wrfarw and WRF nmm keep the storms to the west. For now
continued with a dry forecast...but expect to see an increase in
probability of precipitation if this wave shifts east since there will be 2000 to 2500
j/kg of elevated cape. The wind field is very light, so deep layer
shear is negligible...but that makes heavy rain the primary
threat.

Long term...(friday through wednesday)
issued at 415 am CDT Thursday Sep 3 2015

Friday through Sunday...Friday will start out with the County warning forecast area on the
western fringes of a departing longwave upper level ridge while a large
cutoff low moves onshore the Pacific northwest. The ridge will gradually move
off to the east...allowing a more progressive SW-NE flow to move across
the area. Several shortwave disturbances will ride atop the area
starting late day Friday...more but pronounced Sat into sun as the
Upper Cutoff low becomes negatively tilted over the northern rockies.
This low will then traverse east-northeast into southern Manitoba through Sun
night...bringing along a surface front and surface low pressure system with
it. Scattered showers/thunderstorms can be expected to develop over much of
the area over the weekend...particularly Sat night through Sun night.
Pockets of heavy rain may also develop at times as a prolonged and
persistent surge of moisture from the Gulf of Mexico will bring
much more moisture to the region...to the tune of dewpoints around
70 and precipitable waters easily in excess of 1.50 inches and possibly around 2
inches at times. The surface cold front will reach the eastern Dakotas by Sun
morning then gradually traverse eastward sun and Sun night...making the
Sat night through Sun night time periods the most likely for having
precipitation covering the entire County warning forecast area. As for temperatures...the large
ridge combined with the aforementioned deep surge of moisture will
keep warm/humid conditions in place through the weekend...especially
for Friday and Saturday before decent precipitation coverage
arrives. Highs will climb into the middle-upper 80s. With dewpoints
into the upper 60s to around 70...heat index values will hit the lower
to middle 90s for Friday and Sat. If trends continue where dewpoints run
slightly higher than guidance has shown...then heat index
headlines may well be needed.

Monday through Wednesday...with the southern Canadian system becoming
vertically stacked by Monday morning and its associated cold front near Lake
Michigan...any precipitation will shift off to the east come Monday
morning. High pressure will settle in...but only for the day on Monday as
upper level flow become predominantly east-west zonal...meaning that high
pressure on Monday will give way to a developing system for Tuesday into Wednesday.
While the main low pressure will remain anchored in the plains...a
weak surface trough in advance of the surface low will extend east-northeastward into the
upper miss River Valley. This may well promote scattered showers across the
region...and possibly a few thunderstorms...but the setup looks to be more
of a stratiform/isentropic setup rather than convective. Thunderstorm
chances are downplayed but do not have the confidence to eliminate
it altogether so have capped thunderstorms as slight chance. The bigger change
will be temperatures as much cooler air with noticeably lower
dewpoints will prevail over the region. Highs will range from the
upper 60s to middle 70s while lows bottom out in the 50s for the first
half of next week.

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 608 am CDT Thursday Sep 3 2015

Low stratus and fog has blanketed the region once again...with
widespread LIFR conditions. Forecast soundings show these
conditions improving by middle morning...with VFR conditions the rest
of the day. Later tonight expect another round of
fog/stratus...but only went MVFR since it is toward the end of the
taf period.

Kmsp...
an IFR/LIFR cloud back to the south of kmsp has now crept up to
msp...and should linger around through the early morning rush.
Conditions should quickly improve this morning...with VFR
conditions the rest of the day. Another round of fog and stratus
is possible Friday morning...but did not have confidence to go
below VFR at this time.

/Outlook for kmsp/
Friday...VFR. Wind S at 10g20kt.
Sat...VFR with MVFR and rain showers/thunderstorms and rain possible late. Wind S at
10g20kt.
Sun...VFR with MVFR/IFR thunderstorms and rain possible. Wind S at 15g20kt.

&&

Mpx watches/warnings/advisories...
Minnesota...dense fog advisory until 9 am CDT this morning for mnz047-048-
054>058-064>070-073>078-083>085.

WI...dense fog advisory until 9 am CDT this morning for wiz015-016-
024>028.

&&

$$

Short term...jrb
long term...jpc
aviation...jrb

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