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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1155 am CDT Sat Aug 30 2014

Short term...(today and tonight)
issued at 359 am CDT Sat Aug 30 2014

Well defined middle-level circulation could be seen on radar heading
for Eau Claire at 3 am. To the northwest of this circulation...we have seen
a deformation band of precipitation persist across eastern Minnesota into northwest WI. This
band of rain will slowly work east across western WI...mostly clearing
the mpx County Warning Area near or shortly after 12z as the offending short wave
moves into north central wis. However...this not the only shortwave
we have to worry about today...with the strong wave up near Fargo
looking to take a trip down I-94...ending up near Eau Claire by this
afternoon. As we have seen out in western/central Minnesota all night...this
wave will continue to allow small and weak pop-up showers to develop
from time-to-time on its trek east. As a result...held some 20 probability of precipitation
into the afternoon about as far west as the MS river...which is also
where simulated WV forecasts show deeper moisture residing through
the day...with the drying currently seen across the eastern Dakotas
getting wrapped around the south side of the wave...allowing a
tongue of deeper moisture to get hung up back into central Minnesota.

Beside the showers this morning...the presence of very moist
cyclonic flow around a surface low centered near La Crosse has resulted
in an extensive stratus shield setting up across all but northwest Minnesota and
into adjacent portions of the eastern Dakotas. Given the trailing
shortwave near Fargo...this moist cyclonic flow will more or less
stay in place well into the afternoon...which means clouds will be
with US through most of the day. Given the cloudy scenario that is
expected...favored the forecast for highs today toward the lower end
of guidance...with highs only topping out in the lower 70s for the
most part...with a few places in central Minnesota likely remaining in the
60s today.

For tonight...we will be watching the system impacting US on Sunday
begin to emerge out onto the High Plains. A strengthening low level jet out
ahead of this upper trough will build north out of the Central
Plains...likely fueling an elevated mesoscale convective system that looks to track across
nodak into northwest Minnesota. This activity looks to mainly stay northwest of
the mpx County Warning Area...but enough uncertainty exists with the southward
extent of this activity to keep some 30 probability of precipitation going out in the northwest County Warning Area
late tonight. On the other side of the County Warning Area...will have to watch sky
cover trends as their proximity to the surface ridge will allow the
boundary layer to remain decoupled...which will leave western WI
susceptible to the development of dense fog.

Long term...(sunday through friday)
issued at 359 am CDT Sat Aug 30 2014

Very little change to the forecast on Sunday. We like what the day
shift had for storm timing and the forecast still calls for
"definite" thunderstorms and a "chance" for severe weather in Minnesota
and far western WI on Sunday. This event looks as good a chance
for severe weather as any other event this year...albeit a quiet
year.

The trough expected to move across the northern Continental U.S. Sun-Monday and
bring widespread thunderstorms to the region is now moving into
the Pacific northwest this morning. The middle-upper jet /50-70kts/
that will act to initiate convection and then organize
thunderstorms on Sunday will spread into western Minnesota between 00-06z
Sunday. There is a classic difluent pattern as evident by the
850-300mb thickness Sunday evening to go along with strong fgen
coming out of the Dakotas during the afternoon. Convection should
be widespread with storms already ongoing in the eastern Dakotas
Saturday morning. Elevated convection should transition to surface
based convection with heating and the likely establishment of
large line segments or clusters of thunderstorms due to the large-
scale forcing. We're starting to get a look at some of the cam
guidance for Sunday and the early look shows a couple strong line
segments moving from west to east across the forecast area. The
best severe risk will occur along the cold front during the late
afternoon as the boundary layer warms...bringing SBCAPE between
2000-3000 j/kg in Minnesota. Cips warm season analogs to both the latest
NAM/GFS runs show a good number of severe reports when looking at
similar past events. The number of damaging wind reports
immediately jumped out at US. This would also match what's
expected on Sunday given the likely linear convective Mode. There
was also a fair amount of tornado reports on a few analogs...which
is likely tied to the strength of the forecasted strong low level jet
coincident with peak heating on Sunday. The flow could remain
backed in eastern Minnesota during the early evening...so we might have to
worry about a few kinks in the convective lines and weak tornado
potential...however...it still looks primarily like a wind and
small hail threat in the afternoon and evening hours across Minnesota.
Both the NAM and GFS have 0-3km shear on the order of 25-40kts
from 18z-06z across the forecast area.

Beyond the weekend...the trough flattens out and we're left
with relatively quiet weather and near normal temperatures for the
work week. A cold front will lay out well south of the forecast
are through the middle of next week...so any organized forcing or
significant convergence should be south and east of the forecast
area. We probably should have been more aggressive at removing the
thunder chances on Tuesday and Wednesday. Thursday looks a little
better with a developing trough in the central/northern plains and
moisture advection locally.

&&

Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1141 am CDT Sat Aug 30 2014

High confidence that MVFR ceilings should hold around the region through
the early afternoon before enough mixing and diurnal heating enables
local/S to rise to VFR. However...short term models are depicting a
more pessimistic forecast through the afternoon...and into the evening.
There remains some merit to this forecast as boundary layer
moisture remains robust and surface winds become light this afternoon. In
addition...as winds remain light and variable with a return flow
from the southeast overnight...moisture across WI/Iowa may advect back into
Minnesota creating MVFR ceilings overnight. Only had kstc with this scenario
based on location and the amount of deep moisture in the vicinity. In
addition...LIFR/vlifr conds are very possible at krnh/Keau if
skies clear. Will continue the same trend for these sites. After
12z...most areas will see improvement in the ceilings with gusty southeast
winds developing. Rain showers/thunderstorms and rain will hold off until after 18z.

Kmsp...

High confidence that MVFR ceilings will remain near the Airport
terminal through 19-20z...with a slow lift to low end VFR during the
remainder of the afternoon hours. Some breaks in the cloud cover has allowed
for VFR conds temporarily...but with the amount of moisture in the
lowest 5k...it should quickly fill in. As previously said...am
concern with weak boundary layer winds and the amount of moisture
holding in the area for MVFR ceilings to redevelop this evening.
Will hold off until the 21z amend. Otherwise...VFR conds with southeast
winds developing by late tonight...with gusty southeast winds and the chance
of thunderstorms and rain after 18z.

/Outlook for kmsp/

Sun evening...MVFR/IFR ceilings in +tsra likely. Winds south-southeast at 10-20 kts.
Monday...MVFR/tsra ending early. VFR by afternoon winds west 10-15 kts.
Tuesday...VFR. Winds west-southwest 10 kts.

&&

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

$$

Short term...mpg
long term...clf
aviation...jlt

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