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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
611 am CDT Friday Jul 3 2015

Short term...(today and tonight)
issued at 406 am CDT Friday Jul 3 2015

Two main issues during the short term deal with thunderstorm
chances/coverage along a weak boundary that will be slipping into
the area this afternoon and the potential impact the continued dense
smoke from Canadian fires will have on highs and in turn potential
afternoon destabilization.

Visible satellite imagery toward sunset last night clearly showed
that often dense smoke from Canadian wildfires was spread out across
the northern Continental U.S. From Montana to expect another hazy day
with dense smoke in the middle-upper levels of the troposphere. This
will again keep US from achieving our full potential when it comes
to highs this afternoon...but a good 2-4 degree c warming in the 925-
850 layer will still yield highs a few degrees warmer than Thursday...with
most places climbing to around 80...which is still a few degrees
below normal.

On water vapor imagery...a strong shortwave can be seen heading for
Northern Lake Superior...with a cluster of thunderstorms out ahead of it
that stretches from The Arrowhead into adjoining sections of
Ontario. This shortwave will continue on toward Lake Huron through
the day...but the reason it will play a role in our weather today is
the weak surface boundary it has trailing back to its SW. This boundary
was working across northwest Minnesota this morning and will be to central Minnesota by
the afternoon and will provide what meager forcing we will have for
thunderstorms this afternoon. We will see lower 60 dewpoints work in
out ahead of the boundary...which will aid in developing some
instability this afternoon. However...think dense smoke will make it
tough for US to realize the upwards of 2000 j/kg of MLCAPE the
NAM/GFS have...and instead will keep US capped around 1000 j/kg.
This does not Bode well for seeing widespread thunderstorm activity.
Cam reflectivity forecasts reflect this idea as well. For
probability of precipitation...took 30 probability of precipitation from central Minnesota and worked them over toward western
WI into the evening as this is where the best moisture transport
shows up around 850 mb. Also switched our weather grids from
probability to coverage wording to get the forecast to read isolated
to scattered thunderstorms for this afternoon/evening.

As we loose daytime heating...we will lose the thunderstorms as
well. Main question then for Friday night becomes how quickly can we
clear out to allow for fog formation. Would not be anything
widespread...but the typical low spots and river valleys from
central Minnesota into western WI could see some fog develop again Saturday

Long term...(saturday through thursday)
issued at 406 am CDT Friday Jul 3 2015

Concerns continue to increase in the long term for the Saturday
through Monday period with respect to highs...severe weather and
heavy rainfall.

The period will begin with a nearly stationary front near the
I-90 corridor. The front will lift slowly northeast during the
day as low level south-southwest flow increases. While this is occurring...a
weak short wave will arrive by midday from South Dakota...which
will push into southern Minnesota/northern Iowa during the afternoon. As
instability and forcing increase...there is a small threat for
some showers and isolated thunderstorms to develop along and north
of the front. Various cams suggest southeast Minnesota and adjoining areas of WI
will see widely scattered activity in the afternoon and this is
where small probability of precipitation were placed. A few solutions have some isolated
showers reaching the west and south metropolitan...but confidence was not
high enough to include them at this point. Highs on Saturday are a
concern as the fire smoke the past few days has surely cost US
several degrees on the high temperature. The flow aloft on
Saturday is still had to take this into consideration on
the highs as mix-down and MOS guidance are way warmer than the
going forecast. However...this has been the case for the past two
days with highs being cooler than guidance. Current forecast highs
are between 82 and 85 degrees which is very close to climatology.

Sunday into Monday is the next concern as a cold front pushes
across the region. Timing on the front remains consistent...
stretching from northwest Minnesota through eastern South Dakota Sunday afternoon...from
Duluth through the Twin Cities to Omaha Monday morning and then
east of Eau Claire by Monday afternoon. Temperatures on Sunday are
tricky. Low level south-southeast flow increases across the forecast area which actually
brings in cooler air at 850 mb. The exception is across western Minnesota
ahead of the front where the low level thermal ribbon exists.
Highs on Sunday ended up being very similar to those on Saturday
with west central Minnesota being several degrees warmer. One reason for
keeping the highs up across eastern Minnesota and western WI is the flow
aloft becomes more westerly which should clear out the fire smoke
and allow highs to be closer to mix-down values.

Convection is likely to develop along the front Sunday afternoon
and evening. Storm Prediction Center now has much of the forecast area in a marginal risk with
west central and southwest Minnesota in a slight risk for severe weather.
Surface cape values in the slight risk area increase to between
1500-2000 j/kg by late in the day along with decent middle level
lapse rates. Cape in the surface-3km range is on the order of 150-200
j/kg. Although a veering profile is forecast...deep layer shear
values are not that great for our western area. 0-1km shear is a
little better. A conglomeration of severe weather parameters point
to eastern South Dakota...southwest Minnesota and northeast Nebraska as the Hot
Spot Sunday afternoon and evening. This is also pretty much where
the highest sref calibrated severe probabilities are. Hence...a
few strong to severe storms can not be ruled out heading through
Sunday evening.

The cold front will move through Sunday night and early Monday
with likely to categorical probability of precipitation remaining in place. Precipitable water values
continue to be forecast above 2 inches ahead of the front... with
bouts of heavy rainfall likely. Cips analogs continue to show high
chance probabilities over a large area of our forecast area for greater than
an inch of rain. The current quantitative precipitation forecast grids through 12z Monday indicate
over 1.25 inches of rain west of a St cloud to Redwood Falls line.
Before the rain ends early Monday afternoon...eastern/southern Minnesota
and western WI will likely have an inch or more of rain.

In the wake of the front...dry and less humid conditions will
occur for Monday night through Tuesday night. Another short wave
and associated cold front will pass across the northern plains
and upper Mississippi Valley region Wednesday and Thursday. At
this point...small probability of precipitation begin across western Minnesota on Wednesday with
low chance probability of precipitation across the forecast area on Thursday as the front moves


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 609 am CDT Friday Jul 3 2015

With the hrrr and hopwrf now going out through the
afternoon...the Prospect of thunderstorms is looking pretty continued to keep any precipitation out of tafs. Terminals
most like to see a rain showers/thunderstorms and rain are rnh/eau...though stc/msp can not
rule something out. Fog may be an issues again at eau Saturday
morning depending on how much cloud cover lingers through the
night with the frontal passage this afternoon/ introduced an
MVFR visible for them to end the taf for now.

Kmsp...if msp sees a rain showers/thunderstorms and rain it would be between 23z and
3z...but that threat still looks pretty minimal. Winds will be
pretty much a cross wind for the 30s/12z much of the day...though
with speed generally 8 kts or will have minimal impacts.

/Outlook for kmsp/
Sat...VFR. Winds SW 5-10 kts.
Sun...VFR. Thunderstorms and rain with MVFR likely overnight. Winds S 10-15 kts.
Monday...MVFR/IFR with thunderstorms and rain early. Then VFR. Winds northwest 10 kts.


Mpx watches/warnings/advisories...


Short term...mpg
long term...rah

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