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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
620 am CDT Tuesday Jul 26 2016

Short term...(today and tonight)
issued at 352 am CDT Tue Jul 26 2016

Scattered showers and thunderstorms were occurring early this
morning along the border area of eastern ND/SD. The storms are
moving slowly east and are at the nose of a 40 knot jet in the
925-850mb layer. This wind Max pushes eastward into northwest WI by early
this afternoon while slowly weakening. Various cams that
initialized or developed storms in this area bring the activity
into our far northwest forecast area after 12z with a significant weakening trend
by mid morning. Kept low chance pops for these areas this morning,
but will need to keep monitoring this situation as storm strength
is rising along with cloud top cooling to the northwest of
Aberdeen.

While this is occurring this morning, a cool front across
northern Minnesota will drift south and be over central Minnesota and adjoining
areas of northern WI this afternoon. A low level thermal ridge
will exist just to the south of the front with 850mb temps in the
20-22 deg c range. Highs on Monday with this pattern in the
Dakotas yielded readings in the lower 90s. Therefore, boosted
temperatures a few degrees over the previous forecast, primarily
from west central Minnesota through the Twin Cities to Eau Claire with
around 90 to the lower 90s indicated.

Kept central Minnesota about the same on high temperatures today as we
expect storms to fire along the boundary by mid afternoon and
slide eastward into WI along Highway 8. This idea was supported
well by the Storm Prediction Center/NSSL/can hires and CR-namnest cams. Storm Prediction Center has
indicated a marginal risk for severe weather in this area. The
shear is very low. 850mb winds are below 20 knots while 500mb
winds are near 20 knots. Instability is modest while the progged
dcape is rather impressive at around 1000 j/kg from mid afternoon
Onward. So the thinking here is that there could be a few pulse
severe storms with damaging winds the primary culprit.

The trend from the aforementioned cams is for the activity to
fester for a time this evening across central Minnesota before pushing
across northwest WI during the overnight hours. More convection may reach
west central Minnesota late in the night...associated with a strong upper
wave over the eastern half of Montana and Wyoming early this morning. It
certainly should push into west central Minnesota Wednesday morning. With
confidence high on showers and thunderstorms developing/occurring
across the far northern forecast area this afternoon and evening, indicated a
narrow band of likely pops. Also raised low temperatures a few
degrees tonight over the previous forecast with the boundary hung
up across our northern forecast area along with dew points in the lower to
middle 60s. Lows are close to the mav/met MOS.

Long term...(wednesday through monday)
issued at 352 am CDT Tue Jul 26 2016

For the extended, decent confidence in the pop forecast exists
through Friday, but significant differences in the details show up
for the weekend, with the GFS driving more showers/storms across the
area with the European model (ecmwf) keeping things dry. Next week (and to start
August!), Both the GFS/European model (ecmwf) show h5 heights building into the upper
MS valley once again, with the heat and humidity looking to make a
return.

The front that will be the focus for showers and thunderstorms
today will continue to be a focus for showers and thunderstorms
across the area through Wednesday. However, getting added to the mix
for Wednesday is a boost to forcing from the wave currently
evident on water vapor imagery over central Montana. Have introduced
likely pops to much of the area for Wednesday afternoon, with the
deterministic models all similar in creating fairly widespread,
though light quantitative precipitation forecast Wednesday afternoon as we get to peak heating. Like
today, shear will be lacking considerably Wednesday, but unlike
today, where sunny skies will allow for warmer temps and higher
instability bringing the marginal severe threat, Wednesday will
feature more cloud cover, cooler temperatures, and less instability
than today, so our severe threat Wednesday will be even lower than
the low threat we have today.

For Thursday and Friday, models have finally come into better
agreement, though that is because the European model (ecmwf) has finally backed off
on developing a strong surface low over Iowa that lifts into the
Great Lakes. Instead, the European model (ecmwf) look more like what the rest of the
guidance has been showing with a weak surface inflection going from
Iowa into the southern Great Lakes. This has allowed US to
significantly reduce pops for Thursday night and keep Friday dry with
the European model (ecmwf) no longer showing a deformation band of precip slowly
working across southern Minnesota and into central WI Thursday into Friday.

This weekend we will see our flow transition to the northwest
in the wake of the wave coming through Wednesday/Thursday. The big
difference in the models is how they handle another wave coming
across the Dakotas on Friday. The European model (ecmwf) is still more amplified with
the mid week wave as it heads into the Great Lakes over the weekend,
with the Dakotas energy getting forced down into the base of the
trough and going south of Minnesota/WI, which would keep US dry as our low
level winds slowly transition to the south, resulting in a gradual
increase in temps and dewps. The GFS is weaker with the Great Lakes
wave, which allows the energy coming across the Dakotas on Friday to
just drive right across the upper MS valley Saturday. This results
in a faster return of the warmer temps and higher humidity and the
resultant increase in instability has the GFS pumping out primarily
diurnally driven precip Saturday and Sunday. Though not the same as
the GFS, the Canadian shows a wave working across the area this
weekend as well, which explains the increase in pops for this
weekend.

For next week, both the GFS and European model (ecmwf) show a 595 dm h5 high
developing down around Kansas City, with its ridge axis building
north into the area. This will likely spell a return to seeing highs
up in the 90s with dewpoints in the 70s as the calendar flips to
August.

&&

Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 620 am CDT Tue Jul 26 2016

Main concern during the period is rain showers/thunderstorms and rain threat. Confidence for
this activity is highest across central Minnesota and adjoining areas of
west central WI this afternoon and evening as a cool front settles
south from northern Minnesota. In addition, there will be some showers
and isolated thunderstorms work past kaxn through 15z. This
activity is at the nose of the low level jet that will slowly
wane across central Minnesota this morning. VFR conditions outside of
the rain showers/thunderstorms and rain through the period. S winds this morning 5-10 knots
becoming SW and increasing to 10-15 knots for the late morning and
afternoon hours.

Kmsp...bouts of rain showers/thunderstorms and rain expected to stay well north of the
airfield today and tonight as they migrate eastward across central
Minnesota. Next threat for rain showers/thunderstorms and rain is Wednesday morning near the end of
the taf (15z-18z). Confidence was not high enough to include at
this time with better chances after 18z. Winds similar to those
described above.

/Outlook for kmsp/
Wed aftn/ngt...mainly VFR. Chance MVFR/tsra. Winds S 5 kts.
Thu...mainly VFR. Chance MVFR/tsra. Winds NE 5 kts.
Friday...mainly VFR. Chance MVFR/tsra. Winds east 5 kts.

&&

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

$$

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

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