Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 190342

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1042 PM CDT Thu May 18 2017

Issued at 930 PM CDT Thu May 18 2017

Main concern tonight is the convective debris from storms that
fired over central Kansas during the afternoon is screaming north
and already working into the Twin Cities. This may keep us from
having frost issues, with lows tonight likely staying up a couple
degrees higher than we had, which would be enough to cut back on
the frost potential. At this point, we`ll keep the frost advisory
going, but confidence in the frost potential is decreasing.

For tomorrow, have slowed the northward push of the rain chances
as the 00z NAM has come in line with what most of the hi-res
models are showing with rain making up to about Mankato before dry
air takes over. Still looks like the big slug of rain comes up
after midnight Friday night, with Saturday morning looking rather
ugly with rain and temperatures in the 40s.


.SHORT TERM...(This evening through Friday)
Issued at 253 PM CDT Thu May 18 2017

The low pressure system that moved through yesterday and last night,
is still departing to the east with widespread low clouds in
cyclonic circulation on the back side.  The clouds have been eroding
across northern MN as high pressure across south central Canada
pushes in from the north.  The eroding cloud trend will continue
through tonight, with slow dissipation of the clouds expected across
the area.  The northerly flow is also bringing some pretty chilly air
down from Canada as 850H temps are now flirting with the freezing

So, the main concern is for frost tonight and the most susceptible
area is across northeast MN and northwest WI, and dipping into west
central WI and parts of central MN.  Forecast lows indicate cold
enough temps for frost across these areas so went ahead and issued
a frost advisory.  We will have to watch the wind though because
with the high well to our north, we may keep a slight breeze in our
area tonight, whereas farther north confidence is higher that
temperatures will dip.

For tomorrow, shortwave energy and low level warm air advection
will stream northward through Iowa into southern MN where rain is
likely, but with the stout high pressure in place and very dry air
from central MN and northward, the precip may not make it that far
north.  Another cool day with temepratures in the 50s with that cool
airmass remaining in place.

.LONG TERM...(Friday night through Thursday)
Issued at 253 PM CDT Thu May 18 2017

Early afternoon water vapor imagery together Rap13 heights and winds
showed a powerful cyclone approaching the TX/OK panhandles. This
system will bring widespread rain across the entire region late
Friday night into Saturday. This system will be slow to move out, so
expect low clouds and a few showers to linger on Saturday. At this
point Monday looks dry, but overall expect a cooler more cloudy
forecast for the upcoming week with periodic chances for showers and
thunderstorms. The threat for severe weather is very low.

Saturday will be rainy as a large area of synoptic forcing
associated with the height falls from the Upper Level wave lead to
rising air, saturation, and rain.  This is a large system so feel
very confident that most if not all locations have measurable
rainfall on Saturday. There are some slight timing differences
between the models, and for that reason used 3 hourly precip grids,
but increased the 12hr pop grid. Forecast soundings show little in
the way of instability except for far southeast MN and western WI,
so see this as mainly a light to moderate rain event. Total
accumulations of around 0.75 inches can be expected.

Wrap around could air advection will lead to cool temperatures on
Sunday, and forecast soundings show overcast skies with enough
instability atop the boundary layer to produce a few light rain
showers, so tried to time increased pops during the heating of the
day. Monday will be dry, but another northern stream shortwave will
rotate across the region and bring another round of showers.
Northerly flow will develop which should bring in some drier air and
upper level subsidence for the end of the week.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1045 PM CDT Thu May 18 2017

Only change made to existing TAFs was to remove prob30s for -SHRA
at MSP and RWF. 00z NAM has come in similar to what we are seeing
with the RAP and HRRR that dry air locally will keep any rain
Friday south of the MPX terminal. Main surge of rain Friday night
looks to be coming after 06z.

KMSP...we may see MVFR cigs and -RA moving in right at the tail
end of the TAF, but with the dry air expected to be in place, felt
better about taking a slower route to the arrival of both this far

Sat...MVFR/RA with IFR possible. Wind E at 10G20kt.
Sun...MVFR. Chc -shra. Wind WNW at 15G25kt.
Mon...VFR. Chc MVFR/-shra. Wind NW at 5-10kt.


WI...Frost Advisory until 8 AM CDT Friday for WIZ014>016-025-027-028.

MN...Frost Advisory until 8 AM CDT Friday for MNZ043>045-052-053.



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