Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 182349
AFDMPX

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

.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
mark.

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 00Z TAFS through 00Z Friday evening)
Issued at 649 PM CDT Thu May 18 2017

Not many changes needed to existing TAFs with the 00z set.
Northeast winds will continue through the whole period, which will
have two impacts. One, it will continue to erode MVFR cigs out
there now, which will speed up with the loss of daytime heating.
Two, the dry air these winds bring will make it tough for precip
coming up out of Iowa tonight to make much inroads in MN through
the day Friday. Widespread rainfall is not expected until Friday
night at the end of what will be the 6z TAFs.

KMSP...High confidence in MVFR cigs finally clearing out around
1z. Looking at forecast soundings and reflectivity forecasts,
existing timing for prob30 continues to look like MSPs best shot
at seeing some light rain Friday. Otherwise, steady rain looks to
arrive between 9z and 12z Sat.

/OUTLOOK FOR KMSP/
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.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory from midnight tonight to 8 AM CDT Friday for
     WIZ014>016-025-027-028.

MN...Frost Advisory from midnight tonight to 8 AM CDT Friday for
     MNZ043>045-052-053.

&&

$$

SHORT TERM...SPD
LONG TERM...JRB
AVIATION...MPG



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