Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201045

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
545 AM CDT Sat May 20 2017

.updated for 12z aviation discussion below...

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Sat May 20 2017

The short term concerns are evolution of the rain shield over the
area this morning and possible development of convection over the
eastern cwa into tonight as the upper trough swings through.

Surge of moisture ahead of central CONUS upper trough now lifting
into southern MN. Water vapor imagery shows strong impulse lifting
through eastern Nebraska and Kansas this morning. Overall it
appears the latest HIRES HRRR/ECAM development/movement looks
good and followed this trend into the morning/afternoon. With the
amount of cloud cover and rain moving into the region we dont
expect temperatures to warm much today. Probably remain in the
upper 40s to the west and some lower 50s to the far east...and may
occur into the evening in west central Wisconsin as the occluded
system moves through.

The upper trough is progged to lift northeast into MN this evening
along with attendant mid level drying and occluded surface low.
Instability increases over the eastern cwa into the evening as
well. MUCAPE to 500 j/kg and best LI`s to minus 5 indicated on
the GFS. This verifies fairly well with the 00z NCAR ensemble of
MUCAPE as well. We will spread slight chance thunder over the
southeast portion of the cwa into the evening/overnight. Steep mid
level lapse rates also indicated over western WI overnight. If
something organized can occur some small hail could occur.

QPF looks to range around three quarters to about one inch over
much of the cwa through the day Sunday. The heaviest
precipitation will occur today into the evening however.

.LONG TERM...(Sunday through Friday)
Issued at 400 AM CDT Sat May 20 2017

Sunday through Tuesday...The period will start with the low
pressure center between KMSP and KDLH with its associated occluded
front extending eastward over northern WI to near KGRB while a
trailing surface trough extends NW into southern Manitoba
province. While heavier/steadier rain will have shifted north into
northern MN, scattered light rain showers will persist through the
first half of Sunday and gradually diminish in coverage during the
day. The low will move into northern Lake Superior by the evening
hours, taking nearly all the rainfall with it. The break in the
precipitation will be brief as a series of weak disorganized
surface troughs look to push through the area Monday through
Tuesday. Little in the way of upper level support is available but
the deep moisture column will remain in place into the early part
of next week so there will be just enough energy available from
the low-level troughs to spark scattered rain showers Monday into
Tuesday. With these cloud/rain complications in place,
temperatures will remain cool with highs only in the 50s and 60s
which is still some 10-20 degrees below normal.

Wednesday through Friday...Drier surface high pressure with
northwest flow aloft will be the prevailing features mid-to-late
week. This will allow for some rain-free days and even some
sunshine to warm temperatures back closer to normal values during
the latter half of the week. The area will become warm-sectored
Thursday in advance of a cold front expected to pass through the
region Friday. Additional rain showers are certainly possible with
this frontal passage but no significant impacts are expected for
the area.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 545 AM CDT Sat May 20 2017

Previous forecast reasonable and will follow timing pretty close.
Rain area lifting into southwest MN at this time will work
further north and east through 18z. Cigs lowering to mvfr and then
ifr by afternoon most areas and remaining so overnight. The -ra
will gradually turn over to -dz into the south with fog prevalent.
Some chance of thunder as the occluded low lifts northeast over
the southeast part of MN tonight. Believe it will be isolated so
left out of eastern taf sites. As the low/occluded front moves
through...wind direction will be affected. Expect overall easterly
wind becoming north and eventually northwest late tonight as
colder air rushes into the area.

KMSP...Expect -ra to work into the area through 14z with cigs
becoming mvfr and eventually IFR through 18z. Confidence remains
high on the -ra continuing through the day...tapering to -dz this
evening. Isolated thunder threat possible into the evening but
believe it will remain mainly to the east of the terminal. May
see cigs lower to LIFR overnight before system moves east with
slowly improving vsbys/cigs into Sunday morning.

Sun night...MVFR. Chc -shra. Wind WNW at 15G25kt.
Mon...VFR. Chc MVFR/-shra. Wind NW at 5-10kt.
Tue...VFR. Chc MVFR/-shra. Wind N 5-10 kts.




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