Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 200451

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1151 PM CDT Sat May 19 2018

.SHORT TERM...(This evening through Sunday)
Issued at 409 PM CDT Sat May 19 2018

Clouds have been slow to erode as subsidence beneath convergent
mid level flow has created an inversion that has helped to lock
the low level moisture in place. Forecast soundings from the
NAM/GFS show this moisture sticking around through about 6z, but
quickly drying out after that as we advect in very dry air in in
the 900-600 mb layer.

Water vapor imagery this afternoon clearly shows an upper low
coming out of northeast CO that has been forcing a band of rain
that has been slowly moving north across Neb/IA during the day.
This will spread mid/high clouds up into southern MN, but
combination of the dry airmass, clear skies, and light winds will
result in efficient radiational cooling tonight up across central
MN, where lows sneaking into the upper 30s are certainly possible
from Little Falls over toward Mora. As for that band of precip
heading our direction, it will run into an immovable object that
is the wedge of dry air advecting in between h9 and h6 with all of
the guidance showing the rain falling apart before reaching
southern MN, with nothing more than a few sprinkles expected into
the I-90 corridor.

The upper low coming out of CO will slowly drift toward southeast
SD Sunday. This will continue to spread ample mid/upper clouds
into southern MN, but that dry air looks to win out again, with
very little precipitation expected in MN, so continued trend of
reducing PoPs for Sunday. With more sun expected across central
MN, we`ll see an inverted temperature gradient from what we
normally see, with highs in the low 70s across central MN, while
south central MN sees highs about 10 degrees cooler thanks to the
cloud cover. Deep mixing across central MN will allow humidities
to fall off to between 20 and 30 percent, but sustained winds are
only expected to be around 10 mph, so fire weather concerns are

.LONG TERM...(Sunday night through Saturday)
Issued at 409 PM CDT Sat May 19 2018

The upper low drifting toward SD Sunday will continue to weaken as
it slides across southern MN on Monday. But as it does slide
across the state, the GFS in particular shows scattered showers
working across the area with it. Still, that dry air mentioned
numerous times already will likely limit our precip potential, as
we are seeing with the ECMWF, with mostly cloud cover expected on
Monday, which will hold highs back in the 60s/low 70s.

For the rest of the week, it looks to be fairly active, though
with nothing significant, just multiple chances for showers and
storms. We still expect upper ridging to build up into northwest
Canada, but beneath this a weak h5 low will spin across the
Rockies and northern Plains. The lower heights off to our
northwest will result in a weak, though persistent southerly LLJ
directed up out of the central Plains and into the upper MS
Valley. This LLJ looks start producing scattered thunderstorm
activity locally beginning Tuesday night and we look to have
repeated chances at seeing showers and storms, especially in the
overnight periods as the LLJ strengthens until the weak upper low
forcing the LLJ moves east of the area, which doesn`t happen until
Friday night. Flow looks weak this whole time, so there does not
look to be a whole lot of organization to any of the activity,
hence all of the model differences we see with where they drop QPF
in each 6 hour period. Shear will be a limiting factor, but
instability and lapse rates look to be enough where we will have
some threat for hail/wind with any of the events we see.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1150 PM CDT Sat May 19 2018

Scattered showers/storms were developing just south of the Iowa
border late this evening. These showers and storms will brush far
southern Minnesota during the overnight hours with MVFR cigs
holding along the border. VFR conditions should remain in the
forecast through the TAF period, with winds becoming more
east/southeast toward the end of the period. In addition, some
MVFR cigs will begin to brush southwest/south central Minnesota
between 00-06z/Monday.


No additional concerns with all of the precipitation staying south
of the airport through 12Z Monday. After 12Z, some showers are
possible but confidence remains low on how widespread the showers
become. Winds will be northeast tonight, veer to the
east/southeast Sunday afternoon/evening.


MON...VFR/MVFR cigs with -SHRA. Wind E 5-10 kt.
TUE...MVFR/chc IFR cigs early, then VFR. Wind SE 5 kts.
WED...VFR. MVFR early with SHRA/TSRA. Wind SE 5-10 kts.




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