Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 192110

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
410 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

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 minimal.

.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 18Z TAFS through 18Z Sunday afternoon)
Issued at 101 PM CDT Sat May 19 2018

Satellite shows clouds quickly dissipating as we continue to warm.
Current TAFs were tracking pretty good on improvements to VFR and
continued to run with a blend of the fast to improve HRRR and
slow to improve LAMP. Dry northeast winds will push these clouds
down into Iowa and expect MVFR or lower cigs to only make it about
as far north as I-90 tonight, or south of all MPX terminals.
These dry northeast winds will also keep any rainfall away from
the MPX terminals, with rain currently moving north across Neb/IA
expected to make it about as far north as the I-90 corridor

KMSP...CIG heights are starting to trend up and think we`ll be
018 or higher by 1830z, so started MSP off above 017. Looking at
satellite, stratus happens to be thickest from RWF, through the
Twin Cities and off to RNH, so believe what we are seeing with the
NAM/GFS/RAP in that we will not finally lose these clouds until
around 00z. Rest of the period its VFR as we just see mid/high
clouds stream north from activity down across the Plains.

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




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