Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 202034
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
234 PM CST Mon Feb 20 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 230 PM CST Mon Feb 20 2017

The forecast concern in the short term remains timing of
front/rain shield and overall fog threat after midnight.

Timing of the front/trough a little slower...by about 1 to 2
hours with categorical pops timed into western Wisconsin by this
evening. Some small potential of isolated thunder late
afternoon/evening with front as it moves through...but will likely
be limited to mainly the far south and east. Widespread light
rain and fog developed out ahead of the trough by 18z-19z and this
will remain east of the trough into the evening. Models suggest
some clearing/drying behind the trough as winds become more west.
Not confident of significant drying and a weak ridge builds east
through 12z Tue which will likely spell at least areas of fog
overnight.

Any fog should burn off early Tuesday and we expect mild
conditions to continue ahead of the next frontal system. We have
some lower 60s to the south again...with record or near record
highs expected.

.LONG TERM...(Tuesday night through Monday)
Issued at 230 PM CST Mon Feb 20 2017

The long term starts out with the very warm airmass still in place.
The first order of business was to incorporate some bias corrected
guidance in for Wednesday highs and raise them a couple degrees
across the board.  This produced temperatures in the mid 50s to low
60s across southern MN and West central WI.

With the zonal flow setup, a couple ripples in the upper flow
pattern and vort maxima moving through, along with a frontal
boundary sagging south, have some pops in central MN on Wednesday.
Most of light precip with this still looks to fall north of the
forecast area.  Wednesday will be our last really warm day as the
cold front moves through.

Attention then turns to the large trough digging across the western
CONUS which still looks to spawn a strong low pressure system that
will eject from the lee of the rockies Thursday night and track
northeast toward the western Great Lakes.  The models today
continued wobbling back and forth, not surprising with the event
still in the 3-4 day range (starting Thursday night and lasting
through Friday).  For instance, the GFS was leaning to the south and
the 12Z run shifted north about 50 miles.  Meanwhile the EC which
was leaning to a northern solution shifted south about 100 miles.
Confidence is high that southern MN sees snow despite this.  The
GEFS members are still indicating a lot of uncertainty in amounts
for specific locations such as MSP.  This makes sense given this
looks to have a very tight snowfall gradient; also very common.  So,
with this variability in play, its unwarranted to start talking
amounts for any specific location but wherever the heaviest band
does setup should be able to exceed a foot of snow with this storm.
Will continue to hone in on the track details as that will make all
the difference in amounts and impacts.  Held off on a watch for now
given the aforementioned variability.

Colder air will fill in behind this storm regardless of its exact
track.  Temperatures much closer to normal for late February are
expected, and will likely be even colder for areas covered in a
fresh snow pack.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1120 AM CST Mon Feb 20 2017

Confidence in overall trends low to medium with mvfr to ifr
cigs/vsbys developing ahead of trough ths afternoon. Area of -ra
with embedded shra/isold ts continue to lift n-newrd over the
region. Best potential of isold -tsra will be found mainly over
wester wi into early afternoon. Models trend some instability back
to the southwest ahead of the actual front late afternoon...but
believe any redevelopment will be isolated in nature and will
leave out of tafs for now. Timing of the front is a little
slower..perhaps an hour or two. Some chance of fog forming later
tonight as surface ridge moves into eastern mn late. SREF probs
indicate lowers vsbys to the north and east portion of the region.
Will mention some lower vsbys mainly in the that are with some
3-5sm br elsewhere from about 10z-14z. Then a few high clouds
possible into the day Tuesday. se-s winds ahead of the front and
becoming nw-w with fropa...and more sw-s later tonight under
surface ridge.

KMSP...
Little change in thinking from above discussion. Feel thunder will
be ISOLD if it occur locally so left out of taf for the
afternoon.

/OUTLOOK FOR KMSP/
Tue night...VFR. Wind S at 5-10 kts.
Wed...VFR. Wind SW at 10G15 kts becoming NW late.
Thu...VFR. CHC MVFR/-RA/-SN in the afternoon, then LIFR/+SN
possible Thu night. Wind NE 5-10 kts.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...DWE
LONG TERM...SPD
AVIATION...DWE


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