Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210227

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

Issued at 748 PM CST Mon Feb 20 2017

Updated to include 00z aviation discussion below.


.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 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

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 00Z TAFS through 00Z Tuesday evening)
Issued at 748 PM CST Mon Feb 20 2017

Cold frontal passage on its way from western MN as the bulk of the
rain has shifted off to the east. While there was a brief period
of VFR conditions around the 21/00z initialization time, IFR
conditions are likely over much of the first 4-6 hours of the TAF.
Low stratus is evident on IR satellite behind the higher clouds,
but also trailing is a clearing area in western MN. Conditions
will be tricky overnight since the low stratus/fog currently may
give way to a period of VFR then go back to IFR around sunrise
into late tomorrow morning then go back to VFR for much of the
day. The timing may require multiple amendments but will monitor
and adjust as needed. Winds will shift from SE to WNW with the
fropa then back to southerly with the influx of high pressure.
However, speeds will settle down to less than 10 knots overnight
through tomorrow.

KMSP...Slow improvement has been seen from the IFR conditions at
initialization and will look for conditions to hit VFR prior to
the next routine TAF issuance. Still will look for IFR fog to
settle over the area during the time of the morning push, followed
by VFR conditions thereafter.

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.
Fri...IFR or lower in SN/+SN likely. Wind NE 15-25G35 kts.




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