Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210503

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1103 PM CST Mon Feb 20 2017

Issued at 1052 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 06Z TAFS through 06Z Tuesday night)
Issued at 1052 PM CST Mon Feb 20 2017

Cold frontal passage on its way through central MN as the rain
has shifted off to the east. Conditions have dropped to MVFR/IFR
with the passage of the front and 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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