Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 211657

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1057 AM CST Wed Feb 21 2018

.UPDATE...For 18Z Aviation discussion below


.SHORT TERM...(Today and tonight)
Issued at 315 AM CST Wed Feb 21 2018

Very benign short-term portion of the forecast with arctic high
pressure moving across the region and upper level flow transitions
from zonal to slightly southwesterly with a much drier atmosphere.

Surface analysis shows the center of high pressure over the
Dakotas and this high pressure airmass is expected to shift
easterly over southern Minnesota and into the Great Lakes through
Thursday morning. Nearly all of the moisture associated with the
previous frontal system has also moved well off to the east,
leaving clear skies in place for today. Despite full sunshine, the
cold air advection behind the front will result in highs only
reaching the mid-teens to lower 20s.

While the high pressure area shifts off to the east tonight, a
weak cold front will drop in from the northwest. In addition, a
fairly impressive upper level wave over the Deep South will move
northwest within the digging southwest flow aloft, bringing
another surge of moisture well into the north-central CONUS
tonight. This will result in an increase in clouds overnight
through daybreak Tuesday. However, with the GFS being the fastest
among the models to bring in precipitation prior to 12z, am
considering this an outlier and have gone with consensus to keep
precipitation out of the area prior to 12z.

Lows early Thursday morning will be relatively milder than what is
being reported this morning. While lows this morning will range
-10F to +5F, lows this time tomorrow will run between 0F-10F.

.LONG TERM...(Thursday through Tuesday)
Issued at 330 AM CST Wed Feb 21 2018

Longer term concerns are overall model trends for the snow event
Thursday/Thursday night and the possibility of a more significant
storm Saturday/Saturday night.

Models a fairly consistent on lifting the next short wave across
the area Thursday. Forcing/isentropic lift moves int rapidly
Thursday morning and across much of the cwa through 00z Fri.
Strongest forcing moves across the area Thursday night with fairly
widespread QPF over 0.20 inch then. Snow amounts look to range
from 2 to 4 inches over most of the cwa. If more significant QPF
arrives with the trough, it could drop a little higher snow
amounts with a headline possible. The blended model tries to
remove ice in the dendritic layer fairly quickly, with the GFS
trend much slower. This makes good sense as greatest lift moves
through and we are pretty much saturated in the dendritic layer
per the GFS. The GEFS P-type probability plots indicate snow over
the area as do the SREF plumes. Will trend the loss of ice lifting
north through 12z Friday. This did give some small chance for
freezing drizzle on the tail end of the system.

This system exits the area early Friday leaving another lull in
the overall weather through Friday night. The latest model
guidance continues to show development of a rather potent storm
system over the Oklahoma panhandle region to the southwest late
Friday night. It lifts northeast and deepens to 989mb toward
southeast MN/northeast IA region by Saturday evening. This would
draw warm air ahead other system and we could see mixed rain
changing to snow over the far eastern portion Saturday. From what
I was able to see of the 00z ECMWF, it looked to be similar to
timing with the GFS as well with rather high QPF and snow
potential associated with it. If this trend continues, this could
be a significant snow maker for much of the cwa.

Weak riding aloft develops in the wake of this system with dry and
mild conditions into Tuesday. The GFS reloads the western trough
and lifts some moisture northeast toward the cwa late in the
forecast period. This too will have to monitored for yet another
possible storm affecting the wester Great Lakes later next week. A
more active pattern developing as we head toward Spring over the

Temperatures appear to be trending closer to normal with reading
a little above normal possible into next week.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1058 AM CST Wed Feb 21 2018

Benign conditions into Thursday, and then a notable reduction in
conditions is anticipated Thursday afternoon. By daybreak Thursday
expect to see a mid-level deck in place, which will lower/thicken
by the afternoon with snow spreading across the sites between 15Z
and 21Z. Once the snow begins it should continue through Thursday
evening, with IFR conditions becoming prevalent.

Current onset time for snow on Thursday looks to be between 16z
and 18z. MVFR at onset with IFR becoming prevalent during the
afternoon hours.

Fri...MVFR ceilings in the morning. VFR in the aftn. Wind W 5
Sat...VFR in the morning. MVFR or lower with -SN in the afternoon.
Wind E 5 kts.
Sun...VFR. Wind W 10 kts.




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