NWS Forecast Discussion

FXUS63 KMPX 211119

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
519 AM CST Thu Feb 21 2019

.updated for 12z aviation discussion below...

.SHORT TERM...(Today through Friday)
Issued at 419 AM CST Thu Feb 21 2019

Water vapor satellite showing upper circulation over northern MN is
still circulating low clouds and some flurries across mainly the
northern half of the CWA this morning. This trend will likely
continue into the morning as the upper trough gradually lifts off to
the east. Should see sunshine primarily across the south today with
high temperatures mainly in the upper teens to mid 20s under the
fresh snow.

Later tonight and Friday, the models continue to trend some decent
forcing along at least a mid level frontal boundary over western MN.
Right entrance region of the jet over southern Canada should generate
some FGEN along eventual boundary to the west. Will continue the
higher end PoPs developing to the southwest tonight and over the
west into Friday. At the moment overall blended guidance gives a 2
to 4 inch snow event from tonight through Friday night, mainly
across the west and generally an inch or less farther east. We will
continue to monitor overall trends to see if this event will justify
a headline before the weekend event.

.LONG TERM...(Friday night through Wednesday)
Issued at 419 AM CST Thu Feb 21 2019

The main concern in the extended part of the forecast continues to
be the potent winter storm that could bring blizzard conditions
across parts of the Upper Midwest Saturday into Sunday. The
impressive part of this system is the strong dynamical forcing that
get best be identified by the surface low rapidly intensifying
over the Great Lakes Saturday night. Cold air will follow in
behind this system with little if any warming expected during the
day on Sunday, and overnight lows falling below zero Sunday night.

The deepening surface low together with cold air advection
will lead to strong surface winds. Forecast soundings from the GFS
show several hours with wind speeds of 40 to 45 kts at the top of
the mixed layer, which could easily translate to 40+ mph winds
observed at the surface. The ECMWF is similar in the development and
strengthening of this storm, but there are outliers. The NAM is
starting to capture this storm and keeps the heavy snow and
strongest winds southeast of the forecast area. The same is true
for the GEM.

In summary, we are highly confidence in a narrow band, say 3 to 4
counties wide, of very heavy snow with rates of close to 2 inches
per hour possible. This storm will be moving fast, so overall totals
will remain less than a foot despite the precipitation intensity. We
are also highly confident that strong winds will accompany the end
of this snow, and that will lead to significant blowing and
drifting, and probably whiteout/blizzard conditions.

We are not confident in the track. Since this is a narrow snow band,
a slight shift one way or another will make a major difference in
the snowfall totals. One other thing to consider is the potential
for blowing snow north of the surface low track and falling snow.
There`s a very deep snow pack in place across the region, If this
storm ends up being as strong as forecast, and the winds end up
gusting 40 mph or more, could easily see a ground blizzard coming to
fruition across central and southern Minnesota, and perhaps even
western Minnesota. Needless to say this is a storm to monitor,
especially if you have weekend travel plans.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 520 AM CST Thu Feb 21 2019

Pesky upper trough remains over northern MN this morning and
continues to drive some IFR/Lo end MVFR cigs across the northern
TAF site. Looks like KMSP will remain on the edge of this for much
of the morning. VFR to the south with erosion of lower stratus as
the upper trough exits to the northeast. May hold firm to the far
north per trend of HREF/SREF probabilities. Expect lowering cigs
to the southwest again later tonight with perhaps a shot of -sn as
far east as the metro after 10z. KRWF will see some IFR with
-sn mainly after 09z.

KMSP...On the edge of lower end of MVFR cigs at least through most
of the morning. Then mix of clouds again with cigs lowering
later tonight. We will keep VFR for now. Wind W-SW less than 10kts
becoming light SE into Friday.

Fri night...MVFR cigs. -SN/IFR likely late. Wind SE 5-10 kts.
Sat...Afternoon SN/IFR likely. Wind NE 5 kts becoming NW
Sun...Morning SN/IFR possible. Wind NW 15G25kts.





NWS MPX Office Area Forecast Discussion

Script by Ken True @Saratoga-Weather.org