Area Forecast Discussion
Issued by NWS Twin Cities, MN

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990
FXUS63 KMPX 231243
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
643 AM CST Fri Feb 23 2018

.Updated for 12Z Aviation Discussion...
Issued at 631 AM CST Fri Feb 23 2018

&&

.SHORT TERM...(Today and tonight)
Issued at 422 AM CST Fri Feb 23 2018

Snow will end across the region today, but low clouds will linger
for most of the day. Winds will become west northwest, but switch to
the northeast ahead of the next storm system that will bring a
narrow swath of heavy snow across Minnesota/Wisconsin.

Early morning satellite imagery together with radar and surface obs
showed snow exiting to the northeast this morning. Surface obs
reports some unknown precip, and forecast soundings show a loss of
ice, but so far no freezing drizzle has been observed at the office
so it must be either very spotty or very light. Regardless,
continued to mention freezing drizzle in the forecast but at this
point it does not appear to be accumulating and should have little if
any impact.

Later today high pressure will build in across the region, but
forecast soundings show low level moisture atop the boundary layer
so may have trouble breaking out of the stratus this morning. If
skies do clear Friday night, temperatures could drop off
significantly with the fresh snow pack and light winds.

.LONG TERM...(Saturday through Thursday)
Issued at 422 AM CST Fri Feb 23 2018

The forecast snow event for Saturday-Sunday remains on track and is
obviously the main concern in the long term period.

The main upper trough is currently positively tilted across the
intermountain west.  Over the next 24 to 36 hours, the northern end
will remain relatively anchored, while the strengthening subtropical
jet to the south aids the main wave in advancing eastward, allowing
the system to gain a negative tilt by midday tomorrow.  Meanwhile,
surface cyclogenesis will occur tomorrow morning and by 18Z tomorrow
the surface low will be in south central Kansas.  The 500H trough
and PV advection is impressive but will move northeast rather
quickly.  By midday tomorrow, the jet pattern is quite favorable for
a deepening cyclone given the offset jet streaks working together in
their left exit and right entrance regions in addition to the
impressive 500H wave pivoting and gaining that negative tilt.  So,
it makes sense to see the models deepen the low by 12mb in a 12 hour
period from 18Z tomorrow through 06Z Sunday as it moves from south
central Kansas to southwestern Wisconsin.

So, the forcing looks good with this system and there will be
plenty of moisture to work with.  The issues to be concerned about
when considering the highest snow amount potential is the fact that
the system is moving rather quickly and the forecast convection
along the cold front south of the surface low.  With the speed of
the system slightly faster, QPF and hence snow amounts were trimmed
slightly from the previous shift, but the placement of the heaviest
snow still looks to be from south central MN through the metro
toward eastern Lake Superior.  Much of this area can expect 6-8" of
snow from this system, with some areas of enhancement picking up 8-
10".  Did increase the wind speed forecast over the blended guidance
with the deepening low moving through eastern Iowa and into
Wisconsin.  The winds don`t look overly strong, with peak speeds
forecast to reach the 25-30 MPH range on the back side of the snow.

Beyond this system, the following several days will be quiet.  No
precipitation and near to slightly above normal temperatures are
expected.  There is more potential acitivity to monitor for the end
of next week though, as the guidance continues to show a mid
latitude cyclone moving through the center of the country.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 631 AM CST Fri Feb 23 2018

Clouds will be a challenge today. Snow will end this morning, but
MFVR/IFR stratus will linger this morning. Forecast soundings
show clouds lingering into the afternoon, so pushed back the
timing of VFR clouds. Winds will be northwest, but should turn
northeasterly later tonight ahead of the next storm system.

KMSP...
MVFR/IFR clouds should continue this morning and last into the
afternoon. At this point to not anticipate cloud bases rising
above 1700ft for an extended period of time. Winds will be
northwest, but should become northeast early Saturday morning. At
this point expect snow to begin around 18Z Saturday, so it was not
included in the TAF. Should see IFR/LIFR with the snow Saturday
afternoon and evening, with rates of 1 to 2 inches per hour
likely. If the forecast remains on track, expect an Airport
Weather Warning will be needed.

/OUTLOOK FOR KMSP/
Sun...MVFR. Wind W at 20G25kt.
Mon...VFR. Wind SW at 15G20kt.
Tue...MVFR with -sn possible. Wind NE at 05kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Saturday afternoon through late Saturday
     night for WIZ014>016-023>028.

     Winter Weather Advisory until 9 AM CST this morning for
     WIZ014>016-023>028.

MN...Winter Storm Watch from Saturday afternoon through late Saturday
     night for MNZ043>045-049>053-057>063-066>070-076>078-084-
     085-093.

     Winter Weather Advisory until 9 AM CST this morning for
     MNZ043>045-050-052-053-061-063.

     Winter Storm Watch from Saturday afternoon through late Saturday
     night for MNZ056-064-065-073>075-082-083-091-092.

&&

$$

SHORT TERM...JRB
LONG TERM...SPD
AVIATION...JRB



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