Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 240216 AAB
AFDMPX

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
816 PM CST Thu Feb 23 2017

.UPDATE...
Issued at 815 PM CST Thu Feb 23 2017

Will downgrade northern portions of the headlines shortly. Now
that the event is underway and hi-res models are getting a
relatively good handle on the dry air and where the snow shield
will advance, feel confident on tightening the PoP, QPF, and snow
amount gradients. Global model resolution is too coarse to resolve
the ridiculously tight gradient expected which results in bleeding
the snow too far northward. This means locations like Redwood
Falls and the Twin Cities proper may not see a flake. The 00Z NAM
has shifted south slightly again which confirms this idea.

As for the area that will see snow, we are still not seeing
widespread steady snow, and it appears the models are too eager to
break things out this evening, particularly the NAM. However, it
is still expected to become intense tonight near the Iowa border.
Visibilities are 1/4 mile in several locations of northwest Iowa
and thunderstorms are breaking out just south of there so a
maturing snow shield is under development. Expecting this snow
shield to shift mostly east northeastward tonight, then pivot more
northeast Friday. Amounts on the northern periphery of the
Blizzard Warning may be a little high if the HRRR was to verify,
but can`t get too cute.

This southward shift in the past couple days has been a little
surprising to say the least considering the monster totals
advertised on all the models and their ensembles at one point.
Suspect this is due to the very large upper low over Florida which
deamplified the eastern ridge and resulted in a flatter pattern,
sending the low eastward and taking a more southerly track. The
mid level features aren`t as strong and compact either and
are instead more sheared which will prevent the monster totals
(15-18"+) from falling where the heavy band does set up.

The WSW and the rest of the product suite will be issued shortly.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 342 PM CST Thu Feb 23 2017

Surface analysis this afternoon shows development of a classic
mid-latitude cyclone over the TX/KS panhandles with an extended
surface front from the center of this system ENE into lower MI and
a trailing cold front over NM/AZ. Aloft, a large longwave trough
which moved onshore the lower CA coast has shifts atop the
central-southern Rockies. The upper trough is expected to deepen
over the central-northern Plains during the day tomorrow through
tomorrow night, helping add plenty of energy to the developing
surface low. The surface low will shift across KS tonight and over
northern MO tomorrow morning, on its way to lower Lake Michigan by
tomorrow evening then Lake Huron by Saturday morning. Deep Pacific
moisture will accompany this system, so much so that QPF amounts
for southern MN look to range 1.00-1.50" by the conclusion of this
system. Though there continues to be good model agreement (outside
of the NAM which has and remains a significant outlier) that SE MN
will be in the crosshairs for the highest snowfall totals, the
consensus track took another slight shift to the SE, thus lowering
the snow amounts and hence the impacts mainly N and W of the Twin
Cities metro. As such, some minor reconfiguring of the headline
products were made but the point must still be made that there
will be a very tight NW-SE gradient of snow amounts just to the
south of the Twin Cities metro. As an example, counties like Le
Sueur or Nicollet or Dakota or Brown could see as much as a 6"
difference in snow totals from NW to SE across each respective
county.

Snow has commenced in far SW MN this afternoon and snow will
gradually spread mainly E and slightly N as the overnight
progresses. There may even be a slight mixture with rain at the
immediate onset but any mixture of precipitation will have a short
duration before become all snow. As the surface low shifts ENE
and the upper level trough pivots to help enhance the surface
feature, snow coverage and intensity will increase during the
early morning hours, likely with rates increasing to 1-2"/hr for
several hours in far southern MN and into SW WI. The morning
commute for southern/eastern MN into western WI will likely have
ongoing snow then the snowfall will steadily diminish as the day
progresses. However, strong winds for much of the region will
contribute to the blowing snow issues, making for hazardous
travel conditions for much of southern MN. Another concern is
isolated thunderstorms could develop over far southern MN into
southwestern WI. Instability levels are not entirely zero given
the antecedent moisture levels plus the incoming surge and that
additional lift will be created by the pivoting upper level
trough. Confidence not high enough to include mention at this
point but some thunder cannot be ruled out.

Precipitation will end from west to east late tomorrow afternoon
through tomorrow night and the wind speeds will decrease as well,
resulting in partly to mostly cloudy skies for the start of the
weekend. As for temperatures, once temperatures drop below
freezing later this evening, they will remain below freezing
throughout the duration of this event. Lows tonight to highs
tomorrow will have a very small diurnal range, potentially 5
degrees or less from tonight through tomorrow. As colder air wraps
around this system as it departs, lows will drop into the teens
tomorrow night, temperatures this area has not seen in some time
but will be actually right on par with climatological norms.

.LONG TERM...(Saturday through Thursday)
Issued at 342 PM CST Thu Feb 23 2017

Temperatures will warm through early next week. A fairly large
storm will develop over the Upper Midwest, but thermal profiles
should be warm enough to have mostly rain, especially if the
system translates westward with time.

A weak clipper system will sweep through the region on Sunday and
could bring some snow across MN/WI. On Monday the southern stream
will develop a storm to the southeast over the Ohio river valley.

This will be followed by a third system Tuesday into Wednesday.
This mid-week storm will have a favorable temperature gradient
to work with and should develop strong cyclone. However, there is
a lot of warm air with this storm, so the primary p-type will be
rain, with perhaps some snow mixed in. There is still uncertainty
with this storm, but as of now it appears that the chance is quite
low for this system to develop into a winter storm for the Upper
Midwest.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 553 PM CST Thu Feb 23 2017

There have been rather significant changes to the 00Z set of
TAFs. Per a plethora of latest guidance, the northern edge of the
snow will be very sharp and may miss KRWF, KMSP, and KRNH
entirely. Unfortunately each of these locations is on the edge and
it can shift either way so wasn`t confident in completely
removing the snow but it is possible that will need to be done in
the next several hours. Outside of the snow, VFR conditions will
prevail through the period.

KMSP...As discussed above, KMSP will be on the northern fringe of
the snow later tonight and Friday. Depending where it does set up,
further adjustments to the TAF may be necessary.

/OUTLOOK FOR KMSP/
Sat...VFR. Wind NW 10-15 kts becoming W.
Sun...VFR. Chc MVFR/-SN. Wind SW-W 5-10 kts.
Mon...VFR becoming MVFR. Chance afternoon -RASN. Wind S 5-10 kts.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST Friday for WIZ015-023.

     Winter Storm Warning until 6 AM CST Saturday for WIZ016-024>028.

MN...Winter Weather Advisory until 6 PM CST Friday for MNZ063-069-070.

     Winter Weather Advisory until noon CST Friday for MNZ067-073.

     Blizzard Warning until 6 AM CST Saturday for MNZ074>078-082>085-
     091>093.

&&

$$

UPDATE...BORGHOFF
SHORT TERM...JPC
LONG TERM...JRB
AVIATION...BORGHOFF



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