Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 131730

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1130 AM CST Fri Jan 13 2017

.updated for 18z aviation discussion below...

.SHORT TERM...(Today and tonight)
Issued at 404 AM CST Fri Jan 13 2017

We start the day with a strengthening 1045mb high centered over
central MN. With convergent flow at h5 providing subsidence,
the central pressure of the high will be pushing 1050mb as it slides
into western WI this morning. Although we have this high overhead,
we are seeing ample cirrus spread into southern MN from southern
stream energy, which has slowed cooling along the I-90 corridor
where lows have only bottomed out around -5F. Under the high with
clear skies has seen temepratures down around -25F up around Staples
and Wadena. To the west of the high, we are seeing pretty good WAA
in the h85-h7 layer, which is associated with a band of mainly virga
from north central SD down toward Sioux City, IA. Compared to 24
hours ago, models have really backed off on the light snow potential
with this WAA band for a couple of reasons. One, the airmass
overhead right now is incredibly dry. The PWAT on the 00z
MPX sounding is about as low as you are going to see at 0.03" and RH
time-height plots show this band isn`t around long enough to
saturate the low levels of the atmosphere. The other reason precip
occurrence is not favorable is the mid-level convergence noted
earlier. Q-vector analysis shows current Q-vector convergence over
Neb/SD weakening substantially over MN. In the end, followed the
idea of the NCAR WRF ensemble, with low precip chances working
across I-90 today.

Other than that, we`ll have surface ridging through the
length of the short term, with little spread seen in guidance for
temperatures, so stayed pretty close to blended guidance. This only
resulted in a small cooling of lows tonight, which is likely more
the result of skies looking to be less cloud covered than what we
had earlier.

.LONG TERM...(Saturday through Thursday)
Issued at 404 AM CST Fri Jan 13 2017

Attention in the long term is now centered on the Sunday night
through Tuesday time frame as the potential for a wintry mix
across the FA is increasing.

Deterministic model solutions remain steadfast on bringing an
upper level low, currently approaching northern Baja early this
morning, to north Texas by Sunday evening and then to the Upper
Mississippi Valley by Tuesday. There are certainly some location
differences with this system as it heads northward through the
plains, but the speed is very similar between the ECMWF, GFS and
GEM. The ECMWF is the farther west with the upper low and the
differences mentioned revolve around whether or not there will be
phasing of northern and southern stream energy with this system.
The ECMWF says yes while the GFS and GEM keep just a little bit of
separation between the waves, which pushes the upper low farther
east, resulting in a somewhat colder solution for us. Taking a
look at the GEFS spatial plots for tenth and quarter inch amounts
of precipitation over 12 and 24 hours still show the highest
probabilities to the south and southeast of the FA Monday into
Tuesday. Hence, the deterministic runs are on the northern edge of
the GEFS.

With this system coming in from the due south, there is concern
that the ice storm developing in the central and southern plains
this weekend may just march right up into southern MN and western
WI Sunday night and Monday morning. We certainly have a strong
elevated warm layer developing during this period with surface
temperature remaining well below freezing. Therefore, the
forecast will have the threat for freezing rain spreading into
southern MN early Sunday night and across the Twin Cities by late
in the night and for Monday morning. Thereafter the forecast
becomes more problematic as the GFS and GEM would bring colder air
in with snow becoming the dominate weather type while the ECMWF
would continue to warm with the potential for freezing rain to
persist through the afternoon then change over to rain by evening
for areas along and east of I-35. At this time, due to the spread
in the solutions and the limitations on the elevated warm layer
in FB, the forecast transitions to snow for Monday afternoon
through early Tuesday with plowable snow accumulation likely.
However, if the ECMWF is more correct then we could be looking at
rain Monday night and Tuesday for the eastern half of the FA.
Overall, confidence is high on the freezing rain potential Sunday
night and Monday morning but then confidence diminishes quickly

Another area where confidence is high deals with temperatures well
above normal overspreading the region from mid week onward. Highs
on Wednesday in the lower to middle 30s should reach into the
upper 30s to lower 40s for Friday. Highs next weekend could be even
warmer along with rain as yet another system like the one for
early in the coming week arrives, but further to the west. Hence,
the January thaw is almost here!


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1135 AM CST Fri Jan 13 2017

Isentropic lift continues to spread east and will continue threat
of brief mvfr/ifr cig/vsbys with -sn...mainly across southern
area. KRWF looks to be most affected for another hour or so.
Further east...trend has continued to bring lowering cigs to
around 4k feet across mn...with some threat of flurries. Will
mention vcsh as it moves into Wisconsin for the evening. We should
return to vfr with the passage of this snow area. Surface winds
becoming se-s and near 10kts to the west and below to the east. We
should see wind becoming more westerly into the day Saturday as
the high exits to the east.

KMSP...Main issue will be ceilings lower to around 4k feet this
afternoon and some threat of flurries roughly 20z-23z. vfr
thereafter. Surface winds becoming se 5-7kts and eventually light
south overnight...and then more westerly into Saturday afternoon.

Sat night...VFR. Wind S 5 kt.
Sun...VFR. Wind S 5-10 kt.
Mon...MVFR/IFR. Wintry mix likely. Wind NE 5-10 kt.




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