Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 212037

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
237 PM CST Tue Feb 21 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 236 PM CST Tue Feb 21 2017

Today was another day of record warmth across the Midwest as morning
fog quickly mixed out leaving clear skies. The mid-February sun
together with double digit H850 temps yielded highs in the 60s at
most locations, and upper 50s elsewhere.

Dry weather will continue overnight, but another round of fog
development is possible, but should not be quite as dense as this
mornings since there will be some high clouds. A week upper level
wave will move across the region and develop some rain/snow showers
across northern MN/WI on Wednesday, but areas south of I-94 will
most likely only see virga. Temperatures on Wednesday will be warm
again, but the clouds will keep them a few degrees cooler than today

.LONG TERM...(Wednesday night through Tuesday)
Issued at 236 PM CST Tue Feb 21 2017

The main focus in the forecast is the winter storm that will bring a
harsh reality of snow, wind, and colder air to the region beginning
Thursday night and lasting through Friday. Would not be surprised if
a few locations see over a foot of snow. Right now have a swath of 8
to 10 inches, but reality will probably be more narrow with higher

It was 60 degrees at MSP this afternoon, and in 60 hours it will be
snowing.  That in itself makes this system pretty awesome for lack
of better words. This storm is currently located off the west coast.
Over the next 48 hours the upper level trough will move across the
Rockies and over the Great Plains. Although this sytem is rather low
amplitude, it takes on a negative tilt and will have a very
favorable low level temperature gradient to work with to achieve
maximum potential in terms of sensible weather.

This temperature gradient will be the focus for an area of heavy
precipitation that will develop Thursday evening. The precip will
probably start out as rain, but should quickly transition over to
snow as the intensity increases. Forecast soundings show an
incredible amount of omega along this Fgen band, so expect snowfall
rates of 1 to 2 inches per hour to lift northward overnight into
Friday morning. This should produce a quick 3 to 6 inches of snow.

Then things get a bit challenging. The next round of precip will be
tied to the upper level forcing of the parent shortwave, and this is
always more difficult to predict with confidence. The cyclone will
quickly mature, and should see a well-defined TROWAL by Friday
morning as continually depicted by the GFS. This will produce more
localized heavy snow, so could see another 4 to 6 inches in some
locations. There will likely be a break between these two features
of the GFS pans out, to some extent the ECMWF, and to a lesser
extent the NAM. That is why forecast snow totals are likely to
change, but the high-end potential remains.

A quick look at the CIPS analogs show 12+ inch snowfall amounts with
most other storms that match our current one. There is a lot of
moisture, with strong forcing, and potential for prolonged period of
snow. In addition, forecast soundings show winds of 25 to 30 mph,
with gusts near 40 mph. For that reason, have issued a Winter Storm
watch for much of southern/central MN and western WI. Looking ahead,
temperatures will cool off in the wake of this system with another
round of snow possible early next week.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1205 PM CST Tue Feb 21 2017

Dense fog this morning has cleared at area terminals leading to
VFR conditions this afternoon. Some gusts of 25-30 kts are
expected through early afternoon at RWF, but otherwise winds will
start the period S/SWly around 10 kts to start the period and
diminish through the afternoon. Some fog is expected to develop
overnight at MSP, STC, EAU, & RNH due to the anomalously moist
ground from recent rainfall and light winds. Uncertain on how low
visibilities will go, so monitor future issuances. Fog will clear
by 14-15Z leading to light winds and BKN/OVC mid-level ceilings.


Main concern at MSP will be the possibility of fog developing at
MSP overnight. Due to the anomalous soil moisture from recent
rains and calm winds, conditions look favorable for fog from
10-14Z Wednesday. Confidence is currently low on how far
visibility will drop, will go with 3 SM for now and can reassess
at the next TAF issuance.

Wed...VFR. Wind SW at 10G15 kts becoming NW late.
Thu...VFR. CHC MVFR/-RA/-SN in the afternoon, then LIFR/+SN
likely Thu night. Wind NE 5-10 kts.


WI...Winter Storm Watch from Thursday evening through Friday evening
     for WIZ014>016-023>028.

MN...Winter Storm Watch from Thursday evening through Friday
     afternoon for MNZ053-059>063-065>070-073>078-082>085-091-



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