Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 181129
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
529 AM CST Sat Feb 18 2017

.Updated for 12Z aviation discussion...
Issued at 523 AM CST Sat Feb 18 2017

&&

.SHORT TERM...(Today and tonight)
Issued at 402 AM CST Sat Feb 18 2017

Dry, mild weather continues. Highs will be in the 50s for most
locations with light westerly winds going calm during the evening
and becoming southeasterly by Sunday morning.

Early morning water vapor together with GFS 500mb heights and winds
showed an incredibly active pattern across North America with 5
cyclones scattered across the continent. The Upper Midwest was one
of the few places not affected by one of these storms, as we were in
a regions of weak subsidence and confluent flow downstream of an
upper level ridge. Surface high pressure will build overhead and
lead to dry conditions. Forecast soundings show some high clouds
later today, so afternoon temperatures should be about 5 degrees
cooler than they were Friday.

.LONG TERM...(Sunday through Friday)
Issued at 402 AM CST Sat Feb 18 2017

One could write a novel about the upcoming long term with
regards for more record highs, record warm minimums, record PW, a
risk for severe weather on Monday, then ending with a colossal
snowstorm (blizzard) on Friday. I can`t recall in my 35 years of
forecasting the potential that the week ahead has.

The first order of business was to raise high temperatures from
Sunday through Tuesday using a blend of mix-down from 925 mb along
with EC guidance. This places MSP in record territory for both
Sunday and Monday. The high on Monday in the upper 50s is
conservative if some clearing would occur behind the morning
showers and thunderstorms. We could easily see highs jump into the
middle 60s if some sun occurred ahead of the incoming Pacific
front. We are also on track for a record warm minimum Monday
morning with 46 forecast.

Monday is quite the day weather-wise. Indications are for PW
values to be at or above 1 inch Monday morning across much of the
FA. The MPX sounding climatology shows that we have never had a 1
inch PW value in the month of February. We are really outside the
climate window. We already set an 850 mb temperature record on
Friday. There are several concerns on Monday. The first is an
early morning threat for elevated thunderstorms across eastern MN as
strong 850mb theta-e advection pushes in along with several
hundred Jules of CAPE in the 850-500mb layer. We are also in the
850-300mb thickness ridge along with a strong positive indication
from the differential temperature advection scheme. Therefore,
pushed chance pops a little farther east for 06z-12z period due to
this concern with categorical pops for the morning. The afternoon
is when things could get real interesting. There are indications
that some mid level drying may spread in ahead of the approaching
front. Multiple solutions are showing destabilization taking place
across west central, southwest and south central MN in the early
afternoon with around a 1000 J/KG of CAPE developing. Shear
values are on a severe storm scale with 0-6km at 45 kts with 0-1km
at 25 kts. 500mb winds are at or above 50 kts. Filtered CWASP
values light up in the aforementioned areas in the afternoon and
there are even low probabilities shown with the SigTor Eqn2. Given
how far outside the climate window we are with this current
weather regime, it certainly is possible for a few severe storms
in the afternoon if the destabilization develops. They would be
low top supercells with a freezing level around 8K!

The mild weather will continue for the mid week period with more
50s on Wednesday and then 40s on Thursday. Even though its cooler
on Thursday, highs would still be some 10 to 15 degrees above
normal.

The real fun sets in Thursday night and continues Friday and
Friday night as model solutions remain adamant on driving a
deepening a low pressure system from Colorado to southern
Wisconsin. Categorical pops remain in place. The 00z EC and GFS
both have heavy snow impacting much of our CWA. The core of heavy
snow on the GFS runs from southwest MN through the south metro and
on across west central WI, while the axis of heaviest snow on the
EC stretches from southwest MN through the north metro and on
into northern WI. We`re seeing values in this axis from 12-18
inches on both models. The strongest forcing is during the day on
Friday with snowfall rates at 2 inches per hour for about a six
hour period. So there`s where 12 inches of the snow comes from.
GEFS plumes show quite a bit of spread, and rightly so with the
system 6 days out. However, there are 7 members or so that are
at or above 6 inches for the Twin Cities with the top member at
24 inches. Another concern is for blizzard conditions to the west
and south of the Twin Cities. GFS Bufkit profile data is showing
36 knot winds developing Friday morning at 200 feet with winds
increasing to over 50 knots by 1500 feet. We`ll certainly have
more confidence by early next week once the short wave associated
with this storm system reaches the west coast.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 523 AM CST Sat Feb 18 2017

VFR conditions throughout. Westerly winds will become southerly
this evening as a few high clouds move in, and eventually take on
a southeasterly component.

KMSP...

VFR conditions throughout. Winds should become more westerly this
morning as we mix through a deeper layer, and then gradually shift
southeasterly later tonight.

/OUTLOOK FOR KMSP/

MON...MVFR with SHRA Likely. ISOLD TSRA. Wind S at 10 kts.
Tue...VFR. Wind SW at 5-10 kts.
Wed...VFR. Wind SW at 10G15 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...JRB
LONG TERM...RAH
AVIATION...JRB



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