Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 200954

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
354 AM CST Mon Feb 20 2017

.SHORT TERM...(Today and tonight)
Issued at 354 AM CST Mon Feb 20 2017

Showers and scattered thunderstorms began developing around AXN
at 1 am this morning. They were at the nose of a 45 knot low level
jet along with elevated instability. The activity has now
progressed to north of Brainerd. At one point we had 50 dBZ over
20K with nearly 60 dBZ at 13K north of Morrison county. The next
round of showers and thunderstorms is currently moving northward
across eastern NE and southwest IA. The CAMS are in good
agreement that this activity reaches into southwest MN by 7 AM
and the southwest Twin Cities Metropolitan area by 10 AM, with
the activity continuing to expand north and east through the early
afternoon hours. The precipitation will then end from west to
east during the afternoon and evening. Categorical pops remain in
place. Forecast precipitation amounts rise from around a tenth of
an inch in western MN to six tenths in eastern MN with amounts
from six tenths to nine tenths across western WI.

It will be another potential record setting day with several
records up for grabs, including highs today, record high minimum
being established at MSP along with a new max PW here at MPX.
Highs today in the upper 50s to lower 60s are likely at many
locations. Records highs for today include 57/1981 at STC, 57/1981
at MSP and 59/1930 at EAU. Forecast highs are 58, 60 and 56
degrees respectively for these three stations with new records
being forecast for STC and MSP. Felt the rain will hold on too
long in western WI this afternoon to reach a record, but there is
still a chance.

As for the record high minimum at MSP, we need to stay at or above
44 degrees through midnight to tie or break the record. Current
hourly temps are for 44 degrees at midnight. It will close. So far
overnight, the low temperature has been 48 degrees.

Finally, forecast PW values for this afternoon and early evening
across eastern MN and western WI are shown to be in the 1 to 1.25
inch range. We have never had a PW value in February at or above
one inch. The highest value record was 0.87 inches.

.LONG TERM...(Tuesday through Sunday)
Issued at 354 AM CST Mon Feb 20 2017

The elongated trough that has been providing for an impressive
onslaught of storm systems across the west coast, will begin to move
across the Rockies this week. This will set the stage for a very
powerful storm system to move across the central Plains, and into
the Upper Midwest late in the week. Before this system begins to
affect the Upper Midwest, the anomalous mild temperatures will
continue which means near or record breaking highs for Tuesday and
Wednesday. One piece of energy/short wave, that was associated with
the beginning of the trough moving eastward, will race quickly
across the northern Rockies, and into the Northern Plains, Upper
Midwest by late Tuesday/Wednesday. Behind today`s system, moisture
content will remain quite high for late February leading into
Wednesday system. Although QPF amounts are not high with a few
hundredths of an inch at best for a 6-12 hour period, theta-e
advection and enhanced jet streak may allow for high percentage then
current chances indicate in the forecast. Behind this system, the
beginning of the colder air arrives leading to a strong thermal
gradient for the storm system late this week.

As with previous discussions, the exact track of this storm system
late in the week is critical on snowfall amounts. Over the past few
model runs of the GFS/GEM/EC, timing and placement of the upper
level trough, and surface features have narrowed the heaviest snow
band across south central, southeast Minnesota and into west central
Wisconsin. Although these deterministic runs have come closer on a
overall solution, some of the ensembles have more uncertainty over
the past few runs. For example, the 21 members of the GEFS had a
better probability of a heavy snowfall track across south central
and southeast Minnesota on the 12Z/19 run. However, the latest run
(00Z/20), has more uncertainty or a greater spread of this heavy
snow band across south central, southeast Minnesota. Basically this
adds to uncertainty of where the heavier snow will fall, not so much
that a powerful storm system will move across the Plains, and Upper
Midwest. This system is still 4-5 days out and several more model
runs will hone in on details as we get closer to mid week. I
wouldn`t be surprised to see a winter storm watch out by Tuesday
night if conditions warrant.

Another aspect is the latest CIPS analogs still shows the "mean-
heaviest" snow track from southwest Minnesota, northeast into
east central Minnesota, and northern Wisconsin. This is slightly
northwest of the deterministic runs tonight. The number one analog
is March 4, 2004 which placed the heaviest snow band just south
of the Twin Cities, northeast to west central Wisconsin where 6 to
12 inches fell. The number two analog is March 15, 2002 which has
the heaviest snowfall further to the northwest across west
central to central Minnesota, and into northern Wisconsin.

Beyond Saturday, the mean upper air flow will be quasi-zonal leading
to near or slightly above normal on temperatures. The main storm
track will be across the southern United States where an active jet
will develop.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1021 PM CST Sun Feb 19 2017

VFR conditions to start with upper level ceilings but conditions
will steadily deteriorate during the early morning hours with
ceilings heading to MVFR levels. Showers and a few thunderstorms
are expected at all sites after daybreak tomorrow through late
afternoon at all MN TAF sites and into the evening hours at the WI
TAF sites. Consistency in the model timing of IFR conditions for
central-eastern MN into western WI, generally from midday into the
evening hours from west to east, has allowed for the inclusion of
TEMPO groups showing IFR visibilities with MVFR ceilings during
the expected time of heavier rain. Low ceilings will then linger
beyond the duration of rain, likely to around 21/00z, with VFR
conditions thereafter. The other concern is the continued showing
of strong winds around 2 kft, in the 40-50 knot range, ongoing by
20/06z initialization time and lasting through 09z-12z. Have
maintained LLWS mention at all sites.

KMSP...VFR to start then MVFR conditions expected to develop
between 12z-15z tomorrow morning. Mainly due to ceilings but
visibility may also drop to MVFR should heavy enough showers
develop. IFR conditions also cannot be ruled out and is more
likely with visibility in heavier rain rather than ceiling so have
included a TEMPO group as such. LLWS looks likely to continue into
the morning push with surface SE winds close to 10 kt in
conjunction with SW winds around 45 knots. MVFR ceilings likely to
linger into late Monday afternoon then VFR conditions likely
Monday evening.

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




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