Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201157

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
557 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, February 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 February record high minimum at MSP, we need to stay
at or above 44 degrees through midnight to tie or break this
monthly record set in 1930. Current hourly temps are for 44
degrees at midnight. It will close. So far overnight, the low
temperature has been 48 degrees. The high minimum for today is
an easy one to set with it being 35 degrees in 1899.

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 12Z TAFS through 12Z Tuesday morning)
Issued at 557 AM CST Mon Feb 20 2017

SHRA/TSRA over IA will spread northward into southern MN between
12z-15z and then expand north and east through the late morning
and persist through the afternoon. Another area of SHRA/TSRA will
develop/expand along the SD/MN border with this activity mainly
affecting KRWF and KAXN as it moves NNE. Ceilings will deteriorate
quickly this morning at the MN TAF sites to MVFR then IFR as
incredibly moist low level air (dew points in the 50s) push in
from the south ahead of a cool front over the Dakotas. Improvement
to both ceilings and visibilities will begin in western MN this
afternoon with the passage of the aforementioned cool front. The
front will not reach the Twin Cities until this evening and then
pass across western WI early tonight. A concern during the
upcoming night is the potential for fog formation after all the
rain today as high pressure moves in, skies clear and winds become
light. This will need to be addressed later with many forecast
groups already in place for the SHRA/TSRA.

SCT SHRA and isolated TSRA arriving around 16z then becoming more
numerous for the afternoon before diminishing early this evening.
A period of IFR ceilings possible this afternoon. Kept it just
above at 012 but we may end up in the 005-008 range from 18z-23z
due to the anonymously high low level moisture ahead of the
incoming cool front. The front will pass through in the 00z-03z
time frame with winds becoming westerly.

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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