Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 241118

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
618 AM CDT FRI JUN 24 2016

Issued at 619 AM CDT Fri Jun 24 2016

Updated to include 12Z aviation discussion below.


.SHORT TERM...(Today and tonight)
Issued at 344 AM CDT Fri Jun 24 2016

Things will start to become more interesting during the second
portion (tonight) of the short term period as warm advection sets up
ahead of an approaching surface low and upper level short wave
trough. Until then, things will be fairly tranquil. Latest visfog
imagery shows clear skies across the, with some cloudiness and
convection well to the west over the western Dakotas where
conditions similar to what we`ll see later tonight are currently in
place. The upper ridge evident on water vapor imagery to our west
will build across the area today, with some increase in mid/high
clouds as the day progresses.

For tonight, we`ll see a sharp increase in moisture as we get into
return flow ahead of the approaching surface low/trough. 850 mb
theta-e values look to dramatically increase from west to east
between 21Z and 06Z as the moisture axis works into the area. 850-
500 mb differential theta-e values go negative across our Minnesota
area by 03Z and across the remainder of the area by 09Z. With
convective instability obviously in place tonight, the question is
where the forcing will be for SHRA/TSRA. A look at 850-700 mb RH and
frontogenesis suggests the best chance for activity will be from
north central and northeast Minnesota into western Wisconsin. The
NSSL and NCAR WRF ensembles generally agree with that large scale
assessment, and most members focus activity mostly to our north and
east, although a few NSSL WRF members do show a secondary area of
convection in west central and southwest Minnesota. The NAMNEST,
local WRF, 2.5 km GEM, and HiResWindow runs also generally agree
with the bulk of the activity focusing north/east. Went with the
highest PoPs in the north/east portion of the area, with the highest
values after 06Z, but given the degree of elevated instability, and
a few CAMs suggesting activity, did include lower PoPs across the
remainder of the forecast area.

.LONG TERM...(Saturday through Thursday)
Issued at 344 AM CDT Fri Jun 24 2016

Model solutions still point to a severe weather event occurring
across Minnesota and western Wisconsin on Saturday. The day looks
to start out with scattered activity in or near the forecast area.
The stronger activity is expected during the afternoon and evening
however. By 18z, the cold front looks to be over western
Minnesota, with dewpoints in the upper 60s to lower 70s in the
warm sector ahead of the front. By 21z, several models forecast
sfc based CAPE values of 4000 J/KG nosing into central and east
central MN. Shear will be increasing at that time as well, in
response to a mid/upper level trough moving across the Northern
Plains. The upper trough will supply a nice pocket of
differential divergence smack dab over the forecast area during
the afternoon as well. Convective mode initially looks to be
supercells, with an evolution to linear mode as the storms congeal
over Wisconsin. Threats early in the event still look to be large
hail, damaging winds, and a few tornadoes. The top CIPS analog for
this event is currently July 14th, 2010, which has been showing
up for several days. While not quite the outbreak that the June
17th, 2010 event was, several tornadoes touched down from
Northfield, MN into west central Wisconsin. There were also
nocturnal/morning waves of convection prior to the main event that
afternoon. June 17th, while not as close of an analog at this
point, is still showing up in the sector to the west, so we`re not
out of the woods yet. With precipitable water values in the 2-2.5
inch range, will also need to keep an eye on the potential for
flash flooding-particularly along and east of Interstate 35.

By 09z Sunday expect the convective line to have cleared west
central Wisconsin, with the main story then transitioning to brisk
west-northwest winds on Sunday in the wake of the front. Speeds of
25 to 35 mph should be common, which should yield sufficient
mixing with the favorable directional component of westerly
allowing temperatures to warm up above normal. Cool surface high
pressure then builds in for the first half of the upcoming week,
which will bring below normal temps. Weak disturbances in the
northwest flow aloft could generate some widely scattered showers
and thunderstorms as the surface high begins to drift southeast on
Wednesday into Thursday. Twenty percent chances have been


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 619 AM CDT Fri Jun 24 2016

Most if not all of the period looks to be VFR across the area. The
only potential issue would be the possibility of SHRA/TSRA late
tonight as warm advection and elevated instability work into the
area. Most indications are that activity should mainly be north
and/or east of the forecast area, but there is sufficient
uncertainty to include some mention for KRNH and KMSP late
tonight. If that occurs then there could certainly be a period of
MVFR and possible IFR conditions.

KMSP...Only area of concern and lower confidence is with the
possibility of lower ceilings and visibilities late tonight as
discussed above, otherwise conditions are benign.

Saturday afternoon...MVFR/IFR conditions possible with showers and
thunderstorms. South wind 15 to 25 kt becoming southwest.
Saturday night...MVFR/IFR conditions possible early with a chance
of showers and thunderstorms. Southwest wind 10 to 20 kt becoming
west 5 to 15 kt.
Sunday and Sunday night...VFR. West wind 10 to 20 kt becoming
Monday and Monday night...VFR. Northwest wind 10 to 15 kt becoming
east 5 kt or less.


.MPX Watches/Warnings/Advisories...


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