Tornadoes and Hail in Minnesota, July 9, 2017

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
613 PM CDT Sun Jul 9 2017

.updated for the 00z aviation discussion below...

.SHORT TERM...(This evening through Monday)
Issued at 233 PM CDT Sun Jul 9 2017

The short term concerns remain severe potential this evening.

Timing of convective initiation appears to be 22z in the northwest
cwa. Latest mesoscale analysis shows building CAPE of 1000-2000 J/kg
over far western MN and pooling along the surface boundary northwest
of Alexandria. This boundary is forecast to sag south overnight as a
weak surface low over northeast SODAK into northern Iowa by 12z Mon.
Initial convection should be discrete cells...which could generate
large hail/damaging winds or an isolated tornado. Greatest threat
would be over the northwest CWA early. The convection should become
linear/QLCS form with strong deep layer shear 50-60kts available. It
should arrive in the metro area/east central MN 00z-03z period and
move quickly southeast. Damaging winds and torrential rain would
accompany the complex. The best corridor for this to occur appears
to be over about a 50 mile wide area east of a line from Litchfield
to Mankato...and west of a line from Buffalo to Lakeville...then
southeast...which lines up with a tight instability gradient this
evening.  Most of the convection should exit the area through about
05z-06z. We will retain some small pops mainly to the east and south
after that.

We expect drier conditions to move in behind the system into Monday
relieving the convective threat for the area. Temperatures will
remain on the warm side with readings warming through the 80s.

.LONG TERM...(Monday night through Sunday)
Issued at 233 PM CDT Sun Jul 9 2017

Monday night through Wednesday...The main focus on the extended
will be during the early portion of the week as severe weather
again looks to take shape.

This period will commence with high pressure centered over the
region while a quasi-stationary cold front sits nearly east-west
from the Central Plains over to the Ohio Valley and a nearly
north-south warm front resides over the western Dakotas from a low
pressure center in far southern Saskatchewan province. A ridge
aloft in the Dakotas will flatten, allowing for a more progressive
pattern to develop for Tuesday into Tuesday night, including
enhanced jetting. The low pressure center will drift southeast
into North Dakota and strengthen in advance of a shortwave trough
disturbance developing over far south-central Canada. At the same
time, the front to the south will drift north, which will not only
allow warmer temperatures to creep back north but also a good
surge of moisture which will add to the instability. The front
will move into southern MN by midday Tuesday and nearly reach the
I-94 corridor by Tuesday evening, bringing MUCAPES in excess of
3000 j/kg for much of the southern portion of the WFO MPX coverage
area. Sensibly, this will allow highs to reach the mid 80s for
much of the area, with highs near 90 in western MN. In addition,
would not be surprised to see dewpoints hit 70 degrees in southern
and western MN as the front shifts north. Once the morning cap
breaks, convection is expected to develop in the Dakotas which
will then traverse southeast through central-southern Minnesota
late day through the evening and potentially into the Tuesday
night hours. The initial mode looks to be tornadic but as clusters
of storms develop late day through the evening, a more organized
forward-propagating MCS may develop which may well track along
I-94 through the evening into the nighttime hours. This would
create a large hail and damaging wind hazard for a good portion of
the time, especially considering the duration of 35-45kt of bulk
shear from Tuesday afternoon through early Wednesday morning. The
low pressure itself will shift east through south-central MN
Tuesday night and move to nearly atop the Twin Cities metro by
daybreak Wednesday morning. Precipitation will steadily wind down
during the day on Wednesday behind this system with high pressure
moving into the region. For this upcoming system, it is urged to
stay abreast of the latest forecast discussions from both this
office and the Storm Prediction Center since confidence is growing
on a potentially high end severe weather event.

Thursday through Sunday...Much more benign weather is expected for
the remainder of the week into the weekend as high pressure
reasserts itself across the Upper Midwest and northwest flow aloft
takes hold. The pattern of ridge-west and trough-east will again
develop while deep moisture will be relatively absent, meaning
that chances for precipitation will be limited, humidity will be
relatively lower and temperatures will be fairly steady (although
on a slow climb upward through the 80s).

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 620 PM CDT Sun Jul 9 2017

Still expect convection to develop into west central MN 00-02z and
develop into a line through about 04z and drop southeast
overnight. Could see sig thunder threat mainly over the KMSP-KMKT
area into the early evening. Thunder will include wind gust
potential along with tempo IFR conditions. Activity should exit to
the southeast through 06z or so with perhaps some lower
clouds/mvfr cigs and some BR developing over the eastern areas.
This should give way after 14z Mon with n-ne winds and some sct
cumulus.

KMSP...timing of sig thunder threat 0130z-0330z. Continued wind
gust potential along with tempo IFR conditions. This should move
out thereafter with some lower mvfr cigs possible following the
front overnight. Confidence is high enough to include at this
time. Should see this move out after 14z with cumulus cigs lifting
during the day. se-e winds into the evening becoming ne-n with
fropa.

/OUTLOOK FOR KMSP/
Tue...Mainly VFR. Chc +TSRA/MVFR late. Wind SE 5-10 kts.
Wed...Mainly VFR. Chc TSRA/MVFR early. Wind NW 5-10 kts.
Thu...VFR. Wind NE 5-10 kts.

&&

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

SHORT TERM...DWE
LONG TERM...JPC
AVIATION...DWE

Hazardous Weather Outlook
National Weather Service Twin Cities/Chanhassen MN
1236 PM CDT Sun Jul 9 2017

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
101745-
Douglas-Todd-Morrison-Mille Lacs-Kanabec-Stevens-Pope-Stearns-
Benton-Sherburne-Isanti-Chisago-Lac Qui Parle-Swift-Chippewa-
Kandiyohi-Meeker-Wright-Hennepin-Anoka-Ramsey-Washington-
Yellow Medicine-Renville-McLeod-Sibley-Carver-Scott-Dakota-
Redwood-Brown-Nicollet-Le Sueur-Rice-Goodhue-Watonwan-Blue Earth-
Waseca-Steele-Martin-Faribault-Freeborn-Polk-Barron-Rusk-
St. Croix-Pierce-Dunn-Pepin-Eau Claire-
1236 PM CDT Sun Jul 9 2017

This Hazardous Weather Outlook is for portions of central and
southern Minnesota...and west central Wisconsin.

.DAY ONE...This Afternoon and Tonight

There is an enhanced risk of severe thunderstorms across east
central into southeast Minnesota and a small portion of west
central Wisconsin mainly through this evening. There is a slight
risk across most of the remainder of the area. Large hail,
damaging winds, and heavy rainfall and localized flash flooding
are possible with the storms. The greatest threat of large hail
and widespread damaging winds is located in the enhanced risk
area.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

There is a slight risk of severe thunderstorms late Tuesday
afternoon and Tuesday night. Large hail, damaging winds, and
tornadoes are possible late Tuesday afternoon across western
Minnesota, with a transition to mainly damaging winds Tuesday
night across eastern Minnesota and western Wisconsin. Heavy
rainfall is also possible.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation may be needed later this afternoon and
evening.