Special Weather Statement, NWS Twin Cities, MN

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
617 AM CDT Thu Jul 12 2018

.SHORT TERM...(Today and tonight)
Issued at 415 AM CDT Thu Jul 12 2018

Main issue in the short term is pinning down expected thunderstorm
development in the vicinity of the approaching cold front, which is
expected to weaken and essentially stall out across our area later
today.  One of the main struggles with this forecast is the overall
poor performance of the hi-res cams in handling the overnight/early
morning convection ongoing across northern and into portions of
central MN. In addition, hot and humid conditions will continue
south of the main frontal boundary, hence the heat advisory
remains in place.

As of early this morning, thunderstorm complex just north of Mille
Lacs has begun it's turn to the southeast, following the forward
propagating corfidi-vectors well.  A line of thunderstorms extending
southwest from Mille Lacs through St. Cloud and toward Willmar has
been slowly gaining strength.  This line of storms is expected to
continue due eastward through the early morning hours, whereas the
cluster north of Mille Lacs will eventually move into western WI and
may reach as far east as Ladysmith.  The main threat with these
storms is very heavy rainfall.  PWAT values near 2.0" are in place
and a strong low level jet with both 850H and 925H southwesterly
winds are very strong in the 40-50 knot range.  Strong moisture
transport is focused here as is lift provided by isentropic upglide
and low level convergence along the nose of the low level jet. This
low level jet will weaken over the next few hours and the
thunderstorms and heavy rainfall threat will follow suit.

The aforementioned frontal boundary will stall out across the
area today, and eventually lead to additional thunderstorm
development likely late this afternoon and tonight across much of
southern MN and west central WI with the front draped from north
of Sioux Falls, SD through the north Twin Cities metro area.
Surface dew points in the mid 70s will pool along the boundary
which will again be the focus for convective initiation. The low
level jet support will be much weaker tonight than it was last
night. The heaviest QPF will likely be to our southwest, where the
best low level support will be across portions of South Dakota
and eastern Nebraska.

We maintain a slight risk of severe weather mainly along and south
of the stalled frontal boundary this afternoon.  With strong heating
occurring today and the very moisture-rich boundary layer, the
atmosphere will become very unstable this afternoon with ML CAPE
values in excess of 3,000 j/Kg.  In addition, a subtle shortwave
aloft will lead to height falls this evening across the area.
Effective deep layer shear will be modest but the magnitude of the
CAPE alone poses a risk for some strong to severe thunderstorms to
develop this afternoon. Showers and storms will continue for much of
the night along and south of the stalled out frontal boundary.

.LONG TERM...(Friday through Wednesday)
Issued at 415 AM CDT Thu Jul 12 2018

Long term forecast will feature a welcomed airmass change for many
next week as our tropical airmass in place now will stay with us
through the weekend, but get pushed out of here next week as the
heart of the sub-tropical ridge shifts to over the Rockies,
opening us up to more northwest flow aloft. Until that happens,
we'll have daily thunderstorm chances through Sunday.

The period will get going Friday morning with what could be
fairly extensive remnants of thunderstorms across southern MN into
central WI. Extensive cloud cover Friday will at least end the
need for anymore heat headlines beyond today. The cold front
moving in today will become pretty hard to define Friday and will
really be more of just a series of outflow boundaries. At the very
least, this boundary will get into southern MN by the afternoon
and with dewpoints along it remaining pooled up into the low 70s.
We'll again see ample instability build by the afternoon with a
weakly capped environment to get thunderstorms going, this
boundary looks to remain relatively stationary and we continue to
see some high QPF swaths from the models across northern IA into
southern MN Friday night, though a poorly defined LLJ should lead
to an even lower heavy rain threat from what we are expecting
tonight.

Saturday, said front will have washed out as energy shifts to
another low working across the Canadian Prairies. We'll be left in
a situation with a very moist boundary layer, but little in the
way of forcing as heights build again across the area, just means
we will probably see scattered diurnally driven activity that
quickly dies off Saturday evening with no LLJ to support it
through the night. Pops pick up again area wide as the front to
our northwest comes through on Sunday. This activity looks to be
weak and disorganized with weak convergence along the front
(thanks to virtually no wind in the warm sector) and very little
LLJ support either.

Behind this front, dewpoints will fall back in to the 50s to start
next week, with highs retreating back to around the 80 degree
mark. The ECMWF overnight came into line with rest of the guidance
in keeping Tuesday dry as well, with it looking like our next shot
at precip coming Wednesday or Thursday next week as we see a
shortwave drop in on the northwest flow.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 610 AM CDT Thu Jul 12 2018

Frontal boundary moving in from the northwest today will stall out
and bring showers and thunderstorms to much of southern MN and
western WI late this afternoon and tonight. Confidence is below
average in this forecast given model uncertainty and poor
performance overnight. Otherwise, VFR conds expected during the
day with the main issue obviously being any thunderstorms late
this afternoon. The rain will likely continue into the overnight
period but the thunder will be less widespread.

KMSP...Early morning activity should steer clear of MSP mainly to
the north. No additional concerns.

/OUTLOOK FOR KMSP/
Friday...MVFR possible with a chance of showers & thunderstorms.
Variable winds around 5 kts.
Saturday...MVFR possible with a chance of showers & thunderstorms.
Winds E around 5 kts.
Sunday...MVFR possible with a chance of showers & thunderstorms.
Winds NW 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory from noon today to 8 PM CDT this evening for
     WIZ023>028.

MN...Heat Advisory until 8 PM CDT this evening for MNZ060>063-068>070.

     Heat Advisory from noon today to 8 PM CDT this evening for
     MNZ076>078-083>085-091>093.

&&

SHORT TERM...SPD
LONG TERM...MPG
AVIATION...SPD

Hazardous Weather Outlook
National Weather Service Twin Cities/Chanhassen MN
538 AM CDT Thu Jul 12 2018

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
131045-
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-
538 AM CDT Thu Jul 12 2018

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

.DAY ONE...Today and Tonight

Thunderstorms will slowly diminish this morning from east central
MN into northwest WI. The main threat this morning will be from
heavy rainfall from Mille Lacs Lake down toward Siren, WI.

Thunderstorms are expected to develop again this afternoon from
west central MN, through the Twin Cities into west central
WI. There is a slight risk of severe weather with this activity,
with damaging winds being the main threat. Thunderstorm is
expected to slowly drift south tonight toward southern MN. All
activity today and tonight will be capable of producing torrential
rainfall and localized flooding.

Once again, afternoon heat indices are expected to top out around
100 degrees along and south of a line from New Ulm, to the Twin
Cities and Chippewa Falls, WI.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Chances for Thunderstorms will continue through Sunday night. The
threat for severe weather is low, but a continued risk for
excessive rainfall will exist for south central MN through Friday
night.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation may be needed this afternoon.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
831 AM CDT THU JUL 12 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0654 AM     HEAVY RAIN       BRAHAM 1ENE             45.72N 93.16W
07/12/2018  M3.07 INCH       ISANTI             MN   COCORAHS

            COCORAHS STATION MN-IS-8, BRAHAM 1ENE. THE
            DURATION OF THE HEAVY RAIN EVENT WAS 24
            HOURS.

&&

MKM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
944 AM CDT THU JUL 12 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0900 AM     HEAVY RAIN       GRASSTON                45.79N 93.15W
07/12/2018  M6.48 INCH       KANABEC            MN   MESONET

            MESONET STATION GSTM5, GRASSTON. THE
            DURATION OF THE HEAVY RAIN EVENT WAS 24
            HOURS.

&&

MKM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
945 AM CDT THU JUL 12 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0900 AM     HEAVY RAIN       MORA                    45.86N 93.30W
07/12/2018  M6.80 INCH       KANABEC            MN   MESONET

            MESONET STATION MOAM5, MORA. THE DURATION OF
            THE HEAVY RAIN EVENT WAS 24 HOURS.

&&

MKM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1024 AM CDT THU JUL 12 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1015 AM     FLOOD            4 NNW VINELAND          46.23N 93.79W
07/12/2018                   MILLE LACS         MN   PUBLIC

            3.4" OF RAIN. COUPLE SMALL ROADS WASHED OUT.

&&

JPC

Special Weather Statement
National Weather Service Twin Cities/Chanhassen MN
1043 AM CDT THU JUL 12 2018

MNZ044-051>053-121615-
Isanti-Sherburne-Mille Lacs-Chisago-
1043 AM CDT THU JUL 12 2018

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT NORTHWESTERN
CHISAGO...SOUTH CENTRAL MILLE LACS...ISANTI AND NORTHEASTERN
SHERBURNE COUNTIES...

At 1043 AM CDT, strong thunderstorms were clustered near Spencer
Brook, or 12 miles west of Cambridge, moving east at 30 mph.

Winds in excess of 30 mph and pea size hail are possible with this
storm.

Locations impacted include...
Cambridge, North Branch, Isanti, Zimmerman, Princeton, Spring Lake,
Orrock, Spencer Brook, Stanchfield, Dalbo, Sherburne National
Wildlife Refuge and Cambridge Airport.

This includes U.S. Highway 169 between mile markers 170 and 183.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4548 9302 4543 9382 4556 9381 4556 9376
      4561 9375 4573 9335 4573 9301
TIME...MOT...LOC 1543Z 263DEG 27KT 4558 9349

AMK

Special Weather Statement
National Weather Service Twin Cities/Chanhassen MN
1116 AM CDT THU JUL 12 2018

MNZ052-053-WIZ014-121645-
Isanti-Chisago-Polk-
1116 AM CDT THU JUL 12 2018

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT CHISAGO...SOUTHEASTERN
ISANTI AND NORTHWESTERN POLK COUNTIES...

At 1115 AM CDT, strong thunderstorms were clustered over Harris, or
12 miles east of Cambridge, moving east at 40 mph.

Winds in excess of 30 mph and pea size hail are possible with this
storm.

Locations impacted include...
North Branch, Rush City, Centuria, Spring Lake, Harris, Rush City
Airport, Wolf Creek, Branch, Cushing, Wild River State Park and
Weber.

This includes Interstate 35 between mile markers 144 and 163.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4572 9287 4564 9288 4564 9257 4545 9255
      4544 9315 4573 9314 4573 9285
TIME...MOT...LOC 1615Z 265DEG 35KT 4559 9298

AMK