Special Weather Statement, NWS Twin Cities, MN

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
729 PM CDT Thu Aug 10 2023

.UPDATE...
Issued at 650 PM CDT Thu Aug 10 2023

Updated to include 00z aviation discussion below.

&&

.DISCUSSION...(This evening through Thursday)
Issued at 230 PM CDT Thu Aug 10 2023

KEY MESSAGES:

- Thunderstorms likely tonight. Severe thunderstorms capable of
  damaging wind possible from western Minnesota into the Twin Cities
  metro/

- Isolated severe thunderstorms capable of damaging wind & large
  hail possible Friday afternoon across eastern Minnesota & western
  Wisconsin.

A decaying band of showers continues to move eastwards across
Minnesota into western Wisconsin this afternoon, generated by weak
ascent aloft by an increasing low-level jet. To the west of this band
of clouds/showers, clear skies & increasing dew points will allow for
an unstable atmosphere to develop by late afternoon across the
eastern Dakotas & western Minnesota with surface-based CAPE values
near 3000 J/kg. Severe thunderstorms are expected to develop by this
evening across the Dakotas where the surface forcing is strongest,
with these thunderstorms expected to quickly merge into a line of
thunderstorms. This line of storms is expected to enter western
Minnesota around 8-9 PM, reach the Twin Cities metro around midnight,
& then continue across Wisconsin through the overnight hours. The
potential for damaging wind gusts with these storms is most likely
across western Minnesota, but they are expected to weaken as they
move farther east into Minnesota & into an environment with
decreasing instability. Thus, the threat for damaging winds is lower
across eastern Minnesota & the Twin Cities metro tonight compared to
western & central MN, but certainly can not be ruled out if the line
of storms is able to maintain its intensity. Rainfall with the
storms will likely be heavy, especially across western MN, but the
amounts will be limited by the relatively fast storm motions. Areas
of western Minnesota where the storms are strongest could see
amounts around 1-1.5", while amounts taper down more to 0.1-0.25"
across western Wisconsin & eastern Minnesota when the storms will
likely have dissipated.

ANy lingering rain will be east of the area by shortly after sunrise,
with residual cloud cover expected to clear out through the morning.
This will allow the atmosphere to destabilize by the afternoon, with
1000-2000 J/kg of surface-based CAPE developing across MN & western
WI. Deep shear values will also be seasonally strong as a jetstreak
aloft & surface low pass over the region, providing plenty of
kinematic support for organized strong to severe thunderstorms. The
deep shear vectors are largely unidirectional through the atmosphere
but still oriented perpendicular to the surface forcing boundary,
meaning that storms will remain fairly discrete & a few could become
supercells, but they likely will not exhibit a lot of low- level
rotation. Hi- resolution models generally depict a few well-defined &
intense updraft helicity tracks when looking in the mid-levels (2-5
km), but little or nothing when looking in the low levels (0-2 km).
This supports the general idea that large hail (potentially golf
ball sized or larger) & a few damaging wind gusts are the primary
threats with the strongest storms, while the chance for tornadoes
looks low owing to the weak low-level shear/helicity & very high LCL
heights (cloud bases). The most-likely area for storms to develop
tomorrow afternoon still depends on how fast skies clear out tomorrow
morning & where the surface boundary will be by mid to late-
afternoon when instability will be highest for storms to initiate.
This generally appears to be across the eastern half of Minnesota
(east of a line stretching through Mankato & St. Cloud) with storms
developing by 3-4 PM. Thunderstorms will continue into western
Wisconsin during the evening, with thunderstorms mostly east of the
area by 9-10 PM. Brief heavy downpours will accompany any
thunderstorms, but precipitation amounts will be localized & likely
not more than 0.5-1.00".

Saturday's weather looks quiet but ensemble & deterministic guidance
continues to highlight a good chance for widespread rain Sunday into
Monday, as a strong shortwave deepens into an upper-level low over
the region. The threat for heavy rain does not appear likely at this
time but the NBM does indicate a 30-50% chance for >1" of rain over
the area, meaning there is a good chance that most see locations see
at least some beneficial rainfall Sunday into Monday. Beyond Monday,
temperatures look to be generally cooler than normal as lower
heights aloft persist into next weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 650 PM CDT Thu Aug 10 2023

Still expecting a complex of thunderstorms to move into western MN
from activity currently developing over the eastern Dakotas, then
continue eastward through this evening into the early morning hours,
impacting central-eastern MN into western WI. Most short-term models
have the convection impacting all terminals so have included TEMPO
groups of IFR-visibility and MVFR-ceiling conditions for TSRA at all
sites, along with strong winds indicative of the potential for the
storms to possibly be strong-severe. Some MVFR ceilings are then
possible thru the remainder of the pre-dawn hours. Another round of
precipitation looks likely Friday afternoon. Have included additional
TEMPO groups to account for that timing but have held off the mention
of TS/CB at this point to await better clarification on model
projection.

KMSP...VFR to start but will look for thunderstorms to impact the
terminal in the 04z-08z timeframe. That's not to say that there will
be a solid 4hrs of TSRA but that the window is a 4hr window, during
which time the storms will move through but still some uncertainty
should additional mesoscale/microscale development occur in front of
or behind the main line. The activity will be to the east of MSP by
the early morning hours, with a break from precipitation until Friday
afternoon.

/OUTLOOK FOR KMSP/
Sat...VFR. Wind NW 10-15kts.
Sun...VFR/MVFR, with -TSRA/SHRA likely. Wind S 5-10kts becoming W
15-20kts. Mon...VFR. Wind NW 15-25kt with higher gusts.

&&

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

UPDATE...JPC
DISCUSSION...ETA
AVIATION...JPC

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Preliminary Local Storm Report
National Weather Service Twin Cities/Chanhassen MN
927 PM CDT Thu Aug 10 2023

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

0910 PM     Tstm Wnd Gst     2 S Canby               44.67N 96.28W
08/10/2023  M51 MPH          Yellow Medicine    MN   Mesonet

            Mesonet station MN158 U.s.75 - Canby - Mp
            84.0.

&&

TDH

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Special Weather Statement
National Weather Service Twin Cities/Chanhassen MN
933 PM CDT Thu Aug 10 2023

MNZ064-065-073-110315-
Yellow Medicine MN-Renville MN-Redwood MN-
933 PM CDT Thu Aug 10 2023

...A strong thunderstorm will impact portions of north central
Redwood, east central Yellow Medicine and central Renville Counties
through 1015 PM CDT...

At 933 PM CDT, Doppler radar was tracking a strong thunderstorm near
Sacred Heart, or 20 miles northwest of Redwood Falls, moving east at
50 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

This strong thunderstorm will be near...
  Renville around 950 PM CDT.

Other locations in the path of this storm include Olivia and Bird
Island.

This includes the following highways...
 U.S. Highway 212 between mile markers 53 and 87.
 U.S. Highway 71 between mile markers 83 and 102.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 200 AM CDT for
central, southwestern and west central Minnesota.

&&

LAT...LON 4477 9550 4477 9549 4483 9547 4483 9478
      4453 9480 4463 9551
TIME...MOT...LOC 0233Z 270DEG 43KT 4472 9544

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

TDH