Severe Thunderstorm Warning 170, NWS Twin Cities, MN

169 
WWUS53 KMPX 291957
SVSMPX

Severe Weather Statement
National Weather Service Twin Cities/Chanhassen MN
257 PM CDT Thu Aug 29 2024

MNC015-103-292006-
/O.EXP.KMPX.SV.W.0170.000000T0000Z-240829T2000Z/
Brown MN-Nicollet MN-
257 PM CDT Thu Aug 29 2024

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHEASTERN BROWN AND
NORTHWESTERN NICOLLET COUNTIES WILL EXPIRE AT 300 PM CDT...

The storm which prompted the warning has moved out of the area.
Therefore, the warning will be allowed to expire.  However, gusty
winds and heavy rain are still possible with this thunderstorm. 

A Severe Thunderstorm Watch remains in effect until 900 PM CDT for
south central Minnesota.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
the Twin Cities.

Remember, a Severe Thunderstorm Warning still remains in effect for
eastern Nicollet County. 

&&

LAT...LON 4428 9478 4445 9457 4427 9435 4417 9465
TIME...MOT...LOC 1956Z 231DEG 26KT 4437 9446 

$$

RMD

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1254 PM CDT Thu Aug 29 2024

.KEY MESSAGES...
- Enhanced Risk (level 3 of 5) of severe storms this afternoon
  and evening.

- Pleasant Labor Day weekend, with no major systems expected
  through early next week.

&&

.UPDATE...
Issued at 1240 PM CDT Thu Aug 29 2024

After collaboration with the SPC, much of our CWA was upgraded
to an Enhanced Risk (level 3 of 5) for severe storms this
afternoon and evening. The main driver of this upgrade is the
damaging wind potential, but the risk for a few tornadoes and
large hail also exists, particularly across central Minnesota
near the triple point of the low. While today's storms may not
be quite as strong as Monday's round of severe weather that
brought +70 MPH winds to parts of the CWA, our confidence in
timing, coverage, and storm mode is higher for today. The
timing of the strongest storms still remains on track to develop
sometime between 3-4pm across western/central Minnesota before
growing upscale and marching eastward. They are expected to
reach the Twin Cities metro between 5-7pm and continue into
western Wisconsin from 7pm-10pm.

&&

.DISCUSSION...
Issued at 240 AM CDT Thu Aug 29 2024

Although it was a spectacular evening on Wednesday and the night has
been rather uneventful for us, things are changing... Water vapor
imagery and RAP h5 analysis shows an impressive mid-level low
spinning across the MT/Canada border this morning. In response to
the height falls ahead of it, we've seen a strong LLJ and push of
rich theta-e air surge north across the Dakotas. The nose of the
strongest WAA within this LLJ has helped generate the thunderstorm
activity we've seen overnight across NoDak. This upper low and
strong WAA will all track toward northwest Ontario through the day,
which means the activity we have seen overnight over NoDak will
remain north of the MPX area. However, as the upper low continues to
the east, we will see the warm front currently across eastern SoDak
and northern Iowa surge north across the area through the morning.
The main impact from this warm front surging north across the area
this morning is that we will have extensive stratus develop out
ahead of it from southeast into central MN and across western WI. In
the wake of this warm front though we will see another warm and
humid airmass advect into the region, with highs expected to be in
the mid/upper 80s and dewpoints in the low to mid 70s out ahead of a
cold front that will be moving into western MN this afternoon.

Looking at the severe potential today, what will not be lacking is
instability, with the temp/dewpoint combo mentioned above sending
mlCAPE values up to between 3000 and 4000 j/kg this afternoon. What
we're lacking in the severe parameter space is shear. The mid-level
jet will be up near the h5 low, with deep shear this far south being
near 30 kts. Looking at hodographs, you see a further issue. Though
we have good shear and curvature in the lowest 2 km of the
hodographs, there is a weakness in the flow between 2 and 6 km,
where the hodographs loop back on themselves. Given this setup, you
tend to struggle to maintain prolonged strong updrafts with the weak
mid-level flow causing limited tilt in the updrafts. Though the
parameters do support supercells, bulk shear vectors roughly
parallel to the front means we will trend toward a linear mode
rather quickly after initiation, which is what we see when looking
at CAM reflectivity outputs. Given all of that, a Slight Risk (level
2 of 5) from the SPC for today's threat looks reasonable, with a
typical August severe setup, with the hail and brief tornado threat
most likely at initiation, with a transition to a heavy rain and
wind threat as storms grow upscale. The excessive rain threat looks
isolated at best. We'll have convection with PWATs just under 2",
but storm motion looks sufficient to really limit any sort of
widespread excessive rain threat with storms today.

As for timing, storms are currently expected to fire around 19z
(2pm) in western MN (in the neighborhood of places such as Granite
Falls, Willmar, and Long Prairie). Storm will go linear pretty
quick, with this initial line coming through Twin Cities metro
between 21z and 0z (4pm-7pm), moving across our WI counties between
00z and 3z (7pm to 10pm). There are some indications of a second
area of storms developing behind this primary activity on the cold
front itself, but this activity looks to have limited severe
potential and would just help to add to rain totals. As for
rainfall, most areas that see rain will see a half to three-quarters
of an inch, with a few pockets of 1-2 inches possible if a location
can double dip into both potential rounds of storms.

After this front moves through, the weather will be very quiet
through the first half of next week. We will see a strong and dry
cold front drop across the upper MS Valley on Saturday, which will
bring us a fall preview Sunday and Monday, with dewpoints down in
the 40s, highs in the low 70s and lows on Monday morning dropping
into the 40s for all but the urban core of the Twin Cities metro
area. Southerly flow quickly returns on Tuesday, which will push
temperatures back closer to normal by the middle of next week.
Though we will see increased temperatures and dewpoints with that
southerly flow, there will be split flow aloft and we look to be
stuck in the middle, so there will be little forcing for any
additional precipitation.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1240 PM CDT Thu Aug 29 2024

The IFR/MVFR stratus deck has shifted NE, but will still impact the
western Wisconsin sites for the early afternoon. A pocket of
clearing is visible over much of central Minnesota, while convection
is becoming more widespread along the western MN border. As the
front sags southeast, a period of heavy rain and convective wind
gusts will likely impact each site. Behind the line, cigs will
quickly rise and winds will weaken and shift out of the NW.
There is a chance for low stratus and patchy fog for some locations
overnight, especially over western Wisconsin.

KMSP...Timing is still on track, so not too much change for the
ongoing TAF. Scattered storms could arrive ahead of the front
around 20z, with the main line moving through close to 21-23z.
Some models indicate that more isolated storms storms could fill
in behind the main line, so we have maintained the tempo
through 01z for now.

/OUTLOOK FOR KMSP/
SAT...VFR. Wind SW 10-15kts.
SUN...VFR. Wind N 5-10kts.
MON...VFR. Wind S 5-10kts.
&&

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

&&

UPDATE...Dye
DISCUSSION...MPG
AVIATION...BED

Hazardous Weather Outlook
National Weather Service Twin Cities/Chanhassen MN
349 AM CDT Thu Aug 29 2024

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
300900-
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-
349 AM CDT Thu Aug 29 2024

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

.DAY ONE...Today and Tonight.

A slight risk for severe thunderstorms is present this afternoon
and evening, with damaging wind and large hail the primary threats
with a few tornadoes possible.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation may be needed.