Wurzer weather can’t last forever.
My Morning Edition weather chat partner on MPR News loves it warm. She’s had her share of heat in this great summer of ours. But I hear the dismay in her voice today as we talk about the upcoming forecast deets.
Hang in there, Cathy. Yes, Minnesota’s inevitable fall has arrived. But my weather spidey senses tell me we’re not done with 70-degrees in the Twin Cities this year.
Not just yet.
It’s late September. There’s usually a cold front in our future this time of year.
We squeak out one more 70-degree day today in the Twin Cities before the thermal bottom falls out this week.
Rain spreads east
Showers in northern and western Minnesota spread slowly southeast today as the front nudges along. The frontal rain zone arrives in the Twin Cities late this afternoon. The hours between 5 p.m. and midnight are the favored times for rain in the Twin Cities. Severe weather is not likely.
The National Oceanic and Atmospheric Administration’s North American Mesoscale Forecast System 3 km resolution model tracks the frontal band eastward into Monday night.
Back to around 60
Daily high temperatures hover a few degrees either side of the 60-degree mark for the next 7 to 10 days in the Twin Cities. We may flirt with morning frost in the Twin Cities suburbs as October approaches.
The longer range upper air pattern shows some signs of a milder flow as we move toward the second week in October. A few models suggest we may hit 70 again sometime between Oct. 5 and 10.
Extensive damage in Granada, MN. House pushed off it's foundation, roofs ripped off, large trees uprooted, grain bins destroyed. Confirmed tornado yesterday by a storm chaser. National Weather Service will be sending out teams to survey the damage. #mnwx pic.twitter.com/47CaDuBPCS
— Tom Clements (@TomClementsTV) September 21, 2018
Thursday night’s tornado outbreak was an unusual one. I can’t remember so many “squall-line” tornadoes in an outbreak. Thursday’s tornadoes formed along a rapidly advancing squall line. These so-called quasi-linear convective system (QLCS) tornadoes are different from typical individual tornadic supercells.
Here’s a good description of QLCS from the NWS Office in Louisville, Ky.
A “squall line” refers to a linearly-oriented zone of convection (i.e., thunderstorms). Squall lines are common across the United States east of the Rockies, especially during the spring when the atmosphere is most “dynamic.” A “bow echo” or “bowing line segment” is an arched/bowed out line of thunderstorms, sometimes embedded within a squall line. All these terms fall under the more generic term Quasi-Linear Convective System (QLCS).
Bow echoes, most common in the spring and summer, usually are associated with an axis of enhanced winds that create straight-line wind damage at the surface. In fact, bow echo-induced winds/downbursts account for a large majority of the structural damage resulting from convective non-tornadic winds.
Transient tornadoes also can occur in squall lines, especially in association with bow echoes. These tornadoes, however, tend to be weaker and shorter-lived on average than those associated with supercell thunderstorms.
The Twin Cities NWS is still refining the details on the number and intensity of the tornado outbreak. Right now the tornado count stands at 10.
Public Information Statement…UPDATED
National Weather Service Twin Cities/Chanhassen MN
1030 PM CDT Sat Sep 22 2018
…A BRIEF SUMMARY OF THE SEPTEMBER 20TH TORNADOES…
All of this information is preliminary and will likely change as
more information is gathered. Some tornadoes may be combined to
form longer tracks which may reduce the total number below. Some
ratings are being assessed for modification. Other locations have
yet to be surveyed and more tornadic areas could be added to this
1.) Just west of Ceylon, MN (Martin Co.): Brief EF0
2.) Granada, MN (Martin Co.): EF1
3.) Northwest of Janesville, MN near the Blue Earth/Waseca County line to Waterville, MN (Waseca and Le Sueur Co.): EF1
4.) Morristown, MN (Rice Co.): EF2
5.) Northwest of Faribault near Robards Lake to I-35 (Rice Co.): EF1
6.) Northfield, MN (Rice Co.) to Cannon Falls (Goodhue Co.): EF1
7.) Cannon River Wilderness area (Rice Co.) to between Dennison and Stanton, MN (Goodhue Co.): EF1
8.) Southwest side of Cannon Falls, MN: EF1. This one could eventually be combined with #7 upon further assessment.
9.) South of Dundas, MN to southeast of Northfield, MN (Rice Co.): EF1. This one could be combined with #5 upon further assessment.
10.) Medford, MN (on Steele/Rice Co border) to between Nerstrand and Kenyon, MN (Goodhue co.): EF1
Other areas of interest: Cannon Falls city eastward into Pierce County, WI and Owatonna northeastward toward Zumbrota.