8/12/10 NOW: ND, SD, MN

[Jeff Duda]

The atmosphere appears ready to blow across NE SD and parts of SE ND and W MN. A warm front is clearly evident on KABR as well as in surface obs and satellite imagery oriented roughly WNW-SSE from the central SD-ND border through NE SD and through C MN with pretty good surface flow (10 - 20 kts ESE and gusting) north of the boundary. This is also the location of a strong SBCAPE gradient with up to and over 4000 J/kg SBCAPE into SE SD and SW MN and points south of there. There is also a pocket of > 60 kts effective bulk shear in NE SD, SE ND, and WC MN with a tongue of > 40 kts of effective bulk shear extending SSW from the St. Cloud area towards Sioux City, IA. 0-1 km shear is > 20 kts in a similar area, with a maximum of > 30 kts 0-1 km shear northeast of Aberdeen. As a result, effective SRH is up to nearly 700 m2/s2 around the tri-state area of ND/SD/MN. Low-level CAPE is building in the area also, and with good surface theta-e advection and convergence near the low that is centered in C SD, the forcing is there to get storms going soon. Could be some tornadic supercells early on.

One thing I will add: the effective-layer significant tornado parameter is currently peaking at > 9 in NE SD, and to my knowledge there hasn't been a non-tornadic-supercell day (both no supercells and no tornadic supercells) when that parameter has been so high (for as long as that parameter has been included in analyses).

ADD: as of the 21Z analysis, effective-layer sig tor is up to 11 in the tri-state area.

 

[jshields]

don't know if anyone else is watching the storms still, but i thought i would post something that i don't know if i have ever seen before. currently there is an intense bow echo moving through northern s. dakota and southern n. dakota with this wording for the warning:

SEVERE THUNDERSTORM WARNING FOR...
EMMONS COUNTY IN SOUTH CENTRAL NORTH DAKOTA...
EAST CENTRAL GRANT COUNTY IN SOUTH CENTRAL NORTH DAKOTA...
SOUTHEASTERN MORTON COUNTY IN SOUTH CENTRAL NORTH DAKOTA...
SIOUX COUNTY IN SOUTH CENTRAL NORTH DAKOTA...

* UNTIL 1215 AM CDT/1115 PM MDT/

* AT 1013 PM MDT/1113 PM CDT/...NATIONAL WEATHER SERVICE DOPPLER
RADAR INDICATED A LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING
EXTREME DAMAGING WINDS IN EXCESS OF 100 MPH. THESE STORMS WERE
LOCATED ALONG A LINE EXTENDING FROM RALEIGH TO 6 MILES NORTH OF
SELFRIDGE TO 10 MILES SOUTHEAST OF SELFRIDGE...AND MOVING EAST AT
60 MPH.

in excess of 100 mph there was a report of 93 mph winds in hettinger, and 15 minutes later there were still 70 mph winds in hettinger on a report. since this is a current warning i put it in the nowcast, rather than discussion


update: on the warning update they've lowered the winds to 80 mph, but the line of storms in now moving at 80 mph itself!!

 

[Bart_Comstock]

don't know if anyone else is watching the storms still, but i thought i would post something that i don't know if i have ever seen before. currently there is an intense bow echo moving through northern s. dakota and southern n. dakota with this wording for the warning:

SEVERE THUNDERSTORM WARNING FOR...
EMMONS COUNTY IN SOUTH CENTRAL NORTH DAKOTA...
EAST CENTRAL GRANT COUNTY IN SOUTH CENTRAL NORTH DAKOTA...
SOUTHEASTERN MORTON COUNTY IN SOUTH CENTRAL NORTH DAKOTA...
SIOUX COUNTY IN SOUTH CENTRAL NORTH DAKOTA...

* UNTIL 1215 AM CDT/1115 PM MDT/

* AT 1013 PM MDT/1113 PM CDT/...NATIONAL WEATHER SERVICE DOPPLER
RADAR INDICATED A LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING
EXTREME DAMAGING WINDS IN EXCESS OF 100 MPH. THESE STORMS WERE
LOCATED ALONG A LINE EXTENDING FROM RALEIGH TO 6 MILES NORTH OF
SELFRIDGE TO 10 MILES SOUTHEAST OF SELFRIDGE...AND MOVING EAST AT
60 MPH.

in excess of 100 mph there was a report of 93 mph winds in hettinger, and 15 minutes later there were still 70 mph winds in hettinger on a report. since this is a current warning i put it in the nowcast, rather than discussion


update: on the warning update they've lowered the winds to 80 mph, but the line of storms in now moving at 80 mph itself!!

I have seen this before with vigorous derecho type events. I would not be surprised to see the bow march on for quite a while. It will be interesting to see how it evolves. The bow really doesn't look like a derecho but man is it really starting to accelerate forward. This certainly is entertaining to watch on radar. I wouldn't be surprised if Linton, ND has some pretty serious straight line wind damage reported soon.

I'm a bit surprised that there hasn't been a tornado warning on the area of rotation that now is south of Solen.

 

[jshields]

high wind warning now for the areas behind the bow echo for strong pressure differences immediately behind the line of storms. bismarck wfo is warning of winds gusts to 80 mph for up to 3 hours after the main thunderstorms move through and aberdeen has a high wind warning for n. central south dakota for winds up to 60 mph behind the storms!! very impressive!!

 

[Zach Chappell]

I will say this I talked with a friend who has relations with the NWS and He said this bow echo thats now dieing verified derecho critera. It has 4 80+ reports with 3 widespread 1 in wyoming and 3 spread out in ND numerous 70+ reports wind reports and damage reports go for a long ways from wyoming to central ND. Also this was a classic ND/SD Derecho/Bow the Derechos most of the time start in NE Wyoming and move along the same path.Its not being called a derecho by SPC but i would say it is