7/8/09 FCST: SD

[Brandon Lawson]

Perhaps it is a bit premature, but the GFS is showing a system push into the ridge over the central US during the middle of next week. There is a lot of time between then and now, but if the timing is right and the models hold up, there looks to be a warm front play somewhere across South Dakota on Wednesday. One or two impulses during the days prior should be enough to allow for some better moisture return, with a strengthening surface low over eastern Wyoming/southwest South Dakota developing on Wednesday. Extreme CAPE should exist all along the front. The cap appears to be pretty strong at this point, but if synoptic forcing is strong enough, this could be another good day of storms.

 

[Bob Hartig]

I was looking at this on last night's GFS. Things looked great until I got to the MLCINH. Ugh.

Today's 12Z moves things more into Minnesota, if you go by the GFS, but it hardly matters since the cap is an absolute killer.

However, the NAM-WRF paints a much more optimistic picture, with the cap eroding by 00Z over north-central NE/south-central SD, and less robust (though still potent) CINH elsewhere. Much better surface winds, too. Assuming this latter scenario bears out instead of the GFS, then Wednesday could supply some action in the northern Plains. Finances will force me to sit this one out, but I'll definitely be watching, wistfully, to see how things develop.

 

[Matthew Piechota]

well the new WRF is in, would really like to see some better 500 winds. this run showing winds around 25kts. 850s look good out of the south at 0z but its breakin out precip northwest of the 850 winds where they are alot weaker but that could be due to the model breaking out the precip. this run has a s/w in central SD at 0z

sfc winds are nicely backed with dew coming in around the mid 60's with MLCAPE values AOA 2500j/kg possibly nearing 3500 in spots with the CAP eroding by 0z in central SD. shear looks to be ok but not great.

could be a descent day but still 72 hours out so will have to be watched closely. lets see what the GFS says. got to get those 500 winds stronger.


matt

 

[Mike Hollingshead]

8th(Wednesday) won't be on NAM till 12z tomorrow run. 8th on 0z GFS sort of saying head to blackhills. That or stay home obviously. Not too thrilled with what GFS is doing to the thing now. Think my biggest hope for the 8th is that it doesn't hose the 9th, even though it's trying to look hosed-ish too.

 

[Matthew Crowther]

12Z models suggest a good chance at supercells and maybe a tornado near the "3 corners" of MT/ND/SD on Wednesday afternoon- very good deep layer shear and adequate CAPE is likely near the triple point- the warm sector should be capped during daylight hours so the best place should be just E or ENE of the surface low.

 

[Bob Hartig]

8th(Wednesday) won't be on NAM till 12z tomorrow run.

Well, that's fairly embarrassing. Wonder what I was thinking--probably got snookered by the 00Z time stamp.

Anyway, Wednesday is now well within range of the NAM, and based on cap erosion, the 12Z NAM-WRF seems to suggest two likely areas, depending on whether one leans toward great CAPE with acceptable shear, or great shear with less but still decent CAPE. For the latter scenario, northwest ND would be a likely choice, say around Dickinson, toward the front of the 500 mb jet max. On the other hand, somewhere between Mitchell and Huron, SD, offers bigger CAPE with H5 winds between 30-35 kts and 40 kts of bulk shear.

That's the NAM-WRF. The GFS continues to insist that there ain't gonna be no party, but I'm betting that it's overplaying the cap.

 

[jshields]

i'm surprised that no one has continued the discussion on this thread! there is now a moderate risk of severe storms across south dakota and north dakota. a strong shortwave and jet max is forecast to come out of the rockies across this region this afternoon. low pressure is across eastern wy and southerly flow will pull up enough moisture to make things moderately unstable this afternoon. initially discrete supercells are forecast with large hail and possibly tornadoes with any storm that can ride the warm front/old boundaries. the big issue is the expected development of a possible major derecho event. the low level jet should really kick in above 50kts later today, allowing for a possible long lasting mcs that races across the nd/sd borders and into minnesota before turning southeast. dcape is also over 1500 j/kg pointing towards the possibility a derecho as well.