06/28/05 FCST: Northern Plains

[Bill Hark]

It is still very early, but Tuesday evening June 28 looks interesting for south-central South Dakota. The 12Z June 24 GFS shows 30 to 40 SW flow at the 500 mb level across western South Dakota by 00Z June 29. The trough is shifting eastward. There will be a cap but 700 mb temps are predicted to be 10 or less along the SD-NE border. ALthough dewpoints will be good, I am concerned about the surface features. The gulf is open but the low is predicted to be over western Kansas. Winds show some backing but I would prefer the Low to be farther north. Precip only goes a far south as north-central Nebraska. Farther south, the cap is too strong.

Bill Hark

 

[Rocky Rascovich]

Contemplating a chase

Hey All: I'm seriously considering a trek up to MN/SD/ND for next Tuesday and Wednesday...its going to have to look "real" good for me to go as in reality I barely have the time or money to chase right now, plus we're saving up for our escape out of here (Okla.) for Canada and the MN/U.P of MI. areas later in July when the 100F temps hit.

As of the latest GFS, its looking marginal for me to make the trip...it does bottom the low out at 1000mb.,over norther SD not bad for this time of the year...shear and cape should be no problem but the negative tilt the earlier runs had on the 500 mb. vortmax is not nearly as evident, plus it looks the best action will be north of HWY 2 in ND and MN. I'll be monitoring it close...any extra chases I do will be purely a bonus ontil the fall season.

Ciao Rocky&family

 

[Mikey Gribble]

After looking at the 00Z run of the NAM I am pretty pumped for tomorrow. I think there is a good chance of tornadic supercells if the NAM verifies. There is great directional shear with backed surface winds at 10-15kts. The thing that had been worrying me the most was moisture, but with dewpoints currently in the upper 60's and low 70's over SE South Dakota and surrounding areas, I am thinking upper 60's and low 70's are a sure thing over the target area. LCL's may still be a bit high. Forecast sounding for Pierre shows LCL at 1165m at 21Z with a nice long curved hodograph. LCL's should be a little lower further North. Deep layer shear AOA 50kts and CAPE >2500J/KG with >4000J/KG further South around Pierre will be very favorable for supercells. Throw in a few outflow boundaries and a front and I think there is a good tornado threat tomorrow. I may be a little optimistic since I have been planning on chasing tomorrow for some time now, but other than LCL's being a bit high, I don't see anything wrong with this setup as long as we get good insolation. I am staying the night in Aberdeen and will be leaving around 7 for Mcintosh to get data. I will fine tune the forecast and will probably move South from there. Good luck to anyone who goes out tomorrow.

 

[Glen Romine]

Well, doesn't look like anyone is overly optimistic this morning given the lack of posts. Oh well, guess I'll throw out some thoughts anyway. Last evening's surface cyclone was just east of Goodland this morning (~1008 mb) and continuing to weaken, with a second low developing just east of Billings MT. Surface high pressure ridge to the north was supporting narrow tendril of modest moisture return across the northern plains, with low 60 dewpoints edging into se MT, with mid 60's surging westward from central SD. Low clouds were present across a SD and into western MT, with a very low cloud deck in the upslope flow. Depth of moisture looked rather thin everywhere except UNR in the northern plains - but moist toungue not well sampled by upper air network. Upper jet streak currently over sw US on eastern side of upper trough expected to lift northeastward leading to surface pressure falls over eastern MT, leading to enhanced upslope low-level flow and moisture transport within the narrow tongue. A fairly strong cap is in place across much of the plains, and may preclude development of storms across portions of SD and NE, despite where moisture pooling and convergence enhanced by weakening GLD cyclone might otherwise offer an alternate target area. That said, current activity in the area could generate a sufficiently potent boundary to enhance surface convergence enough to overcome cap strength. Also concerned, given strength of cap and cloudiness over northern region, extent to which storms can initiate into SD along boundary extending southeastward. Guess I could see two targets that look ok - One around Miles City, MT, and another less certain target around the Hastings area. Anyone else have thoughts?

Glen

 

[Edward Ballou]

For once we're not battling LCL heights for today's setup. Moderate cap but very impressive CAPE. It looks like the other elements are there - moisture, higher dewpoints in the south central area of SD. I'm going to have to put my TA as Pierre to Mitchell. Things could develop west of there but the Eta is showing many elements converging in that central part of SD across the border into NE.

EDIT: And as always, I'm a newbie at this so feel free to constructively criticize

 

[Jeff Snyder]

For once we're not battling LCL heights for today's setup.

I'm not so sure. It looks like we may see T-Td deficits in the 15-25 range later this afternoon, which isn't ideal... I prefer T-Td defs <15 degrees. It's not horrible, but not really ideal.

I think the SD portions of the target area have the best probs of supercells. Both the RUC and NAM show a shortwave approaching and entering southwester SD, western NE, and southeastern MT by afternoon. In addition, a nice jet streak at 250mb will begin to nose into western NE and southwestern SD by late afternoon. A surface low will begin to deepen in the left-exit region of this jet streak, being enhanced by favorable transverse circulation. This low will maintain backed surface flow through the afternoon. Dewpoints may increase some more through the afternoon, though I'm not sure the impacts of evapotranspiration in this particular area since I"m not familiar with the terrain up there. Regardless, meager speed shear yet strong directional shear will yield shear profiles favorable for supercells. Assuming Tds end up where expected, strong instability will develop in mainly central portions of SD/NE, again favorable for strong, rapidly-developing supercells. There doesn't really appear to be a good focus for surface convergence in SD, but there may be something near the southern edge of the low clouds in northern SD (differential heating boundary perhaps). OTherwise, we're going to have to wait for some other surface convergence to become better defined this afternoon... DPVA downstream of the shortwave may weaken the cap enough such that only weak surface convergence is necessary -- we shall see. Weak flow at 700/500mb may limit the longevity of tornadic supercells, but we'll see. Unless 850mb flow veers a bit, there won't be much 0-3km SRH ( or low-level shear on the whole) owing to nearly unidirectional flow between the surface and 850mb.