6/6/07 FCST: ND/SD/NE/KS/MN/IA/MO

[Adam Atkins]

Strong zonal westerlies will accompany a fast moving shortwave on Wednesday. The GFS and NAM are in fairly good agreement with the placement of the surface low over Nebraska and ample moisture will be in place for extreme instability coupled with a strong LLJ (300+ helicities). June is typically very warm and the cap will be strong (25-30 C 850mb- enough to preclude any precipitation south of the warm front) but upper level difluence and PVA late in the period should allow isolated convection along the dryline from NE through N TX.

This has the potential to be a very big event which is why I'm posting so far in advance. Such strong baroclinicity is interesting to see in June which leads to strong dynamics more comparable to an early Spring event. Thoughts?

 

[Chris Wilburn]

The data that this mornings NAM put out for Wednesday is insane. Td's 70-75 from Nebraska through Kansas.........am I seeing this right? lol CAPE near 5,000 J/kg from Nebraska through Kansas with a really nice dryline setting up. 977mb surface low at the SD/NE border with really really nice directional and speed shear. This has the potential to be a huge day if the CAP doesn't hold too strong. I think an area further north by the surface low/warm front may be a good play as further south thing may be in a more capped environment. The NAM does breakout precip. near the surface low/warm front by 00z and nothing south of there by this time. Could be a really nice day for central/eastern Nebraska, but only time will tell. I am never one to jump the gun and scream outbreak, but if this verifies and the CAP breaks it will be a significant outbreak. Target as of now would be to find the surface low/warm front and go from there unless the CAP doesn't look horrible down the dryline into Kansas.

 

[Ben Prusia]

I agree that Wednesday has the potential to be a very active day for severe weather. There appears to be two different areas for some severe weather, one is the main area which will be centered around a very strong surface low pressure system in central South Dakota and extending southward along a very nice dryline into Texas. The other appears to be some warm front play in eastern Nebraska into northeastern Kansas and northwestern Missouri. There will be a very strong cap in both locations, especially in the warm front play area. It appears though as CIN weakens as you head north into South Dakota as the NAM breaks out some precip in that area. But the combination of extreme instability, coupled with very well mid-upper level south/southwesterly winds and excellent shear with the cap will give for the chance of some strong isolated supercells wherever storms can develop. This is a day worth watching.

12Z GFS shows the storm system in roughly the same place as the 12Z NAM model run. Albeit at 985mb instead of the NAM's deeper forecast, it is still a very deep and strong low pressure system. GFS does break out precip along the NE/SD border by 0Z Thursday, but there is less instability to play with, but that is the way the GFS has been all year.

 

[afischer]

The forecast intense low- through mid-level WAA preceding the wave reminds me of 8/16/02 (though the overall patterns are not so similar), which was a no-tornado day due in part to high LFCs across the board with a toasty 850-700mb layer. It at least looks like some decent height falls and 700 mb cooling will come out along and north of the SD-NE border, so supercells look like a definite possibility.

 

[Scott Olson]

Operational GFS/EPS/NAM show a strong surface low and shortwave coming through on Wednesday. The ECMWF looks weakest but still significant with a 996mb surface low in ND and a front stretching down through the Dakotas and Nebraska. GFS ensemble shows just short of half of it's perturbations from last night at 984mb or below, with the 12z operational GFS coming around to the deeper low. The NAM is extremely deep for June at <980mb. 700mb temps are quite warm with upwards of 14C 700mb temps nosing in but they are substanial height falls and cooling between 18z-0z. GFS shows a 2C drop in Nebraska and both models show a substanial weakening of the cap in South Dakota. I'm very interested in the area from Mobridge, SD to NC Nebraska. Ample instability/shear extends well into North Dakota and the shear vector orientation suggests the possibility for long-lived supercells. The NAM has a much more intense LLJ at 0z that extends farther north but both have SC SD and NC NE in a nicely favorable veering profile under strong/extreme instability and strong convergence with lowering heights.

Four days out, I'm sure there are some fly's around that could get in the ointment. Obviously the CAP is one as the current solution allows convection only because of the significant height falls. Another thing to watch for is the whole solution slowing down. GFS ensemble from last night has the 988mb low not even into western SD. There has been an exhibited bias with wanting to push these systems through too quickly. This has been especially true this year. In almost all if not all cases the ECMWF has latched on to the slower reality but in this case the Euro is really only a bid farther north, so that may be less of a concern here.

 

[John Hudson]

While I understand the cap could be the real wildcard for Wednesday, it appears to weaken by the late evening, with some serious precip amounts progged for northeast NE.

What really has me excited is the highly sheared environment for the area on Wednesday, with 60 kt WSW @200 mb and winds near the surface nicely backed to the southeast at 40 kt.

That kind of shear, together with the juicy air, has got to produce some impressive sups. Just hope there's not a lot of changes between now and then. I have to say that I'm not real enthusiastic about chasing another nighttime event, either.

John
VE4 JTH

 

[David Wolfson]

I agree on the models' tendency to move troughs too fast this year. My thinking is that the best forcing to break the stout cap will be just southeast of the surface low.

[V] Target: Sioux Falls, SD, by way of North Platte, NE, night of the 5th.

Sioux Falls is an efficient road hub for screaming wherever on what looks to be a very dynamic day (!), and for heading south for later in the week action.

 

[Jeff Piotrowski]

Significant tornado's on Wednesday

Based on 12Z model's very strong triple point in the SC/SD area with 4000 cape’s 0-3km Helicity 300-800 range and 850 winds over 50+ 500 winds 50+ cross over SE-SD NE-NE. There will be a massive cap south of triple point 15C at 700 mb.

The EHI is over 10 SE-SD, NE-NE after 0Z expect Significant tornado's if this verifies.

Bottom line the pattern by all models say's severe weather everyday from June 3-19 in the plains with a number of major outbreaks during that time period.

This may be the best June pattern since June 1995.

 

[Ryan McGinnis]

I was going to say that the GFS is probably taunting us, but it looks like the WRF is giving it a high-five. The UL jet even exits just east of NE-SD. Tds in the 70s (God I hope it's not exxagerating the moisture), 984mb SFC low, ripping LLJ... what's not to like, other than the fact that this is a model 3 days out? Note to self: find Rain-X, get GPS working again.

 

[Michael O'Keeffe]

Ok I don't like to compare setups, but I was doing some comparisons and June 24, 2003 had some striking similarities. Extreme instability was present in C/E NE, but was capped off, while north of the border near the TP the cap was breakable. Tds in the 70-75F range were common that day into SD and the sig tor parameters were around 6 south of Mitchell. Though I don't think that will happen this go around it is still something to look at.

 

[Mike Hollingshead]

Northeast Nebraska and southeast SD are in trouble if this stuff verifies. I can't remember seeing such a setup around here, at least for a few years(May 22nd 2004 might have been a hair better....unless the low levels back more like was shown on previous runs, then this just gets crazy...though I certainly like the larger warm secton shown now).

http://beta.wxcaster.com/models/eta/central/CENTRAL_ETA212_ATMOS_CAPE_72HR.gif

Earl's graphics show greater than 6000 sbcape.

http://beta.wxcaster.com/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_72HR.gif

Cap removed I80 on north.

http://www.wxcaster2.com/CENTRAL_ETA_500_GPHTMPWNDVORT_72HR.gif

Cooling aloft and strong sw flow overspreading the dryline in the afternoon. Increasing to 80 knots up at 250mb.

This run has the low levels not as backed as before, but I don't think it's going to matter much with such instability and flow aloft(and some capping to the south)...with southerly low levels. Any backing to the sfc flow will just be some icing on the cake. It's nice the gfs is in very good agreement with the nam(though the gfs has much better backing to the sfc winds).

I figure picking a small area for a target might just be silly on this one. I'd guess there will be several supercells erupting along the dryline, all with a similar environment. But, midlevel flow may tend to back to the north and I'd want to stay away from that(I've noticed they love to wind up much more backed than prog'd). Right now I'd put a circle/square from Omaha to Kearney up to I90 in SD with the same e-w dimensions...with a big red x near O'Neill NE.

Edit: How often do you see 973 for a sfc pressure in June? lol
http://weather.cod.edu/forecast/GFS/gfsUS_0_prec_84.gif

Or 970 via the nam: http://www.rap.ucar.edu/weather/model/eta84hr_sfc_mslp.gif

If nothing else it'll be a fun system to watch.

 

[Ryan Pfannkuch]

Finally was able to take a detailed look at this setup overnight...and I must say the agreement between the 0z NAM/GFS was pretty amazing for being 72 hours out. As usual, I suspect the NAM is overdoing dews and subsequent CAPE a little, but the mid 60s from the GFS still produces over 3000 j/kg MLCAPE up and down the dryline. Both models pop the cap along the NE/SD border as the left front quad of the mid/upper level jet streak enters the region during the afternoon...with deep layer shear obviously quite potent.

I normally don't get too excited about pinning down specific areas more than 48 hours out...but given the remarkable agreement between the NAM/GFS and assuming that things may slow down at least a hair between now and showtime...I will pick a very preliminary 5-county target area for initiation to be:
Nebraska: Keya Paha, Cherry (northeast quadrant of county)
South Dakota: Mellette, Todd, Tripp

Including the cities of: Valentine and Springview NE
Winner, White River and Rosebud SD

This is likely a little farther west than many might have been thinking...but at least in terms of INITIATION of the "southern storms" of this event and hedging a little on the system slowing down I will run with this for now.

 

[Nick Hartley]

Wowwie I like this set up . I think somewhere along the Bon Homme county, Yankton County line is where the storms will start popping. Hopefully make it down there after work on Wednesday afternoon.

 

[Paul Knightley]

est SPC day 3 outlook goes for a moderate risk - seems quite unusual to see such wording on the day 3...there'll be some very nasty storms around on Weds. Let's just have a quick look at the stats - both ECMWF and GFS show an intense upper low moving out of the Rockies late on Weds, inducing rapid cyclogeneis over the Dakotas. This brings an 850 hPa LLJ of 50-60 knots, increasing to 70 knots in the evening across KS/NE. 500 hPa flow of 50-60 knots should, along with 3000+ J/Kg of CAPE, and fairly low LCLs brings the very real risk of extreme supercells storms with strong-violent tornadoes. I would go for SW or S-cent NE on Weds, as a 1st guess, although maybe a bit further east.

 

[Justin E. Reed]

Definetly expect a high risk area to be issued as soon as tomorrow the way things are shaping up. I'd be highly surprised if it wasn't. This will be a very good day by all means.