5/28/06 FCST: NE / SD

[Bill Schintler]

Chase target:
10 miles E. of Merriman, NE on US 20 (50 miles W. of Valentine).

Timing:
Storm initiation 6 PM CDT.

Comments:
Isolated high-based supercells between 7 and 9 PM, with an evolution into a multicell complex with an impressive lightning show after sunset.

Discussion:
00Z H7 UA analysis indicates digging trough in the WRN US while two shortwaves are approaching the Pacific coast. Forcing provided by the second of these two waves will provide the dynamics for SFC cyclogenesis in NERN CO tomorrow afternoon. A SFC boundary trailing NE from this low will provide the focus for SVR WX as a narrow axis of moisture is advected NW along and just NE of the boundary along upsloping terrain.

This evening, 00Z NAM initialized slightly cool with regard to SFC temps while the observed dryline position was 80mi E of the NAM solution, no doubt due to the model's lack of resolution with the shallow moisture layer which mixed out rapidly. This evening's NAM is very similar to the 12Z run with regard to SFC moisture, temperatures, and QPF for tomorrows 00Z FCST. Even after adjusting the position of the WWRD extent of the moisture to the E and NE, sufficient moisture with a dewpoint of 50F (the target elevation is just under 3000ft) should be in place at the target area. 12Z models (NAM, GFS, UKMET, and NGM) differed somewhat as to the placement of the SFC features, with the NAM and GFS in good agreement with low strength and location. Of those two, the GFS (which has been performing best lately for QPF), delays precipitation onset and places it 30 miles further to the north and west. The UKMET and NAM are both in good agreement with QPF while the UKMET is 70 mi northeast of the NAM with the location of the low. The NGM is the outlier with all parameters and will be discounted.

Adequate instability, with both SBCAPEs and 100mb MLCAPEs of around 1000J/kg, will couple with good shear parameters. A 55kt H5 streak on top of 15kt ERLY SFC flow should result in deep-layer shear to 60kts. Hodograph curves are somewhat of a question, however. Depending on relationship between the speed gradient on the NRN edge of the H85 and H7 jets, SFC-3km SRH's should locally reach 200m^2/s^2. Two FCST concerns relate to the possibility of excessive dry air advection into the target area. the first is the possibility that the DL will advance too far to the NW of the best SFC-H7 flow. The second concern is dry air entrainment into the updrafts, however, it appears as though H7 relative humidities should remain above 50% to the NW of the SFC boundary. A 70kt LLJ will sustain the storm complex as it moves to the E at 30 mph overnight.

- bill

 

[Edward Ballou]

This setup has severe bust potential. Highest CAPE in eastern SD is capped fairly firmly. The highest 0-3km SRH also has very high LCLs. I'm not saying nothing will happen - I'm just wondering if we'll have a repeat of yesterday's events only more south. If I did go out, which I'm debating right now, I'd probably head down to Mitchell area. Hopefully the next model run will look better.

If anyone is headed down this way and wants to kill some time - I'm not doing anything today. Feel free to PM me.

 

[Tony Laubach]

Sitting in Portage, WI on the very edge of reality in terms of making any legitimate target today. Even worse, my analysis leads me to believe that areas in NW Nebraska (near triple point) are the good ones today, a target for which I have no chance of making. I think the entire setup also has a list of problems which could fill a page; high LCLs, cap to name the biggies. Also unfavorable terrain and road network will also create problems in some areas.

Chasing out of Colorado, I would most certainly would target the triple point in NW Nebraska, however, seeing as I am 467 miles out of Mitchell, SD and God-only-knows from NW Nebraska, I think I may write off today and use it to position for upcoming setups.

I do think there will be storms and it won't be a total cap bust, but I think overall tornado potential is slim and while there may be one or two in the area of the triple point, I think today's potential looks rather grim.

 

[Tim Marshall]

TARGET: PIERRE, SD. TIME OF DEPARTURE: 10 AM. Looking at another fun chase day, however, target is still a bit uncertain so I will hold here in Bismarck (in fog) for a while before drifting south. I certainly like the higher dewpoints in MN and backed winds in eastern ND. It is nice to see mid 60 dews again. My concern is the deep trough in the west will tend to keep the upper flow unidirectional, which means more storms seeding each other. So, if surface winds stay backed up here, I'll stay in ND. Also, RUC has surface low and best moisture in ND later today. But, ETA has main surface low in NE CO with best backed flow in SD. Models can't agree even on the short term. Hope to end up wherever the backed surface winds are along the front. TM

 

[Paul Knightley]

Looks a bit messier than it did yesterday evening, with less of a pronounced surface low progged to develop in western Nebraska - this has the effect of allowing the surface front to move somewhat further east...however, through the afternoon, the front looks like it'll stall across S Cent South Dakota, and perhaps even lift a little north into the early evening. Presho will be our initial target (having spent the night in Winner), and will give us better road options. The early evening sees the low-level jet cranking up, and this, together with lowering LCLs could give us a shot at a tornado - perhaps in the Chamberlain area. Haven't got high hopes of storms firing in the warm sector today, but if they do, they should be pretty good.

 

[Mike Hollingshead]

Heading back south to somewhere north of VTN, probably just north on the NE/SD border. I don't care for the flow aloft along the cf, especially as the evening progresses. Might as well hope for tail end charlie. It will also probably help getting into some of the effects of that second surface low. Maybe with the push of the cold front north and the brief pull of the second sfc low, a place in between can get just enough convergence to pop a lone cell. ETA actually prog's warmer 700 temps in e ND than it does in nc NE. Seems like in sc SD there might be a decent mix of convergence and cap.

 

[Kurt Silvey]

For several reasons, the drive, stout cap, post cold front storms, ect, I’m not liking the primary target of central SD as highlighted by the SPC. Instead I’m looking at a secondary target of nc Iowa. Surface cape totals in excess of 4000 j/kg, dew points above 70 F, and a well timed upper level jet streak in the left exit region will help over come the 10 C 700 mb cap. LCL’s around 1100 m and LFC’s below 2000 m, and 3 km helicity of 270 m2/s2 will help develop surfaced based storms with rotation around 00z. My initial target is Mason City, but I’m still undecided about leaving the house, I may go to the pool with the kids and wait for tomorrow and Tuesday.

Edit: Forgot to note a 6 km deep layer shear of 34 m2/s2 should aid in supercell development. Hey, it’s May and anything can happen!

 

[Kurt Silvey]

There appears to be two outflow boundaries left hanging in northern IA and southern MN as seen on Sat and WV images. If these can hang around for a while they could serve as a point of initiation later on. SPC has also moved the “SEE TEXTâ€￾ area toward the east, so the western 2/3’s of IA are now in the outlook area. Time will tell.

 

[Amos Magliocco]

I'm in Sioux Falls, too unimpressed with the displaced shear & instability to move west, and too frustrated about giving up on this pattern to make the only smart choice: get on the highway and head south and not stop until my driveway in Texas.

I don't have anything to add concerning today's potential; I don't see much and the 15z RUC looks worse than the 12z in terms of mixing out the dewpoints and displacing moisture even further east of the flow aloft. No sign of convection even by 3z. With that, what I had pegged at about 10% chance of a lone supercell drops to 5% in my mind, with tornado potential less than 1% for the Valentine to Bassett to Winner area I was considering. I haven't looked at ND; have no intentions of going one more inch north.

I wish I was in the Texas panhandle, where lo and behold on the weekend that LBB's tornado climo numbers are maxed out, it should be no problem for caprock chasers to find one or more photogenic LP supercells. I'd say even with the 40F dewpoint depressions, the tornado probs down there at least match ours here in southern SD/northern NE. I haven't looked to see if a boundary is lurking around the canyons. If so, then double it.

 

[Jason Persoff]

I guess I just have to keep reminding myself that years like this make years like 2004 seem all the more sweet. And I've never seen Amos downtrodden, so that's ominous I guess *eep*. But Amos--who'll pull me out of the mud if you're not out chasing? LOL

Okay...looking at the RUC for 00z tonight, I do see some features that bear some attention. First of all there's an unbelievably strong dry punch along E SD/NC NE today and that can serve as a lift mechanism with the potential to develop rotation...in other words, I wouldn't discount today yet. Tds immediately in advance of the punch will exceed 60+ deg. This will also be in the area of the right front exit region of the 500mb jet with slightly diffluent flow forecast in this vicinity to add the potential for more lift.

Admittedly the RUC forecasts no QPF at 00z, but we're looking for isolated cells, not another damned MCS. Would LOVE to see a mesolow forms to add some backing to the sfc winds. For now the winds continue to be forecast to be out of the south. There will be adequate UVVs in this region as well.

Despite very warm 700mb temps, the "perfect cap" of 5-7.5 deg C are ideal for isolated cells, and in fact the RUC forecasts this to be over this area as well. I like the Winner to Mitchell SD line.

Big caveat will be the all-or-nothing nature of the potential today.

Two other side comments: a) I have read several of Bill Schintler's forecast discussions and think they are some of the best around. Kudos to Bill. B) Great seeing Tim Marshall posting on the ST board! For newbies, he and Tim Vasquez were two of the most important players in creating ST back at its inception and he is a highly valued veteran who helped shape most of us chaser's education early on before the internet became so prominent in chasing.

 

[Mike Peregrine]

Just south of Sioux Falls here trying to make my mind up. After looking through 12z RUC, I'm pretty much up in the air about this. The dry slot punching up into SW Minnesota is indeed disconcerting. All that wonderful deep moisture going to waste over Iowa. My initial target was Chamberlain today, but now I'm wondering a bit about moving west. Wondering if there might be enough shear over NW Iowa to pull something off, even if only briefly. I may go ahead and head over to Chamberlain and see if moisture/instability can somehow scrounge enough to allow a storm or two. Ugh. I guess it's just nice to be out on the road.

PS - Dang it's hot and windy.

 

[Glen Romine]

It's not the best looking setup, for certain, but maybe not a complete lost cause with the southern SD/northern NE play. Winds are backing nicely in response to cyclogenesis in northeast CO, and post frontal moisture in the upper 50's to even low 60's looks better even than some of the dewpoints ahead of the front. As deepening continues, should start to see the dry punch air slide back north over the post-frontal moisture and could be enough convergence to pop up a storm or two. Deep layer shear looks quite adequate for storm rotation if something can only get started. Otherwise, convection now developing over the high terrain (and perhaps the Black Hills) should creep out into better moisture, which the RUC does seem to agree with. Otherwise, strong convergence along the frontal zone might somewhere prove sufficient to initiate a storm in NE late today. The LNX radar suggests the southward boundary surge appears to have halted around Brewster or so. In fact, RUC has fairly strong and persistent convergence in around Brewster to Ainsworth area this evening. So, maybe that area is worth keep an eye on as the afternoon prgresses.

Further north - you'll probably want to cross the border into Canada to take advantage of some of the better environment. Vis sat shows a wavy boundary across eastern ND into northwest MN - but surface obs don't show much of a boundary there. That said - obs are so sparce up there that not all may be representative. RUC forecast 700 mb WAA will fight against the strong low-level convergence, but expect the latter to win out soon. Would probably be tough to beat sitting in Devil's Lake are right now.

 

[afischer]

I agree, things are obviously out of synch today in the plains.. with the moderate deep shear/stronger high-level flow west, and the deep BL moisture east. It should be very interesting to see if the cap attempts to break this evening in southern Manitoba, as the triple point low begins to cross the international border. I'd probably be up there if not for the sad high-level flow and questionable deep shear (considering the 13-hour drive)...

 

[Verne Carlson]

We are in Murdo, SD along I-90 at the Super 8 motel with great wifi and a nice shady spot underneath a huge billboard. I'm liking the surface low developing in sw NE trying to swing those winds around to the east again. Tds are okay, always could be higher. Hoping that initiation isn't too late to get anything before dark. Now it's wait and see.

 

[Edward Ballou]

Latest: Small cumulus field developing over Aberdeen, some convection popping up in southwest SD.

Looks like a theta e ridge around Mitchell...still liking that area but not enough to leave the house. I don't want to be chasing into dusk and after dark. So I'll probably just sit here at home and watch things happen. If anyone needs a nowcaster, shoot me a pm.