06/07/05 TALK: N Plains

  • Thread starter Douglas Mitchell
  • Start date
For tomorrow's moderate area, wind crossover looks pretty good from 850mb to 500mb, moreso in NW IA and NE NE than SE SD, as far as directional shear. However, low level shear looks pretty suspect as 0-1km progged at only 10-15 kts. Looks like since the surface low has a positive tilt, so surface winds don't really back much. Kind of similar to last Saturday's setup over KS, in that respect.

Although good instability further S in NE, reads like SPC believes moderately strong capping inversion is an issue, so proximity to lift from approaching surface convergence in SD may be requisite to break the cap. Surface moisture convergence looks to be concentrated in E Central SD and far SW MN, while more diffuse over NE. However, always the possibility of a mesolow, outflow boundary, etc. triggering something more discrete further out in the warm sector.
 
http://weather.cod.edu/forecast/ETA/offeta...2_thetae_30.gif

Fine sfc backing to the ne of the low along the wf and I don't see any veering ahead of the dryline.

http://weather.cod.edu/forecast/ETA/offeta..._500_spd_30.gif

I really don't like those backing 500 winds but that is due to the small wave. East of that in ne SD might be game. I could also see that end up being alot flatter(not so backed) across all of SD over the warmfront. The warfront ops look to be just as far from me as the dryline ops. I'm already starting to hate tomorrow. Both can produce, both can go to hell and one can only be on one. I'm already really paranoid about messing this one up. ETA shuts down the dryling through 6z, but that is of little value to a chaser I think. No idea why I even look at precip forecasts. I need a map and a dart board is what I need. Target right now is w-nw-n from here...somewhere in that direction...hehe.

Yeah looking more at the 18z eta and thinking about SD and warm fronts I will be on the warm front tomorrow. Pierre or bust....
 
"Bad" forecast be damned, you can bet your ass I'll be on that warm front tomorrow, looking further west maybe in a triangle from Aberdeen/Huron/Mitchell. The models are really tough pinning a precise location, I sympathize with H. I was pulling out my hair last night trying pick a location. Like Tim Marshall (maybe, probably, not really...) once said, "If it's June, and May really sucked, chase..."

EDIT: 0z NAM out, 991 parking over Pierre, everybody and their mothers to the triple-point. CAP maybe an issue, per usual, I'm just hoping that chasing karma will pull through tomorrow.
 
I'm game for meeting up if any of you are interested. Give me a pm.

Aside from being at work till approximately 4, I'm really thinking we're going to see activity drop south. MLCAPE in the 4000s the further SE you go and surface dewpoints into the mid 60's it looks like. I think we'll see initiation at the points already mentioned, but it just seems like it takes a while for things to get going. Of course my opinion goes with a big disclaimer. We'll see what happens I guess.

Final look for now: Huron to Mitchell, I will be watching. Sticking here and will head west at the first sign of towers.

Good luck all and best wishes for safety.
 
Argh! This one is killin' me. I'm zonked tired and sore from driving -- but the 0Z NAM is finally showing backed winds again up in northern South Dakota. Not a very strong backed 850, but it's not unidirectional/veering as it was on the 12Z run. NORTHERN South Dakota... argh. What a long haul. If I go, I'll probably target along the warm/stationary front... I'm thinking Watertown, SD is a good target from tonight's NAM, maybe a bit west.
 
Chase target for June 7

Chase target:
20 mi south of Aberdeen, SD.

Timing:
Storms will be ongoing to the north and east of an Aberdeen to Watertown line throughout the day, while explosive new convection will form along an outflow boundary just to the south of the target area around 3 PM CDT.

Storm type and intensity:
Supercell storms producing a full spectrum of severe weather, including very large hail and tornadoes. Additionally, very heavy rain will be likely tomorrow night as storms train over the same areas that receive heavy rainfall tonight.

Discussion:
A series of S/WV's embedded in the upper trough flow centered in the NWRN CONUS will eject out ahead of the main vort which will be lifting through WY by 00z tomorrow. At the surface, an outflow boundary will serve as the key focus for tomorrow's weather. There is some uncertainty as to the exact location of this boundary, and NAM guidance is used here as the GFS was too far to the S. MCS development is already underway in NE/SD/ND, and by mid-day tomorrow, these storms will be exiting the NERN corner of SD, laying down an outflow boundary that will be situated along a Mobridge/Redfield/Brookings line by mid-afternoon. NAM and GFS analysis suggests extensive low cloud cover N of US-212 based on H85 RH and UVV fields, however extensive warming of the BL along and S of I-90 throughout the day along with thermal advection into the target area will tend to break clouds up by early afternoon. LCL levels should be in the 1000m AGL range in the target area with the broken cloud cover and outflow-cooled air immediately to the north of the boundary.

Prodigious amounts of moisture and instability will be available for tomorrow's convection. 00Z KABR sounding showed a nearly 150mb deep moist layer along with a surface dewpoint of 59F. Elsewhere in ERN SD, 00Z dewpoints were in the 60F to 65F range, and the 00Z NAM has initialized well to moisture both at the surface and H85 levels. Given advertised widespread heavy rainfalls tonight, it is possible that evapotranspiration tomorrow may result in even higher dewpoints. Guidance suggests MLCAPEs in excess of 4000J/kg by late afternoon, in addition to deep-layer shear to 60kts with the approach of an 80kt H50 jet max, and 0-3km SRH's to 300m^2/s^2, supporting a potentially major severe WX outbreak.

- bill
 
I don't like the timing of everything as indicated by the 0Z ETA/NAM...and then I looked at the GFS. I wish I hadn't done that.

Anyway, it looks like it could be a pretty late show. In some ways, that's no big deal, as there's plenty of sunlight to work with this time of year (and it gives me extra time to look over things in the morning). But, with the strong cap, I'm worried whether or not our upper level support will arrive early enough to aid in initiation. I'm also worried about the front hanging back too far north and west. SE SD is an easy enough drive (2-3 hours), but Pierre's a different matter.

I'm on the fence.
 
Tough call ... Quick look at data:

0z GFS: 0-1 km SRH = 175 m^2/s^2 in central SD to 100 m^2/s^2 further to the east; MLCAPE = 3500 J/kg west of Mitchell to 4508 J/kg in Yankton; 0-1 km EHI = 3-4 west of Mitchell, with 7.7 in O'Neil, NE; LCL = 1200 (1000 north of Mitchell); LFC = 1400-1600.

0z NAM: 0-1 km SRH = 90.1 m^2/s^2 in Yankton to 137 m^2/s^2 in NE SD; MLCAPE = 5000 NE of Mitchell; 0-1 km EHI = 3.5 in Yankton; BL-6 km shear = 40.5 east of Mitchell; LCL = 2000; LFC = 1900-2000. Lid strength = 3 most areas, with 1 north of Sioux Falls.

My interpretation of this mess: I was interested in tomorrow until looking at all this tonight - and now I'm just completely on the fence. Instability and shear look great again - BUT don't progged LCL and LFC heights concern anyone? The cap looks do-able even with a relatively high lid because I think the area will see sun and there will be lots of heat. Looks like stronger helicities to the south tomorrow, with more instability to the north (sounds a bit like Saturday). I think I would probably go with the frontal boundary tomorrow - looks like initial storms firing on the DL will possibly be way west, as in the Black Hills. I think high CAPE/shear combo is more than enough to support supercells ... but I do not anticipate a large number of tornadoes at this time due to high bases. It just seems more likely to me that lines of hail producers will likely develop in this elevated environment. This is a borderline call because I really wanted to come up there, but coming down with a cold now and now feeling unsure if it will truly be worth the trip. Somebody will have to talk me into it before morning, I guess ... we've got about four hours or so. :)
 
Today is about as clear as mud (for a layman like me) - but I've read the Day 1 outlook that Rich Thompson wrote and enjoyed it and agree with it.

I AM concerned about LCL and LFC heights.......I guess that is something that will be resolved later in the day. If I were more knowledgeable, I'd be looking at this morning's soundings.......but I'm not. The models were forecasting a fairly stout cap and I am curious to know whether this will verify or not.......but alarmingly the RUC trend for through the morning at least is to BUILD the cap - almost up to the Canadian border with the +10 line at 700mb. While I know it's June and anything CAN happen - I'm a little concerned about the trend to build the cap throughout the day......that's not going in the right direction.

Of course.......I'm not chasing today.

KR
 
Progged 850mb temps on the RUC model approaching 25 degrees celsius, along with very weak 0-6km shear and LCL levels nearing 1900m (dewpoint depression takes you at least 20-25 degrees) means one thing for me: another day staying at home! Good luck to those who are out today.
 
Progged 850mb temps on the RUC model
Click to expand...

Always wait for the 15z RUC as the 12z has the old garbage still in the background. 12z NAM H70 temps in the +9 to +11 range for the target area are plenty breakable given the forcing. Outflow from the morning MCS has added to the complexity of the forecast. I worry some of the juice will be diverted to the east. Evapo-Trans would compenstate a bit. NAM has slowed things down a notch meaning a target a bit further west than originally thought. Still looking like a favorable set-up and I will simply wait a couple hours to see how things shape up before crusing down the freeway.
 
Originally posted by Jeff Lawson
Things look to be setting up much the way I feared: late, and too far west. I'm gonna pass on this one.
Click to expand...

Sensible man.......

I know that we should wait until newer runs of the RUC come out - but does the 12z RUC depiction of a 95oF/60oF initiation environment across much of northeast NE and southeast SD not scare anyone?

:shock:

KR
 
The setup isn't looking as good to me as it once did, but I still see the potential in it, including the potential for a few tornadoes...

I am currently in Brookings and will probably make my way westward to setup for the day within a few hours...
 
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