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6/15/06 FCST: ND / SD / NE / KS / CO

Was looking at the 0Z GFS (hope springs eternal) for this coming Thursday, and figured that conditions could be ripe for a possibly productive chase day. With a surface low advancing on that area , and fair mid-level support, maybe something could fire up with SBCAPE progged at 2500 J/Kg? I know it's going to be well capped, too, but with daytime heating forecast to advance into the high 70's or low 80's my interest is piqued.

I'm still on the upside of the learning curve with all of this, so maybe a few of the more experienced among us could offer their input?

I've got a car at the ready, and am hungry for a Northern Plains chase! B)

John
VE4 JTH
 
Was looking at the 0Z GFS (hope springs eternal) for this coming Thursday...[/b]

Same model still showing the same parameters mentioned. The NAM (has come into view and also offers the same plate. Strong cap and instability, resonable shear, surface boundary, solid H50 wave, and a modest 75-80 kt diffluent jet nosing in. Waters a little muddy as both NAM and GFS showing signs of a nocturnal MCS plowing through NoDak before the day heats up. NAM solution would be the best bet as trough cools down the H70 temps significantly by evening in northeast ND. If you're buying the GFS just wait until the next day (for a different thread).
 
It is interesting to look at the surface obs tonight. It is going on 1 a.m. and McCook in sw NE is 88 degrees with a TD of 53. 35 degree dew point depressions at 1 a.m......fantastic. It doesn't look like there is any better air till you get down to the gulf. I'd say the dewpoints out there tomorrow are going to be exceptionally crappy, even with a strong low level jet. There is going to be some pretty nice shear north of the dryline bulge however. It has me tempted to make that drive yet again. I'm trying to figure the odds of a nicely sculpted LP in such an environment. Part of me is thinking even those need better moisture. I'm also wondering just how much work that LLJ can accomplish from now on, especially since the strongest part is never coming right off the gulf. If it is 88 there now and 87 in Hill City(neither are that hot from any big city heat island effects....obviously) I wonder just how hot they will by tomorrow afternoon. I'm not convincing myself of being able to see a pretty sculpted LP in 110/50.

Maybe I'll make the same distance drive to ne SD, se ND. Neither are really all that tempting, espeically after glancing at the 700 temps out there tonight(18c in nw NE??? in not terribly elevated areas). I hate not being able to sit out events no matter how many times I see flow means nothing when there is utter crap for moisture and insane 700 temps.
 
Chase target:
Chamberlain, SD.

Timing:
Storms initiating just west of the target area at 6 PM CDT.

Comments:
A lone supercell should form just west of the target area and will move to the east at 25mph. Additionally, a large area of mostly multicell convection will develop at around the same time from Pierre to Aberdeen to Jamestown, ND. The rest stop just east of the Missouri River and on the south side of I-90 offers a great view to the west.

Discussion:
A number of disturbances in the WRN trough will affect the WX in SD today. WV imagery shows a broad band of assent extending from NERN CO into SRN SD. At the surface, a nearly stationary CF is analyzed from near Winner SD to just W of Aberdeen. Warm sector dewpoints are holding at around 60F although area soundings indicate that this moisture is skin deep. Model guidance has again gone way overboard with forecasted moisture and attendant instability.

My mid-afternoon, a SFC wave will develop along the CF in SCNTRL SD in the exit region of a compact 55kt H5 speed max. SFC dewpoints AOB 60F beneath mid-level lapse rates of 8C/km will support MLCAPE’s to 2500 J/kg. Bulk shear to 60kts along with (SFC to 3km) SRH’s of 150 m2/s2 will be sufficient for storm organization.

- bill
 
Hmm, it is definatly an interesting setup, I am currently sitting in Jamestown, and debating whether or not to stay right here, since it looks ike the precip on the models is going to break out right over here, but later in the day....but then again, Aberdeen, SD looks very good, maybe even better, and it's within range for us. Theta-E looks great around northern SD...and SE ND.....Vertical Vorticity is decent in bith areas, and the CAPE/MLCAPE is very high, which coul dmake up for the loss of 700 MB shear....It looks like there could be some wall clouds/funels, large hail and damaging winds....I am not sure now about the bases though....they look like they might start out to be non-SFC based, and then lower down some..but nothing for sure...
 
I'm honestly not sure on what to say about today (and not liking any area) given the insane dewpoint depressions (and very warm EML too). With strong diabatic heating generating a deepening mixing layer across much of the central and northern plains, even more moisture could mix out, which will generate even larger depressions. Latest RUC mesoanalysis shows very high LFCs (and LCLs as a result of the dry boundary layer) invof northwest KS convection -- i.e. 4000m AGL or higher -- suggesting that this activity has an inflow source above the boundary layer. At any rate, the low mean BL RH will favor strong cold pool generation (and excessive outflow dominance with any storm).

Now, further north in northcentral SD/southcentral ND... Slightly less intense low-level mixing has maintained relatively-low LCLs, but the insolation has still contributed to a slight increase in the past hour (per RUC mesoanalysis) and this area is also seperated from the best kinematic profiles (with weak deep-layer and low-level shears) and a large amount of CINH still remains across the area -- which is preventing the free convection of low-level parcels (and could potentially inhibit deep convection from developing for the next couple of hours. Perhaps the shortwave perturbation (associated with weak upper-level divergence) moving into the region could remove additional amounts of CINH and allow for LFC heights to lower more, and perhaps generate a more favorable deep-layer shear profile for supercells -- with current RUC mesoanalysis showing weak deep-layer shear across much of the region east of the convergence line). I'd have to say this would be the place to be, regardless.
 
It's nice to see convection finally developing in southcentral ND (with recent mesoanalysis showing weak CINH for a surface-based parcel -- with the 00z ABR sounding being unrepresenitive of CINH for the airmass along the convergence zone) with strong instability (observed ~1700 j/kg on the 00z ABR sounding) across the region. With a weak shortwave perturbation enhancing upward vertical velocities across the area helping to remove some of the negative buoyancy... On the other hand, deep-layer shear is still quite meager further east into the warm sector (~25kts), but could still be sufficient to maintain a supercell structure (with relatively decent ~45kt anvil-level flow). LCLs are pretty low given the small dewpoint spreads (given the onset of nocturnal cooling) -- which could actually help the potential for a brief tornado within the next couple of hours (with strongly backed flow north-northeast of the sfc low in central SD) although the main threat from convection would be large hail.
 
There are indeed a few nice blossoms on GRLevel3 over central ND this evening, but to say that I was unimpressed with the KBIS sounding would be an understatement. The shear we'd all like to see just isn't there (big surprise), so we're just going to end up with a big parade of hail producers.

The hailers I'm looking at now stretch northward from Stutsman county to the Canadian border, and some are showing 60 dB returns. Same old show. <_<

In any case, I might stay out a bit longer for the lightning show.

John
VE4 JTH
 
6/15/06 FCST - A postmortem...

Today was a major disappointment… To start with, the upper support was poorly phased with the surface CF and instability axis. Many folks picked a chase target in the vicinity of the SD/ND border (Aberdeen or north of there). By early afternoon, it appeared as though most of the inhibition had eroded and convection was immanent. A cell went up west of Aberdeen which initially appeared promising. Before long, however, it fell apart. In retrospect, it appears as though subsidence had moved in the wake of a weak H7 wave. H7 temperatures in that area also rose by about 2 degrees C during that period, further increasing the inhibition. The 18Z LBF sounding indicated a convective temperature of 101F, which should have been representative of the environment further to the NE near ABR given similar SFC dewpoints and temperatures (T/Td of about 88/61), along with comparable H85 and H7 profiles and mid-level lapse rates. Even if that area had remained uncapped, chances are that it would have been a multicell mess given fairly high CAPEs juxtaposed with very weak low to mid-level flow (the stronger H85 and H7 flow remained well to the
south and east of NRN SD/SRN ND). I did not pick my target in that area for this reason.

I had picked a target further to the south at Chamberlain, SD. It had appeared that develping SFC low pressure just to the south of there in addition to stronger mid-level winds, due in part to a forecasted H5 speed max, would make this the preferred target location. By early afternoon, however, a number of things conspired against convection there:
1. A thick jet stream CI canopy working NE from NEB and CO. While this was indicative of large scale assent further upstream in SERN CO, the cloud cover served to reduce insolation.
2. A narrow axis of SFC dry air intrusion had worked N from NEB (ONL Td dropped from 57F to 51F in two hours beginning in the late morning). That area is in a serious drought, leading to poor evapotranspiration, and perhaps that was a factor?
3. The evolution of the aforementioned H5 streak was both slower and weaker then forecasted. The strongest assent associated with the entrance region of that max had only reached central NE by 00Z, which fired round of convection there to the north of ongoing storms in NWRN KS.

- bill
 
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