5/24/10 FCST: NE/SD/ND

[Eric Bucsela]

Looks like a very powerful negative-tilt shortwave will rotate through the western trough on Monday. The models have been trending stronger over the past few days/runs with this wave, and slowing it down a bit - the latest GFS is now particularly intense, although the flow ahead of it is mostly meridional.

A surface low should develop somewhere in the vicinity of SW SD with good convergence and decent CAPEs east of it (although not as good as on Saturday, especially according to the NAM, which seems kinda weak). Still a couple days away, but I think it will be interesting to watch how the models converge on this setup.

MODS - Sorry, I forgot to include the word "FCST" in the title.

 

[Jonathan Whitehead]

At this point, this looks to be a a def MDT risk for far NERN CO/NWRN KS/WRN NE.

Very strong jet max will be approaching by peak heating from CO with shear in excess of 75kts. Additionally very strongly backed 850 LLJ will be nosing into the area. This combined with dewpoints in mid to upper 60s and CAPE aoa 3000 will set the stage for very powerful supercells with extremely large hail and potentially strong to violent tornadoes.

NOTE: Storm motions will be in the ballpark of those on May 10th. This is some high shear with very strong upper level winds.

I look for the area around North Platte to Imperial to be the hot spot of the day.

 

[Bill Schintler]

Chase Target for Monday, May 24

Chase target:
20 miles south of North Platte, NE.

Timing and storm mode:
Storms will initiate between 2 and 3 PM and track towards the north-northeast at 35-40 mph into the Sand Hills region, where the road network is generally poor. Supercells will be likely early in storm evolution, with a transition to a linear squall line after 6 PM.

Synopsis:
UA analysis indicates a couple of closed circulations with attendant cold temperatures aloft embedded within a broad, positively-tilted WRN CONUS trough. The first ULVL low is located over SRN CA and NV, while an upstream circulation is tracking S out of WA. Associated with the SRN CA system was a 12-hr H5 height fall of 70 m bulls-eye over extreme SRN CA, suggesting that the trough will continue to dig and become negatively-tilted through 00Z, 05/24. At the SFC, low pressure is centered over WCNRTL CO, with associated pressure falls centered over SERN WY. A nearly stationary front extends E and then NE, bisecting both NEB and MN from SW to NE. A DL extends from ECNTRL CO across extreme ERN NM.

Discussion:
A large area of convection will be ongoing over much of ND and SRN SD N of I-90 during the morning hours. This WAA precipitation will lift N of the area by early afternoon. A CF will extend S of the low where it will intersect a DL in SWRN NEB. The DL will sharpen in extreme WRN NE, KS, and the panhandles; with dewpoints generally in the low-60’s E of this feature. Low pressure will track from the Black Hills area into SWRN ND between 21Z and 00Z, while a secondary wave organizes along the KS/NEB border along the DL. SC will cover most of the warm sector; however, breaks in the cloudiness will allow for sufficient insolation during the afternoon hours. Capping is weak, storms should quickly develop by mid-afternoon.

Renewed convection should initiate first over NWRN NEB and the Black Hills between 18 and 19Z as H7 temperatures cool several degrees with the approach of the ULVL system. Further S, convection will fire along a DL bulge in SWRN NEB as the RRQ of the 80kt H5 streak overspreads the area and H7 omegas increase to -10ub/s. Moderate instability will couple with impressive shear parameters, supporting a full spectrum of severe WX. MLCAPEs should increase to 2000J/kg along a narrow axis immediately E of the DL. Bulk shear will increase to 60 kts as the mid-level streak approaches. Additionally, hodograph curvatures will be maximized N of the secondary low/DL bulge in SWRN NEB. MDL soundings at North Platte indicate an increasing clockwise hodograph curve between 21Z and 00Z, with SFC-3km SRH AOA 300m2/s2 by early evening.

- Bill

12:10 AM CDT, 05/24/10

 

[David Wolfson]

The unidirectional shear and fast storm motion in the NE/SD/ND area bothers me. It looks like lines will tend to form, much like today. I'd opt for farther south with the more conventional dryline synoptics, and would be angling for discontinuous tail-end Charlies moving from about 230 at a manageable 30-35 kts. IMHO the NAM is a little slow to initiate convection to the south and I'd be looking for it by 23Z or so. My target is Liberal, KS. FWIW.

 

[Jared Orr]

In contrast to central NE, the expected low level directional shear in western SD and southern ND is looking sa-weet... Explains the hatched tornado area issued by the SPC. Everything else seems to be coming together as well---lift, instability, and moisture.

I agree with Bill...initiation seems likely around 3ish, which means I better get my lazy chase partners out of bed so we can get moving from where we are now in North Platte, KS.

 

[Brian Stertz]

In a northbound rapid storm motion set up, the key is to find the e-w boundary and get to the backed winds zone for the big tornado threat. Deep layer shear is very powerful today so storm motions in excess of 60mph look quite likely. Massive jet core hits the High Plains this afternoon. Hopefully for chasers the supercells can get up and organized before this blaster hits. If not the supercells will have tremendous lean so stretched out vorticity and updrafts pulling away from ground circulations. I think the MDT is warranted...just have to see how things can initiate and sustain.

 

[Andrew Stoller]

60+mph north storm motions in an area with a meager paved road network - forget it. Forcing will be tremendous today, shear is largely unidirectional unless you get near/north of the warm front or further south where the shear vector becomes a bit more perpendicular to the dry line. I agree Brian - best bet is to park along the warm front in northern South Dakota and wait for storms and haul butt east and west as they pass by at warp speeds.

FWIW, the 4KM WRF does show some more isolated convection firing in southwest KS around 00z. Could be a sleeper play.

 

[Ryan Pfannkuch]

Wow, talk about a broad target area! Not an easy call today. Starting the day out in Colby KS. Plenty of cloud cover, and per 12z RUC/0z 4km WRF-NMM plenty of convection should already break out across western KS/possibly western NE by the late morning/early afternoon hours due to weak capping/ascent from a lead wave. As of 10am, the very first hints of this early convection might be showing its hand across the western OK Panhandle.

So the obvious question then becomes, does the early stuff amount to anything, and if so, what does it mean for later in the day? Will we have multiple rounds of strong/severe convection?

My plan today is to stay south of I-80, and preferably in the northern half of Kansas. So the following doesn't even consider areas well north and south: Considering that even by 0z the RUC only shows the dryline as far east as a North Platte-Oakley-Ulysses line, my inclination would be to hold tight in the Colby area as long as possible. However, with shear profiles as unidirectional as they already are, I don't like the hints of veering occuring in the low levels near the dryline mid-late PM. Clearly the better 0-1km shear/SRH by 21-00z resides farther east, generally east of a line from Lexington NE to Wakeeney KS. Taking the latest HRRR at face value, at least semi-discrete convection should be aligned along this same Lexington-Wakeeney-southward line by 0z. With similar forcing up and down the dryline and points east, I really think today is the proverbial targeting crapshoot...that being said, here is my target area based on the latest short term guidance:

4-county target area in northwest/north central KS: Graham, Rooks, Trego, Ellis

Obviously any effects/temptation from earlier convection could greatly alter these plans, so time will tell...good luck to all, and stay safe driving in the strong gradient winds!

 

[JamesCaruso]

I agree with Ryan P., trying to hold out in northwestern KS as long as possible (in GLD right now). There is no way a drive up to the Dakotas is worth it to me. This system is blasting to the northeast, and I think storms are just going to go up all over the place all at once and end up in a cluster or line relatively quickly. Plus there's convection up there already; I think this is going to be like one of those mid-south systems, where storms start early and intensify over time, with embedded supercells but no discrete storms. Mid-level flow backs from southwest to south, possibly even slightly east of south, by 00Z up in the Dakotas. The best chances for good shear profiles would be along the warm front but that requires going even further north, into northern SD or into ND. South of the warm front in SD and NE the trigger is the cold front, which is going to cause large scale lift over a large area and probably result in a line, with the mid-level flow parallel to the boundary.

Further south, a more "traditional" dry line play is appealing, and the mid-level flow will remain more southwesterly. Northwest KS remains in the right entrance region of the mid-level jet as it moves north.

Question is, northwest KS or southwest KS? The WRF model shows a greater eastward push of the dryline in northwest KS, yet surface conditions right now are sharpening the dryline in southwestern KS. Still, the dynamics are better as you go north.

Problem right now are the clouds, and whether this early weak convection is the start of the main show OR we will have a second round at the proper time.

 

[Robert Edmonds]

Note: 63 in SD across creek/river that feeds Lake Oahe, only one lane is open, and we had to wait for a while at the traffic light setup for the construction. Also, shortly after the bridge there was again another area where one lane was open and we had to wait for the pilot car.

To keep the post appropriate for the thread... Target: Just north of the construction, I like the CU field, good helicity, and I'm enjoying the nice warm moist southerly wind. I'm not much for a talker when it comes to my forecasts.

 

[Justin Turcotte]

My chasing will be limited in time and geographic scope due to not having my vehicle until after 5pm then a midnight shift. Fortunately, the surface front in SD should trickle into southeast ND this afternoon bringing potential action close to home. There is reasonable clearing behind elevated convection rolling through central and eastern ND which will allow for solid instability to coincide with ample helicity along the boundary, provided convectus crappus doesn't develop further south. Upper flow is fairly unidirectional so tornado threat in eastern ND might be brief and limited to cells developing on or crossing the front, however, if the front orients a bit more NE-SW as advertised by some of the guidance then a slightly deviant right mover could track along the boundary and do some damage. As I was typing this SPC has extended the higher pops along the front in eastern ND in the latest outlook. Hopefully storms can hold off just long enough for me to get south of the boundary but if the RUC pans out I might be able to just look out the kitchen window.