5/29/2010 FCST: WY/NE/CO

[Chris Hayes]

18z NAM run is showing an area of sub 1000M LCLs over the Sandhills tomorrow. It's not good chase territory when it comes to roads but there's the LCLs are more favorable for tornado development up there.

 

[Stan Rose]

The NAM has been pretty consistent with this setup. Im sticking with my original target of Mullen NE, south of VTN. The warm front NE of lows has been very kind to tornadoes lately (think SD!). Storms could also fire off the Cheyenne Ridge as Andrew mentions, and could get interesting if rooted in that narrow band of sfc moisture up there.

 

[Bill Schintler]

Chase Target for Saturday, May 29

Chase target:
10 miles west of Mullen, Nebraska (60 miles north-northwest of North Platte).

Timing and storm mode:
Storms will fire from north to south along an advancing cold front, with convection initiating in the target area between five and six PM CDT. Initial storm mode will be high-based supercells and discrete storms, with a transition into linear segments by early to mid-evening. Storm motion will be towards the northeast at 30 mph.

Synopsis:
Changes are on the way for the recent blocky synoptic pattern. A persistent ridge dominating the eastern CONUS will finally deamplify and shift to the east. Meanwhile, the last in a series of disturbances will eject from the western trough into the central and northern Plains. This will push a cold front east into the area, with storms firing north to south from the Canadian boarder into central Nebraska. Low pressure will organize over northeast Colorado, and a diffuse dry line will mix eastward into western Kansas and southwest Nebraska. Convection should remain inhibited areas south of I-80 due to a thermal ridge aloft.

Discussion:
Storms will fire along much of the cold front, and the chase target is at the southern extent of convective development, the “tail-end Charlieâ€￾ storm. This is also near the triple point of the cold front and dry line and in a region of locally backing surface flow. The target area is also along the southern periphery of the strongest upper-level flow. SFC-6km deep-layer shear of 30 to 40 kts will be sufficient for storm organization. Strong capping will once again be the rule; however, convection is certain along the front in Nebraska due to strong forcing. The warm sector will remain largely cloud free save for some scattered CU. Along and west of the front, thick CI will reach the eastern Colorado boarder, to a Valentine, Nebraska line by 22Z; but this post-frontal cloud band will not inhibit insolation.

Once storms fire during the late afternoon hours, ample instability will be available for vigorous updrafts. Steep mid-level lapse rates in excess of 8.5 C/km and a 150mb deep well-mixed boundary layer with dewpoints approaching the mid-60’s will contribute to strong instability with as much as 3000 J/kg of MLCAPE. Discrete supercells are likely early in evolution, with an upscale evolution into a linear storm mode. Cloud bases will be relatively high, suggesting photogenic storms while limiting tornado potential.

- Bill

10:23 PM CDT, 05/28/10

 

[Bill Hark]

I think Saturday does hold some promise of chaseable storms including supercells and maybe a brief tornado for parts of southwestern Nebraska and northeastern Colorado after looking at the 0Z model updates. The NAM shows 30-40 knot southwesterly 500 mb flow over the western Panhandle of Nebraska which should increase overnight and the GFS is slightly more bullish for the western Panhandle. The 850’s will be south to slightly southwesterly. A surface low is northeastern Colorado will give backed surface winds and dewpoints ahead will be up to 65. Forecast CAPE will be 1500 to 2000 with decent helicities. Eventually, the front will shift further south but there is a window of opportunity for good storms. Right now, my preliminary target is Hyannis, Nebraska which will change depending on the position of the surface low. Unfortunately, the countryside is pretty but has a poor road network.

Bill Hark

 

[Mike Heitz]

I think its really interesting how the latest versions of the RUC are keeping the lead low stronger around 1000 mb into ND tomorrow not weakening the lead low and having the trailing low strengthen. Latest version of the RUC at 18hrs can be seen here definitely much different from the nam and gfs, and suggests more of a northern threat but we'll see i know the RUC can got a bit nuts on overdeveloping lows or holding on to long for the transfer of energy. http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/ruc/hr3/images/ruc_p01_018m.gif

 

[Kurt Silvey]

Ummm yes interesting .... as Mike noted the RUC is pushing the area of interest further NE into the sand hills. With roads (other than 3 or 4 Hwy's) pretty much non existent, a large, holiday weekend, chaser crowd will be interesting. I'm hoping the GFS has a better handle on this and the moisture & energy can wrap around the surface low in NE CO. Reviewing WV imaging it appears things may be digging more SE than the last nights model runs are projecting. I'm looking (or wish casting) for one isolated storm in the Julesburg to Big Springs area around 00Z Sun. Will head out W on I-80 and make a final decision in North Platte.

 

[Jason Persoff]

I think my forecast may be getting RUC'd-up at the moment...

Pluses this am:
Morning sfc data for the NE PH area and N KS are showing Tds in the 50-60+ range with sfc winds out of the south at 10-20kt. RUC is forecasting EHI over the Ogallala, NE, area to be in excess of 6 (with 0-3km SRH >400) by 00z suggesting availaible helicity in an area of forecast lapse rates between 6-8deg. SBCAPE will be in excess of 2000 along the I-80 corridor. The LSI shows this area to be under a "perfect" capping inversion (LSIs 1-3) that should suppress convection until either convective temp is reached (unlikely) or convergence/upslope forces convection (possible). The 4km WRF is suggesting that isolated cells will develop by around 22z over Sydney-Ogallala line with a possibly more discrete cell just south into CO.

Negatives this am:
The 00z from yesterday show that the GFS solution for a more progressive trough over the NE PH is unlikely, and that the NAM solution was more correct. This am's RUC appears to split the difference and place the trough just off the WY front range by 21z. Looking at this morning's water vapor image, it seems that the more westerly solution is likely the correct one. If the trough can move a bit more east than that, then the NE PH will be under the influence of the right rear entrance region of the jet and could have further lift from that mechanism as well. This morning's 00z KBLF sounding showed very high LCLs (>1500 ft), and this is without daytime heating that will likely augment the T/Td spreads. Last, an sfc backing is going to have to be due to a mesoscale low event since forecast sfc winds are just a mess on the RUC and NAM for later today.

Preliminary Changes to Forecast:
At this point I'm in Scottsbluff, NE, but will likely begin to meander south to Kimball, NE, where I'll try to further target refine.

EDIT: 00z RUC now up. Low pressure now forecast to develop on CO/NE borders with backing winds along the state borders Sidney-Kimball. RUC 500mb are 40kt over the area (weakest over CO, but excellent over the NE PH).

The 850mb winds are downright wonky...in the C NE region there is a brisk LLJ with a small diffluent spur that will feed into the NE PH. However, most of the 850mb winds appear to be cyclonic out of the NNW from WY eastward. That the 850s appear to loop completely around my target area is not favorable...for that matter...it's not even clear to this novice forecaster what to make of this.

Likely in response to the sfc low, and therefore low-level wind shear, the 0-3 SRH and EHIs in the region look terrific...but the 850s feel like a juggernaut.

No change in target for now...will hold in Scottsbluff another hour or so and then likely drift south toward Kimball, NE.

 

[Jason Persoff]

We've targeted Sidney, NE for now. The latest RUC has forecast sfc winds backing in response to the low much further south than I'd expected. It appears as if the best balance of parameters is from Sidney, NE, to Sterling, CO. Heading to Sidney for lunch and then mesoanalysis at that point. While many chasers' appetites have been sated by the previous weeks, for me this is day #2 of a short chase vacation. I'm game for whatever happens...models be damned.

 

[Mark Blue]

Today is definitely a hard forecast. Early this morning I looked at forecast Skew T's for both the RUC and NAM and felt as though Mullen had the best combination of overall ingredients for a possible tornado this afternoon. Thedford also looked decent, but Mullen's hodograph was definitely curved very nicely, so that's where we're going. SPC's Mesoanalysis has winds out of the north further west in places like Kimball and Sidney, so it looks as though the cold front is on the move. The most noteworthy reading I found for Mullen was the LCL's in the 700-800 range versus other aforementioned targets with twice that number. The one glaring problem with my target is the road network. We did pick up a Nebraska Delorme Gazetteer at a truck stop convenience store so we know what the road situation is down to a finer scale. Whatever happens I wish everyone a safe and happy chase today.

Hey Doc - weren't we chasing almost the same territory about this same time last year?

 

[cdcollura]

Good day all,

I am currently sitting and waiting in Hyannis, NE along Highway 2 and near Highway 61. NSSL / VORTEX II has literally invaded the town after I got here.

I am measureing a 61 DP and 90 F temperature. I notice the slow ststionary / cold front to my NW but an interesting confluence line near Whitman (convergence on North Platte radar in clear-air mode).

Also, the RUC has an interesting (supercell-like) blob of precipitation from 21z on to 23z, with a cluster of storms after that right over the Hyannis to Whitman line.