5/21/08 FCST: NE/KS/CO/SD/IA

[Mike Kovalchick]

I'm currrently on Route 80 nearing the Eastern Iowa border....headed for the area North of Cheyenne and just West of the NE border region for chasing tomorrow afternoon.

Looks like an okay setup. Good chance of some fairly vigorous supercells. Cap will not be a problem. Hail probably will be. Storm motion should be just about straight North. The road network in the area does have a couple of different N/S routes to choose from so hoping for a good start to my chase vacation.....

 

[Bill Schintler]

Chase Target for Wednesday, May 21

Chase target – TX:
Kelton, TX (11 miles northeast of Shamrock along I-40).

Timing and storm mode – TX:
Supercell storms may fire along a dryline between 7 and 8 PM CDT. A threat of tornadoes should increase just after sunset as cloud base heights lower and a LLJ increases, but while updrafts continue to tap into moist boundary layer moisture. A bust is a concern with these storms.

Chase target – NE/CO/WY:
Scottsbluff, NE.

Timing and storm mode – NE/CO/WY:
High-based convection will develop first in ERN WY and over the Rockies in NRN CO by mid-afternoon, and then develop eastward into the deeper moisture through 5 PM CDT. Storm mode will be primarily multicell, with a few embedded supercells. The Scotts Bluff National Monument, located next to the city of Scottsbluff, is a great location from which to observe the developing storms.

Synopsis:
ULVL ridge axis continues to shift slowly EWRD as the WRN CONUS trough deepens, with 60-70m H5 12hr height falls concentrated over NV and UT. Gradual mid-level WAA is underway over much of the high-plains as flow shifts to the SW, and this is contributing to increasing mid-level lapse rates over CO and NM. LLVL moisture remains limited, with 10C H85 dewpoints limited to SRN TX; along with SFC dewpoints in the mid-40s in the TX panhandle NWRD into WRN NEB and ERN CO. Return flow is underway in the high plains. Convection ongoing in NERN NM is connected with an UA disturbance located S of the stronger flow and E of the trough base, as indicated on the WV loop; and thunderstorms should continue through the overnight hours courtesy of a 35kt SERLY LLJ. MDLs have initialized well with LLVL moisture as well as convective trends.

Discussion – TX panhandle:
This FCST is complicated by the presence of boundaries left over by ongoing convection in the NRN TX panhandle. Strong LLVL moisture advection should occur with a 30-40kt SRLY LLJ over the area much of the day. By 00Z, H85 dewpoints AOB 15C and SFC dewpoints AOA 60F should spread into much of WRN OK and extreme ERN TX panhandle. A signal of the moisture return will be an axis of ST along the Red River at 12Z, which will lift N into OK by early afternoon. Capping is a significant concern as H7 temperatures AOB 15C surge into the area and convective temperatures rise into the upper-90s within a zone of large-scale subsidence in the right-exit region of the jet streak, however insolation in the TX panhandle along with orographic lift east of the Caprock where SERLY flow exists may be sufficient to achieve initiation. The intersection of an advancing DL and an OFB from nocturnal convection along I-40 should be a focus for convection. Further S, forcing will be weaker, which should prevent convection there. Instability and shear appear sufficient for supercell storms, however diurnal tornadogenesis may be hampered by LCLs in the 1500m AGL range. A strong SRLY LLJ above orographically enhanced backed SFC flow will result in large hodograph curvatures. After dark, LCLs will lower while the LLJ strengthens, increasing the chance for tornadic storms before convection weakens after 03Z as the LLJ refocuses further N and E.

Discussion – WRN NEB, SERN WY, and NERN CO:
Impressive large scale assent will overspread the region beneath the left-exit region of a 80kt H3 streak and a fanning diffluent pattern. Low-pressure will rapidly develop over SERN CO, while bringing strong SERLY up sloping SFC flow and moisture return to the WRN NEB panhandle. By 22Z, dewpoints should rise to AOA 50F, contributing towards an area of modest CAPEs of 1000J/kg into the region. Storm mode should remain primarily multicell and high-based given the magnitude of synoptic forcing along with modest dewpoints, however LLVL hodograph curvatures beneath a 35kt LLJ suggests embedded supercells.

- bill
10:59 PM CDT, 05/20/08

 

[David Wolfson]

Currently in Tucumcari, NM. The approaching dynamics has kicked off a line approaching severe with some elevated rotation of individual cells approaching in the next few hours. Dews are up to 50.

My original plan for tomorrow was to head north toward Goodland/Colby to arrive for the late show in far sw NE and join the fest the end of the week. However as of this evening the action this evening suggests increased mid-level cool advection which may focus the higher velocities a bit farther south and east than progs have shown up to now. The latest RUC and ETA at 00Z also are suggesting a limited CAPE axis of 1500+ j/kg with minimal CIN nosing upslope on more-or-less a Canadian - Boise City line.

As of now I'm looking at a watch-and-wait afternoon target of Guymon, OK, hoping to see 50+ kts at jet level with some divergence, upper 50s dews, and quite breakable 700mb temps of 8C. Helicity will be ample for rotation if something gets going.

Suggest extending the forecast area to include OK and TX.

 

[Mark Farnik]

For what its worth, there were a number of high based storms, one of which that briefly took on supercellular characteristics, that tracked across far southeastern Wyoming and north central Colorado earlier this evening. In their wake, they left behind a few outflow boundaries over eastern Laramie County, WY and northeastern Weld County, CO. These could act as potential focusing mechanisms for convection tomorrow afternoon. If we could get some decent dewpoints to advect into the area and the cells that form can root into those boundaries, there might even be a sleeper rotating supercell or two with brief tornado potential in the NE/WY/CO border area. As of now, my plan is to leisurely amble up to Kimball, NE in the 3 to 4 p.m. time frame and go from there.

 

[JR Hehnly]

I'm going to be stuck in Oklahoma, still looking for that southern surprise. Cap will not break without some forcing mechanism, but that looks limited to some leftover OFBs from tonights convection. I am happy to finally see some models breaking out precip in sw and w oklahoma. This image gives me at least a bit of hope:

 

[Mark Farnik]

Today's target: Pine Bluffs, WY. Initiation expected by 5 p.m. MDT.
If that model forecast comes to fruition, there should be a nice line of supercells from near Greeley, CO north/northwestward along the dryline towards Douglas, WY by late afternoon.
This morning's Boulder AFD had some intriguing discussion in it:
INITIALLY THE AIRMASS ALONG AND EAST OF THE DRY LINE WILL BE CAPPED HOWEVER BOTH THE NAM AND RUC SHOW THE CAPBEING ERODED AFTER 21Z WITH CAPES RANGING FROM 1500-2000 J/KG. THUSSHOULD SEE SOME ISOLD-WDLY SCT TSTMS DVLP BY LATE AFTN WITH SVRSTORMS A GOOD BET AS SHEAR PROFILE IS FAVORABLE.
HELCITIES ARE FCST TO BE SUBSTANTIAL AS WELL SO CAN NOT COMPLETELY RULE OUT A FEW
TORNADOES, ALTHOUGH THE LCLS WILL BE SOMEWHAT HIGH.

Seeing as that the Boulder WFO tends to be on the cautious side with the way they word their AFD, the fact that they are even mentioning the possibility of tornadoes is a good sign. Right now the region is sitting in the mid 40's dewpoint wise. If we can manage to get upper 40's to low 50's dewpoints to advect into northern CO/eastern WY by late this afternoon/early evening as the surface low deepens over eastern CO and begins rapidly enhancing moisture return, and given helicities in the 250-300 m2/s2 range, I wouldn't be at all surprised to see a brief tornado or two with any supercells that fire along the dryline, especially any cell that interacts with the outflow boundaries leftover from last night's convection near the Cheyenne Ridge. With modest (but not terrible) dewpoints and somewhat high LCL's, I'm expecting widely scattered, rotating LP to classic supercells with a primary threat of large hail and secondary threats of brief tornadoes and damaging winds over far north central Colorado into southeastern Wyoming between 5 and 10 p.m.
If y'all see a black and silver Subaru Forester with Colorado plates, stop and say hi (unless we're actively pursuing a storm, then you can just wave!)

 

[Andrew Stoller]

One thing to look out for is a storm firing on the palmer Divide out towards Limon, CO. This setup is eerily similar to May 10, 2004 when everything was supposed to go north by the Cheyenne ridge but a cyclic beast went up along the Palmer and dropped multiple tornadoes. Moisture is lacking more though today - the NAM however does show 50 degree dewpoints in eastern CO by mid day.

The orographic component of the raton mesa, the palmer divide, and the cheyenne ridge is remarkable.

:edit: we need to get this crappy stratus deck to move off the front range quick though. As I look to the west towards the mountains, I see clear blue sky.

:edit2: Oops, looks like Verne Carlson beat me to it! He can take credit for the palmer divide sleeper if it happens.
http://stormchaserco.blogspot.com/

 

[Bob Schafer]

I was planning to head up towards NE CO/SE WY late this morning, but now it looks as though the moisture is really going to be lacking. 50 is sort of the magic number for Td's in this area, IMO, and the 12Z run of the RUC advertises no more than mid to upper 40's for 00Z. Looking at obs, you generally have to peek all the way down to I-20 to find any moisture at all. There are a few 50's N of there, and it is headed the right direction, but it ain't gonna cut it. Not today. By 2-3Z things might really tease us, especially with all the daylight, but... I'll save all my bullets for the next few days, unless something pops up within 50 miles of here.

I had also considered driving down to Childress, where there's awesome instability progged as well as possible convection, but with lousy upper dynamics there as well as the good possibility of it being a cap bust, I said to myself "nah" to the 700 mile roundtrip.

 

[Andrew Stoller]

Well, a May 10, 2004 repeat is officially ended - dryline is well east of Limon. Burlington, CO has 81/50 and the cloud deck has cleared to the southwest - where a nice cumulous field is going up around central/south central CO along the dryline.

I'd keep east central CO in mind, maybe around Kit Carson to Burlington this afternoon. The stratus deck is still pretty thick in northeast CO/southeast WY - but is clearing. East central CO will have had more clear blue sky.

Just some thoughts