2012-04-26 FCST: CO/KS/NE

[Eric Bucsela]

Potential for some severe on Thursday. I like the negative-tilt trough impacting the High Plains late in the day, putting parts of CO/KS/NE in the left exit region with divergent flow and good directional shear. Instability/moisture are also decent - at least farther south, where NAM and GFS have CAPES over 3000 in OK & S KS, and over 1000 J/kg in parts of E CO.

I'm not clear about the shortwave timing yet - NAM looks fastest, GFS/ECMWF are slower - which will have obvious impacts on initiation. For its part, NAM shows very little CIN in CO and W KS and breaks out precip before 00z. It's a little early for the CO season, but definitely worth watching...

 

[Chuck Robertson]

Potential for some severe on Thursday. I like the negative-tilt trough impacting the High Plains late in the day, putting parts of CO/KS/NE in the left exit region with divergent flow and good directional shear. Instability/moisture are also decent - at least farther south, where NAM and GFS have CAPES over 3000 in OK & S KS, and over 1000 J/kg in parts of E CO.

I'm not clear about the shortwave timing yet - NAM looks fastest, GFS/ECMWF are slower - which will have obvious impacts on initiation. For its part, NAM shows very little CIN in CO and W KS and breaks out precip before 00z. It's a little early for the CO season, but definitely worth watching...

There are a few things really puzzling me about the SPC forecast for this system Thursday. When I read Eric's observations..."negative-tilt trough impacting the High Plains late in the day", and "CAPES over 3000 in OK & S KS", which I totally agree with, I could not help but realize these are very similar attributes that are often associated with even High Risk days. Yet, the SPC is only going Slight and putting out a measly 15% svr area.

So what is so severely missing from the list of ingredients? Perhaps the quality of the BL moisture? Or perhaps SPC is remaining in a "conditional" mode given the strength of the cap. Even if the cap can break, perhaps they are thinking storms would be quite isolated, therefore not warranting higher probabilities.

If the cap can break, which I think it will, then perhaps things could get far more interesting than what the SPC forecast might lead one to believe. This system could have "surprise attack" written all over it.

 

[Will Campbell]

There are a few things really puzzling me about the SPC forecast for this system Thursday. When I read Eric's observations..."negative-tilt trough impacting the High Plains late in the day", and "CAPES over 3000 in OK & S KS", which I totally agree with, I could not help but realize these are very similar attributes that are often associated with even High Risk days. Yet, the SPC is only going Slight and putting out a measly 15% svr area.

So what is so severely missing from the list of ingredients? Perhaps the quality of the BL moisture? Or perhaps SPC is remaining in a "conditional" mode given the strength of the cap. Even if the cap can break, perhaps they are thinking storms would be quite isolated, therefore not warranting higher probabilities.

If the cap can break, which I think it will, then perhaps things could get far more interesting than what the SPC forecast might lead one to believe. This system could have "surprise attack" written all over it.

The biggest problem that I see and I assume is reasoning why this remains a slight potential is the poor moisture return. Add to that low helicity values in NW KS, E CO, and SW NE, with dewpoints that will struggle to reach 50d, I think the 15% and slight are justified at this time. This is per the 00z NAM run for 00z Fri. Granted there can certainly be some upslope effect in the mix but this is far from a high risk day looking at the models. I would be downright surprised if a moderate was even in the thought process at this point. Let's hope to see some better moisture return in future runs and then I will start getting giddy.

 

[Chuck Robertson]

The biggest problem that I see and I assume is reasoning why this remains a slight potential is the poor moisture return. Add to that low helicity values in NW KS, E CO, and SW NE, with dewpoints that will struggle to reach 50d, I think the 15% and slight are justified at this time. This is per the 00z NAM run for 00z Fri. Granted there can certainly be some upslope effect in the mix but this is far from a high risk day looking at the models. I would be downright surprised if a moderate was even in the thought process at this point. Let's hope to see some better moisture return in future runs and then I will start getting giddy.

Please bear in mind I am not saying a high risk is warranted. Perhaps not even a moderate. I'm just expressing that these are some pretty robust attributes, and therefore attention should be payed to such a system kicking out into the plains nearing the peak of the season. But still, I remain that only 15% seems surprising low to me, moisture limited or not.

The 48hr NAM valid Thur evening display much better Td's at the sfc over OK and southern KS, at mid 60's. Perhaps a bit overdone? Perhaps, but maybe not. Also a narrow area of CAPE AOA 3500 in NW OK and SC KS. NAM breaks out convection in the area as well. Sure, storms will start out high based, but could lower toward late evening.

I'm still having trouble turning my back on NW OK and SC KS.

 

[Brett Roberts]

There are a few things really puzzling me about the SPC forecast for this system Thursday. When I read Eric's observations..."negative-tilt trough impacting the High Plains late in the day", and "CAPES over 3000 in OK & S KS", which I totally agree with, I could not help but realize these are very similar attributes that are often associated with even High Risk days. Yet, the SPC is only going Slight and putting out a measly 15% svr area.

So what is so severely missing from the list of ingredients? Perhaps the quality of the BL moisture? Or perhaps SPC is remaining in a "conditional" mode given the strength of the cap. Even if the cap can break, perhaps they are thinking storms would be quite isolated, therefore not warranting higher probabilities.

If the cap can break, which I think it will, then perhaps things could get far more interesting than what the SPC forecast might lead one to believe. This system could have "surprise attack" written all over it.

It's probably a combination of the conditional nature of the threat and lackluster low-level wind fields, as predicted by the GFS and NAM. Without a real longwave trough established yet over the Rockies (come Thursday), the entire setup hinges on a very fast-moving shortwave which will need to be timed almost perfectly in order to maximize the severe potential. If the consensus timing were about 6 hr. faster than it is now, I'd be more excited. As it stands, the cap will certainly be an issue, as well as the tepid low-level response to the late-arriving energy.

Because this potential event is forecast to affect the High Plains, I'm still keeping an open mind WRT chase potential for Thursday. Both the cap and weak synoptic-scale low-level wind fields are issues that can be somewhat less of a problem there than farther east. Re: tornado potential, LCLs could be a third issue to tackle even if we do get initiation -- though, again, you sometimes have more leeway with that out in the higher terrain.

 

[Seth Edge]

Its not as much moisture return as its near 90 degrees if it could cool off about 8 or so degrees and the cap wasn't as strong could be worth chasing. The dew point and temperature are fairly far apart therefore high LCL's thus lower potential for tornados as you all probably know. And a fairly strong cap is in place with weak wind shear therefore only need for a slight risk and will probably be moved further south or extended next outlook as the cap seems its going to break there as well .But looking at the 0z model I believe the cap will break by sunset just clicked on a random sounding not that strong at 7 pm and the instability is there just weak wind shear and high lcl's maybe a brief tornado if everything can line up, but I wouldn't put money on it at this point.

 

[Tom Dulong]

‎***Microforecasting/Wishcasting for Northeast Colorado***

Close look at the 12z 12km NAM for 6pm tomorrow evening (00z/27th) in northeastern CO is encouraging. N-S oriented surface convergence zone along Front Range...moderate mesocyclone vicinity of Denver...sfc dews not great (35-50 deg F) but sufficient for severe wx this area. Also see strong gradient in low level moisture/CAPE and relative minimum in CIN. Surface storm-relative inflow 30kt with 0-1km SRH 100-150 m**2/s**2. Timing will be everthing...slower and the CAP may win til arnd sunset...faster and we may be treated to some nern CO magic!

My inital target will likely be just east of Denver Int'l Airport.

 

[Adam Simone]

Looking at the 12z NAM, I'm definitely not too excited about tomorrow but there is some potential in SW Kansas and in the OK/TX Panhandle. This mornings NAM is showing the cap eroding in that area by 00z and precip breaking out. Looking at the Forecast Sounding for Guymon, OK at 7:00pm tomorrow it's showing CAPE values around 2,800 and CIN around -39. 1km Helicity is around 90 which isn't terrible but LCL Heights of 1,392 is getting a little high. The LCL Heights will obviously lower as the day time temps decrease but the NAM is showing the cap strengthening again by 03z.

 

[Bryan Stokes]

I just got a chance to look over the 36-hr 12Z GFS and NAM while I was eating lunch. I can see why SPC is elevating their concern in SW KS and the OK Pan. It looks to me like moisture may indeed make a decent return. Seasonably warm temperatures, combined with a pretty stout capping inversion, well cause CAPE to reach 2,000-2,500 j/kg. Sfc winds and 850mb winds are strongly backed, and Bulk Shear will be excellent at nearly 60kts.

I'm still concerned about the 700mb temperatures. The models are indicating 700mb temps in the 10-11 C range. According to what I learned from Jon Davies, once you get above 10 C towards the end of April, the CAP may be too strong for storms to fire. (as a general rule of thumb.) I'll have to keep a close eye on the 700mb temps, which may very well be my go/no-go call on Thur morning.

Bryan

 

[Marcus Diaz]

Bryan nailed it for tomorrow. I just got to skim over the 12z NAM. Strong forcing along the DL will aid in cap breakage. 60° dews and the capping inversion will pump up MLCAPE around 2000-3000 J/kg. Triple point looks to setup in SE CO. I believe there might be some storms to fire in the northern TX panhandle - SE CO during late afternoon/early evening. Storms will be high based at first, but as the sun sets...tornado chances go up. Vort max will be over the area, and the LLJ will ramp up. A little concerned about the CIN filling in after 0z, but any storm alive and healthy after 0z will have a decent shot at dropping a tornado. Probably will play this as a local chase, in which I mean I'll go after I get off work. Seeing how I get off at 5, and the target is only a couple hours away.

EDIT - Mods or someone should probably add TX and OK to the title.

 

[Eric Matthews]

I was very bearish on this earlier, but the 18UTC Wed 25 Apr Nam has me very pessimistic. Looking at the 00UTC Fri 27 April timeframe...
There is not a CAPE over 1,000 north of the KS/OK state line, the EHI in non-exixtent at 1km, surface LCL's are 1500m or higher north of the KS/OK state line, surface dewpoints are in the 50 degree range, but as mentioned earlier, this is often sufficient for this area. The only decent hodo's I've found have LCL's over 2000m.
Unless there is a drastic change on the RUC tomorrow morning, this is not a day I will be chasing.

 

[Jeff Passner]

I have to say "no go" on this one... There's not much I really like except the SE Upslope winds. The wave timing is about 3-6 hours too slow and will provide very little lifting, although there is moderate upper-diffluence. There is little directional shear in the lowest 1KM of the atmopshere and 700 hPa winds are forecasted to be from the south at 0000 UTC the 27th. Additionally, the current 0200 UTC satellite shows a heavy shield of mid- and high-level cloud cover which would inhibit the needed heating to break the cap. And finally, it looks like cloud bases will be high to start with as moisture is not very deep. Soundings at DRT, BRO, and CRP show very little moisture although FWD does have better moisture. There are 70 dew points on the Gulf Coast now which is adequate, but it has a long way to go and probably is not very deep based on the RAOBs in south Texas. I think there will be some high-based severe storms on the Colorado-Kansas border possible down into the NW Panhandles later, but right now this one does not seem worth the effort and gas money if a long drive is involved. Obviously if you are already out there or nearby there might be a nice supercell or two to enjoy.