2012-10-12 FORECAST: CO/AZ/NM/TX/OK/KS

[Jason Persoff]

Regarding Friday 10/12 (Day+4). (Thanks to Brad Rousseau for pointing out the setup!).

Target: DEN Metro Area

Pity I work that night, but I'm thinking this will be an early afternoon event for me anyway. NAM is a helluva lot more generous with upper levels than the GFS is at this point. Very short window for SVR as left exit region of H5 subtropical jet about the cutoff low transposes over 60-70 deg (over 40-50 deg Tds; theta-e pool up against the Rockies). In addition, at least initial runs suggest low pressure leading to a lot of upslope over the DEN metro area and mini-triple point. Looks like NE Denver metro will be at the point of maximized vorticity. Rotational shear is weak, but I've chased weaker systems. These would be low CAPE storms (especially if the GFS pans out), but they'll be thunderstorms

! Should be able to make it back to work before 00z.

 

[Jason Persoff]

I'm limiting my view mostly to CO/KS borders for now.

00z model runs offer a lot of hope for October supercells. GFS and NAM are more aligned in terms of cutoff low dragging into NM/CO borders by late Friday night. The left exit region of a SSW jet streak will overlay brisk SE sfc winds in the setting of 60s temps and 45-50s Tds as a cold front sweeps down the Rockies.

Prefrontal cells have potential to take advantage of the narrow dewpoint depressions and favorable, but breakable cap. Lack of significant lapse rates will limit CAPE. That said, increasing LLJ, speed sheer, and cooling aloft will all increase the possibility of tornadoes before cells get mushed together into a line.

It's still +72 hrs, but I really like how this is taking shape. Thanks to Alnado for aiding in nudging me southward .

 

[John Farley]

Mods - several other states, including NM, OK, TX, and probably KS should be added to this thread. Looking at this evening's runs, I don't think there is enough moisture for a play near the Front Range in CO. Rather, it looks to me like the best combination of shear and instability will be in the northern TX Panhandle, at least per the NAM. (Still waiting on GFS.) With the sharp baroclinic zone, plenty of moisture, and great directional shear, I think supercells are pretty likely with this setup. Track of the low and where the warm front sets up Friday afternoon will determine where, and with the low accelerating northeastward, it will likely be a narrow window, so you will need to be in the right place. Right now the length of the drive and the narrowness of the time window have me leaning against chasing this setup, but for chasers in places like Amarillo, this looks to offer some decent potential.

 

[DNewman]

I've been looking at the latest severe forecast models for the north central Texas area on Saturday, and it looks like severe weather is also possible for the Dallas,Tx area as well. What do think the tornadic potential is for right now even though its a bit early and things could change?

 

[Marcus Diaz]

Indeed a great setup for the southern plains shaping up. Things are looking to be hairy around here in the afternoon. With 2000 j/kg SBCAPE by noon over Amarillo...it has me a little concerned for the city. It's been a couple of years since I've seen back strong 850s like that in the panhandle. The main 500mb jet looks to remain west of the moist airmass, but I believe its still enough to support supercells. And with the low level veering shear, tornadoes are a possibility in the panhandle.

 

[Greg McLaughlin]

It appears there is a lot of potential tomorrow in the southern high plains, however much uncertainty regarding cloud cover and precip coverage will limit confidence in forecast through tomorrow morning. I really like the baroclinic boundary progged tomorrow, and the forecast vorticity along the boundary with impressive helicity values progged. Mid-level flow looks optimal for storms to have a chance to root along the boundary, depending on how/where it sets up. We already have widespread upper 50s to low 60s Tdps advecting into the Texas panhandle which is very promising. Simply put, the potential tomorrow appears to hinge on the amount of clearing/heating that can take place and the coverage and evolution of convection. There is way too much potential tomorrow for me to pass this up. Casey Zandbergen and I will be departing from Tulsa around 7am.

 

[Jason Persoff]

I have obviously made the gods mad: in addition to working yesterday as part of jeopardy call-in, the evolution of the weather system I'd hoped to chase (and won't be able to trade shifts to go after anyway) looks to be shaping up well.

The nose of the H5 jet streak should overtake southern CO by 21z tomorrow, pushing east thereafter. Fantastic triple point in SE CO is right on the money with Tds in the 50s before sunset. Midlevel cooling appears delayed until almost 00z, but is countermanded by an intense southerly LLJ which should fuel storm intensity. I think my Spidey sense indicates the tristate (CO/KS/OK) area would be ideal between 22-00z tomorrow for tornadic storms.

Closer to home...since I now know I'm compelled to work tomorrow, I'm confined to the DEN metro area. While certainly not an ideal set-up, mesoscale magic could still occur between here and Byers in response to low pressure and warm conditions. The left exit region of the H5 streak may provide rotational shear sufficient for a brief spin up. Here's to hoping anyway.

 

[Bill Hark]

Wow, now that I had a chance to look at Friday’s set-up, Iam very impressed. There will be decent500mb winds approaching the Texas/Oklahoma Panhandles at 40-50 kts from the southwest. Ireally like the forecast SE 850 mb winds across the same area as I have noticedan association between SE 850 mb winds and photogenic tornadoes. Dewpoints willbe around 60 up to the OK/TX panhandle border with backed surface winds per the 00Z NAM. Iam a bit concerned about marginal forecast CAPE of only 500 to 1000 and SRH of150 to 200 in the panhandle along with early convection. Right now, I would target Dalhart, Texas. Anddespite my concerns, I am very excited for those lucky enough to chase.

Bill Hark

 

[Jason Persoff]

Well, I still have to work tonight, but I'm less bummed about missing the "2nd season" tornado chase. There remains a reasonable possibility for thunderstorms in the Denver Metro area. The NAM shows pooling of moisture and elevated temperatures over the DEN area along a triple point. Tds could get as high as 40 with daytime temps in excess of 70 deg. As we move to sunset, more robust low level winds and the left exit region of a LLJ could set up for some brief spinups in limited CAPE (500J/kg).

Meanwhile regarding my original forecast target from yesterday, it looks more like things are going to be farther southeast than I'd thought (by a long shot)...I really like SW KS to OK PH right now for any prefontal activity that can occur. NAM likes a couple areas of precip. Nighttime lightning should be fantastic behind the line. GL to all those out today.

 

[John Farley]

SPC this morning is confirming what I was thinking last night looking at the NAM - wind fields are really favorable for some rotating storms in the Four Corners area. I think that if the sun can get out and stay out for a while and heat up the atmosphere a little, it could be an interesting day in southwest CO and nearby areas. Wouldn't be surprised to see a funnel cloud or even possibly a tornado somewhere, and with the cold air aloft, at the least there should be some interesting combinations of hail, snow, graupel, etc. depending on altitude. Damaging winds also a possibility, as it would not take a lot of downdraft to bring the strong wind fields down the surface. Storms this morning have been trucking north at speeds of up to 55 mph. So maybe, just maybe, I'll have some chase opportunities today even though I blew off the long trek to the Panhandles.

Edit: While I was typing this a SVR was issued for a storm west of Durango. Game on?

 

[Jason Persoff]

Failure analysis mode:

As cutoff lows like to do, it meandered at its own pace and things were out of synch. As the day went on, it became increasingly clear that severe weather wasn't going to come together. Daytime clouds kept temps cooler than expected. I guess that will just have to hold me until spring.