04/20/05 FCST: South/Central/High Plains

[Tony Laubach]

Finally! Enough of the 12z ETA is out (from COD) for me to play..

The 500mb hasn't updated to the 36 hours yet, but in glancing at the trends out to 24 hours, it looks as if a 500mb jet max will knife into NE Colorado during the day on Wednesday. This will obviously aid with the upper level dynamics a bit. The models seem to hint at the front not making it too far south, which actually holds me sticking true to the I-76 cooridor from about Fort Morgan eastward and northward. Some of the values have slipped away a bit since last night's runs, including a narrow band of 50s 1km SRH right along where the front is forecasted to be at 0z tomorrow. The 3km SRH has a small bulls-eye of 250 sitting in NE Colorado along the same band as the 1km. CAPE values struggle to make 1000 over most of the areas, and I feel this is due largely in part to the cooler temps behind the front. Theta-E values over 300 are pretty common east of the Front Range, higher as you get further and further east. Depoints are closing in on 50 with a tounge moving westward over the Northeast Plains, so some advection will be occuring.

With this run, I would say the best conditions come together around the Akron/Yuma area somewhere along US Hwy 36 east of Fort Morgan. That's about 90 minutes drive time to Akron; 2 hours drive time to Yuma. An easy target if this forecast holds. Temps are my biggest concern at this point. The front will also play as it moves north and probably undercuts storms with the cooler SFC air. We're gonna have to play on the warm side of the front and hope we can catch the storms in a narrow window as the interact with the boundry. I would still anticipate very photogenic storms and a successful, non-bust chase. A couple landspoutish type tornadoes seem likely given the amount of helicity around the front. Will have to play with the 0z ETA tonight and see how things look in the morning when I can play with the Platteville sounding in the forecasting lab.

 

[Jim Bishop]

It looks amazing for tornadic supercells from northeastern Colorado extending north into western Nebraska and east into southwest Nebraska. Too bad I can't chase

With the approach of the next speed max rounding the southern/southeastern side of the closed low, lee troughing will occure over the high plains of Wyoming, Nebraska and Colorado. This will further enhance the current stationary front which extends east-west over most of southern Nebraska into northeastern Colorado.

A strong capping inversion with 850mb temps betwen 14 and 16C will be in place, holding off convection for most of the day. However, once the speed max/vort max reaches northeast colorado/western Nebraska, orographic lift/frontogenetic forcing will be sufficient for storm initiation. Any discrete storms (supercells) that sustain themselves (don't weaken north of the boundary/get undercut by cool air) will have the potential to produce tornadoes.

Shortly after dark the cold front is expected to advance east, undercutting the convection. Consequently, a large MCC should be present throughout the evening hours as it moves northeast through Nebraska and South Dakota. Large hail, damaging winds and heavy rainfall will be the main concern.

 

[Anthony Silver]

As far as the severe threat goes for Wednesday in the KS/MO region, I think very large hail and damaging winds will be the primary threats considering the shear and CAPE values that are forecast to be in place, however I'm not convinced that there will be major tornado threat with any storms that develop, maybe marginal at best. Thursday on the other hand, looks to be a slightly better shot at tornado activity according to the latest model review I just did. I'm guessing that most of the storms that do develop will be supercellular for a short amount of time and then become more linear and evolve into MCSs as time goes on. It will be very interesting on how this will all play out. If every thing looks good early Thursday, my target area will be between TOP and ICT.

 

[Amos Magliocco]

Well, of course the models don't resolve these setups well until
either right before the event or never, but tomorrow looks very
appealing along the warm front in far western Nebraska. Looks like
enough moisture is going to work its way north of the low and follow
the strong easterly flow into an area of >2000 j/kg MLCAPE and
~100-150 m2/s2 0-1k SRH.

LBF forecast sounding shows LCL around 962m so I'm guessing bases will
be plenty low on or just north of the boundary, with midlevel flow of
45 knots normal to the front. Remember that part of Nebraska is well
over 2000 feet above sea level. Screaming east sfc flow into storms
moving north northeast. Looks like tornadoes to me.

 

[Chris Foltz]

Have to agree with Amos with regard to the model differences. Was looking at forecast soundings little farther west at OGA (Ogallala). ~2500 CAPE, -7 LI, almost 60kt 0-6km shear. Only drawback is LCL is a little high at around 1150m. Wish I lived closer. Could be fun tomorrow though the roads out that way are pretty horrible for chasing purposes. Looking forward to what Thursday will bring closer to home....

 

[Anthony Silver]

The Models for this event are very frustrating :x . I dont think there's going to be an accurate portrayal of what will exactly occur. The SPC outlook has shaded Western NE in a MDT risk area, so we'll have to see how it unfolds tornado wise. The SPC is leaning more towards a larga hail threat, but there's certainly enough instability and lifting that tornadoes could develop. It's too bad that I wont be able to go out that far since I have to be at work in the early afternoon.

 

[Tony Laubach]

Here's to hoping the clouds clear..

1km visible satellite showing a thick cloud deck stretching from the foothills and Palmer Divide all the way into Nebraska and Kansas. You can basically overlay the SPC MOD risk on top of these clouds. If they don't go, neither will our storms. I think they'll be cleared in the next few hours; which at the worst may delay initiation for a couple hours. That's fine by me; gives us more time to position and grab some lunch! Althought that Wendy's in Sterling is a biotch to find!

Glancing at the ETA looking at 0z Thursday (12 hours), it does show a healthy amount of helicity over our target area; closing in on 400 in the 3k and over 100 in the 1k. Cape values are over 1000 and pushing 2500 further north and east. The 500mb winds get stronger throughout the day, maxing out at about 40kts over Northeast Colorado right about 0z tonight. A SFC low is forecasted to be over southeastern Weld county about 0z, which when sat beneath the CAPE and SRH values, would keep my target area near Sterling; moving north and east from there as storms fire. Temperatures are a factor today which goes right back to cloud cover and fog. Clear those out, get some heating and hopefully bump those temps up a bit. The ETA is running dewpoints in the upper 40s (NE Colorado) to mid 50s (SW Nebraska). I'm not thinking anywhere in the target area will see temps at 70 or higher as we are on the cool side of the front and most of the warm temps are being held way to the south. Mid 60s at best for temps today with TDs in the low 50s.

My plan of attack; leave campus at 11:30am and make trails to Sterling. From there, we can reanalyze data, check our barings, and make adjustments if we need to. With the clouds hanging around this morning, it'll take a couple hours this morning for the clouds to clear, which oughta keep initiation at bay for a couple extra hours. That gives us at least an hour or two to hang in Sterling and if convection fires around us, make our way to a target storm and go from there. Verne Carlson will be armed with Baron WXworx, so we'll have live field coverage there. May also put a nowcaster to work for us this afternoon as well. Going to be a fun afternoon!

 

[Bill Schintler]

Chase target for today, April 20

Chase Target:
Fairview, KS

Timing:
Storm initiation initially in SW IA around 3 PM CDT, with convection building to the SW towards the target area through 5 PM.

Storm type/intensity:
Supercells with isolated tornadoes and hail to 2.5â€￾.

Discussion:
Synoptic upper-level pattern is similar to yesterdays, with a continuation of shortwave energy ejecting ahead of the main upper-level circulation centered near the Great Salt Lake. WV imagery showed a primary axis of S/WV energy lifting NWRD towards the NE/KS border. The surface fields are complicated, having been affected by numerous outflow boundaries. One such boundary was oriented along a GLD to 20mi S of MCK to LXN line; while another boundary was noted from just S of ODX to 30 mi W of OFK. Visible satellite showed extensive ST generally NW of an IML to ONL line. TOP sounding showed deep moisture up to 700mb, and a large hodograph loop below 750 mb.

Today, the boundaries will generally merge and drop south, reaching the NE/KS border by late afternoon. A mesolow will develop in NERN KS during this period, and will be the focus for renewed convection, despite an apparent absence of a shortwave in this area. Deep layer shear of around 45 kts, (0-3km) SRH of around 200 m^2/s^2, MLCAPE’s near 2500 J/kG, along with LCL’s AOB 800m will support a tornado potential.

- bill

 

[Amos Magliocco]

Surface trends support this target shifting to the southeast, with the cloud cover helping maintain a cooler airmass north of the front. Surface features are pretty diffuse at the moment but even with a poorly resolved surface low, you can see the wedge of instability pointing in the direction its going, the leading edge of which is around Phillipsburg at 15z.

A nearly 10F tempertature difference exists between stations in the northernmost tier of Kansas counties and those along the front just sixty miles or so south southeast, and from the visible satellite you can see dense cu gathering south of a distinct boundary south of the state line, stretching from Mankato to near Hays at 1532.

I'd ride this boundary across the border, wait for that cu field to thin out until a few areas of convergence make themeselves apparent, then watch the show. I'd adjust my target to around McCook to Beaver City, NE.

 

[Mike Hollingshead]

Amos nails my target on the head(I couldn't agree more). I guess if I had to pick one now it would be the Beaver City area. You can almost see the low spin on satellite in nc/nw ks. That boundary might move a smidge north and set up right on the border, but I doubt much more than that. The models are all weaker with the winds on today's runs so I'm not as excited, but still.....there should be a decent show. I think the instability could wind up rather high in that region which I was't expecting in my last night target around Ogallala. Off to the Beaver City region soon.

Edit: Nick's shape of the day, a Whale, heading west....hehehe.

 

[Glen Romine]

Slow to get a chance to look at things this morning. Biggest concern right now appears to be a lack of focus for convection to initiate, and the southward slip in the apparent instability relative to the much better shear to the north. So, my target would be to try and capture the best combination of these to seperate regions. looks to be pretty good convergence/ moisture accumulation along the boundary from about Hayes to Beatrice (sloppy eyeball estimate) noted by a band of cumulus. Low-level stratus starting to burn off which should allow for decent heating - but water vapor imagery and sounding data indicating strong subsidence placing an ominous cap over the region. To improve deep layer shear, and get out from under the strong cap, I'd be favoring a position in the 'backwash' flow north of the low - where dews are around 60 in the Stockton area with east winds of ~10 knots, with a local theta E advection maxima. Very concerned there will be no convection at all at this point - but if it does occur, I like this region as a target for now.

Glen

 

[Douglas Mitchell]

Here's my first dive into the Target Area forecasting threads, here we go...

SPC has tempered its expectations by lowering the risk down to a slight, although it maintains the 5 percent TOR risk over SW NE. Looking at the 12z runs, it appears that the front will stall almost right along the NE/KS border. One positive point is NAM showing a much better wind profile conducive of supercells and tornadoes as directional and speed shear picks up in NW KS. Big question now is the CAP, it's a little stronger today than in other set-ups this season. I'm going to say Stockton, KS right now as my target.

 

[Amos Magliocco]

This is getting more complicated now. Our upper low is wobbling back into Idaho and that's bad news for the surface features which need some tightening under increasing subsidence per the unfavorable jet quad.

Meanwhile, the MCS in MO looks like a meteor streaking through the sky on the vapor loop--LOL. Check it out:

http://www.ssec.wisc.edu/data/east/animati...goeseastwv.html

 

[Glen Romine]

I agree Amos - this situation looks more hopeless all the time for central/western NE and n KS. Seems there could at least be some supercells farther east, say along the MO river valley - but the low-level shear looks sad there for posing much of a tornadic threat. RUC still hanging to the idea of breaking out convection late in two areas, one near Hayes, KS and the other south of Hastings. Surface observation trends show moisture remaining largely in place, aside from a return back up the MO river valley, whereas the thermal field shows two developing maxima - one behind the dryline over nw OK with a mid 60 dewpoint patch to the east (crossover yielding ~ 4500 J/Kg of SBCAPE) as well as a warm axis developing nearly along the I-35 corridor up to about I-70 then arching NW - and absolute clear sunny skies - except perhaps just a few cu in extreme ne TX panhandle - which would be worth watching. Water vapor loop still showing region of subsidence expanding across the central plains, with perhaps some relief just crossing east of the front range. Further south, weak ascent noted in a band across Texas - where convective intiation looks more likely. Storms that should form in Colorado along southern edge of front intersecting front range could manage a landspout or two, but moisture continues to mix out with time making this less favorable. Surface winds across nw KS could best be described as light and variable right now - really need some serious convergence to overcome the cap that appears to be in place. Actually - just saw there was an 18Z sounding at LBF - that cap is probably holding strong. Wow.

http://www.rap.ucar.edu/weather/upper/lbf.gif

Looking more and more like a very late show with mostly elevated convection developing into a large MCS.

Glen

 

[Karen Politte]

Meanwhile........ :wink:

Gene and I are closely monitoring what appears to be some kind of wave coming into the southern Texas Panhandle that is evident by an area of elevated, enhanced cu. This may bear some close scrutiny considering parts of western Oklahoma have CAPE values approaching 4500 - allegedly. It is unlikely that these will develop into anything unless they become rooted which is doubtful - but it may be a sign of just another type of forcing that may help to get things going down here.

KR