Forecasts

2hr RUC Surface-based CAPE valid 20Z 06-June-06

After a disappointing day in south central NE yesterday including 14+ hours on the road, we’re staying put today in KTGX and hoping the cold front fires not far from home.

The cap is quickly eroding, great instability parameters, low LCLs (much more impressive than yesterday’s in NE) and the front is finally on the move. Shear is on the low end so the tornado threat is minimal, but some good structure could be in play. Initiation should come anytime this mid-afternoon, although some cloudcover east of the KC metro may inhibit heating in the regions of the best instability and moisture convergence around KC when the front comes through.

Day 1 (and likely the only day) of our chase vacation is underway with a preliminary target of Hastings, NE as a starting point with revision to the S as needed…given our morning placement, we’d rather be on the southern end of this show, hoping to catch the end of the line rather than racing to the northern edge of the best instability (Norfolk, NE and northward?) as that would be a race against time.

Ongoing overnight convection (MCS) has slopped up the surface data and impeded the models from having a good grasp of the best instability placement for later this afternoon. However, we’re encouraged by the outflow that should be set up on the western edge of this MCS and be available to interact with the cold front as it pushes SW this afternoon/evening. Caveats include the exact placement of this afternoon’s boundaries as well as how quick the clearing comes about. I’m encouraged by the decent decay rate and SW movement of the current convection as giving us a good afternoon window for some heating to encourage surface-based cell growth.

With a cap eroding in the mid-afternoon, the mid-level jet coming into play at ~50kts, a nice low-level jet nosing in through eastern KS, initiation should occur in the 3-5pm timeframe. However, in the last couple of hours, VIS SAT trends do indicate some blossoming convection on the SW edge of the MCS in Western NE and KS which is not what I’d like to see at this point in thte game…clearing and a cap is what we need this morning.

Depending on how far north we travel, the mean storm motion of ~SW should allow us to ride the convection home and if nothing else, provide a nice opportunity to experiment with some lightning photography this evening.

As this looks like our only real SVR shot during our chase vacation window (6/4-6/7), we’re optimistic about the day.

2 m Td; 12 hour NAM valid 00Z SUN … Will this moisture verify?

Today’s shear profiles and instability parameters are looking good as today’s system sets up, although much of KS will be under the CAP, keeping the best of the show on the N and E fringes of the instability. I’m hoping a few nice cells can get rooted and push through the cap in extreme SE NE in the late afternoon, by which time the cap erodes nicely ~00Z throughout much of NW MO so the show should be underway by then.

I’m not sold on the northern tier of the SPC’s MDT risk…there is just no moisture there. The NAM is still out to lunch when it comes to Td’s. Current readings in the upper-50s throughout much of NE KS … even as low as the low-40s in SE NE - the heart of today’s MDT risk as targetted by the SPC. Evapotranspiration isn’t going to do the trick this early in the season, nor is advection. If there is to be a show today, it is going to hug the edge of the cap just north of the KS/NE border and fire into NW MO and the IA/MO border.

I’m not holding my breath for this show, nor am I packing up and heading out quite yet. We’ve got several errands to run and other work to get done around here, so I’ll wait this one out for now and see how things are lookign in a few hours.

Tomorrow is going to be an active day. The dynamics of this system are huge - a ~982mb surface low will slide into central Nebraska, and with it bring the forcing needed to get this juicy air going. Here in northeast KS, the earlier concerns have been resolved: namely the surface moisture: the last system really flushed it out (temps dropped to 30° overnight last night in the dry environment!), but it has rebounded nicely as expected, with Tds in the mid- to upper-50s this evening. A month ago this would have concerned me, but since 3/12 - not only with that event, but several since - I have learned to not be surprised by the quick moisture return that can happen in a single overnight once the LLJ fires up!

Comparisons have been made to 04/11/2001 and, while I could not recall that particular event, upon viewing the surface map and the SPC storm reports pages, I can see the similarities: A particularly potent surface low and two distinct targets - one north, one south.

I see this system playing out with two main targets - one being the first initiation to the north: near the triple point, the other being the southern end of the line that fires much later in the afternoon/early evening. The best surface convergence certainly is not here in KS - we’re sandwiched between the best targets, in my opinion, in a region lacking the best directional shear - an essential ingredient for tonadic supercells. First, the northern target.

If I could chase, I’d love to spot the eastern NE target (~LNK to OFK) if for no other reason but the s l o w e r storm motion vectors. Several of the big events so far this season have have been headlined by storms that were flying at 50 to even 75 mph! Regardless of how good the road grid is, that is tough to chase. Storms that fire along the dryline bulge tomorrow here in Eastern KS, Western MO, and even more so the targets in OK and AR are going to be cruisin’. Instead, I’d like to be on the northern target where storm motion will be a more reasonable 25-35 mph.

The dynamics are going to be wild in Nebraska with such a strong surface low, but with that comes some degree of uncertainty with the winds. It isn’t unheard of for these targets to be a bit of a bust in terms of a significant tornadoes due to wind shear that shreds the cells before they can get deeply rooted. Additionally, the window of opportunity for the northern target is somewhat limited to about a 6-hour time frame stradling the mid-afternoon, shutting off completely when the low continues to stack vertically, losing the needed large-scale dynamics, no to mention that show will shut off quickly once the daytime heating is lost. On the upside, moisture convergence is good and the nice upper level divergence created by the exit region of the jet progged to be in place ~18z.

In terms of Eastern KS, the threat is very real, although it won’t be the region of the best dynamics. Storms dancing along the surging dryline bulge will have to be well-timed to hit the best of the dynamics and luck into some localized enhanced directional shear, but that wouldn’t be surprising. I think the focal point - the centerpoint - of tomorrow’s storm reports will be to our North and South though.

The later and more southern target looks a bit juicier in far eastern OK into AR and also including much of MO. Where supercells quickly fire from clear air and blast ENE, there will be a good evening show into the early overnight hours. I haven’t focused much attention on this area, but am far from discounting it. I feel the TOR threat is higher for this area than the northern target, at least in terms of an outbreak per se as this show gets going later in the afternoon and is likely to include several discrete and deeply-rooted supercells that pop from clear air.

While I’m not completely sold on the need (or rather the justification) of a HIGH risk for tomorrow, I wouldn’t at all be surprised to see that show up with the first Day 1 Outlook overnight.

I will not be chasing as I’ll be working through ~4pm and am simply not geared up in chase mode yet, but will be doing what I can to stay on top of the situation. All this, and the real front won’t even pass until Friday. I’m still learning the dynamics of the dryline, and they are fascintating.

04/06/06 is already looking a lot like the past couple of outbreaks we’ve had in the OK/KS/MO region, including 03/12. While I admittedly have looked at only a few products, it appears the big picture dynamics are coming together for another deep low to our north and good dynamics in place through KS and OK. Moisture should slowly rebound over the next few days following today’s flushing out by the vigorous NW flow. Additionally, nice instability numbers are already appearing on the map.