Interesting near-end-of-season setup

We've both been pretty quiet here recently; most of this is due to personal circumstances but also it's been due to a lack of good storms and setups to chase.

Tomorrow may be different.  Finally, something to talk about.

Moisture: good dewpoints are already in place, in the mid-teens, but 20s are lurking in ND.  They should advect north by tomorrow.

Instability: this is conditionally problematic, but with cooling aloft, should the dry slot of the upcoming system be relatively cloud-free (even for an hour) this will cease to be a problem, with 2000+ j/kg MLCAPE.

Shear: this is interesting; the deep-layer shear will be adequate but the profiles themselves may lead to weird storm modes.

Trigger: not a problem with a sub-1000 mb low coming our way, accompanied by all the requisite fronts.

Here's a prog sounding for Carman, MB, for 7 PM.  Note the implied convection.

So here's what I think will happen: a bunch of overnight and morning storms will drop tons of moisture.  This moisture as well as that advected in will make for potential instability.  The dry slot of the low-pressure system will move over the Red River Valley by mid afternoon, setting the stage.  It'll just be a question of whether the low clouds in the dry slot will mix out.  I think they will, as it'll be a rather windy day (turbulent mixing) and the sun is relatively high in the sky (convective mixing).  Then, around 5 or 6 PM, a few storms will go up and quickly become severe.  I think supercells with heavy rain, wind and hail will occur.  (Justin disagrees with me on the hail because of the warm atmosphere; I think the steep lapse rates and supercell structures will compensate for that and make for loonies or bigger; we have a bet on it.)  The vertical wind profile looks a little bit goofy for tornadic supercells, because it exhibits a veer-back pattern, which tends to make the storms rain into the updraft, and as a result they can't live as long.  As well, the resultant storm motion, aside from strongly deviant motion, will be into lower and lower instability.  So it's not ideal for tornadoes, but it's not horrible.  Low-level turning could provide for a few tornadoes,  but this doesn't scream long-track violent tornadoes, either.  I think tornadoes will be relatively early in the event, if any.  Then it'll blow up into an area of rain and thunderstorms that will move into northwestern Ontario.

Consecutive runs of various models have been pulling the low farther and farther west; a few days ago this setup looked like it would be primarily a northwest Ontario one, and perhaps in the jungles of eastern Manitoba.  Now, it's changing in favour of chasers.

Good luck and stay safe!

Storm chase with CoD

So tomorrow I will be embarking on a chase with CoD.  I'll likely be tweeting and blogging, but I'm not sure which account or accounts I'll be using.  Here are the possible ones:

Blogs:
http://daveandjustinweather.blogspot.com/
http://wxcentral.blogspot.com/

Twitter:
https://twitter.com/StormStructure
https://twitter.com/cod_stormchase

It looks like Saturday will be a chase day, either in Kansas or Nebraska. Long-range models indicate that most days should be chaseable days, too.

(cross-posted at Weather Central Blog)

Saturday, the last day: high risk, high reward?

So today almost every chaser is playing the Black Hills magic.  We would be doing so, too, if we didn't have to be in Omaha early tomorrow morning.

So we decided to play in the area of plan B, a high risk, high reward setup.

All the ingredients--moisture, instability, lift and shear (marginally) are in place today across central Nebraska, and we are going to play the area.  It's entirely possible that we get a sunburn today, but if storms go in the environment, we will likely be looking at either HP or wet classic supercells.  Low wall clouds and big big hail.  Which we will avoid, naturally.

The Black Hills just got a tornado watch as I wrote this, so it would have been our 4th tornado watch during this week-long trip.

Not that *that* has helped us at all.  ;)

Friday's chase: storm structure

We kept saying Wray, Colorado.  That was the place to be.

After a quick lunch in Lamar, CO, we went north to Wray, and when we got there, a good area of cumuli was bubbling up.  It pointed to the fact that there was persistent lift and convergence there, so we waited.

As we watched, storms went up in front of us, and we decided to play a bit north, as a) the best-looking storm (both visually and on RADAR) was there, and b) the deep-layer shear would be better there.

We ended up getting on a couple of LP-looking supercells,one of which produced golf ball sized hail in Holyoke, NE.  It kept going and going, as storms around us kept trying to go up.  But this one persisted.

We (read: I) were ready to abandon the storm numerous times, but cooler heads prevailed--the storm kept on appearing to die on RADAR, but it would still look good visually--a well-separated region of updraft and downdraft.  So we stayed, and we were rewarded with hanging out on the storm of the day.  The one clue that told me that maybe we should stay was that, despite, low reflectivities being present, the echo tops were still above 50,000 feet.  A good top, for sure.

We kept going on and watching this storm which happened to be moving slowly--maybe 30 km/h, at most--and it slowly gained a better look on RADAR.  Soon it got severe warned, with big hail once again being the big threat.

Of course, this had to happen right around dusk, so that chasing wouldn't last too much longer.  And wouldn't you know it, but the storm decided to go absolutely crazy just when it got too dark to see properly--give-up time, in other words.  The tops got even higher, the reflectivity got more of a classic shape, and rotation really got up there.  So much so that the NWS issued a tornado warning on it.

Crap!

Well, we weren't going to chase it at night, as that's just too dangerous.  So we went back to the hotel, secure in the knowledge that a) we were on the right storm and b) we got some good photos from the hours and hours we spent watching it.

Summary of Thursday, May 23

Well, we were on the right storm.

A morning outflow boundary was moving westward through the Texas panhandle, and it would prove to be the focus for severe thunderstorm development.

A clump of agitated cumuli got going east of Plainview early in the afternoon, and we knew that was where we had to go.

When we got to the storm, it had just been tornado warned--a couple of landspouts were reported in its updraft phase.  But it was showing nice reflectivity structure, although it wasn't actually showing much rotation on the Doppler.

We followed this storm for a couple of hours as it moved slowly south, kicking up a tremendous amount of dust as it did so.  At one point, the dust was being kicked up and seemingly ingested into the inflow--something that we will have to look at on video, as it had the chance and was in the right position to be a tornado.  (Personally, I don't think so, but we will see.)

Here's where we were in relation to it.  Our location is the white circle.

After a while, that storm started to collapse and become outflow-dominant, but there were new storms going up to their southeast.  We went after those, and one began to be the dominant storm, showing a good inflow notch and some rotation.

Soon after we got there, it was tornado warned.  It looked more likely to produce, visually, but the low-level rotation never really tightened up.  I'm not sure why--whether it was because the upper level winds didn't evacuate the updraft column quickly enough, or because of some other thing I can't think of right now.

Anyhow, it also turned into this big blob that went linear, so we bailed and decided to make for our hotel room.

On the way, we made a couple of stops; at the first one we met up with a bunch of chasers including Reed Timmer, and at the second we met up with Greg Johnson.

As a bonus, I finally got to eat a long-time storm chaser food staple, an Allsups burrito.Not bad, not great.

Tomorrow looks pretty good in western Kansas and/or eastern Colorado.  We will refine the area tomorrow.

Thursday

Yesterday was a down day, as the cold front had swept the moisture away.  Not too far, however.

This morning we woke up with a lot moire moisture in the air (dewpoint approaching 20) and an outflow boundary nearby from overnight storms in Oklahoma.  The moisture is streaming northwest, and a short-wave trough can be seen coming out of the desert southwest.

As a result, the SPC has issued a moderate risk for severe thunderstorms pretty much in the area we had been focusing on.  Good.

So we will see what today brings, but I remain optimistic.

May 20, 2013

An historic tornado occurred yesterday in Moore, OK.

More on that in a bit.

We started off the morning in Omaha, NE, looking toward OKC as an initial target.  A dryline/cold front intersection was forecast to sit just west of that city.  All the parameters--moisture, instability, shear, lift--were in place, so we figured it was a lock.

We left at about 8 AM, and OKC was reachable by 2 PM.

Then things went wrong.  An 18Z sounding went up from Norman (they actually sent it at 17:15Z, 12:15 PM) and it showed moist and very unstable atmosphere, basically uncapped.

Uh oh.

Soon after that, the MD went out and then a tornado watch.  As expected, it was for serious storms with big hail and damaging winds, in addition to the expected tornadoes (with a few long track/damaging ones possible).

As luck would have it, storms started firing up shortly after 18Z, right along the dryline and the cold front.  We were north of it at this point, still in Kansas, so we had to hurry.

Then.

A storm initiated near Newcastle, just west of Moore.  It got tornado warned almost immediately.  Which was a good thing, as it started to produce a tornado fairly quickly.

An aside about the normal behaviour of supercells.  Usually they initiate and take a long time to wind up and produce tornadoes.  On the order of an hour or so, sometimes 2.

Also as an aside, storm initiation in this part of the world (most of North America, aside from the Gulf Coast) tends to be during the mid afternoon.  3 or 4 PM.  Or sometimes 6 or 7.  So when storms went up in the early afternoon, we weren't ready, and nor were we in position.

This was our eventual downfall, as the storm was crossing our projected path, and there was no way we could get in front of it before it crossed I-35, so we had to cut east and then south, to try and get ahead of the storm without it hitting us and getting the vehicle damaged or destroyed by hail.

After some driving slowness through some towns, we eventually ended up straight east of the storm.

Which was, of course, exactly when the tornado decided to lift.  All the time we had been listening to radio from OKC talking about how big and nasty the tornado was, and how it was grinding through parts of Newcastle and Moore.  The TDWR at KOKC was showing a tightly coiled spiral of reflectivity (note to self: download that later) and the the WSR-88D showed something that I never like to see: a region of high reflectivity in the hook, a huge rotational couplet and associated very low correlation coefficient.  This combination of signatures is fairly well correlated with tornado debris, so much that this combination is called a tornadic debris signature or a debris ball.  (Usually the reflectivity and CC are fairly circular.)

Anyhow, long story short, we didn't see a tornado, and the storm structure, such as it was, was obscured a lot by haze.

We went to our hotel in Ada, OK, to prepare for today.

Speaking of which, it looks like the same kind of conditions are coming together this afternoon (but hopefully not *early* this afternoon) around Dallas, our initial broad target.  I hope it's not a repeat of yesterday.