Sunday, August 29, 2010

Late-season event on Monday?

In the wake of my previous, depression-inducing post, it's only fitting that a severe weather event is potentially going to occur tomorrow. And of course, it's made all the more likely due to the fact that I have a dentist appointment in the afternoon.

Once more, with feeling:

Moisture - the forecast dewpoints are up there around 20, and there's no problem with that, as the dewpoint outside today is in the upper teens (or actually 21 at my backyard weather station).

Instability - it should be there, just by virtue of the fact that the surface will be warm and moist. The forecast MLCAPE is over 1000 J/kg and there are even some hints of over 2000. Looking at the 500 mb map (below, after "shear") I see that there will be slight warming. Will that be enough to suppress storm development?

Lift - there appears to be a warm front progged somewhere over southeastern Manitoba. This will provide lots of convergence. Will it be enough?

Shear - This is a bit of a weakness, as the winds through much of the atmosphere will be aligned (save for at the warm front, where they will be backed) and not terribly strong.

So the question is whether storms will go. I just don't know if it will, but if it does it could be pretty serious. As soon as I get out of the dentist's chair I will likely be off in my car, chasing those elusive severe storms.

What do you think?

Sunday, August 22, 2010

On the winding down of severe thunderstorm season

I've been putting off writing this post for a little while now. It sucks to think about it.

When I say "it" I mean the end of severe thunderstorm season. This of course happens every year, and every year I get the blues about it. It's not only the winding down of severe thunderstorm season but also the winding down of summer itself. Now, last year proved that summer can extend almost into October, but severe thunderstorm season isn't so generous. Usually.

Still, the latest in the year I've ever heard thunder in Winnipeg is the end of November. Not severe, but rumbly.

In 2008 and 2009, my melancholy was exacerbated by the fact that I didn't see any tornadoes those years. This year I had exactly one tornado day (although I could have had 4, had the right decisions been made) and that beats the crap out of zero. That day produced 4 tornadoes from 2 storms, what we call the Campo day.

I will miss you, summer and severe thunderstorms. Until next year.

Wednesday, August 18, 2010

Quiet August; SD chance today and tomorrow

I can't speak for Justin, but I'm in Saskatoon for most of this month and it seems that the severe weather taps got turned off as soon as I got into town.

If I were able to go, though, I would camp out in South Dakota for the next couple of days. Here's today.

Moisture: the morning analysis has surface dewpoints in the upper teens. They should get to 20 no problem this afternoon.

Instability: lapse rates are great across the area 700-500 delta T of 25 degrees at Rapid City), so instability should be easy to realize. In fact, there have already been thunderstorms this morning in southeast North Dakota.

Lift: there's a warm front draped across the ND/SD border that will likely get shunted southward a bit this morning because of outflow from the morning convection. But the convergence along the front should provide plenty of lift.

Shear: the deep shear will be plentiful, as the 500 mb flow is around 40 knots, and with the warm front in place the directional shear looks to be pretty good.

An added bonus is that there's ACC this morning over northwestern South Dakota, a sign that midlevel instability release is occurring.

So as a start I would set today's initial target as Huron, SD.

Tomorrow looks pretty good, too. Great, actually, if the cap breaks.

Moisture will be easy to find, with dewpoints progged to be in the low to mid 20s. Instability should therefore reach MLCAPEs of 4000 J/kg. Lift - a warm front in place. What do you think? And shear will be fine, with a midlevel jet streak progged to come across with winds from 40 to 60 knots. Capping will be an issue, but if a storm goes it will a) likely be along the warm front, and b) likely go explosively. My target: Yankton, SD.

Thursday, August 5, 2010

HobTor:Con: a (lighthearted) flame and origin discussion

HobTor:Con? Really? Urg.

The first time I saw the original Tor:Con was when the 4 of us were chasing on our May/June trip, you know, the one where we saw the Campo, CO tornado. While we would have breakfast each morning, most hotels would have TWC on in the breakfast area. And each morning they would tout this new (to us, at least) concept that they had come up with: the Tor:Con or tornado condition. They would discuss the areas of the country where they figured there was a chance of tornadoes and ascribe it a number, from 1 to 10, of how serious the tornado threat (or "condition", apparently) would be that day.

And Justin went and gleeped this concept. And made it his own.

Lameicus! :P

As for the content of the post, I tend to agree on most fronts; however, I have to inject this piece of wisdom I gained this summer while chasing with CoD.

Justin said, "Again the directional shear will be great...and the speed shear won't be bad either!" Now both being good is a bonus, but I've become a big believer in directional shear, if the storm-relative hodograph is good. The case that makes me think of this was the tough chase in NE and CO. Ultimately, the decision was made to leave the KS storm complex because the hodograph, while very loopy, didn't have the upper flow component that we look for. It did, though, have flow from amazingly different directions at different heights, and only of moderate magnitude, but apparently it was enough to put out multiple tornadoes.

My thinking here is that the hodograph, if loopy enough, doesn't have to be as long as it otherwise would be.

Now that being said, I don't know if all of the above applies to Alberta. Jet stream + Alberta = bad. Maybe the upper flow is more important than the crossing jets like we see farther out onto the plains.

Anyhow, this jet looks impressive: 70 knots at 250? Nice. I agree with the (ugh) HobTor:Con. I think, as long as there's more than a little instability, supercells will happen and the chance of tornadoes is heightened.

Wednesday, August 4, 2010

Increasing Severe Potential for Central Alberta starting tomorrow through Friday

Well a ridge is building in quickly over the next 24 hours and as quick as the ridge comes'll move off paving the way for a couple of rounds of severe thunderstorms for Central Alberta Thursday through Friday.

Tomorrow's action will likely be confined to the foothill regions as the ridge only moves off just a bit. The return flow at low levels associated with the ridge will be decent at around 15-20 knots out of the SSE. The flow at H50 looks somewhat diffluent over the west central part of the province which aligns well with the H85 flow around the Elbow region and points a bit South except for the fact that the flow is around 20-30 knots. In short, I'll say we have great directional shear...but speed shear is okay I guess...moisture is not bad and a trigger will likely be the vort max edging into the province associated with the upper low that'll move into AB for Friday.

Tomorrow's target for initiation will probably be the Nordegg, Rocky Mountain House, and Hinton-Edson regions with storms trying to move off of the hills in the evening. LP Supercells look to be the storm mode if they go big! Non-Zero Tor chances too!

My HobTor:Con for tomorrow would be a 2 out of!

Now onto Friday...

Again the directional shear will be great...and the speed shear won't be bad either! Moisture will be decent with dewpt temps in the low-mid teens...trigger will again be the cooling coming in at H50 as well as a surface trough that looks to dissect the Capital by 6pm. Storms will likely fire along western edge the QE2 corridor between Airdrie and Edmonton and build in intensity as they roll eastward in the evening. Biggest threat for decent supercells will be around Camrose - Provost - Drumheller areas in the evening. For early initiation I'd play East of Drayton Valley towards the Olds area. Tornado chances will be higher compared to Thursday if storms stay isolated near the trough or any other boundary and wherever LCL's can remain relatively low in areas with deeper moisture. HobTor:Con for Friday would be a 4 out of 10.

My HobTor:Con is just a value I make from the top of my essentally means nothing except for the chances 'I think' a tornado will form if a supercell develops...the May 22, 2010 day would have been a 10 out of 10 in NE South Dakota...I know it already happened...but those of us watching earlier that day knew it'd be huge if it went...and it did!