Canadian Weather Community Forums

As we approach the weekend there will be much talk of severe weather. I thought I would post a new thread to allow for "pre-event" forecasting. This will be a fairly general post discussing severe thunderstorms across the country for the weekend. Hopefully this will provoke a more Canadian discussion, rather than just a Southern Ontario, or Southern Manitoba local discussion that sometimes gets going.

The main things I see for the weekend:

1. Southern Manitoba looks to be under the gun for some fairly intense weather on Saturday evening. A strong low-level jet of 30 to 40 knots will pass through South-Eastern and South-Central Manitoba, with SBCAPEs of between 2000 and 3000 J/kg (generally). MLCAPE will stay more moderate as per usual at around or below 2000J/kg. As you go up into the 700 and 500mb range the shear basically stays the same speed, but changes direction a bit to the South-West or West. Some directional shear, with a strong low-level jet is the conclusion for wind parameters. As I mentioned instability is more than sufficient for severe storms, however the cap may be an issue. CINH of -10 to -200 J/kg will be present, which in my opinion will make this a more evening event due to the cap breaking later. Moisture is decent, and I would expect dewpoints to reach between 16 and 20 degrees for the most part, with the isolated reading into the low twenties. Helicity is fairly marginal, only going up to 150m2/s2 if that. This will be something to watch, as there appears to be a possibility of some supercells.

2. Ontario, both Northern and Southern for Sunday. Areas just West of Thunder Bay, and basically all of Southern Ontario from a line South of Parry Sound to Kingston. These areas are much more marginal, especially Southern Ontario. There is no real trigger for the Southern areas, besides daytime heating or maybe lake breeze convergence. CAPEs of only around 1000J/kg hardly provide sufficient instability for the day. With a fairly strong cap, and little shear I would suggest only isolated stronger non-severe storms are likely on Sunday for Southern Ontario at this point. Northern Ontario is similiar, however there is a more definate trigger. A pre-frontal trough will be in the region which could trigger the storms. A weaker cap, and slightly higher instability make this area more probable for severe storms. Shear is fairly good in this area, so I would guess a squall line or several strong multicell storms are possible.

3. Central Alberta looks interesting Sunday. SBCAPE of 1000 to 2500J/kg will center itself around Edmonton and extend East and South. Shear is reasonable in the low levels at between 15 and 30 knots, but dies right off in the mid levels. This leads me to believe isolated cells that produce heavy rainfall and large hail are most likely. Helicity doesn't appear to be anything special right now, and moisture is not very dramatic, with dewpoints in the low to mid teens. One thing going for this is a fairly weak cap, and the foothills as a trigger. Looks to me like a typical summer Alberta severe weather event, with numerous storms rolling off the foothills by late afternoon.

Hope you enjoy this, and maybe some other regions will be added to the list with later model runs!

What about Alberta/Sask tomorrow?!!!? [Friday] All the parameters model wise seem to be in place for Supercell development over east Central Alberta and Sask tomorrow.

Yeah, I saw there's a chance of thunderstorms tomorrow and after all this heat we've been having I'm hoping we can get a good one (it's been around 25-30 and mid 30's with the Humidex almost all week).

I'm in Edmonton by the way :p

Sorry about that. It didn't even occur to me that Friday should be added, well Friday evening is basically the weekend for most part anyway. Here is that "forecast".

4. The latest models run don't look nearly as optimistic for supercellular severe weather on Friday. CAPEs of 1000 to 2500J/kg won't provide nearly the same punch as the previously forecasted 2000 to 4000J/kg. Those higher instability values would help make up for the weaker shear to increase the chances for supercells. Currently I am seeing shear of 15 to 25 knots (850 and 700mb) in the low-levels and up to 50knots in the mid levels (500mb). These values are in Southern Alberta, with little to no shear in the central part of the province and some higher shear again centred around Fort McMurray. This morning's PASPC discussion was suggesting a slight to moderate risk of severe weather in Alberta and Western Saskatchewan tomorrow. I believe that was a very reasonable outlook considering the forecast at the time. Presently I would say that it should be toned down to a slight risk for the most part. The atmosphere won't be quite as unstable as previously predicted, and shear isn't all that impressive. Strong capping will likely hold off any significant convection until the early evening, except right along the foothills. I would suggest that numerous cells will roll off the foothills beginning late afternoon, then by early evening some may become severe generally West of the QE2 highway in Central Alberta. In Southern Alberta most regions will risk a severe storm, although that strong cap may hold off convection East of Lethbridge. I see the greatest potential right now around Fort McMurray, in about a 200km radius of the city. The best low-level shear, and weakest cap in the province will be in place here. The pre-frontal trough will move in by evening, possibly triggering an isolated supercell. For the most part multicells will be the main mode. Otherwise I would expect to see mostly single and multicell storms across Alberta, with an isolated supercell once again in Southern Alberta.

5. Most of Saskachewan will be under the risk of an isolated severe storm. CAPEs of generally 1000 to 2000J/kg will cover the province. Shear is fairly weak, althought it does reach 40knots at 500mb in the center of the province. Since there is no real trigger and a fairly strong cap I would only expect to see an isolated single cell here and there if that. In Western Saskatchewan some storms from Alberta may move in late in the evening to overnight, which may be cause for some severe weather North and West of Saskatoon. Since CINH goes way up as the sun goes down, and instability decreases I wouldn't expect to see too much severe activity in Saskatchewan much after dark.

6. Central Manitoba, including Swan River and Flin Flon will be under a slight risk of severe storms on Friday evening. CAPES of 1500 to 3000J/kg will be present, along with a fairly strong low-level jet. Winds of 25 to 40 knots will be present by evening in these regions at 850mb, but shear is basically non-existant in the mid-levels. I would then conclude multicells would be the only storms mode. Due to a strong cap and no defined trigger I wouldn't be surprised if nothing happened, but since some decent parameters are in place it is worth mentioning. Please note this risk extends into Eastern Saskatchewan a bit, so it overlaps the above forecast somewhat.

Otherwise there is much to talk about in Canada for Friday, the East remains quite with highs in the low to mid twenties, and the West is HOT!

spc appears to have manitoba outlined for a saturday event. Which outlines exactly what you've said. I hope this is a good one.

Glancing over the WRF, it seems that the surface low is way north than previously forecasted. Not the best chase territory in North Eastern Alberta! Will be watching tomorrow, and we'll see what the new model runs have in store.

I'd still not count out the Lloydminster region. The model runs are kind of inconsistent in the surface details, but the upper features are in place--and that's what the models do well.

I just sort of outlined what I saw in the models last night/early this afternoon for the respective "discussions".

I wouldn't be surprised if that Alberta situation tomorrow got better, the latest runs were fairly pessimistic considering how good the previous ones were. As Dave mentioned the Lloydminster/Fort McMurrary areas are currently looking the best. It just boils down to a combination of weaker capping, and better shear. The only thing I am a bit concerned about is the trigger....

Hold on...I just checked the NOAA National Maps / Frontal Forecast (whatever you like to call it), and it is now suggesting a more Eastern Alberta/Western Saskatchewan event. The models are going all squirrelly with this one, however I would expect the previous (before I posted this thread) to be a better forecast now. This would fall more into line with the forecast discussion PASPC put out this morning. I wouldn't go back into detail now, but hopefully the morning runs will finally settle down with this forecast.

See the name on the PASPC discussion this morning? ;)

I agree, with convection going on, the models will be fairly inconsistent with this setup, especially on the surface. Analysis the day-of will be paramount.

Now that you mention it I did see your name on the discussion...I always can tell when you write up the statement as it is usually much more accurate and detailed in the convective end of things.

I am still not really sure what exactly will happen tomorrow, although this morning's rosy outlook probably will be toned down.