Amongst this relatively quiet pattern there appears to be some active weather to be discussed about in Alberta. The pattern has been in place for a while but Saturday afternoon looks like there could be a little more pop. Aloft (500 mb flow) we can see that there is are large upper lows over northern ON and in Alaska (in red) with the ridge (in blue) in between, this is referred to as an omega block. This is what is responsible for this relative stagnant weather pattern. Looking ahead to the 500 mb forecast for Saturday afternoon (second panel) we can see not much has changed, except that the upper low in ON has expanded some and the ridge in the north central part of the country has broken down some.

In response to this pattern at the surface is essentially a general area of high pressure over Saskatchewan in response to the upper ridge and a weak broad area of low pressure in BC in response to the upper low pushing into the Oregon/Washington states. Looking at the 925 mb forecast (I chose this as it is a little “cleaner” to look at) we can see general outflow from the high in SK which generates southeasterly flow into AB, a textbook setup for upslope lift and thus resulting in storms across the foothills.

This pattern has been ongoing for a few days now but Saturday afternoon looks to have some greater potential but also has some issues as well. Working in tomorrow’s favour is the fact that there is much more instability forecasted (SBCAPE forecast from GEM/NAM are both in 2000-3000+ J/kg) than what has been recently and a little bit more moisture to work with. That being said, 850 mb winds are also forecast to ramp up in the evening and early overnight thus increasing low level shear. On top of that hodographs do show some veering with height particularly within the lowest levels. On the down side we can see there is some ridging aloft which will hinder lift some adding some capping issues into the mix. There is also very weak flow aloft which may lead to storms chocking on their own outflow as well. Thus, it seems possible that weak, slow moving supercells are possible tomorrow, with steep lapse rates in place, looks like large hail would be the main risk tomorrow. IF AND I MEAN IF a storm is able to really root itself and tap into the more unstable air, a brief tornado could be possible, but there is very little chance with this type of setup. Looks like storms will stay mostly confined to the foothills with the best action between Hwy 1 and 16, but there is the slight risk of a few stray storms popping up along the QE2 corridor from Calgary to Edmonton, see last panel for surface analysis and risk area outline.