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Wow, it’s May, and I feel compelled to talk about the weather! Go figure!! Especially about events I have witnessed. In these days of hyper-extreme TV “StormChasers” bent on getting closer in/inside vorticies, as if ‘if your face’ is all that matters (sorry, its NOT), I am happy to take some pride in enjoying analyzing and writing up on a weak – but photogenic – convective event.
As with normal weekday life these days I arrived home situationally unaware. Plus this was band rehearsal night. so there was no time to indulge in an array of weather data (and I am happy to report we nailed that night’s attempt at the full album version of The Doors’ “Light My Fire” – we have such a good keyboard player!). So shortly before I need to leave I hear…thunder!
Got out to the Wx-Perch to observe VERY high based convection/precip to my NW. Saw one CG pop out from the side edge of the precip core and got off a couple of wide angle images before leaving to practice. Here is an ultra-wide image of the storm (new feature – click on image for larger version) – the main precip core is roughly eleven miles to my NW:
Pretty good visibility for SW Ontario (this almost looks like some of the high-based stuff you would see on the high Northern Plains, say like E Montana). Here is an ultra-wide image of the sky to the SW – representative of the environment that this brief weak event formed in (click on image for larger version):
Lot’s of broken high Stratus – an environment that is rather stable looking – at least to me! Here is the relfectivity image from around the time the above images were taken (23z) – click on image for larger version (same for all that follow):
Notice the virga all around the area, as well as between the cell and my location (back dot), is doing little to attenuate visibility – it is the main precip core that stands out in the image above. So here is my take on what happened – from the bottom up… Here is the the 23z sfc map:
It is obvious that London, Ontario (CYXU) is on the cool side of a rather significant thermal and moisture boundary to the S and SW (which would be even more obvious if I had done a hand analysis of data from earlier in the day). The T=55 and Td=34 suggest a stable environment and a high Lifting Condensation Level. The mesoscale radar composite shows convection to the south, either on the boundary or in the warm sector:
So we have no explanation for the convection at CYXU. Let’s have a little more detailed look at the 3-D mesoscale environment to try and solve the mystery! SPC’s objective mesoscale 850mb analysis shows the high sfc dewpoints we saw on the surface obs are associated with deep moisture which has advected up from the Gulf of Mexico, right up to Wisconsin and Minnesota.
The dry side of the tight moisture gradient is about 90 miles SW-W of this convective event. Clearly this cell is doing its best to process what little moisture it has to work with!
Let look at Static Stability – and use MUCAPE in an attempt to find any potential buoyancy that might be associated with this elevated convection:
Nope – looks like all the instability is co-located with the deep GOM moisture to the SW-W-NW. This analysis suggests there is effectively no CAPE at CYXU, though one could make the case that, where there is convection there is at least some instability – if that is the case, we can reasonable conclude that the CAPE is meagre! Let look at mid-level lapse rates:
The pattern of very steep mid-level lapse rate is also roughly co-located over the region of deep boundary layer moisture. This suggests a rather expansive region with an EML (Elevated Mixed Layer), with the co-located dry mid and upper-level airmass following a much different trajectory from its origin (intermoutain Western USA).
Lapse rates around CYXU are maybe just slightly above dry adiabatic! The EML is pretty clear on the 00z Skew-T Diagram from KILX (central Illinois):
Though the strong capping inversion means that the potentially explosive convection will be easily kept from initiating to the SW-W-NW. The 00z KBUF sounding shows a very stable environment, and one could suggest one similar to that at CYXU:
CAPE shows up at 38 J/Kg – could London have a similar amount? The real story only comes to light when we examine the atmosphere at upper and mid levels – 300mb: A subtle shortwave trough appears to be rotating around the upper level ridge, with its axis running SSW- NNE over Sault Ste. Marie (MI/ON, take your pick!). 300 mb analysis:
The 500 mp chart show a similar feature – with the mid level short wave trough just a little bit downstream:
A look at the 700 – 500 mb Omega suggests upward motion associated with this feature and the upward motion is destabilizing the airmass below (as well as weakening the cap) :
A look at Water Vapour imagery also shows the effects of the short wave trough – note the small dark region near the Thumb of Michigan:
It is likely that the lift from the mid-upper shortwave trough produced a sufficiently destabilizing and cap-weakening response to initiate elevated convection, that resulted in me seeing a Cloud to Ground bold, and getting a couple of pretty images!! One hopes that a proper diagnosis of the state of the atmosphere before the event would have helped lead to a decent forecast.
A proper top-down subjective analysis (as opposed to the bottom-up approach I chose for effect – and preferably an analysis that was hand-drawn) would have hopefully highlighted the short-wave trough riding around the mid/upper ridge. Ideally, that would have suppoted a 4-D mental model of the day’s setup which could then open the door to a forecast that included some probability of convective activity near CYXU. Hopefully the next SUMM will be for something a little more significant!
