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A look at the Wednesday June 10, 2015 severe storms risk

Some strong to possibly severe storms are possible for this week particularly on Wednesday around southern Ontario. I'll emphasize now there is still a good deal of uncertainty at this point in time since a broad MCS or wide spread convection is possible through the morning hours. This is important as how long the convection lingers and its exact location will alter how the days severe risk will set up. So this will only be a preliminary assessment for the time being but I have low to moderate confidence in the potential since there is generally good model agreement with the synoptic setup. I still keep it low to moderate though as again we will have to wait and see how the morning convection plays out.

I've made a series of 4panel charts for the morning and afternoon using the 18Z NAM. I'm using these just for visuals as I discuss through the forecast.  The image below is the 18Z (2 pm EDT) NAM valid for 15Z (11 am EDT) Wednesday June 10, 2015 which shows, clockwise from top left, 500 mb vorticity+geopotential heights, 500 mb winds+geopotential heights, surface temperatures / mslp / winds with the analysis done by the author, and 850 mb winds+geopotnetial heights. Looking at the vorticity and 500 mb winds we see that there is an upper level wave and 500 mb jet max pushing into north central Ontario. Down to 850 mb we see there is a strong 35-50 knot low level jet (LLJ) pushing in ahead of the upper level wave. At the surface the low is currently projected to be near the Timmins / Kapuskasing areas with the warm front  pushing through south central to north central Ontario. The large scale ascent fromt the upper level wave and the low level lift from the LLJ ridinng up and over the warm front will support the widespread morning convection or MCS. Current trend with models do keep the bulk of the MCS through south central to central Ontario with some scattered thunderstorms possible through southern Ontario as the warm front pushes through. Again how this morning convection plays out will ultimately determine how the afternoon and early evening scenario sets up

Below is the 4 panel chart made based on the same NAM run as above but is valid for 00Z June 11, 2015 or 8 pm EDT June 10, 2015. Assessing the 500 mb panels we have a shortwave trough that will be rounding the base of the 500 mb low with a 50-55 knot jet pushing into southern Ontario. Looking at the surface chart we can see that the cold front will be pushing through southern Ontario with the warm front expected to be up into southern Québec. This should allow deep moisture and high instability to push into southern Ontario. More on this below. The one issue here is with the 850 mb LLJ. We can see that the stronger southwesterly LLJ is expected to be on the U.S. side of the border except for in eastern Ontario with mostly westerly flow at 850 mb for southern Ontario. Thus the veered low level flow will not be particularly favourable for low level rotation. Should more instability be able to push into eastern Ontario, than the low level shear in place there will certainly favour better low level helicity and the potential for supercells. One other issue at this point as well is the speed of the cold front. The front is expected to push through southern Ontario relatively fast which may not allow enough heating for strong organized storms to develop or could quickly undercut any storms that do develop ahead it thus leading to be greater severe potential south of the Great Lakes into the U.S.

Below shows, counter clockwise from top left, the 15Z SREF moisture and MLCAPE valid 21Z (5 pm EDT) Wednesday June 10, 2015 and the bottom is the 18Z NAM valid 21Z (5 pm EDT) Wednesday June 10, 2015 0-6 km bulk shear. Assessing the SREF values it is projecting dew points for southern Ontario getting into the 60F to 65F range which is about 15C to 19C. With rich moisture expected the SREF is also projecting MLCAPE values of 1000-2000 j/kg. These parameters combined with 30-40 knots of 0-6 km bulk shear will certainly lead to organized severe storms. The area in red is there just to point out southern Ontario. Steep mid-level lapse rates will also lead to a fairly substantial hail threat as well again should the storms develop through the mid to late afternoon.

Thus putting it all together the area outlined in purple in where I think there is a general non-severe thunderstorm risk. This area also accounts for the morning convection expected as well. The green area is where I think, at this point in time, where strong to severe storms will be possible on Wednesday. The bottom map shows a zoomed in crop of the strong to severe risk area. SHOULD storms develop Wednesday afternoon in this region, shear and instability will be sufficient for organized storm clusters with the risk of moderate to large hail, frequent lightning, and strong winds. Given the veered winds I think there is a very limited tornado threat unless eastern Ontario is able to have more moisture and instability build in.