A battle ground will be setting up between the heat building in the south and the cooler air aloft (lower heights) from detroit to boston and northwards through Ottawa,Toronto and the great lakes region. Notice the heights lower then 576 in this area making it harder for temperatures to rise. Frequent cloudiness and thunderstorm activity is effecting parts of these areas and may expand. Plenty of energy is diving into the west, then moving over the central ridge before diving into the east and feeding into the trough and the boundary that is setting up. At my house today it is only 20 C and yesterday we were expected to reach 28 C. Doesn't look like that is going to happen. 500mb Heights Today:
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Tommorow morning we can see the same trend with plenty of energy in place and low enough heights at 500 mb. You look for the area at about the 5800 heights field for thunderstorm activity(where a boundary between cold and warm sets up). This is right over our areas. TWN has toronto at 32C and sunny with a humidex of 38C. I expect them to possibly have to bring down temperatures. This is a forecast with big risks. Will there be enough sun to keep temperatures up or will cloud cover get into the way again? The one thing they have going for them is the Euro which has heights a little bit higher in this area allowing surface temps to be about 2-3 degrees C higher which makes a difference. It doesn't have any precipitation in this area this weekend.
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The surface map off the 06z GFS shows more of this trend on friday(with more clusters of thunderstorms popping up) although it doesn't show thunderstorms on thursday at the surface. We will see what happens but if at key points in the day cloud cover gets into these areas temperatures could stay lower or heat could just last temporarily in the next few days. I would be surprised with a heatwave for areas like toronto or ottawa. Windsor is a maybe on this one. This is the opposite of last time when TWN had temps too low.
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More showers and storms on Saturday when TWN is forecasting temps above heatwave status.
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I'm not saying the heatwave won't happen but it just might not be as easy as we thought if the GFS has the right idea. If the euro is right then many areas will experience a heat wave. By sunday we can see thicknesses lowering quickly again in the east. I think this pattern may continue for a while in july because this is the pattern that we seem to be stuck in.
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Another question mark is later in the period around July the 5th. The trough in the west will amplify a little more allowing the ridge to back into the southwest. Will this allow the trough to amplify more into the east like this weeks trough or will it be a flatter trough? Will we see more of these strong troughs or just flat ones allowing for heat to build underneath? It is hard to tell because the modelling usually doesn't catch onto more amplitude until we get closer to the time period. My guess would be a stinger trough but not as strong as this weeks (somewhere in the middle).