Plain-language summary:
Though it is still a bit cool with relatively low humidity and mostly sunny skies today, it will gradually turn hotter and more humid through Thursday, with more clouds and chances of showers and thunderstorms from Tuesday to Thursday, with Thursday being the most likely day for widespread thunderstorms. It will then be modestly cooler for Friday and Saturday before a heat wave likely affects the region for a few days of the following week, with frequent chances of showers and thunderstorms, some possibly strong, when the heat wave breaks down.
Meteorological discussion:
Cool, dry spell about to end with summerlike warmth and humidity building through Wednesday, scattered showers and thunderstorms
After a cool, dry air air mass sneaked into our region on Friday, it is becoming stale now, with the cool surface high pressure moving into the western Atlantic. It is still a bit cool with relatively low humidity today, with sunshine for most except low clouds still stuck in far southern areas. Southwesterly flow beginning Monday will bring in increasingly warm and humid air through Thursday. This is due to the upper-level trough entering the U.S. West Coast today (-PNA) that will promote a downstream upper-level ridge over the central and eastern U.S. through mid-week. On Monday, far southern areas from southern Vermont to southern Maine will still hold onto the low clouds and cooler low-level air that advected in from the north on Friday and enhanced by the cooler marine western Atlantic air. A weak disturbance from the southwest will bring increased clouds and scattered showers and possibly thunderstorms everywhere, though most of the rain will still fall in southern areas, and it might be too cloudy for much instability for thunderstorms. With more breaks in the clouds and low-level moisture still increasing for Wednesday, it will be hotter with more afternoon instability leading to at least isolated to scattered showers and thunderstorms, perhaps mostly over higher terrain given the lack of synoptic-scale forcing.
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| Source: TropicalTidbits |
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| Source: TropicalTidbits |
Hot and humid with thunderstorms for many Thursday, cooler and drier Friday and Saturday
There is still some uncertainty on the timing, but a stronger low-pressure system will move into northern Ontario and western Quebec on Thursday, whose cold front will trigger more widespread showers and thunderstorms in our region, especially in areas where the cold frontal passage occurs near peak afternoon temperatures, which appears more likely in northern New England than in northwestern New York and eastern Ontario, where the front will likely pass earlier. It remains to be seen if any of the storms become strong to severe. It will be quite hot and humid east of the front, with temperatures
reaching or exceeding 86F (30C) and dew points approaching 70F (21C) at
lower elevations. It will turn modest cooler, drier, and sunnier for Friday and Saturday with lower humidity, though it will not be nearly as cool as the last few cool spells have been.
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| Source: TropicalTidbits |
Heat wave looking increasingly likely for following week
There is now almost unanimous agreement, more so than usual for a long-range outlook, for a strong upper-level ridge to develop in the eastern U.S. downstream of an upper-level trough in the western U.S. (continued -PNA) from next Sunday into the middle of the following week. As of right now, the ridge appears to be in an almost perfect position and shape to quickly advect hot, dry air out of the central Rockies northeastward through the Upper Midwest U.S., Great Lakes, and then into our region. This is slightly farther north than model projections a few days ago, which showed the ridge being a bit too suppressed to the south for the hottest air to get as far north as our region. There does not appear to be a cut-off low underneath the ridge that would impede this hot, dry westerly flow. This would not only push the hottest temperatures aloft possible into our region and cut off any moderation from the Atlantic Ocean, but the dry air would also inhibit cloud formation, allowing the strong, near summer solstice sun angle to efficiently heat up the ground and boundary layer air. It has also dried out in our region, especially in central and northern regions, since the extremely wet May. Even with the showers and thunderstorms next week, they appear unlikely to produce enough heavy rain over a large enough area to moisten the ground deeply too much, and there will be a few dry days afterward before the heat wave starts. 850-hPa temperatures exceeding 68F (20C) suggest that widespread lower elevation temperatures of 95-100F (35-38C) are possible on the hottest day, assuming that the current setup holds. However, there was a similar heat wave last June that had similar model projections, but the ridge ended up not being in the perfect position, and the models overdid the heat. After a few days, the upper-level ridge will likely break down somewhat but not completely, allowing our region to be in the "ring of fire" on the northern edge of the ridge, with frequent chances of showers and thunderstorms, similar to late last June. Given the intense heat and humidity in the ridge, these "ring of fire" thunderstorms could be particularly strong, but it is still way too far out to have too much confidence in this or speculate on specifics.
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
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