Plain-language summary:
It will be hot today and then very to extremely hot Monday and Tuesday with high to very high humidity. It turns cooler on Wednesday for the rest of the week, with showers and thunderstorms possibly affecting southern areas for several days. It could turn hot and humid again next Sunday into early the following week, after a day with widespread clouds, rain, and relatively cool temperatures. Such a return in heat and humidity could last a few days and be punctuated with at least scattered showers and thunderstorms. At least moderate heat and humidity is likely to dominate early July after a likely modest cooldown at the beginning of July.
Meteorological discussion:
Heat wave begins but peaks Monday and Tuesday with sunshine, scattered storms on Tuesday afternoon
Today will be the first of 3 hot to very hot days across the region. Today's heat is tempered by a mesoscale convective complex that moved through our region last night and convectively overturned the lower atmosphere, cooling down the low-levels. Still, with mostly sunny skies behind the convective system for most of tomorrow, some lower elevation locations will approach or reach 86F (30C) today, with rather high humidity.
The really intense heat will be advecting from the west on Monday as the ridge in the eastern U.S. is in a perfect position for hot, dry air from the southern and central Rockies to be advected into our region in the most direct, shortest path possible, as mentioned in last Sunday's blog. 850-hPa temperatures will be approaching 72F (22C) west of Maine Monday afternoon, and with very dry air aloft, there will be plenty of sunshine for most. If the warm air is fully mixed down to the surface, temperatures would approach 100F (38C) in lower elevations. It is always questionable how much the warm air aloft can mix down to the surface during heat waves. There isn't really any compressional warming ahead of a cold front, so there isn't really any mechanism for low-level descent to tap into the warm air aloft, except in downslope areas like the Champlain and Ottawa valleys, downsloping off the Adirondacks and Algonquin Park respectively with the relatively weak westerly flow. Less boundary layer mixing will lead to lower surface temperatures but higher surface dew points, perhaps making it feel just as hot. Most areas will experience dew points of at least 70F (21C), possibly even 75F (24C) at times. The hot air will not have reached Maine yet on Monday, leading to temperatures below 90F (32C) there. With the hot air moving in, the high temperature will occur late in the day, and sometimes low-level heat is delayed a bit when it is just coming in, which could affect the highs a bit especially east of the Champlain Valley.
On Tuesday, a diffuse cold front will be entering, with stronger westerly flow and compressional warming ahead of the front, leading to a quicker warmup initially, but the gradual cool advection will lead to temperature peaking earlier with slightly cooler temperatures in the northern Champlain Valley on northwest. On the other hand, it could actually be hotter east of the Appalachians with more of a downsloping west-northwest wind negating any ocean moderation, with temperatures approaching 100F (38C) even up to central Maine. Despite the very intense heat and humidity ahead of the cold front, the front is so diffuse that it won't really be an effective trigger for showers and thunderstorms, especially given the dry air aloft. There will probably still be at least a few showers and thunderstorms perhaps mainly over the higher terrain of the Adirondacks and Green and White Mountains.
(Note that the HRDPS model shown in the bottom 3 panels tends to overdo summertime daytime temperatures at least slightly.)
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| Source: TropicalTidbits |
Cooler starting Wednesday for rest of the week, possible showers and thunderstorms in southern areas, before heat possibly surging back in for end of June
By Wednesday, surface high pressure to the north over Quebec will lead to weak northerly flow and substantially cooler temperatures, with the upper-level ridge slowly weakening. Thursday and Friday will also not be hot with continued northerly to easterly flow, though it won't be particularly cool either with any true cold air mass staying way to the north given the eastern U.S. upper-level ridge. The battle between the cool air mass to the north and still hot air mass to the south will lead to a stalled diffuse frontal zone, most likely in far southern areas or just to our south, where days of showers and thunderstorms with continued high humidity are likely. Our region could be just far enough north to be mostly dry with lower humidity and more sunshine through Friday. The ridge could expand back north next weekend into early the following week, leading to the hot and humid air pushing back northeastward into our region, though likely with a somewhat cooler, cloudy, and rainy day with the warm front before the heat and humidity can re-enter for perhaps a few days, punctuated with at least scattered showers and thunderstorms. With the ridge still not as strong as it is early this week, and some more moisture and cloud cover, it will not get as hot as early this week.
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