Plain-language summary:
An intense heat wave will affect our region through Wednesday, with Tuesday being the hottest day for most. The unusually dry weather in the past 2 weeks, along with the dryness of the heatwave through Tuesday, is leading to a developing flash drought, along with unusually low humidity and nighttime lows for an intense heat wave. Scattered showers and thunderstorms are likely on Wednesday before turning dry again as well as cooler for Thursday and Friday. Heat returns next weekend, but will likely not be as intense or long-lasting as the current heat wave. A more up-and-down temperature pattern is likely for the following week, still leaning warm with some hot days likely. It will likely still be predominantly dry, unless a hurricane in the western Atlantic tracks into our region the week after next week, bringing strong winds and heavy rain, which is just one of many possible scenarios for now.
Meteorological discussion:
Intense heat wave through Wednesday with relatively low humidity, dry and sunny except some scattered showers and thunderstorms Wednesday
An upper-level trough that was over the Rockies yesterday is now lifting into the northern U.S. Plains and central Canada, promoting an upper-level ridge downstream over eastern Canada. It has been incredibly dry across the region over the past 2 weeks outside of scattered afternoon thunderstorms over higher terrain, with many lower-elevation locations having received little or no rain during that period with dry surface high pressure dominating after the push of a big area of cooler, drier air into eastern North America at the end of July. Although the air was cool initially, the lack of replenishment of the cool air, along with plenty of sunshine and some westerly flow advecting warm but still relatively dry air into the region, without any southerly component bringing moisture from the Gulf of Mexico or western Atlantic, it has become hot but with low humidity, somewhat unusual for the middle of summer in our region. With the low humidity, plentiful sunshine, and lack of rain, the ground has rapidly dried out, with a flash drought potentially starting. The U.S. Drought Monitor already showed much of northern New England being abnormally dry even by this past Tuesday, before the dry heat wave. This is allowing it to heat up more during the daytime than otherwise, with less of the sun's energy going into evaporating ground moisture. It is also leading to lower humidity, lower heat indices, and lower nighttime temperatures (especially combined with clear skies and rather light winds with the surface high pressure) than typical for a heat wave in August.
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| Source: NOAA and U.S. Drought Monitor |
As the upper-level ridge slowly pushes to our east, leading to weak southwesterly flow, it will remain sunny and continue to get hotter but only slightly more humid through Tuesday, with still no strong flow of moisture from the Gulf of Mexico or western Atlantic. The hottest locations just to the northeast of the Adirondacks, in far southern Quebec and northern Champlain Valley, with downsloping warming due to the weak southwesterly wind, could approach 100F (38C), the hottest in all of eastern North America east of Texas! This is similar to the late June heat wave, though this heat wave will last longer but also feature lower humidity. The more southerly nature of the low-level flow this time, though weaker, means that coastal New Hampshire and Maine will see more ocean moderation than with the late June heat wave. By Wednesday, a surface low pressure will travel into central Quebec, with its associated cold front triggering scattered showers and thunderstorms over the region, though the best dynamics look to be off to the north, limiting the coverage and severity of the storms. Still, the clouds and any rain that does fall will keep temperatures at least slightly lower than Monday and Tuesday.
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| Source: TropicalTidbits |
Cooler and drier Thursday and Friday, turning hot again next weekend
The cold front will be relatively weak, with the progressive pattern with the strong jet stream retreated to northern Canada (common with the +NAO we currently have) not allowing much surges of cool, Arctic air into our region. Still, the Canadian surface high pressure behind the front will lead to weak northerly flow on Thursday, leading to noticeably cooler (but still near or slightly above climatological average) temperatures for Thursday and Friday, especially along and northwest of the Appalachians, and with dry weather returning. However, another upper-level trough will dig into western Canada by Thursday and Friday, promoting an upper-level ridge in eastern North America again next weekend with it heating up again to perhaps very hot values again next Sunday. It seems doubtful that it will be as hot as this upcoming Monday and Tuesday, with less time for the cooler air mass to recover and the sun angle weakening as we head past mid-August, but the dry ground will likely boost daytime temperatures again.
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
More up-and-down temperature expected after next weekend, still leaning warm with some hot days, likely still dry
Although long-range ensembles continue to show some upper-level ridging prevalent in eastern North America through even late August, the upper-level troughs in western Canada could subside and get replaced by upper-level ridges at times, with a neutral or slightly positive PNA. Also, the NAO is expected to turn to neutral, which could allow the mid-latitude jet stream to penetrate south of our region at times, allowing cooler air masses from Canada to enter our region. These cool air masses are also getting stronger as daylight hours and sun angle start to really decrease quickly after mid-August, making it difficult to sustain hot weather after next weekend. There are signs that surface high pressure systems will frequently travel from Hudson Bay into our region or Atlantic Canada, bringing with them cooler, drier air masses into our region directly from the north, even if these setups tend to not allow the cooler air masses to penetrate much to our south. However, I do still expect temperatures to be overall above average with some hot days, especially given the current dryness, though the more up-and-down temperature pattern could promote more storminess, and it will also take time for the hot air to return after a surge of cooler air.
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| Source: TropicalTidbits |
One potential caveat to the dry pattern is a tropical disturbance currently in the eastern Atlantic that is highly likely to develop into at least at tropical storm if not a hurricane next week (in which case, it will be named Erin) as it heads into the western Atlantic. There is the potential for the storm to track up the U.S. East Coast and bring strong winds and heavy rain to our region for the following week if the track is perfect, but it is way too early to have any confidence on the track, and ensembles currently show a wide range of possible solutions, as you would expect this far out, though most of them show the hurricane going east of our region.
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| Source: Weathernerds |
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