After another quiet and very nice day for Sunday, the weather will turn more unsettled heading into Monday. This will come as another closed upper low will drop down into New England from Quebec. This will provide plenty of instability to fire up scattered to numerous thunderstorms after a partly cloudy start to the day.
The timing of the storms for Monday is looking to be the typical timing New England sees. That is to say isolated storms will likely begin to pop up across northern and western areas in the late morning to early afternoon before becoming more numerous dropping south and east later in the afternoon and into the evening. There are signals that some storms may pop up in the early to mid morning across northern and western Maine, which would limit afternoon activity in that area should these morning storms come together.
HRRR showing potential weather from noon to 8pm Monday:
At this point, this isn't looking like a major severe weather event, but there are some parameters in place to allow for strong to a few severe cells, especially later in the day across southern New England. This type of setup (an upper low dropping south from Quebec) can lead to organized, mature storms moving across southern New England, bringing strong winds. Conditions may also be favorable for large hail. Again, this isn't looking like a severe weather outbreak, so not all storms will pack a punch.
The overall setup is similar to thunderstorm days that were seen earlier this summer when hail became a threat. Lapse rates (the rate of decrease in temperature with altitude) on Monday are looking steep (when the rate of decrease in temperature is rapid, which indicates instability). The freezing level will be lowered to 10,000-11,000 feet for southern and eastern New England as the cold pool aloft is centered over eastern Massachusetts.
Euro showing the forecast freezing altitude Monday evening. This shows (in feet) how high above sea level the temperature drops to 32°. You can see levels around 11,000 across the coastal plain:
As far as the other ingredients for severe weather, there will be plenty of lift provided by the upper low. Moisture will also be on the increase with increasing humidity levels. This will allow for heavier rainfall rates, though flash flooding potential is low. The big inhibitor to strong to severe storms will be very weak shear.
Shear is arguably the most important ingredient to pushing a thunderstorm to severe levels. The fact that shear will be weaker is the main reason why severe storms will likely be more isolated rather than numerous despite other ingredients lining up.
Euro showing forecast shear values Monday evening. Values are weakest where storms will likely be more numerous:
After Monday, high pressure and low pressure will likely continue to trade places all week as more zonal flow sets up. This flow allows weather systems (both high and low pressure) to move quickly across the country without anything getting hung up. This will result in periods of unsettled weather followed by a period of dry weather. As of now, it looks like Monday, Wednesday and possibly the weekend will be unsettled with Tuesday, Thursday and Friday being calmer.
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