If you love low humidity than this past weekend was just for you. After an intense round of t'storms moved through southern New England on Wednesday a much direr airmass has settled into southern New England. This is all about to change. A developing southwesterly flow is working to bring in a much warmer and more moist low-level airmass into the region. In fact, dewpoints across the region are slowly beginning to work their way into the lower 60's and by tomorrow mid to even upper 60's dewpoints will have worked into much of the region and by Tuesday we could be looking at dewpoints approaching 70F! With a warmer low-level airmass moving into the region as well temperatures both Monday and Tuesday should reach the mid to upper 80's and possibly 90F in the hottest locations. With the increased humidity and moisture the threat for t'storms will also increase and both Monday and Tuesday feature interesting potential across southern New England. We will take a closer and more detailed look at each individual day.
Overnight Sunday into early AM Monday:
As dewpoints continue to increase through the evening and overnight period and PWATS increase as well we will begin developing some elevated instability across the region. In fact, a few computer models also develop some fairly weak surface instability overnight into early AM. Later on this evening/overnight computer models are showing a weak piece of shortwave energy moving through aloft in the mid-level flow. Given the presence of developing elevated instability and perhaps some weak surface instability some showers and perhaps a few t'storms are possible during the overnight and early AM period. Winds aloft are on the weak side and mid-level lapse rates aren't particularly steep and with not much in the way of instability severe weather is not expected overnight. Any storm though will of course carry a lightning risk along with torrential downpours given the increasing moisture.
Monday afternoon/evening:
Several computer models are developing a lee trough just to the west of southern New England during the late morning and early afternoon hours. With surface temperatures into the mid to upper 80's, dewpoints into the mid to upper 60's, and mid-level lapse rates around 6.5 C/KM the atmosphere may become moderately unstable tomorrow afternoon. While initially winds aloft are on the weak side and mid-level lapse rates won't be particularly steep both do increase as the afternoon goes on. By the afternoon mid-level lapse rates should be between 6.5-7 C/KM with deep layer shear increasing to around 30-35 knots by late afternoon/early evening. Some models also develop a LLJ across the region which helps to increase low-level shear and helicity. At this point it's a bit unclear as to exactly how tomorrow will unfold, however, given some of the pieces in place some thunderstorms are possible tomorrow afternoon and evening. Given some of the favorable parameters some strong to severe storms can't be ruled out. Some simulated radar models actually develop a squall line by late afternoon and move it through western CT late tomorrow evening so this will have to be watched. While the main threat should be torrential downpours/isolated flash flooding given the presence of high moisture damaging winds and large hail are also possible in some of the stronger storms.
Tuesday:
Tuesday appears a bit interesting although it appears we will dodge what could be a much more widespread and significant severe weather outbreak. Over the past few days computer models continue to be faster with the frontal passage and move the cold front through much of the region by mid to late morning. Due to this winds in the boundary layer shift from southwest to a more westerly/northwesterly direction and we start drying out the mid levels of the atmosphere and this dry air mixes down to the lower levels thus preventing stronger instability from developing. Shear/lapse rates are expected to be fairly impressive on Tuesday as well. While a major chunk of southern New England looks to miss out the potential for severe weather may still exist across eastern MA as the front may not move through here until mid-afternoon or so. This would allow for this area to destabilize much greater and have a great combination of strong winds aloft/instability. It's possible eastern MA could see quite a decent severe weather event. We'll still have to closely pay attention to this though as if the front does slow down by several more hours this could increase the threat for severe weather for areas further west.
After Tuesday all eyes turn to Friday as some computer models have a fairly impressive setup for severe weather across New England. However, given this is still several days out and alot can change we won't get into the details now. We'll worry about tomorrow and Tuesday first but it does appear to be an active week coming up.
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