Pleasant for now, showers later this week, warming trend this weekend

Although an area of persistent troughing which has kept the area chilly this spring has remained in place, a high pressure system to our north led to downsloping westerly and northwesterly winds this afternoon. This warmed temperatures up to around 70 in most of the area, while keeping the atmosphere very dry, with dewpoints in the low 30s. The dry conditions in combination with the trough that is still in-place will allow temperatures to drop pretty quickly tonight, as areas in the interior could have temperatures falling into the upper 30s, and frost is possible. Elsewhere, low temperatures will probably fall in the 40s — still definitely chilly enough for the light jacket tonight.

Starting tomorrow, the weather pattern will begin to change. Warmth and moisture from the south and west will try to push towards our area, while the troughing will remain to our north and east. This will create a battleground, and a resulting warm front.

The above image shows the frontal boundary pretty clearly — the front is shown more clearly at the 850mb level, since surface temperatures are a bit more uniform due to continued downsloping flow. This will once again make surface temperatures a bit warmer for tomorrow than what they normally would be in our otherwise cooler airmass. This will allow high temperatures to approach 70 degrees again. Warm 850mb temperatures result in the potential for greater warmth given sunshine, but that potential is not always realized — and this is where the forecast becomes a bit more tricky for later in the week, which will be illustrated shortly.

Where the strong southwesterly flow at 850mb meets with the much lighter winds, is the general location of the frontal boundary, further illustrated by the strong temperature gradient. The continued northwest flow on the cold side of the boundary at 850mb will help keep things dry tomorrow, but once those southwest winds from 850mb approach in association with the front, our 850mb temperatures will rise, and the moisture in the atmosphere will increase significantly. This allows for the chance of showers and potentially even a thunderstorm on Wednesday night into Thursday morning. The warmer airmass will not allow temperatures to fall as much, as they will remain around 50.

The forecast becomes much more tricky starting on Thursday. Some data has the warm front continuing to plow past our area, which would place our area solidly in the warm sector, allow for peaks of sunshine, resulting in temperatures shooting through the 70s, with perhaps a few scattered convective thunderstorms. However, other data, including the most recent trends, has the front stalling over or just south of our area on Thursday. We favor this scenario given that the residual trough will not easily scour away, and the chilly ocean temperatures also can act to initially resist a warm frontal passage.

Despite warming 850mb temperatures, today’s NAM shows temperatures remaining chilly on Thursday, as the warm front stalls just to our south (weather.cod.edu).

The image above is the surface temperatures for Thursday afternoon, instead of the 850mb temperatures. 850mb temperatures will warm up to between +6 and +8C, with the approach of the warm front. However, the front itself will not completely pass the area. This allows for continued lift in association with the boundary, which provides plenty of clouds, keeping temperatures down. Additionally, being right near the vicinity of the warm front means that the surface winds tend to be southeast instead of southwest — the southeast winds bring in chillier, Atlantic Ocean air, further helping to keep our temperatures down. Thus, Thursday can expect plenty of clouds, with a few scattered showers, and temperatures in the upper 50s to low 60s.

Fortunately, by the time Friday rolls around, the front will finally be able to push a bit further north. As it approaches, temperatures will be able to warm into the low to mid 70s in most of the region, with upper 60s along the coast. A few clouds and showers may still linger, but some peaks of sun will also be expected.

Today’s 18z NAM for valid for Friday shows temperatures warming back up (weather.cod.edu).

Notice how in the above image, the southwesterly winds on the warm side of the boundary have finally prevailed over much of the northeast. A sea breeze boundary may still exist along the immediate coast, however, which is why temperatures will be a tad chillier there. Once Saturday rolls around, the front will clear the area a bit more, placing our area solidly in the warm sector. This is when we can potentially expect temperatures to approach 80 degrees!

Today’s 12z GFS shows dewpoints exceeding 60 degrees overspreading the area by Saturday (weather.cod.edu).

Unfortunately, humidity will also be on the increase, which may finally give us our first true classic warm and humid feel to the atmosphere. Friday will be a bit muggy as well, but Saturday is when we will really start to feel it, as dewpoints could potentially exceed 60 degrees. Additionally, a weak cold front will be approaching from the west on Saturday — which combined with the warm and humid conditions — could trigger some scattered showers and thunderstorms with the potential for heavy downpours come Saturday evening. That being said, however, there still should be periods of sun earlier in the day, so outdoor activities may still be had.

The cold front will cross on Saturday night into Sunday morning, which may help for clouds to initially linger, before clearing throughout Sunday. Temperatures will not be all that chilly behind the front; plus we may once again have downsloping winds to offset the slightly cooler atmosphere, allowing temperatures to once again rise well into the 70s for Sunday and early next week.