Today certainly featured a wide variety of weather conditions. This morning waking up it was muggy with showers. Then the sun came out, the humidity dropped significantly and it became very dry, but it got hot. This evening, the temperature dropped sharply after winds shifted to the northwest and the humidity rose to a more reasonable level. A breezy morning also turned quite gusty by nightfall.
This is all in some way related to a cold front that crossed through late this morning. Even though it got hot, dewpoints dropped off substantially into the low 40s as strong winds and subsidence mixed down very dry air from the mid levels. An upper low currently sliding east over Quebec will close off tomorrow. As a result, it will slow down tonight and turn southeast as it begins to cut off from the flow while a ridge slides over it. This will move the center of the low across northern New England tomorrow through tomorrow night. Heights will continue falling overnight and begin to level off during the day tomorrow. A sharp 850mb temperature gradient moved through this afternoon, and mid level temperatures in the low 60s this morning dropped to around 50 this evening, and will continue falling into the mid 40s by early tomorrow. The upper low will meander until it gets picked up by a high latitude trough on Friday. Until then, the northern stream trough will remain in control of our weather, with much cooler temperatures than we have been experiencing for a while now.
The Labor Day weekend cool down, which featured a stronger/broader low/trough combo and cool nighttime temperatures, still fostered warm daytime highs. This was the result of a strong westerly wind trajectory at the surface which resulted in significant downsloping. This was why my forecast highs for last weekend were on the upper end of the statistical model guidance. The center of the low remained over Canada, and we were positioned on the southeastern side of the low. This upper low on the other hand is weaker but more compact, and it will come farther south into northern New England. The main difference for us is that we will be on the southwestern side as the low digs east of our longitude, and this will make for a northwesterly wind trajectory at the surface as high pressure builds down from Canada rather than across from the midwest. This, combined with a lot of cloud cover and mid level temperatures in the mid 40s both Thursday and Friday, will result in cool daytime lows and highs this time around. Temperatures have dropped off very quickly this evening, and lows will be near 60 by daybreak. Highs tomorrow and Friday will be in the low 70s. There should be more sun on Friday as the low begins to pull away, but the wind will be stronger tomorrow and from a slightly better direction for some downsloping. This is why I believe that high temperatures will be similar both tomorrow and Friday.
I’m planning on updating again tomorrow in more detail with a look at the weekend as well.
Updated: 5:04 AM GMT on September 09, 2010
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