Latest Northeast US Temperatures (click to enlarge)

The cool weather which we've been advertising for days has settled in to the area this morning, and made itself established first on Friday. Temperatures only reached into the low to mid 60's in most areas (with the exception of the urban areas, which typically run a few degrees warmer regardless of the airmass), and winds were out of the northwest and a bit blustery in the morning. Dew points were also dramatically lower, adding to the crisp and clear air. Air quality was great on Friday, for the first time in several weeks, as a high pressure remained in control. However, the forecast is slowly changing and transitioning (as it always is) and the first signs were easily visible late Friday afternoon as high clouds moved in and blocked the sunlight. These clouds were moving towards our area in response to a disturbance in the middle levels of the atmosphere. This disturbance will remain over the region today, causing skies to range from partly to mostly cloudy throughout the day. The high clouds over the area may re-appear during the day today, and although the sun won't be totally muted as it is during overcast skies, it will be noticeably less sunny. Temperatures, as a result, will be held into the mid 60's once again.

WHY WAS IT A BIT WARMER FRIDAY NIGHT?


It's interesting to note, in a post-mortem sort of way, how the high clouds prevented temperatures from falling rapidly Friday night into the early hours of this morning. The answer lies in the feature we discussed in the Friday afternoon blog post, "radiating". When the skies are clear under a cool airmass (or any airmass, really), the atmosphere can "radiate" overnight. Essentially, in the most simplistic of terms, the heat from the day at the surface (radiation) can escape into the atmosphere under clear skies and light winds. The calm winds are important, too, as they prevent the atmosphere from mixing..but we'll save the mixing of temperatures conversation for another day. Clouds, however, make the story more complicated. The clouds can hold the radiation near the surface, keeping the temperature warmer. This is way in some cases, on overcast nights, the temperature only drops a few degrees with the loss of the sunlight. On clear nights, it can drop several degrees.  


As we saw Friday night into the early hours of this morning, the clouds over the area prevented the favorable radiating that would have allowed another big drop in temperatures. Instead, areas farther north over New England (sans the clouds) dropped to unseasonably cool temperatures once again, and although our area was still below normal, temperatures were not as cold as they were Thursday Night.


THE FORECAST...


Today (Saturday): Partly to mostly cloudy, high temperatures near 67. Winds turning from northwest to east at 5 to 10 miles per hour. We'd definitely recommend jeans, but the long sleeves is a bit of a toss up given the temperatures nearing 70 in the afternoon. It really depends on your preference! Overall, not too bad of a Saturday. 


Tonight (Saturday Night): Partly cloudy, and cool once again, with a low in the low 50's. Cooler inland and north of the city (mid to upper 40's). Sounds like sweatshirt weather to us! 


A look ahead: Fair weather looks to be in control through Tuesday, when a warm front approaches the area..bringing with it a chance of scattered showers through at least Wednesday. 


Article written by John Homenuk, September 17th, 2011 at 12:49am. Looking for a forecast? See New York Metro Weather's Long Range Forecast for the upcoming weekend, or view our Technical Forecast Discussion for the more serious weather enthusiasts. Also, check out our new Forecast Overview tab. For up to the minute details on forecasts, watches, warnings, and alerts, follow us on Twitter and Facebook.