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    Elliot Abrams

    DC to Boston: Fine Until Friday, Then Showery

    By Elliot Abrams, AccuWeather chief meteorologist
    7/30/2014, 5:43:06 AM

    Wednesday morning

    Today's video includes a time-lapse movie with cumulus clouds as well as the forecast through the coming weekend. Around the Great Lakes, stubbornly cool air aloft contributes to the chance of daily afternoon showers or thunderstorms. However, at most times and most places, the vast majority of the time will be dry.

    Some of the cool air aloft moves over the Northeast as well, and that can lead to spotty afternoon showers and thunderstorms... mainly west and north of I95. This weekend, a switch to more southerly flow aloft can bring very moist air toward the region, leading to widespread showers from the Appalachians to the Atlantic. In areas where clouds and showers are most numerous, daytime temperatures will not get out of the 70s (rare for the first weekend of August).

    On the following map, we see the upper air flow around 3.5 miles overhead. I also highlighted the temperatures at two spots. The site in Michigan had a temperature of -18 C, which is just below zero degrees Fahrenheit. Near Las Vegas, the temperature at the 500 mb level was -4 C, which is 25 degrees F. In a trough, the 500 mb height is lower than it is in a ridge. It is interesting to contemplate that even when Death Valley, California, has a temperature of 110 or 120 degrees, you only have to go up a little more than 3.5 miles to find temperatures at or below freezing.


    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com


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    Elliot Abrams