Monday, March 7, 2005

Mid-day: Springing back to winter

To paraphrase the poet, "What is so rare as a day in March?" In Washington so far this month, that would be an actual March day. Of the 7 March days including today, only one (yesterday) has had a high temperature which would be considered normal for any day in March. By late morning today, temperatures around the DC area were already at 60 or higher in many locations with generally south winds. The long-term average high for the last day of the month is 61. At noon, Washington National was at 63, and by 1pm, most reporting stations were in the upper 60's, with 70 in a couple of places. Today's record high of 77 doesn't look in jeopardy, but it does happen to be equal to the lowest record high for any day in March.

Momma Nature finally shut the freezer door at the Weather Grill over the weekend, but it's going to be flying right off the hinges this week. As Jason explains below, winter temperatures will be back by mid-day tomorrow. As Josh showed in the 10-day outlook on Thursday, this is caused by a strong high-pressure ridge at upper levels in the atmosphere over western North America, along with a strong trough developing over the eastern part of the continent. Under the ridge, California is drying out from their recent near-record rains. Under the trough, as it deepens, cold air will move steadily southward from Canada to the East Coast. This pattern also has a lot of energy associated with it, so there will some storm activity at the surface, although the Weather Grill chefs are still trying to decide exactly where and when to serve the spiciest dishes later in the week. On this morning's weather map, this is reflected in a strengthening low-pressure area centered over Michigan with a cold front extending southward to Texas.

We tend to focus our attention upstream (westward), since that's where our weather comes from, but the Northern Hemisphere circulation pattern continues to the east after our weather leaves us. The high-amplitude pattern, with a large north/south component of the upper-level wind direction, continues around the rest of the hemisphere. There is another strong ridge over the Atlantic and a corresponding trough over Europe, which accounts for the cold weather over there. The "Beeb" has posted slide shows of the snow and cold in Britain and the Continent.

Image: An abandoned car covered in snow in Kent, southern England, from BBC

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