Stratospheric Change Could Foretell Cold Waves
Thursday 10 a.m.
As a high pressure area moves east from Ohio, sunshine is the rule in the Northeast today. Meanwhile, heavy rain is affecting the lower Mississippi Valley, and some of the moisture from that area will cause rain in Chicago tonight and over toward Philadelphia and New York City tomorrow.
In and east of the Appalachians, areas of dense fog and low cloudiness may persist into Saturday even after the rain is gone. Detailed analyses of some the computer forecasts suggest that while it will reach the 60s in Virginia Saturday, it may be reluctant to climb far through the 50s in eastern Pennsylvania, New Jersey and places farther northeast. However, with an increasing southwesterly flow even those places should be warmer Sunday.
The video shows more, including the chance of snow in Chicago Saturday night and the slow advance of the chill toward the Middle Atlantic states next week.
We have looked at pressure analyses in the high stratosphere over the north polar region from time to time. Research has shown that if the usual low pressure vortex that resides there splits, breaks down or reverses to a high pressure area, very cold air masses can be expected to push farther south than usual 10-15 days later. Blocking high pressure areas at the surface end to develop, and this forces the prevailing westerlies to move farther south than average. With storms taking more of a southern track, snowstorms become frequent. Such a reversal has just occurred, so we will see if it happens this time. In past situations, the new regime often lasts for at least few weeks and sometimes lasts for months.
The maps below show the pressure pattern last night and from a month before that. The H's and L's mark the centers of high and low pressure areas, and an orange line shows the ridge axis as it existed last night. For better reference to things on the maps, labels for Alaska and Greenland are added, and N shows the position of the North Pole. I left one low pressure label off the right-hand map. Can you find it? Hint: Look in Asia.
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