by Susie
Of highly unusual weather!
A highly unusual week-long heat wave is building over much of the U.S., and promises to bring the warmest temperatures ever seen so early in year to a large portion of the Midwest. The exceptional heat will also be exceptionally long-lasting: record-breaking temperatures 20 – 30 degrees F above normal are expected today through next Wednesday for much of the Midwest and Northeast U.S. The weather system responsible is a large upper-level ridge of high pressure that is “stuck” in place–a phenomenon known as a “blocking pattern.” The jet stream is bending far to the south over the Western U.S., then bending far to the north over the Rockies and into Canada, and lies far to the north of the eastern U.S.
Since the jet stream acts as the boundary between cold air to the north and warm air to the south, the current looping pattern is bringing colder than normal temperatures and snow to the mountains of the West, and summer-like warmth to the Eastern U.S. It is common for the jet stream to get stuck in a blocking pattern for a period of a week or more, but not in to this extremity. If the current model forecasts prove correct, a high pressure ridge over the U.S. bringing heat this intense and long-lasting in March will be unprecedented in the historical record, going back to 1872.
