Posted by: splillo | April 17, 2012

Drought

A quick verification of my forecasts from the last post ...

Multiple severe weather episodes occurred in the Plains last week culminating in a major tornado outbreak on Saturday. And ridging returned to the East, featuring sunny skies and near record warmth.

Whether you've noticed or not, New England has fallen into a moderate to severe drought so far this spring. This is a combination of a number of factors.

To begin with, the well below normal snowfall this winter has left us with very little snowmelt in the spring. Normally this time of the year, the rivers are bursting with fresh cold water pouring from the mountains. Spring is the season greatest prone to significant flooding for this reason alone. Not this year.

In addition, we have been under a monster ridge of high pressure this spring. The ridge pushes storms to our north, keeping precipitation out of the region (see the image above, courtesy of the HPRCC). It also features incredible heat, which I'm sure you have noticed. March 2012 was not only the warmest on record for the United States, but also shattered 25 individual state records across the country. April has just continued where March left off. This past weekend featured near record breaking high temperatures across the Northeast. All the while, the sunny warm conditions evaporate water from the ground, and the rivers run lower and lower.

There's a saying, "drought begets drought" which means that once a drought begins, it tends to support itself and it's tough to break. Dry ground heats up faster, expanding the high pressure ridging, generally preventing precipitation, and we just get drier. It's a feedback loop that's tough to reverse. This is why you hear of places in the U.S. and around the world with multi-year droughts. These are extreme cases, and I don't think we're not heading in that direction, but at some point we need to get some appreciable rainfall to break the downward spiral. An event of this nature may be in the forecast.

Model guidance has a number of disturbances riding east from the Pacific which could bring some showers to the area by the weekend ...by no means a drought-buster. However by early next week, the forecast models have a significant trough developing in the East, pumping moisture from the Gulf of Mexico into New England. This is a long range forecast, so some changes are likely, but the signal remains for a notable storm next week.


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