Cool air already leaving, warmth returning
By Skip Rigney
A cold front moved through the area Thursday morning, but the coldest air has already moved to our east. The upcoming work week will be relatively mild.
Numerous showers and thunderstorms accompanied the cold front as it approached the area from Texas on Wednesday, passed us, then moved into Florida Thursday morning. Rain totals in Pearl River County for Wednesday and Thursday ranged from one-half to two inches.
Earlier this week the Pearl River had fallen to its lowest levels this year at Nicholson and the lowest since mid-December at Bogalusa according to stream gauge data from the U.S. Geological Survey (maps.waterdata.usgs.gov). But Wednesday’s and Thursday’s rains were even heavier in the Pearl River watershed to our north than in Pearl River County. Accumulations of two to four inches were common between Columbia and Jackson.
Much of that water will be making its way down the Pearl River. The river is forecast to inch back up to the water levels seen during much of January. Forecasts for the Pearl River and for West and East Hobolochitto Creeks are updated daily by the hydrologists at the National Weather Service’s River Forecast Center in Slidell (www.weather.gov/LMRFC/).
The wind flow in the atmosphere from three up to seven miles above us will be mostly from the west and southwest over the next week. That will keep bringing Pacific moisture into the air above us. Computer models predict several disturbances will be carried along in the southwest flow aloft. Although their timing is difficult to predict, it’s a good bet that the upcoming week, beginning Monday, we will see more clouds than sun, and probably a few rounds of showers.
The west and southwest winds aloft from Texas across the southern U.S. and northeastward to New England also means that the cold air is staying bottled up to our north and west. Temperatures will be mostly in the 60s and 70s from Sunday through Thursday when the next cool front is predicted to push through.
The upcoming mild weather, and, for that matter, the relatively mild winter we’ve experienced, is associated with a much larger weather pattern known as the positive phase of the North Atlantic Oscillation.
This oscillation refers to changes in the sea-level pressure difference between an area of low pressure usually located near Iceland and southern Greenland and a semi-permanent high pressure system centered in the eastern North Atlantic near the Azores Islands.
When the pressure difference between these two systems is small, the NAO is said to be in its negative phase. This is often accompanied by the jet stream dipping southward over eastern North America, then boomeranging northward toward Greenland. That pattern opens the door for cold air to pour into the eastern United States.
However, this winter the Icelandic Low and the Azores High have each remained quite strong, making for a large difference in sea level pressure between the two. This positive phase of the NAO is associated with fewer deep southward excursions of the polar jet stream and milder winters for us.
Computer model predictions for the next ten days show the NAO staying positive. Of course, we’ll still get cold fronts, but the odds of truly frigid air reaching us anytime soon is even less than normal.