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Progressive weather pattern this week

By Skip Rigney

Twice each day forecasters at each local National Weather Service Office issue a description of the weather systems affecting their area and the meteorological reasoning behind their predictions. For our area they are available online at www.weather.gov/LIX under the link labeled “Forecast Discussion.”

On Friday morning the forecast discussion characterized our weather pattern over the next week as “quite progressive.” Does this imply an incursion of politics into meteorology? Are fronts now predicted to move toward the left on the weather map? Should we expect liberal amounts of sunshine? When can we expect a return to a more “conservative” atmosphere?

It does seem that almost every topic and every corner of our lives is being colonized by politicians, political commentators, and even friends and neighbors with a political ax to grind. However, when meteorologists refer to a “progressive” pattern, it has nothing to do with politics.

In meteorology, a progressive pattern means that the troughs of low pressure and ridges of high pressure in the atmosphere are moving briskly from west to east. While the term applies to all altitudes in the atmosphere, weather maps of atmospheric pressure at the surface tend to look messier and more chaotic because of interactions of the atmosphere with land and ocean.

It’s usually easier for forecasters to see the big picture by looking higher up in the atmosphere. A favorite altitude to analyze is around 18,000 feet above sea level. This is a good “middle” level connecting the higher altitudes with the surface. The jet stream often begins to show up at this altitude. The troughs and ridges of low and high atmospheric pressure at this higher altitude often cause or influence the strength and movement of weather systems at the surface of the Earth, which is what most of us care about.

This week those high-altitude troughs and ridges in the atmospheric pressure field will be moving quickly from west to east. This “progressive” pattern at high altitudes will translate into rather unsettled weather for those of us living down at the Earth’s surface. Expect an abundance of clouds through Wednesday. Rain chances bounce around between 20 and 60 percent from today through Wednesday night or Thursday.

The first couple of troughs and ridges that pass over us are forecast to be relatively small waves. That means relatively small fluctuations in our temperatures through midweek. Today will probably be the warmest with afternoon highs climbing into the 80s.

However, the upper-level trough and associated surface cold front predicted to pass through on Wednesday or Thursday are predicted to be much stronger. Behind them, drier and cooler air are expected to clear our skies and drop our temperatures below normal.

Thursday and Friday will perhaps qualify as the “Easter cool snap” that my grandparents insisted would always occur. High temperatures are forecast to stay in the 60s, while lows are likely to fall into the 40s. There’s a slight chance that we could see some 30s in Pearl River County early Friday or Saturday morning.

But, thanks to the progressive pattern, the cool, upper-level trough will keep moving eastward. By next Saturday it will be replaced by a ridge of high pressure at high-altitudes, which should bring a warming trend for Easter weekend.