Dry stretch comes to an end this week

Published 7:00 am Tuesday, May 17, 2016

After two weeks with no rain, we are likely to have several rainy days this week.
Forecasters at the National Weather Service’s Weather Prediction Center in College Park, Maryland, are expecting one to three inches of rain across south Mississippi this work week.
We are likely to have several rounds of showers and thunderstorms starting today and extending through Friday. The timing of when the heaviest rain will fall is proving a challenge to forecasters because of uncertainty in the timing of the systems causing the rain.
For the rest of the work week, the upper level winds several miles above the surface will be from the west and southwest above the Gulf Coast. The triggers for our unsettled weather will be a series of disturbances in that upper level wind flow interacting with a stalled surface frontal boundary.
These disturbances will be a few hundred miles in width. That’s significantly smaller than the larger jet stream features that often cover half the North American continent. Because of their smaller size, and because the disturbances show up as troughs of low pressure on upper air weather maps, meteorologists refer to them as “short wave troughs.”
The air tends to rise on the eastern side of these short waves as they move from west to east. That upward motion is enough to lift the humid air over us. As the rising air cools, the water vapor condenses and clouds form. With enough lift, we get showers and even thunderstorms.
While all the computer weather models predict that several short waves will pass by us this week, their relatively small scale is a major reason for the uncertainty in predicting exactly when they will impact us.
As for temperatures, forecasters were right about last week’s temperature and humidity feeling almost summer-like. Highs reached the middle and upper 80s across most of south Mississippi and southeast Louisiana Tuesday-Saturday of last week.
Morning lows were in the middle 60s except for Saturday morning when dry air behind a cool front allowed the daytime heat to radiate away. Temperatures across the county dropped into the upper 50s early Saturday morning.
We were merely on the edge of last weekend’s cool air mass. The heart of the cold was centered over the Midwest. Frosty air spilled as far south as east Tennessee.
A new record low for the date was set at Tri-Cities, Tennessee, when the mercury fell to 35 degrees early Sunday.
We’re done with that kind of cool air until autumn. But, this work week’s afternoon highs will be a little cooler than last week because it will be a lot cloudier. Overnight lows will be in the muggy high 60s.
By this weekend an upper level trough sets up to our east shifting the winds several miles above our heads from west to northwest. Those winds may be just strong enough to finally push the previously stalled surface front down into the Gulf, which will allow us to partially dry out. But, don’t bet just yet on a completely dry weekend. Some of the models show at least isolated showers hanging around. Check the latest forecast changes from the National Weather Service by typing in your zip code at www.weather.gov.

By Skip Rigney

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