Christmas weather likely very different from last Sunday’s
Published 7:00 am Tuesday, December 20, 2016
If anyone gave out prizes for cold, wet, blustery weather, Sunday could easily win the prize as the rawest day so far this winter in south Mississippi.
Rain started early Sunday morning and continued to fall off and on all day and into the evening. Amounts across the county totalled between one and two inches.
But, rain wasn’t the only thing falling. Temperatures started out balmy in the early morning hours Sunday at near 70 degrees. But then, instead of starting their normal climb at daybreak, temperatures across the county took a nosedive. Starting at about 5:30 a.m. in the northwest corner of the county and about 6:30 in Nicholson, temperatures plummeted nearly 20 degrees in one hour.
As a stiff north wind continued, the thermometer continued downward throughout the day Sunday, ending up in the middle 30s by mid-afternoon. The combination of wind and cold air made it feel like it was in the 20s.
Not only were raindrops and temperatures falling. Some folks heard a tick-tick sound on their windows. Sleet, or as the National Weather Service prefers to say, “ice pellets,” were mixed in with the raindrops at some locations.
Undoubtedly, the appearance of a little sleet caused some to hope that maybe the white, fluffy stuff would be close behind. That didn’t happen, however, for reasons I will discuss in a moment.
Obviously, the rapid drop in temperature and sudden increase in north winds Sunday morning signaled the passage of a strong cold front. But, even the casual follower of our weather knows that when a cold front passes, the rain that precedes the front usually comes to an end. Typically, the air behind the front is not only colder, but also drier.
Two things made Sunday’s situation unusual. First, just after passing to our east, the front slowed down as its position became almost parallel to strong southwest winds at upper levels of the atmosphere. The alignment of the upper flow and the shallow cold air near the surface caused the air to rise.
Behind the front, the cold air was very shallow.
The air from about 2000 feet above the ground to nearly 10,000 feet was warmer than at the surface and very humid.
The combination of rising air and plenty of moisture usually means condensation, clouds and rain. Sunday was no exception.
Some of the raindrops fell through very thin layers of freezing air and froze into ice pellets. Although they were melting as they fell through the thicker warm layers in the lower atmosphere, a few pellets reached the surface before completely melting.
Christmas Day is still five days away. Our current weather pattern is such that systems are moving rapidly across the country.
That makes it difficult to accurately forecast the timing of those systems and their associated weather more than about three days in advance.
So, as Christmas approaches, check the National Weather Service forecast at www.nws.noaa.gov to get the latest for our area or for wherever you may be traveling.
There is one thing about which the models are giving forecasters high confidence. This coming Sunday will be a lot warmer than this past Sunday. You may get an opportunity to wear your best pair of Christmas shorts.
By Skip Rigney