Warm-up to follow spring cold snap

Published 7:00 am Tuesday, March 22, 2016

High temperatures this week will climb back up into the 70s after a chilly start to astronomical spring.
For recordkeeping purposes, meteorologists and climatologists define spring as beginning on March 1st and lasting until May 31st. However, the astronomical first day of spring, also known as the vernal equinox, is on March 20th, although sometimes it can happen on the 19th or the 21st.
On the first days of astronomical spring and fall, the sun’s rays shine directly on the equator. On these days the earth’s axis of rotation has no tilt with respect to the sun. However, as we move further into spring, the northern hemisphere tilts more and more toward the sun, bringing the sun’s rays more directly overhead and giving us longer days and shorter nights.
More direct sun angles are the main driver for warming in the spring and summer. But, the weather on March 20th, or any other particular day in March, is much more directly affected by the usual weather makers of high and low pressure systems, cold and warm fronts, jet streams, etc.
So, it’s no surprise when temperatures drop below average on the “first day of spring.” It’s just an example of the normal up and down swings of temperatures typical in spring.
That was the case on Sunday and Monday in the wake of a strong cold front that moved through on Saturday. On Monday morning, temperatures fell into the 30s, although most locations in the county stayed above freezing. Similar conditions were forecast for this morning.
That certainly qualifies as a spring “cold snap.” In last week’s column I noted that it’s very typical for us to have one or more cold spells in late March and April.
But, I also wrote, “if there are to be any this year, they’re not yet in sight.” While that was the case last Monday morning when I wrote that column, the cold air mass very soon came into view.
Even by last Monday afternoon, March 14th, National Weather Service forecasters were calling for temperatures behind the weekend’s cold front to drop into the low 40s. As the week wore on, the computer models predicted cooler and cooler temperatures, and forecasters kept adjusting the forecast lows downward for Sunday, Monday, and Tuesday. By late last week, they were calling for lows early this week in the middle 30s, eight degrees cooler than the forecasts issued just a few days earlier.
But, this cold spell is now over. As the cold dome of surface high pressure slides to our east, our winds will switch around to the south, bringing in warmer and much more humid air. As a cold front to our northwest moves closer on Thursday, expect showers and thunderstorms to develop. Friday we will be behind the front and back into cooler air.
But not for long. Forecasters predict that developing low pressure over the Southern Plains will drag the front back out of the Gulf, increasing our rain chances again as early as Friday evening and continuing through at least part of the upcoming weekend.

By Skip Rigney

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