Notorious spring temperature swings have arrived
By Jared Shelton News-Press NOW meteorologist
One of the biggest hallmarks of the heartland’s climate is the wide range in temperatures felt from season to season.
Being centrally located within the continental United States, the American Midwest and Great Plains are situated hundreds of miles from the moderating effects of Earth’s oceans, a recipe that allows for scorching summers and frigid winters. Aside from location, the geography of the region itself also plays a role, as wide open land and gently rolling hills provide little obstruction against ice-cold polar air masses and sultry tropical ones.
In addition to high seasonal variability, America’s heartland is also prone to massive swings in temperature in much shorter periods, including weeks, days or even hours. Spring is a notorious time for these rapid temperature shifts, as deep low-pressure systems ride along the polar jet stream, pulling masses of warm air hundreds and sometimes thousands of miles north.
As these systems track in a general west-to-east motion, the counterclockwise swirl within them forces a surge of polar air southward in the form of a sharp cold front. This week’s weather was a prime example of just how quickly temperatures can change here in Northwest Missouri when a strengthening low-pressure system tracking near the Canadian border generated an impressive temperature gradient extending hundreds of miles to the south.
It started with two days of record warmth here in St. Joseph, as an already unseasonably warm air mass was amplified by strong southerly flow and sunny skies. The mercury rose to the low 80s on Monday afternoon and the upper 70s on Tuesday, both setting new daily record highs at Rosecrans Airport. Shortly after 1 p.m. Tuesday, a northerly breeze began to stir, quickly becoming a gusty gale that suddenly broke the summer-like warmth, dropping temperatures by six to 10 degrees per hour through the evening.
By 9 p.m. Tuesday, winter had returned with a vengeance, as temperatures plunged into the low 20s, snow began to blow in the frigid air and wind gusts of 40 to 50 mph resulted in single-digit wind chills. The snow was short-lived, with only a dusting left behind as skies cleared by midnight, yet temperatures continued dropping slowly through early Wednesday morning. By 7 a.m. Wednesday, the temperature bottomed out at an icy 12 degrees, an astounding 66-degree drop from only 18 hours prior.
Given the right atmospheric conditions, sharp cold fronts like the one seen this week can be a catalyst for violent spring severe weather outbreaks. Tuesday’s system was lacking deep moisture when it passed through Northwest Missouri, curtailing any chance for strong thunderstorm development locally. However, this will not always be the case as moisture availability is bound to increase as spring progresses.
Until then, the greatest threat from passing fronts will be periods of elevated fire danger. Gusty winds associated with frontal passage can foster out-of-control grass and brush fires, especially when combined with dry air, fuel, and mild temperatures. For this reason, Red Flag warnings have been issued across the Central Plains on multiple occasions this week. It’s a trend that could continue into early March given a generally mild, dry and breezy pattern in the forecast for the next five to seven days.
