Summer's Leading Edge

Those of us who live in the Temperate Zones of Planet Earth generally recognize four seasons, based on astronomical, biological, meteorological and cultural events.  However, in my view, spring and fall are primarily transitional periods between our two major seasons: summer and winter; unlike the latter seasons, the timing and progression of spring and fall varies widely from year to year as stagnant weather patterns delay or accelerate their course.

During spring and fall, winter and summer battle for dominance, fueled by the changing intensity of solar radiation and an unruly jet stream; weather conditions and their effect on nature's cycle are far from predictable.  In some years, the crocuses bloom by mid February and tree frogs are calling from icy ponds by the end of the month; in other years, ice and snow coat the landscape well into March, delaying these early signs of spring.  While brief periods of warmth may occur throughout winter, the transition to summer must await an enduring thaw.

This week will likely prove to be the leading edge of summer in central Missouri.  After a frigid and snowy February, mild, sunny weather is forecast for the next week or so, putting an end to winter's reign.  While cold spells will surely occur over the next two months, warm conditions will steadily prevail as winter retreats to the north.  Unchallenged from May through September, summer will begin to fade in October, when winter's first, tentative incursions invade Temperate latitudes.  Of course, global warming will gradually shift this cycle, shortening the duration of winter and lengthening the course of mild weather; its potential effect on regional precipitation remains uncertain.