A broad dip in the jet stream encompasses the western half of the U.S., bringing much needed snow to the mountains and the Front Range urban corridor. Its leading edge crossed the Colorado Piedmont yesterday afternoon, producing a sharp contrast between the spring-like morning and the wintery evening. Intermittent snow fell through the night and has left about 4 inches of white gold on our Littleton farm; following almost two weeks of warm, dry weather, the precipitation and seasonal temperatures are more than welcome.
Ahead of this trough, Gulf air has swept northward across the Southern Plains and Midwest, bringing a dose of summer in mid winter. As the cold front approaches, strong thunderstorms (some tornadic) will ignite in that warm, humid air, stretching from east Texas to the Ohio Valley and southern Great Lakes. In the coming days, the trough of winter is expected to flatten out across the country, restoring seasonal conditions to most regions and pushing mild air back to the Gulf Coast.
While gyrations of cold and warm air (due to atmospheric troughs and ridges, respectively) are common in spring and fall, the current scenario has, in the past, been relatively uncommon in the middle of winter when the jet stream remained stable across the southern U.S. However, as our climate continues to warm, an unstable weather pattern, characterized by dramatic shifts in temperature and potent storm systems will likely stretch through winter as well.