A Brief Intense Upslope

After a warm, sunny week, yesterday dawned cool and cloudy along the Colorado Front Range; periods of light drizzle moistened the pavement and the temperature hovered in the mid thirties (F).

Then, about 10 AM, flurries appeared in the air and, within15 minutes, intense snowfall enveloped our farm; two inches fell over the next 90 minutes, coating the trees, shrubs and grass but melting on the warm pavement.  By noon, the show was over and patches of blue appeared in the overcast.

Such brief periods of intense snow are not unusual along the Front Range urban corridor, especially in March and April.  As an unruly jet stream steers cold fronts down from the northwest, northeast winds just behind the front shove moisture from the Great Plains toward the Continental Divide.  Rising with the landscape, the air cools and condensation occurs, often producing bands of intense snow comparable to lake effect snows of the Great Lakes region; as the cold front moves off to the east, the upslope band shifts southward, eventually dissipating along the Palmer Divide beyond which the air flow is forced to descend, warm up and dry out.