The Southwest Monsoon generally begins in June as high pressure over the Southern Plains and low pressure near the upper Baja Peninsula combine to sweep moisture north from both the Gulf of California and the Gulf of Mexico. This precipitation, combined with the summer heat, ignites thunderstorms over the Desert Southwest in early-mid summer and the pattern shifts northward over the following weeks.
Here in Colorado, the monsoon rains tend to peak from mid July to mid August, bringing much needed relief to the parched landscape. While most of the annual precipitation along the Front Range falls from March to May, in the form of upslope snowstorms and widespread rain events, the monsoon thunderstorms can dump excessive amounts of rain in a very short time, often producing a flash flood; on the other hand, these storms are hit and miss in nature and some areas benefit while others remain dry. This year, for instance, heavy rains have fallen near and north of Denver while our Littleton farm has received only a few brief showers.
All could change over the next few days as the monsoon flow is expected to increase across the Front Range. Building over the mountains, the storms wax and wane as they move toward the urban corridor, where anxious residents watch their approach and hope for a direct hit on their parched lawn and gardens. Alas, for any given round of storms, most of us are losers.