If you’ve experienced Colorado weather since this summer, you’ve probably noticed that we’ve been warmer and drier than normal. The monsoon never really kicked in; September 2010 was the 112th warmest and 18th driest (out of 116) September on record; October was the 102nd warmest October on record (with average precipitation state-wide); November is going to come close to average for temperature, and could do so for precipitation, though the northwest mountains have received above-average precipitation while the Front Range continues to track well below average.
Part of the blame for these conditions is the historically dramatic switch from strong El Nino conditions last winter to moderate-to-strong La Nina conditions by this fall. Note the rapid change from the +1.9C SST anomaly to the -1.5C SST anomaly just 9 months later from the Australian Bureau of Meteorology’s ENSO monitoring webpage:
Colorado tends to be warmer and drier under La Nina conditions, as this pdf from the Boulder NWS office shows (esp. pp 12&18). Coincident with this La Nina, which should abate by next summer, is even more snow for northwest Colorado and more warm & dry conditions southeastward from there.
A few notes for those interested: The last El Nino event was the strongest on record since 1997-98. The last El Nino’s strength and durations wasn’t forecasted particularly well by the suite of models used to do such things. The current La Nina’s strength was much more accurately forecasted, although the rapidity of regime change wasn’t handled quite as well. Neutral El Nino/La Nina conditions should return by next summer or fall.
ENSO continues to be one of the strongest causes of monthly and seasonal temperature and precipitation trends. Underlying ENSO and other oscillations is global warming, which is already directly affecting the Arctic and will show up more prominently at lower latitudes in coming years. The effects on ENSO and other oscillations by global warming is an area of ongoing research.
Cross-posted at SquareState.