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Long Term Climate - Colorado

Summary of Climatic Conditions -May 2002

Nolan Doesken
Research Associate
nolan@ccc.atmos.colostate.edu

May weather is tracking normal patterns in many ways with increased humidity east (esp. NE) of the mountains and warm and dry weather dominating over SW Colorado. The opportunities for precipitation have been increasing. NE Colorado picked up some chilly rains 11-12th and much of the state got rain on the 16th -- heaviest amounts were all over the NE quarter of the state. The N. Front Range Mountains got a nice snow 11-12th. But, when you compare to our longterm average, even the areas getting precip still aren't keeping up with average. May typically brings 2-3" of precip to NE Colorado and the mountains with lesser amounts over SE Colorado and lesser still over W. Colorado. There are a few places that have gotten close to an inch of moisture so far this month but that is the exception, not the rule.

Things are still looking relatively green over portions of NE Colorado with the help of these recent rains and with the help of cool temperatures. This is the part of the state that got the most fall moisture and a few modest winter and spring storms. It shows!! May has been cooler than average so far over NE Colorado. Thankfully, there have been very few days with hot, dry winds so far this month and no prolonged early heatwave like what we saw in 2000, so plant water demand has not yet been excessive. No heatwave is yet in sight, I am pleased to say. That is not the case, however, over southern and SW portions of the state where the dry conditions are resulting in an early onset of summer. Where snow has melted out early, the spring temperatures in and near the mountains have been much higher than average. Some places at elevations abover 9,000 feet came close or set new records fot the warmest April.

It is now May 20 and only a few weeks of our spring wet season remain. Temperatures will inevitably be warming now with more 80s and eventually 90s showing up. This will mean more stress for vegetation. There is very little chance now of adding to the winter snowpack, although mountain snows still can happen until well into June. With sparse and dry vegetation and more limited vegetation, it is very possible that we will see extremely hot daytime temperatures later this summer. The flip side is that during extreme drought in this part of the country, nighttime temperatures are normally quite cool and drop very quickly after sunset.

All in all, while the humidity is climbing, and thunderheads are building now, we haven't had any really big rains as we often do in May, and there is still nothing major in sight. We are at the time of year, now when scattered showers and thunderstorms will develop on many days, and this will be helpful for some small areas that are in the path of the storm, but the large, slow-moving storm system that can bring 2 or 3 days of soaking rains to much of the state at the same time in April, May, and early June has not appeared. It is not too late, even in June, but it is not looking good.

Snowmelt runoff projections remain pitiful -- even if it rains now. Surface water irrigators have little to be excited about but will have the opportunity to use what water they do get very carefully.

Just to keep you on your toes, I will bring up too years from the past which were in the middle of drought episodes -- 1955 and 1965. Both years saw late season (May in 1955 and mid June in 1965) upper level low pressure areas pump incredible moisture into the state. Colorado's worst and most widespread flooding of the 20th Century resulted in June 1965. The flooding was limited in 1955 to parts of SE Colorado.


 


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