FLOOD10416 - Laserfiche WebLink

Home Browse Search

Historical Perspectives on Colorado Drought pressuTC introduces moisture into Colorado from both the Gulf of Cali fomi a and the GulfofMcxico. :\100\000 thunder!ltorms bring ~-- July Mean Flow at 18,000 Feet / -- (from Douglas 1993) The data in the preceding figure is analogous to an area of high pressure at approximately 18.000 ft above sea level. Droughts that have occurred during the summer and Early Fall period arc typically associated with an unseasonable north\vard migration of this area of high pressure resulting in two physical impacts. The first impact would cll"t:ctively funnel the rich sub.tropical moisture to areas further west of Colorado in the direction of California, Arizona, and Utah. The second impact is that a more local presence oflhis mid-level ridge over the state can result in relatively wanner temperatures at these levels. Unseasonably wann air (between 10,000 and 20,000 ft above sea level) can act as"a lid on the atmosphcrc", acting to suppress the strength of convectivc activity across the region which rcduccs the occurrences of summer thunderstonns. The longer-tenn persistence of this ridge over Colorado can result in below-nonnal amounts of precipitation on a more widespread basis. Jet streams, storm tracks, EI Nino's and La Nina's The production of precipitation across the stale is attributed 10 the general positioning and strength of the jet stream. which typically traverses the state in a west-to-cast manner during winter and spring. A majority of the moisture that falls across the Page 18 recycled content paper HDR Engineering, Inc. Printed on 30% post-<:onsumer Jiummcr raimo, Courtesy NOAA - \~ J , -~-" l~ "-I ,?~<~~ pf /). I \ Jr'~ /- ?'{ --- L-i 7( \ \ '- -""J i '-... , , . " ,- .., , I '-- ( Figure 15 long-term average of the 500 MB height field for July