Excellent Colorado-centric winter outlook by Meteorologist Dave Aguilera making sense of the dangerously dry pattern locked in place over much of the country. The weekly drought monitor came out late last week and it shows Colorado and most of the western half of the country are feeling the effects of this no-moisture season.
The primary reason most of the moisture making storms have only been hitting the PNW, Great Lakes and northeast is the jet stream. The jet stream is the river of strongest winds around about 30,000ft that drives storms and cold waves. For the last several months the jet stream has been locked over the northern United States and southern Canada.
This has kept most moisture end of storm systems away from many western and southern states since the summer months. Part of the reason the jet stream has not dipped into the southern Rockies is “La Nina.” La Nina is the cooling of ocean currents off the coast of south and central America.
In a typically strong La Nina year, our winter storm producing storms tend to stay over the northern tier of states in the U.S. keeping the southern stretches warm and dry. That seems to be the case this year.
For Colorado, to get a heavy snow storm or a blizzard we need two of four things to happen: First we need the jet stream to buckle and dip southward allowing cold, Arctic air to ooze into the southern states. Then, we need a strong, old fashioned upslope to hit the Rockies. Upslope is a wind pushing east or northeast against our Colorado mountains. This can be caused either by a back door cold front or a storm system riding the jet stream south into southeastern Colorado or over the panhandle of Oklahoma. Or thirdly, a cut-off low needs to push into that southeast Colorado area pushing moisture back towards the Front Range.