Northern Plains Likely to See Below Normal Temps This Spring
Normal to Above Normal Moisture Also Likely
As robins huddle in masses around Lincoln, it is a constant reminder that spring is just around the corner. I can't help but wonder what inspired them to arrive just as another surge of Arctic air invades most of the eastern United States. That being said, they are a reminder to gather my thoughts on the type of conditions that we may experience as we move into the meteorological spring season of March through May.
I don't think anyone can argue that this winter has been cold with frequent Arctic air intrusions, especially across the eastern half of the state. Nebraska temperatures are averaging 4-7°F colder across the eastern half of the state and 3-5°F colder across the western half of the state. This is the coldest winter since 2009-2010 when we kept snow cover from the pre-Christmas blizzard until early March.
The winter of 2000-2001 stands in record books as the next coldest winter, but we maintained considerably greater snow cover which aided prolonged periods of below normal temperatures. If we look at sub-zero low readings, you would have to go back to the 1983-84 winter to find a comparable benchmark.
Considering that much of the winter has been snow-free, we could have easily added 10-15 additional days of sub-zero lows if we would have had snow cover on the ground during January. On a statewide basis we have had approximately 20 days with sub-zero low temperatures this winter. In a normal winter we would expect from five days in southern Nebraska to 10 days across our northern border.
Very few areas of the state have seen above normal moisture this winter. The southern half of the Panhandle and a small pocket of north central Nebraska reported above normal moisture, while the northeastern corner of the state received less than 25% of normal moisture. However, there has been a substantial uptick in snowfall during the last 30 days across the western third of the state with most locations receiving 10 and 20 inches of snow.
So the ultimate question is whether this winter's temperature and precipitation patterns will continue through spring. Based on the depth of cold brought to the upper Midwest this winter, I would be inclined to believe that temperatures are likely to be below average like last spring, if not more intense. Since mid-February 2012, eastern Nebraska has averaged two days of below normal temperatures for every day above normal. Western Nebraska is running three days below normal to every two days above normal.
The recent upswing in moisture across western Nebraska during the past 30 days can be directly tied to the relaxation of the western U.S. upper air ridge in response to warmer waters developing in the Gulf of Alaska. This energy is now regularly making its way into the western U.S. instead of being shunted into the Alaskan interior. When we begin to see low pressure systems come into central and northern California, it usually translates into an active pattern across the central United States.
In fact, the latest three-month Drought Monitor outlook shows improvement for central Nebraska and limited improvements in all the remaining drought areas in Nebraska. If the current snowpack in the central Rockies continues its impressive pattern for the remainder of the winter, this should translate into improved precipitation chances for western Nebraska into early summer.
As of last Thursday, snow water equivalent estimates of the current snowpack in north central Colorado stood at 134% of normal, while south central Wyoming estimates were at 118% of normal. This would indicate a snowpack of 125-150% of normal. In fact, some of the higher elevation sites are currently reporting snowpack levels usually reached at the beginning of March.
Typically March and April are the two biggest snow months in the central Rockies. If the stormy pattern continues, I expect substantial recovery for all reservoirs on the northern branch of the Platte, with an outside chance of complete recovery. Even with normal moisture over the next two months, I would envision that the reservoir inflows will exceed one million acre/feet and bring the entire reservoir systems from 50% of capacity to at least 75% of capacity.
In my 25-year career at UNL I have never seen a major drought develop when May snow levels in the central Rockies exceeded 120% of normal. Furthermore, I just don't see a major pattern shift that would bring an abrupt halt to the favorable moisture trend for the central Rockies and bring a sustained period (more than 30 days) of abnormal heat before this summer.
In short, I believe that this spring we will experience a repeat of 2013 spring conditions that would favor below normal temperatures and normal to above normal moisture for the central Plains. In fact, it is entirely possible that the first half of this spring will be colder than last year simply because of the extensive cold that remains locked into place across central and southern Canada, the Great Lakes region, and most of the eastern Corn Belt.
Extension State Climatologist