The Climate Prediction Center (CPC) released their long-lead outlooks this morning (February 18th) and they have increased their odds of dryness and warmth for this spring (Mar-May) when compared to the January outlook for this same period. CPC continues to project below normal moisture and above normal temperatures for Nebraska, with a slight northward shift of probabilities that the outlook will occur.
The official Spring temperature outlook (Figure 1) calls for above normal temperatures across the southern 2/3 of the United States. Only a small sliver of the Pacific Northwest is titled toward below normal temperatures. When the current temperature outlook is compared to the January release (Figure 2), there is a northward areal shift of above normal temperatures by approximately 150 miles.
The official Spring precipitation outlook (Figure 3) indicates a broad area of below normal moisture is expected from the southwestern United States northeastward through southern South Dakota. Compared to the outlook issued in January (Figure 4), CPC has shifted their areal extent northward about 100 miles and increased probabilities of the event occurring, particularly over southwestern Texas and southeastern New Mexico.
The recent Arctic air intrusion over the past two weeks has left a widespread snowpack and significant ice accumulations on area lakes, rivers, and streams. The current snowpack will slow down surface warming in the near term as it melts, increasing the odds that air temperatures will remain below normal. Once the snow disappears, soil surfaces should be at field capacity and will be slower to absorb solar radiation, further limiting the ability of air temperatures to warm rapidly.
The area most likely to experience above normal temperatures going into March would be the western 1/3 of the state. The drought of 2020 left soils parched and storm activity has largely remained north and south of the area. With dry soils, surface temperatures will warm quicker than wet soils and will be more supportive to above normal temperatures until a regular precipitation pattern returns to the region.
As we move through March and into April, I suspect that the storm activity we have seen the past two months will continue. If you examine overall storm tracks this winter, both the southern and northern jet streams have produced exceptionally strong storms. Since there are no signs presently that this atmospheric pattern will break down, I expect that several major storm events will develop across the central and northern Plains through mid-April.
If the southern stream continues to kick out energy into the southern Plains as we progress through April and May, we are likely to see several significant severe weather events across Texas, Oklahoma, and Kansas. Usually when this happens, widespread moderate to heavy rainfall/snowfall (elevation dependent)occurs on the northwestern flank of the upper air trough across Nebraska, South Dakota, and North Dakota. Therefore, I am more inclined to believe that normal to below normal temperatures and normal to above normal moisture will occur across the eastern 2/3 of the state when the final Spring numbers are tallied. However, we are likely to experience wild swings between periods of above and below normal temperatures.
Western Nebraska would currently be favored to receive above normal temperatures the first half of this Spring with normal to below normal moisture. During the second half of this spring, I expect storm activity to increase in response to the jet stream pulling northward and upper air troughs taking a path across the central, instead of the southern Rockies. The increase in storm activity would support below normal temperatures due to cloud cover and wetter soil surfaces. If the rains fail, then above normal temperatures will dominate the entire Spring period.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office