How Dry Was it This Winter? A Climatologist Reviews the Numbers
In this March 28 Market Journal segment, State Climatologist Al Dutcher gives the forecast for the coming week.
By all appearances, average temperatures for the month of March will come in below normal across the entire state. The eastern third of the state has experienced departures of 3-6°F below normal, while the western two-thirds of the state is running 1-3°F below normal for the first 25 days of the month. In addition, the only area of the state currently showing surplus moisture for the month is the western half of Sioux and Scottsbluff counties.
Fall Moisture Surpluses Mostly Eliminated
The eastern two-thirds of Nebraska has been persistently dry since mid-November and four-month precipitation trends are running 25-50% of normal. Most locations within this wide area have failed to receive 25% of normal moisture during March, including a 45 mile wide area from Geneva to Omaha where less than 5% of normal moisture has fallen.
On December 1, most of eastern Nebraska was carrying surplus moisture of 2-5 inches from the generous early October and November precipitation events, but these surpluses have rapidly disappeared. Moisture in eastern Nebraska averaged 0.75-1.25 inches below normal from December through February, with most of the fall surplus moisture lost during this dry March.
Seasonal snowfall totals across the western third of Nebraska this winter are running near average to above average. For the Panhandle, the highest seasonal snowfall concentrations have been reported from the Scottsbluff and Harrison areas where they saw 55-65 inches. This amounts to two feet of additional snow when compared to normal. The extreme northern and southern Panhandle have reported seasonal snow totals ranging from 35 to 40 inches, or approximately 2-5 inches above average.
Across the southwest, seasonal snowfall totals are in the 22-30 inch range and every location is within 5 inches below to 5 inches above average. These snow totals hide the fact that most locations in the southwest had not broken the 10-inch mark for season snowfall at the beginning of February. So for the vast majority of Arctic air intrusions, little appreciable snowfall occurred to protect alfalfa and wheat from the bone chilling cold.
The intense Arctic outbreaks that have dominated most of our winter have been devoid of significant moisture, especially across the eastern two-thirds of the state. It is not like we haven't seen frontal passages on a regular basis during the last four months. No less than 25 fronts have swung through the state since early December. At least one-third of these events were accompanied by a maximum temperature drop of at least 20°F within a 24-hour time span.
These low-moisture snow events were easily blown around during windy periods and resulted in little, if any protective cover for wheat and alfalfa. Without the protective cover, bitter cold temperatures were able to penetrate soil surfaces and drive a deep frost layer that unofficially reached 3-4 feet deep at some of our northern locations.
The High Plains Regional Climate Center indicated that soil temperatures at the 4-inch depth under bare soil ranged from 15°F at Gordon to 26°F at Scottsbluff. By all appearances, minimum soil temperatures failed to drop below 20°F south of the northern counties bordering South Dakota. Soil temperatures south of I-80 ranged from 7°F at McCook to 25°F at Nebraska City. Minimum soil temperatures for most locations across southwest and south central Nebraska ranged from 15°F to 22°F.
The overall coldest soil temperature readings recorded this winter occurred across north central and northeast Nebraska with temperature readings ranging from the low to middle teens. The coldest soil temperature reading across this region was 7°F just east of Ainsworth. Most of the minimum soil temperature readings occurred during the first 15 days of January when snow cover was non-existent across the entire state and the large "Polar Vortex" had locked into position across the eastern half of the United States.
Some Sites See Extreme Lows
Preliminary Cooperative Weather Station data for the Panhandle and southwest Nebraska indicates that almost every long-term station recorded 20 or more days where the minimum temperature reached 0°F or lower. In fact, when you look at historical rankings, every station was in the top 20 percentile for this metric. There were 21 days meeting this criteria at Culbertson, 22 days at Kimball and Scottsbluff, 23 days at Hayes Center, 24 days at Imperial, 28 days at Chadron, and 29 days at Imperial.
These extreme temperatures were not limited to western Nebraska, as every station north of the I-80 corridor experienced at least 20 days where the minimum temperature reached 0°F or below. However, little wheat is grown north of a line from North Platte to Omaha and it just too early to assess whether alfalfa was negatively impacted from these extreme temperature conditions because soil temperatures have not warmed sufficiently to promote extensive spring growth.
Nebraska State Climatologist