April 12, 2013

Two storms expected for next week

An exceptionally strong and slow moving upper air trough moved through the central United States this week, bringing the most significant and widespread moisture Nebraska has experienced in over a year. Areas immediately adjacent to a line extending from south central Dundy County northeast into eastern Holt County reported 3 to 5 inches of moisture. Snow totals approached 20 inches across the northern Panhandle and blizzard conditions were common across the western third of the state.

High temperatures dropped nearly 50°F from Monday (April 8) to Tuesday in the western third of the state, while drops of 30-40°F were common across eastern Nebraska. As the system moved east from Nebraska, heavy rainfall was reported across large sections of Iowa, Illinois, Indiana, Michigan, Minnesota, and Ohio. Heavy snowfall blanketed much of South Dakota, central Minnesota, northern Wisconsin, and northern Michigan.

Here in Nebraska, the greatest unofficial liquid equivalent storm total was 4.73 inches near St Libory and 24 inches of snowfall southwest of Chadron.

Drought Monitor Assessment Improves for Nebraska

The copious precipitation totals led to a major revision of the Drought Monitor’s depiction of Nebraska. Nearly all D4 (exceptional) drought was improved to D3 (extreme) drought. Areas previously depicted in D2 (severe) or D3 drought remained unchanged.

Since hydrological drought is not the primary focus of the Drought Monitor at this time of year due to low water demand, short-term agricultural indicators take precedence. In order to move from D4 to D3, the time periods analyzed (one to six months) must improve from a one in 50-100 year return interval to a one in  20-50 year return interval. (This reflects the likelihood of having the stated degree of drought during the time period.)

The second criteria necessary to reduce the drought from D4 to D3 is that the top foot of the soil profile needs to reach field capacity. According to the High Plains Regional Climate Center soil moisture monitoring network, all locations that received at least 0.75 inch of moisture are now at field capacity in the top foot. Areas that received over two inches of moisture are at field capacity down to 2 feet.

There should now be sufficient moisture for crop planting and establishment. Unfortunately, deep subsoil moisture (below 2 feet) is significantly lacking and will require several more storms of this magnitude to reach field capacity down to 4 feet. Statistical analysis of period of record data from these soil moisture sites indicates that peak soil moisture in the profile typically occurs within the first 15 days of May.

While this recent system was welcome, we have a long way to go before there is enough soil moisture to support several weeks of crop growth without irrigation or precipitation. Even though this month-long stretch of below normal temperatures is delaying corn planting, it’s allowing soil moisture to improve before crop water demand cranks up in late May.

Cool Temps, Snow, and Rain Expected Next Week

If you are planning on temperatures rebounding enough to warm soil temperatures to an acceptable level for planting, you are likely to be disappointed in the short term. Two systems are expected to move through Nebraska next week, bringing well-below-normal temperatures and moisture. The first will move through the Dakotas this weekend and bring a chance of scattered showers across the northern third of the state.

The second, more powerful system is expected to swing out of the central Rockies late Monday into early Tuesday. It's expected to bring accumulating snowfall to the northern Panhandle and western Sandhills from Tuesday to Wednesday, according to a European model. The American model indicates the storm may track further south, moving through the southern Panhandle and southwest Nebraska. Enough cold air will be drawn into the system to limit high temperatures to the upper 20s to upper 30s.

Weather models indicate that by Wednesday moisture will move into eastern Nebraska, with potential for accumulating snow across the central third of the state. A mixture of rain and snow is possible across eastern Nebraska with the greatest potential for accumulations across the northeast corner. High temperatures will struggle to reach 40°F next Wednesday and Thursday. Total storm water equivalent moisture is projected to be 0.75-1.25 inches across the Panhandle, 0.50-0.75 inch in the central third of the state, and 0.75-1.00 inch across eastern Nebraska.

After next Thursday (April 18), models indicate a moderating temperature trend April 20, 22, and 24. During the last full week of the month, a strong upper air ridge is forecasted to develop across the western third of the United States and build into the western Cornbelt. If this does occur, a dry pattern will develop and high temperatures in the 70s will provide excellent planting conditions.

Al Dutcher
UNL State Climatologist