Frozen soil on the Wisconsin River basin is some five feet thick based on reports from plumbers thawing septic tanks and utility workers boring holes for power poles. Solid ground, as it were, to that depth has significantly reduced the natural movement of water through the soil on the 12,000 square mile drainage and consequently the flow in the state's largest river according to Wisconsin Valley Improvement Company (WVIC), Wausau.

WVIC operates 21 headwater storage reservoirs under license from the Federal Energy Regulatory Commission to regulate a uniform flow in 430-mile long river.

Frost penetrated deeply because there was no snow to insulate the soil from the Arctic express that made winter bitterly cold from mid-January to present.

The frost may be slow to melt in spring because a layer of snow from a Feb. 3-4 snowstorm will insulate it until the snow melts and bare ground can absorb solar heat. WVIC said the situation may contribute to a greater amount and rate of snowmelt and rainfall runoff reaching reservoirs and the river when melting occur because moisture will not percolate the frozen soil.

It was like an Arctic desert in the Wisconsin Valley Feb. 7-13. The sun shone daily in mostly cloudless skies while wind produced dangerous wind chills. Precipitation was minimal with just a dusting of powder north and brief intense snow squalls south Feb. 11. Temperatures were below normal and fell to single and double digit below zero readings each night and rose only to the single digits or teens each the day.

A Feb. 13 snow water equivalent map of the continental United States produced by the National Weather Service (NWS) National Operational Hydrologic Remote Sensing Center, depicted snow water content over Wisconsin as ranging from half an inch central to as much as 4 inches over the lake effect snow region along the Wisconsin-Michigan line. (Emailed Wisconsin River Report see color map on page 4)

With the movement of water through the soil and on the surface reduced by cold, Wisconsin River weekly average regulated flow declined Feb. 7-13 except at Merrill where adjustments to reservoir releases resulted in a slight increase.

Wisconsin River flow at Eagle River Feb. 13 was 154 cubic feet per second (cfs), 117 cfs less than Feb. 6 and 36 percent of the 426 cfs February normal. The decrease was evidence of how average low temperatures of minus 10 degrees reduce the flow of water.

Back in November when the soil was wet from above normal rain and reservoirs were full, WVIC's hydrologic analysis suggested that natural or base flow in the Wisconsin River would run at or above normal during the winter ahead. Then precipitation essentially ceased and Arctic cold changed moist bare soil to rock. As winter progressed, natural drainage to the Wisconsin River, as well as other streams in the state, decreased dramatically.

As a counter measure to the less than normal moisture situation, WVIC gradually reduced the amount of water released from reservoirs. Reservoir release in average cfs, for example, was reduced 30 percent from Feb. 3-9. Reservoir water was 30 percent of the 1,941 cfs regulated flow. The target flow at Merrill through Feb. 16 will be 1,800 cfs.

An aberration of note in both the trends of cold and of decreasing natural flow, a warm spell Jan. 31-Feb 4 when a snowstorm occurred, contributed to a rise in natural flow, the flow that occurs without reservoir operation. Natural flow Feb. 2 was 930 cfs. It rose to 1,351 cfs Feb. 9, 111 percent of or 136 cfs more than the 1,215 cfs February normal natural flow.

Weekly average temperatures in the Wisconsin Valley Feb. 7-13 were 16 degrees below normal at Willow reservoir in Oneida County and 17 degrees below normal at Wausau. Willow reported minus 26 degrees Feb. 7. It may have been the last of this winter's deep cold.

The NWS Climate Prediction Center, in its Feb. 14-25 assessment, observed that an area of anomalously warm sub-surface Pacific Ocean water had increased in area but decreased in depth. It said there were indications that the current El Nino, or warm episode, was beginning to weaken.

The assessment said the jet stream would move further north, cut off the flow of cold from the Arctic and allow warmer air from the Pacific to flow across the continent. Storms would occur along the Canadian border and over the southern tier of states.

-End of Report-

This is the Feb. 13 National Snow Water Equivalent map produced by the National Weather Service National Operational Hydrologic Remote Sensing Center.