Jan. 23, 2015

Our meteorological winter has reached its midpoint and Nebraska has been fortunate enough to have escaped the endless string of bitter cold temperatures we experienced last winter.  There is no denying that we have experienced periods of bitter cold temperatures during the 60 plus days, but these distinct cold periods have been sandwiched between periods of warmth that were of equal or greater magnitude.

Temperature and precipitation outlooks from the Climate Prediction Center (CPC), National Oceanic and Atmospheric Administration
 

A indicates above normal; B indicates below normal; N indicates normal; and EC indicates equal chances for any of the three.

Part of the reason for this continual swing in temperatures lies is that a weak El Nino event is ongoing and the sub-tropical jet is driving systems eastward through the extreme southern U.S.  This leaves a substantial portion of the central and northern Plains between the southern and northern jet streams when storms enter the western U.S.  When the southern jet weakens, the northern jet becomes stronger and it is much easier for Arctic air to invade the eastern half of the country.

Bitter cold temperatures during the first two weeks of November brought back memories of the 2013-14 winter when the United States was dealing with a persistently strong upper air trough (Polar vortex) over the eastern half of the country. Our precipitation events were generally in the form of Alberta Clippers that brought light snow events, except across the Panhandle where cold air damming up against the Rockies resulted in several moderate upslope snow events.

This pattern quickly broke down as the trough weakened and was replaced by an upper air ridge.  As the eastern ridge began to strengthen, the western U.S. came under the influence of an upper air trough in the Gulf of Alaska.  A series of storms pressed on shore through the third week of December, resulting in above normal temperatures and below normal precipitation for most areas between the Rocky and Appalachian mountain ranges.

There was only one significant precipitation event during this period (12/14-12/16) and it came in the form of rain for the most part.  Fortunately the stretch of warm weather preceding the event thawed out soils and allowed for substantial infiltration of this moisture into the upper soil profile. Rainfall reports across the western half of the state indicated individual locations received anywhere from 50% to over 100% of the precipitation expected during a normal winter.

Precipitation totals across the eastern half of the state weren't as generous during this storm system, with most locations receiving 75% to 150% of normal December precipitation.  An area situated from Hebron eastward to Fairbury and northward to Highway 2 reported moisture of 0.25 to 0.50 inches.

A return to cold temperatures from late December through mid-January signaled a return to the Polar Vortex pattern, but as happened in November, the pattern once again broke down and the western U.S. ridge shifted eastward, resulting in our present January thaw.  A stormy pattern appears to be developing across the western U.S., but it's uncertain as to whether this activity will eventually move eastward and impact Nebraska or pass south of the state.

The most recent Climate Prediction Center 30- and 90-day outlooks suggest that stormy weather entering the western United States will persist into spring.  The 30-day outlook suggests a sizable area from southern California through the southern Plains (including Kansas) will see above normal moisture.  The only difference in the 90-day precipitation outlook (February-April) is for an expansion northward of above normal moisture to include southwest, west central, and the southern Panhandle of Nebraska.

The temperature outlook for February contains considerable uncertainty as the CPC shows no climatological trend for Nebraska.  CPC suggests a weak tendency in the 90-day outlook for below normal temperatures across southwest and south central Nebraska, with no distinct trend indicated for the remainder of the state.

CPC data analysis of late winter and early spring climate tendencies during El Nino events indicates that colder than normal temperatures, above normal moisture, and above normal snowfall can be expected 60%-70% of the time from Kansas southward through Texas from February through April.  Nebraska sits on the northern boundary of this region.

Colder than normal temperatures, above normal moisture (including snow) occurs a little over 60% of the time for Nebraska during the March-May period, with the highest probabilities assigned to the western half of the state.  It remains to be seen whether these conditions will occur this winter, but cattle producers may want to aware that heavy, wet snows are fairly common during a majority of El Nino springs.

Al Dutcher
State Climatologist