March 11, 2014
State climatologist Harry Hillaker with the Iowa Department of Agriculture & Land Stewardship on March 7 released the summary of the 2013-14 winter season for Iowa. And the data shows this winter was the coldest in the past 35 years and the 9th coldest of all time for Iowa—for as long as records have been kept—which is 141 years in Iowa.
"It has certainly seemed like a long, cold winter and the numbers from our State Climatologist's office bear that out," says Iowa Secretary of Agriculture Bill Northey. "Everyone is certainly looking forward to spring."
ROUGH WINTER: Everyone is looking forward to spring, as Iowa has gone through one of the coldest winters in over three decades. The persistent cold has allowed the soil to freeze to unusually great depths.
"The meteorological season of winter runs from December 1 through February 28. This past winter season has been the coldest experienced in Iowa in 35 years and ranks as the 9th coldest winter in 141 years of records. Temperatures this winter season averaged 14.7 degrees or 7.2 degrees below normal," says Hillaker. Here is his report:
On a month-by-month basis all three winter months were unusually cold this past season:
6.7 degrees colder than average
17th coldest December
4.7 degrees colder than average
35th coldest January
10.5 degrees colder than average
7th coldest February
A colder December was last recorded in 2000, a colder January in 2010 and a colder February in 1979. Historically there have been only 24 winters among the past 141 seasons where all three winter months averaged colder than normal. Temperatures this winter have varied from about 10 degrees below normal in northeast Iowa to 4 degrees below normal over the southwest.
The cold has been very persistent this winter with nearly one-half (44) of all days averaging more than 10 degrees colder than normal while only four days averaged more than 10 degrees above normal.
Persistence has been the primary characteristic of the Iowa weather pattern this winter as there have been very few daily record low temperatures set. Elkader has recorded the lowest temperature of the winter with a minus 29 degree reading on the morning of January 28. Slightly more than one-half of all Iowa winters have brought a lower statewide minimum temperature than the -29 recorded this winter.
Number of subzero days this winter vary from 15 to 50 across Iowa
A popular measure of cold weather is the number of days with temperatures falling to 0 degrees or lower. The number of subzero days this winter (through March 7) have varied from 15 at Shenandoah to 50 at Decorah while typical seasonal totals vary from 10 to 30 days across Iowa.
Not only has the three mid-winter months been unusually cold, so was the late fall of 2013. The second one-half of October averaged 4.9 degrees colder than usual (coldest for the period since 2006). November 2013 averaged 2.9 degrees colder than normal (coldest since 2000). Additionally the first six days of March have averaged 20.4 degrees colder than usual (coldest start to March since 1962).
Frost in the soil has reached unusually deep this winter
The persistent cold has allowed the soil to freeze to unusually great depths, despite abundant snowfall which acts to insulate the ground from the colder air above the snowpack. National Weather Service measurements indicate that soils under sod have frozen to a depth of about 2 to 3 feet while Iowa DOT data shows the frost depth has extended as much as 5½ feet beneath roadways. The good news is that the depth of frozen ground has reached its maximum for the winter.
The thaw will primarily begin at the surface but there likely will also be a very slow thaw at the base of the frozen soil layer. The best guess is that soils will be completely frost free by about April 10 statewide. Unusually warm and/or rainy weather would accelerate the rate of thaw while persistent cold or snow could delay the thaw even further.
Best guess is soils will be completely frost-free by about April 10
While the cold has been very persistent and widespread over the winter, the amount of snow fall has been highly variable across Iowa. Snow totals so far this winter have been as much as 50% less than usual across portions of far western Iowa while the southeast corner of the state has seen about double the usual amounts. County snowfall averages vary from 15 inches in Montgomery County in southwest Iowa to 57 inches in Fayette, Clayton and Buchanan counties in northeast Iowa.
The statewide average snowfall stands at 36.0 inches and already exceeds the long-term average with about six weeks of the snow season remaining. This marks the seventh snow season of the past eight with greater-than-normal snowfall (the long-term snowfall average is 31.0 inches) for Iowa.
The current snow cover across the state shows a huge variation. Not only has western Iowa seen less snowfall this winter, they have also had more frequent periods of temperatures above freezing, thus keeping the snow pack to a minimum in that area. Parts of northeast Iowa, however, have yet to see a substantial warm up with Charles City, Northwood and Osage not seeing temperatures climb above 42 degrees since November. As of the morning of March 6 snow was gone from all but sheltered areas over parts of southwest Iowa while depths in excess of 25 inches were common across northeastern areas.
What kind of weather will Iowa likely have this spring?
What might we expect for spring weather after this long and cold winter? The past two springs have brought an amazing variety of weather to Iowa. The spring of 2012 was the warmest of record in the state and unusually dry. Then in 2013 Iowa recorded a record wet spring along with near-record cold as well. The confidence with long-term weather outlooks is not very high. However, there is an expectation of mostly colder- than-normal weather for much of the remainder of March. It is worth noting that even a record cold March would still be 8 degrees warmer than what we just experienced in February. The National Weather Service spring outlook also slightly favors below normal temperatures for the period through May. There is no strong indication for spring precipitation in 2014—so that's anyone's guess.
Additional information and maps on the winter weather can be found at the Iowa Department of Agriculture website under "Hot Topics."
Volunteer precipitation observers sought: Accurate flood forecasting, as well as drought assessments, depend upon reliable precipitation information. The State Climatologist Office of the Iowa Dept. of Agriculture & Land Stewardship, as well as the National Weather Service, strongly encourage Iowans to become involved in a nationwide volunteer precipitation observation network known as the Community, Collaborative Rain, Hail and Snow Network (CoCoRaHS).This network was established in Fort Collins, Colo. in 1998 in response to a serious flood event and has spread to all 50 states and parts of Canada.
Iowa joined the CoCoRaHS network in July 2007. Volunteer observers nationwide utilize 4-inch diameter plastic rain gages to insure uniform quality of observations. There is no cost to join other than the need to obtain the standardized rain gage. Data is reported via the Internet and various other electronic options with data automatically archived and transmitted to the user community as soon as it is reported. All reporting details can be found online. Observers are needed statewide with particularly great needs in data-sparse portions of the state such as Adair, Adams, Cedar, Emmet, Keokuk, Louisa and Wapello counties.
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