Arctic Invasion Dominates December

Wed, Jan 03, 2018

Oklahoma’s seemingly endless supply of mild weather came to an abrupt halt during the third week of December, ushering in a frigid end to a warm 2017. A bulge in the jet stream allowed frosty air to plunge southward and place most of the country into an arctic deep freeze. Oklahoma’s introduction to the cold air came on Dec. 21 and lasted through the end of the year. Highs in the 60s and even a few 70s were common during the first three weeks of December, topped by a high of 83 degrees at three Mesonet sites in southwest Oklahoma on the fourth. Following the arctic front on the 21^st, much of the state endured more than 150 hours at or below freezing through the rest of December, topped by Beaver and Slapout’s 216 hours. Mother Nature saved the coldest air for December’s final day with temperatures dipping into the single digits and wind chills of minus 10 degrees or lower across northern Oklahoma. The month’s lowest temperature of zero degrees was recorded at the Eva Mesonet site on the 31^st. With the cold air in place, small storm systems brought bouts of occasional wintry weather in its usual forms. Sporadic stretches of light snow provided joy to some, while freezing drizzle caused travel problems for others. Despite the chilly end, December was warm for the most part. According to preliminary data from the Oklahoma Mesonet, the month finished above normal by about a degree with a statewide average of 39.8 degrees. Those records date back to 1895.

The dry weather that had plagued the state since early October continued through December. Of the 120 Mesonet sites, five in northwestern Oklahoma received no moisture for the month, and an additional 39 recorded a quarter-inch or less. The Mesonet site at Beaver had not recorded a drop of precipitation for 85 consecutive days as of Dec. 31, dating back to Oct. 7. Several storm systems managed to squeeze out significant moisture across far southeastern Oklahoma. Eleven stations in the southeast recorded at least 3 inches of rain, with Valliant leading the way at 5.65 inches. Unfortunately, the totals dropped rapidly to the northwest leaving approximately 90 percent of the state below normal for the month. The snowfall was light for the most part, although the Tulsa area accumulated as much as 2.5 inches on the 23^rd.

Drought increased at an unusually rapid pace during December, when evaporation and consumption are diminished. The extended dearth of precipitation began to cause significant harm to Oklahoma’s wheat and cattle industry, however. The percentage of drought coverage in the state increased from 40 percent in late November to 76 percent at the end of December according to the U.S. Drought Monitor. Most of that increase occurred across southern and western Oklahoma. The drought intensity was lessened across far southeastern Oklahoma thanks to the beneficial rains, although the area remained in drought. The percentage of the state in drought at the end of December was the most since late March.

Although the statistics paint 2017 as a warm and wet year, the shorter time scales portray Oklahoma’s normal highly variable climate. According to preliminary data from the Oklahoma Mesonet, the year was the 13^th warmest since records began in 1895 with a statewide average of 61.8 degrees, 1.8 degrees above normal. The highest temperature recorded by the Mesonet in 2017 was 108 degrees at Kingfisher on July 22, although the heat index calculated at Copan was 115 degrees that same day. The lowest reading of minus 19 degrees came at Kenton on Jan. 7. On that same day, the wind chill calculated at Hooker bottomed out at minus 28 degrees. 2017 also ranked as the 29^th wettest year on record at 2.02 inches above normal with a statewide average of 38.52 inches. That rain came in fits and spurts, however. Extended dry stretches occurred during February-March, June-July, and again during the final three months of the year. April and August were both exceedingly wet, ranking as the third and second wettest on record for those particular months, respectively. November ranked as the fifth driest on record. Hugo led the Mesonet with 56.9 inches of rain for the year. Buffalo had the lowest total at 21.1 inches. The National Weather Service’s preliminary tornado count of 86 was well above the 1950-2016 average of 56. May was the big twister month with 57 reported touchdowns, including a deadly EF2 tornado in Beckham and Washita counties that resulted in one fatality. An EF2 tornado injured 30 and caused significant damage to businesses in the midtown Tulsa area on Aug. 6.

The precipitation and temperature outlooks for January from the Climate Prediction Center (CPC) indicate increased odds of below normal temperatures and above normal precipitation across eastern Oklahoma. No clear signal was apparent for the remainder of the state. The CPC January-March outlooks released on December 21 show increased odds for above normal temperatures and below normal precipitation across the entire state, but especially across western Oklahoma. The January Drought Outlook from CPC calls for either persistence or intensification within the drought stricken areas across the western two-thirds of the state. Far eastern Oklahoma could see improvement or even drought removal by the end of the month. La Niña – the cooling of waters in the eastern equatorial Pacific Ocean that tilts the odds for warmer and drier cool seasons across the southern tier of the United States – is expected to continue through mid-to-late spring according to the most recent CPC advisory.