National Climate Report - December 2017
- Climate Highlights — December
December Average Temperature Departures
December Percent of Average Precipitation
- The December nationally-averaged temperature was 34.8°F, 2.1°F above the 20th century average, and ranked among the warmest third in the historical record.
- Much-above-average temperatures were observed in the Southwest, with above-average conditions stretching into the Rockies and Central Plains. Parts of the Southeast were also warmer than average.
- Locations from the Midwest to the Northeast had near- to below-average temperatures for December. The first half of December was quite warm for much of the East, with much-above-average temperatures stretching from the Plains to the East Coast. A cold air outbreak impacted most places east of the Rockies the last week of December, suppressing the monthly temperature values for those regions and the nation as a whole. The cold wave continued to impact the East into early 2018.
- Alaska had its warmest December on record with a statewide average temperature of 19.4°F, 15.7°F above average. This bested the previous record of 17.3°F set in 1985. Record warmth was observed across large parts of western, central and northern Alaska. Numerous locations, including Barrow, McGrath and Bettles were all record warm. This was the second consecutive month of record breaking temperatures in Barrow.
- The contiguous U.S. average maximum (daytime) temperature during December was 45.3°F, 2.6°F above the 20th century average, ranking in the warmest third of the record. Much-above-average maximum temperatures were observed in the Southwest with above-average conditions in parts of the Northwest, Great Plains and Southeast. Below-average maximum temperatures were observed in parts of the Northwest, Midwest and Northeast.
- The contiguous U.S. average minimum (nighttime) temperature during December was 24.2°F, 1.6°F above the 20th century average, also ranking in the warmest third of the record. Above-average conditions were observed for parts of the West, Rockies, Northern and Central Plains and Southeast. Below-average conditions were observed in the Midwest and Northeast.
- During December there were 4,110 record warm daily high (2,359) and low (1,751) temperature records, which was about 40 percent more than the 2,903 record cold daily high (2,033) and low (1,416) temperature records.
- Based on NOAA's Residential Energy Demand Temperature Index (REDTI), the contiguous U.S. temperature-related energy demand during December was 15 percent below average and ranked as the 38th lowest value in the 123-year period of record.
- The contiguous U.S. precipitation total for December was 1.55 inches, 0.80 inch below average. This was the ninth driest December on record and driest since 1989.
- Large parts of the nation were drier than average with 15 states across the West and parts of the Central Plains, Midwest and Mid-Atlantic having much-below-average precipitation. Parts of the Northern Rockies, Southern Plains and Lower Mississippi Valley were wetter than average.
- According to NOAA data analyzed by Rutgers Global Snow Lab, the December snow cover extent was 120,000 square miles below the 1981-2010 average and the 20th smallest in the 52-year period of record. Above-average snow cover was observed for the Midwest, Northeast, Northern Rockies and parts of the Southeast. Below-average snow cover was observed in the Southwest, Central and Southern Rockies and the Great Plains.
- According to the January 2 U.S. Drought Monitor report, 27.7 percent of the contiguous U.S. was in drought, up about 6.6 percent compared to the end of November. Drought developed, expanded and intensified in the Southwest, Southern Plains and Mid-Atlantic. Drought improved in parts of Texas, the Lower Mississippi Valley and Northern Rockies.
**A comparison of the national temperature departure from average as calculated by NCDC's operational dataset (nClimDiv), the U.S. Historical Climatology Network (USHCN), and the U.S. Climate Reference Network (USCRN) is available on our National Temperature Index page.**
These regional summaries were provided by the six Regional Climate Centers and reflect conditions in their respective regions. These six regions differ spatially from the nine climatic regions of the National Centers for Environmental Information.
- Northeast Region: (Information provided by the Northeast Regional Climate Center)
- The last month of the year was a cold one for the Northeast. The region's average temperature for December was 25.7 degrees F (-3.5 degrees C), which was 2.7 degrees F (1.5 degrees C) below normal. All twelve states saw below-normal temperatures, with departures ranging from 0.7 degrees F (0.4 degrees C) below normal in West Virginia to 4.5 degrees F (2.5 degrees C) below normal in Maine.
- December featured below-normal precipitation in the Northeast. The region received 2.31 inches (58.67 mm) of precipitation, 66 percent of normal. All twelve states were drier than normal, with seven states ranking this December among their 20 driest: Delaware and Maryland, fifth driest; West Virginia, eighth driest; New Jersey, 11th driest; Pennsylvania, 12th driest; Connecticut, 13th driest; and Rhode Island, 17th driest. Precipitation ranged from 28 percent of normal in Maryland to 98 percent of normal in Maine. At the local level, Erie, Pennsylvania, had its wettest December on record.
- The U.S. Drought Monitor released on December 7 showed parts of central and southern Maryland, totaling 1 percent of the Northeast, in a moderate drought and 14 percent of the region as abnormally dry. During the month, moderate drought was introduced in eastern Pennsylvania and abnormal dryness generally expanded in the region. Some areas experienced below-normal streamflow and groundwater levels. The U.S. Drought Monitor released on December 26 showed 3 percent of the Northeast in a moderate drought and 18 percent of the region as abnormally dry.
- A storm from December 9 to 10 dropped up to 11 inches (28 cm) of snow on the region. While impacts were limited to flight delays and slick roads, it provided the first measurable (0.1 inches [0.3 cm]) snow and the first inch (2.5 cm) of snow of the season for more than a dozen major climate sites. For some sites, such as Albany, New York, and Pittsburgh, Pennsylvania, the snow was past due as they typically see their first measurable snow on November 15. However, for other sites, such as Atlantic City, New Jersey, and New York City's airports, the snow was nearly a month ahead of schedule, as these sites do not typically see their first inch of snow until early January. Erie, Pennsylvania, experienced a historic snow event from December 24 to 26 that shattered numerous records. On the 25th, the site had its all-time snowiest day on record with 34.0 inches (86.4 cm) of snow. The previous record was 20.0 inches (50.8 cm) on November 22, 1956. The following day, on the 26th, the site received 26.5 inches (67.3 cm) of snow, which made it the second all-time snowiest day on record. Preliminary data indicates that the two-day snow total of 60.5 inches (153.7 cm) is the all-time greatest 2-day snowfall for Pennsylvania. The previous record was 46.0 inches (116.8 cm) in Seven Springs from March 13 to 14 in 1993. Erie wrapped up December with 121.3 inches (308.1 cm) of snow, making it the site's all-time snowiest month on record. The previous record was 66.9 inches (169.9 cm) in December 1989. Erie's 121.3 inches (308.1 cm) of snow in December 2017 is the all-time greatest monthly snowfall for Pennsylvania. The previous record was 117.8 inches (299.2 cm) in Laurel Summit in February 2010.
- For more information, please go to the Northeast Regional Climate Center Home Page.
- Midwest Region: (Information provided by the Midwest Regional Climate Center)
- December precipitation was well below normal for nearly all of the Midwest. A swath across northern Missouri and central Illinois had less than 25 percent of normal precipitation for the month. Surrounding areas with less than 50 percent of normal extended into every Midwest state except Kentucky. Iowa (5th driest) and Illinois (7th) ranked among the driest Decembers in their records (1895-2017), while Missouri, Indiana, and Ohio ranked in the teens. Above-normal precipitation was only observed in the northern areas of Minnesota, Michigan, and Wisconsin. Annual precipitation was above normal for the region, at 104 percent of normal. The statewide annual value for Michigan in 2017 set a new record (1895-2017 period of record) while Ohio (7th) and Wisconsin (8th) ranked among the 10 wettest years. Illinois, Iowa, and Missouri had annual totals that were below normal.
- December temperatures were below normal for much of the northern and eastern halves of the region. Missouri and Iowa, along with western Illinois and southern Minnesota, had near normal temperatures. The average temperatures were a combination of a few warm weeks followed by a bitter cold week to end the month. More than a thousand record low temperature records were set in the last seven days of the month. Minimum temperatures averaged below 0 degrees F (-18 C) for much of the northern half of the region during this week and temperatures dipped below 0 degrees F (-18 C) in many locations in the southern half of the region. Some of the coldest readings were in northern Minnesota where temperatures fell to -40 degrees F (-40 C). Annual average temperatures in 2017 were among the warmest on record for the Midwest. The region as a whole ranked as the 8th warmest in its record (1895-2017). All nine states in the region ranked among the warmest 10 percent of their individual records (also back to 1895).
- Severe convective storms struck the Midwest on the 4th. Reports of large hail, strong thunderstorm winds, and two tornadoes stretched from southwestern Missouri to west central Illinois. The tornadoes were rated as EF-1 and EF-2 and there were no reports of injuries. There was an injury related to strong thunderstorm winds in Randolph County, Missouri.
- Drought expanded slightly and intensified in the Midwest during December. An area of extreme drought in south central Missouri was the first extreme drought in the region since early October (Iowa) and the first extreme drought in Missouri since 2012. The area affected by drought expanded into more of Missouri, Illinois, and Iowa in December and remained for a small area in north central Minnesota. Areas noted as abnormally dry also expanded and covered nearly all of Missouri, much of Iowa, and most of southern Illinois.
- Lake-effect snows kicked off early in December as shots of cold air began to move across the Great Lakes. The cold air masses picked up heat moisture from the relatively warm and ice-free lake surface and dumped snows downwind of the lakes. Very cold air pushed across the lakes late in the month and added to the lake-effect snow totals. Seasonal snowfall totals were above average at the end of the month on the downwind shores of the Great Lakes but were below normal for much of the remaining areas of the Midwest. The largest deficits were in southern Minnesota and southern Wisconsin where some locations were more than 10 inches (25 cm) below normal for the season.
- For further details on the weather and climate events in the Midwest, see the weekly and monthly reports at the Midwest Climate Watch page.
- Southeast Region: (Information provided by the Southeast Regional Climate Center)
- Temperatures were above average in much of Florida, Georgia, South Carolina, Puerto Rico, and the U.S. Virgin Islands, while near-average to below-average temperatures were observed across Alabama, North Carolina, and Virginia. No extremes in monthly mean temperature were recorded across the mainland portion of the region, as none of the 178 long-term (i.e., period of record equaling or exceeding 50 years) stations observed December mean temperatures that were ranked within their ten warmest or coolest values on record. Despite the lack of monthly temperature extremes across the region, periods of unusually warm and cold temperatures were observed during December. The warmest weather of the month occurred on the 5th, 19th, and 23rd, as daily maximum temperatures reached at least 70 degrees F (21.1 degrees C) in portions of every state. On the 8th, Fort Myers, FL (1892-2017) tied its second highest daily minimum temperature on record for December, at 72 degrees F (22.2 degrees C). On the 18th, Pensacola, FL (1879-2017) tied its fifth highest daily maximum temperature on record for December, at 80 degrees F (26.7 degrees C). In contrast, the coldest weather of the month occurred from the 10th through the 11th and the 28th through the 31st, as polar high pressure systems ushered in unusually cold air from the northwest. Daily minimum temperatures fell below 32 degrees F (0 degrees C) across much of the region, with portions of northern and western Virginia reaching 0 to 10 degrees F (-17.8 to -12.2 degrees C) from the 28th through the 31st. On the 10th and 11th, daily minimum temperatures in Florida ranged from the middle 20s F (-4.4 to -3.3 degrees C) in portions of the Panhandle to the 40s F (4.4 to 9.4 degrees C) across much of the southern Peninsula. Several locations in Virginia and southeastern Florida observed their coldest December minimum temperatures since 2010, with some extending back to 2004 or earlier. After recording a minimum temperature of 48 degrees F (8.9 degrees C) on the 12th, Miami, FL (1895-2017) ended its longest streak of 687 consecutive days with a minimum temperature at or above 50 degrees F (10 degrees C), surpassing the previous record by 289 days.
- Precipitation was near normal to well below normal across much of the Southeast region during December. The driest locations were found across portions of central and southeastern Florida, northern and western North Carolina, and Virginia, where monthly precipitation totals were 50 to less than 25 percent of normal. At least 22 long-term stations observed December precipitation totals that were ranked within their five lowest values on record. Seventeen of these stations were located in Virginia and the Washington, D.C. area, including Roanoke, VA (1912-2017; 0.36 inches, 9.1 mm), Charlottesville 2 W, VA (1893-2017; 0.48 inches, 12.2 mm), Washington, D.C. (1871-2017; 0.50 inches, 12.7 mm), and Lynchburg, VA (1893-2017; 0.69 inches, 17.5 mm). Several long-term stations tied their second or third highest count of December days with no measurable precipitation, including Orlando, FL (1893-2017; 30 days), Vero Beach, FL (1942-2017; 28 days), Raleigh, NC (1887-2017; 27 days), and Lynchburg, VA (26 days). From the 13th through the 31st, Norfolk, VA (1874-2017) observed its longest December streak of 19 consecutive days with no measurable precipitation. Measurable snowfall was recorded in every state across the region during the month, with the greatest accumulations occurring in portions of central Alabama, northern Georgia, Upstate South Carolina, and western North Carolina. Much of the monthly snowfall in these areas was observed from the 8th through the 9th, as an early-season winter storm produced 3 to more than 12 inches (76.2 to 305 mm) of snowfall in a continuous swath extending from southwestern Alabama to east-central Virginia. Some of the highest snowfall totals reported in these areas included 26.0 inches (660 mm) on Mt. Mitchell, NC, 14.0 inches (356 mm) near Clayton, GA, 13.0 inches (330 mm) near Fruithurst, AL, and 10.8 inches (274 mm) on Caesars Head, SC. With 1 inch (25.4 mm) of snow recorded on the 8th, Mobile, AL (1895-2017) observed its earliest measurable snowfall on record, surpassing the previous record (1 inch on December 18, 1996) by 10 days. Snowfall totals were exceptionally high in areas located north and west of Atlanta, GA, with seven long-term stations observing their greatest 1-day snowfall on record for December. Three of these stations observed their second greatest 1-day snowfall for any month on record, including Dallas 7 NE (1948-2017; 12.3 inches, 312 mm), Taylorsville (1939-2017; 8.8 inches, 224 mm), and Carrollton (1942-2017; 8.0 inches, 203 mm). Over 325,000 customers lost power in northern Georgia, and more than 800 flights were cancelled at Hartsfield-Jackson International Airport in Atlanta. On the 9th, Mt. Mitchell, NC (1980-2017) observed its highest 1-day snowfall for December and its fourth highest 1-day snowfall for any month on record, with an accumulation of 25.0 inches (635 mm). Highlands, NC (1893-2017) observed its highest 2-day snowfall for December and its second highest 2-day snowfall for any month on record, with an accumulation of 15.3 inches (389 mm).
- There were only 13 severe weather reports across the Southeast during December, which is about 30 percent of the median monthly frequency of 44 reports during 2000-2016. All of the severe weather reports occurred in Alabama, Georgia, and Florida, and most (10 of 13) of these reports were for thunderstorm winds. On the 9th, a 58 mph thunderstorm wind gust was recorded at Naples Municipal Airport, as a squall line moved through southwestern Florida. Only 2 EF-0 tornadoes were confirmed across the region during the month, which is much less than the median frequency of 9 tornadoes observed during December. On the 20th, one of the EF-0 tornadoes tracked 3.1 miles across Meriwether County, GA, resulting in a collapsed barn and damage to a home, garage, and fruit stand. Following the passage of a strong cold front on the 12th, non-convective wind gusts of 67 and 99 mph were recorded in Boone, NC and on Grandfather Mountain, NC, respectively. Non-convective wind gusts exceeding 50 mph were also observed at a few other locations during the month, including Birmingham International Airport, AL (54 mph on the 5th) and Roanoke Regional Airport, VA (52 mph on the 25th).
- Moderate (D1) drought continued to expand in coverage across the Southeast during December, increasing from 15 percent on November 28th to 28 percent on December 26th. By late December, moderate drought covered at least 15 percent of every state in the region, including central Virginia, central North Carolina, north-central South Carolina, southern Georgia, west-central and southeastern Alabama, and the Florida Panhandle. The greatest statewide extent of moderate drought was observed in Virginia (43 percent), Georgia (40 percent), and North Carolina (29 percent). More than half of the USGS gages in North Carolina and Virginia recorded well-below-normal (i.e., less than the 10th percentile) streamflows at the end of the month. During early December, citrus producers reported that a few nights with minimum temperatures ranging from 35 to 45 degrees F (1.7 to 7.2 degrees C) allowed citrus trees in central and southern Florida to build up their tolerance for cold weather. However, sub-freezing temperatures produced frost damage in livestock pastures across portions of northern Florida. In northwestern Georgia, the roofs of several barns and poultry houses collapsed from the heavy snowfall on December 8th. While the cold weather was beneficial for fruit and nut crops in Georgia to accumulate sufficient chill hours before the spring growing season, livestock in northern portions of the state were stressed by the frigid temperatures. Cold, dry conditions impeded the growth of small grains and caused some injury to fruit crops in parts of North Carolina. In late December, foggy conditions across portions of southern Florida increased disease pressure on some vegetable crops.
- For more information, please go to the Southeast Regional Climate Center Home Page.
- High Plains Region: (Information provided by the High Plains Regional Climate Center )
- Precipitation was scarce throughout much of the High Plains during December, especially in Colorado and Kansas. Numerous locations had a top 10 driest December on record and these conditions were, in large part, a continuation of dryness since around mid-October. These dry conditions have contributed to widespread below-normal snowfall across the region, particularly in the Rockies of Colorado where the snowpack season was off to an abysmal start. A combination of these factors led to the expansion of abnormally dry conditions and drought during December, according to the U.S. Drought Monitor. While drought impacts tend to be minimal this time of year, dry soils and below-normal precipitation during winter often lead to impacts during the spring. The only state in the region that was spared from dry conditions was Wyoming, where above-normal precipitation continued to boost snowpack. As for temperatures, most of the region had normal to slightly above normal temperatures for December on the whole; however, early to mid-December was extremely warm while late December was extremely cold.
- Warm, dry, and windy conditions also contributed to the spread of wildfires in December, which is outside the typical fire season in the High Plains. The most notable fire was the Legion Lake Fire, which burned over 54,000 acres and became the third largest on record in both the Black Hills and the state of South Dakota. The fire ravaged Custer State Park and threatened wildlife, such as bison, deer, and elk. The fire also damaged fences, trails, and roads, forcing the park to close temporarily to make repairs. According to Darren Clabo, South Dakota State Fire Meteorologist, the Legion Lake Fire behaved more like a summer fire in that there was high crown mortality and areas were burned beneath the overstory on the surface. Clabo stated that the ongoing drought in the area likely played a role in the large number of acres burned because heavier fuel types would have to be dry enough to burn, and that would only happen if there had been a prolonged period of precipitation deficits.
- On the whole, December temperatures were near normal to slightly above normal throughout the majority of the High Plains. Departures were greatest across areas of Colorado and southern Wyoming, where temperatures were 3.0-8.0 degrees F (1.7-4.4 degrees C) above normal. Alamosa, Colorado had its 5th warmest December on record. However, areas that experienced near-normal temperatures for the month saw extremes on both ends of the spectrum, as temperatures were both well above and well below normal during December.
- The first two-thirds of December yielded very warm temperatures across the region, averaging 10.0-20.0 degrees F (5.6-11.1 degrees C) above normal in most areas. These warm temperatures extended the fall season, which had both positive and negative impacts to agriculture. For instance, increased recreational tillage was observed, and extended fall grazing limited the need for hay during the early part of winter. However, the extension of warm soil temperatures increased the likelihood of leaching of the soil, as well as the loss of fall-applied nitrogen.
- The temperature pattern changed dramatically during the last ten days of the month, as an Arctic front brought a frigid air mass that settled over the central and eastern U.S. for the remainder of the month. Temperature departures of 20.0-30.0 degrees F (11.1-16.7 degrees C) below normal combined with moderate wind speeds to create dangerous wind chills across much of the Northern Plains. Despite this impressive cold snap, it was not enough to sway monthly departures toward colder than normal in most locations.
- Dryness continued to prevail for much of the region to begin the winter season. A broad area that includes Colorado, Kansas, and eastern and central portions of the Dakotas and Nebraska received paltry amounts of precipitation during December. The driest area was southern and central Kansas, where precipitation was less than 5 percent of normal. For instance, only a trace of precipitation was recorded in Garden City, which tied several years for its driest December on record. Precipitation was also scarce across most of Colorado, where several locations had a top 10 driest December. On the other hand, wet conditions continued across Wyoming, with much of the state receiving greater than 150 percent of normal precipitation. In fact, Casper had its 2nd wettest and 6th snowiest December on record.
- While a few snowstorms did occur in December, the High Plains region has been abnormally dry during the past few months, which has resulted in widespread below-normal snowfall. For instance, as of the end of December, Grand Junction, Colorado had only received 0.1 inches (0.3 cm) of snowfall this season, which was 7.3 inches (19 cm) below normal and the 2nd least snowiest July-December period on record (period of record 1893-2018). Other locations in Colorado are experiencing a similar 'snow drought' as well. According to the Denver Post, the ski industry took a hit, as there was very little open terrain available for skiing due to exposed grass, and opening dates were pushed back. On the other hand, snowfall was plentiful in Wyoming and, according to CBS Denver, ski resort areas in Jackson Hole accumulated 100.0 inches (254 cm) of snow before opening day!
- Perhaps what makes the widespread snowfall deficit more interesting is the fact that some areas of the Southeastern U.S. have received more snowfall so far this season than the High Plains! A rare snowstorm impacted parts of the Southeast in early December. For instance, Jackson, Mississippi received 5.1 inches (13 cm) of snowfall, while 4.0 inches (10 cm) of snow fell in Birmingham, Alabama. Jackson's normal July-December snowfall is only 0.1 inches (0.3 cm), while Birmingham normally gets 0.3 inches (1 cm). Despite this peculiar snowfall pattern, it is important to point out that it is still very early in the snow season. A couple of large snowstorms could quickly erase the deficit in the High Plains, and there is plenty of time to catch up.
- Mountain snowpack continued to be above normal in the Northern Rockies during December. According to the U.S. Army Corps of Engineers, Snow Water Equivalent (SWE) in the Missouri River Basin above Fort Peck Reservoir and between Fort Peck and Garrison Reservoirs was 118% and 134%, respectively, as of the end of December. Snowpack was still above normal in the Rockies of Wyoming, thanks to continued above-normal snowfall. However, snowpack was still faring poorly in Colorado, due to a continuation of abnormally warm and dry conditions into December. As for Plains snowpack, the northern portion of the region was covered in snow by the end of December because of a snowstorm that impacted the region toward the end of the month. However, the Colorado Plains and the southern two-thirds of Kansas were snow-free.
- Dryness in November persisted into December across southern and eastern portions of the High Plains, which resulted in a wide expansion of abnormally dry conditions (D0) on the U.S. Drought Monitor map. The area depicted in dryness or drought (D0-D4) nearly doubled in December, from 41 percent at the end of November to 81 percent in late December. December precipitation was less than 50 percent of normal in areas where dryness spread.
- Moderate drought (D1) expanded further into western Colorado. Above-normal temperatures and widespread dryness contributed to a continued lack of snowfall. In Kansas, drought expanded to encompass approximately one-third of the state, and persistent dryness since October in a portion of southern Kansas warranted the introduction of severe drought (D2) on the U.S. Drought Monitor map. October-December precipitation in this area of the state ranged from only 10-50 percent of normal.
- Prolonged drought has contributed to some impacts this winter. For instance, livestock producers in North Dakota have reported a shortage of winter feed, so a hay lottery was established to help producers locate the feed that is needed for the winter. Also, drought likely played a role in the development and rapid movement of the Legion Lake Fire in South Dakota. More recently, the combination of abnormal dryness, the lack of snowfall, and above-normal temperatures followed by a cold snap may have caused winter crop damage, which will likely not be realized until spring.
- For more information, please go to the High Plains Regional Climate Center Home Page.
- Southern Region: (Information provided by the Southern Regional Climate Center)
- December temperatures were slightly above normal for most of the Southern Region. A few areas in central Oklahoma and western Texas were 4—6 degrees F (2.22 to 3.33 degrees C) above normal. Central and southeastern Oklahoma, parts of northern and northeastern Texas, western and central Arkansas, central Mississippi, and extreme southeastern Louisiana were 2—4 degrees F (1.11 to 2.22 degrees C) above normal. In contrast, southern and a part of western Texas were 2—4 degrees F (1.11 to 2.22 degrees C) below normal. Southern and central Louisiana, eastern and southern Texas, and a few areas throughout Tennessee, Mississippi, eastern Arkansas, and western Oklahoma had slightly below normal temperatures. The statewide monthly average temperatures were as follows: Arkansas—42.80 degrees F (6.00 degrees C), Louisiana—51.10 degrees F (10.61 degrees C), Mississippi—47.80 degrees F (8.78 degrees C), Oklahoma—41.10 degrees F (5.06 degrees C), Tennessee—39.90 degrees F (4.39 degrees C), and Texas—48.20 degrees F (9.00 degrees C). The statewide temperature rankings for December were as follows: Arkansas (forty-fourth warmest), Louisiana (fifty-second warmest), Mississippi (forty-fourth warmest), Oklahoma (fortieth warmest), Tennessee (fifty-second warmest), and Texas (forty-seventh warmest). All state rankings are based on the period spanning 1895-2017.
- Precipitation values for the month of December varied spatially throughout the Southern Region. Northwestern Oklahoma and northern Texas received 25 percent or less of normal precipitation. Areas of central, eastern, and northern Oklahoma, central and extreme eastern Texas, north, central, and extreme southeastern Louisiana, central and eastern Tennessee, northern Arkansas, and central Mississippi received 25—70 percent of normal precipitation. In contrast, southwest Texas received 300 percent or more of normal precipitation. South, northeast and west Texas, southeast Louisiana, southwest Mississippi, and southwest and central Arkansas received 150—200 percent of normal precipitation. The state-wide precipitation totals for the month were as follows: Arkansas—5.04 inches (128.02 mm), Louisiana—4.83 inches (122.68 mm), Mississippi—5.24 inches (133.40 mm), Oklahoma—0.92 inches (23.37 mm), Tennessee—4.24 inches (107.70 mm), and Texas—1.96 inches (49.78 mm). The state precipitation rankings for the month were as follows: Arkansas (forty-first wettest), Louisiana (fifty-fourth driest), Mississippi (fifty-sixth wettest), Oklahoma (thirty-second driest), Tennessee (fifty-fourth driest), and Texas (forty-third wettest). All state rankings are based on the period spanning 1895-2017.
- Over the month of December 2017, drought conditions worsened from severe to extreme drought in north central Arkansas and a small area in northern Texas. Conditions worsened from moderate to severe drought in northern Oklahoma, northern Texas, northern Louisiana, and central Mississippi. Moderate drought conditions expanded throughout central Oklahoma and abnormally dry conditions appeared in southeast Tennessee. In contrast, conditions improved from extreme to severe and moderate drought in central Arkansas. Conditions improved from severe to moderate drought in northeast Texas, southeast Oklahoma, and southern Arkansas. Moderate drought improved to abnormally dry conditions in northern Mississippi and southeast and western Texas. Conditions improved to normal in extreme southern Mississippi and south central Louisiana.
- In December there were 32 severe weather events (15 tornadoes, 14 wind, and three hail events) were reported throughout the Southern Region. All 15 tornado events occurred during December 19 in Texas and Louisiana. Most of the wind events also occurred in Texas and Louisiana during December 19. The three hail events occurred on December 4 in Oklahoma and Arkansas. The only state not reporting any severe weather during December was Tennessee.
- On December 4, 2017, three severe hail events occurred between Oklahoma and Arkansas. A strong wind event snapped trees and blew over a well house in Saline, Arkansas.
- On December 19, 2017, 13 tornadoes were reported in Texas and Louisiana. In Rusk, Texas, an EF-2 tornado with estimated winds of 115 mph (185.08 kph) moved a home 15 yards into the forest. Another tornado displaced the roof on Faustos restaurant in Calcasieu, Louisiana. Nine severe wind events were reported in Texas and Louisiana. In Cherokee, Texas, severe winds tore roofs off of three homes. Natchitoches and Jackson, Louisiana also reported damaged homes from severe winds.
- On December 20, 2017, two tornadoes were reported in Mississippi which caused an occupied mobile home to be moved off of its foundation and a storage shed to be overturned in Walthall, Mississippi. One severe wind event was reported in Walthall, Mississippi.
- For more information, please go to the Southern Regional Climate Center Home Page.
- Western Region: (Information provided by the Western Region Climate Center)
- December brought well below normal precipitation to most of the West (record dry in the Southwest) with the exceptions being primarily Montana and Wyoming where some areas saw record wet conditions. Temperatures were above normal for much of the Southwest and Four Corners states, and below normal in parts of the Pacific Northwest.
- A persistent ride of high pressure in the Pacific Northwest that extended into the Gulf of Alaska led to anomalous warmth across most of the region. The greatest departures from normal were found in the Southwest. In Arizona, Tuscon (57.3 F/14.1 C) recorded its second warmest December and Phoenix (59.1 F/15.1 C) saw its 4th warmest with records beginning in 1948 and 1933, respectively. Southern Nevada was also warm with Las Vegas (52.2 F/11.2 C) recording the 2nd warmest December on record dating back to 1948. Persistent high pressure caused strong temperature inversions throughout the Great Basin leading to cold air pooling and poor air quality in valley locations. Inversions actually lead to below normal temperatures in some locations. Fallon, Nevada (30.2 F/-1 C) was 4 F (2.2 C) below average, the 13th coldest December dating back to 1945.
- Southern California eastward through the Four Corners states was extremely dry this month. Santa Barbara, California recorded no precipitation (normal is 3.04 in/77.2 mm) for only the 6th time since records began in 1893 and Los Angeles (normal is 2.33 in/59.2 mm) observed 0.01in (0.3 mm), 13th driest, with records dating back to 1877. Climatologically, December is one of the wettest months for southern California and the lack of precipitation led to continued and increased wildfire danger (see Significant Events). The dry December led to expansion or introduction of abnormally dry, moderate drought, or severe drought categories in California, Nevada, and all of the Four Corners states. A large area in southern Utah is now in severe drought as of the end of December. In Arizona, 100% of the state is now is moderate or severe drought.
- In contrast to the dry Southwest, Montana and Wyoming saw well above normal precipitation for the month. A series of powerful, cold storm systems during the second half of December brought heavy precipitation (in the form of snowfall) and well below normal temperatures to the region. Billings, Montana observed 1.81 in (46.0 mm) of precipitation (362% of normal) making it the 5th wettest December since records began in 1934. Billings also recorded 25.3 in (642.6 mm) of snow (309% of normal), the 3rd snowiest December on record. Casper, Wyoming saw its 2nd wettest December with 1.37 in (34.8 mm) of precipitation (280% of normal) since records began in 1948. Small pockets of drought improvements were made in Montana due to the wet conditions. Biggest improvements were made in Wheatland County, Montana where a two category improvement from moderate drought (start of December) to no drought (end of December) was made.
- Snowpack in Oregon, California, Nevada, and all of the Four Corners states was well below normal at the end of the month due to persistent warm and dry conditions. Snow water equivalent at Donner Pass, California (CSS Lab, SNOTEL) was only 30% of normal at the end of December. In parts of Oregon and Washington water year precipitation (October through December) remains near or above normal while snowpack is below normal indicating the presence of warm snow drought conditions. Within this area, the Central Oregon Cascades having the lowest snowpack, 40-50% of normal. In northern Idaho, Montana, and much of Wyoming the snowpack is above normal and in some cases well above normal (>150%).
- Many locations in Alaska observed record warm December temperature including Utqia'vik (5.7 F/-14.6 C), Kotzebue (18 F/-7.8 C), McGrath (19.3 F/-7.1 C), and Tanana (11.6 F/-11.3 C) with records beginning in 1901, 1897, 1941, and 1902 respectively. Records were shattered by a large margin. For example, at Kotzebue a 15.7 F (8.7 C) anomaly was observed breaking the previous record set in 2000 and 1985 (anomaly of 10.6 F/5.9 C). Little Port Walter in southeast Alaska observed its 6th wettest December (40.8 in/1036.3 mm) with records beginning in 1936 while Anchorage was quite dry (0.44 in/11.2 mm) seeing its 12th driest December back to 1953. In Hawaii, Kahului observed the 5th wettest (7.92 in/201.2 mm) December dating back to 1905. Most of that precipitation came from a single storm event that dropped 7.21 in (183.1 mm) December 20-21 with 6.40 in (162.6 mm) falling on the 20th.
- All of December: Wildfires impact southern California: More than two dozen wildfires started in December, most during the first week of December driven by several strong Santa Ana wind events and extremely dry conditions during the fall and start of winter. The Thomas fire (92% contained as of January 3, 2018) is now the largest fire in California's history with more than 280,000 acres burned, more than 1,000 structures destroyed and one confirmed death. Fires also forced more than 230,000 people to evacuate, closed schools and businesses, degraded air quality, and cause power outages.
- Most of December: Unhealthy air quality in Salt Lake City, Utah: Persistent air temperature inversions lead to fine particulate matter becoming trapped near the surface in Salt Lake City causing unhealthy air quality. Some schools in the region were forced to move recess inside due to PM 2.5 levels above 55.5 ug/m3.
- For more information, please go to the Western Regional Climate Center Home Page.