NATIONAL WEATHER SUMMARY
DECEMBER 2017
3-9: A sustained period of offshore (Santa Ana) winds fueled the spread of several wildfires across coastal southern California. The erratic and gusty winds were especially destructive in Ventura and Santa Barbara Counties, where the Thomas fire
scorched more than 230,000 acres of vegetation and destroyed nearly 800 structures. Meanwhile, high pressure centered over northern sections of the Great Basin and Intermountain West led to poor air quality and cool, foggy conditions. Farther east,
mostly dry, breezy weather accompanied generally mild weather across the Plains. In fact, weekly temperatures averaged at least 10F above normal across portions of the northern High Plains. Early in the week, warmth continued across the South and
briefly surged across the Plains and Midwest. Daily-record highs for December 3 soared to 79F in Dalhart, TX, and 78F in Dodge City, KS. December 4 was the warmest winter day on record in Minnesota locations such as Rochester (64F) and Minnesota City (
61F). Rochester’s highest winter reading had been 63F, set on December 17, 1939, and February 17, 1981. Minnesota City’s winter temperature had previously peaked at 60F on December 3, 2012, and December 1 and 5, 1998. Elsewhere on the 4th, daily-
record highs climbed to 80F in Shreveport, LA; 78F in Tulsa, OK; 72F in Kansas City, MO; 69F in Des Moines, IA; and 64F in Milwaukee, WI. In Texas, record-setting highs for December 4 rose to 87F in Brownsville, 85F in Austin, and 84°F in Dallas-Fort
Worth. Warmth lingered along the central Gulf Coast through December 5, when daily-record highs in Louisiana surged to 85F in New Orleans and 84F in Lafayette. In Florida, daily-record warmth occurred through December 8, when Miami attained 87F and
Melbourne achieved 86F. At week’s end, record-setting warmth replaced previously cool conditions in southern California, where highs on December 9 included 87F in Long Beach and 86F in Los Angeles (LAX Airport). Days earlier, on December 5-6, Santa
Barbara, CA, had posted consecutive daily-record lows (29 and 31°F, respectively). Farther east, a push of cold air resulted in several daily record lows. Brownsville, TX, tied a daily record with a low of 34F on December 8. The following day, record-
setting lows for December 9 dipped to 19F in Vicksburg, MS, and 29F in New Orleans, LA.

10-16: Extremely dry conditions persisted in several areas, including nearly all of the nation’s southwestern quadrant. Similar to the previous week, cold weather across the eastern U.S. contrasted with mild conditions on the Plains. Weekly
temperatures were as much as 10F below normal in the lower Great Lakes region and southern Florida, but averaged 10 to 20F above normal across the northern Plains. Meanwhile, a high-pressure system parked over the northern Intermountain region
contributed to cool, foggy conditions in many Northwestern valleys and warm, breezy weather in southern California and the Desert Southwest. As a result, temperatures averaged at least 5F below normal across the interior Northwest, but averaged as much
as 10F above normal in coastal southern California. Early-week warmth was prominent across California and parts of the Plains. On December 10-11, consecutive daily record highs were set in California locations such as El Cajon (83 and 84F) and Paso
Robles (75 and 79F). Meanwhile on the Plains, record-setting highs for December 10 included 68F in Russell, KS, and 60F in Valentine, MT. Warmth on the northern High Plains peaked on December 12, when daily-record highs soared to 70F in Sheridan, WY,
and 63F in Stanford, MT. In coastal southern California, extremely dry air favored warm days and cold nights. On December 13, Paso Robles tied a daily-record low (22F) and set a daily-record high (73F). Elsewhere in California, record-setting highs
for December 13 soared to 87°F in Woodland Hills and Camarillo. Warmth continued for much of the week in the West, with South Lake Tahoe, CA, noting consecutive daily-record highs (58 and 59F, respectively) on December 14-15. In contrast, a handful of
daily-record lows were reported in the Great Lakes region, with Pellston, MI, registering -12F on December 14.

17-23: Firefighters neared full containment of the Thomas fire — which at more than 280,000 acres became the largest single wildfire in modern California history. On the central and southern High Plains, where dry conditions also persisted. Mild
weather in place for much of the week, temperatures averaged at least 10F above normal in many locations from the Gulf Coast northward into the Ohio and middle Mississippi Valleys. However, a brief Western cold spell resulted in freezes— especially on
December 21 and 22—in California’s San Joaquin Valley. In addition, warmth across the South led to several daily-record highs. Record-setting highs for December 19 included 87F in Harlingen, TX, and 79F in Columbia, SC. Concurrent warmth in the
Northwest brought daily-record highs for the 19th to locations such as Pendleton, OR (62F), and Walla Walla, WA (59F). General warmth prevailed nearly nationwide during the mid- to late-week period. On December 20, daily-record highs reached to 85F in
Miami, FL, and 7F in Lafayette, LA. Record-setting highs for December 21 rose to 69F in Fayetteville, AR, and Joplin, MO. During a final flurry of Southern daily-record highs on December 22, temperatures soared to 89F in McAllen, TX; 82F in Jackson, MS;
81F in Baton Rouge, LA; and 80F in Mobile, AL.

24-30: Most of the country experienced dry weather and a sharp turn toward very cold conditions. Notable exceptions included warm, dry weather in California and the Southwest (locally more than 10°F above normal); stormy, often snowy weather from the
Pacific Northwest to the northern High Plains; and locally intense snow squalls downwind of the Great Lakes. Late-week temperatures dipped to 0F or below north of a line from northern Kansas into the middle Mississippi Valley, northeastward into southern
New England. (Even colder weather, which arrived on New Year’s Eve and New Year’s Day, will be covered next week.) The harshest weather engulfed areas from the northern Plains into the Northeast, holding weekly temperatures 10 to 25F below normal.
Elsewhere, periods of light precipitation—mostly rain—fell across the Deep South from the western Gulf Coast region into the lower Southeast. Early-week warmth lingered across Florida, where Jacksonville posted a daily-record high of 83F on December
24. Farther west, Sandberg, CA, noted nine consecutive daily-record highs, ranging from 65 to 73F, to end the year. Warmth in southern California expanded by mid-week, when Woodland Hills tallied a trio of daily-record highs (86, 88, and 89F) from
December 27-29. Similarly, Flagstaff, AZ, registered three consecutive daily-record highs (61, 65, and 62F) from December 28-30. As warmth briefly spread to the High Plains, record-setting highs for December 29 included 81F in Dalhart, TX, and 71F in
Pueblo, CO. The following day, daily-record highs for December 30 rose to 82F in Tucson, AZ, and 66F in Wendover, UT. Wendover’s reading also set a monthly record, previously established with a high of 65F on December 15, 1946. In dramatic contrast,
the first of several waves of bitterly cold air arrived on the Plains by December 24, when Sidney, NE, logged a daily-record low of -23F. Two days later, record-setting lows for December 26 plunged to -27F in Cut Bank, MT, and -17F in Grand Island, NE.
The chill further deepened on December 27-28, when consecutive daily-record lows were reported in Michigan locations such as Marquette (-17 and 18F, respectively), and Grand Rapids (-12 and -10F, respectively). Grand Rapids’ reading of -12F marked its
lowest December temperature since December 19, 1983, when it was 18F. Other daily-record lows for December 27 included -37F in International Falls, MN; -27F in Antigo, WI; -24F in Grand Forks, ND; -9F in Springfield, IL; and -7F in Concordia, KS. In
New York, Glens Falls closed the week with three consecutive daily-record lows (-20, -19, and -21F) from December 28-30. Elsewhere in New York, Watertown plunged to -32F, a record for the date, on December 28. Augusta, ME, also collected three daily
record lows (-9, -15, and -14F) from December 28-30. Elsewhere on the 30th, maximum temperatures in North Dakota peaked at 18F in Minot and -17F in Jamestown.

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