NATIONAL WEATHER SUMMARY

DECEMBER 2020

 

1-5: A generally dry weather pattern ended late in the week with the passage of a storm system across the Southeastern and Atlantic Coast States.

 

Southern California endured a protracted period of offshore (Santa Ana) winds, leading to the rapid expansion of several new wildfires. Weekly temperatures averaged at least 10°F above normal in parts of eastern Montana and the Dakotas. Meanwhile, readings averaged 5 to 10°F below normal from the southern Rockies into the Southeast. Freezes reached deep into the South but did not affect citrus production areas in Florida or Texas. Although several light freezes affected California’s Central Valley, most of the Far West avoided significant cold-related concerns. Early in the week, persistently chilly conditions settled across California’s Central Valley, where Modesto posted a daily-record low of 28°F on November 29. In early December, cold air pushed into the South. Daily-record lows for December 1 dipped to 19°F in Batesville, AR, and 22°F in Austin, TX. Farther east, however, warmth surged northward along the Atlantic Seaboard in advance of a strong cold front. The 1st was the warmest December day on record in Maine locations such as Caribou and Houlton—both reached 60°F. The previous record in Caribou had been 58°F on December 5 and 12, 1950, while Houlton’s monthly record had been 59°F on December 5, 1950, and December 11, 1969. Caribou also set a record high for any winter (December to February) day; previously, the record had been 59°F on February 20, 1994. Elsewhere in New England, daily-record highs for December 1 reached 66°F in Burlington, VT, and 62°F in Bangor, ME. Later, warmth arrived in the Pacific Northwest, where Seattle, WA, registered a daily-record high of 60°F on December 2. Warmth replaced previously cool conditions in much of California, where Red Bluff posted a daily-record high of 74°F on December 4. Farther inland, however, lingering cold weather led to record setting lows for December 4 in Winslow, AZ (3°F), and at Utah’s Kodachrome Basin State Park (-6°F). At week’s end, another round of warmth overspreading the Northwest produced record-setting highs for December 5 in Astoria, OR (61°F), and Seattle, WA (58°F).

 

6-12: Mild, dry weather dominated large sections of the country.  On December 8, according to the U.S. Drought Monitor, drought covered 78.5 percent of the 11-state Western region and 49.1 percent of the Lower 48 States. Generally light precipitation fell in several areas of the West, but sustained storminess was mostly limited to the Pacific Northwest. Late in the week, however, precipitation spread as far south as central California. Parts of the Southwest also received variable amounts of much-needed rain and snow. Elsewhere, mostly dry weather across the northern Plains and upper Midwest contrasted with widespread but mostly light precipitation from the central and southern Plains into the mid-South and lower Midwest. On December 11-12, however, several inches of snow accumulated in a stripe across the Midwest from southern Nebraska into northern Lower Michigan, with more than an inch of rain (and mixed precipitation) just to the south. Weekly temperatures averaged as much as 10 to 20°F above normal in portions of the north-central U.S., as a warm weather pattern that had developed in early December further amplified. Mild weather gradually returned in the South, but a lingering chill held temperatures 5 to 10°F below normal across Florida’s peninsula. Scattered frost was reported on December 9 as far south as interior southern Florida, near Lake Okeechobee. Early in the week, record-setting warmth developed in the West and quickly expanded eastward. December 7 featured daily-record highs in California locations such as Death Valley (83°F), Ukiah (77°F), Stockton (76°F), and Santa Rosa (75°F). California’s warmth lingered through December 8, when daily-record highs soared to 84°F in Oceanside Harbor and 80°F in Santa Barbara. In Wyoming, Sheridan posted a pair of daily-record highs (67 and 72°F, respectively) on December 7-8. Sheridan’s high of 72°F represented its warmest December day since 1981, when a reading of 72°F occurred on December 6. The only warmer December days in Sheridan were observed in 1939, with highs of 77 and 73°F, respectively, on December 5 and 6. Similarly, Miles City, MT, tied for its third-warmest December day, with a high of 67°F on December 8. It was the warmest December day in Miles City since December 4, 1979, when it was also 67°F. Meanwhile on the Plains, consecutive daily-record highs were established on December 8-9 in Rapid City, SD (68 and 70°F); Lincoln, NE (64 and 66°F); and Livingston, MT (61 and 62°F). Subsequently, a pair of daily-record highs were set on December 9-10 in Fayetteville, AR (73 and 75°F); Springfield, MO (71 and 72°F); and Rockford, IL (55 and 57°F). Warmth also arrived in the South, where daily-record highs rose to 79°F (on December 9) in Dallas-Fort Worth, TX, and 78°F (on December 10) in Shreveport, LA. A final day of warmth in Texas led to record-setting highs for the 10th in San Angelo (83°F) and Abilene (82°F). Farther east, however, high temperatures on December 8 in Florida peaked at only 61°F in Melbourne and 64°F in Miami—lower than the previously mentioned daily-record highs observed on that date in Sheridan (72°F), Rapid City (68°F), and Miles City (67°F). By the morning of December 9, lows in Florida fell to 29°F in Brooksville and 37°F in Melbourne and Daytona Beach. For Brooksville, it was the first freeze since January 22, 2020. Before cold air settled across Florida’s peninsula, there were heavy showers. On December 7, daily-record totals across southern Florida included 2.45 inches in Naples and 1.40 inches in West Palm Beach. Meanwhile, some light snow fell in the mid-Atlantic, with Richmond, VA, reporting an inch on December 7.

 

13-19: Warmer-than-normal weather prevailed from the Pacific Northwest to the northern Plains, near- or below-normal temperatures covered most other areas of the country. Weekly temperatures averaged at least 5 to 10°F above normal from Washington and northern Oregon to Montana—but were 5 to 10°F below normal in many locations from the Four Corners region to the lower Mississippi Valley. Readings also averaged more than 5°F below normal in parts of the Northeast. Following early-week snow, numerous readings below 10°F were reported on the High Plains as far south as western Kansas and eastern Colorado, as well as northwestern Oklahoma and extreme northern Texas. In the wake of the Northeastern snow, late week temperatures plunged to 0°F or below throughout eastern New York and interior sections of New England. Early-week warmth in the East was quickly swept away, following a cold front’s passage. In New England, lingering mild weather on December 13 produced daily-record highs in Providence, RI (63°F), and Hartford, CT (61°F). Meanwhile in Wyoming, temperatures on the 13th dipped to daily record levels in Laramie (-17°F) and Big Piney (-16°F). Despite a quick shot of cold air across the north-central U.S., mild weather quickly returned. Grand Forks, ND, reported its first sub-zero reading of the year (-9°F on December 14), but experienced an average temperature of 24.8°F (11.8°F above normal) during the first 3 weeks of the month. Elsewhere in North Dakota, Fargo’s December 1-21 average temperature of 25.9°F was 10.4°F above normal. 

 

20-26: Dry weather covered many other areas of the country, including a broad area stretching from southern California to the High Plains. Offshore winds brought another round of enhanced wildfire risk to southern California, where the Creek Fire was ignited on December 23 near Fallbrook and later spread onto Camp Pendleton, scorching more than 4,200 acres of vegetation. In much of the western half of the country, drought remained a concern with respect to the health of rangeland, pastures. 

 

cold weather in the Southeast contrasted with near- or above-normal temperatures across much of the remainder of the country. Weekly temperatures averaged more than 5°F below normal in several locations from Florida northward into the southern Appalachians. Meanwhile, temperatures averaged at least 10 to 15°F above normal across northern New England and the northern and central High Plains. However, a dramatic, late-week pattern shift resulted in cold air driving southeastward across the Midwest and into the East. By December 26, freezes reached deep into the Southeast, with temperatures dipping below 32°F in northern Florida. However, with freezes staying northwest of the Tampa-to-Orlando corridor, there were no major freeze concerns for citrus, strawberries, sugarcane, and winter vegetables. Early-week temperatures reached record-setting levels in parts of the West, in advance of approaching Pacific storminess. On December 20, daily-record highs rose to 83°F in Anaheim, CA, and 60°F in Sheridan, WY. Anaheim notched another daily-record high (84°F) on December 21. Other daily-record highs for the 21st included 87°F in Woodland Hills, CA; 65°F in Walla Walla, WA; and 62°F in Portland, OR. By December 22, warmth arrived on the Plains, where daily-record highs in South Dakota soared to 68°F in Pierre and 67°F in Rapid City. Subsequently, temperatures plunged across the Plains and Midwest. On December 23, calendar-day temperatures fell more than 40°F in locations such as Moline, IL (from 63 to 17°F); Burlington, IA (from 60 to 16°F); Rochester, MN (from 47 to 5°F); and Sisseton, SD (from 42 to -1°F). The readings of 63°F in Moline and 47°F in Rochester were record highs for the date. By December 24-25, cold wave reached the Southeast, where Jacksonville, FL, experienced a temperature drop from 78 to 31°F in less than 18 hours. Jacksonville’s only larger 24-hour temperature declines in December occurred on December 9-10, 1978 (from 81 to 30°F), and December 22-23, 1967 (from 82 to 34°F). In the Northeast, however, lingering warmth on the 25th led to record-high temperatures for Christmas Day in Burlington, VT (65°F); Scranton, PA (64°F); and Bangor, ME (61°F). In fact, consecutive daily-record highs were set on December 25-26 in Maine locations such as Millinocket (59 and 54°F, respectively), Houlton (58 and 56°F), and Caribou (57 and 55°F).

 

27-31: For the second week in a row, near- or above normal temperatures dominated most of the country, although cooler-than-normal conditions were common across the central Rockies, Intermountain West, and Southwest. The most dramatic week-over week change occurred in the Southeast, where cool weather was replaced by temperatures averaging as much as 10°F above normal. Above-normal temperatures again prevailed across the nation’s northern tier, with some of the most persistent warmth (temperatures at least 5 to 10°F above normal) covering much of Montana and the Dakotas, as well as New York and New England. 

 

On December 30, warmth in advance of a cold front led to a daily record-tying high of 75°F in Galveston, TX. Vero Beach, FL, reported a low of 71°F on December 31, marking the record-breaking 204th day of the year with a minimum temperature of 70°F or greater (previously, 202 days in 2015). Later, the warmest New Year’s Day on record occurred in Eastern locations such as Daytona Beach, FL (84°F), and Charleston, SC (80°F). The balmy start to 2021 followed the warmest year on record in numerous Southeastern cities, including Miami, FL (annual average temperature of 79.3°F); Naples, FL (77.8°F); and Savannah, GA (70.4°F). In all listed cases, previous records had been set in 2015, 2017, or 2019, or a combination of those years. With an annual average temperature of 59.5°F, Roanoke, VA, tied a record set in 2012 and 2019.

 

 

Jim G. Munley, jr.
http://www.jimmunleywx.com