Welcome to the month of December, named from the Latin word "Decem", for the number ten, representing the tenth month of the year in an early Roman calendar that commenced at the vernal equinox in March. Today marks the start of meteorological winter, the three-month interval used for weather recording purposes.
THE BIG PICTURE -- The surface weather maps for late Thursday night included three storm systems -- one off the East Coast, a second in the Northern Plains and a third off the Pacific Northwest coast -- that indicate a continuation of a pattern where a succession of storms have moved across the country with a spacing of several days.
LINGERING EFFECTS -- The storm system that had moved from the Midwest into the Northeast on Wednesday was off the New England Coast by Thursday. By evening, the low pressure center with a central pressure of 980 mb was located to the southeast of Cape Sable, NS. Relatively brisk north to northwest winds circulating around the west side of this system continued across New England. Lingering precipitation associated with this system also fell in the form of snow across Maine, northern Vermont and the Adirondacks of Upstate New York. Earlier in the evening, lake-enhanced snow fell across some areas downwind of Lake Ontario as cold winds associated with the storm system traveled over the relatively warm lake surface.
With the continued northeastward movement of the storm system on Friday, the winds should slacken and most of the precipitation dissipate across New England. However, lake-effect snow could continue downwind of Lake Ontario as winds continue from the northwest. Farther to the west, a lake effect snow warning was in effect for the thumb of Lower Michigan along Lake Huron as 6 to 8 inches of snow could fall through Friday.
A MIDWEST SNOW-PRODUCER -- A storm system that traversed the northern Rockies late Wednesday night traveled across the northern Plains on Thursday. As of late evening, this system consisted of a low pressure center that was located over eastern Nebraska and a cold front that trailed westward across the central Plains and then northwestward along the east slopes of the Rockies. This system was characterized by snow and windy conditions. Snow fell to the east and north of the system, in an area that extended from Iowa across southern Minnesota, eastern Nebraska and the Dakotas. Between 4 to 7 inches of snow had fallen across southwest Minnesota and eastern South Dakota by mid evening. Even as snow continued to fall during the late afternoon, 7.6 inches of snow had fallen at Aberdeen, SD, setting a new daily snowfall record. While the band of snow was fairly confined because of the relative lack of moisture, the impressive snowfall totals resulted from the fluffy nature of the snow due to low temperatures.
In addition to the snow, the storm also generated windy conditions across the Plains on Thursday night, with winds gusting to 25 mph at some locales. Earlier on Thursday morning, strong winds with gusts in excess of 60 mph were reported to the west of the system across the High Plains and the Rockies. In the Nebraska Panhandle, Alliance had a gust to 62 mph and Sidney had 60 mph gusts, while Chugwater in eastern Wyoming registered a gust of 62 mph.
The storm system is expected to move toward the southeast, reaching northwestern Missouri by Friday morning and west Tennessee near Memphis by evening. The band of snow should continue to accompany this system, spreading southeastward across Iowa, southern Wisconsin and Illinois by morning. Winter storm warnings remained in effect on Thursday night for portions of northeastern South Dakota, while a variety of winter weather and snow advisories were posted for eastern South Dakota, southwestern Minnesota and Iowa. An additional 1 to 2 inches of snow was expected in most areas.
A NEW STORM ON THE DOORSTEP --A storm moving northeastward across the North Pacific has begun to influence the weather across the Pacific Northwest on Thursday night. This storm system consisted of a low pressure system that was approximately 500 miles west of Vancouver Island and a cold front that trailed southward off the West Coast. The low is expected to continue to the northeast toward the Gulf of Alaska, while the cold front moves toward the West Coast.
While no precipitation was falling across western Washington, southwesterly winds were beginning to increase in speed as the system slowly approached the coast. Gale warnings were in effect for the Washington and Oregon coasts from Cape Flattery, WA to Florence, OR. Farther south, a heavy surf advisory was posted for overnight hours along the California coast from Point Piedras Blancas to Point Conception, as surf could rise to 10 to 15 feet.
Between 0.25 and 0.50 inches of precipitation is expected to fall across the Olympic Peninsula by Friday evening. A flood watch was in effect for the Skokomish River in western Washington.
CHILLY WEATHER ACROSS THE SOUTHEAST -- High pressure centered over the Ohio Valley as of Thursday night was responsible for tranquil weather across the Southeast. This weather did not hinder the launch of the Space Shuttle Endeavor from the Kennedy Space Center in Florida on Thursday night. However, the air mass associated with this system was relatively chilly, as afternoon high temperatures across the region ranged between 5 and 10 degrees below the 30 year average highs for the end of November. With clear skies and weak northerly winds, another chilly night is expected across the Southeast. As a result, a freeze warning was issued for Thursday night for all of southeast Alabama, much of southern Georgia and inland portions of the Florida Panhandle.
UPPER AIR -- The 500 and 300 mb charts for 00 Z Friday indicated a relatively zonal flow where the prevailing westerly winds traveled across the country with few deviations. A "short wave" trough, representing a slight southward deflection of the wind flow was found over the Plains states, in association with the surface snow-producing storm system. Another trough was located along the Eastern Seaboard, associated with the storm system that was located to the south of Nova Scotia. The zonal pattern of the winds as well as the height contours is related to the east-west patterns in the isotherms of the high temperatures for Thursday. This zonal flow also reflects the eastward tracks of the series of storm systems that have moved across the country in the last week.
YESTERDAY'S TEMPERATURE EXTREMES IN THE LOWER 48 -- Thursday's lowest temperature was 3 degrees above zero at Grand Forks, ND. Thursday's highest temperature was 81 degrees at Miami, Opa Locka and Tamiami, FL.
ALASKAN WEATHER -- Much of Alaska was dominated by arctic high pressure that was centered over the Chukchi Sea on Thursday afternoon. This high pressure system was accompanied by an unseasonably cold air mass. Once again, wind-chill temperatures fell to 62 degrees below zero at Anaktuvuk Pass. The southern boundary of the arctic air mass was a stationary front that extended across southern Alaska from the Alaska Peninsula eastward across Kodiak Island to the Kenai Peninsula to a trough of low pressure located near Anchorage Bowl and then eastward to the southern Yukon Territory. Warm air was found to the south of this front. Farther west, southerly winds on the east side of a large storm system off the Kamchatka Peninsula drew relatively warm air northward across the central western Aleutians. With the exception of the interior, much of the state was cloud-covered.
The lowest overnight temperature in Alaska on Thursday morning was 42 degrees below zero at Huslia and Selawik, while the mid-afternoon highest statewide temperature was 47 degrees at Annette.
HAWAIIAN WEATHER -- An elongated ridge of high pressure located approximately 200 miles north of Oahu was responsible for light and variable winds across the northern islands on Thursday afternoon. Since the Big Island experienced slightly stronger trade winds on the order of 10 mph, the windward coast of that island was cloudy. Afternoon clouds surrounded Mt. Haleakala on Maui indicating an afternoon sea breeze regime. An increase in the intensity of the trade winds to between 10 and 20 mph is expected over the weekend as a stronger high pressure system moves to the north of the 50th State. Restoration of the trades should signal a return of the typical trade showers.
END OF A SEASON -- Yesterday was the last day of November, marking the end of both meteorological autumn and the official hurricane season in the North Atlantic basin. For more details, please check Friday's optional Supplemental Information.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
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URL Address: datastreme/learn/f_sum.html
Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
© Copyright, 2000, The American Meteorological Society.