DATASTREME DAILY SUMMARY

Friday, 8 December 2000


00Z Weather Systems


MORE SNOW FOR THE MIDWEST -- An Alberta Clipper system traveled swiftly southeastward from the Prairie Provinces into the Midwest on Thursday. By late evening the low pressure center was located in northwest Indiana, with a warm front that extended to the east-southeast across the Appalachians to northern Virginia and a cold front that trailed southwestward across the mid-Mississippi Valley to the central Plains.

Except where lake-enhanced snow fell, this storm system was accompanied by relatively light amounts of snow, with several inches of accumulation. Since relatively warm air was brought into the system from the south and southwest, some areas along and to the south of the storm track also received some freezing rain and drizzle. This combination of light snow and freezing drizzle slowed traffic and caused numerous accidents across southern Wisconsin on Thursday morning. By late evening, light snow had spread eastward into central Pennsylvania, producing a band of snow that extended from the Keystone State westward to east central Illinois, and northward into Lower Michigan. Several pockets of lake-enhanced snow were also detected across northeast Wisconsin and the Upper Peninsula of Michigan.

This Alberta Clipper is expected to move toward the east, reaching northeast Ohio by Friday morning and off the New England coast by evening. A light blanket of snow, with no more than several inches of accumulation, is expected across the Middle Atlantic States on Friday. With cold air moving into the Midwest behind the departing low pressure system, some lake-effect snow is expected to fall across the western Lakes. A variety of advisories and winter storm warnings were in effect for the eastern portion of Michigan's Upper Peninsula and extreme northern Lower Michigan. Between 3 to 5 inches of additional accumulation is anticipated. Winds across the Upper Peninsula could also produce blowing snow conditions that would reduce visibility. Winter weather advisories were issued for northern Ohio, western Pennsylvania and portions of western Maryland.

A wind-chill advisory was posted for northern Maine as wind-chill equivalent temperatures are expected to fall to between 30 and 40 degrees below zero during the overnight hours.

ANOTHER FOGGY DAY -- While the fog dissipated across the valleys of California, it has remained a problem across the Pacific Northwest. High pressure across the region has contributed to the persistent fog in the valleys of Washington, Oregon and Idaho. Dense fog once again occurred with visibility ranging from 0.25 miles to 100 feet. There were dense fog advisories for the Magic Valley of Idaho.

SOUTHWESTERN PRECIPITATION -- Widely scattered rain fell across California on Thursday night in association with a weak low pressure system off the coast. The precipitation is expected to move inland, reaching the 4 Corners area by early Friday morning. Some of the precipitation could change over to snow at the higher elevations.

OF NOTE -- Early on Thursday morning, a wind gust of 83 mph was measured at the NCAR (National Center Atmospheric Research) Mesa Lab near Boulder, CO.

WHAT'S COMING -- Output from the various numerical weather prediction models indicate that some of the coldest air that the West has seen in the last 2 to 4 years will spread southward across the Plains, Rockies and Intermountain West by the end of the weekend or the start of next week. As of Thursday night, an arctic air mass stretched across the Arctic Ocean from near the North Pole into the Northwest Territory near Great Bear Lake. This air mass is expected to move southward along the eastern slopes of the Rockies. The National Weather Service Forecast Offices across the West have been issuing special weather statements informing the public of the potentially serious situation as wind-chill equivalent temperatures are expected to fall to extremely dangerous levels.

To compound the problem, a major winter storm is expected to develop along the leading edge of the arctic outbreak. This storm is forecast to develop along the eastern slopes of the southern Rockies and move northeastward toward the Midwest by Monday.

UPPER AIR --The flow pattern on both the 500 and 300 mb constant pressure charts for 00Z Friday returned to a more west-to-east flow. A weakened trough corresponding with cold air over Canada was situated over the eastern half of the nation, while a slight height ridge was found across the West. A strong 300 mb jet had wind speeds reaching 150 knots over the Upper Mississippi Valley.

YESTERDAY'S TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Thursday was 9 degrees below zero at Pellston, MI. Thursday's highest temperature was 86 degrees at San Diego/Gillespie, CA.

ALASKAN WEATHER -- A large and complex storm system over the western Aleutians dominated the weather across western Alaska on Thursday afternoon. The double low pressure centers were located near Attu Island, with a frontal system that curved eastward across the western Bering Sea and then southward across the central Aleutians near Adak Island. With a central pressure of approximately 965 mb, this storm system generated gusty winds across the Bering Sea and the Aleutians. Cold Bay had winds to 47 mph, while Dutch Harbor experienced 44 mph gusts. Southerly winds to the east of the storm system brought relatively warm air northward across southwestern and western Alaska, replacing the arctic air that had been in place for several days. The northern boundary of this warm air was a stationary front that stretched southeastward from the Lisburne Peninsula in northwest Alaska to near Fairbanks and then to the Alcan border near Northway in southeast Alaska.

Except for the southern half of the Cook Inlet, most of Alaska was cloud covered. Snow was reported at many locations in the interior as well as in the Anchorage Bowl. Rain was reported across the Aleutians in association with the western storm system and at several locations in the Panhandle.

The lowest overnight temperature in Alaska on Thursday morning was 22 degrees below zero at Arctic Village, while the mid-afternoon highest statewide temperature was 45 degrees at Sand Point.

HAWAIIAN WEATHER -- Pleasant trade weather continued across the islands on Thursday as a result of a subtropical ridge located to the north of Hawaii. Since this ridge was relatively close to the islands, the pressure gradient was relatively weak, resulting in light trade winds. Some showers were found mainly along the windward slopes of the islands. The pleasant trade weather is expected to continue through the weekend, with easterly trade winds turning to a more southeasterly direction by early next week. An increase in clouds and showers is then anticipated. The surf along the northwest facing shores of the islands diminished on Thursday, which resulted in a lowering of the high surf advisory. The next high surf event could occur late Saturday.

AN UPDATE -- Bill Gray of Colorado State University released his year 2001 North Atlantic hurricane season forecast on Thursday. He has forecast that next year's hurricane season will be close to average, and not as active as the last five seasons with 9 named tropical systems (both tropical storms and hurricanes), 5 of which should be hurricanes. He also forecasts that 2 hurricanes could be intense, or being Category 3 or higher on the Saffir-Simpson Hurricane Intensity Scale. Long-term averages for the basin include 9 named storms, 6 hurricanes and 2 intense hurricanes. He also anticipates an above average probability that a major hurricane would make landfall along the U.S. coastline.

REPORTS FROM THE FIELD -- A big "Thank You" is extended to all correspondents who contributed to this Reports from the Field section during the fall. Your reports have been interesting and they serve as a reminder to "keep a weather eye out". EJH

STAY TUNED! -- While today is the official end of the fall 2000 DataStreme course, a Daily Weather Summary will be posted for each day next week, 11-15 December 2000. We hope that you continue reading them. If you plan on taking leave of us with this Summary, have a happy and safe holiday season! DataStreme Daily Summaries and Activity files will return with the Spring 2001 DataStreme course during Preview Week on Monday, 22 January 2001. EJH


HISTORICAL WEATHER EVENTS - 8 December

From the files of the Aviation Weather Center, Kansas City, MO and Intellicast

9 December

10 December


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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.