DATASTREME DAILY SUMMARY

Friday, 15 December 2000


00Z Weather Systems


GETTING OFF EASY -- The storm system that produced the icing conditions across the Southern Plains on Wednesday quickly moved across the Northeast on Thursday, causing less weather related problems than initially anticipated. The widespread icing that was anticipated across the Middle Atlantic States did not materialize because the near surface air in many locations was too warm, with rain falling rather than freezing rain. However, the icing was scattered, with approximately 0.5 inches of ice accumulated on surfaces in portions of Maryland. Some locations across interior New York State and New England did receive 4 to 8 inches of snow.

By Thursday night the low pressure system was located in the Gulf of Maine. Some light snow was falling across northern Maine. By Friday morning the low should have moved to the northeast of the Maritime Provinces, resulting in the end of the snow in New England.

AN INTERLUDE -- High pressure located over the Ohio Valley on Thursday night was responsible for tranquil weather across much of the eastern half of the nation. This high pressure follows on the heels of two winter storm systems that moved across the country during the first part of the week -- one that produced heavy snows across the Midwest, and the second, the above mentioned system. High temperatures for many locations were 10 to 15 degrees below the average highs for this time of the year.

The high pressure system is expected to drift to the east, reaching western Maryland by Friday morning, and New England by dusk. With weak winds and clear skies under the high pressure system, radiational cooling should cause temperatures to fall to the dewpoint, producing fog. Dense fog advisories were issued for portions of Georgia and the western Carolinas. The Northeast should experience quiet, but cool weather on Friday. For the nation's midsection, the tranquil weather of Thursday will be short-lived, since the next series of storms are expected to arrive.

MORE WINTRY WEATHER AHEAD FOR THE MIDWEST -- A weak low pressure system is expected to develop over the lee slopes of the Colorado Rockies on Friday morning and move across the central Plains toward the Midwest by late in the day. Moisture drawn northward into this low pressure system is expected to fall as snow across the upper Mississippi Valley into the western Great Lakes by Friday night. Farther to the south, freezing rain is expected across the mid-Mississippi Valley as warm moist air is drawn northward over the shallow cold dome of air. Consequently, winter storm watches were posted for portions of southwestern Wisconsin, northwest Illinois, eastern Iowa and southeastern Minnesota.

In anticipation for the powerful storm moving across the northern Plains from the Pacific Northwest, winter storm watches have been posted effective Friday night and Saturday for northwest Wisconsin, northern Minnesota and eastern North Dakota.

SNOW ACROSS THE NORTHWEST -- A storm system moved into the Pacific Northwest on Thursday spreading precipitation eastward into the interior. The low pressure center was located over Vancouver Island, with an occluded front that trailed southward along the Washington and Oregon coasts. Rain fell along the coast, while snow was falling across the Cascades and the mountains of eastern Washington, Oregon, northern Idaho and northwest Montana.

This system is expected to move eastward, crossing the Canadian Rockies by Friday morning. Between 12 to 18 inches of snow are expected in the Washington and Oregon Cascades, as cold air should cause the snow level to fall to approximately 2000 feet. A variety of winter storm warnings, snow advisories and winter weather advisories cover much of the Northwest, from the Olympic Peninsula of Washington State east to the Montana Rockies and south to northern Colorado.

In addition to the snow, this storm is expected to generate strong winds with gusts ranging between 55 to 70 mph as the system crosses the Rockies. High wind warnings were posted for the Columbia Basin of Washington and Oregon, the mountains in eastern Idaho, the upper Yellowstone Valley of southern Montana and the mountains of southeastern Wyoming. Farther south, wind advisories were also posted in the Sierras for 30 to 40 mph winds.

UPPER AIR --The 500 and 300 mb constant pressure charts for 00Z Friday revealed a relatively zonal (west to east) flow with a small trough over the Intermountain West.

YESTERDAY'S TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Thursday was 24 degrees below zero at Cambridge, MN, while the day's high was 86 degrees at Fort Myers and Punta Gorda, FL.

ALASKAN WEATHER -- The main players in Alaska's weather for the last several days-- high pressure over the Yukon Territory and low pressure over the Bering Sea -- remained relatively stationary on Thursday. The pressure gradient between these two weather features continued to generate gusty southeasterly winds to a large portion of the state. Cold Bay had winds of 54 mph, while Golovin had 46 mph winds. Early Thursday morning 62 mph winds were recorded at Douglas, across the Channel from Juneau and 107 mph gusts were reported at Sheep Mountain, 3500 feet above Juneau.

As a result of the southerly flow, above average temperatures were found across northwest Alaska, while below average temperatures were concentrated in the southeast. Much of Alaska was relatively cloud-free, except for the clouds along the Bering Sea, the southern portion of the Alaska Peninsula and the northern Gulf coast. Snow fell at Yakutat, while Sand Point and Seward reported rain.

The lowest overnight temperature across the state as of Thursday was 34 degrees below zero at Northway. The highest midafternoon temperature was 45 degrees at Chignik.

HAWAIIAN WEATHER -- The subtropical ridge of high pressure that maintained the trade winds over the Aloha State shifted toward the east away from the islands. As a result, winds across the islands weakened and shifted to a more southeasterly direction on Thursday. Clouds and isolated showers formed over the interiors of the islands during the afternoon. Normal east to northeast trade winds are expected to return on Friday as another high pressure cell passes to the north of the islands.

Strong winds off Japan produced ocean swells that propagated across the Pacific toward Hawaii. The ocean swells is expected to generate surf that could reach 10 feet on the north shore of Oahu by Friday morning. As a result, high surf advisories were posted for the northwest shores of the islands.


A TIME OUT -- Today's Daily Weather Summary discussion is the final one for the fall 2000 course. If you are looking for an alternative description of daily weather, you could try:

http://www.usatoday.com/weather/wlead.htm

DataStreme Daily Summaries and Activity files will return with the Spring 2001 DataStreme course during Preview Week on Monday, 22 January 2001. Have a happy and safe holiday season! EJH

Several noteworthy events that will occur during the next several weeks include:


HISTORICAL WEATHER EVENTS - 15 December

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

16 December

17 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.