DATASTREME DAILY SUMMARY

Friday, 14 December 2001


00Z Weather Systems


The following highlights of the national weather have been extracted from the surface weather map for Thursday night:

ACTIVE WEATHER ACROSS THE MID-SOUTH -- Heavy rains along with strong to severe thunderstorms continued across the central Gulf Coast and the Lower Mississippi Valley on Thursday evening. This precipitation shield, which extended northward to the Ohio Valley, was associated with a low pressure system that developed during the late afternoon along a frontal boundary that lay along the Gulf Coast. By evening the low pressure center was situated over Louisiana. Earlier during the afternoon, some of the thunderstorms produced high winds that caused damage from east Texas across Arkansas to Mississippi. Large hail, with diameters up to 1.25 inches in diameter, also fell from these thunderstorm cells. Severe thunderstorms continued across southern Alabama and over the Gulf of Mexico near Mobile Bay until after local midnight. A slight risk of severe weather continues across the lower Mississippi Valley through Friday morning.

The storm system is expected to move northward, reaching western Kentucky by daybreak on Friday and to northeast Ohio by evening. A large band of heavy precipitation is expected to parallel the storm track, with forecasted 24 hour precipitation totals by Friday evening ranging between 0.50 to 1.75 inches extending from the Mississippi Delta northward to the Ohio Valley and eastward into the Middle Atlantic States. Flood and flash flood watches were in effect across Middle Tennessee and essentially the northern half of Alabama. Some locations across the watch area had received between 2 to 4 inches of rain on Thursday.

STORMY WEATHER HITS THE NORTHWEST -- A large precipitation shield has spread across the Pacific Northwest in association with a frontal system that reached the coast Thursday evening. This storm consisted of a low pressure system that was located over Vancouver Island and an occluded front that extended southward along the Washington and Oregon Coasts before becoming a cold front that curved southwestward away from the northern California coast. Rain was falling along the coasts and over the lower elevations from Vancouver Island southward to northern California and eastward into the some locations in the eastern portions of Washington and Oregon. Snow was falling over the higher terrain. Eureka, CA had 2.01 inches of rain on Thursday, a record for the date. As a result of the recent heavy rains, several rivers in western Washington and Oregon have reached flood stage.

The storm system is expected to move eastward across the Canadian Rockies with the trailing frontal system traversing the Cascades and the northern Montana Rockies by Friday morning. With cold air accompanying the storm as it moves inland, snow levels are expected to drop. Heavy snow is expected along the western slopes of many of the mountains, with upward of 2 feet of snow expected by Friday night in the Washington Cascades at elevations above 2000 feet. Similar amounts are also anticipated for the southern Sierras above 7000 feet near Yosemite National Park. As a result, winter storm warnings have been posted for the Olympics, the Cascades, the Siskiyous, the Sierra. Additional winter storm warnings were in effect for the mountains of eastern Washington and Oregon, northern Idaho, western Montana and northern Nevada.

In addition to the heavy snow, high winds with gusts to more than 70 mph in some locations are expected to cause blowing and drifting snow, resulting in significantly reduced visibility. High wind warnings were also issued for many locations across the western states. Storm warnings for winds in excess of 54 mph were in effect for the coastal waters along the Oregon and Washington coasts from Point St. George, CA northward, including the Strait of Juan de Fuca. To the south, gale warnings were posted for the California coastal waters from Point St. George to Pigeon Point. Heavy surf advisories were posted for the coast from Cape Flattery, WA to Point Piedras Blancas, CA. A coastal flood watch was in effect for those areas of Washington along the Strait of Juan de Fuca and surrounding Puget Sound.

The southern portion of the cold front is expected to travel across the southern portions of the Great Basin later on Friday. Snow advisories were posted for Friday afternoon through Saturday morning covering the high plateau and rim country of northern Arizona, where up to 6 inches of snow could fall. Winter storm watches were also posted for many of the mountains for Utah and western Colorado.

WARM WEATHER CONTINUES AROUND THE LAKES -- Unseasonably mild conditions continued across the eastern Great Lakes and along the Eastern Seaboard. Afternoon high temperatures across the eastern Lakes and the Ohio Valley were nearly 20 degrees above the average highs for mid December. Record high temperatures were also set Thursday afternoon at North Myrtle Beach, SC (74 degrees), Morgantown, WV (65 degrees) and Zanesville, OH (62 degrees)

COLD WEATHER CONTINUES ACROSS THE SOUTHWEST -- Relatively cold weather continued across the Southwest, extending from the lower Colorado Valley in southeastern California eastward across the Four Corners area to Texas. High temperatures across this region were on the order of 10 degrees below the long-term average highs for the date.

With another night of anticipated clear skies and weak winds, frost and freeze warnings were issued for much of southern Arizona.

UPPER AIR -- Both the 500 and 300 mb charts for 00Z Friday had a height trough that had moved eastward across the Rockies into the Southern Plains.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 18 degrees below zero at Craig, CO. Thursday's highest temperature was 85 degrees at Ft. Myers, FL.

ALASKAN WEATHER -- A storm system located in the northern Gulf of Alaska brought winds and some light precipitation to southern Alaska on Thursday. The storm consisted of a low pressure center situated near Cordova and a weakening front that trailed eastward across the Copper River Basin and Yakutat. This storm system generated high winds in the Prince William Sound area and other locations on Thursday morning. Whittier had southwest winds to 52 mph while Middleton Island had northwest gusts to 49 mph and at Seward to 45 mph. Another storm system was moving eastward across the eastern Bering Sea near Nunivak Island. Arctic air remained across much of interior Alaska, where afternoon temperatures remained below zero. A ridge of high pressure was situated over the Arctic Ocean and northwest Canada.

The lowest overnight temperature in Alaska on Thursday morning was 35 degrees below zero at McGrath and Sleetmute, while the mid-afternoon highest statewide temperature was 42 degrees at Annette.

HAWAIIAN WEATHER -- Winds and rains continued across the islands on Thursday as a trough of low pressure moved westward to the south of Hawaii. A tightened pressure gradient had developed between the relatively stationary high pressure cell to the northeast of the Aloha State and the trough to the south, resulting in stronger trade winds. Clouds and rain accompanied this trough of low pressure, which was a cold pool of air that extended up into the mid-troposphere. As the trough moves westward away from the islands and weakens, improving weather conditions along with weaker trade winds are expected over the weekend. Winter storm warnings were continued for the summits of the Big Island, were wind gusts to 80 mph produced blizzard conditions, as well as the high wind warnings for Haleakala on Maui. With high winds, gale warnings were in effect for all state waters and a high surf warning was continued for the east-facing shores of the islands.


A TIME OUT -- Today's Daily Weather Summary discussion is the final one for the Fall 2001 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 2002 DataStreme course during Preview Week on Monday, 21 January 2002. Have a happy and safe holiday season! EJH

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


HISTORICAL WEATHER EVENTS - 14 December

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

15 December

16 December



URL Address: datastreme/learn/f_sum.html
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.