DATASTREME DAILY SUMMARY

Thursday, 13 December 2001


00Z Weather Systems


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

WET WEATHER SPREADS NORTH AND EAST -- A large, widespread area of precipitation spread north and eastward from the Lower Mississippi Valley across the Midwest and into the Northeast ahead of two weather systems. One storm system consisted of a low pressure system located in southern Missouri with a warm front that extended to the southeast toward the Gulf Coast and the Florida Panhandle, while a cold front trailed southwestward toward the Texas Gulf Coast. The second storm system involved a low pressure system located along the western shores of James Bay in Ontario with a cold front that stretched southward across the western Great Lakes and mid-Mississippi Valley before curving westward across the southern Plains.

Heavy rainshowers and active thunderstorms were associated with the southern storm system, with much of the activity occurring along and ahead of the cold front extending from western Tennessee southwestward to the Texas Gulf Coast near Houston. Early Wednesday morning thunderstorms spawned at least one tornado in Brazoria along the Texas Gulf Coast. The tornado caused damage to buildings over a 10 block area. During the midday thunderstorm winds caused damage at several locations in west central Louisiana. El Dorado, AR received 2.51 inches of rain on Wednesday, a record for the date. Because of the rain, some rivers were either flooded or just below flood stage in Texas, Louisiana, Arkansas, Mississippi and western Kentucky. A slight risk of severe thunderstorms continues across the lower Mississippi Valley and portions of the western Gulf Coast through Thursday morning.

Farther north, a large area of rain stretched across Great Lakes and the Ohio Valley into the Northeast. Most of the rain was found to the east of the cold front associated with the northern system. Some widely scattered light snow was falling across Iowa, Nebraska, Kansas, Texas and New Mexico in the cold air behind the cold front that trailed from the northern storm system. A wintry mixture of snow, ice pellets (sleet) and freezing rain was falling across northern New England, as the precipitation was moving into a region of sufficiently cold air.

The southern storm is expected to move toward the northeast, reaching northern Lake Huron by sunrise on Thursday. The cold front associated with this system should travel eastward across the Mississippi Valley. The area with the slight risk of severe weather is expected to expand eastward across the Tennessee Valley on Thursday, remaining in the warm sector of the storm system located to the east of the cold front. Between 1.0 and 2.9 inches of rain could fall during the 24 hours ending on Thursday evening in a region that extends from the Cumberland Plateau in eastern Tennessee southwestward to coastal Louisiana. As a result of the recent heavy rains, coupled with the additional anticipated rain, flood and flash flood watches remain in effect for the lower Mississippi Valley, to include portions of Louisiana, Mississippi, and western Tennessee.

The northern storm is expected to move eastward across James Bay with the cold front moving across the Upper Lakes before merging with the southern storm on Thursday afternoon.

While much of the eastern half of the country experienced widespread clouds and rain, some areas along the Eastern Seaboard had some relatively cloud-free skies on Wednesday. After dark, dense fog began forming as the air cooled to saturation. Dense fog advisories were posted for many locations southward from the Middle Atlantic as visibility was reduced to 0.25 miles or less.

WINTRY WEATHER ACROSS THE NORTHERN ROCKIES -- Strong westerly winds traveling across the northern Rockies have contributed to heavy snow across the mountains of eastern Washington, northern Idaho and Montana. This precipitation was also associated with a Pacific storm system that was moving into western Washington State on Wednesday evening. Heavy snow warnings have been posted for Montana and Idaho, where some locations could receive as much as 12 inches of snow by late Thursday. High wind warnings were in effect through Thursday morning on the lee slopes of the Montana and Wyoming mountains. Livingston, MT had sustained winds of 40 mph with gusts to almost 70 mph early Thursday morning.

ANOTHER STORM SYSTEM -- A powerful storm system was expected to reach the Washington coast by Thursday evening. A cold front trailing southward from this storm should move onshore along the Oregon and California coasts later. This storm is expected to generate strong southerly winds as the storm approaches the coast. A gale warning was in effect for coastal waters extending north of Point St. George, CA, to include the Strait of Juan de Fuca, while a coastal flood watch was posted for the coast of northern California.

In addition, a winter storm watch was posted for the mountains of northern California along with the western slopes of the northern and central Sierra in California, where up to 18 inches of snow could fall between Thursday night and Friday morning at elevations above 5000 feet.

AND IN THE SOUTHWEST -- A cold, dry air mass along with ideal nighttime radiation conditions, has meant another cold night across the Southwest. A frost warning was posted for southeastern Arizona, to include the Tucson metropolitan area.

UPPER AIR -- The mid-tropospheric 500 mb constant pressure chart and the upper-tropospheric 300 mb chart for 00Z Thursday both have a large height trough across the West, resulting in a meridional flow pattern. The trough axis, reflecting the center of the cold pool of air that extends upward through the troposphere, has drifted slowly eastward over the last 24 hours. The merdional flow pattern consists of northerly winds over the West Coast traveling southward long the west limb of the trough and southwesterly winds just to the east of the trough.

TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 18 degrees below zero at Jackson, WY, while the Wednesday afternoon highest temperature was 86 degrees at Tampa, FL.

ALASKAN WEATHER -- A large low pressure system located along the southeast coast of the Kenai Peninsula dominated the weather across much of Alaska on Wednesday. A weak trough of low pressure extended northwestward across central Alaska. An arctic front stretched from the Alaska Peninsula eastward to near Kodiak Island then northeastward to the Anchorage Bowl before running southeastward to the Panhandle and then into northwestern British Columbia. This front separated cold air to the north from relatively warm air to the south. Rain fell across the Panhandle.

The lowest temperature in Alaska on Wednesday morning was 20 degrees below zero at Kaktovik and Ugnu Kuparuk. The highest statewide temperature as of Wednesday afternoon was 45 degrees at Hydaburg.

HAWAIIAN WEATHER -- An upper level disturbance moved westward and passed to the south of the islands by late Wednesday, increasing the gusty trade winds and producing heavy rainfall. A high pressure system located to the northeast of Hawaii has produced strong trade winds, but with the passage of the disturbance, the pressure gradient has tightened, resulting in stronger, gusty winds. Thick clouds and showers were spreading across the islands. The rain should continue into Friday. Winter storm warnings were continued for the summits of the Big Island. Mount Haleakala on Maui could experience winds from 50 to 70 mph. Flood watches were in effect for Maui and the Big Island. The increased winds have necessitated the posting of gale warnings for all state waters and wind advisories for all islands. A high surf warning was in effect for the east shores of the islands.


HISTORICAL WEATHER EVENTS - 13 December

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



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