DATASTREME DAILY SUMMARY

Wednesday, 28 November 2001


00Z Weather Systems


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

SNOW CONTINUES ACROSS THE UPPER MIDWEST -- The first major snowstorm of the season moved eastward from the northern Plains across the Great Lakes on Tuesday, spreading heavy snow and windy conditions across the region. As much as 17 inches of snow had fallen by Tuesday morning near Deadwood in the Black Hills of South Dakota. Many locations in Minnesota and northern Wisconsin had more than a foot of snow. However, the most snow as of Tuesday evening was 30 inches of snow reported at Willmar, a farming community approximately 80 miles west of the Twin Cities. The water equivalent of this snow was in excess of one inch. Strong winds accompanied this storm, with 52 mph winds reported at the Aerial Lift Bridge in Duluth Harbor. Nearby, the wind-driven waves caused shoreline erosion.

As the storm moved toward the east it had undergone a typical occlusion process. A primary low pressure center remained over southeastern Minnesota as of Tuesday evening, while a secondary low was located over southern Ontario to the west of Buffalo, NY. This secondary low had formed near the point of occlusion at the end of the occluded front where the surface warm and cold fronts intersect. The occluded front had weakened and was indicated on some of the surface analyses on Tuesday night as a trough line. A warm front extended southeastward across the Middle Atlantic States, while a cold front trailed southward from the secondary low across the Ohio Valley and along the Appalachians to the Gulf Coast, where the front traveled westward to the Rio Grande Valley of south Texas.

Some snow continued falling across portions of the eastern Dakotas, northern Minnesota, northern Wisconsin and Michigan's Upper Peninsula. Freezing rain also was reported in northeastern Wisconsin. As a result, winter weather advisories remain in effect across portions of northeastern Wisconsin and northern Lower Michigan. The storm system is expected to weaken on Wednesday, with some lingering precipitation continuing along a stationary front that is forecast to stretch across the Great Lakes. As much as 0.1 inches of additional liquid-equivalent precipitation is anticipated to fall across the region by Wednesday evening.

WARM WEATHER CONTINUES IN THE EAST -- Much of the nation east of the Mississippi River experienced warm weather. High temperatures across the eastern half of the country were above average, with the largest temperature departures found across the Ohio Valley where highs were 20 degrees above average. A large high pressure center located over the Southeast contributed to the relatively warm conditions, with clear skies and sinking motion. Record high temperatures were either tied or set in Georgia at Augusta (83 degrees); in South Carolina at Myrtle Beach (79 degrees) and Greenville-Spartanburg (75 degrees); in North Carolina at Charlotte (77 degrees); and in Virginia at Blacksburg (73 degrees).

COLD AIR SPREADS ACROSS THE WEST -- A pool of cold air spread southward across the Plains and Rockies in association with a large high pressure system. As a result, much of the nation west of the Mississippi River experienced unseasonably cold conditions on Tuesday as high temperatures ranged from 20 to 25 degrees below the long-term average across the western Plains and the Rockies. The low temperature (41 degrees) at the Oakland (CA) Museum was a record low.

The cold air is expected to remain across the region, resulting in another cold night. Consequently, freeze warnings were posted across portions of Texas to include the Hill Country near Austin and west of the Pecos, as well as in southern New Mexico. Frost and freeze warnings were also issued for the valleys of southern Arizona and in southern California.

WINTRY WEATHER DEVELOPED OVER THE SOUTHERN PLAINS -- The cold air across the southern and central Plains located to the north and west of a nearly stationary cold front helped produce a wintry mix of precipitation. The front separated the cold air across the Plains from the warm Gulf air across the lower Mississippi Valley and the eastern Gulf Coast. Warm moist air from the Gulf was flowing up and over the shallow dome of cold air to the north of the surface front, resulting in overrunning precipitation. This overrunning precipitation took the form of rain near the front, freezing rain and ice pellets farther from the front and snow several hundred miles to the north and west of the front. A band of snow stretched from southern New Mexico across west Texas and Oklahoma into southern Missouri. Earlier, snow had fallen farther to the north and west. By mid-morning between one and four inches of snow had fallen across the southern Rockies of Colorado.

Close to the front, precipitation had been heavy. Galveston received 2.71 inches of rain on Tuesday, a record for the date. Some flooding had occurred on Tuesday morning in Natchez, MS and in eastern Arkansas. Flooding of various rivers in Mississippi and Louisiana continued late Tuesday, necessitating the issuance of flood warnings. Thunderstorm winds caused some damage in northwestern Alabama on Tuesday morning and in southwestern Louisiana on late Tuesday night. Strong to severe thunderstorms with waterspouts continued into the late night over the coastal waters of the western Gulf of Mexico near Galveston Bay.

The front is expected to move northward as a warm front on Wednesday. However, a wintry mix of precipitation should continue in the colder air to the north of the front. A variety of winter storm warnings, winter weather advisories and snow advisories have been posted from the mountains of southern New Mexico across much of Texas, Oklahoma, northwestern Arkansas, Missouri and west central Illinois. Five to eight inches of snow are expected across portions of Oklahoma near Tulsa. Ice pellets (sleet) and freezing rain are also forecast for the region. A winter storm watch was in effect for south central Texas. Flash flood watches were posted in a band that extended from the Texas Gulf Coast across Louisiana, eastern Arkansas, western and northern Mississippi and western Tennessee.

A slight risk of severe thunderstorms continues into Wednesday morning along the western Gulf Coast, from the Mississippi Delta westward along the entire Texas Gulf Coast. A slight risk of severe weather remains across the lower Mississippi Valley on Wednesday.

A NEW STORM TAKES AIM ON THE PACIFIC NORTHWEST -- A storm located more than one thousand miles west of the Washington State coast is expected to be the next major storm to affect the Pacific Northwest for the rest of the week. While this storm with a trailing cold front is not expected to reach the coast of Washington and Oregon until late Wednesday afternoon, the winds associated with the system have preceded it. As the storm approaches Vancouver Island, it is forecast to deepen, with central pressure falling from a current value of approximately 987 mb to a forecasted value on late Wednesday afternoon of 976 mb. Southerly winds are expected to increase in advance of the storm. For maritime interests, storm warnings (for anticipated winds exceeding 54 mph) were posted along the coast from Point St. George, CA north to Cascade Head, OR, while gale warnings (for winds between 39 and 54 mph) were in effect northward from Cascade Head to Cape Flattery, WA. A high wind warning was in effect through Wednesday for Coast Range in Oregon and coastal counties extending from the vicinity of Cape Mendocino, CA to near Grays Harbor, WA. Southerly winds are expected to increase and gust to 65 mph in the mountains.

In addition to the strong winds in advance of the storm, a widespread precipitation shield should reach the coast by Wednesday morning. Between 1.0 and 2.7 inches of liquid-equivalent precipitation is forecast to fall in the 24 hours ending late Wednesday afternoon along the coast and the western slopes of the Coast Range and the Cascades of Oregon and Washington. Snow levels are expected to drop as the storm eventually moves into interior sections of the Northwest. As a result, a variety of winter storm warnings and watches, snow advisories and winter weather advisories covered essentially all of Oregon, Washington, northern California, northern Idaho and northwestern Montana. Anticipated snow totals by Thursday ranged from one to three inches in the Siskiyous of northern California to as much as 17 inches of snow in the Cascades of Washington. A foot of snow is expected in the mountains near Glacier National Park in Montana. Strong winds could also reduce the visibility.

Farther south the trailing cold front is expected to move across California on Thursday. Winter storm watches were in effect for the Sierra in California where a foot of snow could fall on Thursday, and for the mountains in Utah between Wednesday night and Friday as one to two feet of snow are anticipated.

UPPER AIR -- Both the 500 and 300 mb charts for 00Z Wednesday indicate a more meridional circulation pattern, the result of the deep height trough in the West and the height ridge in the East. The height trough across the Rockies and the Great Basin, extending southward to the Four Corners region, reflects the pool of cold air that extends upward through the troposphere across the West. Farther east, the warm air maintains the height ridge. A fairly strong jet stream is found at 300 mb, with northerly winds reaching in excess of 130 knots over Idaho and Nevada on the west limb of the trough, while southwest winds on the east limb of the trough reached 120 knots over the central Plains.

YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US --Tuesday morning's lowest temperature was 6 degrees below zero at Wells, NV, while the highest temperature on Tuesday was 88 degrees at Harlingen, TX.

ALASKAN WEATHER -- Much of mainland Alaska remained under an arctic air mass associated with a ridge of high pressure that extended westward across the state from northern Canada. As a result, skies across interior Alaska were relatively cloud-free. Fog was found at some locations, to include Barrow. Early afternoon temperatures across interior Alaska ranged from 17 degrees below zero at Northway to 4 degrees above zero at Nenana. With southeast winds gusting to over 20 mph, some locations across the interior had wind-chill equivalent temperatures of 25 degrees below zero. A stationary front that marked the southern boundary of the arctic air mass extended from the Yukon-Kuskokwim Delta eastward along the north Gulf Coast to southeast Alaska where the front curved to the southeast to run along the Panhandle and the British Columbia coast. Rain was reported at Kodiak, while snow fell at Yakutat. A high wind warning was posted through Wednesday covering portions of the Panhandle, to include Juneau as northeast winds with gusts to 60 mph are expected to develop as cold air surges westward from the high pressure center in Canada. To the west, a storm system that was developing across the western Bering Sea spread clouds across the Aleutians and southwestern Alaska.

The state's lowest overnight temperature on Tuesday morning was 27 degrees below zero at Northway. The highest temperature by mid afternoon of Tuesday was 42 degrees at Kodiak.

HAWAIIAN WEATHER -- A Kona low that developed to the southwest of Kauai continued to spread across the islands, with heavy rainshowers and isolated thunderstorms over Molokai, Lanai, Maui and the Big Island. A flash flood warning was issued for late Tuesday night across southern portions of the Big Island, to include Volcanoes National Park as strong thunderstorms developed over the region. Winds were from the south across the islands. The Kona low is expected to move toward the west, resulting in a cessation of the rain on Wednesday, followed by a return to trade winds by Friday as a strong surface high moves to the north of the islands. Flood watches were in effect for Molokai, Lanai, Maui and the Big Island. Small craft advisories continued for the waters around Kauai and Oahu.

EYE ON THE TROPICS -- Hurricane Olga moved in a series of small loops across the North Atlantic on Tuesday. By late night, Olga was nearly stationary and was located 525 miles east of Bermuda. Maximum sustained surface winds were 90 mph.

TORNADO SEASON -- With one month remaining in the year, approximately 1000 tornadoes have been reported across the United States during 2001, with 37 fatalities. For more information concerning this year's tornado statistics, consult Wednesday's optional Supplemental Information.


HISTORICAL WEATHER EVENTS - 28 November

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


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