DATASTREME DAILY SUMMARY

Tuesday, 14 November 2000


00Z Weather Systems


WINTRY WEATHER ACROSS THE MIDWEST -- The storm system that produced heavy snow accumulations across the Plains over the weekend continued to move slowly across the Midwest on Monday. As of late Monday night the storm system consisted of two low pressure centers, with one low pressure center located over northeastern Wisconsin and a slightly more intense low pressure center over the eastern extremity of Michigan's Upper Peninsula. An occluded front stretched southeastward from this latter low pressure center to western Pennsylvania, where it became a cold front that continued southward to the western Panhandle of Florida.

Light snow continued to fall across the Midwest to the west of the storm system. Some of the snow immediately downwind of Lake Superior across northern Wisconsin and the Upper Peninsula and in the lee of Lake Michigan over western Lower Michigan was lake-enhanced snow. Strong northerly winds surrounding the low pressure center were transporting cold air southeastward across the relatively warm lake surfaces. As a result of passage of the cold air across the lakes, snowfall associated with the low pressure system was enhanced. However, some of the snow across southwestern Wisconsin and northeastern Iowa was associated with the weak trough line that was passing across the region. This trough line, emanating like a spoke from a wheel represented a region of slightly lower pressure and a region of localized convergence along a slight shift in the counterclockwise wind flow around the low pressure center.

The center of the storm system is not expected to move significantly by Tuesday morning. The accompanying cold front is expected to move eastward, and by afternoon move off the Eastern Seaboard. As a result, a new low pressure center is forecasted to develop near the point of occlusion where the occluded and cold fronts merge. By Tuesday evening this new low pressure center should be located off the coast of Cape Cod. At that time, the original surface low pressure center is expected to have moved a short distance eastward to a position just north of Georgian Bay. With a continued northwesterly wind flow, lake-effect and lake-enhanced snow should continue over the western Lakes. A winter storm warning was in effect for the western portion of Michigan's Upper Peninsula, while a winter weather advisory was posted for northern Wisconsin and snow advisories were issued for surrounding locations in the Upper Peninsula and northern Wisconsin. Between 0.25 and 0.50 inches of liquid equivalent precipitation could fall across the Upper Peninsula between Monday and Tuesday evenings. Similar amounts are also forecast for southern New England where the cold front is expected to pass.

WET WEATHER ACROSS THE SOUTHEAST -- Welcome rains fell across portions of the Carolinas, south Georgia and northern Florida that have experienced persistent dry conditions. This precipitation originated from rainshowers and imbedded thunderstorms that were along and ahead of the cold front that was moving eastward across the Southeast on Monday evening. A weak low pressure center had developed along the cold front over the northeastern Gulf of Mexico.

Rainfall totals for the 24 hours ending on Tuesday evening should range between 0.25 and 0.50 inches across coastal portions of the Carolinas as the cold front continues eastward.

UNSEASONABLY COLD CONDITIONS CONTINUE ACROSS THE WEST -- A large high pressure center remains anchored over the Rocky Mountains and western Plains on Monday evening. This high, which extends from Wyoming to central Texas, is associated with an unseasonably cold air mass. Afternoon high temperatures across the high Plains and the Rockies ranged between 20 and 30 degrees below the average highs for the date.

The high pressure region is expected to slowly drift to the southeast by Tuesday morning. As a result of the clear skies and weak winds, enhanced nighttime cooling is expected. As a result, freeze warnings were in effect from southwest Arkansas and northwest Louisiana southwestward across Texas to the Rio Grande Valley near Del Rio.

UNSETTLED WEATHER ALONG THE WEST COAST -- A storm system located along the California coast produced a large area of precipitation across California, southern Oregon and western Nevada. The storm system consisted of a low pressure center that was located off the Oregon Coast near Cape Blanco and an accompanying frontal system that had moved onshore along the California coast. An occluded front stretched southeastward to a secondary low pressure center located near Lake Tahoe in western Nevada. A cold front curved southwestward from this secondary low across central California. The precipitation was in the form of coastal rain and high mountain snow.

The secondary low pressure center is expected to continue eastward into the Great Basin of central Nevada by Tuesday morning, while the original low was forecast to remain along the Oregon coast. Precipitation in the form of low altitude rain and high altitude snow should spread eastward across Nevada and into Utah. As much as 0.5 inches of liquid equivalent precipitation was anticipated along the western slopes of the Sierras in California during the 24 hours ending on Wednesday evening.

UPPER AIR -- The upper level flow patterns on both the 500 and 300 mb charts for 00Z Tuesday contained a large cyclonic circulation regime over the western Great Lakes. This counterclockwise circulation surrounded a cold pool of air that extended upward through the troposphere as a "vertically stacked" system. The closed height troughs on both the 500 and 300 mb surfaces were nearly directly over the surface low pressure feature over northeastern Wisconsin. Such a vertically stacked low is typical of an occluded storm system. A strong jet steam continues across the Southern States, south of the 300 mb trough. Jet-stream winds at 300 mb had speeds that reached 120 knots over the Tennessee and lower Mississippi Valleys.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 17 degrees at Big Piney, WY, while Monday's highest temperature was 85 degrees at Opa Lacka, FL.

ALASKAN WEATHER -- A strong storm system in the Bering Sea generated windy weather along with precipitation across western Alaska on Monday afternoon. The low pressure center with a central pressure of 960 mb was located northwest of Nunivak Island. An occluded frontal system curved northward from the low pressure center across St. Lawrence Island then eastward across Norton Sound and then southeastward across western Alaska, crossing the Kenai Peninsula before continuing out across the Gulf of Alaska and the North Pacific Ocean. The tight pressure gradient surrounding this storm system produced strong southwesterly winds across the Bering Sea, reaching 60 mph at Dutch Harbor, 55 mph at Gambell on St. Lawrence Island and 51 mph at Cold Bay. Heavy rain fell at Cold Bay, where 2.27 inches fell in the 24 hours ending on Monday morning. Rain was falling on Monday afternoon at Yakutat, Seward and Homer. Snow and blowing snow was reported at Wainwright, Galena, Tanana and Kivalina. Blizzard conditions continued in Kotzebue. High pressure was found across the Panhandle.

The state's lowest temperature on Monday morning was 18 degrees below zero at Arctic Village. The highest temperature across Alaska as of midafternoon on Monday was 47 degrees at Palmer.

HAWAIIAN WEATHER -- Northeasterly trade winds with speeds of approximately 20 mph were found across the islands on Monday. High pressure was located to the northeast of Hawaii. Sunday's clouds moved south and were affecting only the southern half of the Big Island. Elsewhere, skies were relatively cloud-free on the leeward sides of the other islands. Some clouds associated with trade showers were confined to the windward slopes. Small craft advisories remained in effect for state waters as a result of the strong trade winds. A high surf advisory was posted for the northwest facing shores.


CONCEPT FOR THE DAY - WINTER STORMS

Has winter arrived yet? The answer depends upon whom you ask. Most of us would say no, since the popular definition of winter would require us to wait until the winter solstice, in about five weeks. A climatologist would say that winter would begin on 1 December, two weeks from Friday. We have already seen several storms move into the Pacific Northwest and across the Rockies during the last several weeks that have produced considerable snowfall and freezing rain.

A winter storm is a widespread set of weather conditions with winter-type precipitation - snow, ice pellets or freezing rain - often accompanied by strong winds and cold temperatures. They may form any time from late autumn through spring and affect, not just the northern states, but everywhere from the West to the Gulf Coast. They can range from a minor annoyance to the "Storm of the Century" that paralyzed the Gulf and East Coast in March 1993. In the 1999 winter season, 41 deaths across the United States and territories were attributed to winter weather (39 winter storms and 2 ice storms). Extreme cold claimed an additional 7 lives, and 26 people were killed by avalanches. Winter weather also caused 444 injuries.

Low pressure systems in the cooler season of the year may include precipitation that can fall as snow, often heavy, that is accompanied by high winds and wind-chill equivalent temperatures cold enough to be life-threatening. The winds and falling or blowing snow may produce blizzards with poor visibility. Hazards range from roof collapses to transportation gridlock. Slightly warmer temperature patterns may bring rain that freezes after contacting cold surfaces (freezing rain or drizzle). The build-up of ice during freezing rain can paralyze impacted areas for days from loss of power, communications disruptions and blocked roadways.

For a description of the terminology used in the official statements issued by the National Weather Service to inform the public of adverse winter weather conditions, please read the Tuesday optional Supplemental Information.

QUESTIONS:

To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications, Week 10 Chapter Progress Response Form, under section B. Daily Summary.

  1. Winter storms [(are) (are not)] limited to the Northern States.
  2. The weather conditions associated with winter storms may include [(freezing rain) (cold temperatures) (heavy snow) (all of the above)].

HISTORICAL WEATHER EVENTS - 14 November

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


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URL Address: datastreme/learn/t_sum.html
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2000, The American Meteorological Society.