DATASTREME DAILY SUMMARY

Tuesday, 13 November 2001


00Z Weather Systems


The following discussion is based upon the major weather features appearing on Monday night's surface weather maps:

MORE WELCOME PRECIPITATION IN STORE FOR THE WEST -- A second major storm system in the last week moved into California on Monday, with a third storm not too far behind. These storms are providing much needed precipitation for a region that had little precipitation during the last winter rain season. As of Monday evening low elevation rain and mountain snow had spread along the Pacific Coast from the Los Angeles Basin northward to Puget Sound in Washington State, and inland into Nevada. This precipitation accompanied a low pressure system that was located in northern Nevada with a cold front that trailed southward to the Los Angeles Basin. By early evening record-setting rains had fallen across the Bay area and into the central valleys of California, to include Kentfield (2.70 inches), Downtown San Francisco (2.09 inches), San Rafael (2.07 inches), Santa Rosa (1.99 inches), Napa (1.54 inches), Fresno (1.05 inches), Salinas (0.90 inches) and Bakersfield (0.37 inches). These heavy rains caused some mudslides and necessitated the issuing of an urban and small streams advisory for the San Joaquin Valley. A similar advisory was in effect for awhile in the Los Angeles Basin. By evening 4 to 6 inches of snow had fallen in the Sierras at Donner Summit and Echo Summit near Lake Tahoe and at Mammoth Lakes.

The low pressure system was expected to move to the northeast, reaching the Snake Valley in southeastern Idaho by Tuesday morning. The precipitation associated with this system should expand eastward across Arizona, Nevada and southern Idaho. Some lingering precipitation is anticipated to remain across California where the winter storm warning for the southern and central Sierra was to expire at midnight local time. However, a snow advisory was to continue across a large portion of Nevada where 4 to 6 inches of snow could fall at elevations above 7000 feet. Southwesterly winds with gusts to 40 mph could reduce visibility in blowing snow. As much as 1.2 inches of liquid equivalent precipitation could fall in the 24 hours ending late Tuesday afternoon along the Sierras and the mountains of southern California surrounding the Los Angeles Basin. Between 0.3 to 0.6 inches could fall during that time across Nevada and northern Arizona.

A frontal system associated with a strong storm system in the Gulf of Alaska was moving across the eastern North Pacific Ocean toward the Pacific Northwest. The front was not expected to make landfall until Tuesday evening. Strong southerly winds were developing ahead of this frontal system. As a result, gale warnings for 39 to 54 mph winds were in effect for the Washington and Oregon coasts from Cape Flattery, WA southward to Point St. George, CA. A high wind warning was posted along the southern Oregon coast for Tuesday as sustained south winds along the headlands could reach 45 mph with gusts to 55 mph. Farther north, a high wind watch was issued for the central and northern coasts of Oregon as winds could reach speeds of 35 mph with gusts to 65 mph from Tuesday afternoon through Wednesday morning. Precipitation associated with this system should also spread across western Washington, Oregon and portions of northern California. Between one to two inches of rain could fall along the coast and the western slopes of the coastal mountains during the 24 hours ending late Tuesday afternoon.

UNSEASONABLY WARM WEATHER IN THE NATION'S MIDSECTION -- A large portion of the country, extending westward from the Great Lakes to the Intermountain West experienced unseasonably mild weather on Monday. A broad southerly flow of air across the Plains was responsible for the mild weather. A warm front that extended across Canada from northern Saskatchewan southeastward to just north of Lake Superior in Ontario marked the northern edge of the warm air mass. High temperatures were as much as 20 to 25 degrees above average over the northern Plains and northern Rockies. Record high temperatures were either tied or set in Iowa at Sioux City (69 degrees); in South Dakota at Sioux Falls (68 degrees); in Minnesota at Minneapolis-St. Paul (65 degrees) and Rochester (62 degrees) and in Michigan at Marquette (51 degrees). Farther west in eastern Washington Pullman also had a record high (63 degrees). A high minimum temperature record was established at Dodge City (73 degrees).

The southerly flow of warm, humid Gulf air also produced several areas of rainshowers and imbedded thunderstorms. One area was located in Texas, where Waco had 1.99 inches of rain while Corpus Christi had 0.86 inches by late afternoon, which set rainfall records for the date at both locations. Rain also fell in Kansas, Iowa, Minnesota and western Wisconsin. The precipitation was associated with a weak low across the eastern Dakotas. Rain should continue to fall across portions of the upper Mississippi Valley and western Great Lakes through Tuesday morning.

Dense fog was beginning to form in the humid air across the Plains. Dense fog advisories were posted for East Texas, the Texas Panhandle, northwest Kansas, southwest Nebraska, north central Nebraska, and eastern North Dakota. Slippery conditions are also possible as temperatures are close to the freezing point in western Kansas and in North Dakota.

COOL WEATHER CONTINUES ACROSS THE NORTHEAST -- High pressure across the Middle Atlantic States was responsible for tranquil weather across the region, but it also allowed for chilly weather across the Northeast. With relatively cloud-free skies and weak winds, radiational cooling caused overnight temperatures to fall. Record low temperatures were set on Monday morning in New Jersey at Trenton (24 degrees) and Atlantic City (20 degrees). A northwesterly wind flow on the northern flank of the high meant that high temperatures across New England on Monday afternoon were several degrees below the long-term average highs for the date.

UPPER AIR -- Both the 500 and 300 mb charts for 00Z Tuesday showed a height ridge across the Intermountain West in association with a dome of warm air, but a height trough across the Eastern Seaboard that reflects the cold pool of air in the Northeast.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 10 degrees at Plentywood, MT, while Monday's highest temperature was 88 degrees at Gila Bend, AZ.

ALASKAN WEATHER -- A strong storm system moving across the western Gulf of Alaska generated clouds and strong winds across southwest Alaska, Bristol Bay and the Alaska Peninsula. The low pressure center, with a central pressure of approximately 970 mb, was located south of Kodiak Island. An occluded front curved eastward and then southward across the Gulf. High pressure was building across the western Bering Sea which tightened the pressure gradient and increased the winds across the Bering Sea and the Aleutians. The storm system had the effect of pushing the stationary front that separated the arctic air over the mainland from milder maritime air northward. By late Monday afternoon the stationary front extended eastward from the Bering Sea across southwest Alaska near Bethel along the Alaska Range to near Yakutat in southeast Alaska before entering western Canada. High pressure remained across the Arctic Ocean. Snow fell at Barrow, Kotzebue, Nuiqsut, Bettles and McGrath. Rain was reported at Seldovia and Whittier.

The state's lowest temperature on Monday morning was 23 degrees below zero at Northway. The highest temperature across Alaska as of midafternoon on Monday was 46 degrees at Annette and Metlakatla.

HAWAIIAN WEATHER -- Clouds and showers associated with a wind shear line moved across the windward sides of the islands from Kauai to Maui on Monday evening. The wind shear line represented the trailing end of a mid latitude front. Additional showers were found to the southeast of Hilo. These showers are expected to move across the Big Island late Tuesday. High pressure to the north of Hawaii was moving southward and weakening, resulting in a weakening of the trade winds across the islands. Northwest ocean swell is expected to increase on Tuesday generating surf on the northwest facing beaches of the islands. Small craft advisories were continued for state waters.


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 over 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 - 13 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, 2001, The American Meteorological Society.