DATASTREME DAILY SUMMARY

Wednesday, 5 December 2001


00Z Weather Systems


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

MORE RECORD WARMTH ACROSS THE EAST -- A persistent high pressure system located over the Carolinas continued to contribute to the unseasonably warm weather experienced by most of the country to the east of the Rockies, with high temperatures that were at least 10 degrees above the average highs for early December. While winds were relatively weak near the center of the high in the Southeast, sufficiently strong southerly winds across the Mississippi Valley and the Plains spread unseasonably warm air northward. As a result, the mid-Mississippi Valley had the greatest temperature departures from the average, as highs were on the order of 30 degrees above average. Record high temperatures were either tied or set in Arkansas at Ft. Smith (79 degrees), Little Rock (77 degrees) and Fayetteville (71 degrees); in Oklahoma at McAlester (74 degrees); in Missouri at Joplin (74 degrees), St. Louis (74 degrees) and Kansas City (69 degrees); in Kansas at Topeka (72 degrees), Chanute (71 degrees), Wichita (70 degrees); in Wisconsin at La Crosse (64 degrees), Green Bay (60 degrees), Madison (60 degrees), Milwaukee (60 degrees), Wausau (58 degrees) and Eau Claire (56 degrees); in Iowa at Mason City (58 degrees) and in Minnesota at Rochester (56 degrees). Farther east, record highs were also tied or set in West Virginia at Elkins (71 degrees) and Morgantown (68 degrees); in Virginia at Blacksburg (70 degrees) and in North Carolina at Asheville (70 degrees).

The magnitude of the warm air advection across the Plains and the Midwest was also evident in the number of locations in Texas, Kansas, Missouri, Iowa and Wisconsin that established new high minimum temperature records. The minimum temperature of 54 degrees at Des Moines was the highest ever recorded there during meteorological winter, the three months from December through February.

Advection fog was a problem in some snow-covered locations across South Dakota, Minnesota and Michigan as warm and humid air traveled northward over the relatively cold snow that had fallen earlier.

A CHANGE IN THE WEATHER -- The unseasonably warm air over the Plains and Midwest is about to be replaced by colder air and precipitation more typical of the season. A storm system is expected to develop along a front that extends across the Plains from an occluding storm system over Hudson Bay to an area of low pressure over northeast Colorado. Light snow was falling on Tuesday night in the cold air to the north and west of the front across the Dakotas, eastern Montana and eastern Wyoming. This new low pressure area is forecast to develop and move toward the northeast, reaching southern Minnesota by Wednesday morning and to near Lake Nipigon in western Ontario by evening.

As the low moves northeastward, the trailing cold front should sweep eastward across the Plains to the western Great Lakes and the mid-Mississippi Valley by evening. Temperatures should fall to more seasonal values as the front moves eastward. Strong to severe thunderstorms could develop on Wednesday ahead of the cold front, over a region that extends from the Red River Valley in north Texas to the southern Great Lakes. A large shield of precipitation is expected in the cold air to the north of the surface low. This precipitation should include snow along with some freezing rain. Consequently, winter storm warnings were posted across portions of North Dakota and northwestern Minnesota, where 6 to 8 inches of snow are anticipated through Wednesday night.

WINTRY WEATHER ACROSS THE SOUTHWEST -- A cold pool of air was found across the Great Basin. High temperatures across the Southwest were below average, with portions of Arizona and Nevada having highs that were nearly 15 degrees below the long-term averages for the date. By early evening as much as 7 inches of snow had fallen over those portions of the Mogollon Rim in Arizona that were above 6000 feet. Heavy snow was falling in Colorado, with 10 inches of snow reported at Wolf Creek Pass by early Wednesday morning. Snow advisories were in effect over western Colorado and northern New Mexico. A frost warning was posted for some of the valleys in southern Arizona in the vicinity of Tucson.

UNSETTLED WEATHER IN THE NORTHWEST -- A storm that reached the Pacific Northwest on Monday night spread precipitation across the region on Tuesday. Many mountain locations across the Pacific Northwest received 4 to 5 inches of new snow as of Tuesday morning. As of Tuesday night, mountain snow along with coastal and valley rain continued across Washington, Oregon and northern California, the result of prevailing westerly onshore winds that were being carried over the various mountain ranges. Between 0.5 to 1.5 inches of liquid-equivalent precipitation could fall along the coast and western slopes of the mountains of the Pacific Northwest during the 24 hours ending on Wednesday evening. A variety of winter storm warnings and snow advisories were in effect for portions of the Oregon Cascades, the northern California mountains and the northern Sierra. Between 8 to 12 inches were expected in the vicinity of Crater Lake National Park in southern Oregon, with only several inches anticipated farther to the south into northern California.

A new storm system is expected to impact the Northwest late Wednesday. Winter storm watches were posted that were to extend from Wednesday into Thursday morning across portions of Washington, Oregon, Idaho and Montana. Up to 18 inches of snow could fall in the Olympics and northern Cascades, while 5 to 8 inches of snow could fall across the mountains to the east. Strong winds are also possible with this storm, thereby reducing visibility.

UPPER AIR -- A deepened height trough across the West was apparent on both the 500 and 300 mb charts for 00Z Wednesday. This height trough was associated with the cold pool of air over the Southwest. Farther east, the warm air produced a ridge in the heights of the pressure surfaces. Consequently, the upper tropospheric jet as indicated by the strongest 300 mb winds took a southward excursion across the Southwest and then moved toward the northeast.

YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US --Tuesday morning's lowest temperature was 4 degrees below zero at Fraser, CO, while the highest temperature on Tuesday was 84 degrees at Brownsville and Harlingen, TX and Winter Haven, FL.

ALASKAN WEATHER -- A ridge of high pressure extending southeastward from the Arctic Ocean across the Chukchi Sea into northwest Alaska continued to maintain an arctic air mass across mainland Alaska. Northwest Alaska experienced relatively cloud-free skies, while interior Alaska had mostly cloudy skies. Subzero temperatures were reported during the early afternoon across the interior, with the lowest at Fort Yukon with 35 degrees below zero. A low pressure system over the northeastern Gulf of Alaska to the southwest of Yakutat spread clouds and snow across Southeast Alaska, where 11 inches fell at Port Alexander, 6 inches at Juneau and 5 inches at Annette. A cold front extended westward from the low pressure center across the western end of the Alaska Peninsula into the Bering Sea. This front separated the cold arctic air over interior Alaska from warmer air over the North Pacific Ocean. Farther west, a strong storm, with a central pressure of 963 mb, was moving slowly eastward across the western Aleutians. With high winds associated with this storm, a high wind warning for wind gusts to 60 mph remained in effect across the western Aleutians, to include Adak Island.

The state's lowest overnight temperature on Tuesday morning was 38 degrees below zero at McGrath. The highest temperature by mid afternoon of Tuesday was 41 degrees at Dutch Harbor.

HAWAIIAN WEATHER -- The islands experienced moderate to strong trade winds on Tuesday, the result of a large and strong high pressure cell located off the California coast, to the northeast of Hawaii. Wind speeds have ranged between 15 to 30 mph. Some trade wind showers have been detected on the windward slopes of the islands, particularly during the nighttime and early morning hours. A slight weakening of the trade winds is forecast for later in the week when the high moves farther to the northeast. Small craft advisories continued for coastal waters, along with high surf advisories on the east shores of the islands.

EYE ON THE TROPICS -- Tropical Depression Olga continued weakening as it moved erratically eastward across the western Atlantic Ocean. By late afternoon the maximum sustained surface winds had dropped to 30 mph and the system was becoming disorganized. As a result, the National Hurricane Center issued its last advisory for Olga, which was located approximately 665 miles to the east of Nassau, Bahamas. Movement was to the southeast at 5 mph.

IT'S SURE DARK! -- Have you noticed that the sun is setting early these days? During the first ten days of December, many locations throughout the country will experience their earliest sunset times of the year. The exact day for the earliest sunset depends upon the latitude, so you may want to check the date in your locale from the sunrise tables appearing in on-line, interactive service available for the entire year at most cities in the United States. The reason for the earliest sunsets occurring in early December rather than on the winter solstice (midday of Friday, 21 December 2001) is because the sun is not as precise a time-keeper as our watches. Because of a combination of factors involved with the earth's elliptical orbit about the sun and the tilt of the earth's spin axis with respect to the plane of the ecliptic, the sun appears to "run fast" by as much as 15 minutes as compared with clock time in November. However, with the approach of the winter solstice and perihelion (2 January 2002), the apparent sun slows during December and finally lags the clock by 12 minutes in February. As a result, a noticeable and welcome trend toward later sunsets can be detected by the end of December, especially by those residents in the northern part of the country. However, the latest sunrises occur at most locales in early January, meaning that early risers will continue seeing dark and dreary mornings for another month.

A WHITE CHRISTMAS -- The first week of December has not been very wintry across a large portion of the country east of the Rockies. As we approach the holiday season, many of us get in the mood only when they see a snow cover. What is the probability that your area will experience a White Christmas? Consult Wednesday's optional Supplemental Information for additional information.


HISTORICAL WEATHER EVENTS - 5 December

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.