DATASTREME DAILY SUMMARY

Thursday, 6 December 2001


00Z Weather Systems


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

A RECORD DAY -- Unseasonably warm conditions were found across the eastern half of the nation on Wednesday, with some locations in the Mississippi Valley and western Lakes having high temperatures that were between 30 to 35 degrees above the average highs for the first week of December. More than 60 daily record high temperature records were either tied or set from Nebraska and Missouri east to Maine. Of note were high temperature records that were set for the month of December at Flint, MI (70 degrees), at Rockford, IL (67 degrees) and in Wisconsin at Milwaukee (66 degrees), Green Bay (64 degrees) and Madison (64 degrees), while the high temperatures at Pittsburgh, PA (73 degrees) and Zanesville, OH (72 degrees) were the second highest for the month.

The record-setting warmth was a result of the high pressure system that continued to remain along the Eastern Seaboard and the strong southerly winds ahead of a strong storm system that developed in the Plains. Compressional heating associated with sinking motion in the high pressure center contributes to the warming along with relatively cloud-free skies. The southerly winds brought warm and humid Gulf air northward into the nation's midsection. Some of the record highs across the Mississippi Valley were set relatively early in the day following a night when the overnight low temperatures were at near record high readings.

A STORM DEVELOPS -- A relatively potent storm intensified and moved northward from the Plains to the western Great Lakes on Thursday accompanied by thunderstorms on the south side of the system and snow on the northern flank. The storm developed late Tuesday night as a weak low pressure area along a warm front that stretched eastward from the Plains into the Mississippi Valley. By Wednesday morning the low pressure center was located over the Missouri Valley separating northwest Iowa from eastern Nebraska and southeastern South Dakota. During the day the storm system intensified, with the central pressure falling from approximately 1000 mb to 990 mb. A distinct cold front developed and moved eastward across the Plains toward the Mississippi Valley. By evening the storm system had begun to occlude as the primary low pressure center had moved northward across western Minnesota and had reached the vicinity of Lake of the Woods along the Canadian border. An occluded front extended a short distance eastward from the low pressure center to a point of occlusion. A warm front continued eastward from this point to southern New England. A cold front stretched southward from the point of occlusion along the western shore of Lake Michigan, across the Mississippi Valley to the western Gulf Coast.

Rainshowers and embedded thunderstorms were found along the cold front, extending southward from Michigan's Upper Peninsula to southern Missouri. To the north of the storm system, snow was falling across northern Minnesota and eastern North Dakota, as well as southern Ontario. As much as 6 inches of snow had fallen across North Dakota by midafternoon. Williston had received 4.4 inches of snow and a liquid equivalent precipitation total of 0.51 inches; both values represent daily records.

The storm is expected to continue intensifying as it accelerates northeastward across Ontario. By daybreak on Thursday the low pressure center is forecast to reach James Bay and by evening into northern Quebec to the east of Hudson Bay.

A MAJOR CHANGE -- The cold frontal passage eastward across the Midwest was impressive. For example, at Kansas City, MO the temperature at 2 PM CST was a record 73 degrees along with southwesterly winds, but in one hour following passage of the front, the temperature had fallen 15 Fahrenheit degrees to 58 degrees as the winds had shifted to a northwesterly direction. Similarly, the temperature at Minneapolis-St. Paul, MN fell from a record high 63 degrees at 11 AM CST to 53 degrees at noon, and then to 40 degrees within the next 3 hours as winds shifted from southerly to westerly.

During the late morning through the late afternoon thunderstorms accompanying the cold front generated strong winds that produced some damage along with large hail with diameters up to one inch across eastern Iowa, northern Missouri and northeastern Wisconsin. These thunderstorms developed as warm moist air was brought northward by southerly winds. Following frontal passage, strong, non-thunderstorm winds downed trees and power lines and caused damage across northeastern Wisconsin late Wednesday night. These westerly winds were the result of the tight pressure gradient found in the southwest quadrant of the storm system. During the evening gusts had reached 55 mph at Grand Marais along the North Shore of Lake Superior in northeast Minnesota. Some damage was also sustained. High wind warnings were placed in effect for Wednesday night for the lakeshore counties of Minnesota, Wisconsin and Michigan surrounding the western half of Lake Superior as gusts to 60 mph are anticipated. In addition, storm warnings were posted for marine interests covering Lake Superior, while gale warnings covered Lakes Michigan, Huron and Erie.

WINTRY WEATHER ACROSS THE WEST -- High temperatures across the Intermountain West on Wednesday were either at or slightly below the averages for early December. Prevailing westerly winds resulted in continued snow across the Northwest. Earlier in the day, some locations in southwestern Oregon received upwards of 2 inches of rain. The ski resort Mt. Shasta reported 12 to 18 inches of snow overnight. Some places in Idaho had received between 12 to 14 inches of new snow in the 24 hours ending on Wednesday morning.

A new storm system that was approaching the Washington and Oregon coasts on Wednesday evening was spreading more coastal rain and mountain snows across the region. The storm system consisted of an occluded low pressure system located along the British Columbia coast near the Queen Charlotte Islands and an occluded front that extended southward to near the mouth of the Columbia River. This front is expected to move eastward across the Cascades by Thursday morning. A variety of winter storm warnings and snow advisories were posted for the mountains in Washington, Oregon, Idaho, Montana, Utah, and Wyoming. Upwards of 20 inches of new snow could fall on the western slopes of the Olympics and the Cascades of Washington and Oregon by late Thursday afternoon. Farther east, the Blue Mountains in northeast Oregon and eastern Washington could receive 12 inches of snow by Thursday night.

In addition the snow, windy conditions were also found elsewhere across the West. High wind warnings were in effect for Southern Wyoming where winds could gust to 70 mph and for the Sangre de Cristo Mountains of southern Colorado, where gusts to 90 mph could occur above the timberline. A blizzard warning was posted for southwest Wyoming as high winds coupled with snow could reduce the visibility to near zero.

UPPER AIR -- The mid-tropospheric 500 mb constant pressure chart and the upper-tropospheric 300 mb chart for 00Z Thursday both contained a height trough over the Rockies and the Western Plains, while a height ridge was located over the East. The trough reflects the cold air being brought on the west side of the surface low pressure feature, while the ridge is associated with the warm air across the East. The southwesterly wind flow around the eastern flank of the trough on the 300 mb surface contributed to the uplift that helped develop, maintain and steer the surface storm system. The core of strong winds and the directional spreading of the winds produced the necessary upper tropospheric divergence which compensates the near surface convergence.

TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 17 degrees below zero at Big Piney, WY, while the Wednesday afternoon highest temperature was 84 degrees at Brownsville, TX.

ALASKAN WEATHER -- Arctic air remained in force across much of Alaska as the result of a large area of high pressure located over the Arctic Ocean to the north and west of the state. The onshore flow produced clouds across the Arctic coast, the North Slope and portions of the interior. A low pressure center near the Queen Charlotte Islands spread clouds and precipitation across the Panhandle. Snow was reported at Juneau, Sitka and Skagway. A winter storm warning was posted for a portion of the Panhandle, as 6 inches of new snow could fall by Thursday morning. A developing storm system was located in the northeastern Gulf of Alaska to the south of Prince William Sound. This storm was responsible for spreading clouds, snow and strong northeasterly winds across southeastern and south central Alaska. Snow fell at Kodiak. A strong storm was also affecting the western Aleutians.

The lowest temperature in Alaska on Wednesday morning was 37 degrees below zero at Bettles. The highest statewide temperature as of Wednesday afternoon was 41 degrees at Annette.

HAWAIIAN WEATHER -- Relatively strong and gusty trade winds continued across the islands, the result of a large high pressure cell located to the northeast of Hawaii. This high pressure cell is expected to remain to the northeast well into next week. As a result, strong trade winds along with relatively pleasant trade weather are expected to continue with relatively cloud-free skies, except for the usual nighttime trade showers on the windward slopes of the islands. A large ocean swell continues to produce high surf along the east-facing shores of the islands. This swell has been generated by the strong easterly trade winds traveling over a long fetch (distance across open water). As a result, a high surf advisory remained in effect for the east shores of the islands.


CONCEPT FOR THE DAY - WEATHER ON THE INTERNET

This week concludes the fall 2001 edition of the DataStreme course. The purpose of the DataStreme Project is teacher enhancement, providing you with the opportunity to learn some meteorological principles that you can use not only in your classroom, but as a Weather Education Resource Teacher. The experiences that you have gained in the weather sciences as well as in accessing the Internet should now allow you to expand your horizons to work with other teachers.

On the Wednesday, Week 12 activity, you were introduced to the DataStreme Junction Homepage. DataStreme Junction is intended as a site where course alumni can go beyond information available via the now-familiar DataStreme Homepage and the DataStreme course materials. The term "Junction" is used because the new homepage will be a connecting point to other weather-related sources on the Internet. You are encouraged to visit DataStreme Junction from time to time as you proceed as a DataStreme Weather Education Resource Teacher.

You should add the DataStreme Junction Homepage to your browser's "Bookmark" or "Favorite Places" list so you can easily reach it when you are on-line.

The familiar DataStreme Homepage will continuously deliver current meteorological data throughout the year, including the summer. The DataStreme Daily Summary will contain only the selected Historical Weather Events for each day from this coming Monday through mid January, when Daily Summaries and other DataStreme course materials will return to the Homepage during Preview Week on Monday, 21 January 2002 for Spring 2002 course participants. Hopefully, you will frequently visit to read the Daily Weather Summary and the fresh activity materials prepared each Monday and Wednesday during future course offerings.

For a behind-the-scenes view at how the daily weather summary is built, please read the Thursday optional Supplemental Information.

QUESTIONS:

To be submitted on the lines for Thursday on the Study Guide, Part B, Applications', Week 12 Chapter Progress Response Form, under section B. Daily Summary.

  1. In the United States Weather section of the DataStreme Junction homepage, under the final item, "U.S. National Weather Service, Local Offices", my nearest local National Weather Service Office that provides weather coverage to my home or school [(is) (is not)] in the lists of stations.
  2. Under the section, Other Educational Sites, the "National Science Education Standards" [(is) (is not)] the actual contents of the National Academy of Sciences publication describing the National Science Standards.

HISTORICAL WEATHER EVENTS - 6 December

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


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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.