DATASTREME DAILY SUMMARY

Friday, 3 November 2000


00Z Weather Systems


A TALE OF TWO SEASONS IN THE NORTHERN PLAINS -- After experiencing summer-like severe weather, residents of the Dakotas got an early taste of winter on Wednesday and Thursday with a variety of weather conditions to include heavy snow, high winds, blizzard conditions, falling temperatures, and low wind-chill equivalent temperatures. The cause of these conditions was a potent storm system that developed on the eastern slopes of the Colorado Rockies and moved northeastward across the Plains, reaching the Lakes region of southern Manitoba on Thursday night. Ahead of this storm severe weather, to include tornadoes moved across North Dakota and Minnesota. Incidentally, the tornado that tore through a portion of Bismarck damaging at least 40 homes on Wednesday marked the first time a tornado had occurred in North Dakota during the month of November since official records began in 1916. In the cold air behind the storm system, snow fell, with more than 4 feet accumulating in the Black Hills of South Dakota.

During its northeastward journey, the storm was undergoing an occlusion process, with the cold front catching the warm front forming an occluded front. The primary low pressure center was situated in the vicinity of Winnipeg in southeastern Manitoba on Thursday night. A secondary low pressure system formed near the point of occlusion located northeast of the primary low in western Ontario. A warm front continued to the northeast, while a cold front extended southeastward from this secondary low, first crossing the Great Lakes before curving southwestward and turning into a stationary front stretching from the mid-Mississippi Valley to west Texas.

Some residual snow continued across the Dakotas late Thursday night in the wake of the departed storm system. This snow was accentuated by the passage of a weak trough line that extended like a spoke of a wheel southward from the primary low pressure center. Earlier, heavy snow had fallen from the Black Hills across western North Dakota, as rain ahead of the system turned to snow with the advance of cold air following passage of the cold front. The 3.9 inches of snow that fell at Williston, ND on Thursday set a daily record. In addition, the total liquid equivalent of 2.36 inches that fell at Williston during the first two days of November established a new monthly precipitation record.

The rainshowers and thunderstorms that had accompanied northern portions of the cold front on Wednesday night had dwindled as they moved eastward. By Thursday night an area of showers and thunderstorms was found across the Ohio Valley in advance of the cold front.

As the cold front passed eastward into the western Great Lakes, the abnormally warm conditions found across the Upper Midwest because of strong southerly winds were replaced by more seasonal temperature readings accompanying westerly winds. Many locations in the Upper Mississippi Valley and western Lakes were experiencing temperatures late Thursday night that were 10 to 20 degrees lower than had been observed 24 hours before.

Windy conditions continued across the northern Plains in association with the tight pressure gradient that was maintained by high pressure over western Kansas and the storm to the north. Westerly and northwesterly winds across the Dakotas produced wind-chill equivalent temperatures that were in the teens late Thursday night.

The storm system is expected to continue to move northeastward across Ontario and Hudson Bay on Friday. The cold front is forecast to move eastward, reaching the eastern Great Lakes by Friday evening. Little significant precipitation accumulation is anticipated across the northern tier of states from the Plains to the eastern Lakes.

TEXAS SIZE TORRENTS -- The cold front associated with the storm system in the northern Plains advanced southward and stalled over Texas on Thursday. The southern terminus of this front separated warm and humid Gulf air to the south from cooler and drier air to the north. Rainshowers and thunderstorms continued across Texas along this stationary front on Thursday night. Earlier, severe thunderstorms produced large hail and damaging winds across central Texas on Thursday afternoon and early evening. The hail diameters were as large as golfball size.

In addition to the severe aspects of these thunderstorms, heavy rain fell across the region. Several rainfall records were set across the Lone Star State on Thursday, including San Antonio (3.39 inches), Austin (Bergstrom with 2.30 inches and Mabry with 2.17 inches), Lufkin (1.60 inches) and Tyler (1.16 inches).

Rain is expected to continue across the region through Friday as the stationary front is forecast to remain stretched across Texas. Much of Texas could see 0.5 inches of rain by Friday evening, with as much as 5 inches forecast for the Texas Hill country near Austin. Because of the heavy rains that fell on Thursday and in anticipation of additional heavy rain, flash flood watches were posted for a large portion of central Texas on Thursday night.

WHAT'S HAPPENING ELSEWHERE? -- The Eastern Seaboard, stretching from New England southward to the eastern Gulf Coast, remained relatively tranquil as high pressure dominated the region. Likewise, relatively quiet weather conditions were found across the West, the result of an elongated ridge of high pressure that extended from the Pacific Northwest into the central Rockies. However, a storm system off the Washington and British Columbia coasts could produce some precipitation across the Pacific Northwest late Friday.

UPPER AIR WEATHER CONDITIONS -- The 500 mb and 300 mb upper air charts for 00Z Friday both show a relatively strong counterclockwise circulation around the storm system in the northern Plains. This occluded storm system in essence represents a whirlpool of cold air that extends upward through much of the troposphere. As a result of the cold column of air, the heights of both the 500 mb and 300 mb constant pressure surfaces are depressed into what are displayed as upper level troughs over the northern Plains. A ridge of higher heights above warm air is found across the eastern Great Lakes.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 3 degrees above zero at Laramie, WY. Thursday's highest temperature was 89 degrees at Kingsville, TX.

ALASKAN WEATHER -- A strong system moving across the southern Bering Sea produced northerly winds to 50 mph in the Bering Strait. Wind gusts to 60 mph were reported at Gambell. Another strong storm system was situated over the north Pacific Ocean south of Adak Island in the Aleutian chain. A weaker storm system was located in the Gulf of Alaska. This latter system produced clouds and precipitation across southern Alaska. Snow fell at Northway, Bethel and Haines, while rain was reported at King Salmon, Kodiak, Juneau, Ketchikan and Yakutat. A ridge of high pressure extending westward from Canada produced some breaks in the clouds and relatively cold conditions across eastern interior Alaska. Midday temperatures remained in the teens across portions of the interior, while single digits and a few subzero readings were found near the Brooks Range.

The lowest overnight temperature in Alaska on Thursday morning was 18 degrees below zero at Arctic Village, while the mid-afternoon highest statewide temperature was 53 degrees at Sitka.

HAWAIIAN WEATHER -- The heavy rainshowers and occasional thunderstorms that had produced the deluge on the Big Island late Wednesday and early Thursday finally began to move off to the east. Within a 22 hour span between Wednesday and Thursday mornings, Hilo Airport received 24.33 inches of rain, which set an all-time 24 hour rainfall record for that station. Other locations on the Big Island also received heavy rains that produced floods which washed out roads and flooded homes. The culprit was an upper tropospheric pool of cool air that moved eastward across the southern islands to help destabilize the atmosphere. Easterly and southeasterly surface winds brought low-level warm and humid air to aid in the storm development. Unsettled weather with weak southeast winds are expected through Saturday, before an anticipated return to a more typical northeast trade wind regime.

WINTER AWARENESS -- On Saturday (4 November) Kansas will observe Winter Weather Awareness Day. Residents of Kansas should become aware of the hazards associated with winter weather and review the safety oriented materials prepared by their local National Weather Service Offices.

REPORT FROM THE FIELD -- Mark Seeley, LIT Member and extension climatologist with the University of Minnesota-Twin Cities reported that in addition to the record high minimum temperature of 57 degrees set on Wednesday at the Minneapolis/St. Paul International Airport, a 63 degree dewpoint was reached. This dewpoint was the all-time highest dewpoint for the month of November in the Twin Cities, resulting from the strong water vapor advection on southerly winds ahead of the strong low pressure system that moved across the Plains. Mark noted that this record dewpoint was comparable to the water vapor content in the atmosphere at the Twin Cities during mid July and it is roughly four times that of a typical November day.


HISTORICAL WEATHER EVENTS - 3 November

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

4 November

5 November


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