DATASTREME DAILY SUMMARY

Friday, 6 October 2000


00Z Weather Systems


MORE ACTIVE WEATHER ALONG THE FRONT -- A stationary front that had stretched from the Middle Atlantic States southwestward to the western Plains since earlier in the week began moving on Thursday as a result of the intensification of a low pressure center along the front and the advance of a cold air mass from Canada. As of Thursday night, the low pressure center was located over the Ohio Valley near Cincinnati. To the east of the low, a warm front extended eastward across the Middle Atlantic States to the Del-Mar-Va peninsula, the result of a northward advance of warm air across the east. Southwest of the low, a cold front trailed to the Red River Valley in north Texas.

A widespread area of precipitation was found to the north of the storm system, stretching from New England across the Great Lakes States and Ohio Valley. Another band of precipitation in the form of rainshowers and thunderstorms were found along the cold front, extending from the Ohio Valley southwestward to Oklahoma. Of note is the location of the precipitation -- the bulk of the precipitation was found in the cold air behind the cold front rather than in a more typical location ahead of the advancing cold front. Some of the thunderstorms that moved along the front on Thursday afternoon and evening turned severe across Kentucky, Missouri, Arkansas, Louisiana, Oklahoma and Pennsylvania. These storms produced large hail that reached as large as golfball size (1.75 inches in diameter) and high winds that caused some damage. At least one tornado was reported in southern Illinois.

By Friday morning the low pressure center is forecast to be in northeastern Pennsylvania, with the cold front having swept eastward to the Appalachians and southward to near the Texas Gulf Coast. The bulk of the precipitation is expected to shift northeastward into New England, just to the north of the warm front, which should extend eastward across the New York City metropolitan area. A slight risk of severe thunderstorms continues overnight for the Ohio and mid-Mississippi Valleys, in a region along the cold front.

THE FIRST BIG CHILL -- Unseasonably cold air is pushing southeastward across the nation's midsection on Thursday evening. This Canadian air mass accompanies a large sprawling high pressure system with a center that stretched along the eastern slopes of the northern Rockies in Montana and Wyoming. The eastern and southern periphery of this cold air mass was the cold front that stretched from the Ohio Valley to north Texas, while to the west, a stationary front paralleled the Continental Divide. The core of the coldest air was along the eastern slopes of the Rockies, where record low temperatures were either tied or broken on Thursday morning in Montana at Cut Bank (11 degrees), Butte (16 degrees), Glasgow (16 degrees), Great Falls (20 degrees) and Billings (24 degrees) and in North Dakota at Williston (17 degrees). Afternoon high temperatures across that region ranged between 20 to 30 degrees below the long-term average high temperatures for early October. The high temperature of 40 degrees at Bozeman, MT on Thursday was a record low high temperature for the date.

The cold air is expected to continue pushing eastward and southward on Friday as the cold front moves toward the Atlantic Seaboard and the Gulf Coast. The high pressure center is forecast to build, or increase in central pressure, and expand southward into the central Plains. As a result of the cold air mass, coupled with the favorable nighttime cooling conditions afforded by proximity to a high pressure center, freeze warnings were posted from west central Wisconsin south and westward across portions of southern Minnesota, a large part of Iowa, western Illinois, eastern Nebraska, northern Kansas and eastern Colorado. A freezing drizzle advisory was also posted for the Colorado Springs area, as anticipated rain in the warm air aloft should fall into the shallow cold air in the valleys to the north and west of Pikes Peak.

The southward advance of the cold air will mean a sharp change in the weather across the southern Plains. On Thursday, afternoon high temperatures across north Texas and eastward into the mid-Mississippi Valley were 10 to 15 degrees above the average highs for the date. In Texas, both Austin-Bergstrom and Corpus Christi reported record high temperatures of 96 degrees. However, temperatures on Friday across the Plains should be 10 to 20 degrees lower than on Friday.

LAKE EFFECT SNOW -- With cold northwesterly winds flowing across the western Great Lakes, the start of the lake effect snow season is about to begin. Winter storm watches were posted on Thursday evening for the traditional snow belt of Michigan's Upper Peninsula. Anticipated snowfall totals by early Saturday ranged between 8 to 12 inches in the counties along Lake Superior. Lesser amounts are also expected for northwest and north central Wisconsin. Cold air moving across the relatively warm lake surfaces will cause the air to become saturated and ultimately produce snow as the air is sufficiently cold.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 6 degrees at Havre, MT. Thursday's highest temperature was 104 degrees at Death Valley, CA.

ALASKAN WEATHER -- A nearly stationary storm system located just to the south of the Alaska Peninsula dominated the state's weather on Thursday afternoon. The occluding storm system consisted of a low pressure center hugging the coast of the Alaska Peninsula and an occluded front that curved northeastward along the North Gulf Coast. As a result, widespread clouds and a variety of precipitation types were found across a large portion of Alaska, exclusive of western Alaska. A southerly wind flow to the east of the storm system carried warm, moist air northward into the state, where it was carried over colder air near the surface. Resulting in moderate to heavy rain falling along the coastal sections from the northeast Gulf to the Panhandle, while inland, the rain changed to freezing rain and snow. To the west of the storm system a tight pressure gradient between high pressure over eastern Siberia and the low pressure center produced strong northerly winds across western Alaska. Winds in the region from the western end of the Alaska Peninsula north to the Seward Peninsula gusted to 40 mph, with Nunivak Island having a peak gust of 49 mph. Western Alaska also experienced partly cloudy skies.

The lowest overnight temperature in Alaska on Thursday morning was 2 degrees above zero at Nuiqsut, while the mid-afternoon highest statewide temperature was 57 degrees at Metlakatla.

HAWAIIAN WEATHER -- Typical trade wind weather with relatively cloud-free skies and scattered mountain showers continued across the islands on Thursday as a ridge of high pressure intensified to the north of the 50th State. Northeasterly winds increasing from 15 to 20 mph are expected to continue over the weekend. A series of tropical disturbances or waves could move westward and pass south of the islands producing gusty winds later in the weekend.

EYE ON THE TROPICS -- On Thursday Tropical Storm Keith intensified as it moved first westward across the Bay of Campeche, becoming a hurricane once again. During the afternoon Keith curved to take a northwestward course, making landfall along the Mexican coast north of Tampico, with winds reaching 90 mph. As it moved inland across mountainous terrain, Keith quickly weakened, and was downgraded to a tropical depression. By early Friday morning Keith had winds of 35 mph and was located 70 miles west-southwest of Ciudad Victoria, Mexico, traveling to the west at 13 mph. A large area of rain associated with Keith still remained over northern Mexico, south of the Rio Grande Valley. Ultimately, some of this moisture may be carried northward into Texas.

The area of low pressure that had developed in the trough of low pressure over south Florida earlier in the week and then was classified on Wednesday as a subtropical depression was reclassified on Thursday as Tropical Storm Leslie, the twelfth named tropical system in the North Atlantic basin this season. This reclassification reflected the change in the characteristics of the low pressure system from one that contained cold air to one that contained a warm core, typical of a tropical system. As of early Friday morning Leslie had 40 mph winds and was located 500 miles west-southwest of Bermuda, moving toward the east at 13 mph.

In the eastern North Pacific, Tropical Storm Olivia with 50 mph sustained surface winds continued moving westward at 6 mph, approximately 520 miles south of Cabo San Lucas, Mexico.


HISTORICAL WEATHER EVENTS - 6 October

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

7 October

8 October


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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2000, The American Meteorological Society.