DATASTREME DAILY SUMMARY

Friday, 15 September 2000


00Z Weather Systems


STORMY WEATHER MOVES EAST -- A cold front that had produced severe weather across the Midwest on Wednesday night moved eastward across the Great Lakes on Thursday, accompanied by rainshowers and thunderstorms. As of Thursday evening the cold front stretched from a region of low pressure over Lake Ontario southwestward along the Ohio Valley to the Ozarks and then to the southern Plains. A widespread region of rain fell ahead of the front from the St. Lawrence Valley southwestward along the Appalachians to the Virginias.

Some of the thunderstorms caused wind damage across North Carolina in the vicinity of Greensboro and Winston-Salem early in the evening. Because of the heavy rains falling on ground saturated by previous rains, flash flood watches were posted for southern Pennsylvania.

By Friday morning the low pressure center is forecast to move eastward, reaching the Adirondacks of Upstate New York. The cold front is anticipated to reach the Atlantic Seaboard. A slight risk of severe thunderstorms is anticipated through Friday morning to be in the area ahead of the advancing cold front that extends across the Middle Atlantic States from central Pennsylvania southward into North Carolina. Most of the precipitation should fall across the Hudson Valley of New York State and much of New England. As much as one inch of rain could fall across sections of New England on Friday and early Saturday morning.

In the warm and muggy air to the east of the cold front, Cape Hatteras, NC tied a record high of 87 degrees on Thursday afternoon.

COOL WEATHER FOR THE UPPER MIDWEST -- A large ridge of Canadian high pressure followed the cold front into the Midwest on Thursday. The high pressure system associated with this cool and dry air mass was centered over North Dakota by early evening. Light northwesterly winds were found across the western Great Lakes, bringing cooler weather southward.

The high is expected to drift slowly southeastward, being positioned over Minnesota by Friday morning. Favorable conditions for extensive overnight cooling should result because of clear skies and relatively weak winds near the center of the high pressure system. As a result, frost advisories were posted for northern Minnesota for Thursday night and Friday morning.

HOT WEATHER CONTINUES ACROSS THE WEST -- Much of the western half of the country experienced abnormally warm weather on Thursday. A persistent large ridge of high pressure that extends several thousand feet upward above the earth's surface has maintained the hot and dry conditions with few clouds. Afternoon high temperatures were as a much as 10 to 15 degrees above average across the northern Rockies. Numerous daily record highs were either tied or broken across Idaho, Nevada, Utah, Arizona and New Mexico. Tucson had 107 degrees that tied the monthly high temperature record for September and was the highest temperature for so late in the season. Several stations in northwest Oregon and western Washington State had record high minimum temperatures on Thursday, to include Portland with 64 degrees for a low.

In addition to the above average temperatures, Oklahoma City, OK experienced its record 46th consecutive day without precipitation. With an afternoon reading of 100 degrees, Oklahoma City registered its seventh day of 100 degree or higher temperatures during September, which is a record number. Passage of the cold front on Thursday should bring some relief with slightly cooler weather, but little chance for precipitation as drier air is found behind the front.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 29 degrees at Plentywood and Wisdom, MT. Thursday's highest temperature was 115 degrees at Lake Havasu City, AZ.

ALASKAN WEATHER -- Skies began to clear at many locations across southwest and south central Alaska on Thursday as high pressure pushed into the region. As a result of the clear skies associated with high pressure, record low temperatures were reached at Saint Paul Island and Cold Bay on Thursday morning. A weak trough of low pressure over southeast Alaska was responsible for some heavy rainshowers, to include some embedded thunderstorms, between Sitka and Yakutat. Winds in excess of 40 mph were reported in the Panhandle, to include Juneau. Farther north, scattered areas of light rain fell across interior Alaska, to include Fairbanks. With high pressure located across the Beaufort Sea, an onshore wind produced light snow at Barrow. A mixture of rain and snow was reported at Kotzebue.

The lowest overnight temperature in Alaska on Thursday morning was 23 degrees at Anaktuvuk Pass, while the mid-afternoon highest statewide temperature was 63 degrees at Ketchikan and Big River Lakes.

HAWAIIAN WEATHER -- While the center of high pressure located north of Hawaii was moving northeastward away from the islands on Thursday, high pressure is expected to strengthen on Friday. As a result easterly trade winds should remain light to moderate with wind speeds ranging from 10 to 20 mph. Fine trade weather should also continue with relatively cloud-free skies except for the windward slopes of the islands where brief showers could develop.

EYE ON THE TROPICS -- Tropical Storm Florence continued to wander around the western Atlantic Ocean. As of late Thursday night Florence had sustained winds of 45 mph and was nearly stationary at a position approximately 510 miles west-southwest of Bermuda. Tropical storm watches are in effect across Bermuda.

A low pressure system in the Caribbean became Tropical Depression 11, which was located over Mexico's Yucatan Peninsula approximately 110 miles west southwest of Cozumel. Winds associated with this system were 30 mph.

REPORT FROM THE FIELD -- Wendy Walker, a DataStreme participant from Cumberland, MD, reported on the severe thunderstorm that passed through her community in western Maryland on Monday evening. She said that 3.5 inches of rain fell in less than two hours, flooding many homes, businesses and city streets on the west side of town.


HISTORICAL WEATHER EVENTS - 15 September

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

16 September

17 September


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