DATASTREME DAILY SUMMARY

Wednesday, 15 November 2000


00Z Weather Systems


UNSETTLED WEATHER CONTINUES ACROSS THE NORTHEAST -- The storm system that brought wintry weather to the northern Plains and Great Lakes region at the beginning of the week continued eastward into the Northeast states on Tuesday. This system had undergone an occlusion process; the primary low pressure center was located to the north of Georgian Bay in Ontario. An occluded front, which dissipated later in the evening, extended southeastward to a secondary low pressure center that had developed at the point of occlusion over southern New England. A warm front extended southeastward out over the western Atlantic Ocean, while a cold front stretched southward off the Eastern Seaboard before crossing the Florida Peninsula.

A broad area of precipitation that covered most of New England was found to the north of the secondary low pressure system. Most of this precipitation fell in the form of rain, but snow was reported across the northern mountains of Vermont, New Hampshire and Maine by evening. Farther west, lake effect and lake-enhanced precipitation fell across the Great Lakes as the westerly and northwesterly winds circulating around both the primary and secondary low pressure centers were transporting cold air across the Great Lakes. Most of this precipitation fell as snow, except for rain that fell along the Lake Ontario shores of western New York State.

The strong southwest to westerly winds across the Great Lakes also produced problems. Scaffolding on the Ambassador Bridge spanning the Detroit River between Detroit, MI and Windsor, ON collapsed, throwing several workers into the river. West winds to 40 mph also pushed the water in Lake Erie toward the east end of the lake, causing the water level on the west end near Toledo to fall below the critical level needed for safe navigation.

The storm system is expected to continue moving to the northeast, with the secondary low pressure center reaching the Maritimes by Wednesday evening. The primary low should dissipate over Ontario. The precipitation shield accompanying the system should move away with little further accumulation across New England. Gale warnings were posted for the New England coast from Rhode Island Sound, off of Block Island, RI to Eastport, ME as west winds were expected to range between 39 and 54 mph. Lake effect snow advisories were in effect through Wednesday morning for the lakeshore counties in Lower Michigan, northeast Ohio, northwest Pennsylvania and Upstate New York that are downwind of Lakes Michigan, Erie and Ontario. Between 4 to 6 inches of snow could fall, especially in New York State's Tug Hill Plateau east of Lake Ontario.

THE NEXT STORM ORGANIZES -- A diffuse region of low pressure was found across the southern Rockies and the Intermountain West on Tuesday night. Some widely scattered light mountain snow was falling across Nevada, southern Idaho and northern Utah. Snow advisories were in effect for Tuesday night covering portions of southern Idaho, where 3 to 5 inches were anticipated and in the Wasatch Mountains of Utah where between 4 to 8 inches could fall by late Wednesday.

By Wednesday morning, a low pressure system is expected to organize on the eastern slopes of the Rockies in southern Colorado. Warm air should be brought northward ahead of the system and carried over the shallow dome of cold air at the surface. With freezing rain anticipated, a freezing drizzle advisory was issued through Wednesday morning for southwestern Nebraska and northwest Kansas. During the day, the storm is expected to move eastward across the Plains. A cold front that was located across the Prairie Provinces on Tuesday night is expected to move quickly southward, spreading cold air across the Plains before interacting with the storm system over Kansas. A winter storm watch was posted for northeastern Nebraska and western Iowa that extended from Wednesday afternoon through Wednesday night in anticipation for as much as 6 inches of snow from this next storm.

THE COUNTRY SHIVERS -- Much of the country experienced unseasonably chilly weather on Tuesday, as high temperatures at most of the major stations were below what is considered typical for this time of year. A large high pressure system accompanying a chilly Canadian air mass was responsible for the unseasonable conditions. The West continued to experience the larger departures from the long-term averages for mid November. Afternoon high temperatures across the West ranged between 15 and 20 degrees below the average highs for the date. Record low temperatures were set at Glasgow, MT (6 degrees below zero), Garden City, KS (13 degrees), Austin-Bergstrom, TX (28 degrees). Even in sunny California, record low temperatures were reported at Los Angeles (33 degrees), Santa Barbara (34 degrees) and Moffett Field (36 degrees).

The large ridge of high pressure located over east Texas is expected to become centered over the lower Mississippi Valley by Wednesday morning. With weak winds and relatively cloud-free skies under high pressure, many areas are expected to experience considerable nighttime heat loss by long wave radiation. Consequently, freeze warnings were posted through Wednesday morning from the northern Piedmont and coastal Plain of the Carolinas, southwestward across northern and central Georgia, central Alabama, most of Mississippi, southeast Arkansas and central Louisiana.

UPPER AIR -- The 00Z Wednesday upper air charts (for both 300 and 500 mb) contain two separate height troughs. One trough, associated with the surface occluded storm system over the Northeast, had now become an open wave trough over the Great Lakes. The closed cyclonic circulation accompanying this system early in the week had now become more of a wave pattern. The second trough was found as a closed cyclonic circulation regime over the Great Basin. This system is associated with the next surface weather system that is expected to develop to the lee of the Rockies.

YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US --Tuesday morning's lowest temperature was 21 degrees below at Fraser, CO, while the highest temperature on Tuesday was 84 degrees at Opa Locka, FL.

ALASKAN WEATHER -- Three separate storm systems were affecting Alaska's weather on Tuesday afternoon. One storm system was located over the North Bering Sea. The low pressure center, which was showing some signs of weakening, was located north of St. Lawrence Island. An associated stationary front extended eastward along the Brooks Range, separating arctic air located to the north from the warmer air to the south. A second storm system was an elongated trough of low pressure located over the eastern Gulf of Alaska near the Panhandle. A third storm system was developing over the central Aleutians and moving toward the northeast. An occluded front associated with this system curved eastward across the eastern Aleutians. Much of the state was cloud covered, except for breaks in the overcast over the Alaska Peninsula. During the 24 hours ending on Tuesday morning, Portage Glacier had received 2.82 inches of rain, while Cordova had 1.37 inches. By afternoon, rain was reported at Sitka, Yakutat and Bethel, while snow fell along the North Slope and over the Northwest, along with several locations in the interior.

The state's lowest overnight temperature on Tuesday morning was zero degrees at Umiat. The highest temperature by mid afternoon of Tuesday was 46 degrees at Klawok and Sitka.

HAWAIIAN WEATHER -- Strong east to northeast trade winds continued across most of the islands on Tuesday, as a subtropical high pressure cell was located to the northeast of Hawaii. However, an easterly to east-southeasterly flow was found over the Big Island. The flow of moisture toward the Big Island, coupled with unstable atmospheric conditions, increased the threat of heavy trade showers and possible thunderstorms over the windward slopes of that island. As a result, a flash flood watch was posted for the north and east sides of the Big Island. Elsewhere, relatively cloud-free skies were reported with few trade showers. The trade winds should continue through the rest of the week with speeds ranging between 10 to 25 mph. The strong trades necessitated maintaining a small craft advisory for state waters. A new ocean swell is expected to arrive on Wednesday.

TRACKING THE STORMS: HANDS-ON EXERCISE -- Learn how to track storm systems as well as high pressure systems in Wednesday's optional Supplemental Information.


HISTORICAL WEATHER EVENTS - 15 November

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, 2000, The American Meteorological Society.