Today is Earth Day, first proposed by former Senator Gaylord Nelson of Wisconsin in 1970 as a teach-in to heighten awareness in the environment. NOAA has a webpage entitled Earth Day 1999 Focus on People -- Environment Connection http://www.erl.noaa.gov/EarthDay/ .
WIDESPREAD THUNDERSTORM ACTIVITY -- On Wednesday night, numerous thunderstorms formed a large arc that stretched from the eastern Great Lakes westward to the Missouri Valley and then southward across the Great Plains to central Oklahoma.
These thunderstorms formed along both the warm and cold fronts of a developing storm system over the Plains. The Wednesday night position of the low pressure center was in northeast Kansas. A warm front extended east from the low to West Virginia, where it continued as a stationary front out into the Atlantic Ocean. A cold front trailed southwestward from the low toward a second low that had formed along the front in the Oklahoma and Texas Panhandles.
Many of these thunderstorms were classified severe because they produced hail that had diameters three-quarter inch or greater -- one of the criteria for a severe thunderstorm. During the daylight hours, large hail was reported from several large thunderstorms that erupted along and to the north of the warm front over Nebraska, Iowa and northern Kansas. Later these storms moved into Illinois and Indiana, by late Wednesday night and early Thursday morning, thunderstorms moving eastward through Ohio into western Pennsylvania produced large hail. Wind damage was also reported from Illinois. One tornado was reported in Nebraska. Severe thunderstorms also developed along the cold front, as reports of large hail came from southern Kansas and Oklahoma. Near Wichita in southern Kansas, 2.5 inch diameter hail was reported to have caused structural damage. Some flooding occurred in Kansas as a result of the heavy rain. Flash flood warnings were posted for streams in eastern Nebraska, Iowa and Illinois.
Ample moisture was made available by southerly winds that brought warm and humid air northward from the Gulf into the southeastern quadrant of the surface low. In this warm sector, afternoon high temperatures on Wednesday were as much as 15 degrees above the typical afternoon high temperature for this time of year, with the largest departure across the Ohio and Mid-Mississippi Valleys.
A slow northward movement of the warm front is expected overnight, with a large precipitation shield extending from the Middle Atlantic westward across the Great Lakes into the central Plains. Several severe thunderstorm watches were in effect through early Thursday for portions of the southern Plains to include eastern Kansas. The region where a slight risk of severe thunderstorms is expected through much of Thursday will extend from the Red River Valley in the southern Plains northeastward to the prairies of central Illinois.
A ROCKY MOUNTAIN SNOWSTORM -- A low pressure system that was developing in the Texas-Oklahoma Panhandle has the potential for generating a major late season snowstorm over the Rockies and Front Range in Colorado. As of late Wednesday evening, heavy snow had fallen near Colorado Springs. The low is expected to remain over the Panhandle until Thursday morning as it intensifies. A widespread region of precipitation is forecast to form over the Rockies from northern New Mexico north to Wyoming. While adequate moisture is available, the major problem is sufficient cold air. Afternoon high temperatures across the Northern Rockies and the Intermountain West were approximately 15 degrees below the average highs for this time of year. A variety of winter storm watches and warnings have been posted for a large portion of Colorado.
LITTLE RELIEF IN SIGHT --- Dry conditions continued across the Southeast on Thursday as high pressure continued to dominate the weather over Florida, Georgia and Alabama, effectively blocking storms from bringing rain to the entire moisture-starved region. As of late Wednesday night the center of the high pressure ridge had shifted to the east, becoming centered over the Atlantic Ocean east of the Carolinas. Even though a southwesterly wind flow around the west limb of the ridge has brought warm, humid Gulf air into the Southeast, the warm air in the high pressure cell extends upward through the much of the troposphere and has suppressed convection.
The fire danger across Florida and neighboring states continued to remain exceeding high. Most of the large wildfires that have consumed more than 100,000 acres during the last several days have been contained. However, Alligator Alley (I-75) was closed again on Wednesday.
UPPER AIR -- As indicated by the 500 and 300 mb charts for 00Z Thursday, a large height trough has developed over the West. Cold air brought into the West has caused the altitude of the constant height surfaces to drop. Across the Eastern Portion of the countrry, a height ridge had devloped.
YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- The lowest temperature on Wednesday was 19 degrees at Stanley, ID. Wednesday's high was 99 degrees at Lajitas and Presidio, TX.
ALASKAN WEATHER -- An elongated and diffuse region of low pressure, identified as a trough extended from near Bristol Bay to the eastern interior. A stationary front separating warm air to the southeast from cold air to the northwest was located along this trough axis. The trough also separated two areas of high pressure that affected the state. A ridge of high pressure located over the eastern Pacific Ocean extended northward, crossing the Panhandle. Another region of high pressure was located over Far Eastern Russia, extending into the western Bering Sea and the northwest corner of Alaska. As a result, relatively cloud-free skies were found across the Panhandle and the middle Yukon Valley, with partly cloudy conditions over the interior and southern Alaska. Clouds accompanied by rain and snowshowers were found over the Alaska Range, the Talkeetna and Wrangle Mountains, as well as across the Pribilofs and Aleutians. Snow fell along the North Slope from Umiat to Barrow and Prudhoe Bay. During midafternoon, temperatures reached the mid 50s in the southern Panhandle, but to the northwest of the stationary front, while along the Arctic and Chuckchi Sea coast, temperatures remained in the single digits.
The lowest overnight temperature in the state as of Wednesday was 15 degrees below zero at Shishmaref. The highest statewide temperature as of midafternoon Wednesday was 55 degrees at Circle.
HAWAIIAN WEATHER -- Weak winds from the southeast replaced the usually northeast trade winds on Wednesday as the large high pressure cell to the northeast of the island moved farther away from Hawaii, while a cold front was approaching Kauai from the northwest. Some isolated showers are expected to develop over the islands on Thursday as the local sea breeze develops in the afternoon. By late Thursday, the trade winds should increase in speed.
FLOODS -- The Thursday optional Supplemental Information file describes the terminology used in the official statements issued by the National Weather Service to inform the public of floods and flash floods. Also included are major meteorological factors leading to flash flooding.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological Society.