DID YOU NOTICE THE AUTUMNAL EQUINOX? -- The Autumnal Equinox occurred last Saturday evening (at 2305Z, or 7:05 PM EDT, 6:05 PM CDT, etc.). At that time the noontime sun appeared directly above the equator. Within the next several days the length of daylight will become noticeably shorter.
WEATHER OVER THE WEEKEND -- A progression of weather systems continued to move across the eastern half of the country over the weekend, while the West continued to experience hot, but relatively tranquil weather.
A cold front that had produced heavy rains along the Eastern Seaboard on Thursday finally moved off the coast late Friday. Rain continued to fall over New England on Friday morning. However, this system was quickly followed by another storm system from the Midwest that brought more rain to portions of New England.
This next storm consisted of a low pressure system that had produced heavy rains across the mid-Mississippi Valley on Thursday night. On Friday the storm moved eastward across the Great Lakes. Thunderstorms associated with this low produced strong winds and large hail in southern Lower Michigan and northern Ohio during the mid- to late- afternoon hours of Friday. After this system moved into the Northeast, high pressure followed, first providing the Great Lakes with a pleasant day on Saturday, and then the Northeast with one on Sunday. Southerly winds brought milder weather across the East on Sunday, resulting in afternoon highs that were on the order of 10 degrees above the average highs from the Carolinas northward to New England.
Several other clusters of thunderstorms were found across the southern Plains on Friday in association with a low pressure disturbance along the western end of the cold front. Thunderstorm winds also caused damage in southeast Texas in the vicinity of Houston.
The next storm in the series of storms that affected the eastern half of the country over the weekend developed in the Dakotas early on Saturday. This system moved slowly eastward across the Plains into the Mississippi Valley by Sunday morning. A broad area of rain and embedded thunderstorms accompanied this storm system. Some of the thunderstorms that moved across the Plains on Saturday became severe. As many as five tornadoes were reported on Saturday evening to the east of Hastings in southern Nebraska. Thunderstorm winds reached speeds of 70 mph in portions of southwestern Minnesota in the early afternoon and in northeast Kansas during the early evening. Several waves of thunderstorms that moved across the Plains early on Saturday morning and again on Saturday evening also produced large hail across portions of southern Minnesota, Iowa, southeastern Nebraska, Kansas and northern Oklahoma. Rochester, MN received 1.21 inches of rain, a record 24 hour rainfall total for Saturday.
As the cold front moved eastward on Sunday, thunderstorms developed along and ahead of the front. Thunderstorm winds caused damage in Arkansas, Tennessee, Kentucky, Indiana and into southern Lower Michigan during the afternoon and evening. Hail was reported across southern Missouri, northern Arkansas, western Kentucky, southern Indiana and middle Tennessee on Sunday afternoon and evening.
Following in the wake of the storm, cold air started moving southward into the northern Plains on Saturday night. This cold air was associated with a large Canadian high pressure system moving eastward across the Canadian Prairie Provinces. Northerly winds on the eastern flank of the high carried cold air southward. The push of cold air southward across the nation's midsection was quite impressive. Temperatures on Sunday morning across the Plains stretching from the Canadian border south to the Texas and Oklahoma Panhandles ranged from 10 to 25 degrees lower than the temperatures 24 hours earlier on Saturday. Residents in the northern Plains and the western Great Lakes experienced below average high temperatures on Sunday, with the largest temperature departures from average occurring over Nebraska, where highs were 15 degrees below the average highs for this time of year.
Thunderstorm winds also caused damage in southeast Georgia and in Florida near Sarasota and Jacksonville late Saturday afternoon.
The West remained unseasonably warm, with high temperatures on Friday and Saturday ranging from 10 to 15 degrees above the average highs over the region stretching westward from the eastern slopes of the Rockies to the Cascades and Sierras, and from the Canadian border southward to the Four Corners region of the Southwest. On Friday Phoenix had a record tying 108 degrees. On Sunday, highs across the region were on the order of 20 degrees above average. Record high temperatures were set Sunday in Arizona at Organ Pipe Cactus National Monument (107 degrees), Tucson (103 degrees), Sedona (100 degrees) and the South Rim of the Grand Canyon (84 degrees). Records were also set or tied on Sunday in Utah at St. George (102 degrees), Cedar City (89 degrees) and Bryce Canyon (78 degrees); in Nevada at Battle Mountain (95 degrees), Wells (92 degrees), Reno (91 degrees), Elko (90 degrees) and Ely (86 degrees); in Idaho at Pocatello (90 degrees) and in Washington at Walla Walla (90 degrees).
WEATHER FOR THE START OF THE NEW WEEK -- The following highlights of the national weather have been extracted from the surface weather map for late Sunday night.
A storm system located in the Great Lakes was responsible for a significant portion of the rain that was falling across the country on Sunday evening. This storm consisted of a low pressure center that was located over eastern Lower Michigan and a cold front that trailed southwestward across the Ohio and mid-Mississippi Valleys into the southern Plains. A large area of rain and thunderstorms stretched from Lake Huron to the south and southwest to northern Texas. Some widely scattered showers were also detected in the warm and humid tropical air mass over the Southeast and the lower Texas Gulf Coast.
By Monday morning the low pressure system is expected to be centered near Toronto on the western shores of Lake Ontario. The cold front is forecast to extend southward along the western slopes of the Appalachians. The system is then expected to move slowly eastward by evening. Widespread rain is anticipated across the eastern Lakes, extending southward along the Appalachians and along the Gulf Coast. As much as 2 inches of rain could fall across the mountains of the western Carolinas during the 24 hours ending on Monday evening. A slight risk of severe thunderstorms continues into Monday morning in the vicinity ahead of the cold front, extending from middle Tennessee northward into northern Ohio. The Middle Atlantic States, extending northward from the Carolinas into the Upstate New York, are expected to experience a slight risk of severe thunderstorms on Monday.
High pressure was continuing to build southward across the Plains from a high pressure center over western Ontario. The tight pressure gradient, or difference in pressure between the high and the low pressure center over Michigan produced strong northerly winds across the upper Mississippi Valley and the western Great Lakes. This pressure gradient was evident by the tightly packed isobars over the region on Sunday night's surface analyses.
By Monday morning the axis of the high pressure ridge is expected to be located over Minnesota. In addition to the cold polar air that has spread into the region, clear skies and relatively weak winds near the axis of the ridge should cause temperatures to fall to some of the lowest readings of the season. Frost advisories extend from the Red River Valley of the eastern Dakotas and western Minnesota southward to the Platte Valley of central Nebraska. Freeze advisories were posted for the Arrowhead of northeast Minnesota.
Gale warnings for winds anticipated between 39 to 54 mph were in effect for the California coast and adjacent waters from Point Arguello to Santa Cruz Islands.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Sunday, the lowest temperature reported in the continental U.S. was 19 degrees at Bondurant, WY, while Sunday's highest temperature was 110 degrees at Bullhead City, AZ and Death Valley, CA.
ALASKAN WEATHER -- A strong storm system over the Alaska Peninsula dominated the weather across much of Alaska on late Sunday afternoon. This storm consisted of a deep low pressure system with a central pressure of 972 mb located along the southern coast of the Alaska Peninsula east of Sand Point, with an accompanying front that curved eastward into the Gulf of Alaska and then southwestward across the central North Pacific to west of the Dateline. The tight pressure gradient between higher pressure to the southwest and the low was responsible for the strong northwesterly winds to the west of the storm. Winds exceeded 40 mph at Dutch Harbor. The storm system also was responsible for widespread rain across southwest Alaska. A broad onshore flow of moist, maritime air on strong southerly winds to the east of the system also caused some locations across the Panhandle to receive over 2 inches of rain. Relatively cloud-free skies were found across the North Slope and northwest Alaska, while clouds were found across much of the interior.
The lowest overnight temperature in Alaska as of Sunday was 25 degrees at Sheep Mountain and Anaktuvuk Pass, while the midafternoon highest statewide temperature was 61 degrees at Eielson AFB and Nenana.
HAWAIIAN WEATHER -- Showers and thunderstorms were found over and close to the Hawaiian islands as a result of a weak westward moving tropical disturbance that was approximately 570 miles to the south of Lihue, Kauai on Sunday. Persistent clouds and rain kept the afternoon high temperature in Hilo at 75 degrees, thus establishing a new low maximum temperature for the date. Isolated thunderstorms were also expected over the Big Island and along the coastal waters off the Kona and Kau coasts on Sunday night. A large ridge of high pressure close to the Dateline extended eastward within 1000 miles to the north of the islands. The northeast trade winds increased to speeds between 15 to 30 mph on Sunday as a result of the tightening of the pressure gradient between this high and the disturbance passing south of Kauai. Tropical Depression 2C (see below) could approach the islands later in the week. Ocean swell is expected to reach the islands from the northwest on Monday producing surf along the northwest facing shores of the islands to as high as 7 feet. Because of the stronger trade winds, small craft advisories were in effect for state waters.
EYE ON THE TROPICS -- In the western North Atlantic, the tenth tropical depression of the season formed to the south of Bermuda on Friday and moved toward the northwest. By Saturday afternoon this system had intensified to become Tropical Storm Humberto, the eight named storm system (to include tropical storms and hurricanes) of the season, and 24 hours later, it reached hurricane status. As of late Sunday night Hurricane Humberto had maximum sustained surface winds of 100 mph and it was located 150 miles to the west-northwest of Bermuda. Movement was to the north at 10 mph. Humberto is expected to continue moving northward on Monday before curving toward the northeast.
In the eastern North Pacific, the tenth named storm of the season formed off the Guatemala coast on Friday as Tropical Storm Juliette, and then became a hurricane. As of Sunday night Hurricane Juliette was 315 miles south-southeast of Manzanillo, Mexico and moving to the northwest at 3 mph. Maximum sustained surface winds were 135 mph. Tropical storm warnings and hurricane watches were in effect for portions of the west coast of Mexico. Farther to the west-northwest, the twelfth tropical depression of the season formed early Saturday. This depression became Tropical Storm Kiko. As of Sunday night Kiko was moving to the west at 8 mph and was located 1040 miles west-southwest of Cabo San Lucas, Mexico as of Sunday night. Kiko had maximum sustained surface winds of 70 mph.
In the central Pacific, the second tropical depression of the hurricane season, Tropical Depression 2C, developed on Saturday. As of late Sunday afternoon, Tropical Depression 2C was located approximately 725 miles to the south-southeast of Hilo and was moving to the west-northwest at 16 mph. Maximum sustained surface winds were 35 mph. Gradual strengthening of this system to tropical storm status, with sustained winds of 39 mph or greater is expected. If this status were attained, the tropical storm would be called Alika.
ONE FOR THE RECORD BOOKS -- If you would like more background information concerning how various temperature records are identified, please consult Monday's optional Supplemental Information .
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, 2001, The American Meteorological Society.