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Sincerely,
Ed Hopkins
Today is the observance of Martin Luther King Day, a Federal Holiday.
The following discussion is made based upon the surface weather analysis for late Sunday night:
MESSY WEATHER IN THE MIDWEST -- A large low pressure system that was situated over western Wisconsin on Sunday night was responsible for a potpourri of precipitation across the upper Mississippi Valley, the Great Lakes and the Appalachians. The various types of precipitation were affected by the temperature pattern surrounding this surface low. The counterclockwise circulation around the low brought warm air northward on winds from the south along the east side of the low, while cold air was brought southward on winds from the north around the system's western flank. Consequently, an intensification of the temperature gradients resulted in a series of fronts associated with the storm system. An occluded front, representing the merging of cold and warm front, extended southeastward from this low pressure center to central Indiana, where a warm front stretched eastward across the Ohio Valley, while a cold front continued southward to middle Tennessee, before curving southwestward and then westward into north Texas. The warm front was the leading edge of the northward flow of warm air, while the cold front was the leading edge of the colder air from the west and northwest. This storm system was expected to move to the east-northeast, with the low pressure center reaching Michigan's Upper Peninsula by Monday morning. The trailing fronts were anticipated to move east toward the Appalachians.
Snow was found in the cold air to the north and west of the storm. Several inches of snow had fallen across eastern Minnesota and western Wisconsin by late Sunday night, following the passage of the storm system and cold front. Snow and blowing snow advisories continued across much of eastern South Dakota, southern Minnesota, western Wisconsin and Michigan's Upper Peninsula until Monday morning as a result of the snow and accompanying 30 to 40 mph winds that were expected to continue around the west side of the low pressure system.
Rain and freezing rain were found in the warmer air to the east of the system. Freezing rain spread across the Midwest as warm air to the east of the low produced rain that fell upon cold, subfreezing surfaces. A tour bus flipped over on icy Interstate 80 near Princeton in western Illinois, resulting in 50 injuries. Fog and "black ice" (a layer of ice that builds upon a surface and does not appear to the unsuspecting motorist) were responsible for a major pileup involving more than 50 vehicles on Interstate 94 near Detroit on Sunday morning. Several injuries were reported.
Thunderstorms were found to the southeast of the storm, to as far north as northern Indiana. However as noted below, the majority of the thunderstorms were farther to the south.
The warm weather and rain that was falling across the eastern Great Lakes, Middle Atlantic and Appalachians also created another concern. Flood watches were in effect for southwestern Pennsylvania and the northern Panhandle of West Virginia as some of the tributaries of the Ohio River could flood as a result of ice jams that developed on the rivers.
SEVERE WEATHER ACROSS THE MID SOUTH -- A line of powerful thunderstorms developed along the cold front that trailed southward from the surface low in the upper Midwest. This long line of thunderstorms, called a squall line, moved quickly eastward across Mississippi and Tennessee Valleys from late Sunday afternoon, extending into late Sunday night. The thunderstorms developed in the warm, humid air that flowed northward from the Gulf and lifted along the rapidly advancing cold front.
As of late Sunday night, severe thunderstorms continued from central Kentucky across middle Tennessee and northern Mississippi. Many of these thunderstorms became severe, as thunderstorm winds exceeded 58 mph, and hail had diameters that exceeded 0.75 inch. Numerous tornadoes were also reported by eyewitnesses or detected by radar from northeastern Arkansas near Jonesboro, across southern Missouri, Kentucky and western Tennessee. Tornadoes caused at least one fatality in Jackson, TN, where 15 houses were leveled. Another fatality caused by a tornado was reported in Lexington, TN. Other tornadoes were responsible for at least three injuries in Arkansas, and an injury in Tennessee. High winds also produced at least three injuries in Kentucky. An 81 mph thunderstorm wind gust was measured at Calvert City, KY on Sunday evening. Wind damage and large hail were also reported across Arkansas, Missouri, Kentucky, southern Illinois, Tennessee, Mississippi and Georgia.
The chance for severe weather is expected to continue across the South on Monday in a region to the east of the cold front.
UNSEASONABLY WARM WEATHER ACROSS THE SOUTH -- To the south of the cold front, afternoon high temperatures across the southern portion of the nation were well above the long term climatic average highs for this time of the year. Record high temperatures for the date were either tied or exceeded in Texas at Brownsville (86 degrees), San Antonio (82 degrees), Austin (81 degrees) and Longview (77 degrees); at Orlando, FL (83 degrees); at Shreveport LA (79 degrees); at El Dorado, AR (78 degrees) and at Albuquerque, NM (62 degrees).
With nightfall and cooling fog began to form as the humid air cooled to the saturation point. A dense fog advisory was issued for south Texas along the Rio Grande Valley as fog caused visibilities to drop to between one quarter and one half mile.
STORMY WEATHER IN THE NORTHWEST -- On Sunday night, a strong storm sytem located off the Pacific Coast had begun to make its presence felt across the Pacific Northwest. The low pressure center was situated to the northwest of British Columbia's Vancouver Island, with an occluded front extending southeastward across Washington State's Olympic Peninsula and into the Oregon Cascades, before becoming a cold front that extended southwestward across northern California. A large area of precipitation extended across Washington State, the Idaho Panhandle, Oregon and northern California. Heavy rain fell along coastal regions, while snow fell at the higher elevations and in the interior, away from the moderating influence of the Pacific Ocean. Between 4 and 6 inches had fallen in Idaho as of Sunday evening. Winds gusted to 59 mph along the Oregon Coast during Sunday. The strong winds to the east of the storm system prompted the posting of a variety of heavy surf advisories and gale warnings along the coast from Washington State south to Point Arena in California. High wind warnings were also posted for the Oregon coast and headlands.
This storm system is expected to move inland toward Idaho and western Montana by Monday morning. As a result, heavy snows are expected across the high elevations of the Pacific Northwest and the northern Rockies into Monday. Snow advisories for as much as 6 inches of new snow were in effect for the Olympics and the Cascades of Washington. Winter storm warnings were posted for the Oregon Cascades for as much as 15 inches of snow and for portions of the Sawtooth Mountains of Idaho above elevations of 5500 feet. Snow and blowing snow advisories were also issued for the mountains of western Wyoming and the Wasatch Mountains of Utah.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Sunday, the lowest temperature reported in the continental U.S. was 2 degrees above zero (Fahrenheit) at West Yellowstone, MT, while Sunday's highest temperature 88 degrees at McAllen, TX.
ALASKAN WEATHER -- A large region of high pressure that stretched from one high pressure center in the upper Yukon Valley near Fort Yukon to another center near the Alaska Peninsula dominated the weather in the eastern half of the state on Sunday. With relatively clear skies under high pressure, nighttime cooling allowed temperatures to fall to between 20 below and 30 below zero over south central and eastern interior portions of Alaska. Several weak low pressure systems were also found. One cell was found moving eastward across the Bering Sea near the Pribilof Islands. Clouds and snow were found at St. Paul Island, where an unusually large amount of snow, seven inches, fell. Light snow also fell across the southwestern quadrant of Alaska to include Bethel, Cold Bay, McGrath and Tanana. A second low pressure cell was found in the northwestern corner of the state, near Cape Lisburne. Light snow associated with this system fell from Kotzebue to the Chuckchi Sea coast. A third low pressure system was located to the south of the southeast Panhandle near the Queen Charlotte Islands of British Columbia. The winds around the north side of this low pressure system were from the east. As a result of this downslope and offshore flow, skies cleared over the Panhandle from Wrangell to Ketchikan. Whittier had winds that gusted to between 30 and 35 mph for much of Sunday. Temperatures warmed into the upper 30s.
The lowest overnight temperature in Alaska as of Sunday was 35 degrees below zero at Cantwell and Bettles. The midafternoon highest statewide temperature was 39 degrees at Metlakatla.
HAWAIIAN WEATHER -- A large high pressure system to the north of Hawaii on Sunday was responsible for maintaining steady winds across the islands that were from the northeast. These winds are familiarly called the "northeast trade winds", resulting from the clockwise wind flow circulating around the southern flank of the high pressure system. Because of the proximity of the high pressure system, sinking air also maintained relatively dry conditions over the islands. The high pressure system to the north is expected to remain through much of the upcoming week maintaining the dry trade wind pattern.
AN INVITE -- If you witness some interesting weather phenomena or would like to share some weather-related experience with others in the Online Weather Project, we cordially invite your contributions. Please email these to the address appearing below. Some of these may appear in the section titled "Reports from the Field"
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.