ANOTHER DAY OF SEVERE WEATHER -- Severe thunderstorms that contained large hail, damaging winds and several tornadoes continued to batter the nation's midsection on Wednesday. The thunderstorms were part of a large storm system that was moving slowly to the northeast across the northern Plains. As of late Wednesday night this storm system consisted of an occluding low pressure system centered in west central Minnesota. An occluded front curved northeastward and then southward across central Wisconsin, continuing to a point of occlusion over northern Illinois. A warm front extended eastward across northern Indiana and Ohio, while a cold front trailed southward from the point of occlusion running along the Mississippi Valley to the Texas Gulf coast.
Numerous thunderstorms formed a squall line that was situated ahead of the cold front and stretched from the Ohio Valley south to the Gulf Coast. This line of thunderstorms moved quickly eastward on Wednesday night. High winds, large hail and frequent lightning were reported across Alabama and middle Tennessee. Earlier in the afternoon reports of severe weather were made from south central Illinois, southern Indiana, the Bootheel of Missouri, western Kentucky, Arkansas, Louisiana and east Texas. A report of four inch diameter hail was made from Mt. Vernon, IL. Tornadoes were reported in Mississippi near Greenwood and Yazoo City. Farther north, a large area of rain with embedded thunderstorms were along the warm front and the occluded front, covering the western Great Lakes and upper Mississippi Valley. Severe weather was reported well to the north late Wednesday afternoon, as a short-lived tornado caused some damage near Tomahawk in northern Wisconsin and large hail fell near Wausau. Heavy rains also produced flooding across the Mississippi, Ohio and Tennessee Valleys.
The storm system is expected to move slowly eastward, with a secondary low forming near the point of occlusion. The precipitation shield to the north of the storm should expand eastward across the Great Lakes. To the south, the thunderstorm activity is anticipated to move eastward into the southern Appalachians.
TEMPERATURE CONTRASTS -- The storm system in the center of the county is found in a region of temperature contrasts. Warm weather was found across much of the eastern half of the country, while cool weather remained over the west.
On Wednesday morning, a record low temperature was reported from Eureka, CA (39 degrees), while Spokane, WA (27 degrees) and Klamath Falls, OR (23 degrees) tied record low temperature readings.
On Wednesday afternoon the temperature at Brownsville, TX reached a daily record high of 102 degrees, making day the warmest in Brownsville since 9 June 1989. Corpus Christi also reached a record high of 93 degrees. In the northeast, Caribou, ME tied a record 82 degrees.
Ellsworth AFB near Rapid City, SD reported 70 mph wind gusts on Wednesday morning and during the afternoon, Broadus, MT had a non-thunderstorm wind gust to 67 mph.
UPPER AIR -- The mid and upper tropospheric charts for 00Z Thursday reveals a large closed cyclonic (counterclockwise) circulation regime over the Great Plains on both the 500 and 300 mb constant pressure charts. Closed height contours surround a region of lower heights for these surfaces, indicating a cold pool of air over the central Rockies and the western Plains. This upper air feature is related to the surface low located over western Minnesota. The 300 mb winds show a strong jet stream that enters the West Coast over Washington State , then are deflected far to the south over Texas then curve to travel north toward the Great Lakes. The region of strongest winds, found around the base of trough and along the east limb provide a mechanism for the development and maintenance of the severe thunderstorms and active weather along the cold front.
YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- The lowest temperature on Wednesday was 12 degrees at Stanley, ID. Wednesday's high was 106 degrees at McAllen, TX.
ALASKAN WEATHER -- A large storm system located to the southwest of the Queen Charlotte Islands affected the weather across Alaska on Wednesday. This strong storm system, with a central pressure of approximately 977 mb, generated storm-force winds as a result of the strong pressure gradient. Gusty winds, with speeds reaching to at least 30 mph were reported along coast sections of the Alaska Peninsula, Prince William Sound, and southeast Alaska.
This storm was moving toward the Panhandle. A high wind watch was in effect for most of the night across southern portions of southeast Alaska, while a wind advisory was posted for central southeast Alaska. Cloudy skies accompanying this system spread across most of the state, with the exception of portions of the Kuskokwim and Kobuk Valleys, where skies contained fewer clouds. Snow was also reported early Wednesday in the northern Susitna Valley and the Copper River Basin.
The lowest overnight temperature in Alaska as of Wednesday was 2 degrees below zero at Shishmaref. The highest temperature as of midafternoon was 52 degrees at Skagway.
HAWAIIAN WEATHER -- The islands continued to experience light southeasterly winds on Wednesday as an elongated ridge of high pressure remained to the northeast of the islands. The increased humidity, coupled with afternoon heating of the islands produced light showers. This pattern is expected to continue through Friday.
REPORT FROM THE FIELD -- Joe Moran, author of the Online Weather Studies text, reported on a spectacular black dust devil during a field trip in northeastern Wisconsin last weekend. The warm and exceedingly dry conditions caused black organic rich soil from a muck farm to the lifted upward from the surface by a whirlwind.
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.