DATASTREME DAILY SUMMARY

Friday, 7 September 2001


00Z Weather Systems


WELCOME TO DATASTREME - The Daily Summary file will describe the current weather pattern across the U.S. The Tuesday and Thursday files will also contain the "Concept of the Day" with a question to be answered on the weekly Chapter Response Form. Additional Supplemental Information Files will provide optional background material.

The following highlights of the national weather have been extracted from the surface weather map for Thursday night:

SEVERE WEATHER MOVES INTO THE MIDWEST -- Two separate regions of thunderstorms were moving from the Plains into the Midwest on Thursday evening. Some of these thunderstorms became severe, spawning tornadoes, generating strong and damaging winds, and producing large hail.

The first set of thunderstorms was associated with an upper level disturbance and band of precipitation that had moved northward from the southern Plains after producing flooding rains across Texas earlier in the week. As of late Thursday evening these thunderstorms were found across the western Great Lakes, stretching from Illinois and Indiana northward into Wisconsin and Michigan's Upper Peninsula. These thunderstorms moved along with the southerly winds (from the south) that brought warm and humid Gulf air northward into the Midwest. This cluster of thunderstorms had a history of severe weather. During Thursday afternoon several tornadoes were spotted across Iowa. The first of the six tornado reports was from near a community approximately 20 miles to the southwest of Des Moines, while the last two tornado reports were from near Dubuque in the northeast corner of the Hawkeye State. At least one tornado that traveled through West Des Moines caused an injury, as well as property damage. A tornado was also spotted on Thursday evening near Rhinelander in northeastern Wisconsin. Some property damage was also sustained. In addition to the thunderstorms, strong thunderstorm winds also inflicted some damage and uprooted trees at various locations through Iowa, Illinois, and Wisconsin. Strong thunderstorm winds were also reported in Tennessee.

The second set of thunderstorms was along the cold front that stretched across the Plains from northern Minnesota southwestward to Colorado. Several clusters of strong to severe thunderstorms were found along the cold front. One cluster was found across the Red River Valley separating the Dakotas from western Minnesota. Another cluster was located over Nebraska and northern Kansas. Some of the thunderstorms generated wind gusts that reached 70 mph in Nebraska and North Dakota. Large hail with diameters ranging from 0.75 to 1.75 inches fell from thunderstorms across Kansas, Colorado, Nebraska, North Dakota, and Minnesota. Because of the heavy rains, a flash flood watch was in effect during the evening hours for portions of eastern North Dakota and northwestern Minnesota.

Strong to severe thunderstorms continued across Nebraska well into the early morning hours of Friday. A 63 mph thunderstorm wind gust was reported at O'Neill in northeastern Nebraska. Large hail was also reported from some of these early morning thunderstorms in the Cornhusker State. A slight risk of severe thunderstorms continues through Friday morning across the Plains, extending from western Kansas northeastward into western Minnesota. A severe thunderstorm watch was posted early Friday morning for an area that extended from northwest Iowa southwestward to north central Kansas. During the remainder of Friday, the area that could experience a slight risk for severe weather shifts to the east, to run from north Texas to southern Wisconsin.

A ZONE OF CONTRAST -- The cold front that serves as the focus for some of the severe weather across the Plains and Upper Midwest represents a distinct contrast between warm air to the south and east from colder and drier air to the west. Southerly winds across the Plains and the Mississippi Valley were circulating in a clockwise fashion around in a large high pressure cell located along the Eastern Seaboard. These southerly winds were bringing warm and humid air northward from the Gulf. Even at 10 PM CDT, temperatures across Minnesota, Iowa and Wisconsin were in the low to mid 70s. Earlier, Marquette, MI reported a low temperature of 61 degrees on Thursday morning, which established a new high low temperature record for the date. Afternoon high temperatures across northern Minnesota reached 20 degrees above the local average highs for the date. On the other side of the front, northerly winds were bringing cooler air southward. Temperatures at 10 PM across the Dakotas were in the 60s, or about 10 Fahrenheit degrees lower than several hundred miles to the east.

The cold front is expected to move slowly eastward across the Plains on Friday. Several areas of low pressure are expected to develop and move northward along the cold front. Some heavy rainfall could result from some of these disturbances that propagate along the front. As much as 1.25 inches could fall across portions of Minnesota, western Iowa and Nebraska by Friday evening.

COLD WEATHER INVADES THE NORTHWEST -- To the west of the front, a chilly air mass has pushed into the Pacific Northwest. On Thursday morning, the low of 50 degrees, at Downtown San Francisco tied a record low temperature for the date. Afternoon high temperatures across portions of Montana, the northern Rockies and the Great Basin were as much as 20 degrees below the average highs for this time of year. Pocatello, ID had a high temperature of only 57 degrees, which set a low high temperature record for the date. Six inches of new snow were reported in the mountains of central Idaho on Thursday.

With a cold and dry air mass over the region, temperatures are expected to fall rapidly overnight because of the rapid loss of heat to space by radiation. As a result, a variety of frost and freeze warnings have been issued for portions of south central Oregon, northern California and northern and eastern Nevada.

ACTIVE WEATHER IN THE SUNSHINE STATE -- Widespread rainshowers and embedded thunderstorms continued to cross Florida in the warm tropical air mass to the south of a stationary front that stretched across the Southeast. During the morning a tornado was reported along the Atlantic Coast near Palm Beach. Near St. Petersburg, a man was injured from a nearby lightning discharge. Daytona Beach received a record 3.06 inches of rain, resulting in the issuance of an urban and small stream flood advisory for the region.

Thunderstorm activity is expected to continue across the Sunshine State on Friday. As much as 0.6 inches of rain are forecast to fall in central Florida during the 24 hours ending on Friday night.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 29 degrees at Bridgeport and Truckee, CA. Thursday's highest temperature was 109 degrees at Laughlin, NV.

ALASKAN WEATHER -- Much of the state remained cloud covered except for the eastern quarter of the state where large breaks in the overcast were detected. A low pressure center was located just to the north of Barrow, with a trough line, which represented an elongated region of lower pressure and a shift in the winds, extending southward across western Alaska. Light winds and widely scattered light rain were found across the region. The breaks in the clouds in eastern Alaska were associated with a ridge of high pressure that extended northward along the Alcan border from a large high pressure cell over the eastern North Pacific. A storm system located south of Kodak Island in the North Pacific was moving northeastward into the Gulf of Alaska. As a result, winds were from the south along the northern Gulf coast to the east of the Kenai Peninsula, but from the northwest across the southern portions of the Alaska Peninsula. A large ridge of high pressure was moving across the western North Pacific and the western Aleutians.

The lowest overnight temperature in Alaska on Thursday morning was 30 degrees at Nenana, while the mid-afternoon highest statewide temperature was 62 degrees at Annette and Ketchikan.

HAWAIIAN WEATHER -- The subtropical high pressure cell that has dominated the weather across the Pacific has moved to the northeast toward the West Coast of North America. As a result of the weakening pressure gradient across the islands, the trade winds over the Aloha State have weakened to between 5 to 15 mph. Showers moved across the islands on Thursday. Some isolated showers should linger into the beginning of the weekend. The trade winds are expected to remain light to moderate through the weekend.

EYE ON THE TROPICS -- In the western tropical North Atlantic, Tropical Depression Erin weakened into a tropical wave late Wednesday, but on Thursday, it intensified sufficiently to once again become a tropical depression. As of late Thursday night, Tropical Depression Erin, located 610 miles to the southeast of Bermuda, had estimated surface winds of 30 mph. Erin was moving to the north-northwest at 7 mph.

In the eastern North Pacific, Hurricane Gil continued to intensify, with maximum sustained surface winds estimated at 100 mph. It was 1345 miles west-southwest of Cabo San Lucas, Mexico and was traveling to the west at 10 mph. Tropical Storm Henriette was 880 miles west-southwest of Cabo San Lucas and moving to the west-northwest at 17 mph. Maximum sustained surface winds were estimated to be 65 mph.

A SOLEMN ANNIVERSARY -- The National Oceanic and Atmospheric Administration (NOAA) issued a press release commemorating the Galveston, TX hurricane of 1900. This release contains links to historic photos and a excerpts of an eye-witness description of the storm by the chief forecaster of the Galveston U.S. Weather Bureau Office.


HISTORICAL WEATHER EVENTS - 7 September

From the files of the Aviation Weather Center, Kansas City, MO and Intellicast

8 September

9 September


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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.