DATASTREME DAILY SUMMARY

Friday, 21 September 2001


00Z Weather Systems


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

WET WEATHER PUSHES INTO THE EAST -- A slow-moving storm system with an accompanying cold front brought widespread rain along the Eastern Seaboard from southern Georgia northward to New England on Thursday evening. This occluding storm system consisted of a low pressure center that was situated over Georgian Bay and northern Lake Huron and an occluded front that stretched southeastward to a point of occlusion over the Mohawk Valley of eastern New York State. A warm front extended eastward from this point of occlusion across southern New England while a cold front trailed southward along the Appalachians and the Piedmont before curving southwestward across Georgia and the Gulf Coast, to merge with a warm front over southwest Louisiana.

This storm system was undergoing a portion of its typical life cycle where the cold front was moving faster than the warm front, resulting in the formation of an occluded front, which essentially represents the amalgamation of the characteristic cloud and precipitation properties of a warm and cold front. Relatively widespread and steady precipitation was found across New England to the north of the warm front. More intermittent rainshowers and imbedded thunderstorms stretched southward to the east of the cold front. During the late afternoon, a tornado was observed during the late afternoon near Culpepper in northern Virginia.

Rain should continue along the Eastern Seaboard as the storm system moves toward the northeast on Friday. By sunrise the low pressure system should have drifted only 100 miles to the northeast from Georgian Bay, while the occluded front and the cold front push eastward across New England and off the Middle Atlantic coast. The system is forecast to have weakened and essentially dissipated by evening. Between 1.0 and 1.5 inches of rain could fall during the 24 hours ending Friday evening across the Northeast, to include much of New England and the Hudson Valley of New York and New Jersey. Farther south along the cold front, as much as one-third of an inch of rain is anticipated across the Carolinas.

SEVERE WEATHER TARGETS THE MIDWEST -- A relatively potent low pressure system developed along a trough of low pressure over the Plains and moved toward the Mississippi Valley. This storm system and associated cold front were accompanied by strong to severe thunderstorms that began forming in the morning. Some of this thunderstorm activity continued well past local midnight. As of Thursday night the low pressure center was situated over central Iowa with a cold front that trailed to the southwest across Kansas. At that time widespread rain and thunderstorms stretched from northern Wisconsin southwestward to Missouri and Kansas. Some of the thunderstorms remained severe.

The severe thunderstorms associated with this system spawned two tornadoes and produced large hail. During the late afternoon, a tornado downed some trees in south central Iowa, while another tornado was spotted near St. Joseph in northwestern Missouri. Many of the thunderstorms that moved across Kansas and Nebraska into Missouri, Iowa and southern Minnesota during the morning and afternoon also were hail producers. Two inch diameter hail broke car windows in Iowa. In addition to the tornadoes and hail, flooding rains also accompanied this storm system, with one observer in southeastern Iowa reporting an accumulation of 1.30 inches of rain in 45 minutes. Rockford, IL received a record 2.40 inches of rain, all but 0.10 inches of which fell within two hours during the evening. Chicago's O'Hare Airport also received a record 1.33 inches of rain. As a result, an urban and small stream flood advisory was posted for northern Illinois.

The low pressure system is expected to travel eastward on Friday, reaching southern Lake Michigan by sunrise and near Detroit by evening. The cold front should also continue its travels across the southern Great Lakes and the Ohio Valley. A region along and to the east of the cold front was expected to continue experiencing a slight risk of severe thunderstorms until sunrise on Friday. This region extended from southern Wisconsin to north Texas. Rainfall accumulations by Friday evening could be on the order of an inch across northern Indiana and southern Michigan.

MORE SEVERE WEATHER FOR THE SOUTHERN PLAINS -- Once again strong to severe thunderstorms traversed the southern Plains. Severe thunderstorms continued until after local midnight across portions of Texas and Oklahoma. Most of these thunderstorms were associated with a low pressure area and associated warm front that were situated over the Texas Panhandle. However, some of the thunderstorm activity was also associated with the cold front that was moving southward across Kansas. During the late afternoon thunderstorms produced wind damage across portions of north central Texas near Abilene, where thunderstorm wind gusts were registered at 73 mph. Large hail was also reported across the Texas Panhandle, extending northeastward across Oklahoma and into south central Kansas. Farther to the southeast along the warm front thunderstorms generated high winds in southeastern Texas near Houston and across southern and western Louisiana.

With thunderstorm activity anticipated to continue through much of Friday across the Lone Star State, heavy rain is expected, with as much as 2 inches of rain falling across the Red River Valley and into southern Oklahoma by evening. A flash flood watch was in effect for portions of southern Oklahoma, with some counties under flash flood warnings.

TRANQUIL WEATHER CONTINUES ACROSS THE WEST -- Relatively high pressure continued to maintain its grip across the West. The development of much needed rain has been inhibited by the warm dome of air that has remained firmly entrenched over the region.

Onshore winds from the cool waters of the Pacific kept the high temperature at Monterey, CA at only 62 degrees, a record low maximum temperature for the date. Monterey has now experienced an unusual five consecutive days with record low highs. However, in the Great Basin of eastern Nevada, record high temperatures were recorded at Wells with 89 degrees, Ely and Eureka, both with 85 degrees.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 17 degrees at Wisdom, MT. Thursday's highest temperature was 108 degrees at Bullhead City, AZ.

ALASKAN WEATHER -- A storm system moved eastward across the Bering Sea spreading clouds across western Alaska. This system consisted of low pressure that was approaching Bristol Bay and an accompanying front that stretched southeastward across the Alaska Peninsula. A weak low pressure system located over the eastern Gulf to the west of the Queen Charlotte Islands was moving to the northeast toward the southern tip of the Alaska Panhandle. Most of the significant precipitation across Alaska was limited to southeast Alaska. A weak ridge of high pressure extended from northwest Canada across the North Slope and the northern sections of interior Alaska. As a result, relatively cloud-free skies were found across northeastern Alaska on Thursday afternoon.

The lowest overnight temperature in Alaska on Thursday morning was 25 degrees at Arctic Village, while the mid-afternoon highest statewide temperature was 64 degrees at Elmendorf AFB and McGrath.

HAWAIIAN WEATHER -- Moderate east to northeast trade winds along with relatively cloud-free skies continued across the Aloha State as the result of a large subtropical high pressure ridge located to the north of the islands. Isolated trade showers were also found across the windward slopes of the islands, especially on the northeast side of the Big Island. Several weak disturbances were traveling westward and passing south of the islands. These disturbances contain tall convective type clouds with tops that are being carried toward the islands by the winds aloft.

THE AUTUMNAL EQUINOX -- The Autumnal Equinox will occur tomorrow, Saturday afternoon (at 2305Z, or 7:05 PM EDT, 6:05 PM CDT, etc.). At that time the noontime sun will appear directly above the equator, representing one of the two times during the year for such an occurrence, with the other being at the vernal equinox in March. Within the next several days the length of daylight will become noticeably shorter.

REPORT FROM THE FIELD-- Faye McCollum, Project Atmosphere AERA from Columbus, GA reported seeing the first yellow leaf of the season. She said that while fall weather has not arrived in Georgia yet, her chrysanthemums are in full bud, indicating a progression toward fall.


HISTORICAL WEATHER EVENTS - 21 September

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

22 September

23 September


Return to DataStreme Homepage

URL: datastreme:/learn/f_sum.html
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.