DATASTREME DAILY SUMMARY

Wednesday, 19 September 2001


00Z Weather Systems


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

WET WEATHER ACROSS THE MIDWEST -- A low pressure system that was moving northeastward into the mid-Mississippi Valley spread a large area of heavy rain across the Midwest. This low pressure system was located near St. Louis, MO on Tuesday evening. A complex system of fronts stretched eastward across the Midwest from the vicinity of this system, while a cold front trailed southwestward from this low pressure center. The precipitation shield associated with this storm system stretched from the Ohio Valley northward into the southern Great Lakes. Southerly winds to the east of the low pressure system helped produce the relatively heavy precipitation as the air was carried aloft over the frontal surface across Illinois and adjoining states. Thunderstorms were embedded in this precipitation shield. Some of these thunderstorms near St. Louis, MO and Indianapolis, IN approached severe limits.

The storm system is expected to travel to the northeast on Wednesday, with the low pressure center forecast to reach the Chicago metropolitan area by morning and to Lower Michigan by evening. As much as 1.2 inches of rain could fall across eastern sections of the Corn Belt during the 24 hours ending Wednesday evening.

SEVERE WEATHER IN THE SOUTHERN PLAINS -- A line of thunderstorms was found along and to the east of the cold front that trailed across the southern Plains. By mid-evening, most of the active thunderstorms were found from southern Missouri across Arkansas, eastern Oklahoma and northern Texas. Earlier in the evening some of these thunderstorms became severe as a result of the high winds and large hail. Thunderstorm winds caused damage in north Texas, to include the suburbs of Dallas-Fort Worth. Several locations reported thunderstorm wind gusts to 70 mph. Large hail, with diameters ranging between 0.75 to 1.75 inches, was also reported near Denton and across north central Texas near San Angelo and Abilene. Some of the thunderstorms near San Angelo produced heavy rain, with radar-estimated totals between 1 to 3 inches. Even to the north of the front, thunderstorms also produced large hail in the Nebraska Panhandle near Alliance on Tuesday evening.

Relatively warm and humid Gulf air that was carried northward into the southern Plains and lower Mississippi Valley on southerly winds provided the moisture supply for these thunderstorms. The cold front that was moving to the south and east across the southern Plains provided the lifting mechanism needed to cause the thunderstorms to develop. Cooler and drier air traveled southward in the wake of the cold front. In addition to the cooler air moving southward , the widespread clouds and rain helped keep high temperatures some 10 degrees below the average highs for the date across the central Plains on Tuesday.

The cold front is expected to continue moving to the southeast on Wednesday, reaching the lower Mississippi Valley and southeast Texas by evening. As much as 1.2 inches of rain could fall from the lower Ohio Valley southwestward to the eastern portions of the Lone Star State.

ANOTHER CHILLY START IN THE SOUTHEAST -- High pressure centered over Georgia provided relatively quiet weather across the Southeast on Tuesday, with relatively cloud-free skies and weak winds. These conditions contributed to relatively low overnight temperatures as rapid radiative cooling took place. On Tuesday morning, daily record low temperatures were either tied or established in North Carolina at Charlotte (48 degrees), in South Carolina at Florence (50 degrees), North Myrtle Beach (54 degrees), Charleston's Airport (55 degrees), in Georgia at Augusta (52 degrees) and in Florida at Tallahassee (56 degrees).

This high pressure system is expected to drift off the coast on Wednesday, while winds become more southerly ahead of the next storm system moving across the nation's midsection.

FLORIDA WEATHER -- While high pressure produced relatively quiet weather across much of the Southeast, thunderstorms were found over south Florida. Several waterspouts were spotted over the Florida Strait several miles to the south of Key West during the early afternoon. Rainshowers and thunderstorms are expected across the Florida Peninsula on Wednesday. Several tenths of an inch of rain could fall by evening.

RELATIVELY QUIET WEATHER CONTINUES ACROSS THE WEST -- High pressure located over the Great Basin helped maintain relatively quiet weather across a large portion of the West on Tuesday. A weak cold front moved inland across the Pacific Northwest. Except for some precipitation over southwest Montana near Bozeman, this front has little precipitation. Afternoon high temperatures across the West, to include the northern Rockies and the Pacific Northwest were on the order of 10 degrees above the average highs for mid-September. However, along the coast, the high temperature of 59 degrees at Monterey, CA set a new low high temperature record for the date.

YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Tuesday morning's lowest temperature was 27 degrees at Randolph, UT, while the highest temperature on Tuesday was 105 degrees at Bullhead City, AZ.

ALASKAN WEATHER -- A storm system in the eastern Gulf of Alaska continued to bring clouds and rain across much of southern Alaska. The low pressure center was situated to the west of Juneau, with a trough line extending southward along the Panhandle. Another weak low and associated trough were found over south central and interior Alaska. A weak high pressure cell was found along the Yukon-Kuskokwim Delta. Partly cloudy skies were reported over portions of interior Alaska. Farther west, two storm systems were moving across the North Pacific and the Bering Sea.

The state's lowest overnight temperature on Tuesday morning was 23 degrees at Arctic Village. The highest temperature by mid afternoon of Tuesday was 59 degrees at Ft. Wainwright and McGrath.

HAWAIIAN WEATHER -- A ridge of high pressure located approximately 600 miles to the north of the islands continued to bring trade weather to the Aloha State, to include relatively cloud-free skies and moderate northeast trade winds, with speeds ranging from 10 to 25 mph. Some nighttime and morning trade showers were also found along the windward sides of the islands. The relative proximity of the ridge to the north of the islands and an equatorial trough to the south has produced a relatively tight pressure gradient that generates the moderate trade winds. This weather regime is expected to continue through the end of the week.

EYE ON THE TROPICS -- Because Tropical Storm Gabrielle had lost most of its tropical characteristics, and had evolved into a system similar to a midlatitude storm, the National Hurricane Center issued its last advisory for that storm late Tuesday night. At that time Tropical Storm Gabrielle was located 350 miles to the south-southwest of Cape Race, NF and was continuing to move toward the northeast at 21 mph. Maximum sustained winds were estimated at 70 mph. The Canadian Weather Service has issued storm warnings to mariners in the waters off the Maritime Provinces and a heavy rain warning for portions of Newfoundland.

Farther east in the Atlantic, former Hurricane Felix weakened to a tropical depression and by late Tuesday night, Tropical Depression Felix had maximum sustained winds of 30 mph, and was drifting at 2 mph to the south at a location approximately 380 miles southwest of the Azores. This system is expected to dissipate within the next day.

PROBING THE ATMOSPHERE -- In order to monitor the weather conditions in the free atmosphere, weather instruments are sent aloft twice daily attached to weather balloons launched from more than 70 sites across the country. Some of these data are available on the DataStreme Homepage as product under the heading of Upper Air Data-Text. If you would like additional information concerning how to read these upper air data files, please consult Wednesday's optional Supplemental Information .


HISTORICAL WEATHER EVENTS - 19 September

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

...1947...The eye of a hurricane passed directly over New Orleans, and the barometric pressure dipped to 28.61 inches. The hurricane killed fifty-one persons, and caused 110 million dollars damage. It produced wind gusts to 155 mph while making landfall over Fort Lauderdale, FL two days earlier. (David Ludlum) (The Weather Channel)


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