DATASTREME DAILY SUMMARY

Friday, 12 October 2001


00Z Weather Systems


NOTE: Due to apparent coding errors, the yellow dashed trough line appearing in the accompanying satellite-fronts insert that runs from the western Atlantic off the Middle Atlantic Coast to northern Mexico should be ignored.

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

SEVERE WEATHER MOVES ALONG THE GULF COAST -- Thunderstorm activity continued late into Thursday night across the lower Mississippi Valley and the Gulf Coast in association with a slowly moving cold front that stretched southwestward from the eastern Great Lakes to the vicinity of the Texas Gulf Coast. The thunderstorm activity developed in the warm and humid air to the east of this front.

Severe weather to include tornadoes, high winds and hail moved across the central Gulf Coast and lower Mississippi Valley starting on Thursday morning and continuing until late afternoon. As many as nine tornadoes were reported across southeast Texas, along the Mississippi River in Louisiana and in central Mississippi. One of the tornadoes on Thursday morning produced a 3.5-mile long path of destruction through Pasadena, a suburb of Houston. Preliminary estimates indicate that this tornado could have reached F-2 intensity on the Fujita Scale. Numerous reports were made of wind damage associated with the strong thunderstorm winds across Texas, Louisiana, Arkansas, Mississippi and Tennessee. A man sustained an injury near Longview in northeast Texas as thunderstorm winds toppled a tree onto him. Large hail with diameters reaching 1.75 inches also fell near Jackson, MS. Heavy rain also fell, with new daily rainfall records being established at Memphis, TN (3.15 inches), Houston/Intercontinental, TX (3.02 inches), Jackson, TN (2.71 inches), Tupelo, MS (2.22 inches) and in Arkansas at Jonesboro (1.21 inches), El Dorado (1.17 inches) and Texarkana (1.03 inches). With the heavy rains, flooding of some rivers in northern Mississippi and western Tennessee necessitated the issuance of flash flood warnings on Thursday night.

Southern sections of the cold front are expected to move eastward on Friday before dissipating in the afternoon. A slight risk of severe thunderstorms continues across the lower Mississippi and central Gulf Coast through Thursday night to sunrise on Friday. Thunderstorm activity should increase on Friday afternoon across the southern Plains when the next cold front currently over the Rockies sweeps eastward across the region. As a result, much of east Texas and adjoining portions of Louisiana and Arkansas are forecast to be under a moderate risk of severe thunderstorms on Friday.

The clouds and rain contributed to holding the high temperatures on Thursday to 10 degrees below average across the mid and lower Mississippi Valleys. However, with abundant moisture from recent rains and clearing nighttime skies, dense fog was forming across portions of the southeastern Texas, eastern Oklahoma, northern Arkansas and southwestern Missouri late Thursday night and early Friday morning. Where the dense fog was expected to limit visibility to less than 0.25 miles, dense fog advisories were issued.

WARM WEATHER ACROSS THE NORTHEAST -- The Northeast, particularly northern New England and Upstate New York, experienced an unseasonably warm day, as high temperatures were on the order of 10 to 15 degrees above the average highs for mid October. Record high temperatures were established in Maine at Houlton (74 degrees) and Caribou (72 degrees), and a record high of 78 degrees was set at Dulles Airport in northern Virginia near Washington, DC. Warm air advection associated with southerly winds spiraling out of the high pressure cell off the Del-Mar-Va Peninsula and to the east of the advancing cold front contributed to the unseasonably warm weather.

WINTRY WEATHER ACROSS THE ROCKIES -- A cold front moving eastward across the Rockies was producing some wintry weather in the higher terrain. This cold front trailed southward from a low pressure system over Saskatchewan across the western Dakotas and eastern Wyoming before curving westward across Utah, Nevada and central California. Cold air was found behind this front as high temperatures across the western slopes of the Rockies and northern sections of the Intermountain West were 10 degrees below the average highs for the date.

Widely scattered precipitation was associated with this cold front. Rain was falling across the lower elevations of the western Dakotas, eastern Montana and north central Wyoming. Snow was falling across the mountains of Wyoming and Colorado.

The passage of the cold front produced high winds across the Great Basin, as the result of a tight pressure gradient that developed between high pressure along the Oregon Coast and lower pressure over the central Rockies. Winds had reached 56 mph in Utah's Salt Flats near Dugway on Thursday evening. A high wind warning remained in effect for the Dixie and Zion National Park regions of southwest Utah. As the front moved eastward across the northern Plains, a wind advisory was in effect through Friday morning for the Black Hills of South Dakota and the high plains to the east as gusts could reach 50 mph. The pressure gradient should remain relatively strong across the northern Rockies into the weekend. Consequently, high wind watches were issued for Friday night and Saturday across northwestern and central Montana where wind gusts to 60 mph are anticipated.

While the cold front is expected to continue eastward across the Plains on Friday morning, westerly winds associated with high pressure building into the Great Basin should continue the snow across the western slopes of the Colorado Rockies through midday on Friday. As a result, snow and blowing snow advisories were posted through Friday morning for the northern mountains of Colorado, as 4 to 8 inches could fall west of the Continental Divide, accompanied by winds with gusts to 60 mph.

MORE WELCOME RAIN FOR THE NORTHWEST -- Badly-needed rain fell across the interior of the Pacific Northwest on Wednesday night and Thursday. New rainfall records were established in Oregon at Cove (0.72 inches), La Grande (0.71 inches) and at the Pendleton Experimental Station (0.63 inches), in Idaho at Porthill (0.57 inches), in Washington at Whitman Mission (0.57 inches) and in Montana at Bozeman (0.45 inches).

Another cold front was expected to move onshore along the Washington coast on Friday afternoon, accompanied by rain that should fall across the Olympics and the northern Cascades. As much as 0.5 inches of rain could fall across Washington State by evening.

A CHILLY START -- High pressure across the Four Corners area of the Southwest allowed overnight temperatures to fall to record low readings on Thursday morning at Window Rock, AZ (17 degrees) and at Arches National Park, UT (37 degrees).

DEVELOPMENT OF SANTA ANA WINDS -- With the development of a strong high pressure system over southern Idaho on Friday afternoon, an easterly wind flow is expected to develop across southern California. These winds, called Santa Ana winds for a mountain range near Los Angeles, could become relatively strong because of the tight pressure gradient that is forecast to develop on the southern flank of the high pressure cell to the north. Strong Santa Ana winds are notorious especially in autumn since they typically exacerbate the wildfire situation with hot and dry winds that are channeled through the canyons surrounding the Los Angeles Basin. Wind speeds are expected to reach as high as 45 mph in some canyons and mountain passes late Friday. As a result, wind advisories were in effect through Friday afternoon for the Inland Empire and the Santa Ana Mountains of southern California.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 16 degrees at Bridgeport, CA and Alamosa, CO. Thursday's highest temperature was 96 degrees at Borrego, CA.

ALASKAN WEATHER -- A developing storm system moved across the southwestern Gulf of Alaska on Thursday afternoon. The low pressure center, with a central pressure of approximately 970 mb, was located approximately 350 miles south of Prince William Sound. An occluded front extended southeastward across the Gulf of Alaska, to become a warm front that continued southward across the eastern North Pacific and a cold front that curved to the southwest across the North Pacific toward Midway Island and the Dateline. Rain associated with this system had moved onshore, spreading across the Panhandle. A weakening trough of low pressure extending across eastern Alaska helped bring cold air and snow across interior and south central Alaska to include Eielson AFB, Tanana and the higher terrain around the Anchorage Bowl. Colder air was found to the north of a stationary front that stretched along the Brooks Range, with some locations across the North Slope reporting single-digit midday temperatures.

The lowest overnight temperature in Alaska on Thursday morning was 5 degrees at Anaktuvuk Pass, while the mid-afternoon highest statewide temperature was 51 degrees at Ketchikan.

HAWAIIAN WEATHER -- Trade winds weakened slightly across the Aloha State on Thursday as the subtropical high pressure cell responsible for the trade winds moved toward the northeast and a cold front located well to the northwest of the islands moved southeastward. However, this front should not reach the islands, but pass to the north. A weak ridge of high pressure following the front should maintain weak trade winds. Trade showers on the windward slopes of the islands should continue through the weekend. While high surf advisories remained in effect for the east shores of the islands, a weakening in the winds could drop the surf height permitting the canceling of the advisories.

EYE ON THE TROPICS -- In the eastern Pacific, the tropical depression that formed on Wednesday intensified into Tropical Storm Manuel, the thirteenth named tropical system (to include tropical storms and hurricanes) of the current season in that ocean basin. As of Thursday night, Tropical Storm Manuel had 50 mph maximum sustained surface winds and was located 500 miles to the south-southeast of Cabo San Lucas, Mexico. Movement was to the west-northwest at 13 mph.


HISTORICAL WEATHER EVENTS - 12 October

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

13 October

14 October


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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
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