STORMY WEATHER MOVES TOWARD THE NORTHEAST -- The storm system that produced severe thunderstorms across the southern Plains and snow over northern Minnesota on Monday moved quickly toward the northeast on Tuesday. During its travel, the storm system continued to undergo a process of occlusion, where the cold front moves more rapidly than the warm front. As of late Tuesday night the low pressure system was located in Ontario just south of James Bay. An occluded front extended southeastward from the low center to a point of occlusion or triple point over the Finger Lakes of western New York State, where a warm front extended toward the southeast and a cold front curved toward the southwest, reaching the central Gulf Coast.
During the overnight hours, the severe thunderstorm activity along the cold front began to diminish in intensity. On Tuesday afternoon, a severe thunderstorm developed near Lake Erie and moved eastward into western New York State. Most of the precipitation associated with this system as of late Tuesday night was located to the north and east of the warm front, extending across Ontario and Quebec, with some precipitation moving eastward across New York State and New England. Several severe thunderstorms developed over southern Alabama and western Georgia along the cold front. A thunderstorm produced golfball-sized hail near Montgomery, AL. Some light precipitation was also detected across northern portions of Michigan's Lower Peninsula.
Windy conditions developed across the Great Lakes states as the low moved into Canada. The strong westerly to northwesterly winds were associated with a strong pressure gradient between the high pressure that built in over the mid-Mississippi Valley and the Canadian low. Wind gusts exceeded 40 mph from Chicago eastward across northern Indiana and Ohio to western New York State as the cold front moved eastward.
The storm system is expected to continue moving toward the northeast, with the trailing frontal system and accompaning precipitation affecting Maine and New Hampshire on Wednesday morning.
QUIET WEATHER DEVELOPS ACROSS THE NATION'S MIDSECTION -- A large ridge of high pressure developed across the Midwest in the wake of Monday night's storm. As of late Tuesday night, the center of the high was situated near the confluence of the Ohio and Mississippi Rivers. Relatively cloud-free skies stretched from the upper Mississippi Valley south to Louisiana and from the Appalachians west to the Rockies. The high should move eastward over the Ohio Valley on Wednesday. As a result, southerly winds on the west flank of the high should spread northward across the Plains.
Some widely scattered light rainshowers were spreading eastward across the Dakotas on Tuesday night associated with a weak trough of low pressure that was situated over Saskatchewan. This system is expected to move quickly eastward toward the upper Lakes.
MORE WINTRY WEATHER FOR THE SOUTHWEST -- Another storm system that moved into Southern California on Tuesday spread more precipitation that included low-elevation rain and high-elevation snow from California's central valleys southward to the Mexican border. As of Tuesday evening, a low pressure system was located over southern Nevada. The widespread clouds and precipitation helped keep temperatures unseasonably low. High temperatures across central and southern California were as much as 20 degrees below typical highs for this time of year. The storm system is forecast to move eastward, with the region of precipitation spreading into the Great Basin. Snow advisories were in effect for the mountains of southern California at elevations over 3500 feet.
WARM WEATHER ACROSS THE GULF COAST -- Record high temperatures were tied or set Tuesday afternoon in Florida at Tampa (89 degrees) and Fort Myers (90 degrees); at Houston/Intercontinental, TX (86 degrees) and at New Orleans/Audubon Park, LA (87 degrees).
UPPER AIR -- The 500 mb chart for 00Z Wednesday revealed a cold pool of air in the mid-troposphere along the California coast. A height trough extends westward into the Pacific ocean. This cold pool is associated with the surface low pressure system in southern Nevada that spread snow across the mountains of southern California. The effects of this cold pool in the upper troposphere were also seen on the 300 mb chart for 00Z Wednesday, where an upper trough is also apparent along the West Coast. The winds at this level flow southward from British Columbia along the Pacific Coast before being diverted out to sea to circulate in a counterclockwise fashion around the trough. The winds across much of the rest of the country on this 300 mb surface are predominantly west to east or zonal. A trough extends southeastward over the Great Lakes in association with the surface storm system over Ontario.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Tuesday, the lowest temperature reported in the continental U.S. was 8 degrees at Flagstaff, AZ, while Tuesday's high was 93 degrees at Laredo, TX.
ALASKAN WEATHER -- Several areas of low pressure were found across the state on Tuesday. One low pressure region was located in the northwest near Point Hope, another region across southwest interior and a third near Yakutat. A front extending southwestward from a large trough of low pressure located over southeast Yukon Territory was responsible for clouds and precipitation across southeast Alaska. As of late Tuesday afternoon, Sitka had received 1.01 inches of precipitation, with lesser amounts at Juneau, Annette, Yakutat and Cordova.
A large ridge of high pressure was located over the North Pacific Ocean to the southwest of Dutch Harbor.
As of Tuesday, the lowest overnight temperature in the state was 17 degrees below zero at Deadhorse. By midafternoon, the highest temperature was 45 degrees at Petersburg, Ketchikan and Hoonah.
HAWAIIAN WEATHER --Trade winds continued to increase in speed and become northeasterly across Hawaii on Tuesday as a low pressure cell to the northwest of the islands continues to weaken and high pressure to the northeast is reinforced. Winds may increase to 30 mph. A band of clouds and showers moved from the Big Island across Maui during the daylight hours of Tuesday and stalled across Oahu and Kauai on Tuesday evening. Except for the usual trade showers that usually occur at night on the windward slopes of the islands, relatively cloud-free skies are expected across Hawaii throughout the second half of the week. Small craft advisories were issued at noon as the trade winds increased.
MONITORING EL NIÑO and LA NIÑA -- Scientists have suggested that some of the abnormal weather patterns that have affected not only the United States, but other countries, for nearly a year following July 1997, were linked to an event called El Niño. Within the last year, the signs associated with an episode identified as La Niña have appeared. For more details on how to monitor these phenomena, please read the optional Supplemental Information for Wednesday.
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.