WINTRY WEATHER PROGRESSES EASTWARD --- The storm system that made landfall on Monday was moving eastward across the Rockies on Tuesday. As of late Tuesday night, the storm consisted of a broad low pressure system that was located in the upper Snake Valley of eastern Idaho with a warm front that extended eastward and a cold front that trailed southwestward across Nevada and into Southern California. A broad area of precipitation associated with this system stretched from the Idaho Panhandle south into the Great Basin and then into Southern California. Snow was reported in the cold air to the north, while rain fell across the south.
As the storm moved across the Sierras, heavy snow fell across the higher elevations, with some locations receiving several feet of new accumulation. Heavy snow was also reported in Oregon and Idaho. On Tuesday morning, heavy rain, with amounts ranging from 0.50 to 2.00 inches within the previous 12 hours, fell in Reno, NV, resulting in urban flooding. Heavy rain was also reported in California.
The air following in behind the storm system was unseasonably cold. Tuesday afternoon high temperatures, especially in the Pacific Northwest on the western slopes of the Cascades, were on the order of 10 degrees below the average highs for the date. Pea sized hail was reported in Idaho, indicating the presence of cold, unstable air aloft. The onshore west winds in the wake of the storm system continued to produce precipitation on the windward sides of the Coastal Range, the Cascades, and the Olympics late Tuesday.
High winds also accompanied this storm. Winds gusting to more than 60 mph were anticipated over Utah and portions of Nevada. Gale warnings for winds ranging between 39 and 54 mph were posted for Tuesday night along the Pacific Coast from Cape Flattery, WA to Cape Lookout, OR and from Point Conception to Guadeloupe Island in California. Wind advisories were issued for the mountains of southern California surrounding the Los Angles Basin area.
This storm system is forecast to continue moving eastward across the northern Rockies, before reorganizing on the high Plains on Wednesday morning. A fairly complex storm system should result. A cold front along the leading edge of significantly colder air to the east of the Canadian Rockies is expected to move southward. This cold air is anticipated to be pulled into the storm system eventually.
The parade of Pacific storms, coupled with a persistent onshore flow contributed to making the recently concluded three months of November, December, January the wettest three-months in Olympia, WA with 40.20 inches of liquid equivalent precipitation.
UNSEASONABLY WARM TO THE EAST OFT OF THE ROCKIES --- A large high pressure cell located over the mid Mississippi Valley produced quiet weather conditions with relatively cloud free skies from the Appalachians west to the Rockies. Afternoon high temperatures across much of the country to the east of the Rockies were above the average highs for this time of the year. Some locations across the central Plains were approximately 20 degrees above average. Record high temperatures were either tied or set on Tuesday at Galveston, TX (75 degrees), Salt Lake City (62 degrees), Grand Junction, CO (64 degrees), Moline, IL (56 degrees) and Cedar Rapids, IA (55 degrees). The high temperature record was set at Salt Lake City with 62 degrees as a result of strong southerly winds before passage of the cold front that was moving to the east. By evening, the temperature dropped and snow was anticipated.
SEVERE WEATHER ACROSS THE SOUTHEAST -- Thunderstorms developed along and to the south of an essentially stationary cold front that was situated over the Tennessee Valley, to include Louisiana, Mississippi and Tennessee on Tuesday night. Some of these thunderstorms tuned severe as large hail was reported to have fallen near Atlanta, GA and in central Mississippi. Floods were also the result of thunderstorms in Louisiana.
The front separated warm, tropical air to the south from cooler and drier hair to the north Thunderstorms developed in the warm air because the tropical air mass contained low level moist for thunderstorm development. The front assisted in the thunderstorm development by providing a rising motion in lifting the warm moist air upward.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Tuesday, the lowest temperature reported in the continental U.S. was 8 degrees below zero at Presque Isle, ME, while Tuesday's high was 92 degrees at Laredo, TX.
ALASKAN WEATHER -- The center of the cold ridge of high pressure situated over northern and central Alaska shifted slightly to the east on Tuesday. Record low temperatures were set at Bettles wit 60 degrees below zero; Tanana at 59 below, Galena at 56 below and McGrath at 52 below. The daily record low temperature at Cold Bay was broken as the temperature fell to five degrees below zero, which tied the all-time lowest temperature for the month of February. For another night, clouds and light snow over the eastern interior, to include Fairbanks, had a cloud cover that helped keep nighttime temperatures warmer than otherwise would have occurred. Light snow was reported over the Tanana Valley, covering an area that stretched from Fairbanks to the Alcan border. Tuesday was the fifteenth consecutive day that the daily high temperature at Fairbanks had not reached 20 degrees below zero. The longest stretch is eighteen days.
A slowly weakening low pressure system continued to remain essentially stationary in the northern Gulf of Alaska. Clouds and precipitation associated with this system were found over Southeast Alaska and the Panhandle. Farther west, another storm system was located in the western Bering Sea, with a trailing cold front that crossed the Aleutian chain. The storm system brought warm air northward across the central Aleutians. As this front moved eastward, rain fell ahead of the system while a mixture of rain and snow fell in the wake of the system.
The low ambient air temperatures meant that even with relatively weak winds, extremely low wind-chill equivalent temperatures cod result. With dangerously low wind-chills anticipated, wind-chill warnings were issued for the Kotzebue Sound, the Seward Peninsula and the passes of the Alaska Range. Selawik, located to the east of Kotzebue Sound, had the lowest wind-chill equivalent temperature on Tuesday with 97 degrees below zero. Winds produced by the strong pressure gradient between the high pressure center in central Alaska and the low over the Gulf helped produce blizzard conditions in the Alaska Range and along the west coast as blowing snow reduced visibility.
Tuesday's overnight lowest temperature across Alaska was 62 degrees below zero at Bettles , while the mid-afternoon high in the state was 37 degrees at Adak.
HAWAIIAN WEATHER -- The northeast trade winds over the islands slackened on Tuesday as the ridge of high pressure to the north of Hawaii weakened. Trade wind showers were relatively light and widely spaced. The southern end of a mid-latitude cold front approximately 700 miles northwest of Kauai is expected to move south and affect the islands during the later part of the week. Small craft advisories remained in effect for state waters.
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 Online Weather 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.
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.