A SNOWSTORM MOVES TOWARD THE MIDWEST -- A storm accompanied by snow moved eastward across the Plains from the lee slopes of the Colorado and Wyoming Rockies on Monday. As the system moved eastward, strong winds caused blowing and drifting snow conditions across Nebraska and eastern Kansas. By late Monday evening, snowfall totals across Iowa and Nebraska were as much as 10 inches. At that time the storm sytem consisted of a primary low pressure system that was located over northeastern Nebraska and a secondary low that was situated along the trailing cold front over north Texas. A trough line, representing the axis of a broad area of low pressure, extended northward from the primary low into western North Dakota.
Most of the precipitation associated with the northern low was falling as snow over a broad area of the Northern Plains and the Missouri Valley, from central Missouri northward along the trough line to eastern North Dakota and eastward to the Mississippi River. Some rain fell farther to the south along the Red River Valley in conjunction with the southern system.
By Wednesday morning this storm system is expected to have moved slowly to the east-southeast, with the low pressure center forecast to be situated over northern Missouri. The area of snow should also move eastward into the Mississippi and Ohio Valleys. Snow advisories were posted for the region near St. Louis for three to five inches of snow accumulation.
A COLD DAY ALONG THE EAST COAST -- A cold Canadian high pressure system continued to dominate the weather over the eastern third of the country on Monday. This ridge of high pressure extended southward from a high center over northern Quebec near James Bay to the Florida Panhandle and the Gulf of Mexico as of late Monday night.
In addition to the cold air mass, relatively cloud-free skies were found from the Mississippi Valley eastward to the Atlantic Coast. As a result of conditions conducive for significant nighttime radiative cooling, record low temperatures were set on Monday morning at Jackson, KY (17 degrees) and at Mrytle Beach, SC (28 degrees). Afternoon high temperatures over much of the Eastern Seaboard ranged between 10 and 15 degrees below the 30 year climatological high temperatures for this time of year.
The ridge of high pressure is expected to move slowly to the southeast on Tuesday morning. In anticipation of subfreezing temperatures that could persist for several hours in agricultural areas, freeze warnings were issued for north Florida, to include the Jacksonville vicinity. Temperatures across northern New England were expected to fall to 20 degrees below zero or lower by morning. Wind-chill warnings were in effect for portions of Maine as wind-chill equivalent temperatures were expected to fall to as low as 60 degrees below zero, while wind-chill advisories were posted for southern New England for wind-chill equivalent temperatures of 25 degrees below zero.
THE STORMS CONTINUE IN THE PACIFIC NORTHWEST -- The newest Pacific storm system in the series of storms to batter the Pacific coast made landfall and was moving eastward. As of Monday night, the center of this storm was a low pressure system that could be found over northern British Columbia, together with a trailing cold front that had crossed to the eastern portion of Washington State. While some precipitation was found in advance of the cold front, a large area of precipitation was situated along coastal areas to the west of the departed front.
Earlier in the day, the approach of the storm system had produced high winds, especially along the coast. As the storm system moved inland, the heavy surf that had reached heights of 23 feet along the Oregon coast began to subside, resulting the cancellation of the heavy surf advisories for the Washington and Oregon coasts on Monday evening.
The storm was also accompanied by heavy rain for low-lying coastal areas and heavy mountain snow. Parts of Interstate 90 were closed in Washington's Cascades because of the danger of avalanches. Some locations along coastal Oregon received more than three inches of rain upon already saturated ground, resulting in river flooding . Snow advisories continued overnight for the Oregon and Washington Cascades, where an additional four to eight inches could fall.
By Tuesday morning this storm system should have moved eastward, with the low in western Alberta and the cold front shifted farther east, across the mountains of northern Idaho and western Montana.
TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature in the lower 48 states on Monday was 19 degrees below zero at Marquette, MI. Monday's highest temperature was 80 degrees at Santa Ana, Monrovia and Montebello, CA.
ALASKAN WEATHER -- A large storm system with a low pressure center over the Gulf of Alaska and an accompanying occluded front that stretched over the Panhandle spread clouds and precipitation along the Gulf coast. A dissipating low pressure system remained over the central Bering Sea also was responsible for clouds and precipitation across the Bering Sea and the western Alaska, to include the Alaskan Peninsula. On Sunday, a daily record 7.6 inches of snow fell at Kodiak. Cloudy skies were also found across the northwest corner of the state and along the North Slope.
A cold high pressure cell over the Yukon Territory early on Monday was responsible for maintaining cloud-free skies across interior portions of Alaska. As a result, radiative cooling produced overnight low temperatures that reached 30 below zero near the Alcan border. Windy conditions and air temperatures near zero degrees caused wind-chill equivalent temperatures to remain near 30 degrees below zero across northern Alaska on Monday afternoon.
On Monday morning, the lowest temperature in the state was 33 degrees below zero at Cantwell and Northway. The midafternoon high across the state on Monday was 43 degrees at Sitka.
HAWAIIAN WEATHER --The clouds and showers from the shear line that remained over the islands throughout the weekend began to slowly dissipate on Monday. Light trade winds returned to a more easterly direction. By Monday afternoon, only a few trade showers continued along the windward sides of the islands. Cold conditions were found in the mid troposphere as snow fell on near the summits of the 13,700 foot volcanic peaks of the Big Island early Monday morning. Small craft advisories continued for all Hawaiian waters.
ESTIMATING WARM AIR AND COLD AIR ADVECTION -- For details describing how you can use a surface weather map to determine regions of warm or cold air advection, consult Tuesday's optional electronic 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.