Sincerely,
Ed Hopkins
NEW YEAR CELEBRATIONS -- The moon passed through its new moon phase early this morning, officially 0739Z on 23 January (2:39 AM EST or 1:39 AM CST, etc.). This new moon also marks the commencement of the Chinese New Year celebration today, marking the start of the Year of the Dragon. This Spring Festival event continues for 15 days, ending at the time of the full moon (7 February 2012). The Chinese calendar, introduced in 2600 BC by Emperor Huang Ti, is based upon a combination of the lunar and solar cycles. The Chinese New Year's day is the first day of the first month of the Chinese calendar (lunar year 4709), or the first day of the second new moon following the winter solstice (22 December 2011). Therefore, this event varies from 21 January to 20 February on the Western Gregorian calendar. Today also marks the start of the three-day Vietnamese New Year of Tet celebration for the year of the Dragon.
WEATHER OVER THE WEEKEND --Unlike several of the previous weekends, no major winter storms created havoc across the nation over the weekend. However, unseasonably chilly conditions were found across the eastern half of the nation, while mild weather was experienced across the West.WEATHER FOR THE START OF THE NEW WEEK -- The following discussion was based upon the major features appearing on the surface weather maps of late Sunday night.
Other than a few widely scattered snowshowers, relatively cold and dry weather dominated New England and the Middle Atlantic States on Sunday evening, as a large area of high pressure was centered over the Ottawa Valley of eastern Ontario west of Canada’s capital city of Ottawa.
The clockwise circulation of winds around the high pressure system was readily apparent on the evening weather maps. To the east of the high pressure center, winds were out of the west-northwest and northwest across New England. To the south and east of the high, northerly winds (out of the north in accordance with meteorological tradition for naming winds from direction of origin) across sections of the Middle Atlantic coast. To the southwest of the high pressure center, southeasterly winds were reported across the Ohio Valley. West of the high, winds were from the south across sections of the upper Midwest. In this region, the southerly winds were also a part of the counterclockwise circulation around a low pressure system moving across the Canadian Prairie Provinces.
The high pressure system over Ontario was forecast to drift to the south-southeast on Monday, helping to maintain the quiet and cold weather across New England and several of the Middle Atlantic States. As of sunrise, the center of the high was expected to have moved into Upstate New York east of Lake Ontario. By evening, the high was to have moved out over the waters of the North Atlantic offshore of New York State’s Long Island.
A large area of clouds and precipitation was spreading eastward from the Mississippi Valley into sections of the Midwest and the Southeast on Sunday evening. Snow was falling across the Midwest north of the Ohio Valley, while the rain was primarily detected south across the Tennessee and lower Mississippi Valleys. These clouds and precipitation were associated with a complex low pressure system located over the Mid-South. Several separate low pressure centers were part of the low pressure system. The main low pressure center was situated near Shreveport in northwestern Louisiana, while a second low pressure center was located over south central Missouri. A nearly stationary warm front extended eastward from the main low pressure center across the lower Mississippi Valley, while a cold front trailed to the south-southwest across eastern and southern sections of Texas.
The low pressure system was forecast to move to the north-northeast on Monday. By morning, the low was to have moved into southwestern Illinois and by evening, the low should have consolidated with a low pressure system from over the Canadian Prairie Provinces moving eastward across the Great Lakes. Precipitation associated with the low should continue across sections of the Midwest. A winter weather and a freezing rain advisory were posted through midmorning on Monday across sections of southern and central Illinois. Freezing rain and freezing drizzle were expected, as rain and drizzle formed in the relatively warm air several hundred feet above the earth’s surface would fall into a shallow layer of subfreezing air at the surface, with the rain and drizzle freezing on contact with the surface.
The cold front trailing southwestward to Texas was to move east toward to the Lower Mississippi Valley. A new low pressure center was expected to develop along southern sections of the cold front offshore of the lower Texas Gulf Coast. The new low pressure center could move to the northeast across the western Gulf. A broad area of rainshowers along with several isolated thunderstorms could spread along the upper Texas and Louisiana Gulf coasts. An inch of rain was forecast to fall along the Texas Gulf Coast during the 24 hours ending Monday evening.
Scattered areas of snow were traveling eastward across the Northern Plains and into the upper Midwest on Sunday evening. This snow was out ahead of a warm front that was moving across the Dakotas. The warm front, which was attached to a low pressure center located over southwestern Manitoba, stretched southward across the eastern Dakotas. The counterclockwise circulation of air around the low pressure center meant southerly winds across the upper Mississippi Valley to the southeast of the low pressure center and east of the warm front. However, to the west of the warm front (or to the south and southwest of the low pressure center), winds across the western Dakotas were primarily from the west. These westerly winds were bringing warm air eastward. The warm front marked the eastern extent of this warm air at the earth’s surface. However, the warm air would be lifted above the dome of colder air to the east of the front. As this warm air “overruns” the colder air, “overrunning” precipitation would form, as was the case on Sunday evening over the eastern Dakotas.
The low pressure center over Manitoba was forecast to travel southeastward across southern Manitoba and northern Minnesota early Monday before curving toward the east and moving across Lake Superior by evening. Following passage of the low pressure center, winds should turn to a northwesterly direction and become strong and gusty. Winter weather advisories were to continue through Monday morning across North Dakota and adjoining counties in Minnesota and Montana, as northwest winds gusting to 35 mph could produce blowing snow conditions that would limit visibility to near zero.
Except for some rain moving into the Northwest and some scattered light snow traveling southeastward along the northern Rockies, weather conditions across the West were relatively tranquil. A large area of high pressure centered over Nevada’s Great Basin was responsible for the generally quite weather conditions. Westerly winds from off the Pacific were transporting humid air onshore. The onshore flow was being lifted over the Olympics, Cascades and the Coastal Ranges found in western Washington and Oregon. The lifting of the humid air over these mountain barriers was enhancing the precipitation falling along the west-facing sides of the mountain ranges. Since the air was relatively warm, most of the precipitation was falling as rain rather than snow. To the east, a weak disturbance was traveling southeastward along the Rockies, producing the snowshowers across Montana and Wyoming.
Relatively quiet weather should continue across a large section of the West on Monday, as high pressure remains in control across the Great Basin and the western slopes of the Rockies. A cold front accompanying a storm along the British Columbia coast was expected to approach Washington State’s Olympic Peninsula by late Monday. Coastal sections of Washington could receive over one inch of rain during the 24 hours ending late Monday afternoon.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Sunday, the lowest temperature reported in the continental U.S. was 39 degrees below zero (Fahrenheit) at Embarrass, MN, while Sunday's highest temperature was 84 degrees at North Island NAS, CA.
ALASKAN WEATHER --Clouds were spreading northward across mainland Alaska late Sunday afternoon, replacing the clear to partly cloudy skies that had been across a large section of the state earlier in the day. The clouds moving northward across southern Alaska were associated with a large area of low pressure with two low pressure centers over the Alaska Peninsula and the eastern Aleutians. An accompanying frontal system curved eastward and then southeastward across the northern Gulf of Alaska. In addition to the clouds, some locations along the Alaska Peninsula, the eastern Aleutians and the northern Gulf of Alaska had snow and blowing snow at Dillingham, but rain at Dutch Harbor. Rain was also reported on Kodiak Island and at Juneau. To the north, a large ridge of high pressure stretched across interior and northern Alaska, which was responsible for the relatively cloud-free skies. This ridge extended from Siberia in eastern Russia eastward across the state to the Yukon and Northwest Territories of Canada. The ridge was accompanied by a cold arctic air mass. Afternoon temperatures at some locations failed to reach above 30 degrees below zero. With cloud-free skies across the northern half of Alaska, some locations reported fog as the air near the surface cooled due to the escape of radiation to space. This cooling resulted in fog when as the air became saturated with respect to water vapor. A tight pressure gradient (difference in pressure over a distance) had developed between the high pressure ridge to the north and the low pressure system over southwestern Alaska and the northern Gulf of Alaska. This tight pressure gradient was responsible for the winds that gusted to over 60 mph along the Bering Coast.
The lowest overnight temperature in Alaska as of Sunday was 53 degrees below zero at Bettles, Ambler and Galena, while the midafternoon highest statewide temperature was 46 degrees at Metlakala.
HAWAIIAN WEATHER -- Satellite imagery indicated clouds moving westward across the Big Island and Maui late Sunday afternoon and early evening. These clouds were being carried along by trade winds from the east. These easterly trade winds are the usual prevailing winds across the Hawaiian Islands, which circulate out of the equatorward flank of high-pressure systems usually found across the subtropical Pacific Ocean. An elongated ridge of high pressure was located approximately 400 miles of north of Kauai and Oahu. The easterly trade winds at the surface were moderate in speed. However, winds at altitudes near the summits of the volcanic peaks on the Big Island were relatively strong. The air mass over the islands was relatively dry and stable, as indicated by the little shower activity.
The high pressure ridge was forecast to remain north of the islands on Monday, which would result in a continuation of the moderate trade winds. However, the winds were expected to decrease by late Monday evening as a front located well to the northwest of Kauai moves toward the islands. A wind advisory was to remain in effect for the Big Island summits through Monday afternoon. Some showers should be carried along by the easterly trade winds, affecting the windward (east facing) sides of the islands. The moderate winds were responsible for a small craft advisory for many of the state waters. A high surf advisory was in effect for the north and west facing coasts of Oahu, Kauai and Niihau through early Tuesday morning.
PUERTO RICO/U.S. VIRGIN ISLANDS WEATHER -- Skies became partly cloudy across Puerto Rico, Culebra, Vieques and the Virgin Islands by Sunday evening. The clouds and rainshowers from late in the afternoon had either dissipated or had moved offshore during the early evening. These afternoon clouds and showers were associated with an area of humid air embedded in the trade winds that had passed across the islands. Radar indicated that by late evening, a few isolated rainshowers were traveling westward over area waters, while little significant shower activity was found across the islands. The prevailing winds across the islands on Sunday evening were light and generally from the east. These easterly trade winds were circulating in a clockwise direction around the south side of a large high pressure system located to northeast of the islands. The distance of the high pressure system from the islands, meant that the islands were relatively light.
Drier air was expected to spread to the west across the islands on Monday, which should limit shower activity. However, a few light showers could travel across the islands. Afternoon clouds and showers could develop across the interiors of the islands due to daytime heating.
TOUR OF THE AMS WEATHER STUDIES HOME PAGE -- The AMS Weather Studies home page contains a variety of weather information. To help you get an overview of this page, consult Monday's Supplemental Information…In Greater Depth
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
Return to AMS Weather Studies Homepage
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2012, The American Meteorological Society.