The following highlights of the national weather have been extracted from the surface weather map for Tuesday night:
UNSETTLED WEATHER CONTINUES SPIN THROUGH MIDWEST -- A large swirl of clouds accompanied by scattered areas of rain covered a large area in the central and eastern sections of the nation on Tuesday evening, as slow-moving storm moved northward across the mid-Mississippi Valley. As of early evening, the storm's low-pressure center was located near the St. Louis metropolitan area of east central Missouri. This storm had traveled northward by less than 200 miles since Tuesday evening. The slow and somewhat erratic track northward was due to the upper tropospheric flow around this system being cut off from the main westerly steering currents. During its northward travels, the storm underwent an occlusion process, with the faster moving cold front overtaking and merging with the slower moving warm front, resulting in the development of an occluded front. By evening, this occluded front curved southeastward from the low-pressure center and then southward to a point of occlusion near the Atlanta metropolitan area of northwestern Georgia. A warm front stretched southeastward from this point of occlusion or triple point, while a cold front continued southward across the western Florida Panhandle to the Gulf of Mexico.
As the storm traveled northward, drier air was entrained into the system, resulting in a reduction in the amount of precipitation. Between one and two inches of rain fell across sections of Illinois and Indiana on Tuesday, according to radar estimates. These totals were less than some of the totals that had fallen on Monday. Sufficiently warm air was brought into the system that the snow that had accompanied the system earlier had changed to rain.
The storm was forecast to continue its slow travel northward on Wednesday. The storm's low-pressure center was expected to travel north and even to the north-northwest, reaching northeastern Missouri by evening. The northern sections of the occluded front were expected to continue moving north toward the southern Great Lakes. Southern sections of the front should move eastward across the Southeast. Therefore, the main area of precipitation was expected to be across the Southeast in the vicinity of southern sections of the front. Over one inch of rain could fall across the southern Appalachians in northeastern Georgia and the western Carolinas during the 24 hours ending Wednesday evening. Up to one half inch of rain could fall across sections of the Midwest on the north side of the storm, where the flow of humid air from the Gulf would be diminished.
COLD TO THE SOUTH, RECORD WARMTH TO THE NORTH -- A large area of high pressure was producing relatively tranquil weather across the Plains and the Rockies on Tuesday. The presence of this high and the circulation around it provided for cooler than average weather conditions across the southern Plains, but above average temperatures across the north. Afternoon high temperatures across the Ozark Plateau and the southern Plains were 5 to 10 Fahrenheit degrees below the average highs for mid November. Clouds associated with the storm over the mid-Mississippi Valley also contributed to the below average temperatures. Farther to the north, southwesterly winds across the northern Plains were being heated as they flowed downslope. High temperatures across the Plains of eastern Montana and the Dakotas were as much as 20 Fahrenheit degrees above the averages for this time of year. More than one dozen high temperature records across eastern Washington, Idaho and Montana were either tied or broken on Tuesday.
With clear skies and weak winds associated with high pressure, radiative cooling of the nighttime air should cause temperatures to fall across the Plains. Where the growing season had not ended, freeze warnings were posted for Wednesday morning across sections of the southern Plains, extending from south central Kansas southward to the Hill Country of south central Texas.
STORMY WEATHER CONTINUES ACROSS THE NORTHWEST -- Clouds along with several bands of precipitation covered much of the Northwest along with northern California on Tuesday evening. Coastal and low elevation rain was detected moving northeastward across the region, while snow was confined to the higher elevations of the Olympics, the Washington and Oregon Cascades, California's northern Sierras and the northern Rockies of Idaho and Montana. These clouds and precipitation were associated with another cold front in a recent series that had reached the coast early Tuesday morning and moved inland during the day. As of early evening, this cold front, which trailed from a low-pressure system over northern Alberta, stretched from northwestern Montana southwestward to near San Francisco Bay in northern California.
Locally heavy precipitation accompanied the front. Over two inches of rain were reported along coastal sections of Oregon as of late Tuesday evening. Strong winds also accompanied the front. Winds gusted to 74 mph along the southern Washington coast on Tuesday morning. Farther east, winds gusted to over 60 mph along Montana's Rocky Mountain Front near the east entrance to Glacier National Park.
After sections of the cold front stall early Wednesday across the Intermountain West, the cold front was forecast to continue traveling eastward later Wednesday. By evening, the front should stretch from the western Dakotas southwestward to the lower Colorado Valley separating California and Arizona. Scattered areas of precipitation should continue to fall across the region, primarily associated with the orographic lifting of the southwesterly winds following behind the cold front. Some of the heaviest precipitation should be found across the western Washington during the afternoon as a warm front associated with a new storm approaches the coast. Between one and two inches of liquid-equivalent precipitation was forecast to fall across the Olympic Peninsula and coastal sections of Washington during the 24 hours ending late Wednesday afternoon. Elsewhere across the Northwest, up to one half of an inch of precipitation was possible, primarily along the northern Sierras in California and the mountains in Idaho's Panhandle.
The new weather system that will affect the Pacific Northwest was a storm with a low-pressure center moving across the southern Gulf of Alaska on Tuesday evening. By Wednesday evening, the low-pressure center would be located over Queen Charlotte Sound along the British Columbia coast between Vancouver Island and the Queen Charlotte Islands. At the time, a frontal system accompanying this storm would approach the Washington and Oregon coasts. Since the storm's center was forecast to deepen, reaching a minimum central pressure between 970 and 975 mb, strong southerly winds should precede the arrival of the front later Wednesday evening. This new front will continue to affect the region into late Thursday.
A winter storm watch was posted for the western slopes of Washington's northern Cascades beginning Wednesday afternoon and running through Friday morning. Anticipated snowfall totals ranged between one and two feet at elevations above 4000 feet. The strong winds, relatively warm air and the precipitation being brought across the Olympics and Cascades in northern Washington in association with the approaching front could increase the avalanche danger on Wednesday. Therefore, an avalanche watch was posted for late Wednesday for the western slopes and passes in the Olympics and the North Cascades.
Storm warnings were posted through late Wednesday for the coastal waters of Washington and northern Oregon, extending from Cape Flattery, WA southward to Cascade Head OR. South to southwest winds should gust to 60 mph as the next cold front arrives. Farther south, storm warnings will be posted on Wednesday and run through Friday afternoon for the coastal waters of southern Oregon and northern California to as far south as Point Arena. In addition, a high wind watch was in effect for the coastal communities along the southern Washington and northern Oregon coasts for Wednesday afternoon and evening due to southerly winds gusting to 70 mph along some of the beaches and headlands.
UPPER AIR -- Both the 500 and 300-mb charts for 00Z Wednesday showed the vertical structure of the storm system over the mid-Mississippi Valley. A height trough encircled by closed circular height contours was found on both charts, indicating a relatively cold column of air that extended upward through the entire troposphere. The centers of these "cutoff lows" were over southeastern Missouri, resulting in what is often called a "vertically stacked system", where the centers are directly over those at pressure surfaces lower in the atmosphere and the surface low pressure center. This situation is common to occluding storms. The circulation of the winds at each level was in a counterclockwise direction around the center of the trough. In addition, this vertically stacked circulation feature was detached from the upper tropospheric westerly winds that were displaced far to the north over southern Canada. This detachment of the system from the larger scale circulation regime led to its sluggish movement.
YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Tuesday morning's lowest temperature was 13 degrees below zero at Lake George, CO, while the highest temperature on Tuesday was 86 degrees at Pembroke Pines, FL and Riverside, CA.
ALASKAN WEATHER -- A large ridge of high pressure centered over Far Eastern Russia stretched eastward across western and northern Alaska late Tuesday afternoon. This high-pressure ridge was accompanied by an arctic air mass that stretched across a large area of mainland Alaska. Subzero temperatures were reported during the afternoon across sections of northern and interior sections of the state. While relatively cloud-free skies were reported across western Alaska, some snow was reported across interior sections of the state. The southern edge of the arctic air mass was a stationary front that stretched along coastal sections of southern Alaska, from the Kenai Peninsula eastward to northern sections of the Panhandle. To the south, a large area of low pressure with multiple low-pressure centers remained over the northeastern Gulf of Alaska and over southeastern sections of the 49th State. Snowshowers were found across the Panhandle. A tight pressure gradient across sections of south central Alaska produced strong and gusty winds, such as gusts to 57 mph at Whittier. Farther west, a front accompanying a weakening storm over the Bering Sea stretched across the eastern Aleutians, where snow was reported.
The high temperature at Cold Bay was only 26 degrees on Tuesday, which represents a new daily low high temperature record.
The low ambient air temperatures due to an arctic air mass, coupled with strong winds were generating dangerously low wind-chill temperatures. Therefore, wind-chill advisories were in effect through late Thursday morning for the Susitna Valley between Talkeetna and Denali National Park and for Thompson Pass in the Chugach Mountains northeast of Valdez, as wind-chill temperatures could fall to 45 degrees below zero.
The sun will set at 1:39 PM Alaska Standard Time today (18 November 2009) at Barrow, the northernmost city in Alaska, for the last time this year. The next time the sun will rise above the local horizon in Barrow will be at 1:01 PM AST on 23 January 2010. While the sun will be below the horizon for the next 66 days, residents of this city will have roughly three hours of some diffuse sunlight each day that is equivalent to civil twilight, provided the cloud cover is not too thick.
The state's lowest overnight temperature on Tuesday morning was 45 degrees below zero at Tanana. The highest temperature by mid afternoon of Tuesday was 43 degrees at Adak and Atka.
HAWAIIAN WEATHER -- Moderate to strong easterly trade winds persisted across the Aloha State on Tuesday afternoon. Low clouds and scattered rainshowers were being carried across the region by these winds, primarily affecting the windward slopes of the islands. Since the trade winds were relatively strong, some of the showers were carried to the leeward sides of several of the smaller islands. An upper tropospheric pool of cold air over the region helped destabilize the lower troposphere, which contributed to the formation of the convective type clouds and showers. The air mass across the region was also sufficiently humid to support the showers. The moderate to strong trade winds were caused by a tightened pressure gradient across the islands due to a strong high pressure ridge approximately 1200 miles north of Kauai and the low pressure trough associated with the Intertropical Convergence Zone near the equator. While the tight pressure gradient across the islands should begin to relax by Wednesday, resulting in slightly weaker winds, the relatively breezy and wet trade wind pattern should remain across the region through at least Thursday. The air mass should begin drying, resulting in fewer showers.
The strong trade winds were producing high seas that were being detected by the instrumented buoys moored in the waters surrounding Hawaii. These seas were expected to peak late Tuesday night or early Wednesday and then decrease slowly. Therefore, small craft advisories due to the strong winds and high seas were to be continued for all state waters through Wednesday. The wind driven seas also produced high surf with heights exceeding eight feet along the east facing shores of the islands, where a high surf advisory was to remain in effect until Wednesday evening.
PUERTO RICO/US VIRGIN ISLANDS WEATHER -- Skies were partly cloudy across Puerto Rico, Culebra and Vieques on Tuesday evening, while variably cloudy conditions were reported over the Virgin Islands. Radar detected isolated to scattered showers traveling to the north-northeast across the waters of the Caribbean and the Atlantic surrounding the islands, while a few isolated showers were found over the islands. The clouds and showers were associated with a weak trough of low pressure that was located over eastern Hispaniola and the Atlantic waters to the west and northwest of Puerto Rico. While surface winds were relatively light and from the south to southwest, winds from the southwest to west-southwest extended upward through the lower to mid troposphere. This change in wind direction with height help bring drier air across Puerto Rico. The drier weather should prevail across the islands through the remainder of the weak, with the typical isolated to scattered afternoon rainshowers expected to form due to daytime heating.
EYE ON THE TROPICS -- No organized tropical cyclones were detected across the North Atlantic or the eastern North Pacific basins on Tuesday evening; no cyclone development was anticipated through Thursday.
TORNADO SEASON -- With slightly more than one month remaining in the year, more than an estimated 1250 tornadoes have been reported across the United States during 2009, with 22 fatalities. For more information concerning this year's tornado statistics, consult Wednesday's Supplemental Information…In Greater Depth.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast