Welcome to the month of December, named from the Latin word "Decem", for the number ten, representing the tenth month of the year in an early Roman calendar that commenced at the vernal equinox in March. Today also marks the beginning of meteorological winter, the standard three-month interval (December, January and February) used by meteorologists for describing seasonal events.
WEATHER OVER THE WEEKEND -- Many areas of the nation experienced relatively tranquil weather at the start of the four-day Thanksgiving Day weekend. However, a storm system moved into the Southwest last Wednesday, bring wet weather to southern California, Arizona and southern Nevada. This storm system traveled eastward across the southern tier of states at the end of the week. By late Saturday an active front extended across the Gulf Coast States. This front ultimately developed into a storm system that dominated the weather across eastern section of the nation by Sunday afternoon, causing travel problems for many holiday travelers returning home.
On Sunday, severe thunderstorms were reported across the Florida Peninsula to the south of the frontal boundary. An unconfirmed tornado that produced some damage to a vehicle was reported during the early afternoon near Walt Disney World theme park outside of Orlando. Straight-line thunderstorm winds also caused damage to some mobile homes, as well as downing trees and power lines in various scattered locations across the northern and central sections of the Sunshine State.
WEATHER FOR THE START OF THE NEW WEEK -- The following highlights of the national weather have been extracted from the surface weather map for late Sunday night.
Clouds along with a variety of precipitation types covered approximately the eastern third of the nation on Sunday evening. Satellite imagery (as indicated by the accompanying insert) showed a large comma shaped cloud shield extending from the Mississippi Valley eastward to the Atlantic and from the New England southward to Florida. Radar and surface reports indicated widespread rain across southern New England, the Middle Atlantic States and coastal sections of the Southeast. Snow was falling across the Great Lakes, Midwest and northern sections of Upstate New York and New England. Some areas of freezing rain and ice pellets (or sleet) were found in the transition regions between the rain and snow, especially in New England.
These clouds and precipitation were associated with a large storm system moving northeastward from the lower Mississippi Valley to the eastern Great Lakes. During its travel, the storm underwent a typical occlusion process. By Sunday evening, the storm consisted of a pair of low pressure centers located over northern sections of Indiana and Ohio, along with several weaker low pressure centers along the Eastern Seaboard that had formed along the accompanying warm front. An occluded front curved southeastward from the primary low pressure system near Toledo, OH to a point of occlusion and one of the weak secondary low pressure features over the Piedmont of North Carolina. At this triple point or point of occlusion, a warm front extended to the northeast along the Middle Atlantic coast, while the cold front continued southward across coastal sections of the Carolinas, Georgia and northern Florida.
The widespread rain across the Middle Atlantic and southern New England States and the snow across New England were overrunning precipitation along the storm's warm front. To the north and west of the primary low pressure centers, the snow across the Great Lakes and the upper Mississippi Valley was wrap around precipitation, enhanced by cold air traveling across the relatively warm waters of the Lakes on northeast winds. Well to the southeast of the storm's center, a squall line, consisting of a linear arrangement of strong to severe thunderstorms, had developed across the Florida Peninsula in the storm's warm sector more than 100 miles to the east of the cold front. By late Sunday evening, most of the thunderstorms had moved out over the Atlantic and dissipated, leaving a few lingering thunderstorm cells over the northern Bahamas.
The storm was forecast to continue its travel to the northeast on Monday. One of the primary low pressure centers was expected to reach cross southern Lake Huron by sunrise and reach central Quebec by evening. The accompanying frontal system should continue sweeping to the east and north across the Eastern Seaboard during the morning, moving off the coast by afternoon. An area of rain should linger along the Middle Atlantic and southern New England coasts through Monday, while a variety of winter precipitation types that include freezing rain, ice pellets and snow should continue across northern New England and Upstate New York through the morning. Winter weather advisories were in effect through midmorning on Monday across a large section of the Northeast, extending northward from northern Pennsylvania to northern Maine. While one to three inches of snow were forecast for interior and elevated sections of New England, freezing rain and ice pellets were anticipated to make travel difficult as warm air was forecast to bring rain northward over a shallow dome of subfreezing air over New England. Some of the advisories across New York State were to extend into Tuesday due to lake-enhanced snow, with some locations downwind of Lakes Erie and Ontario receiving up to seven inches.
Farther to the west, lake-enhanced snow was forecast to continue across the Midwest southward across the upper Ohio Valley to the southern Appalachians of east Tennessee as cold air continues to stream southward across the Lakes on northerly winds. A variety of winter storm warnings, winter weather advisories and lake effect snow advisories blanketed the eastern Wisconsin, northern Illinois, the eastern sections of Michigan's Upper Peninsula, nearly the entire Lower Peninsula of Michigan and sections of northern Ohio. Depending upon location, some of these warnings and advisories were to extend into the mid to late afternoon of Monday, with additional snowfall that would bring storm total snowfall accumulations to over five to eight inches. Winter storm warnings were also in effect through midday Tuesday as the northerly winds continue to provide lake-enhanced snow and upslope snow across the western slopes of the Smoky Mountains, with some locations potentially receiving between six and eight inches of snow.
In addition to the wintry mix of precipitation, the storm was also generating strong winds. Gale warnings were issued for coastal waters along the New England coast and for several of the Great Lakes, as winds surrounding the storm's center could gust to over 40 mph. Wind and lake wind advisories were also posted for much of Monday across sections of the Southeast due to strong and gusty northwest and west winds following behind the cold front that had passed across the region.
In contrast to the inclement weather across the East, much of the western half of the nation experienced relatively tranquil weather on Sunday evening. A large ridge of high pressure centered over the interior Northwest and Nevada's Great Basin was responsible for the reasonably quiet weather and relatively cloud-free skies that prevailed from the Rockies westward to the Pacific coast. While most of the West had quiet weather, scattered areas of snow fell across the central Rockies in Colorado and southern Wyoming. A weak area of low pressure that developed near the surface across southwestern Wyoming, together with a disturbance in the upper tropospheric winds were responsible for this snow. A winter storm warning and a winter advisory were posted for the northern mountains of Colorado and the northeastern section of New Mexico through early Monday morning.
The high pressure ridge across northern sections of the Intermountain West was forecast to drift southeastward on Monday. By evening, the high pressure center was expected to be located over the Four Corners area of southwestern Colorado and northwest New Mexico. Relatively tranquil weather should continue across most sections of the West. Afternoon high temperatures were on the order of 10 Fahrenheit degrees above the long-term average highs for the end of November.
Some locations in the West will see an end to the quiet weather by Monday evening. Clouds along with rain were forecast to spread across western sections of Washington State and Oregon by late afternoon. These anticipated clouds and precipitation would be out ahead of a storm system that would approach the coast of the Pacific Northwest. In addition, a cold front trailing a low pressure system traveling eastward across northern British Columbia should sweep southward into northern Montana by late Monday evening. This cold front should result in a marked drop in temperature, in addition to snow and strong winds. A winter storm watch was posted for the northern Rocky Mountain Front of northwestern Montana and the adjacent high Plains to the east of the Continental Divide, extending from Monday evening into Tuesday afternoon. Several inches of snow were expected to accompany the strong winds that could gust to 40 mph and the falling temperatures.
UPPER AIR -- The 500 and 300 mb charts for 00Z Monday showed that the storm system over the eastern third of the nation extended upward through the entire troposphere, tilting slightly with increasing altitude toward colder air to the west. A large and slightly elongated height trough was centered over the mid-Mississippi Valley at the 500-mb level, while height trough at 300 mb was displaced slightly to the west. A vigorous counterclockwise circulation surrounded the height troughs at each pressure level. The jet-stream winds at 300 mb entered the country over the Pacific Northwest and then turned southward along the Rockies, circulating around the southern flank of the upper tropospheric trough. Strong northerly winds along the western limb of the trough reached speeds in excess of 150 knots across sections of Wyoming, Colorado and South Dakota. To the east of the trough, a core of jet stream winds from the south and southwest exceeded 150 knots across the Southeast and Middle Atlantic States.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Sunday, the lowest temperature reported in the continental U.S. was 5 degrees at Grayling, MI, while Sunday's highest temperature was 87 degrees at Thermal, CA.
ALASKAN WEATHER -- A large and complex area of low pressure located over southeastern Alaska was beginning to weaken late Sunday afternoon. Several distinct low pressure centers were found, with one center located over Prince William Sound, with another low pressure center had moved across the southeast Panhandle of Alaska and into northwestern British Columbia and southwestern Yukon Territory. A frontal boundary stretched across the northern Gulf of Alaska and adjacent coastal areas of central and southeast Alaska connecting the low pressure centers. The front also served as the boundary between warmer air over the Gulf and colder air across interior Alaska. Some light snow was reported across the Anchorage Bowl and the Matanuska and Susitna Valleys of south central Alaska, while rain fell at Valdez before the cold front passed south and the rain changed to snow. To the southeast, the relatively mild air from the Gulf produced coastal rain along the Panhandle, while some inland locations along the British Columbia border had rain and snow. A powerful storm system was moving eastward across the North Pacific, passing south of the central and eastern Aleutians. This storm was deepening, with a minimum central pressure that had fallen to 964 mb by late afternoon. With a tight pressure gradient surrounding this low pressure center, strong northeast and north winds were reported along the Aleutian chain. Adak and Dutch Harbor had gusts to almost 60 mph. A weak low pressure center along the Seward Peninsula produced overcast skies and light snow across northern and northwestern Alaska.
The lowest overnight temperature in Alaska as of Sunday was 23 degrees below zero at Sleetmute and the midafternoon highest statewide temperature was 50 degrees at Ketchikan.
HAWAIIAN WEATHER -- A weakening wind shear line stalled across the Hawaiian Islands late Sunday afternoon. This shear line represented the southern end of a midlatitude cold front and was accompanied by light south and southeast winds to the south of this line, while east and east-northeast winds remained to the north. Some low clouds and showers associated with the shear line were passing across the region during the early evening hours. These clouds and showers were beginning to dissipate. However, a thin veil of high level cirriform clouds was spreading eastward across Kauai and Oahu. A weak and elongated ridge of high pressure should settle across the Aloha State on Monday and Tuesday, maintaining the light south and southeast winds. Hazy conditions were anticipated as a plume of VOG, or volcanic smog, spreads northwestward from the Kilauea Volcano on the Big Island. Some of the islands should experience daytime sea breeze circulation regimes. The ridge was forecast to move northward by midweek, permitting the return of more typical light to moderate easterly trade winds.
Relatively high surf generated earlier by strong winds continued to affect the north and west facing coasts of most of the islands. A high surf advisory was to remain in effect along these shores into early Monday. A small craft advisory also was continued for the windward waters and the inter-island channels of the western islands.
PUERTO RICO/US VIRGIN ISLANDS WEATHER -- Skies ranged from clear to partly cloudy across Puerto Rico, Culebra, Vieques and the Virgin Islands late Sunday night. Satellite imagery showed patches of clouds moving westward across the Atlantic to the north of the islands. Radar also detected isolated showers traveling across the coastal waters of the Atlantic and along the coastal sections of Vieques, and eastern sections of Puerto Rico. Moderate easterly winds prevailed across the region as high pressure was located across the western North Atlantic to the northeast. This large subtropical high pressure system also was responsible for the stable and generally fair weather across the islands. While this weather pattern was expected to persist through midweek with most of the islands having dry conditions, a tropical wave was forecast to travel westward across the Caribbean Sea to the south of the islands. This westward traveling tropical wave could increase humidity levels across interior sect ions of Puerto Rico, resulting in an increased in shower activity.
Increased east to northeasterly winds were expected to cause higher wind-driven seas on Monday, which could necessitate the posting of small craft advisories on Monday.
WATCH THE EVENING SKIES-- Tonight, Venus, Jupiter and a thin crescent moon should form a nice grouping in the southwestern sky just after sunset. So, if you have clear skies, look for this astronomical spectacle. [Editor's note: This reporter thanks Professor Jim Lattis of the University of Wisconsin-Madison's Space Place for this information. EJH]
EYE ON THE TROPICS -- No organized tropical cyclones were detected across the North Atlantic and eastern North Pacific basins on Sunday evening and no cyclone development was anticipated through Tuesday. See this week's Weekly Weather and Climate News for discussion of tropical weather activity over the North Indian Ocean this past week.
HURRICANE SEASONS REVIEW -- The official 2008 hurricane season in both the North Atlantic and North Pacific ended yesterday, 30 November 2008. As a quick review of this year's statistics consult Monday's optional Supplemental Information.
For those who are interested in obtaining historic hurricane information, the "Historical Hurricanes Mapping & Analysis Tool" developed by NOAA allows the search and display of detailed tropical cyclone data and coastal population trends based upon a data set that runs from 1851 to 2007.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
Return to DataStreme Atmosphere website
Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
© Copyright, 2008, The American Meteorological Society.