The following discussion is based upon the major weather features appearing on Monday night's surface weather maps:
TWO STORMS AFFECTING NATION'S MIDSECTION -- A variety of precipitation types were found across the Mississippi, Ohio and Tennessee Valleys on Monday evening due to two weather systems that were ultimately expected to consolidate and form a major winter storm that could affect the Northeastern States. Snow was falling across a large section of the Midwest that included the upper and mid-Mississippi Valleys along with the Ohio Valley. This snow was associated with a storm moving slowly across the upper Mississippi Valley. Farther south, widespread and locally heavy rainshowers along with a few thunderstorms were moving across the Mid-South and the Southeast, extending from the lower Mississippi Valley eastward into the Tennessee Valley. The rainshowers and thunderstorms were accompanying a storm moving from the southern Plains into the Gulf Coast States.
The northern storm that brought snow across the Midwest had moved southeastward from the Red River Valley that separates the eastern Dakotas from northwestern Minnesota. By early evening the low pressure center was located over northeast Iowa. This low-pressure center was located on a frontal boundary that curved across sections of the Upper Midwest and out across the central Plains.
At the same time, a low-pressure center had developed over west Texas near El Paso and moved eastward across the Lone Star State on Monday. By early evening, the low-pressure center was located over east Texas to the north-northeast of the Houston metropolitan area. A nearly stationary warm front stretched to the northeast of the low, while a cold front trailed to the southwest across the coastal plain of southeast Texas.
On Tuesday, the two storms would consolidate. The northern storm was forecast to continue traveling toward the southeast, with the low-pressure center reaching the Ohio Valley during the morning hours, while the southern storm would move eastward with the low center reaching the Mississippi Gulf Coast. The cold front trailing the northern storm would become an occluded front and absorb the southern low-pressure center. By evening, the northern low pressure center was expected to be located over central Ohio, while the southern low pressure center would have reached the coastal plain of South Carolina.
WINTRY WEATHER ACROSS MIDWEST -- By late Monday evening, between six and nine inches of snow had fallen across sections of Minnesota and Iowa, while three to four inches of snow fell across sections of Missouri and Illinois. Daily maximum snowfall records were set on Monday across the upper Midwest at Rochester, MN (6.0 inches) and Waterloo, IA (5.4 inches). Farther south, daily snowfall records were set in Arkansas at Jonesboro (6.0 inches) and Little Rock (7.2 inches) and in Tennessee at Memphis (5.0 inches) and Jackson (3.0 inches). This snow was associated with the northern storm. Most of the snow was falling to the east of this low-pressure center and accompanying front. Farther to the north, some lake-enhanced snow was falling across sections of northeastern Minnesota and northwestern Wisconsin due to northeast and east winds off Lake Superior.
A broad area of snow, together with a narrow transition zone of freezing rain, should spread eastward from the Midwest into the Middle Atlantic States on Tuesday. With snow continuing or anticipated, winter storm warnings, winter weather advisories and winter storm watches were in effect for sections of at least 25 states as of late Monday night. The area under the warnings, advisories and watches extended from South Dakota in the west to Cape Cod in eastern Massachusetts in the east and from northern Wisconsin southward to the Arkansas and northern Georgia. Some of these warnings and advisories were to run through late Tuesday morning across the western sections of the affected region, while winter storm watches for southern New England were to run from Wednesday morning through the late night hours. Many areas were expecting between six and ten inches of snow. Locations near the Great Lakes could receive additional snowfall due to lake-enhanced snow. Strong winds could develop in association with the storm, resulting in blowing and drifting snow.
ACTIVE WEATHER TO THE SOUTH -- Southerly winds associated with the developing storm over Texas on Monday brought warm, humid and somewhat unstable air from the western Gulf to the Lone Star State. The influx of humid air near the surface, plus an unstable atmospheric environment in the lower troposphere were two of the ingredients needed for thunderstorm development. A cold front trailing from the low-pressure system provided the necessary uplift to trigger the thunderstorms. The rainshowers and thunderstorms moved quickly from the Hill Country in central Texas to the Houston metropolitan region during the afternoon and evening. One of the thunderstorm cells became severe as it produced up to 1.25-inch diameter hail during the midafternoon between Austin and Houston. By late evening, the thunderstorms had moved from Texas and into interior and coastal sections Louisiana, with most of the activity over the Gulf waters offshore of the state.
Some isolated thunderstorm activity was expected along the north central and northeastern Gulf Coast on Tuesday as the southern low pressure system and accompanying cold front move eastward. This potential thunderstorm activity would more eastward from southeastern Louisiana to the Florida Panhandle during the day. However, no major severe weather outbreaks were expected.
COLD AIR TO FOLLOW -- A large and extended ridge of high pressure was beginning to build southward across the northern Plains on Monday in the wake of the northern storm system. The center of the high was located over northern Manitoba. A cold air mass accompanied this high-pressure ridge, with the leading edge of the cold air marked by the cold front traveling southward. By Monday evening, the cold air had reached as far south as the Panhandles of Oklahoma and Texas. Subzero temperature readings were found across the Plains of eastern Montana late Monday night, while single digit temperatures were found across the Dakotas.
The cold high-pressure center was forecast to continue spreading southward on Tuesday, reaching the Dakotas by evening, with an extension southward into Oklahoma. The cold front was expected to have moved out over the Gulf of Mexico and northern Mexico. Strong winds were expected across the Plains due to a tight pressure gradient between the high-pressure ridge and lower pressure to the west. These strong winds in combination with the cold air should cause wind chill temperatures to fall to dangerous readings. Therefore, wind chill advisories were posted across sections of the north central Montana and northern Nebraska through much of Tuesday morning as wind chill temperatures could fall to at least 30 degrees below zero.
STORMY WEATHER CONTINUES ALONG WEST COAST -- A large area of rain along with some mountain snow was spreading southeastward across northern and central California on Monday evening. This precipitation was in advance of a weakening storm that was approaching the northern California coast from the northwest. During the late afternoon, the system's low-pressure center was located approximately 100 miles off the coast northwest of the entrance to San Francisco Bay.
The low-pressure center located offshore of the California coast and accompanying cold front was forecast to continue traveling southeastward on Tuesday. After arriving onshore during the predawn hours of Tuesday, the low-pressure center was to move along the Coast Ranges of central California during the day. By Wednesday morning, this low was expected to reach the lower Colorado Valley in southeastern California.
A large area of rain and mountain snow was expected to accompany the weak low-pressure system as it travels across central and southern California. Nearly one half of an inch of liquid equivalent precipitation was forecast to fall along the coast and over the western slopes of the mountains during the 24 hours ending late Tuesday afternoon. Winter weather advisories were posted for the mountains in the Coast Range from south of San Francisco Bay to near Santa Barbara through Tuesday evening, as three to seven inches of snow could fall at elevations above 3000 feet. A winter storm warning was in effect from Tuesday noon through midafternoon on Wednesday for the mountains in southern California surrounding the Los Angeles Basin. While nearly one foot of snow could fall across these mountains, higher elevations in the San Gabriel Mountains could receive up to 16 inches of snow Strong winds could reduce the visibility in blowing snow. To the east, winter storm watches were in effect across the southern Sierras, the deserts of southern California and the mountains of southern Nevada. In addition to the snow, some small hail could fall across the coast and mountains from thunderstorms that would develop in an unstable air mass moving into the region. The showers and thunderstorms could also produce locally heavy precipitation late Tuesday at rates ranging between one half inch to one inch per hour. These rainfall rates could result in flash flooding and debris flows in and below the areas of Santa Barbara and Los Angeles Counties burned this past fall by wildfires. Therefore, a flash flood watch was issued for these recent burn areas for Tuesday afternoon and evening.
TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 23 degrees below zero at Jordan, MT, while Monday's highest temperature was unavailable.
ALASKAN WEATHER -- Clouds were spreading north across mainland Alaska in association with a major storm that was moving to the east-northeast across the North Pacific just south of the Aleutian Islands. This complex storm consisted of three low-pressure centers that stretched from the central Aleutians near Adak Island to southeast of Dutch Harbor at the eastern end of the island chain. An occluded front connected the three low-pressure centers. With one of the storm's low-pressure centers having a minimum central pressure of approximately 958 mb, a tight pressure gradient had developed around the storm. This tight pressure gradient was particularly evident across the southeastern Bering Sea, in the region between a ridge of high pressure over Far East Russia's Chukchi Peninsula and the storm's center over the North Pacific. East and northeast winds had developed in response to this tight pressure gradient, with winds gusting to between 60 and 65 mph over the Pribilofs and the eastern Aleutian chain. A tight pressure gradient was also found across the Gulf of Alaska, between a weak ridge of high pressure across the eastern Gulf near the Panhandle and the storm. Strong southerly winds were found across the northern Gulf and over southern Alaska. These winds were bringing the clouds and precipitation northward across the region. Snow fell along the coast and areas along the south facing slopes of the Alaska Range. Rain along with mixtures of rain and snow were reported along the Aleutians and the Alaska Peninsula. Farther east, a mixture of rain and snow fell at Ketchikan in the southern Panhandle. A weak ridge of high pressure extended across interior sections of the state.
A blizzard warning was posted through early Tuesday evening for the region of the Kenai Peninsula near Turnagain Arm and Portage Valley as blowing snow from east winds with gusts to 75 mph along with snow would result in visibility levels less than one quarter of a mile. Winter weather advisories also were issued through Tuesday evening across southwestern and south central sections of the state, from the Yukon and Kuskokwim Deltas to the Susitna Valley. A blizzard watch was in effect through late Tuesday night for the Bering Strait coast and St. Lawrence Island.
The state's lowest temperature on Monday morning was 35 degrees below zero at Barrow. The highest temperature across Alaska as of midafternoon on Monday was 45 degrees at Annette.
HAWAIIAN WEATHER -- Some low clouds and isolated rainshowers were being carried to the southwest across the Aloha State by light to moderate trade winds late Monday afternoon. These trade winds were from the northeast, circulating around the southern flank of a large area of high pressure that stretched across the eastern and central North Pacific to the north and east of the islands. The ridge of high pressure located approximately 250 miles north of the main islands was sufficiently close that a reasonably weak pressure gradient had developed across the region, resulting in the light to moderate trade winds. While the surface winds were light to moderate, winds at altitudes of approximately 14,000 feet that were passing over the volcanic summits of the Big Island were strong and gusty. Northeast winds measured at the Mauna Kea Observatory had wind speeds of at least 30 to 35 mph. A dry and reasonably stable air mass also was associated with the high-pressure ridge. Therefore, typical trade wind weather was found across the islands, with the clouds and light showers affecting the windward slopes of the islands and the higher terrain, while dry weather was found on the leeward sides of the islands. A cold front trailing from a powerful storm over the North Pacific near the Aleutians was moving toward Kauai and the western Hawaiian Islands. This weakening cold front was expected to reach Kauai by late Wednesday and Oahu by early Thursday before it dissipates.
A large and powerful storm well to the northwest of the Hawaiian Islands was generating ocean swell that had propagated to the southeast across the Pacific toward waters surrounding the islands. The ocean swell was expected to cause surf heights to rise above high surf warning threshold levels late Tuesday along the north and west facing coasts of the islands.
PUERTO RICO/U.S. VIRGIN ISLANDS WEATHER -- Skies ranged from partly cloudy to clear on Monday night across Puerto Rico, Culebra, Vieques and the Virgin Islands. Radar indicated a few isolated rainshowers over the offshore waters of the Atlantic, but essentially no precipitation was found over the land areas of the islands. The showers were associated with an approaching cold front that was approximately 100 miles northwest of San Juan on Monday evening. The proximity of the cold front meant that the easterly trade winds across the islands had weakened and become more variable in direction. The cold front was expected to stall north of the islands early Tuesday morning. Since the air mass across the region was relatively dry and stable, generally fair weather should be found across the islands on Tuesday, few clouds and a few isolated showers, which would develop primarily during the afternoon due to afternoon heating of the interiors of the islands.
Weather at a particular location is like one piece of a jigsaw picture puzzle. Observations of atmospheric conditions at one place, just as a single puzzle piece, cannot reveal the whole picture. Weather systems that typically dominate local weather can stretch over areas thousands of kilometers in breadth. Only through the analysis of local observations made at many locations at the same time can these changing and moving systems be delineated. Weather maps permit (1) convenient reporting of numerous single-site observations, and (2) depiction of existing broad-scale "weather makers" resulting from analysis of the observational data.
Local observations are depicted on weather maps as numbers and symbols plotted in, on, and around circles drawn at each station location, forming a "station model". The station model on which DataStreme Atmosphere maps are based can be seen by clicking on the DataStreme Atmosphere website "DataStreme Weather Map Symbols". More details are provided in DataStreme Atmosphere Investigation 2A and Tuesday's Supplemental Information…In Greater Depth.
Weather systems change over time while moving across the earth's surface. Studying recent and current weather maps allows us to follow the progress of weather systems. These maps provide valuable information to the weather forecaster who needs to know what the weather was and is in order to predict what the weather will be.
To be submitted on the lines for Tuesday on the Investigations Manual, Chapter 2 Progress Response Form, under section B. Daily Summary (found in Week 2 section of Investigations Manual and also on DataStreme Atmosphere website).
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, 2010, The American Meteorological Society.