The following discussion is based upon the major weather features appearing on Thursday night's surface weather maps:
STORM TAKES AIM ON MIDDLE ATLANTIC STATES -- Widespread rain, rainshowers and a few thunderstorms covered a large section of the southeastern quadrant of the nation on Thursday evening. This precipitation shield, which was associated with a developing storm along the central Gulf Coast, extended from the lower Mississippi Valley northward to the lower Ohio Valley and eastward to the Outer Banks of North Carolina. Radar indicated moderate to heavy rain falling over sections of Alabama and the western Florida Panhandle. A few thunderstorm cells were found along the Gulf Coast near Mobile, AL and Pensacola, FL, while additional thunderstorms were detected out over the waters of the northern Gulf of Mexico. Daily maximum rainfall records for the date were set on Thursday at Jackson, MS (2.51 inches); Tuscaloosa, AL (2.03 inches); Waco, TX (1.76 inches). Farther to the north, snow was falling along the northern edge of the precipitation shield, primarily over the higher terrain of the Appalachians from western North Carolina across southwestern Virginia and into West Virginia. Some locations were also reporting freezing rain. Asheville, NC received 3.0 inches of snow, which established a new maximum snowfall record for the date.
The storm that was producing the widespread precipitation across the Southeast consisted of a surface low pressure center that had formed over the lower Rio Grande Valley near Brownsville, TX late Wednesday evening and moved eastward across the northwestern Gulf of Mexico on Thursday. By early evening, the storm's low-pressure center was located off the Mississippi Delta in southeastern Louisiana. The low was situated along a stationary front that stretched along the Gulf Coast, from south Texas eastward to northern Florida. This frontal boundary separated warm and humid air over the Gulf of Mexico to the south from cooler and drier air to the north over interior sections of the Mid-South. A broad southwesterly flow of humid air was found to the east of the surface low, extending upward through the lowest 10,000 feet of the atmosphere. This southwesterly flow was bringing abundant amounts of water vapor from the Gulf of Mexico as well as from the tropical eastern North Pacific. The near surface winds were being lifted over the dome of the cooler and denser air mass north of the stationary front, resulting in the widespread precipitation across the Southeast.
The storm's surface low-pressure center was forecast to travel to the east-northeast on Friday, passing across southwestern Alabama by dawn and to near Augusta in east central Georgia by evening. On Saturday, the low-pressure center was expected to move off the Middle Atlantic Coast near the mouth of Chesapeake Bay, where it will intensify. The minimum central pressure was expected to drop, which would result in a tightening of the pressure gradient surrounding the low-pressure center along with a corresponding increase in surface winds.
On the south side of the storm, locally heavy rainfall totals were anticipated. Between two and three inches of rain were forecast to fall across sections of the Southeast during the 24 hours ending on Friday evening, with the largest amounts running along a band from the Alabama Gulf Coast northeastward across northern Georgia and into the Upstate of northwestern South Carolina. Other locations across the Southeast could receive at least one inch of rain. The anticipated heavy rainfall totals prompted numerous flood and flash flood watches to be posted across the Southeast, extending from the Mississippi Delta of southeast Louisiana to the southern sections of the Del-Mar-Va Peninsula.
Thunderstorm activity could be expected across sections of the Southeast on Friday as warm, humid and unstable air being brought into the southeastern quadrant of the storm would be lifted along the advancing cold front. Southern and central sections of the Florida Peninsula were under a slight risk of severe thunderstorms, extending from late Friday afternoon into the evening. Individual thunderstorm cells or a cluster of thunderstorm cells could develop that could spawn several tornadoes as well as produce damaging straight-line thunderstorm winds.
On the northwestern or cold side of the storm, locally heavy snow could fall, along with a mixture of ice pellets and freezing rain. The plume of humid air would be lifted over the dome of cold air associated with high pressure that was centered over the eastern Great Lakes and the central Appalachians on Thursday evening. This cold air would remain trapped along the Appalachians as the humid air would flow to the northeast ahead of the developing storm. Forecasted storm total snowfall from the storm ranged from one to two feet in some locations, including the nation's capital, Washington, DC. In addition to the southwesterly flow of humid air from the Gulf, northeasterly to easterly surface winds would be bringing additional humid air from off the western North Atlantic warmed by the Gulf Stream. This humid air would be carried up over the cold air in the higher terrain of the Piedmont and the Appalachians. Numerous winter storm warnings and winter weather advisories were posted across a large swath north of the projected storm track, extending from the southern Indiana in the Ohio Valley eastward to the New Jersey along the Middle Atlantic Coast. The warnings and advisories across the western sections of the affected area would run through early Saturday morning, while those farther to the east would run through Saturday evening. A blizzard warning was issued for coastal sections of New Jersey running from Friday afternoon through Saturday evening, as some locations could experienced visibility less than one quarter of a mile in heavy snow and blowing snow caused by strong northeast winds.
WINTRY WEATHER ACROSS THE NATION'S MIDSECTION -- Light snow was falling across the central and northern Plains along with sections of the mid and upper Mississippi Valley on Thursday evening. A disturbance in the westerly wind flow at altitudes ranging between 20,000 and 30,000 feet were responsible for this widespread snow.
Scattered areas of snow were expected to remain across the Plains and sections of the Midwest through Friday. Winter weather advisories were posted across eastern Montana, the Dakotas, Nebraska, Kansas, Minnesota, western Iowa and Missouri.
Fog and freezing fog advisories were posted across a large section of the southern Plains and the Ozark Plateau, covering most of Oklahoma, along with the Texas Panhandle, west Texas and northwest Arkansas.
MULTIPLE STORMS TO HIT CALIFORNIA -- A broad area of low elevation rain and mountain snow was spreading across the West Coast early Thursday evening, extending from coastal sections of central California northward to Washington State's Olympic Peninsula and eastward across the Sierras and the Cascades into the Great Basin of northern Nevada and southern Idaho. This precipitation was associated with the first of two storms that were expected to hit the West Coast during the first half of the weekend. This first storm consisted of a low pressure center that was located approximately 400 miles west of the mouth of the Columbia River and a frontal system that extended to the south-southeast along the Oregon and California coasts. A second storm was moving eastward across the North Pacific. As of late Thursday afternoon, the low-pressure center was approximately 1000 miles west of San Francisco Bay along the central California coast.
The cold front associated with the first storm was forecast to move onshore along the California and Oregon coasts before dawn on Friday morning. By evening, northern sections of the front were expected to dissipate, while southern sections of the front would travel across the central and southern Sierras in California. The second storm would reach the central California coast early Saturday morning. Widespread precipitation in the form of coastal rain and mountain snow was anticipated. Between one and two inches of liquid equivalent precipitation were forecast to fall across coastal sections of central and northern California in addition to the western slopes of the Sierras during the 24 hours ending on late Friday afternoon. Farther to the north, precipitation totals between one half and three quarters of an inch were expected for that same time interval. This precipitation would be associated with the first storm.
Snow levels were expected to drop with the initial storm. Winter storm warnings and winter weather advisories were in effect along the Sierras and other mountains of California, stretching from the Siskiyous in the north to the Tehachapis in the south. Some of the warnings and advisories in the northern mountains were to run through late Friday morning, while those farther south were to continue into Saturday afternoon. While the snow from the first storm should taper off on Friday, additional snow from a second storm could result in up to two feet of snow along the northern Sierra by Saturday morning. In addition to the snow, strong winds could gust to 75 mph near the crest of the Sierras.
SUPER SUNDAY FORECAST -- The National Football League's Super Bowl will be held in Miami, FL on Sunday evening between the Indianapolis Colts and the New Orleans Saints. Forecasted weather conditions in Miami would appear to be nearly ideal for the game, with fair skies, temperatures at kickoff expected to be in the upper 60s and light north winds.
TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 12 degrees below zero at Watertown, NY, while the day's highest temperature was 81 degrees at Naples, Key West NAS and Miami (Kendall-Tamiami), FL.
ALASKAN WEATHER -- Skies across a large section of mainland Alaska were partly cloudy late Thursday afternoon because of a ridge of high pressure that extended eastward across the state and southeastward across the Bering Sea from a strong high pressure cell that was centered over Siberia. A weaker high-pressure ridge was also located over northwestern Canada. An arctic air mass accompanying the high-pressure ridge was positioned across the state. Locations across northern interior Alaska reported afternoon temperatures that were in the mid 20s below zero. Northwest winds along Alaska's northern coast were responsible for clouds and snow along the coast and sections of the North Slope. Clouds and precipitation continued across coastal sections of southern Alaska in association with a weak area of low pressure located over the northwestern Gulf of Alaska near Kodiak Island. This low-pressure center was located on the remnants of a weakened stationary front that extended eastward across the northern Gulf to the northern Panhandle and then across northern British Columbia to the southeast. This frontal boundary separated the cold arctic air mass over interior Alaska from a milder and more humid air mass over the Gulf of Alaska to the south. Snow was reported along the Alaska Peninsula, on Kodiak Island, around Prince William Sound and the northern sections of the Panhandle, while rain fell along the southern Panhandle.
A tight pressure gradient was found across Alaska and the Bering Sea, situated between the high-pressure ridge over northwestern Alaska and low pressure over the Gulf of Alaska. Northerly winds across the Bering Sea resulted in gusts to 45 mph at Cape Romanzof and to 35 mph on St. Paul Island in the Pribilofs. Strong winds were also found across south central Alaska, where northerly winds reached 50 mph at Thompson Pass and to almost 40 mph at Seward. A wind advisory was in effect through late Friday evening for the southern inner channels of the Panhandle around Ketchikan as east to southeast winds could gust to between 40 and 50 mph. Farther to the west, wind-chill advisories were posted to run through Saturday morning for the lower Kuskokwim Valley and Delta due to an anticipated combination of northerly winds to 40 mph and ambient air temperatures of 15 degrees below zero that would yield wind chill air temperatures to at least as low as 45 degrees below zero.
The lowest overnight temperature in Alaska on Thursday morning was 42 degrees below zero at Fort Yukon, while the mid-afternoon highest statewide temperature was plus 45 degrees at Annette Island.
HAWAIIAN WEATHER -- Although a dry and stable air mass had spread across the Aloha State on Thursday, low level clouds flowed southward across the islands. Negligible rainshower activity accompanied the clouds that produced mostly cloudy skies by late afternoon. These low clouds were carried southward by northerly near surface winds circulating around an eastward moving high pressure cell that was passing approximately 400 miles north of Kauai. The high-pressure ridge was moving across the waters of the subtropical North Pacific in the wake of a midlatitude cold front that had passed across the islands on Wednesday. Once the center of the high-pressure ridge passes to the east of the islands on Friday, winds should return temporarily to a more typical easterly trade wind direction. Winds were expected to weaken and become southerly in direction on Saturday before another cold front would pass north of the islands early Sunday. The southerly winds on Saturday should result in VOG (volcanic smog) from the Kilauea Volcano on the Big Island being carried across the western islands.
The ocean swell generated by distant storms over the North Pacific was beginning to subside on Thursday, which could result in surf along the coasts of the islands to fall briefly below high surf advisory thresholds on Friday. However, new ocean swell was forecast to reach Hawaiian waters on Friday, which could result in new high surf advisories being posted to run from Friday night through Saturday night.
PUERTO RICO/U.S. VIRGIN ISLANDS -- Skies ranged from clear to partly cloudy across Puerto Rico, Vieques, Culebra and the Virgin Islands through late Thursday night. Isolated to scattered rainshowers were detected by radar to be located over coastal sections of northwest Puerto Rico and the local waters of the Atlantic and the Mona Passage. With high pressure located well to the northeast of the islands, a weak pressure gradient had developed across the region resulting in light easterly winds with speeds to 10 mph. The relatively stable air mass was expected to remain across the region through the upcoming weekend, resulting in continued fair weather conditions with isolated light rainshowers.
WHAT WILL THE GROUNDHOG SEE? -- Will cloudy conditions next Wednesday morning (2 February 2011) prevent the groundhog from casting a shadow at early morning celebrations in several locates, including Wisconsin and Pennsylvania? For more details on the significance of Groundhog Day, please refer to Friday's Supplemental Information…In Greater Depth file.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2012, The American Meteorological Society.