WEATHER OVER THE WEEKEND -- The East Coast continued to experience unsettled weather over this past weekend due to the persistent storm system that remained close to the Carolina coast for the first half of the weekend before finally migrating away from the coast. The nation's midsection had unseasonably warm weather over the weekend, while farther west, the passage of a cold front resulted in a chilly weekend for residents of the West.
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 and some widely scattered showers continued across northern New England on Sunday evening out ahead of a cold front moving eastward across the Northeastern States. The cold front was associated with a low-pressure center that was moving to the northeast across northern Quebec. By Monday morning, northern sections of the cold front were expected to have moved offshore, bringing a momentary spell of quiet weather to the Northeast.
While northern sections of the cold front were responsible for some light precipitation across New England, central and southern sections of the cold front were more active, with widespread rain and a few thunderstorms. One of the areas of precipitation extended from central Texas northeastward to the southern Great Lakes. Thunderstorms continued into the late evening across central and north Texas in the warm air along the cold front. Another area of precipitation was farther to the west, with rain across sections of the Midwest, while snow was found across the Plains of western Nebraska and Kansas. Several weak low-pressure centers located along the front across southern Missouri and northern Texas contributed to the formation and maintenance of the precipitation.
One of the low-pressure centers located along southern sections of the cold front was expected to intensify and move northeast ward along the front on Monday. By dawn on Monday morning, the low-pressure center was forecast to be located over southern Missouri and by evening, it should have reached southern Illinois. The development and movement of this low pressure center would cause a section of the front to the northeast of the low to become a warm front as warm air moves northward on southerly winds. To the west of the low-pressure center, the cold front would sweep to the southeast toward the central Gulf Coast.
Widespread and locally heavy precipitation was expected to accompany the developing storm over the Mid-South and sections of the Midwest. A large swath of rain should fall from the east Texas northeastward to near the Chicago (IL) metropolitan area, with some locations in Missouri and Illinois near the St. Louis (MO) metropolitan area receiving over two inches of rain during the 24 hours ending on Monday evening. This anticipated rainfall was responsible for flood watches and warnings to be issued through midday on Monday for southern and eastern Missouri along with western Illinois. Some thunderstorm activity could occur on Monday along the central Gulf Coast, as well as over sections of the lower and mid-Mississippi Valleys, in the region out ahead of the advancing cold front. However, no major severe thunderstorm activity was anticipated.
The rain that was falling across the central Plains on Sunday night could turn to snow as colder air is brought into the region early Monday. Therefore, winter storm warnings and winter weather advisories extended eastward across northern Kansas into southeastern Nebraska and northwestern Missouri. These warnings and advisories were to remain in effect through early Monday evening across western sections of the affected areas, but to run into early Tuesday morning farther east. Snowfall totals ranging between two and eight inches were anticipated. Strong winds could result in hazardous driving conditions and reduced visibility in blowing and drifting snow.
Relatively quiet weather was found across the Southeast on Sunday evening, courtesy of a large area of high pressure centered over southern sections of Alabama and Georgia. Relatively cloud-free skies were found across much of the region extending from the Atlantic Coast westward to the lower Mississippi Valley and from the Gulf Coast northward into Tennessee.
High pressure was forecast to remain relatively stationary across the Southeast on Monday, resulting in another day of tranquil weather. The weather also should be favorable for the launch of Space Shuttle Atlantis on Monday afternoon from Cape Kennedy Space Center in Florida.
A coastal flood watch was in effect along the Georgia and Carolina coasts through midmorning on Monday. A combination of high astronomical tides associated with Monday's new moon and the continued ocean swells reaching coastal waters from the storm that had plagued the Middle Atlantic coast over the last week. Some coastal flooding was anticipated in low-lying areas, such as in sections of downtown Charleston, SC.
Some scattered rainshowers were found across western sections of Washington State on Sunday evening. This precipitation was just ahead of a warm front that approaching the Washington and Oregon coasts. The warm front extended southward from a low-pressure center that was located on the northern end of British Columbia's Vancouver Island. Farther to the west, a cold front trailed southwestward across the eastern North Pacific.
The warm front was expected to move onshore late Sunday night, followed by the arrival of the cold front along Washington's Olympic Peninsula during the predawn hours of Monday, as the low-pressure center moves into central British Columbia. By evening, the cold front could stall across western Washington. Eventually, the cold front was forecast to move across the interior Northwest on Tuesday as another low-pressure system traveling across the eastern North Pacific was expected to reach the British Columbia coast.
Locally heavy precipitation totals were expected to accompany the warm and cold fronts, enhanced by orographic lifting as a broad flow of southwesterly winds would bring humid air from off the North Pacific. Over four inches of precipitation was forecast to fall along the Olympic Peninsula during the 24 hours ending late Monday afternoon, while one to at least three inches were possible along the western slopes of the northern Cascades. The warm air being carried onshore should cause snow levels to rise. Therefore, much of the precipitation should fall as rain, while snow would be limited to the highest terrain of the Cascades.
Although locally heavy rains were accompanying the approaching frontal system, strong winds appeared to be an even greater threat associated with this system. A variety of high wind warnings, watches and wind advisories were in effect across much of western Washington and sections of the Oregon coast. These warnings, watches and advisories were to extend through late Monday or into Tuesday, depending upon location. Sustained southerly winds could reach 50 mph with gusts to 80 mph on Monday night in some locations across the region. Gusts to 95 mph were possible on the coastal headlands in Oregon. Storm warnings were also posted for the coastal waters from Cape Flattery, WA southward to Point St. George, CA, along with Washington's northern inland waters, as southwest winds could gust to 60 mph. To the east, high wind warnings and wind advisories were in effect for several scattered areas across the interior Northwest, including the northern Rocky Mountain Front in northwest Montana.
Warm and windy weather along with the additional heavy precipitation that would fall upon the recent snow pack had increased the risk of avalanches across the Olympics and the northern Washington Cascades. Both natural and human triggered snow slides and avalanches were possible along the steep terrain. Therefore, an avalanche warning was in effect across these mountains through Monday.
Relatively quiet weather was found across the Great Basin and the Southwest on Sunday evening due to a large ridge of high pressure that was centered over northern Utah's Great Salt Lake and southern Idaho's Snake Valley. This high-pressure ridge was accompanied by a cool and dry air mass. Northerly winds circulating around the eastern flank of the high was responsible for cold air advection that caused a fall in temperatures across the Southwest on Sunday evening. Some locations across Arizona, New Mexico and west Texas had late evening temperatures that were nearly 10 Fahrenheit degrees below readings taken at the same hour on Saturday night.
The high-pressure ridge was expected to remain stationary across the Intermountain West on Monday. With clear skies and weak winds along with a chilly and dry air mass, early morning temperatures could fall due to radiative cooling. Therefore, frost advisories were in effect for early Monday in the central valleys of California. A freeze watch was in effect across sections of west Texas for early Tuesday morning.
UPPER AIR -- An amplified wind flow pattern was apparent on both the 500 and 300 mb charts for 00Z Monday, due to a deep height trough over the Rockies and western Plains and height ridges over both the East and West Coasts. The height trough over the Rockies was due to cold air moving southward across the region behind the surface cold front. The southwesterly winds in the upper troposphere (300 mb) on the eastern flank of this trough were helping intensify the surface storm by providing a region of divergence that would compensate the inflow into the surface low-pressure center.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Sunday, the lowest temperature reported in the continental U.S. was 7 degrees below zero at Stanley, ID and Lake Yellowstone, WY, while Sunday's highest temperature was 89 degrees at McAllen and Laredo, TX.
ALASKAN WEATHER -- Except for partly cloudy skies across sections of western and sections of central interior Alaska, clouds were found across much of mainland Alaska late Sunday afternoon. The clouds were associated with a large area of low pressure centered over the northern Gulf of Alaska southeast of Seward on the Kenai Peninsula. Snow was reported across eastern sections of Alaska, from the northeastern Gulf Coast northward across the interior around Fairbanks to the eastern Beaufort Sea coast. The fair skies across western and interior sections of the state were attributed to the influence of a large ridge of high pressure centered over Far Eastern Russia. This high-pressure ridge was responsible for an arctic air mass that spread across interior Alaska, where afternoon temperatures were at least 20 degrees below zero. A tight pressure gradient was found across coastal sections of the state and the Bering Sea, between the large Russian high-pressure ridge and the low-pressure area over the northern Gulf of Alaska. This tight pressure gradient was responsible for strong northerly winds that gusted to near 50 mph at Hooper Bay near Cape Romanzof of western Alaska, to 45 mph at Sand Point on the Alaska Peninsula and to almost 40 mph on the Pribilofs.
A high surf advisory was in effect through midday Monday for coastal sections exposed to northerly winds along the Bering Strait, including St. Lawrence Island. North winds to 35 mph should produce 10-foot seas, which could also result in beach erosion.
The lowest overnight temperature in Alaska as of Sunday was 33 degrees below zero at Huslia, while the midafternoon highest statewide temperature was 43 degrees at Annette and Metlakatla.
HAWAIIAN WEATHER -- Moderate to fresh easterly trade winds prevailed across the Hawaiian Islands late Sunday afternoon. Low clouds and scattered rainshowers embedded in this easterly trade wind flow was producing relatively wet weather along the windward sides of the islands along with the mountain peaks. A tight pressure gradient located over the Aloha State with high pressure across the North Pacific to the northwest and the Intertropical Convergence Zone over the equatorial Pacific was responsible for the strong trade winds. The atmosphere remained relatively humid and slightly unstable, permitting shower activity to persist on the windward sides of the islands and even on some of the leeward sides of the smaller islands. By mid Sunday afternoon, rainfall totals ranged between one-quarter to one-half of an inch along the windward Big Island. The high pressure cell located to the north should remain for the first half of the workweek, causing the strong trade winds to continue, with a possible slight increase in speed on Tuesday as the high pressure center passes north of the islands.
Instrumented buoys moored in the waters surrounding the islands reported a continuation of high seas approaching the islands from the east-northeast. These wind-blown seas were continuing to produce large and rough surf along the east facing slopes of the islands, where a high surf advisory was in place through Tuesday evening. The winds and high seas also caused a small craft advisory to be continued for all state waters through at least Wednesday evening.
With moderate to breezy trade winds developing across the region's waters, small craft advisories were posted through Tuesday for all state waters by mid evening for rough, wind-driven seas. These seas could also necessitate a high surf advisory for the east facing coasts of most islands.
PUERTO RICO/US VIRGIN ISLANDS WEATHER -- Unsettled weather, with mostly cloudy skies, numerous rainshowers and isolated thunderstorms were reported across Puerto Rico, Culebra, Vieques, the Virgin Islands and the surrounding waters late Sunday night. The clouds and showery precipitation were associated with the deep storm system located well to the north of the region. In addition, a weak trough of low pressure stretched across western sections of Puerto Rico and surrounding waters. Surface winds across the islands were relatively light due to the weak pressure gradient. Aloft, a general southerly wind flow was bringing humid air northward across the region. Unstable atmospheric conditions should continue into Monday as the deep storm north of the islands remains stationary and southerly winds should persist across the region. Showers and thunderstorms could be expected across the islands.
EYE ON THE TROPICS -- No organized tropical cyclones were detected across either the North Atlantic or the eastern North Pacific basins on Sunday evening; no cyclone development was anticipated through Tuesday.
See this week's Weekly Weather and Climate News for additional discussion of tropical weather activity over the Indian Ocean this past week.
HOLD ON TO YOUR HATS -- The National Weather Service alerts the public to these windy conditions with special advisories, watches and warnings as described in Monday's Supplemental Information…In Greater Depth.
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, 2009, The American Meteorological Society.