DATASTREME DAILY SUMMARY

Tuesday, 5 December 2000


00Z Weather Systems


ARCTIC AIR SWEEPS SOUTHWARD -- The coldest air of the season was moving across the northern Plains into the Upper Midwest on Monday night. This arctic air mass traveled southward, accompanying a high pressure cell that was located over central North Dakota. The leading edge of the arctic air was a cold front that trailed from a storm system in northeast Canada, crossing the western Great Lakes and the Upper Mississippi Valley before curving westward and then northwestward across the Plains.

The temperature contrast across the front was impressive, with temperatures at 10 PM locally (04 Z) remaining at about 30 degrees in the warm air ahead of the front across southern Wisconsin, while about 250 miles to the northwest near the Twin Cities, temperatures behind the front had fallen to 7 degrees. Some locations in the Dakotas had experienced a 40 Fahrenheit degree temperature fall in 24 hours following frontal passage.

Strong northerly winds also accompanied the frontal passage. These winds were in response to a tight pressure gradient over the western Lakes. The winds coupled with the low temperatures caused wind-chill equivalent temperatures to fall to 30 degrees below zero.

On Monday night the cold front had advanced only as far south as central Iowa. By Tuesday morning the cold front is expected to have pushed as far south as Arkansas and the Red River Valley of north Texas, with eastward movement across the western Lakes to northern Ohio. The southern advance of the front is forecast to stall by late afternoon, while the northern sections of the front should reach the Eastern Seaboard, having crossed the eastern Lakes.

A new snow producing storm system could develop along the cold front over the western Plains on Tuesday afternoon.

LAKE EFFECT SNOW RETURNS -- With cold air sweeping southward behind the cold front, lake effect snow should increase in intensity first across the western Great Lakes and then across the eastern Lakes. Some bands of lake effect snow had formed across Lake Superior and Michigan's Upper Peninsula near Marquette on Monday night following frontal passage and a turn to northerly winds. Some lake effect snow was also detected on the westerly winds ahead of the cold front across northern Lower Michigan near Traverse City. Southwesterly winds found across the southern and eastern lakes were transporting air that was too warm to cause lake effect precipitation.

A variety of winter weather advisories, lake-snow advisories and winter storm warnings covered the counties downwind of the Great Lakes from northern Wisconsin through the Upper and Lower Peninsulas of Michigan, as well as New York State for Monday night extending into Tuesday. Snowfall totals were expected to be on the order of 2 to 4 inches. However, strong winds to 30 mph could reduce visibility in blowing snow and with falling temperatures, wind-chill equivalent temperatures could fall to 40 degrees below zero, especially in the Upper Peninsula. As much as 7 inches of new snow were expected in the typical snowbelt of New York State. A lake-effect snow watch was in effect for Tuesday afternoon and evening for several counties in northwest Pennsylvania.

The strong southwesterly winds that reached speeds to over 40 mph caused a drop in lake level across western Lake Erie to below critical levels for navigation late Monday.

CHILLY WEATHER ACROSS THE SOUTH -- As the new wave of cold air pushes southward across the country, the South was experiencing unseasonably cool conditions on Monday as high pressure was located across the region. The Carolinas were still digging out from the weekend's storm that produced as much as a foot of snow. Record low temperatures were either tied or set at Lynchburg, VA (10 degrees), London, KY (13 degrees), Charlotte, NC (18 degrees), Greenville-Spartanburg, SC (19 degrees), El Dorado, AR (21 degrees) and Dyersburg, TN (23 degrees). A low maximum temperature record was also established at Corpus Christi as the temperature could only reach 49 degrees.

With cold high pressure remaining over the Southeast, a freeze warning was posted for Monday night for southeast Alabama, most of southern Georgia and the inland areas of the Florida Panhandle.

FOGGY CONDITIONS ACROSS THE WEST -- High pressure, a temperature inversion and low-level moist air all combined to maintain fog across the West on Monday. The weak winter sun and the highly reflective fog bank did little to erode the fog in some areas. High pressure across the Pacific Northwest and the Great Basin meant that at night the weak winds and clear skies enhanced the nocturnal radiative cooling of the near-surface layers of air to the dewpoint. The weak winds associated with the high do not allow for mixing and ultimate dissipation of the fog. The temperature inversion with its increased static stability served as a cap thereby inhibiting mixing of drier air downward. Finally, the low-level moisture from proximity to the Pacific Ocean was needed to saturate the air and cause the fog to form.

Fog was once again a problem late Monday and should continue into Tuesday across California, Oregon, Washington and Idaho. Dense fog advisories were posted as the fog reduced visibility to less than one-eighth mile in some locations in the San Joaquin and Sacramento Valleys of California and the Treasure Valley of Idaho. Cloud seeding operations were conducted at the Boise, ID airport late Monday afternoon in an attempt to temporarily dissipate the fog for landing and takeoff operations.

The high pressure along the West Coast did permit the temperature at the Oakland (Museum), CA to reach a record-tying 67 degrees.

UPPER AIR -- The 300 mb constant pressure chart for 00Z Tuesday had a deepening trough in the height of the pressure surface across the Great Lakes, reflecting the pool of arctic air found in the lower troposphere. A strong jet with winds reaching speeds of 110 knots was found around the southern edge of this height trough.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 7 degrees below zero at West Yellowstone, MT, while Monday's highest temperature was 82 degrees at San Diego/Gillespie, CA.

ALASKAN WEATHER -- Arctic air continued to dominate much of Alaska on Monday as high pressure was centered over the Arctic Ocean to the north of the state. Wind-chill equivalent temperatures fell to 69 degrees below zero at Barrow and Deadhorse. Some modification of this air mass was evident as temperatures continued to slowly rise. The only regions not under the domination of the arctic air stretched from the Aleutians and Bering Sea eastward across south central Alaska to the Panhandle. A large and powerful storm system was situated to the south of the Alaska Peninsula. Strong southeasterly winds were found across coastal areas to include Kodiak Island and the Kenai Peninsula. Some rain fell across the Panhandle and the Alaska Peninsula, while Valdez and McGrath reported snow.

The state lowest temperature on Monday morning was 27 degrees below zero at Fort Yukon. The highest temperature across Alaska as of midafternoon on Monday was 45 degrees at Sitka.

HAWAIIAN WEATHER -- An approaching shear line -- the remnants of a cold front -- was within 150 miles to the northwest of Kauai on Monday afternoon. As a result, the clouds and number of showers increased. Trade winds have been weak. However, the shear line is expected to stall and dissipate before actually reaching the islands. As this shear line dissipates, an increase in pressure and winds are expected. The buoy moored to northwest of Kauai indicates that by Monday night the northwest surf should reach 6 feet.

REPORT FROM THE FIELD -- Karyl Rosenberg, a DataStreme participant from Thiensville, WI reported on the relatively infrequent lee side lake effect snow that accumulated last Friday. Most lake effect snow from Lake Michigan falls in Lower Michigan as prevailing winds are typically from the east across the lake. However, with a northeast wind associated with a storm system in the Mississippi Valley, several inches of lake effect snow fell at Thiensville and Mequon, lakeshore communities north of Milwaukee.


CONCEPT FOR THE DAY - COASTAL FLOODING and MARINE WEATHER

A coastal flood occurs when low lying land areas bordering a large body of water are inundated. Coastal flooding may be caused by abnormal rise in water level associated with an approaching ocean storm or by large breaking waves on the shore from large ocean swells. The extent of coastal flooding depends upon the tide levels, the underwater and shoreline topography and the runoff from rivers and estuaries.

Coastal floods are often associated with high water from a storm surge, caused by winds generated by tropical (hurricanes) or extratropical cyclones. Coastal flooding can be produced also by a tsunami, a seismic sea wave produced by earthquakes, landslides or volcanic activity; these waves are erroneously called tidal waves. Alaska, Hawaii and the Pacific coast are most vulnerable to a tsunami.

The greatest danger and damage associated with most tropical cyclones (hurricanes) is the storm surge. A storm surge is a dome of water, perhaps 50 miles wide that sweeps across the coastline ahead of a tropical cyclone landfall. The magnitude of a storm surge depends upon the strength of the storm, the ocean bottom conditions where the surge comes onshore, the storm's movement relative to the shoreline, and the tides at landfall time.

In addition, the destruction of the storm surge is often compounded by the hammering effect of the breaking waves. Because many tropical cyclones produce excessive rainfall rates and total amounts of precipitation even after landfall, they may be also responsible for floods and flash floods. The strong and gusty winds, coupled with the possibility of tornadoes, are added perils to residents of areas near the landfall of a hurricane.

Coastal floods and beach erosion can also be associated with extratropical cyclones, such as the "nor'easters", that may batter the East Coast from Cape Hatteras to Maine, especially during the winter season. Coastal flood watches and warnings are issued by certain designated National Weather Service Offices and pertain to the region extending from the ocean beaches inland, including waterways, estuaries and river mouths.

The National Weather Service issues various public statements for tropical weather systems as well as for other types of situations that can cause coastal floods. These statements follow the advisory, watch and warning format previously described, and they are intended to inform the coastal residents and commercial and recreational marine interests of a potentially hazardous weather situation. A full description of these statements appears in the Tuesday optional Supplemental Information.

QUESTIONS:

To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications', Week 12 Chapter Progress Response Form, under section B. Daily Summary.

  1. The most damaging aspect of a hurricane to coastal inhabitants is usually the [(high wind), (storm surge), (heavy rain), (low pressure)] .
  2. Coastal flooding is not caused by [(tropical systems) (extratropical systems) (normal lunar tides) (tsunamis)].

HISTORICAL WEATHER EVENTS - 5 December

From the files of the Aviation Weather Center, Kansas City, MO and Intellicast


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URL Address: datastreme/learn/t_sum.html
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2000, The American Meteorological Society.