DATASTREME DAILY SUMMARY

Tuesday, 17 October 2000


00Z Weather Systems


UNSETTLED WEATHER ACROSS THE OHIO VALLEY -- A large area of precipitation covered the Midwest northward from the Ohio Valley on Monday night. This precipitation, stretching from the St. Louis (MO) metropolitan area eastward across southern Illinois to southwestern Ohio, was associated with a weak low pressure disturbance that was located along an east-west oriented frontal system. This front extended eastward as a stationary front from the low pressure area located near the Bootheel of Missouri along the Ohio Valley to the East Coast. To the west of the low, the front was in the form of a cold front that trailed southwestward to north Texas. Earlier on Monday, as much as 3 inches of rain fell across north Texas and Oklahoma in association with this system. The inclement weather conditions across Missouri, to include rain and dense fog, may have contributed to the plane crash approximately 25 miles south of St. Louis that took the life of the Missouri governor on Monday evening. Dense fog advisories have been issued for portions of the mid-Mississippi and Ohio Valleys, as the fog has developed and reduced the visibility.

The low pressure system is forecast to move eastward through the Ohio Valley on Tuesday, reaching the vicinity of Louisville, KY by morning and Parkersburg, WV by evening. Between 0.25 and 0.5 inches of rain are anticipated to fall along the Ohio River Valley by Tuesday evening as the system moves eastward.

RAIN ACROSS SOUTHERN TEXAS -- An area of rain continued to fall across east Texas to the south of the cold front that extended southwestward from the Missouri low pressure system. The rain should continue across much of southern Texas as the cold front moves southward from its Monday night position across the northern sections of the Lone Star State. By Tuesday evening the front should stall, becoming a stationary front along the Gulf Coast. At least 0.5 inches of rain could fall along the Rio Grande by evening.

Some thunderstorms continued across west Texas and eastern New Mexico along the western terminus of the cold front on Monday night. During the afternoon, thunderstorms produced wind gusts to 60 mph and large hail near Waco. Hail reaching 1.75 inches in diameter was also reported near Lubbock. Because of the locally heavy rains associated with the thunderstorms, an arroyo and small stream flood advisory was posted to remain in effect until early Tuesday for some of the watersheds near Roswell, NM.

BLUSTERY CONDITIONS ACROSS THE NORTHEAST -- A cool high pressure center over eastern Canada and northern Maine was responsible for a chilly and blustery day across New England and Upstate New York. Afternoon high temperatures across the Northeast were on the order of 10 degrees below the long-term average highs for mid October. Earlier on Monday, some light snow and ice pellets fell across the higher elevations of New England. The cool air pushed southward behind a "back door cold front" on Sunday, causing a noticeable drop in temperatures across the Northeast. Eventually, this cold front stalled, becoming the stationary front that extended eastward from northern Virginia and Chesapeake Bay. This high pressure is expected to remain and maintain cool weather across the Northeast on Tuesday.

WET WEATHER ACROSS THE NORTHWEST -- A warm front associated with a storm system located west of the Washington State coast spread clouds and precipitation across much of that state. The storm system, one of several along a frontal system in the eastern Pacific, is expected to move toward the northeast, reaching the coast of British Columbia north of Vancouver Island by Tuesday evening. A cold front trailing this low pressure system is forecast to move eastward to become located just off the Washington coast at that time. The western slopes of the Olympic and the Cascade Mountains should receive nearly continuous rain through Tuesday as the cold front approaches. As much as one inch of rain could fall across portions of the Olympic Peninsula within the 24 hours ending on Tuesday evening. Following the cold frontal passage on Tuesday night, the cold air that follows should cause snow levels to descend across the mountains. Southwesterly winds should also increase on Tuesday as gusts could reach to near 50 mph along the Washington and Oregon Coasts.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 15 degrees at Fraser, CO, while Monday's highest temperature was 92 degrees at Lake Havasu City, AZ, Thermal, CA and Alice, TX.

ALASKAN WEATHER -- A weakening storm system in the Gulf of Alaska east of Kodiak dominated the weather across a large portion of southern Alaska. A trough line associated with this system extended northeastward from the low center across southeastern Alaska. Clouds and rain were found across southern Alaska from the Aleutians to the Panhandle, where winds gusted to 30 mph. Interior Alaska had some breaks in the overcast. A weak stationary front was located across northern Alaska. Snow fell along the Arctic coast. Barrow and Wainwright experienced snow and freezing drizzle. Port Hope had wind gusts to 43 mph, while Gambell had a 40 mph gust.

The state's lowest temperature on Monday morning was 3 degrees above zero at Anaktuvuk Pass. The highest temperature across Alaska as of midafternoon on Monday was 53 degrees at Shemya.

HAWAIIAN WEATHER -- Typical trade weather continued across Hawaii on Monday because of the subtropical ridge of high pressure located approximately 600 miles north of Honolulu. This weather regime, which is expected to continue through Tuesday, consists of moderate to locally fresh northeast trade winds with speeds ranging from 10 to 25 mph, along relatively cloud-free conditions with the exception of the windward showers. A disturbance or tropical wave moving to the west helped provide the Big Island with heavy rains. Locations near Hilo had as much as 2 inches of rain during the 24 hours ending on Monday afternoon. Residual showers could linger over windward slopes of the Big Island into Tuesday morning as this wave continues moving to the southwest of the islands. Another disturbance approaching to the southeast could brush south of the Big Island by Thursday, increasing the chance of windward showers. Small craft advisories were downgraded to cautionary status on Monday evening.

EYE ON THE TROPICS -- The seventeenth tropical depression developed from a low pressure area in the western Atlantic Ocean between the Bahamas and Bermuda on Monday. As of late Monday night, Tropical Depression 17 had winds of 35 mph and was moving to the east at 3 mph, some 405 miles west southwest of Bermuda. Northeast swells generated by this system are expected along the North Carolina coast by Tuesday, producing waves between 3 to 5 feet in height.

REPORT FROM THE FIELD -- Marie Carter, a DataStreme LIT member from Waldorf, MD, reported on her trip back to her hometown of Hale, MO for a class reunion this past weekend. She said that thunderstorms moved through the farming community, causing considerable wind damage and producing 0.25 inch hail, which led to her comment of "Hail in Hale". Tree limbs caused damage to many buildings as well as to her sister's van. Speculation was that a tornado may have passed within several miles of her sister's farm. Fortunately, no one was injured and the homecoming parade had perfect weather.


CONCEPT FOR THE DAY - SATURATION

The chemical compound that we call water is a unique substance in that it can exist in three phases within the ranges of temperatures and pressures found in the atmosphere. At very cold temperatures, water is a solid, ice, that covers our lakes and puddles. Warm it some and it melts to liquid that covers almost two-thirds of the Earth and falls from clouds above. At all temperatures some water exists in the invisible vapor phase. The transition between these forms is crucial to the conditions we associate with "weather". A volume, even without air in it, has a maximum capacity for vapor that depends on the temperature. As the temperature rises, more ice can sublimate or water can evaporate to provide additional vapor for the volume. As the temperature falls, some vapor must condense back to the liquid or solid form. The maximum amount of vapor in the volume at its associated temperature produces the condition called saturation.

Normally a volume of air is not saturated, meaning that less than the maximum possible vapor is present. Saturation can occur in one of two ways. More vapor can be added to the volume to reach the maximum. This addition is seen just above the spout of a boiling tea kettle, or with so-called steam fog, a version of your breath on a cold day. Generally the atmosphere creates saturation a second way, by cooling the air volume to reach saturation with the amount of vapor originally present. Cooling to saturation can be by one of two processes. Rising air cools as it expands into lower surrounding pressures at higher altitudes. Saturation and clouds can result. Overnight radiational cooling near the ground may create fog.

For more information describing the global hydrological cycle, you may consult the optional material in Tuesday's electronic Supplemental Information .

QUESTIONS:

To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications, Week 6 Chapter Progress Response Form, under section B. Daily Summary.

  1. As the temperature increases, the amount of water vapor in a volume at saturation [(increases) (is constant) (decreases)].
  2. Clouds [(are) (are not)] usually formed by air being cooled by expansion.

HISTORICAL WEATHER EVENTS - 17 October

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.