WELCOME TO DATASTREME - The Daily Weather Summary file will describe the current weather pattern across the U.S. The Tuesday and Thursday files will also contain the "Concept of the Day" with a question to be answered on the weekly Chapter Response Form. Additional Supplemental Information files will provide optional background material.
SEVERE WEATHER MOVES ACROSS THE MIDWEST -- A cluster of thunderstorms developed along a front that stretched from the Midwest into the Plains on Wednesday afternoon and evening. Some of these thunderstorms became severe as they moved across northern and western Iowa. An unconfirmed tornado was reported southeast of Spencer. Large hail fell in nearly a dozen locations across north central and western Iowa during the evening, with hail sizes ranging from 1 to 1.75 inches in diameter. Thunderstorm winds peaked to 70 mph. As the thunderstorms moved eastward, large hail was reported in eastern Iowa near Davenport, one of the Quad Cities. A severe thunderstorm watch was posted for much of the southwestern quadrant of Iowa, valid through early Thursday morning.
The thunderstorms were associated with a cold front that stretched southwestward from a low pressure center near James Bay in Ontario. The frontal analysis appearing in the satellite image insert indicates that the western portion of the front, stretching along the Iowa-Minnesota border westward into Nebraska was a stationary front. Later analyses indicate that this front became a cold front that was moving southward across Iowa. Before the passage of the cold front, Carroll, in western Iowa, reached a record high temperature of 92 degrees.
A large area of rain with some embedded thunderstorms was found to the north of the cold front, across Minnesota, Wisconsin and portions of Michigan's Upper Peninsula.
The cold front is expected to move eastward and southward on Thursday. The northern portion of the front is forecast to pass across the Great Lakes by morning, while the western portion of the front should stretch across northern Missouri and Kansas. A slight risk of severe thunderstorms continues across essentially all of the Hawkeye State until after sunrise on Thursday as the front moves southward. By evening, the front is anticipated to stretch from the eastern Great Lakes across the Ohio and mid-Mississippi Valleys. During the 24 hours beginning on Thursday morning, a slight risk of severe thunderstorms is anticipated from the Ohio Valley east to the Chesapeake Bay and north to Lake Ontario.
WEATHER IMPROVES ACROSS THE EAST -- High pressure moved eastward across the Great Lakes and Middle Atlantic States in the wake of a cold front that moved off the coast on Wednesday. Cool and drier air replaced the warm and humid air along the East Coast.
WET WEATHER ALONG THE GULF COAST -- Widely scattered rainshowers and thunderstorms were found along the Gulf Coast from south Texas to Mobile Bay in Alabama. These cells were along and to the south of a stationary front that stretched from the Carolinas to central Texas on Wednesday evening. By late afternoon, Galveston had received 3.40 inches of rain, which set a daily precipitation record. Some flooding was reported in Galveston and in Houston, TX.
With the stationary front not expected to dissipate until Thursday evening, widespread rain should continue across the south on Thursday. Numerical weather prediction models indicate that 0.5 to 1.0 inches of rain should fall over coastal Texas and the Florida Panhandle during the 24 hour interval commencing on Thursday morning.
HOT WEATHER IN THE WEST -- A large region of high pressure across the Western States helped maintain relatively hot weather across the West, from the central Plains to Southern California. Afternoon high temperatures on Wednesday were at least 10 degrees above the long-term average highs for this time of year. The infrared satellite imagery insert shows that the Southwest appears dark, indicating hot surface temperatures under relatively cloud-free skies.
Record high temperatures for Wednesday were either tied or exceeded in Goodland, KS (98 degrees), and in Arizona at Phoenix (109 degrees), Organ Pipe National Monument (109 degrees), Safford Ag. Station (103) and Douglas (99 degrees) and Winslow (95 degrees). An offshore wind helped Cuyama and Lompoc in southern California to tie daily high temperature records of 100 and 91 degrees, respectively.
TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 30 degrees at Dillon, CO, while the Wednesday afternoon highest temperature was 114 degrees at Coolidge, AZ.
ALASKAN WEATHER -- Several low pressure systems found in the vicinity of Alaska contributed to the widespread clouds over the state on Wednesday afternoon. One low pressure center was located near Kodiak, with a front that extends southeastward over the Gulf of Alaska to near the Panhandle. A second low pressure system was located over the Chukchi Sea near Point Hope. A third storm system was located in the North Pacific just to the south of the central Aleutians. Most of the precipitation in the state was found across the southern portion of the state, stretching from Cold Bay and Kodiak in the west, through Seward and Whittier to the southeast Panhandle. A weak region of high pressure was found along the Arctic Coast. Some breaks in the overcast were found in the interior.
The lowest temperature in Alaska on Wednesday morning was 23 degrees at Buckland. The highest statewide temperature as of Wednesday afternoon was 59 degrees at Eagle.
HAWAIIAN WEATHER -- The subtropical high pressure cell remained relatively stationary to the north of Hawaii on Wednesday. As a result, northeasterly to easterly trade winds were reported across the islands. In addition, relatively cloud-free weather conditions were found across the islands, except on the windward slopes where trade showers formed. Since the high pressure cell is forecast to remain relatively stationary through Friday, typical trade wind weather with moderate trade winds is expected into the weekend.
EYE ON THE TROPICS -- On Wednesday afternoon Hurricane Florence, a minimal hurricane that was located off the Carolina coast, was downgraded to tropical storm status as its sustained near-surface winds dropped below 75 mph. As of Wednesday night, Tropical Storm Florence had sustained near-surface winds of 70 mph and was moving to the east-southeast at 3 mph, located approximately 525 miles west southwest of Bermuda. While Florence is not expected to reach the U.S. Mainland, waves generated by this system created high surf along the Carolina coast. Two people died in North Carolina, drowning as the result of strong rip currents.
Off the Pacific Coast, Tropical Storm Lane was downgraded to tropical depression status. By Wednesday evening, this system had 30 mph winds and was moving toward the north-northeast at 18 mph approximately 275 miles west of San Diego, CA. Lane generated surf with heights between 10 to 15 feet on south-facing beaches in southern California. This system is expected to dissipate on Thursday.
IN THE NEWS -- The National Oceanic and Atmospheric Administration (NOAA) issued a report on Wednesday indicating that the recently concluded meteorological summer (consisting of June, July and August) was the eleventh warmest nationwide since 1895, the year when a sufficiently dense observation network became available nationwide. While this rank is based on a nationwide average, the Northeast experienced the eighteenth coolest summer since 1895. The Southwest had the second warmest summer on record and the West the tenth warmest June-August.
With the 2000 Summer Olympic Games about ready to commence in Sydney, Australia, the National Climatic Data Center has produced and made available for free electronic download a climatological report for Sydney. This 22 page document can be downloaded by going to the "What's Hot" page and scrolling down to the particular link.
Sel Kerans, Coordinator of Project Atmosphere Australia On-line (a weather education outreach program modeled after the American Meteorological Society's Project Atmosphere), encourages visiting their homepage http://www.schools.ash.org.au/paa and inspecting the page entitled "Weather and Sport Activities: Sydney 2000 Olympics". Students and teachers from any country may email paa-data@rite.ed.qut.edu.au to take part in "Link-up" associated with Project Atmosphere Australia Online.
REPORT FROM THE FIELD -- Tammie Niffenegger, a DataStreme participant from Port Washington, WI, reported on her "new respect for lightning" as thunderstorms moved across southeastern Wisconsin on Monday morning. Apparently, lightning struck the chimney of the school building that she was in, placing a 6 foot hole in the chimney and scattering bricks in all directions. A power surge destroyed 6 computers, including hers, and the network connection. Luckily, no injuries were sustained even as students were leaving the building for lunch.
NOTE: This Concept for the Day is a repeat of that which appeared in the previous week's Thursday Weather Summary.
Frequently, you may hear of a cold air mass moving southward from Canada or of Gulf (of Mexico) air dominating the Midwest. What is an air mass, and how can we detect the presence of an air mass on the surface weather map? Air masses are large volumes of air that are relatively uniform in their horizontal temperature and humidity characteristics. They are generally identifiable by the "Highs" or "H's" written on maps which represent the centers of large high pressure regions. These centers of high pressure are at the same time often locations of the centers of air masses.
Air masses form when air resides over a land or water surface with fairly uniform surface properties for several days or more. The air gradually assumes the temperature and moisture characteristics of that underlying surface. Sooner or later, these broad expanses of "conditioned" air begin to move. Masses of air from northern latitudes are usually cold and termed "polar" while those from southerly latitudes are warm or "tropical". If the surface of the source region were land, the air would probably be relatively dry or "continental", whereas ocean air would be more humid or "maritime".
Coterminous U.S. weather is mainly prone to continental polar air masses from central Canada, maritime polar air masses from the northern Pacific Ocean, or maritime tropical air masses from the Gulf of Mexico and their transitions. While rare, continental tropical air would develop over the desert Southwest and the Mexican Plateau.
For an additional explanation of air masses and their properties, call up the Thursday's optional Supplemental Information .
To be submitted on the lines for Thursday on the Study Guide, Part B, Applications', Chapter 1 Progress Response Form, under section B. Daily Summary (found in Week 1 section of Part B and also on DataStreme Homepage).
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
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URL: datastreme/learn/r_sum.html
Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
© Copyright, 2000, The American Meteorological Society.