WELCOME TO DATASTREME - The Daily 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.
A BREAK IN THE TEXAS HEAT? -- Following many days of triple-digit temperatures, residents in the northeastern portion of the Lone Star State saw some relief as afternoon high temperatures failed to crack the century mark. Dallas-Ft. Worth had a high of 94 degrees. Elsewhere across the state, temperatures did reach 100 degrees or higher as daily record high temperatures were either tied or set on Wednesday at Del Rio (110 degrees), Midland (104 degrees), Amarillo (102 degrees), San Antonio (102 degrees), Austin Bergstrom (100 degrees), Brownsville (100 degrees), Houston Intercontinental (97 degrees). The high at Del Rio also set the September monthly record. Record highs for the date were also reached in Kansas at Garden City (105 degrees), Hill City (105 degrees), and Dodge City (102 degrees) and in Nebraska at McCook (105 degrees). Much of the Southern Plains should experience cooler weather by the end of the week.
In addition to the recent heat wave, rain remained a scarce commodity across the southern Plains as Oklahoma City, OK experienced a record-tying 39 consecutive days without rain on Wednesday, while Dallas-Ft. Worth continued to extend its record number of days without precipitation to 68.
MORE RAIN FOR THE SOUTHEAST -- A stationary front that was oriented in an east-west direction across northern Florida was the focus for some heavy precipitation across moisture-starved sections of the Southeast. This stationary front represented the remnants of a cold front that had moved southward earlier in the week and had stalled along the Gulf Coast. A relatively warm and humid air mass lay to the south of the front, while a slightly cooler and drier air mass was located to the north of the front. As of late Wednesday night clusters of thunderstorms and rainshowers continued over a widespread area along the front, extending from southern Georgia westward to the Mississippi Delta in Louisiana. Nearly 10 inches of rain were reported on Wednesday near Valdosta, GA, and 4 inches fell at Jacksonville, FL. A Doppler-indicated tornado may have been responsible for the thunderstorm damage near Jacksonville.
With little movement of the stationary front anticipated through Thursday evening, the Southeast could see continued precipitation. Between 0.5 and 1.0 inches of precipitation are forecast to fall across portions of the Gulf Coast from Louisiana eastward to southeast Georgia during the 24 hour interval commencing Thursday morning.
RAIN ACROSS THE PLAINS -- A weak region of low pressure and cold front moving eastward across the Dakotas brought rainshowers and thunderstorms to the Northern Plains. Severe thunderstorms produced large hail and winds reaching 70 mph near Huron, SD late Wednesday afternoon. As of late Wednesday night thunderstorms stretched from the Red River Valley separating North Dakota and Minnesota southward into north central Nebraska.
The cold front is expected to continue moving eastward on Thursday, extending across Minnesota by morning and Lake Michigan by evening. The rainshowers and thunderstorms accompanying this front should produce relatively small amounts of precipitation, with little more than 0.25 inches anticipated across the Upper Mississippi Valley and the western Great Lakes.
A COOL DAY IN THE NORTHEAST -- A Canadian air mass associated with the high pressure cell centered over New England on Wednesday evening meant a chilly day across the Northeast. Nighttime temperatures fell as a result of the presence of this air mass, with its relatively dry air, clear skies and weak winds. Record low temperatures were either tied or broken across the Northeast on Wednesday morning in Maine at Bangor (33 degrees) and Caribou (34 degrees), in Vermont at Montpelier (34 degrees) and in New York State at Massena (36 degrees), Syracuse (39 degrees) and Rochester (40 degrees). In the Midwest, record lows were also set at Traverse City, MI (38 degrees) and Ottumwa, IA (44 degrees). During the day, temperatures remained in the 60s even with abundant sunshine.
Since the high pressure cell is expected to drift slowly toward the southeast, another chilly night is anticipated. Frost advisories were issued for the northern counties in Maine as temperatures could dip to near 32 degrees by dawn on Thursday.
ANOTHER CHILLY START IN THE WEST -- An area of high pressure over the Great Basin provided a situation conducive for another chilly night over many locations across the West. Record low temperatures were either tied or set in southern California at Paso Robles (43 degrees), Lancaster (45 degrees) and Chatsworth (50 degrees) and in Nevada at Ely (30 degrees), Eureka (30 degrees) and Winnemucca (31 degrees).
While the air cooled overnight, afternoon temperatures along the West Coast recovered quickly. The position of the high pressure system provided for an offshore wind that prevented the flow of cool air off the ocean.
TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 25 degrees at Stanley, ID, while the Wednesday afternoon highest temperature was 110 degrees at Del Rio and Laredo, TX.
ALASKAN WEATHER -- Much of Alaska experienced clouds with light rain on Wednesday as several regions of weak low pressure were found across the state. A strong storm system moving across the northeastern Gulf of Alaska near Yakutat produced rainy and windy weather across the Panhandle and Southeast Alaska. Several stations to include Skagway and Juneau had wind gusts between 50 to 65 mph. To the west of the storm system, strong winds were also reported along Southwest Alaska and the Alaska Peninsula, where Cold Bay reported a gust to 46 mph.
The lowest temperature in Alaska on Wednesday morning was 30 degrees at Kenai and Umiat. The highest statewide temperature as of Wednesday afternoon was 60 degrees at Klawok.
HAWAIIAN WEATHER -- Clouds began to dissipate across the islands on Wednesday as a wave of low pressure to the south of the islands moved toward the west past Kauai. Some of the moisture associated with this wave may have been remnants of former Tropical Storm John. A large high pressure cell that was located to the northeast of the 50th State is expected to move westward by the end of the week and become stationary to the north of the islands. As a result, the islands should experience a return to the more typical northeast trade winds with speeds ranging between 10 to 20 mph.
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.