DATASTREME DAILY SUMMARY

Thursday, 4 October 2001


00Z Weather Systems


The following highlights of the national weather have been extracted from the surface weather map for Wednesday night:

TRANQUIL WEATHER ACROSS THE EAST AND SOUTH -- A large high pressure cell centered off the East Coast and extending westward to the western Gulf Coast was responsible for another pleasant autumn day across much of the Eastern and Southeastern States. Skies were relatively cloud-free. While winds were relatively light across the Southeast, a broad southwesterly flow was found across the Mississippi and Ohio Valleys. As a result, afternoon high temperatures across portions of the Ohio Valley, the eastern Great Lakes and the Middle Atlantic States were as much as 15 degrees above the average highs for early October.

The pleasant weather experienced by residents of the Northeast should change on Thursday as a cold front moves eastward from the Midwest.

COLDER AIR INVADES THE MIDWEST -- A cold front trailing southwestward across the Great Lakes and mid-Mississippi Valley from a low pressure center over Georgian Bay was heralding the arrival of colder air. As this cold front moved toward the south and east, southwesterly winds and relatively warm conditions were replaced by northwesterly winds and noticeably colder air. For example, the high temperature in Minneapolis-St. Paul, MN on Wednesday was 60 degrees, which was 26 degrees lower than Tuesday's high of 86 degrees.

A second cold front trailing from a low pressure center located to the north of the Manitoba Lakes region was moving across the Dakotas. A third cold front was stretched across northern portions of the Prairie Provinces. These next two fronts represented successive reinforcements of the invasion of cold air that is expected across the northern Plains.

Because of a relative lack of available moisture, only widely scattered light rainshowers were found across the upper Mississippi Valley and the Plains between the first and second cold fronts.

The first cold front is expected to move to the east and to the south on Thursday as the low pressure center associated with the front moves from near Georgian Bay to central Quebec by sunrise and more slowly toward the northeast by evening. Northern portions of the cold front should travel eastward across the eastern Lakes and into New England. However, southern and western sections of the front are anticipated to stall over the mid-Mississippi Valley and the central Plains. The extreme western portion of the front is expected to remain anchored along the eastern slopes of the Colorado and Wyoming Rockies. Increased precipitation is also expected to fall along this stationary front as increased moisture becomes available from the Gulf on southwesterly winds. With thunderstorm activity anticipated over the Plains in conjunction with the front, a slight risk of severe thunderstorms exists across most of Oklahoma and adjacent portions of Arkansas, Missouri and Kansas on Thursday. Between 0.1 and 0.7 inches of rain could fall during the 24 hours ending on Thursday evening along the nearly stationary front stretching from the Ohio Valley westward to the Nebraska Panhandle. Some of the precipitation could fall as snow across the higher terrain in Wyoming.

The second cold front is expected to travel southeastward across the northern Plains and the upper Mississippi Valley by Thursday morning. With colder air anticipated to follow behind this front, frost advisories have been issued for northwest and north central North Dakota. The third cold front could reach northern Minnesota by evening.

MORE RAIN IN THE SOUTHWEST -- Rainshowers and thunderstorms continued across Arizona and New Mexico on Wednesday, the result of the moisture available from the remnants of former Hurricane Juliette. Earlier, thunderstorms produced hail of 0.75 inch diameter in Payson along the Mogollon Rim in central Arizona.

Some rainshowers could continue across southern portions of Arizona and New Mexico into Thursday. Precipitation totals could reach 0.1 inch.

WARM WEATHER ACROSS THE WEST -- High temperatures across central California and adjacent sections of Nevada on Wednesday were on the order of 15 degrees above average.

TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 23 degrees at Stanley, ID, while the Wednesday afternoon highest temperature was 109 degrees at Death Valley, CA.

ALASKAN WEATHER -- A major storm system developed over the eastern Bering Sea on Wednesday, bringing clouds, rain and high winds to western, southwest and south central Alaska, to include the Alaska Peninsula. The low pressure center, with a central pressure of 978 mb, was located in the vicinity of the Pribilof Islands. An occluded front stretched eastward into Bristol Bay, where a warm front continued eastward across northern portions of the Alaska Peninsula and into the northern Gulf of Alaska, while a cold front extended southward across the western Alaska Peninsula and over the North Pacific to within 1000 miles of the Hawaiian Islands. Rain was falling at Bethel, Cold Bay, Dillingham, Kodiak, Homer, the Anchorage Bowl and Whittier. With the relatively low central pressure, coupled with one high pressure cell over western Canada and another over eastern Siberia, a tight pressure gradient surrounded the surface low, ensuring high winds. Strong easterly winds in excess of 40 mph were found across southwest Alaska, to include King Salmon, Iliamna and Saint Marys. These easterly and southeasterly winds brought temperatures in the mid 50s across the Alaska Peninsula and southwest Alaska. Brisk northwesterly winds on the western side of the storm were found across the central and western Aleutians, where temperatures were in the mid 40s. A stationary front running from west to east across interior Alaska separated cold arctic air to the north from milder air across southern portions of the state.

The lowest temperature in Alaska on Wednesday morning was 6 degrees at Nuiqsut. The highest statewide temperature as of Wednesday afternoon was 57 degrees at Port Alexander, King Salmon and Port Heiden.

HAWAIIAN WEATHER -- Some high clouds were found across Kauai and Oahu, while showers were found in the vicinity of the Big Island. An elongated east-west running ridge of high pressure was located within 300 miles of the islands, resulting in relatively weak trade winds. An increase in the speed of the trade winds over Hawaii was expected on Thursday as a larger and stronger high pressure cell located near the Dateline was expected to pass north of the islands. While relatively dry weather is anticipated, the increase in the trades should also increase the chance of trade showers on the windward slopes of the islands. High surf advisories were continued for the north and northeast facing shores of the islands.

EYE ON THE TROPICS -- In the eastern North Pacific, Tropical Storm Lorena curved from its northwestward course and began to move toward the north, closing in on the Mexican coast. As of Wednesday evening, Lorena was located approximately 195 miles southwest of Manzanillo, Mexico, with movement to the north at 7 mph. Maximum sustained winds were 40 mph.

The fourteenth depression of the season formed approximately 1000 miles to the southwest of Cabo San Lucas, Mexico on Wednesday, however further development was not likely.


CONCEPT FOR THE DAY - CALENDARS and SEASONS

Humans have used the idea of time to mark past experiences and anticipate future happenings. To quantify time, we have traditionally used observable periodic natural phenomena, such as the daily and yearly paths of the apparent sun through the sky and the monthly phases of the moon. The sun is especially important as its uneven heating distribution drives weather systems. The orbital points of the solstices and equinoxes define portions of the year in terms of the solar input into the Earth's energy balance, yielding the so-called astronomical seasons. From the viewpoint of the astronomical seasons, we are in early fall, since astronomical autumn started two weeks ago with the passage of the Autumnal Equinox and will continue to the Winter Solstice during the third week of December.

Similar to the astronomical seasons, we can define meteorological seasons that are meant to fit our calendar as well as the temperature cycle. These seasons are for meteorological observing and forecasting purposes and they are more closely tied to our monthly civil calendar. With this designation, we are now in the middle of meteorological fall. The current transition interval, "autumn", between the year's warmest and coldest portions of the year can be closely linked to the calendar months of September, October and November. We can also have Winter Outlooks and monthly and seasonal averages and records. This information is useful for agriculture, commerce and other purposes. For a more detailed description of seasons, see Thursday's optional Supplemental Information - Meteorological Seasons.

QUESTIONS:

To be submitted on the lines for Thursday on the Study Guide, Part B, Applications', Week 4 Chapter Progress Response Form, under section B. Daily Summary.

  1. The month was originally based upon cycles of the [(sun), (moon)].
  2. The Northern Hemisphere is currently in the [(astronomical fall) (meteorological fall) (both)] season(s).

HISTORICAL WEATHER EVENTS - 4 October

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


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URL Address: datastreme/learn/r_sum.html
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.