DATASTREME DAILY SUMMARY

Tuesday, 4 September 2001


00Z Weather Systems


WELCOME TO DATASTREME - The Daily Summary file will describe the current weather pattern across the United States. 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.

The following discussion is based upon the major weather features appearing on Monday night's surface weather maps:

ACTIVE WEATHER ACROSS THE MIDWEST -- A cold front moved southeastward across the western Great Lakes and upper Mississippi Valley on Monday. This cold front trailed southwestward across Lake Huron, Lower Michigan and into northern Illinois from a low pressure center near James Bay along the Ontario-Quebec border. This cold front represented the leading edge of cooler air that pushed southward across the Midwest. Unseasonably warm weather was found in advance of the front across the western Great Lakes. As a result, thunderstorms developed along and to the south of the cold front. As of late Monday evening, most of the activity stretched across southern Ontario into lower Michigan near Detroit. Weaker thunderstorms were found across southern Lake Michigan and northern Illinois. During the late afternoon some of the thunderstorms produced strong winds that downed trees near Waukesha and Racine in southeastern Wisconsin and near Fox Lake in northeast Illinois.

Northern portions of the cold front are expected to sweep eastward on Tuesday, with the front reaching the eastern end of Lake Ontario by sunrise and to the New England coast by evening. A slight risk of severe thunderstorms exists on Tuesday across the Northeast in advance of the front, covering an area that extends from the eastern Great Lakes into New England and south to Maryland. As much as one-third of an inch of rain could fall across the Northeast by Tuesday evening. Southern and western portions of the front are expected to stall just to the north of the Ohio Valley. A second cold front that was located to the north of Lake Superior and the Arrowhead of Minnesota on Monday evening is expected to push southward across the Great Lakes and dissipate on Tuesday as high pressure spreads into the region.

MORE SEVERE WEATHER ACROSS THE SOUTHERN PLAINS -- Active thunderstorms continued across Texas on Monday night that included both the Panhandle and a broad region from north Texas near Dallas-Fort Worth southward across the Hill Country to near San Antonio and Del Rio along the Rio Grande River. Some of these thunderstorms turned severe during the late afternoon hours as thunderstorm winds reached 60 mph near Abilene, TX and dime to golfball size hail (with diameters ranging from 0.75 to 1.75 inches) fell across southwestern Oklahoma near Lawton. These thunderstorms were associated with a weak trough of low pressure that was situated across the southern Plains, extending from Kansas southward into Texas.

Record rainfall fell at several locations across the South Central States on Sunday, with 1.83 inches at San Antonio and 1.32 inches at El Dorado, AR. As a result of the heavy rains that have fallen across the Lone Star State, flash flood watches extend across a large portion of southeast and south central Texas from near Houston westward to near Del Rio. An additional one to two inches of rain could fall across portions of south central Texas by Tuesday evening.

WET WEATHER FOUND ACROSS THE SOUTHEAST -- A large area of rainshowers and imbedded thunderstorms continued across the Southeast, extending from the mountains of western North Carolina southward to the south Florida. A large portion of this precipitation was found along a stationary front that stretched westward from a weak low pressure center off the North Carolina coast into South Carolina and northern Georgia. Rain also was falling in the warm, humid and unstable tropical air mass situated over Florida to the south of the front. Some of the thunderstorms across Florida were active. On Monday afternoon, a waterspout, which is a tornado vortex found over water, was reported approximately one mile off the coast at Miami Beach. Wind damage was also sustained from thunderstorms near Jacksonville in the northeastern portion of the Sunshine State. Afternoon high temperatures were suppressed across the Southeast as a result of the widespread clouds and rain. Regional highs were on the order of 10 degrees below the average highs for early September.

The stationary front is expected to remain across the Carolinas through Tuesday morning, accompanied by the area of showers and thunderstorms. As much as two inches of rain could fall across the mountainous areas of the western Carolinas. Consequently, flood watches continued for the region.

AND IT DOES RAIN IN SOUTHERN CALIFORNIA -- Thunderstorms were found across the southern Sierras of California and into central Nevada. Some of the moisture appears to have been the remnants of Hurricane Flossie that had moved northward across the eastern North Pacific Ocean last week. Flash flood watches were posted for a large portion of east central and southeastern California, as well as adjoining portions of Nevada on Monday afternoon and evening. Unusually heavy downpours of rain have fallen across desert regions and mountains where much of the rain runs off as flash floods. As much as 0.3 inches of additional rain are anticipated across portions of southeastern California, south central Nevada and southwest Utah during the 24 hours ending on Tuesday evening as the pocket of moisture drifts eastward.

LITTLE RELIEF FOR FIRE FIGHTING -- Winds continued to be a problem for firefighters who have been battling wildfires in and around Glacier National Park in northwest Montana. Earlier on Monday, a high wind warning was in effect as a trough of low pressure moved across the northern Rockies and increased the winds. These winds, coupled with the relatively high temperatures and low humidities increased the fire danger across portions of Montana and adjoining states. Record high temperatures were either tied or set on Monday in Montana at Helena (96 degrees), Bozeman (95 degrees) and Lewistown (93 degrees). The high temperatures at Helena and Bozeman represented the second highest September temperatures on record for the respective cities. Other record highs were reached near Wheatland, WY (99 degrees) and at Alliance, NE (97 degrees).

A cold front moved into western Washington State on Monday afternoon. However, little precipitation accompanied this front, and none is expected to fall across the Pacific Northwest as the front is expected to stall across the region on Tuesday.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 32 degrees (Fahrenheit) at Whitefield, NH, while Monday's highest temperature was 114 degrees at Death Valley, CA.

ALASKAN WEATHER -- Much of Alaska was mostly cloudy on Monday. Winds and rain were found across much of the Panhandle, the result of a weakening low pressure system located over the southern Panhandle. Some rain also was reported earlier on Monday in the Anchorage Bowl. A ridge of high pressure over the North Pacific extended northward across southwestern Alaska, to include the Alaska Peninsula. A storm system moved northeastward into the central Bering Sea. This developing low pressure system with a cold front that trails southwestward into the North Pacific has produced strong winds and rain across the central Aleutians. Rain also fell earlier at Kotzebue and Saint Paul. High pressure located over the Arctic Ocean was responsible for onshore winds across the Arctic coast and the North Slope. With temperatures below 32 degrees Fahrenheit, freezing drizzle fell at Barrow. A weakening front across the interior separated this cooler Arctic air to the north from warmer air to the south.

The state's lowest temperature on Monday morning was 31 degrees at Barrow. The highest temperature across Alaska as of midafternoon on Monday was 70 degrees at Big River Lakes.

HAWAIIAN WEATHER -- An elongated ridge of high pressure that stretched across the central North Pacific Ocean to the north of the Hawaiian Islands maintained pleasant trade wind weather across the islands on Monday. The trade winds emanate out of the equatorward flank of these large subtropical high pressure cells. Because of the position of the highs, these winds are from the east-northeast with speeds ranging from 10 to 20 mph. The proximity of the high also meant that skies were relatively cloud-free through Monday, except for some trade showers that formed on the northeast or windward slopes of the mountainous peaks of the islands. With the high pressure system remaining relatively stationary, the trades are expected to continue through midweek. However, increased atmospheric moisture should increase the frequency of trade showers across the islands.

EYE ON THE TROPICS -- Tropical Storm Erin continued to move westward across the tropical Atlantic Ocean on Monday. As of late Monday night Erin had satellite-estimated near-surface winds of approximately 45 mph and it was moving to the west-northwest at 18 mph, as it was situated approximately 800 miles to the east of the Leeward Islands.

AUGUST EXTREMES -- While the monthly climatological data for the just-completed month of August are being compiled and analyzed, the National Climate Data Center (NCDC) has listed Selected U.S. City and State Extremes August 2001 that includes several noteworthy extremes in the temperature, precipitation and snowfall records across the nation. This list could be updated in the near future.

REPORTS FROM THE FIELD -- If you experience some interesting weather phenomenon that you would like to share with other DataStreme participants as a "Report from the Field", please email your message to the address below.


CONCEPT FOR THE DAY - TIME ZONES and "Z" TIME

You will find that all DataStreme meteorological maps and charts are labeled with numbers followed with a "Z", such as 00Z, 12Z, 1915Z, etc. These labels indicate the time of observation in Universal Coordinated Time (UTC). The UTC or "Z" time is used because weather observations must be taken at the same time everywhere to accurately represent the state of the atmosphere. But how can you tell from the reported Z time when the observations were made where you live?

Z time is the time along the Prime Meridian, 0 (zero) degrees longitude. Life would be easy if you lived in England because your local time and Z time are the same. But what about where you live? For example, if you are looking at today's 12Z weather map, what time was it in your time zone?

Because you live in the U.S. and the earth rotates toward the east, your local time will be earlier than the local time at the Prime Meridian -- that is, the sun rises in England hours before it does in the U.S. Presently, many of us observe Daylight Saving Time. Therefore, 12Z (noon in England) would be 8 AM Eastern (4 hours earlier than local time in England), 7 AM Central (5 hours earlier), 6 AM Mountain (6 hours earlier), and 5 AM Pacific time (7 hours earlier). However, UTC time does not change seasonally. So when the entire country reverts to Standard Time at the end of October for the winter season and we set our own clocks back one hour, 12Z would then become 7 AM Eastern (5 hours earlier than local time in England) .

A table of time conversions for the U.S. is listed in the DataStreme Homepage User's Guide. For additional Z-time explanation, call up Tuesday's optional Supplemental Information.

QUESTIONS:

To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications', Week 1 Chapter Progress Response Form, under section B. Daily Summary.

  1. A time of 2100Z is equivalent to ____ Central Daylight Time.
  2. In Los Angeles, 1 PM Pacific Daylight Time would be ___________ Z.

HISTORICAL WEATHER EVENTS - 4 September

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


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