DATASTREME DAILY SUMMARY

Tuesday, 10 October 2000


00Z Weather Systems


ANOTHER COLD START -- More than 80 record low temperatures were either tied or set on Monday morning from the Plains to the East Coast as the large arctic high pressure system moved slowly across the nation's midsection. Not only were the number of individual daily records impressive, but some of the records were remarkable for the timing of the event. For example, the record low of 29 degrees at Huntsville, AL and the 31 degrees at Wichita Falls, TX were the earliest occurrence of a freeze on record at these two sites.

As a result of the cold start to the day because of the cold air, afternoon high temperatures remained well below average. Afternoon highs ranged between 20 to 25 degrees below average across the Southeast and Middle Atlantic states as well as in portions of the Southern Plains.

With the center of the high forecast to be over the Bootheel of Missouri by sunrise on Tuesday morning, another cold night is expected across the South and East. The core of the cold air had shifted toward the Southeast, with some locations across Florida falling to near record low readings during the evening hours. Freeze warnings have been posted from Indiana southward into the Ohio and lower Mississippi Valleys to Arkansas and then eastward across the northern counties of Mississippi, Alabama and Georgia, as well as the western portions of the Carolinas. Frost advisories were also posted across central Georgia, the Piedmont of the Carolinas and southern Virginia.

WARMER TO THE NORTHWEST -- The clockwise circulation around the high pressure system produced an unusual situation on Monday. The southerly winds along the western flank of the ridge were responsible for warm air advection, causing the temperatures at locations across the northern Plains to be higher than those across the Southeast. For example, Rapid City, SD had a high temperature on Monday of 71 degrees, while Atlanta, GA could only struggle to a high of 56 degrees. Highs across the western Dakotas and into Montana were also 10 degrees above the average high. As of late Monday night, temperatures across the northern Plains were as much as 10 degrees higher than they had been 24 hours previously.

WET WEATHER ACROSS SOUTH TEXAS -- A large area of rain continued to fall across south Texas on Monday night. The bulk of the precipitation was south of an east-west line that stretched from Houston to Del Rio. The thick clouds and rain also held afternoon temperatures along the Rio Grande Valley to at least 30 degrees below the average high. Del Rio with a high of 44 degrees and Brownsville with 50 degrees on Monday set monthly lowest maximum temperature records for October. Near-surface winds from the east brought moist air from the Gulf inland.

The rain is expected to continue through Tuesday, with as much as 0.5 inches falling in the 24 hours from Monday through Tuesday evenings.

SNOW ACROSS THE NORTHEAST -- Northwest winds continued to pass across the relatively warm waters of the eastern Great Lakes, resulting in lake-effect snows along the downwind shores of Lakes Erie and Ontario. The inch of snow that fell at Binghamton, NY on Monday was the earliest occurrence of an inch of snow there.

In addition to the lake-effect snows across Pennsylvania and New York State, snow associated with an Atlantic storm system fell across the higher elevations of northern New England. The storm that had formed along a cold front over the Atlantic had moved northward to a position within several hundred miles of Cape Sable, NS. Northern and eastern New England were under the cloud and precipitation shield of this storm system on Monday.

This storm is expected to continue moving toward the Maritimes by Tuesday morning, resulting in the continuation of snow across northern Maine and New Hampshire on northerly winds that would carry wrap-around moisture from the Atlantic inland. Between 0.5 and 1.0 inches of liquid-equivalent precipitation could fall between Monday and Tuesday evenings over northern Maine, with the interior receiving snow.

UNSETTLED WEATHER IN THE PACIFIC NORTHWEST -- A cold front that entered the Pacific Northwest on Sunday evening moved eastward across the Cascades on Monday, spreading precipitation from Washington State southward into northern California. As of Monday night, the cold front stretched southward from the Idaho Panhandle across Nevada into southern California, reaching the Pacific Ocean near Santa Barbara. Widespread precipitation stretched along coastal mountains and the Cascades from Washington State southward across Oregon and into northern California. Earlier in the evening, severe thunderstorms were detected by radar in California's central valleys and foothills to the Sierras.

The precipitation, in the form of valley rain and high altitude snow should fall across the Cascades and Sierras on Tuesday as the front moves slowly toward the east. Winter storm warnings were in effect for the Sierras of California and Nevada for snow accumulations of as much as 10 inches at altitudes above 7000 feet. Farther to the south, a slight risk of severe thunderstorms is expected on Tuesday, for an area ahead of the advancing cold front that encompasses southern and western Arizona .

A SCRUB -- Monday's launch of the Space Shuttle Discovery from Cape Kennedy was postponed because of high crosswinds gusting to 50 mph at the launch pad.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 5 degrees at Rochford, SD, while Monday's highest temperature was 101 degrees at Death Valley, CA.

ALASKAN WEATHER -- A strong storm system moving to the northeast across the North Pacific south of the Aleutians produced windy conditions across this island chain. Dutch Harbor reported wind gusts to 40 mph. Another weaker storm system located along the Northeast Gulf coast near Cordova was responsible for clouds and precipitation across the Panhandle and Southeast Alaska. Rain fell across the Panhandle at Juneau and Yakutat. High pressure across interior Alaska produced relatively clear skies over the Kuskokwim Delta and across south central Alaska from the Shelikof Strait near Kodiak to the Yukon Flats in the center of the state. However, snow did fall at such interior locations as Bettles, McGrath and Tanana. Low pressure north of Barrow contributed to snow over the north at Barrow, Kotzebue and Wainwright. At midafternoon Anaktuvuk reported a wind-chill equivalent temperature of 14 degrees below zero.

The state's lowest temperature on Monday morning was 3 degrees below at Bettles. The highest temperature across Alaska as of midafternoon on Monday was 54 degrees at Ketchikan.

HAWAIIAN WEATHER -- A large high pressure system to the north of Hawaii was responsible for the moderate northeast trade winds on Monday. Relatively cloud-free weather with few trade showers were also found across the islands. This high is expected to move eastward and weaken slightly by Wednesday, resulting in slightly diminished trade winds. Because of the strong trade winds, small craft advisories continued for the state waters on Monday.

REPORT FROM THE FIELD -- Mark Seeley, LIT Member from the Minneapolis-St. Paul, MN and the Extension Climatologist for the University of Minnesota, reported on the nearly dozen minimum temperature records that fell on Monday morning across Minnesota.


CONCEPT FOR THE DAY - AIR PRESSURE CHANGES

Highs and Lows, with their comings and goings, are our major weathermakers. Being in the paths of these migrating weather systems, local measurements of air pressure often can be our major forecasting guide to the weather heading our way. Changes in air pressure due to passing weather systems are not great compared to the total air pressure. They are tens of millibars at most within a range from about 970 to 1040 mb corrected to sea level. This change is only a few percent of the total pressure, a small amount compared to the change going straight up where a one millibar drop occurs for approximately every 10 meter ascent in the lower atmosphere! But the change in pressure along the horizontal, and the distances and times involved still create strong storms such as the low pressure system off the Maine coast on Monday. On the other hand, small horizontal pressure changes over large distances are associated with the expansive high-pressure system that dominated the weather over the eastern two-thirds of the nation during the last several days.

Atmospheric pressure readings, corrected to sea level, are reported by the National Weather Service each hour with changes over three hour intervals (0Z to 3Z, etc.), also listed as a "pressure tendency". The DataStreme meteogram, (short for meteorogram), provides a graphical display of the hourly weather conditions at some station over the past 24 hours. The bottom panel of the chart is a plot of the time series of sea-level pressure readings, similar to the trace provided by a barograph, such as that found in Figure 5.4 of Part A. Falling pressure values usually denote approaching storms (a low or front) while rising values accompany clearing or continued fair weather associated with an approaching high pressure cell.

These changes have long been the basis of forecasting when based purely on local observations, "when the glass (barometer) is low, expect a blow"!

For more details describing variations in pressure with time, see Tuesday's optional Supplemental Information .

QUESTIONS:

To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications, Week 5 Chapter Progress Response Form, under section B. Daily Summary.

  1. If a Low were moving away from you, the atmospheric pressure at your location would probably be [(increasing), (decreasing)] .
  2. Being near the center of an expansive High, you would expect [(little or no) (a rapid)] change in pressure over the next several hours.

HISTORICAL WEATHER EVENTS - 10 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.