DATASTREME DAILY SUMMARY

Tuesday, 30 October 2001


00Z Weather Systems


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

STORMY WEATHER SPREADS ACROSS CALIFORNIA -- A large area of precipitation moved into northern California and southern Oregon on Monday night. Widely scattered precipitation was also detected across northern Oregon and Washington. This precipitation, a precursor of the first major storm of the season, was associated with a low pressure center that was situated several hundred miles west of northern California's Cape Mendocino.

The area of precipitation is expected to expand across California and into western Oregon and Washington on Tuesday as a low pressure center moves onshore and into Nevada by evening. Between 1 and 2 inches of liquid equivalent precipitation could fall in the 24 hours ending on Tuesday evening along the California coast north of Point Conception and along the western slopes of the Sierras. Farther north, between 0.4 and 0.9 inches are possible across Oregon and Washington.

Snow levels are expected to fall as cold air is brought inland with the storm system. A winter storm warming was in effect for the Sierras in California. As much as a foot of snow could fall over the northern Sierras at elevations about 7000 feet by late Tuesday evening. In addition, southwest winds with speeds reaching 40 to 50 mph could reduce visibility at higher elevations, to include the passes. The southern Sierras in the vicinity of Yosemite National Park could receive between 8 to 14 inches of snow above 7500 feet.

To the north, gale warnings for winds between 39 to 54 mph were posted along the Washington and Oregon coasts from Cape Flattery, WA to Florence, OR.

WARM WEATHER CONTINUES ACROSS THE INTERMOUNTAIN WEST -- The Intermountain West continued to have unseasonably warm weather, with afternoon highs on the order of 15 degrees above average. Record high temperatures were set on Monday afternoon in Arizona at Tucson and Safford (both 92 degrees) and in Texas at El Paso (85 degrees). The low temperature at Grand Junction, CO on Monday was a mild 50 degrees, tying the daily high minimum temperature record.

CHILLY AIR REMAINS ACROSS THE SOUTHEAST -- The Southeast experienced cool weather on Monday as a cool and dry air mass remained across the region. Record low temperatures were either tied or set on Monday morning at BWI Airport outside Baltimore, MD (26 degrees), Lynchburg, VA (25 degrees), Charlotte, NC (27 degrees), Macon, GA (27 degrees) and Jackson, KY (32 degrees). Afternoon high temperatures along the Gulf and Atlantic coasts were between 5 and 10 degrees below average.

As of Monday evening a large area of high pressure remained across the Tennessee Valley of northern Alabama. With clear skies and nearly calm conditions, another chilly night is expected across the Southeast. As a result, frost and freeze advisories were posted across northeast Mississippi, as well as much of South Carolina and portions of eastern Georgia.

A CHANGE IN THE WEATHER ACROSS THE MIDWEST -- High pressure across the northern Great Lakes produced relatively tranquil weather across the Midwest on Monday. This cool high pressure center was located to the north of a cold front that stretched southwestward from the Canadian Maritimes across the Northeast, the Ohio and Mississippi Valleys before becoming a stationary front over the western Plains. On Tuesday morning the western portion of the front is expected to begin moving northward as a warm front. This front will represent the leading edge on the earth's surface of warm air moving northward across the Plains and Mississippi Valley. As the warm air lifts over cooler air to the north of the front, precipitation is expected to develop. This "overrunning precipitation" found to the north of the front should result in as much as 0.4 inches of rain by Tuesday evening.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 14 degrees at Berlin, NH, while Monday's highest temperature was 93 degrees at Gila Bend, AZ.

ALASKAN WEATHER -- A storm system moving eastward into the western Gulf of Alaska along with a dissipating low pressure system over southern Yukon Territory contributed to heavy precipitation across southeast Alaska on Monday. As of late morning, the following locations had more than one inch of precipitation accumulated over 24 hours: Annette (1.84 inches), Ketchikan (1.42 inches), Petersburg (1.36 inches) and Klawok (1.07 inches). The storm system moving into the western Gulf was located south of Kodiak Island and had a central pressure of approximately 976 mb. Windy conditions accompanied this storm, as Cold Bay and Sand Point on the Alaska Peninsula experienced northwest gusts of 40 mph. These stations also reported snowshowers. The weakening storm located over the Yukon was accompanied by a weakening front that extended across the northern Panhandle. Another storm was located over the western Bering Sea to the east of the Kamchatka Peninsula. A front associated with this system stretched across the western Aleutians. Weak high pressure was situated across the North Pacific and the central Aleutians. High pressure located over the Canadian Archipelago continued to spread cold air across the North Slope and into interior Alaska. While much of the state was relatively overcast, relatively clear skies were found across portions of the interior in the Yukon Flats and Denali areas.

The state's lowest temperature on Monday morning was 20 degrees below zero at Farewell Lake. The highest temperature across Alaska as of midafternoon on Monday was 46 degrees at Ketchikan.

HAWAIIAN WEATHER -- Gusty northeast trade winds continued across the islands on Monday as a high pressure ridge was located to the north of the state. Relatively cloud-free skies were also found over the islands, except for the scattered trade showers on the windward slopes of the islands. This pattern is expected to continue through Wednesday as the ridge is expected to remain stationary. Because of the persistent and strong trade winds, a gale warning was in effect for all inter-island channels, while small craft advisories remained in effect for all other state waters. A high surf advisory also was continued for the east shores of all islands.

EYE ON THE TROPICS -- Tropical Depression 14 continued moving westward across the tropical North Atlantic and intensified to become Tropical Storm Lorenzo on Monday evening. As of late Monday night Tropical Storm Lorenzo, with maximum sustained surface winds of 40 mph, was moving to the west-northwest at 12 mph. Its location was 1250 miles west-southwest of the Azores. Another tropical depression, identified as Tropical Depression 15, formed along the coast of Nicaragua on Monday afternoon. On Monday night TD-15 was located 15 miles south of Puerto Cabezas, Nicaragua and moving to the north at 5 mph. Maximum sustained surface winds were 35 mph. Estimated central pressure was 1005 mb. Heavy rains were falling across coastal regions of Nicaragua, Honduras and Belize.

REPORT FROM THE FIELD -- An unnamed correspondent from Florence, OR reported a large bright fireball that left beautiful red streaks in the sky on early Sunday morning. This may have been a meteor that passed through the upper atmosphere. The reporter thought that some pieces could have reached the earth's surface.


CONCEPT FOR THE DAY - WHAT'S THE WEATHER GOING TO BE?

So you are off on a trip away from civilization, but you forgot to take your NOAA Weather Radio. Do you have any way of making more than a guess about the forthcoming weather for the next half day or so? Sure, you can.

Stand out in the open with your back to the wind. Raise your left arm to a horizontal position and then move your arm slightly forward. Your left hand is now pointing toward low pressure.

Why is that relationship so? Check it out by using the knowledge you have learned in the DataStreme course, while keeping in mind that you are in the Northern Hemisphere. On a piece of paper, draw a couple of concentric isobars around an "L". Draw some curved arrows showing the winds circulating counterclockwise around the low pressure center. Imagine yourself on the map you just drew (but not at the "L") with the wind to your back and your left arm extended. Your arm would be pointing toward the "L". Buys-Ballot, a Dutch meteorologist, noticed this rule on weather maps in the mid 1800's. If you stand with the wind at your back, the low pressure center will be to your left.

To make a weather prediction, you also have to recall that weather systems tend to travel from west to east. So, if you are facing north while the wind is to your back, the lower pressure is to your left (to the west of you). And, the low would be coming toward you. As you know, low pressure approaching you often means stormy weather is on the way. That would be your forecast. Conversely, if you observe a northerly wind, the low would be to your east, and you could forecast that the weather should improve as the low pulls away and the high pressure moves toward you.

So how can we make our own wind observations, and what can we learn from our observations? If you are curious, refer to the optional Supplemental Information for Tuesday.

QUESTIONS:

To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications, Week 8 Chapter Progress Response Form, under section B. Daily Summary.

  1. If your back is to the wind and you are facing south, you could expect to experience [(fair) (stormy)] weather during the next half day or so.
  2. If you are standing in a large, flat open area with your back to the wind, higher air pressure would be to your [(left) (right)].

HISTORICAL WEATHER EVENTS - 30 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, 2001, The American Meteorological Society.