DATASTREME DAILY SUMMARY

Tuesday, 27 November 2001


00Z Weather Systems


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

AN ACTIVE STORM PATTERN -- The second in a series of storms since Thanksgiving was traversing the nation on Monday, bringing a variety of weather that ranged from tornadic thunderstorms to heavy snow and blizzard conditions. Additional storms appear to be poised to move across the country in the wake of the current storm. As of late Monday night the main storm system consisted of an occluding low pressure system located in northwest Iowa. An occluded front extended eastward across the Hawkeye State to a point of occlusion where a warm front continued eastward across the Mississippi Valley into the southern Great Lakes, while a cold front extended southward just to the west of the Mississippi River and then southwestward across southern Texas.

This storm system has developed along a zone of temperature contrasts. To the east of the storm, high temperatures across much of the eastern half of the country ranged from 10 to 15 degrees above the average highs for late November. Record highs were either tied or set in North Carolina at Wilmington (80 degrees), Raleigh-Durham (76 degrees), and Charlotte (75 degrees) and also in New England at Providence, RI (67 degrees) and Concord, NH (64 degrees). To the west of the storm system, the cold air that moved southward across the Rockies and Intermountain West resulted in high temperatures that were 15 to 25 degrees below the average highs for the date.

The storm system is expected to continue to undergo a typical occlusion process as it moves slowly to the east-northeast. By sunrise on Tuesday morning the primary low pressure center is forecast to have reached north central Iowa and by early evening the primary low should be located in southwestern Wisconsin, with a secondary low that is anticipated to form near the point of occlusion over southern Ontario to the southeast of Detroit, MI. A warm front should extend to the southeast of the secondary low across the Appalachians, while the cold front should stretch southward across the Ohio and Tennessee Valleys toward the central Gulf Coast.

SEVERE THUNDERSTORMS HIT THE MID-SOUTH -- Summer-type weather was found on the warm, southern side of the storm. Thunderstorms formed along and ahead of southern portions of the cold front as it moved across the lower Mississippi Valley. Some of these thunderstorms turned severe, spawning tornadoes, generating damaging high winds and producing large hail. During the late afternoon and later into the late night, several tornadoes were reported in northern Mississippi, southeastern Arkansas and western Tennessee. A tornado caused one death and seven injuries near Springville along Kentucky Lake in northwest Tennessee. Property damage was associated with each tornado, to include the destruction of several homes in Tennessee. In addition, strong straight-line thunderstorm winds also produced damage across east Tennessee, Texas, Louisiana, Arkansas and Mississippi. Several injuries were sustained by the thunderstorm winds near Memphis, TN. The thunderstorms also produced large hail with diameters to 1.75 inches across the Lower Mississippi Valley.

Severe thunderstorms continued into early Tuesday, accompanied by damaging winds across portions of Louisiana and Tennessee. Heavy rains also accompanied the thunderstorms in Texas, where as much as 4 inches of rain fell in approximately 4 hours along the San Jacinto River. As a result, a flash flood warning was issued for the region to the north of Houston. The lower Mississippi Valley remained under a moderate risk of severe thunderstorms through Tuesday morning and tornado watches remained in effect. A slight risk of severe weather continues through Tuesday across much of the western Gulf of Mexico, extending from the Mississippi Delta westward to include the entire Texas Gulf Coast.

WINTRY WEATHER MOVES TOWARD THE MIDWEST -- Cold air to the north of the storm produced a band of snow, ice pellets (sleet) and freezing rain that stretched from the central Plains to the Upper Mississippi Valley and the western Great Lakes. Heavy, wet snow fell across South Dakota. Sioux Falls received 11.4 inches of snow by Monday evening, which set a snowfall record. The liquid water equivalent of this snowfall was 1.10 inches, which also set a daily precipitation record. Aberdeen received a record 6.4 inches snowfall, with a liquid water equivalent of 0.68 inches, which was also a record.

Snow accompanied by strong winds continued into the late night across the Upper Midwest as the storm moved slowly toward the east. A variety of winter storm warnings, winter weather advisories and snow advisories were in effect from the Sand Hill country of north central Nebraska to Michigan's Upper Peninsula, to include much of South Dakota and Minnesota, as well as portions of North Dakota and northern Wisconsin. As much as 14 inches of snow were expected along a line that extended from southwest Minnesota into northwest Wisconsin. A blizzard warning was also posted across portions of northeast South Dakota, as northeast winds reaching speeds of 35 mph were anticipated to reduce visibility to near zero in blowing and drifting snow.

WINTRY WEATHER ANTICIPATED ACROSS THE SOUTH -- With cold air moving southward across the southern Plains behind the cold front and moist Gulf air located to the south, a potentially dangerous weather situation could develop across portions of the southern Plains late Tuesday as some of the precipitation could fall as snow, ice pellets (sleet) or freezing rain. Winter storm watches have been posted along a track that extended from central New Mexico eastward across north Texas and then northeastward across eastern Oklahoma and southern Missouri into west central Illinois. These watches are in effect for late Tuesday and extending into Wednesday.

COLD WEATHER ACROSS THE WEST -- Of more immediate concern was the cold air that moved across portions of the Lone Star State behind the cold front. A freeze warning was in effect Monday night for a portion of south central Texas near San Angelo. Farther west, cold air associated with high pressure that was expected to move into the Great Basin could bring frosty conditions to various agricultural areas. A frost advisory was posted for portions of the Sacramento and San Joaquin Valleys in central California and some of the valleys in the southern part of the Golden State. Windy conditions could mix warm air downward and reduce the potential frost damage. A freeze warning was in effect for the valleys of southern Arizona near Tucson.

A storm that was expected to reach the Pacific Northwest by Wednesday could start spreading snow across the region beginning on Tuesday night. As a result, winter storm watches were posted for the Washington Cascades, the Blue Mountains of northeast Oregon and the mountains of southern Idaho for Wednesday. As much as 12 inches of snow could fall.

FOGGY CONDITIONS -- With longer nights and relatively clear skies under high pressure, some locations along the Eastern Seaboard and the Gulf have experienced dense fog recently. Dense fog warnings were posted on Monday night extending through Wednesday morning for portions of Maryland, the Virginias and North Carolina and also along the Gulf Coast in Florida and Alabama.

UPPER AIR -- Both the 500 and 300 mb charts for 00Z Tuesday exhibit a large trough in the height contours across the West. This trough is related to the cold air that has moved into the region and extends upward through the troposphere, resulting in lower altitudes for the individual constant pressure surfaces. A height ridge is found across the East, reflective of the warmer air there. As a result, the jet stream at 300 mb undergoes a more wavelike pattern, being deflected well to the south across the West and then to the north over the East. The strongest core of winds on the 300 mb chart are found to the southeast of the trough with winds over 120 knots over the southern Plains.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 7 degrees below zero at Alamosa, CO, while Monday's highest temperature was 87 degrees at Harlingen, TX.

ALASKAN WEATHER -- Arctic air continued to dominate the weather across much of mainland Alaska on Monday as a ridge of high pressure extended westward across the state from northern Canada. Relatively clear skies were found across interior Alaska, where midafternoon temperatures ranged from 20 degrees below zero at Fort Yukon to the teens above zero. Gusty winds were found overnight and on Monday across northern portions of the Panhandle as cold air spilled westward across the Panhandle. Juneau reported east winds with gusts to 56 mph. Fog and drizzle were reported across south central Alaska, to include the Anchorage Bowl. The western and southern edges of this cold air was marked by a stationary front that stretched southeastward along the Yukon-Kuskokwim Delta, then eastward across the northern portion of the Alaska Peninsula and the Gulf Coast to the Panhandle, where it curved southward into western British Columbia and the "Lower 48". As a result, only the Aleutians and the southwestern portion of the Alaska Peninsula remained unaffected by the arctic air. To the west, a large storm system remained over the western Bering Sea near the Kamchatka Peninsula. Clouds associated with this storm were found across the Aleutians and most of the Bering Sea. A relaxation of the tight pressure gradient meant that the high winds that had buffeted southwestern Alaska for the last few days had diminished. However a high wind warning remains in effect overnight for the western Aleutians from Adak to Kiska as winds are expected to reach speeds of 50 mph, with gusts to 65 mph.

The state's lowest temperature on Monday morning was 26 degrees below zero at Fort Yukon. The highest temperature across Alaska as of midafternoon on Monday was 43 degrees at Cold Bay.

HAWAIIAN WEATHER -- A trough of low pressure to the west of Kauai produced southerly winds across most of the islands on Monday. These southerly winds were bringing warm and humid tropical air northward, resulting in showers and isolated thunderstorms that were approaching the Aloha State. Heavy rain fell across the southern half of the Big Island. By late Monday night heavy rain should begin to fall across Kauai, where relatively strong winds necessitated the posting of a wind advisory. Flood watches were in effect through Tuesday morning for Kauai and the Big Island. High surf advisories were continued for the northwest shores of the islands, while a small craft advisory remained in effect for state waters.

EYE ON THE TROPICS -- The seventeenth named tropical system of the season formed in the North Atlantic on Monday and was named Hurricane Olga. It is also the ninth hurricane of a six-month season that officially ends on Friday. By late Monday night Hurricane Olga had maximum sustained surface winds of 85 mph and it was located 495 miles east of Bermuda. Movement was to the north at 8 mph. Long-period ocean swells generated by Olga were reaching the north-facing coasts of Puerto Rico and the US Virgin Islands.


CONCEPT FOR THE DAY - PUBLIC WATCHES and WARNINGS

The National Weather Service is mandated by Federal law to monitor, predict and provide necessary information to the public on impending destructive weather or hydrologic events. These events can be grouped into local convective or severe weather, tropical, marine, winter storm and other non-precipitation events. Public statements issued for various winter storm events were previously described in the Week 10 Tuesday Concept for the Day. These statements conform to a specific wording that the National Weather Service uses to alert the public to various hazardous events. In general, the following terms are used:

Most of the watches for the country, to include all severe local storms, are currently issued by the Storm Prediction Center in Norman, OK. Watches for tropical weather events are issued from the National Hurricane Center near Miami, FL. However, warnings for specific local weather events are issued by the local Weather Service Offices when hazardous weather events are occurring in their area of responsibility.

For a description of the terminology used in the official statements issued by the National Weather Service to inform the public of severe local storms, please read the Tuesday optional Supplemental Information .

QUESTIONS:

To be submitted on the lines for Tuesday on the Study Guide, Part B, Applications, Week 11 Chapter Progress Response Form, under section B. Daily Summary.

  1. A weather watch indicates that a hazardous weather event [(has occurred), (is presently occurring), (may occur)] .
  2. A warning of severe local weather would be issued by [(Storm Prediction Center), (local Weather Service Office), (National Hurricane Center)] when the weather phenomenon was imminent or actually occurring.

HISTORICAL WEATHER EVENTS - 27 November

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.