DATASTREME DAILY SUMMARY

Tuesday, 31 October 2000


00Z Weather Systems


BLUSTERY WEATHER CONTINUES ACROSS THE NORTHEAST -- A storm system located over Massachusetts Bay late Monday night was responsible for the continued chilly, wet and windy weather across the Northeast. This storm system had originally moved northward across the western Atlantic at the end of last week before curving to the northwest near the Canadian Maritimes at the end of the weekend. During its northward journey, the storm intensified over the relatively warm ocean waters because of the temperature contrast that developed as cold air was fed into the system from the northwest. The storm system began to occlude, a stage in the life cycle of a midlatitude storm where the cold front overtakes the warm front to produce an occluded front. In this case, following the development of the occluded front, a secondary low pressure center formed near the point of occlusion, where the surface warm, cold and occluded fronts intersect. On Monday the older primary low pressure center moved southwestward from the Bay of Fundy to Massachusetts Bay near Boston. A secondary low remained located south of Nova Scotia.

As of late Monday night, precipitation continued across most of New England and New York's Long Island. Some light snow continued across northern Maine. Over the weekend, as much as 14 inches of snow had fallen across the higher terrain of Maine. Because of a tight pressure gradient between a ridge of high pressure over the eastern Great Lakes and the offshore low pressure center, brisk northerly winds were found across the Northeast on Monday night. These northerly winds helped bring cold air southward. The cold air coupled with the clouds and precipitation meant that high temperatures were 10 to 15 degrees below the average highs across New England. Wind-chill equivalent temperatures were in the teens late Monday.

By Tuesday morning, the storm system is expected to have moved northeastward, resulting in a dissipation of the precipitation across the Northeast. Little additional accumulation is anticipated.

WINTRY WEATHER ACROSS THE ROCKIES -- A storm system that was situated over the Great Basin late Monday night was expected to produce hazardous wintry weather across the Rockies on Tuesday. Beccause of the cold pool of air coupled with the clouds and precipitation, afternoon highs across the West on Monday were as much as 20 degrees below average over the Great Basin of eastern Nevada. This occluding storm system consisted of a primary low pressure near Utah's Great Salt Lake and a occluded front that extended southward to a secondary low pressure center near the Four Corners. A cold front continued southward across Arizona to Baja California. A small area of snow was falling across northeast Nevada late Monday near the primary low pressure center. Some rain was falling across Arizona in the vicinity of the cold front.

This storm system is expected to intensify as it moves slowly eastward on Tuesday. The low pressure center and accompanying cold front are forecast to reach the high plateau of western Colorado by evening. However, during the 24 hours ending on Wednesday morning, between 0.25 and 1.0 inch of liquid-equivalent precipitation is expected to fall across Colorado and Wyoming. As a result, a variety of snow advisories, and winter storm watches and warnings have been issured for portions of Utah, Arizona, New Mexico, Colorado and Wyoming. As much 18 inches of snow could fall by Wednesday on the west-facing mountain slopes near Rocky Mountain National Park, while 14 to 16 inches of snow are expected in the Big Horn Mountains of north central Wyoming by Tuesday night.

MORE SUMMER-LIKE WEATHER IN THE PLAINS -- While the Northeastern and the Western States experienced unseasonably chilly conditions, the center of the country began to warm as southerly winds were found from the Midwest to the east slopes of the Rockies. As a result, above average temperatures were found across the nation's mid section, with highs on Monday that were as much as 15 degrees above average in the mid-Mississippi Valley. On Monday afternoon the high temperature at Mobile, AL was a record tying 85 degrees.

A trough of low pressure is expected to develop to the lee of the Rockies by Tuesday morning. As a result, a slight risk of severe thunderstorms is forecast to exist across Oklahoma and southern Kansas until morning. On Tuesday, the risk area expands to stretch from the Rio Grande Valley of south Texas north to central South Dakota.

TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 15 degrees at Pellston, MI, while Monday's highest temperature was 90 degrees at Alice, TX.

ALASKAN WEATHER -- A potent storm system moving across the Gulf of Alaska dominated Alaska's weather on Monday afternoon, producing clouds that covered approximately two-thirds of the state, over an area south of the Brooks Range. However, some scattered clouds were found over Bristol Bay and vicinity, to include the Alaska Peninsula and the Aleutians. The low pressure center moving slowly to the northeast was positioned south of Prince William Sound with an occluded front that spiraled around the west and north side of the low, and then paralleling the north Gulf coast before turning southward along the Panhandle outer coast. Most of the precipitation associated with this storm was confined to the south central and southeast, to include the Panhandle. Snow fell at Home and Seldovia in south central Alaska. As much as 4 inches of snow fell at Skagway and Haines where temperatures were 32 degrees, while other locations in the Panhandle where the temperatures were in the 40s had rain. Gusty winds were found across the Panhandle, with Ketchikan experiencing gusts to 37 mph. Across the northwest, conditions were relatively mild. A weak low was located near Point Hope. Along the Arctic coast, Barrow with 25 mph winds had a mid-day wind-chill equivalent temperature of 25 degrees below zero. Deadhorse had 0.5 mile visibility in freezing fog, while snow was reported at Wainwright and Kotzebue.

The state's lowest temperature on Monday morning was 17 degrees below zero at Arctic Village. The highest temperature across Alaska as of midafternoon on Monday was 48 degrees at Cordova and Hydaburg.

HAWAIIAN WEATHER -- While the pattern that brought this past weekend's heavy rainfall has changed, some lingering showers are expected to continue into Tuesday. Winds remained from the east with speeds to 20 mph.

REPORTS FROM THE FIELD -- Marsha Rich, LIT Leader from New Hampshire, reported that as of noon on Monday, the Observatory on top of Mount Washington had received 34.9 inches of snow for October, which is a new October snowfall record. Additional snow was expected. For comparison, average October snowfall is about 11.8 inches.

Renee Miller, a LIT member from south central South Dakota reported that a gentle rain that produced from 0.3 to 1.5 inches of total accumulation was very welcome because of the extended dry conditions. As a result of the rain, the grass began to turn green once again.

HALLOWEEN -- Tuesday is Halloween, derived from "All Hallowed Eve" since it is associated with a Christian observance, All Saints Day (1 November). However, today's festivities date back to pre Christian times because today represents the "cross quarter" day marking the halfway point between the autumnal equinox (22 September 2000) and the winter solstice (21 December 2000).


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 - 31 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.