DATASTREME DAILY SUMMARY

Friday, 29 September 2000



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HAPPY NEW YEAR -- Rosh Hashanah, the Jewish new year, will begin at sundown. The Jewish new year falls on the sabbath following the new moon nearest the autumnal equinox. This month's new moon was on Wednesday (1953Z on 27 September) and the autumnal equinox was last Friday (22 September). The upcoming year in the Jewish calendar is 5761.

COOL WEATHER ACROSS THE NORTHEAST -- A large, sprawling Canadian high pressure cell centered over Lake Ontario as of Thursday night provided residents of the northeastern quadrant of the country with some chilly weather. Morning minimum temperatures across the eastern Lakes and New England ranged between 5 to 15 degrees lower than the long-term average lows for the end of September. The morning low temperatures at Traverse City, MI set a new daily record with 27 degrees, while at Buffalo, NY the 36 degree low tied the record. Even with sunny skies, afternoon high temperatures across the Middle Atlantic States were on the order of 10 degrees below the long-term average seasonal highs. The maximum temperature at Rochester, NY only reached 50 degrees, tying a low high record for the date.

The high pressure system is expected to drift slowly eastward, becoming centered over the Adirondacks of Upstate New York on Friday morning. With relatively clear skies, low amounts of atmospheric water vapor and weak winds, overnight low temperatures should fall to near the dewpoint temperature as strong radiational cooling takes place. As a rule of thumb, overnight low temperatures often coincide with the previous afternoon's dewpoint temperature, a measure of the atmospheric humidity defined as the point where the atmosphere just becomes saturated. Once the air temperature reaches the dewpoint, additional cooling is retarded as condensation releases latent heat in the phase change. With dewpoints ranging from the upper 20s to the low 30s across the Northeast, frost and freeze advisories were issued for all of Vermont, much of Massachusetts, New York State and Connecticut, the eastern two-thirds of Pennsylvania, western Maryland, and portions of West Virginia, northern Virginia and Maine.

A WARMING TREND ACROSS THE PLAINS -- Southerly winds developed across the Plains, causing temperatures to rise to above average readings. These winds were on the western flank of the large high pressure cell found across the East. Afternoon high temperatures across central Nebraska and the Dakotas were 20 degrees above the average highs for this time of year. The leading edge of the warm air was a warm front that stretched southeastward across the eastern Dakotas and western Minnesota.

As the high pressure cell moves eastward, the southerly flow of warmer air is expected to spread eastward across the Upper Mississippi Valley into the western Lakes states on Friday.

The warm, dry weather and the gusty southerly winds have increased the danger of wildfire across the Plains, stretching from the Texas Panhandle north to western South Dakota.

STORMS CONTINUE ACROSS SOUTH FLORIDA -- Rainshower and thunderstorm activity continued over south Florida in association with a stationary front that stretched in a northeast-southwest orientation across the Miami metropolitan area. Several inches of rain fell near Melbourne. As of Thursday night most of the thunderstorms were found along the Florida Keys and offshore on both the Atlantic coast and Gulf coast sides of south Florida. Several waterspouts were spotted near Key West.

The front is expected to remain essentially stationary on Friday. Between 1 and 1.5 inches of rain could fall along the front across southern Florida during the 24 hours commencing on Friday.

AFTERNOON RAINS PEPPER THE SOUTHWEST -- Thunderstorms produced on the order of 0.5 inches of rain in Tucson, AZ on Thursday afternoon. Some flooding was reported in the metropolitan area. Widely scattered, light precipitation continued across southern Arizona late Thursday night. The precipitation was related to the southerly wind flow that brought sufficient moisture into the Southwest.

The southerly wind flow is expected to expand north toward the Four Corners on Friday. As result, on Friday, as much as 0.5 inches in the San Juan Mountains of southwest Colorado.

UNSETTLED WEATHER ACROSS THE PACIFIC NORTHWEST -- A region of weak low pressure across the Pacific Northwest produced rain over western Washington State. A cold front was situated off the west coast of Vancouver Island. On Friday, the areal coverage of rain is expected to expand eastward into the northern Idaho. On the order of 1 inch of precipitation is expected to fall by Saturday morning along the windward slopes of the Olympics and northern Cascades.

TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Thursday's lowest temperature was 18 degrees at Stanley, ID. Thursday's highest temperature was 105 degrees at Lake Havasu City, AZ.

ALASKAN WEATHER -- High pressure dominated most of Alaska on Thursday resulting in relatively clear skies and chilly conditions across western and central Alaska. Gusty northerly winds were found across south central Alaska, the Alaska Peninsula and Kodiak Island. With morning temperatures in the low 20s and gusty winds, wind-chill equivalent temperatures fell to 5 degrees below zero across the north, to include Barrow. An elongated low pressure system with two centers just to the south of Cordova in the northern Gulf of Alaska and near Whitehorse in the southern Yukon Territory produced a variety of wintry weather across southeast Alaska. To the north of the low, heavy snow fell across portions of the upper Tanana Valley, with 20 inches reported along the Alaska Highway east of Delta Junction. Freezing rain fell at Northway during the morning. To the south, clouds, rain and windy conditions were found over the Panhandle.

The lowest overnight temperature in Alaska on Thursday morning was one degree above zero at Anaktuvuk Pass, while the mid-afternoon highest statewide temperature was 57 degrees at Metlakatla.

HAWAIIAN WEATHER -- The disturbance in the trades marked by a trough of low pressure that passed over the islands on Wednesday continued moving westward from Kauai on Thursday afternoon. Showers lingered over Kauai and Oahu on Thursday afternoon while the other islands experienced clearing conditions with a decrease in the high humidity. Winds across the islands were light and from the east to southeast. These winds will remain from the southeast as a ridge of high pressure to the northeast of Hawaii drifts away from the islands and a trailing cold front from a midlatitude storm system approaches the islands from the northwest.

High surf advisories remained in effect for the north and west shores of the islands, the result of continued ocean swell generated from an earlier major storm system.

EYE ON THE TROPICS -- Hurricane Isaac intensified to become a category 4 hurricane on the Saffir-Simpson Hurricane Intensity Scale. This major hurricane had sustained near-surface winds of 130 mph late Thursday night as it continued moving to the north-northwest at 17 mph within 620 miles to the east-southeast of Bermuda. Hurricane Joyce was located approximately 855 miles east of Barbados and moving west at 14 mph with sustained surface winds of 85 mph. Over the northwestern Caribbean, a tropical disturbance intensified and organized into Tropical Depression 15. This system with sustained surface winds of 30 mph was nearly stationary at a location 85 miles north of Cape Gracias a Dios, Honduras. Due to the slow movement of the depression, heavy rains could produce dangerous mudslides along the rugged coast of Honduras.

REPORT FROM THE FIELD --Renee Miller, a LIT member from near Presho in central South Dakota, reported that after last weekend's first killing frost of the season, the temperatures have returned to near 90 degrees by the end of this week. She lamented that the forecasted rain of last Friday never materialized. On Thursday afternoon she could see the smoke from prairie fires that continued to be a problem because of the dry conditions in the high Plains.


HISTORICAL WEATHER EVENTS - 29 September

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

30 September

1 October


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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2000, The American Meteorological Society.