DATASTREME DAILY SUMMARY

Wednesday, 26 September 2001


00Z Weather Systems


The following highlights of the national weather have been extracted from the surface weather map for Tuesday night:

WET WEATHER CONTINUES ACROSS THE NORTHEAST -- An occluding storm system continued to dominate the weather across the Northeast on Tuesday. This slow-moving storm system was progressing through the later stages of its life cycle as indicated by the development of an occluded front. The primary low pressure center as of Tuesday evening was located over Georgian Bay in Ontario, having moved slowly toward the northwest from a position over northern Pennsylvania in the previous 24 hours. This low pressure center is forecast to rotate in a counterclockwise direction over Georgian Bay during the next 24 hours. Such an apparent erratic track of the primary low pressure center occurs frequently as an occluding storm begins to decay. An occluded front, representing the amalgamation of a cold front with a warm front, extended northeastward from the primary low pressure center into Quebec, where a warm front continued across the lower St. Lawrence Valley and a cold front stretched southward across New England and just off the Middle Atlantic Coast.

Several widespread areas of rain associated with this storm system continued across New England and the Great Lakes as of late Tuesday night. One major area of precipitation was found in the warm sector of the storm between the warm and cold fronts across southern New England, extending off the Middle Atlantic coast. Another area of rain was located to the north of the warm front, extending across northern New England and adjacent portions of Quebec and New Brunswick. Smaller areas of precipitation were also found across Lake Michigan and Lower Michigan to the west and southwest of the low pressure center, representing wrap-around precipitation carried around the storm.

On Wednesday a secondary low pressure center is expected to form at the point of occlusion over the mouth of the St. Lawrence River, marking the point of intersection of the warm, cold and occluded fronts. Farther to the south, the cold front is expected to continue to move eastward off the New England coast. Several areas of precipitation should continue across New England and the Great Lakes states. Between 0.5 and 0.9 inches of rain could fall in the 24 hours ending on Wednesday evening over New England, with approximately 0.5 inches possible over the Lakes.

ANOTHER CHILLY DAY ACROSS THE NATION'S MIDSECTION -- Cold high pressure continued across the Mississippi Valley on Tuesday. The cold air mass coupled with weak winds and relatively clear skies allowed overnight temperatures to fall because of strong radiational cooling during the night. Record low temperatures were set at Springfield, IL (36 degrees), Columbia, MO (37 degrees), Jackson, KY (42 degrees) and Tulsa, OK (42 degrees). Despite relatively sunny skies, the temperatures did not rebound quickly, in part because of the cold air being carried southward on northerly winds. Afternoon high temperatures were on the order of 10 to 20 degrees below the long-term average highs for the date across a large portion of the nation's midsection stretching from the Great Lakes to the Gulf Coast and from the Appalachians to the southern Plains. The largest anomalies, or differences between the actual and average temperatures, were found near Lakes Huron and Erie, where the actual highs were 20 degrees below the average highs. The high temperatures at Grand Rapids (45 degrees) and Lansing (44 degrees) in Michigan and at Lexington (55 degrees) and Louisville (57 degrees) were record low high temperatures for the date.

High pressure should remain across the Mississippi Valley on Wednesday. Consequently, frost advisories were posted for Tuesday night and Wednesday morning covering portions of central Wisconsin, southwest Iowa and the valleys in east Tennessee and southwestern Virginia.

THE HEAT CONTINUES ACROSS THE WEST -- A large region of high pressure across in the Intermountain West continued to maintain unseasonably warm weather across the region. Afternoon high temperatures ranged from 15 to 20 degrees above the average highs for late September across much of the West, with the greatest anomalies centered over Montana. Daily record high temperatures were either tied or exceeded in Montana at Havre (96 degrees), Helena (95 degrees), Great Falls (93 degrees), Cut Bank (89 degrees), Kalispell (88 degrees), Butte (86 degrees) and West Yellowstone (83 degrees); in Idaho at Pocatello, ID (92 degrees); in Utah at Wendover (93 degrees), Salt Lake City (92 degrees) and Logan (88 degrees); in Wyoming at Rawlins (88 degrees), Rock Springs (83 degrees) and Laramie (78 degrees) in Colorado at Grand Junction (89 degrees) and at Alamosa (80 degrees) and in Arizona at the South Rim of the Grand Canyon (84 degrees). The afternoon high at Pocatello also was the highest temperature for so late in the season.

UNSETTLED WEATHER IN THE NORTHWEST -- A low pressure system and trailing cold front moved into the Pacific Northwest on Tuesday. The cold front extended from the low in western Montana across Idaho into Nevada. Several large areas of precipitation associated with this system were found across Montana, northern Idaho and portions of Washington State. Another eastward moving cold front was approaching the coasts of Washington and Oregon.

The first cold front is expected to move across the northern Rockies by late Wednesday, while the second cold front is forecast to move onshore and cross the Cascades. Cumulative precipitation totals for the 24 hours ending on Wednesday evening should range from 0.4 inches to 1.4 inches across northern Idaho, Washington and northern Oregon. The largest totals are anticipated along the western slopes of the Olympics, Coast Range and the Cascades, the result of the onshore flow of moist air being lifted along these mountain barriers.

Farther south, strong winds developed across the mountains of southern and central California along with adjoining portions of Nevada. Winds reached 68 mph along the Sierras in east central California on Tuesday morning. High wind warnings and advisories were in effect across the region through Tuesday evening.

YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US -- Tuesday morning's lowest temperature was 22 degrees at Hibbing, MN, while the highest temperature on Tuesday was 110 degrees at Death Valley, CA.

ALASKAN WEATHER -- Widespread clouds and rain were found across south central and southeastern Alaska on Tuesday as the result of a storm system located in the Gulf of Alaska. Yakutat recorded 2.36 inches of rain in the 24 hours ending on Tuesday afternoon. Haines, Ketchikan and Petersburg also received at least one inch of rain. Farther west, a frontal system associated with a storm system over the western Bering Sea spread clouds and windy conditions across the Bering Sea and the Aleutians. A low pressure system over the Beaufort Sea north of the Yukon Territory spread clouds over northeast Alaska. Relatively cloud-free skies were found across interior Alaska to the east of Tanana.

The state's lowest overnight temperature on Tuesday morning was 21 degrees at Manley Hot Springs. The highest temperature by mid afternoon of Tuesday was 63 degrees at Big River Lakes.

HAWAIIAN WEATHER -- Showers were expected to increase across the islands on Tuesday night and Wednesday as a shear line approached the Aloha State. This region of enhanced clouds and showers together with a change in the winds represented the remnants of a former midlatitude front. The showers were found along a 100 mile wide band of low clouds located to the windward sides of the island chain. Trade winds are expected to increase as the shear line and showers pass on Wednesday. A large ridge of high pressure was situated to the north and northwest of Kauai.

EYE ON THE TROPICS -- In the North Atlantic, minimal Hurricane Humberto continued to move toward the northeast away from North America. As of late Tuesday night, Hurricane Humberto had sustained maximum surface winds of 75 mph and its location was 260 miles south of Cape Sable, NS. Forward motion was to the northeast at 12 mph.

In the eastern North Pacific, Tropical Depression Kiko continued to weaken and final advisories were issued on Tuesday afternoon. At that time maximum sustained surface winds had fallen to 30 mph and Kiko was located 1290 miles to the west-southwest of Cabo San Lucas, Mexico with movement to the west at 8 mph. Hurricane Juliette continued to strengthen into a major Category 4 hurricane on the Saffir-Simpson Hurricane Intensity Scale. With maximum sustained surface winds estimated to be at 145 mph on Tuesday evening, Hurricane Juliette was 430 miles south-southwest of Cabo San Lucas, Mexico. Movement was to the west-northwest at 9 mph. A variety of tropical storm watches and warnings have been posted for portions of the west coast of Mexico and southern Baja California.

NORTHERN LIGHTS? -- Solar physicists have announced major solar activity on Monday and Tuesday. The coronal mass ejection could produce a major auroal display over the next several nights. This auroal display is also known as northern lights. If skies are relatively clear, take a look.

LEAF PEEPING? -- Read the optional Wednesday Supplemental Information to learn more about why deciduous trees turn color in autumn and find the current updates on the progression of the fall coloration through the National Forests across the country.


HISTORICAL WEATHER EVENTS - 26 September

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


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URL: datastreme:/learn/w_sum.html
Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.