WINDY WEATHER MOVES ACROSS THE UPPER MIDWEST -- A compact storm moved east-northeastward from the Great Plains to the upper Great Lakes on Wednesday. As of late Wednesday night the low pressure center, with a central pressure of approximately 992 mb, was located over eastern Lake Superior. An occluded front extended to the southeastward across Lower Michigan to a point of occlusion, or triple point where the occluded front met the warm front that extended to the east into the Middle Atlantic States and a cold front that curved southwestward to west Texas. Because little moisture was available to the system, this storm system had a relatively small precipitation shield, primarily consisting of lake-enhanced snow that fell over the Arrowhead of Minnesota, across northern Wisconsin and Michigan's Upper Peninsula.
The main feature of this storm system was the winds. A relatively strong pressure gradient especially to the west of the low pressure center, as indicated by a tight packing of the isobars on Wednesday night's surface analyses, produced the strong winds that gusted to 65 mph at La Crosse, WI. The strongest winds were found primarily behind (or to the west of) the advancing cold front. Wind damage was reported in northwest Minnesota and across south central Wisconsin on Wednesday afternoon as winds gusted to 52 mph. This storm system had a history of strong winds as a 63 mph wind gust was recorded at Billings, MT on Tuesday, which was a record gust for the month of March. Earlier on Wednesday, snow fell from eastern North Dakota into northern Minnesota. This snow was accompanied by high winds.
A reasonably strong temperature contrast was produced by the counterclockwise wind circulation around the low pressure center. Strong southwesterly winds to the south and east of the storm brought warm air north toward the eastern Great Lakes, where Buffalo, NY reported late evening temperatures in the upper 50s. Wednesday afternoon high temperatures across the Ohio Valley and into the Middle Atlantic States were between 15 and 20 degrees above the 30 year average high temperatures for this time of year. On Wednesday afternoon, a record high temperature was reported at Blacksburg, VA (70 degrees).
To the west of the surface low pressure system, the strong northerly winds were responsible for cold-air advection across the upper Mississippi Valley and the northern Plains. While temperatures of this region were seasonal, the winds helped reduce wind-chill equivalent temperatures to the single digits over the Dakotas and Minnesota.
By Thursday morning the storm should have moved into Canada, with the low pressure center located near Ottawa, ON. The region of strongest winds should shift eastward. The precipitation should be confined primarily to areas north of the Lakes. The cold front is forecast to have crossed the Appalachians, meaning that the unseasonably warm weather that residents had across the region on Wednesday will come to a temporary end on Thursday.
SEVERE WEATHER DEVELOPS ACROSS TEXAS -- A storm system moved into west Texas accompanied by severe thunderstorms. The low pressure center was situated over the Permian Basin of west Texas with a cold front that extended southward across the Big Bend into northern Mexico. This low pressure system was just south of the southwestern terminus of a cold front that extended across the southern Plains from the Great Lakes storm system.
A southeasterly wind flow on the east side of the surface low brought warm, humid Gulf air into Texas. In the vicinity of the cold front, severe thunderstorms moved across west Texas and eastern New Mexico on Wednesday evening, with large hail and a rotating wall cloud reported at Hobbs, NM. A rotating wall cloud is often considered as a precursor to a tornado.
In the cold air to the north and west of the storm snow continued across the mountains of Arizona and New Mexico on Wednesday morning, with Flagstaff, AZ receiving about 3 inches of snow.
This system is expected to move slowly eastward by Thursday morning. A slight risk of severe thunderstorms continues across central Texas through Thursday in the region of the warm sector to the southeast of the low pressure center. The rain over the Texas and Oklahoma Panhandles could turn to snow by daybreak, where a winter storm watch had been posted. Since the slow movement of the system is expected to produce heavy amounts of rain, flash floods could be possible across portions of central and east Texas north to the Red River Valley.
A NEW STORM APPROACHES THE PACIFIC NORTHWEST -- One storm system moved into the Pacific Northwest on Wednesday as low pressure system reached the British Columbia coast and a trailing cold front crossed into Washington and Oregon. By late Wednesday night the cold front had weakened and formed a trough line to the east of the Cascades. The next storm system, located several hundred miles to the west in the eastern Pacific is expected to approach the coast by Thursday morning. A heavy surf advisory remained in effect for the Washington coast from Cape Flattery to Cape Shoalwater until early Thursday morning as 20 to 24 foot swells reached the coast.
YESTERDAY'S TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Wednesday was 7 degrees below zero at West Yellowstone, MT. Wednesday's high was 89 degrees at Laredo, TX.
ALASKAN WEATHER -- A blizzard warning was posted for Cold Bay and vicinity extending through Thursday as blizzard conditions were anticipated because of the possibility of southeasterly winds gusting to 65 mph together with heavy snow, accumulating to 7 inches.
A large storm system over the Bering Sea to the west of Adak with a front that curved southeast across the eastern Aleutians spread clouds and precipitation across the Aleutians and the Alaska Peninsula A strong pressure gradient surrounding this storm system produced strong winds at Adak, where gusts reached 42 mph and at Dutch Harbor with gusts to 45 mph. Elsewhere, Tin City had sustained 21 mph winds with a wind-chill equivalent temperature of 61 degrees below zero. Another dissipating low pressure system near Kodiak Island produced some clouds along the western Gulf Coast. To the southeast, a storm system moved on shore along the coast of British Columbia near the Queen Charlotte Islands, and spread some clouds and light precipitation across the southern Panhandle.
A ridge of high pressure extending across northern Alaska from one center in Far East Russia to another in western Canada helped provide much of the Alaska mainland with relatively cloud free-skies on Wednesday afternoon..
On Tuesday morning the temperature at Kodiak fell to 2 degrees, a record low reading for the date.
The state's lowest overnight temperature on Wednesday morning was 31 degrees below zero at Sleetmute. The midafternoon state highest temperature was 44 degrees at Ketchikan and Klawok.
HAWAIIAN WEATHER -- Following passage of clouds and showers early Wednesday morning, relatively sunny skies returned to the islands. On Wednesday afternoon a large ridge of high pressure was located approximately 600 miles north of Honolulu helping generate moderate to strong east-northeast trade winds across the islands. Trade wind showers were also found especially along the windward slopes of the islands. This high pressure system is forecast to continue moving slowly toward the southeast. High surf advisories were to be continued for the northwest shores of the islands until early Wednesday evening, when they could expire. Small craft advisories remained in effect for state waters.
A SERIOUS FLOOD POTENTIAL -- At a meeting held Wednesday, top National Weather Service officials stated that the several areas of the country face flood danger because of the size of the snowpacks produced by persistent weather patterns over the winter. One area of concern was the Red River of the North, where a disastrous flood occurred in the spring of 1997. Another area of concern was in the Pacific Northwest and adjacent portions of Idaho, Montana and northern California where storms have deposited a near record snow pack. Northern New England has substantial snow cover.
According to John J. Kelly, director of the National Weather Service, floods kill 100-140 people annually and cause an average of $4.5 billion in damage, accounting for three-quarters of presidential disaster declarations.
THE STÜVE DIAGRAM -- For more information describing the various sets of lines on a Stüve Diagram and how you can make graphical determinations from a Stüve Diagram, you may consult the optional material in Thursday's electronic Supplemental Information.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological Society.