WINTRY WEATHER ACROSS THE NORTHERN PLAINS -- An occluding storm system continued to move slowly northward through western Minnesota on Tuesday. By late evening, the center of this low pressure system was located along the Red River Valley just east of Fargo and Grand Forks, ND. An occluded front curved first northeastward from the low pressure center to the north shore of Lake Superior before turning southeastward to Lower Michigan where a point of occlusion was located. This triple point represented the junction of the occluded front with a warm front that stretched southeastward, rounding the southern end of the Appalachian mountains in northern Georgia, and a cold front that continued southward to northern Alabama, where the front turned into a nearly stationary warm front that stretched southwestward along the Gulf coast to across the lower Rio Grande Valley of south Texas.
A wintry mix of precipitation was found across the upper Midwest in association with this storm system. Relatively heavy snow fell earlier across North Dakota, with Williston recording 12.1 inches, which sets an all-time 24 hour snowfall total for that location. While some rain was reported across northern Minnesota as warm air with above freezing temperatures was drawn into the system on easterly winds, snow was falling around the western and southern sides of the storm as cold air was being carried southeastward across southern Minnesota. Freezing rain was also reported across the Red River Valley as warm air was carried above the colder air at the surface. Thundersnow -- where thunder was reported with the snow -- was also reported, indicating some instability.
While the low pressure center had started to fill on Tuesday night as the central pressure had increased by about 8 mb over the previous 24 hours, a tight pressure gradient remained especially to the west of the storm system. As a result, strong winds were found across the northern Plains. These winds contributed with the snow to producing near-blizzard conditions across the Dakotas.
The storm system is expected to move northward to the vicinity of Lake of the Woods and the Northwest Angle of Minnesota by Wednesday morning, and to western Ontario by evening. The accompaning occluded and cold fronts are expected to push eastward across the Great Lakes. Snow is expected to continue across eastern North Dakota and northern Minnesota for much of Wednesday. As a result, winter storm warnings remained in effect across North Dakota east of the Missouri River and some counties in South Dakota, while winter weather advisories were posted for western Minnesota.
SEVERE WEATHER ACROSS THE GULF COAST -- Thunderstorms erupted along the nearly stationary front that stretched along the Gulf Coast on Tuesday night. Several of these thunderstorms appeared to become severe as Doppler radar indicated at least one possible tornado along the Texas Gulf Coast just past local midnight. These thunderstorms were moving toward the northeast. Earlier in the late afternoon, thunderstorms produced quarter-sized hail across north central Louisiana near Monroe.
A low pressure system along the front is expected to intensify and cause the front to begin to move northward as a warm front. A slight risk of severe thunderstorms is expected to continue across the western Gulf Coast through Wednesday morning, in a region from the Mississippi Delta west to the Texas Gulf coast near Corpus Christi. This region is expected to expand eastward to include the Florida Panhandle on Wednesday.
The heavy rain that fell across Texas on Tuesday necessitated the issuance of flood watches for eastern, central and southern Texas.
Relatively warm weather was found along the Gulf Coast. Record high temperatures were reported at Brownsville, TX with 88 degrees and Huntsville, AL with 79 degrees.
SNOW ACROSS THE SOUTHERN PLAINS -- Snow fell in the cold air across west Texas and the plains of eastern New Mexico as of late Tuesday night. High temperatures on Tuesday across the region ranged between 25 and 35 degrees below the average high temperatures from the long-term averages for the date. Several record low high temperatures were reported in Texas at Austin (56 degrees) and Wichita Falls (46 degrees) and in Oklahoma at Oklahoma City (38 degrees).
This snow was part of a larger area of precipitation that stretched across the southern Plains to the north of the essentially stationary front that lay along the Texas Gulf Coast. By late Tuesday evening, as much as 14 inches of snow had fallen at Ruidoso in the Sacramento Mountains of southern New Mexico and 8 inches at Amarillo in the Texas Panhandle. Snow was reported as far south as Midland, TX.
The snow is expected to continue across the southern Plains through Wednesday morning. Winter storm warnings remained in effect for several counties in southeastern New Mexico, and a portion of the Texas Panhandle and mountains of West Texas, while winter weather advisories were posted for central Texas.
Elsewhere, in Colorado, Colorado Springs had a record low temperature of 13 degrees on Tuesday morning, while the afternoon high at Grand Junction was 38 degrees, a record low high temperature. In Wyoming, record low highs were also tied or broken at Cheyenne (24 degrees), Rawlins and Laramie (both with 19 degrees).
STORMY WEATHER FOR THE PACIFIC NORTHWEST -- A storm system off the coast of the Pacific Northwest produced some precipitation across northern Oregon on Tuesday night. The low pressure center was located west of the northern end of Vancouver Island, with a warm and a cold front extending southward along the Washington and Oregon coasts.
On Wednesday, the center of this occluding storm system should move into Puget Sound by morning and to southeastern Washington State by evening. Low elevation rain and high elevation snow are anticipated across the Pacific Northwest. Winter storm warnings were in effect for portions of central and eastern Washington State, much of eastern Oregon and northern Idaho. Winter storm watches were found across southwestern Montana, eastern Idaho, southwestern Wyoming, and much of Utah.
UPPER AIR -- Both the 500 and 300 mb charts for 00Z Wednesday show a "stacked" system over the Upper Midwest, characteristic of most occluded low pressure systems. In other words, a closed cyclonic (counterclockwise) circulation regime at each level is located essentially above that of the lower levels, extending from the upper troposphere down to the earth's surface. The cyclonic circulation regime corresponds to height troughs at each level, where the cold air in the intervening layers between the surface and those levels has dropped the heights of all the constant pressure surfaces. Strong jet stream winds across Texas were helping produce the strong to severe thunderstorms along the Gulf Coast.
YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US --Tuesday morning's lowest temperature was one degree below zero at Butte, MT, Stanley, ID and Aspen, CO, while the highest temperature on Tuesday was 93 degrees at McAllen, TX.
ALASKAN WEATHER -- High pressure across the Arctic Ocean continued to bring cold, arctic air into Alaska on Tuesday afternoon. Midafternoon temperatures were as low as 22 below zero at Arctic Village. The southern boundary of this air mass was a stationary arctic front that extended from the Yukon Delta in western Alaska across the Anchorage Bowl to the Wrangell Mountains in the southeast. Onshore winds across the Arctic coast produced foggy conditions over the North Slope. Some relatively cloud-free skies were found across the interior. A powerful storm system was moving across the Bering Sea. An occluded front curved eastward from the low pressure system then southward, crossing the eastern Aleutians. As a result, clouds were found across the eastern Aleutians and the Alaska Peninsula, to include rain at Cold Bay and St. Paul. Southeasterly winds gusting to nearly 50 mph were found at Cold Bay, Dutch Harbor and St. Paul Island. A weakening storm system was located in the Gulf of Alaska. The low pressure center remained just south of Kodiak Island, accompanied by an occluded front that stretched eastward and then southeastward along the Panhandle. Some rain and drizzle were reported over southeast Alaska, while snow fell during the morning across the northern Panhandle at Skagway and Haines.
The state's lowest overnight temperature on Tuesday morning was 29 degrees below zero at Umiat. The highest temperature by mid afternoon of Tuesday was 50 degrees at Dutch Harbor.
HAWAIIAN WEATHER -- Trade wind weather continued across Hawaii as a subtropical high pressure system was located to the northeast of the islands on Tuesday afternoon. These conditions are expected to continue through much of the remainder of the week. Relatively cloud-free skies prevailed across the islands, except where trade showers fell primarily over the windward slopes. Some traveling weak disturbances could enhance these showers. East to east-northeast trade winds had speeds that ranged between 10 to 25 mph. The high surf advisory that had been in effect for the north and west facing shores of the islands was canceled late Thursday afternoon as the surf subsided.
MONITORING EL NIÑO and LA NIÑA -- Scientists have suggested that some of the unusual weather patterns that have affected not only the United States, but other countries last year, are linked to an event called La Niña. The La Niña episode has persisted. For more details on how to monitor these phenomena, please read the optional Supplemental Information for Wednesday.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast