ACTIVE WEATHER CONTINUES ACROSS THE PLAINS -- Numerous rainshowers and embedded thunderstorms continued to move across the Plains states ahead of a slowly advancing cold front late Wednesday night. The area of precipitation extended from southern Minnesota south to north Texas, with the most intense thunderstorms located southward from central Kansas. The cold front trailed from a low pressure center situated over South Dakota southward to west Texas. This cold front was the leading edge of cooler and drier air that was replacing warm and humid air that was found across the Plains. The southerly winds ahead of the cold front helped pump warm humid air northward, helping to maintain the thunderstorm activity.
Late Wednesday afternoon severe thunderstorms developed across southwest Kansas and the Oklahoma Panhandle. One thunderstorm spawned a tornado near Dodge City, KS, remaining on the ground for 7 minutes according to a spotter. Hail ranging between quarter and half dollar size fell from these severe thunderstorms. To the north of Dodge City, hail was piled to the depth of 10 inches on the east side of a house.
While the cold front is expected to weaken and become a trough line by Thursday morning, the widespread precipitation should continue across the Plains. As much as 2 inches of rain could fall between Wednesday and Thursday evenings across the Red River Valley of north Texas and southern Oklahoma. Because of the anticipated heavy rain on top of recent rain events, flash flood watches were in effect for south central Kansas, to include Wichita.
CONTINUED BATTERING OF THE FLORIDA COAST -- A storm system with gale-force winds (ranging between 39 to 46 mph) was continuing to develop over the Atlantic Ocean just to the east of the Bahamas. As a result of the tight pressure gradient between the high pressure system centered over the Middle Atlantic and the low pressure system, northeasterly winds continued to gust to 30 mph. As a result of these onshore winds, seas to heights of 8 feet have produced heavy surf conditions along the Atlantic Coast, especially in Florida. Consequently, heavy surf advisories were continued for the Florida coast from Flagler Beach southward to Ocean Reef. The heavy surf has produced hazardous rip currents and beach erosion, especially at high astronomical tide.
UNSETTLED CALIFORNIA WEATHER -- A storm system was located along the northern California coast. The occluded front associated with this system extended southeastward from the low pressure center, crossing into coastal California near Eureka, then curving to the southwest over the central valleys and continuing off shore as a cold front south of Monterey Bay. A large area of precipitation associated with this storm system extended across the northern half of California, along with northwestern Nevada and southeastern Oregon.
This storm system has produced windy conditions and an ocean swell that had recorded heights to 26 feet north of Point Conception early Wednesday. As this storm develops and moves southeastward, northwest swells could generate surf to as high as 10 feet along the west and northwest facing beaches. Consequently, heavy surface advisories were posted along the central California coast from Point Piedras Blancas north to Point Arena.
The storm is expected to move southeastward and come onshore over central California on Thursday. The accompanying precipitation should fall as rain at lower coastal elevations, with mountain snow in the higher elevations of the central Sierras. Some coastal locations south of Big Sur could receive as much as an inch of rain by Thursday evening.
MORE FOG -- The area under high pressure across portions of the Great Lakes and New England was once again susceptible to the formation of dense fog late Wednesday night as air cooled to the dewpoint. With visibility falling to less than 0.25 miles in many cases, dense fog advisories were issued for selected counties in Indiana, Lower Michigan, Ohio, New York State, Massachusetts and Rhode Island. The fog is not likely to dissipate until midmorning in many locations as a combination of solar heating and wind mixing occur.
UNSEASONABLY WARM CONDITIONS -- Much of the nation east of the cold front in the Plains experienced relatively warm weather on Wednesday, as afternoon high temperatures were at or above the long-term average highs for the date. Some locations across the mid-Mississippi Valley had highs that were more than 15 degrees above the average. Record high temperatures were either tied or set on Wednesday afternoon in Tennessee at Memphis (86 degrees), Chattanooga (84 degrees), Jackson (83 degrees) and Dyersburg (82 degrees), in Alabama at Huntsville (84 degrees) and in Kentucky at Paducah (82 degrees).
The southerly winds on the western flank of the large high pressure system helped maintain these warm conditions. In addition to the high temperatures, the overnight low temperatures across the Midwest were elevated not only because of southerly winds but also due to the low clouds and fog that prevented significant nocturnal radiational cooling. In Iowa, Des Moines and Dubuque had record high minimum temperatures of 59 and 57 degrees, respectively.
WET WEATHER TO BRUSH THE LAKES -- A weak low pressure system along a cold front was situated across the northern Plains and upper Mississippi Valley on Wednesday night. This system was accompanied by rain that stretched from eastern Montana across the Dakotas into northern Minnesota.
The low is expected to drift east toward Lake Superior by Thursday evening, with the cold front pushing southeastward. About a half inch of rain is expected across northern Minnesota during this time frame.
TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 20 degrees at Truckee, CA, while the Wednesday afternoon highest temperature was 90 degrees at Alice, TX.
ALASKAN WEATHER -- A storm system with several low pressure centers was located over western and south central Alaska on Wednesday afternoon. The center of the complex was located in the central Bering Sea. One low pressure center was located in the Bering Strait, another in the Susitna River Valley and a third in the south central Gulf of Alaska. Heavy rain fell across south central Alaska in association with the complex storm system. Snow fell on Wednesday afternoon at Barrow.
The lowest temperature in Alaska on Wednesday morning was 15 degrees below zero at Deadhorse. The highest statewide temperature as of Wednesday afternoon was 52 degrees at Birchwood.
HAWAIIAN WEATHER -- With the subtropical high pressure system remaining to the north of the Hawaiian Islands, northeast trade winds remained relatively strong with 20 mph wind speeds on Wednesday afternoon. A cold pool of air to the northeast of the Big Island was beginning to move southwestward, resulting in an increase in clouds and showers.
EYE ON THE TROPICS -- The eighteenth tropical depression of the eastern North Pacific hurricane season formed off the Central American coast on Wednesday. As of Wednesday night, Tropical Depression 18E had maximum sustained winds of 35 mph and was moving to the west at 16 mph approximately 880 miles south-southwest of Cabo San Lucas, Mexico.
Question: What do meteorologists, police and television baseball announcers have in common? Answer: Doppler radar, for one thing.
Radar, RAdio Detection And Ranging, uses a pulse of microwave energy sent out and echoed back by a distant target. Using radar, we can spot targets at various distances and directions. Tracking airplanes was the first goal of radars. Meteorologists have long used radar to spot the locations, intensities and movements of precipitation that are associated with storm systems. Recently the National Weather Service installed a network of new radar units across the U.S. that can also detect motions of raindrops, snowflakes, and hail using the Doppler principle. When a moving target echoes back part of the radar pulse, the frequency of the electromagnetic energy is shifted slightly from the original signal value. The amount of shift relates to the speed of target movement directly toward or away from the receiver. With a weather radar this means we can infer the wind speeds and directions that move the raindrops and other particles in the storm.
Police agencies have also used Doppler radar units in enforcing speed limits. A traffic radar aimed at a moving car will tell the car's speed directly toward or away from the unit. The sports media have been quick to use this technology to impress viewers with the speed of a baseball pitch or tennis serve. While the speed of a pitch from the mound to home plate can be "measured" because it travels toward the radar, a throw from third to first base would not because it is moving across the radar beam. So Doppler weather radar interpretation is much more complex than baseball and chasing speeders. Storm motions are scanned across the entire atmosphere surrounding the radar site for hundreds of kilometers out and several kilometers up, with no "seventh inning stretch"!
Another additional feature of the new Doppler radar units operated by the National Weather Service is the capability to estimate the accumulated rainfall over a given area near the radar unit and then alert the radar operator to the possibility of flooding if some critical threshold were reached. As a result, flash flood watches and warnings can be issued more promptly.
For more information describing interpretation of DataStreme radar summary products, you may consult Thursday's electronic Supplemental Information .
To be submitted on the lines for Thursday on the Study Guide, Part B, Applications', Week 7 Chapter Progress Response Form, under section B. Daily Summary.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast