Wednesday Daily Weather Summary

ONLINE DAILY WEATHER SUMMARY

Wednesday, 21 April 1999

THUNDERSTORMS FIRE OVER THE MIDWEST
DRY WEATHER CONTINUES ACROSS THE SOUTHEAST
IMPROVING WEATHER ACROSS THE NORTHEAST
MORE UNSETTLED WEATHER OVER THE ROCKIES
UPPER AIR
TEMPERATURE EXTREMES ACROSS THE LOWER 48
ALASKAN WEATHER
HAWAIIAN WEATHER
TORNADO STATISTICS
HISTORICAL WEATHER EVENTS

THUNDERSTORMS FIRE OVER THE MIDWEST -- Rain, showers and thunderstorms developed along and to the north of a warm front that stretched across the mid-Mississippi Valley on Tuesday night. This warm front was associated with a low pressure center that was located near Kansas City, MO. To the east, the warm front connected with a cold front that was located over the Carolinas. These fronts separated a warm air mass across the Gulf Coast states from cooler air over the Midwest. By early evening, some of the thunderstorms over Missouri became severe, as they produced large hail over north central Missouri near Columbia. Farther to the north of the warm front, a large region of non-convective rain stretched across much of Indiana, northern Illinois, eastern Wisconsin and eastern Iowa.

The warm front is expected to shift slowly to the north before becoming stationary across southern Iowa and central Illinois by Wednesday morning. The region near the front from central Kansas through central Illinois is expected to experience a slight risk for severe thunderstorms through Wednesday.

DRY WEATHER CONTINUES ACROSS THE SOUTHEAST -- A persistent ridge of high pressure remains anchored over the Gulf Coast. As a result, a large portion of the Southeast continues to remain relatively cloud-free and dry. While the fire danger remains extremely high, some wildfires in Florida have been contained. The portion of I-75 east of Naples called Alligator Alley was reopened on Tuesday. Little significant precipitation is forecast for the next several days.

Despite the hot daytime weather, the presence of an unusually dry air mass with low dewpoints together with weak nighttime winds has allowed for significant radiative cooling at night, even over the Florida Peninsula. Consequently, record low temperatures were set on Tuesday morning at St. Petersburg, FL, Melbourne, Orlando (all with 50 degrees) and West Palm Beach (55 degrees). Farther to the west, a record high temperature was set at Midland, TX (93 degrees).

Some rain did fall across portions of the Southeast, associated with thunderstorms that developed along a frontal boundary that was found across the Tennessee Valley. During the early morning hours of Tuesday, several severe thunderstorms moved across northern Alabama and Georgia, producing large hail with diameters as large as one inch.

IMPROVING WEATHER ACROSS THE NORTHEAST -- The rain and rainshowers that dampened many of the cities in the Northeast during the day were replaced by clearing skies by Tuesday night. Some widely scattered light precipitation remained over the Champlain Valley of Upstate New York and Vermont. The precipitation that fell earlier was associated with low pressure that moved from the Ohio Valley toward the Middle Atlantic Coast, and then out over the Atlantic Ocean. A ridge of high pressure located over Pennsylvania late Tuesday night was responsible for the clear skies. This high pressure system is expected to move eastward toward the Delmarva Peninsula on Wednesday morning.

MORE UNSETTLED WEATHER OVER THE ROCKIES -- A storm system with several weak and diffuse low pressure centers moved across the Rockies on Tuesday night. The main low pressure center was located over northeast Montana, with a cold front that trailed to the southwest toward the Rim country of northern Arizona. Widely scattered precipitation associated with the system was found across Montana, Wyoming and northern Colorado. Earlier, small hail and winds gusting to 35 mph were reported in eastern Washington on Tuesday afternoon. Farther west, precipitation continued along the Washington coast and into Puget Sound, the result of orographic lifting of prevailing onshore winds.

This system is expected to move eastward, with several of the low pressure systems to be located over the high Plains on the lee of the Rockies by Wednesday morning. Low elevation rain and mountain snow are expected across the Rockies and western Plains.

UPPER AIR -- The mid and upper tropospheric weather charts for 00Z Wednesday reveal a relatively zonal wind flow, with little of the north-south excursions exhibited near the end of last week when a more meridional circulation was in control with large ridges and troughs. Several small waves in the flow can be found on both the 500 and 300 mb constant pressure surfaces. These features are associated with the surface pressure systems. The general eastward progression of these surface systems should be the result of the zonal flow aloft. Except for 300 mb winds that exceeded 110 knots along the West Coast, wind speeds in the 300 mb jet have been weaker and displaced slightly to the north.

TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Tuesday, the lowest temperature reported in the continental U.S. was 21 degrees at Cadillac, MI, Taos, NM and Gunnison, CO, while Tuesday's high was 103 degrees at Thermal, CA.

ALASKAN WEATHER -- An elongated trough of low pressure with several low pressure centers stretched from southwest to northeast across Alaska. One low pressure center was located north of Dutch Harbor, another low was situated over the Alaska Peninsula near Chignik and a third low was found north of Fairbanks. A stationary front ran across the interior, as temperatures reached the low 60s over the lower Tanana Valley, while temperatures in the single digits were found across the northwest corner of Alaska. These lows brought clouds and precipitation to the southern and northern thirds of the state on Tuesday. Rain was found along portions of the northern Gulf coast and along northern portions of the Panhandle. Snow fell across the North Slope and the Arctic coast. Snowshowers were also found over some of the islands in the Bering Sea, while freezing rain was reported on Tuesday afternoon on St. Paul Island.

A weak high pressure cell was located over the southern tip of the Panhandle, while a large ridge of high pressure located over Far Eastern Russia extended east toward the Bering Strait. The strong pressure gradient between the high pressure center over Russia and low pressure over Alaska produced strong winds ranging from 25 to 35 mph along the Chuckchi Sea coast in northwest Alaska. Kivalina reported a wind-chill equivalent temperature of 37 degrees below zero.

For a third consecutive day, the unseasonably mild conditions across the Tanana Valley help set some new record high temperatures on Tuesday. Fairbanks had an daily maximum of 60 degrees, Delta Junction (50 degrees) and McGrath (57 degrees).

The lowest overnight temperature across the state as of Tuesday was one degree below zero at Wainwright Airport. The midafternoon highest temperature in the state was 63 degrees at Eielson AFB and Fort Wainwright.

While the snow season is not over, several locations in south central Alaska have already set new seasonal snowfall records as of a week ago, to include: Whittier with 413.8 inches, Seward (214.0 inches), Dutch Harbor Airport (169.0 inches) Cold Bay (149.3 inches) and Homer (130.9 inches). The heavy snow, which exceeded 15 feet at some mountain locations, created avalanche conditions. Flooding is also a potential problem especially near Homer and Seward.

HAWAIIAN WEATHER -- Trade winds over the islands have weakened as the ridge of high pressure has moved well to the northeast of Hawaii, approximately half-way to California. A cold front is located over 1000 miles to the northwest of Kauai. Light trade showers are expected to continue across the windward sides of the islands.

TORNADO STATISTICS -- The second half of April marks the beginning of a two month interval that usually contains the most tornadoes across the country on average. April also is the month that typically has the highest tornado-related death toll. For more information on various tornado statistics, check Wednesday's optional Supplemental Information.

HISTORICAL WEATHER EVENTS - 21 April

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

...1857...The Genesee Suspension Bridge, in Genesee, New York, collapsed under the weight of 12 inches of wet snow weighing 19 pounds per cubic foot. Snow fell to a depth of 48 inches at Liberty in the Catskills. (Intellicast)
...1882...Monticello, MS was virtually destroyed as an F4 tornado ripped through the town. Only 3 houses on the outskirts of town were left standing. Ten people were killed and 100 were injured. (Intellicast)
...1887...Twenty one people were killed and 250 were injured as an F4 tornado tracked 60 miles through Anderson and Lima counties in Kansas and Bates county in Missouri. Total damage was $1 million, one of the few million dollar tornadoes in the 19th century. (Intellicast)
...1958...Portions of Montana were in the midst of a spring snowburst. Snowfall amounts ranged up to 55 inches at Red Lodge, 61 inches at Nye Mine, and 72 inches at Mystic Lake. (David Ludlum)
...1967...Severe thunderstorms spawned 48 tornadoes in the Upper Midwest. Hardest hit was northern Illinois where sixteen tornadoes touched down during the afternoon and evening hours causing fifty million dollars damage. On that Friday afternoon twenty four people were killed, 500 were injured, and $22 million in damage was done in Belvidere, IL as a F4 tornado ripped through the city. Another F4 tornado cut a path through Cook county and killed 33 people and injured another 500, with the Chicago suburb of Oak Lawn being hard hit. (David Ludlum) (Intellicast)
...1980...The temperature at International Falls, MN hit 90 degrees. (The National Weather Summary)
...1987...Unseasonably warm weather prevailed from the Gulf of Mexico to New England and the Great Lakes Region, with twenty-nine cities reporting record high temperatures for the date. Afternoon highs of 82 degrees at Caribou, ME, 94 degrees at Mobile, AL, 95 degrees at Monroe, LA, and 93 degrees at New Orleans, LA, were records for the month of April. (The National Weather Summary)
...1988...After having had just twelve rain-outs in the previous twenty-six years at Dodger Stadium, a third day of heavy rain in southern California rained out a double-header at Dodger Stadium which had been scheduled due to rain-outs the previous two days. (The National Weather Summary) (Storm Data)
...1989...The temperature at Las Animas, CO soared to 100 degrees to establish a state record for April. Twenty-two cities in the central and southwestern U.S. reported record high temperatures for the date. Eight cities equaled or exceeded previous April records. Tucson, AZ experienced its fourth consecutive day of record heat with an afternoon high of 104 degrees, bringing the total number of days during the month of April 1989 to 11 when record high values had either been matched or broken. (The Weather Channel) (The National Weather Summary) (Intellicast)
...1990...Afternoon and evening thunderstorms produced golf ball size hail in Oklahoma, and also caused some flash flooding in the state. Thunderstorms over the Southern High Plains produced golf ball size hail at Roswell, NM and El Paso, TX. Easterly winds and temperatures near zero produced wind chill readings as cold as 50 degrees below zero for the spring festival (Piuraagiaqta) outdoor events at Barrow, AK. (The National Weather Summary) (Storm Data)
...1992... Two inches of snow fell at International Falls, MN, bringing the winter season snowfall to 106.7 inches and setting a new all-time record for the city. The old record was 104.7 inches set back in the 1988-89 winter season.
The biggest late season snowstorm on record for northeastern Nebraska came to an end. The 9.3 inches of snow that fell at Omaha was the heaviest April snowfall on record in addition to being the latest. Snowfall from the storm was even heavier in other sections of northeastern Nebraska. Brownville checked in with 14 inches and Offutt Air Force Base measured 12 inches. (Intellicast)