MORE WELCOME RAIN -- Thunderstorms developed across the Florida Peninsula for a second day. Radar estimated rainfall totals, coupled with conventional rain gage observations indicated that between one and two inches of rain fell over a major portion of the Florida on Wednesday. These rains were welcome after a spring that has been exceptionally dry across the Sunshine State. The fire danger across Florida was somewhat reduced by higher humidity. However, some of the thunderstorms, especially those across the central Peninsula became severe. Strong thunderstorm winds caused damage near Daytona Beach, Lakeland and Orlando. A tornado also produced damage near St. Cloud, to the south of Orlando. Several reports of large golf-ball sized hail were made from the central region of the state.
COOL WEATHER FOUND ACROSS THE EAST -- High pressure along the Eastern Seaboard pushed unseasonably chilly weather southward along the Appalachians into the Carolinas on Wednesday. This air mass originated in Canada. Afternoon high temperatures over the Piedmont were in the 40s and 50s, well below typical values for this time of year. Clouds and rainy weather have also contributed to the chilly situation. The southern edge of this cool air mass was found along the front that stretched across Georgia.
A STORM WEAKENS -- The storm that brought heavy rain to the mid-Mississippi Valley on Tuesday moved toward the southeast and began weakening on Wednesday. By late evening, the low pressure center was located over middle Tennessee. A warm front stretched southeastward across northern Georgia, while a cold front traveled southwestward across the Lower Mississippi Valley. A large area of precipitation continued to surround this system, extending from the Carolinas and Georgia into the Ohio and mid-Mississippi Valleys. A thunderstorm imbedded in the precipitation shield north of the low produced large hail in southern Kentucky. Thunderstorms to the south of the low over central Georgia produced large hail and high winds that caused some minor damage on Wednesday evening.
Flooding continued to be a problem across many areas of the Midwest from eastern Nebraska to Kentucky as a result of the heavy rains during this week.
An area of weak low pressure should remain over Tennessee into Thursday morning. A large precipitation shield should continue across the Ohio Valley, the Cumberland Plateau and the southern Appalachians into northern Georgia. During the day, severe thunderstorms could develop over southern Georgia and northern Florida.
PLEASANT WEATHER ACROSS THE PLAINS -- High pressure over the Lake Superior was responsible for relatively cloud-free skies and southerly winds across the central and northern Plains into the upper Mississippi Valley and western Great Lakes on Wednesday. This high should remain across southern Canada and the Upper Great Lakes through Thursday, meaning a continuation of the pleasant spring weather for the upper Midwest.
SEVERE THUNDERSTORMS ALONG THE ROCKIES -- Thunderstorm activity increased along the Rockies on Wednesday. Some of the thunderstorms were associated with a cold front that stretched from a low pressure system in north central Montana southward across the northern Rockies into the Great Basin. Thunderstorms moved across Montana and Wyoming on Wednesday. Some of these storms reached severe limits, as large hail fell near Billings, MT and Riverton, WY. A tornado was also spotted east of Riverton late Wednesday afternoon.
Additional thunderstorms developed across the southern Rockies, near a region of low pressure over southern Colorado. A thunderstorm near Colorado Springs, CO produced nearly two inches of hail accumulation. By late evening, severe thunderstorms, together possible tornadoes, had developed in eastern New Mexico and moved into west Texas. The risk of severe thunderstorms continues through Thursday across west Texas from the Panhandle south to the Rio Grande.
COLD WEATHER ALONG THE WEST COAST -- A large area of high pressure was found across the West behind a cold front that ran from the northern Rockies into southern portions of the Great Basin. Unseasonably cool weather has accompanied this system. Record low temperatures were set Wednesday morning at Oakland (Museum) with an overnight low of 46 degrees and at Redmond, OR with 18 degrees, while the 27 degree minimum at Yakima, WA tied the daily record. Snow fell across the high elevations of the Pacific Northwest to include Idaho and Oregon, while four inches of snow fell at Squaw Valley in California.
A snow and blowing snow advisory was in effect through Thursday morning for the north central Colorado mountains above 10,000 feet, while winter storm warnings were posted for the San Juan and the Sangre de Cristo Mountains for up to 10 inches of snow above 10,000 foot altitude.
Elsewhere, the afternoon high temperature at New Orleans (Audubon Park) reached a record tying 92 degrees.
UPPER AIR -- The mid and upper tropospheric charts for 00Z Thursday contained a pattern that has been referred to as an "omega block". The reason for the name is that the height contours have formed into a pattern resembling the Greek capital letter omega. Specifically in the current case, one trough of lower heights has formed along the West Coast, while another trough is found along the East Coast at roughly the same latitude. Between these troughs a large ridge in the height field has formed, offset slightly poleward of the two troughs. The looping flow pattern that develops in such a situation causes weather systems, particularly low pressure features, to be carried around the large ridge in the center. Such a diversionary pattern is said to "block" the typical west to east progression of pattern. An omega block may signal a fairly stagnant weather regime.
Inspecting the 300 mb chart, one trough is found centered over the central Sierra and the other is found over the Middle Atlantic, with a westward extension into the Ohio Valley. Cold weather was reported along both east and west coasts, resulting in the deep upper troughs. The ridge is located over the Rockies and Plains. As a result, the 300 mb flow is highly meridional with large north-south excursions.
YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- The lowest temperature on Wednesday was 18 degrees at Redmond, OR. Wednesday's high was 95 degrees at Laredo and Cotulla, TX.
ALASKAN WEATHER -- A large portion of northern Alaska was under the influence of a large high pressure ridge that extended from the Arctic Ocean north of Prudhoe Bay to near Great Slave Lake in northwest Canada. As a result, easterly winds ranging between 15 to 25 mph were reported across the north. Savoonga had southeast winds gusting to 36 mph and Gamble gusts to 33 mph. The shorefast ice along the Arctic coast between Barrow and Wainwright has become unstable as 15 to 20 mph east winds has caused the ice to break free from the shore with little warning.
A storm system located over the Pacific Ocean spread clouds across the southern Panhandle and Kodiak Island. Another storm system was found over the western Bering Sea, with clouds associated with this system having spread across the Pribilofs. A weak low pressure system was located near Talkeetna.
The lowest overnight temperature in Alaska as of Wednesday was 12 degrees below zero at Barter Island. The highest temperature as of midafternoon was 55 degrees at Ketchikan.
HAWAIIAN WEATHER -- A large ridge of high pressure to the northeast of Hawaii produced light to moderate trade winds across the islands on Wednesday. This ridge is expected to erode, resulting in the weakening of the trade winds through Friday. As the trade winds weaken and become variable, the local sea breeze circulation should become dominant, along with afternoon showers over the interiors of the individual islands.
WEATHER ON THE INTERNET -- For a behind-the-scenes view at how the daily weather summary is built, please read the Thursday optional 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.