Thursday Daily Weather Summary

ONLINE DAILY WEATHER SUMMARY

Thursday, 1 April 1999

WARM CONDITIONS ACROSS THE GREAT LAKES STATES
WET CONDITIONS ACROSS THE SOUTHEAST
WINTRY WEATHER RETURNS TO THE WEST
WINDY WEATHER IN THE SOUTHWEST
THE UPPER AIR
YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE LOWER 48
ALASKAN WEATHER
HAWAIIAN WEATHER
THE UPPER AIR CHARTS
HISTORICAL WEATHER EVENTS

Welcome to April! The word April comes from "Aprillus" after the Latin "Aperio" or 'Aperire, the Latin word for "to open", in honor of the first buds of spring that open and begin growing during this month. Today is Passover.

WARM CONDITIONS ACROSS THE GREAT LAKES STATES -- A broad area of strong southerly winds brought unseasonably warm air into the states surrounding the Great Lakes. The southerly winds resulted from the presence of a large ridge of high pressure off the Carolina coast.

On Wednesday afternoon, record high temperatures were either tied or broken in Michigan at Alpena (72 degrees); Houghton Lake (72 degrees) , Sault Ste. Marie (63 degrees) and Marquette (66 degrees). The overnight temperature on Wednesday morning at Green Bay, WI was 51 degrees, which represented the highest minimum temperature ever recorded there on the last day of March. For comparison, the average daily minimum temperature based on 30 years of climatic record is 28 degrees.

An east-west oriented stationary front located to the north of the Lakes marked the northward excursion of the warm air. This front extended from the St. Lawrence Valley westward to west central Minnesota. Several weak low pressure systems were moving along this front that is not expected to move significantly by Thursday morning.

WET CONDITIONS ACROSS THE SOUTHEAST -- A large area of scattered light rain continued across the Southeast on Wednesday night in association with a slow moving area of low pressure. This weak region of low pressure was situated over north central Alabama, having traveled from a position along the Louisiana Gulf Coast since Tuesday night. Some of the heaviest precipitation fell over Georgia and the southern Appalachians of the western Carolinas, with lighter rain extending northward into the Ohio Valley and southern Indiana. As much as 2 inches of rain was estimated to have fallen across portions of Alabama by Doppler radar. Afternoon high temperatures across portions of the Southeast, in particularly in the Tennessee and Ohio Valleys, were 10 to 20 degrees lower than neighboring locations, the result of clouds holding down temperatures by blocking the sunlight.

The low pressure system is expected to weaken, but the area of precipitation is expected to continue to move toward the northeast by Thursday morning. Rain is expected from northern Ohio southward to the coastal Georgia.

WINTRY WEATHER RETURNS TO THE WEST -- A storm system that developed along a front stretching across the western Plains was responsible for snow that fell across the Dakotas and Montana on Wednesday. Some areas of central Montana had as much as 14 inches of snow by daylight on Wednesday. Snow also fell across western Montana, Idaho, Utah and Wyoming. More than a foot of snow also fell in the Sierras of California and Nevada.

As of late Wednesday night, a surface low was located along the front in Colorado. The front separated cold air to the north from warmer air to the south. Air temperatures across the northern Dakotas and into the northern Rockies were in the 20s and 30s, or between 30 and 40 degrees colder than across the central Plains. Record low temperatures were set on Wednesday morning in California at Redding (30 degrees), at Red Bluff (32 degrees) and at Downtown San Francisco (42 degrees).

The region of snow is expected to continue through Thursday morning as the frontal system is expected to make only slow movement toward the southeast. A slight risk of severe thunderstorms exists in the warm air to the south of the front. This region would extend from Nebraska and South Dakota east toward the western Great Lakes.

WINDY WEATHER IN THE SOUTHWEST -- Strong winds associated with the cold front that trailed southwestward from the low pressure system in Colorado caused damage across the Southwest. Very strong non-thunderstorm winds from a southwest direction caused damage across northern and eastern Arizona. St. Johns reported a gust to 104 mph, Winslow to 93 mph and Meteor Crater to 90 mph. One person was killed in a 10 vehicle collision on I-40 near Winslow due to the high winds and blowing dust on Wednesday.

THE UPPER AIR -- The suite of upper air charts for 00Z Thursday showed the effects of the cold air moving into the western part of the nation and the warm tropospheric air in the East. Progressing upward from the lowest constant pressure surface:

The 850 mb chart depicted the topography of all points in the lower troposphere having a pressure of 850 mb. Height contours drawn on this chart show a "trough" or a distinct region of lower height of this surface enclosed within a set of concentric contours over Colorado, where the lowest altitude of the surface was 1283 meters at Denver. Note that in the Colorado Rockies the 850 mb surface is actually underground, as the elevation of the Mile High City of Denver is 1600 meters. This feature also corresponds to the low pressure system on the surface weather map. The highest altitude of the 850 mb surface was in a "ridge" with 1569 meters over Cape Hatteras, NC. With winds approximately paralleling the contours, southerly low tropospheric winds were found bringing warm air (with temperatures of greater than 10 degrees Celsius ) northward from the Gulf of Mexico over the Plains and the Mississippi Valley into the Upper Midwest. Along the West Coast, the northerly winds were transporting colder air (with temperatures less than 0 degrees Celsius) southward.
The 700 mb chart shows that the 700 mb constant pressure surface, higher in the low troposphere, had a similar topography to the 850 mb surface. A distinct trough of lower height appears within the closed contours over the Great Basin, where the lowest point on this surface would be at approximately 2869 meters (over Salt Lake City, UT). On the other hand, a ridge of higher heights, was found along the Eastern Seaboard, with a height reaching 3150 meters (over Charleston, SC). Northerly winds at this level move southward along the West Coast, skirting the western trough, then turn to be come southwesterly over the central portion of the country, before curving to the east to pass on the northern side of the ridge along the East Coast.
The 500 mb chart for the mid-troposphere continues to reflect a topography where the 500 mb constant pressure surface stands lower in a trough over the West and is at higher altitudes along the East Coast. Specifically, the lowest altitude for the 500 mb chart appearing over the US was at 5370 meters over Boise, ID, while the highest altitude was at 5830 meters over Key West, FL. At this level, the western trough is not as distinct as at lower levels, since an "open wave" appears in the contours, with no closed contours appearing. In addition, the coldest air at this level appears within the western trough, with temperatures of 30 degrees Celsius below zero and the warmest air resides in the eastern ridge with temperatures reaching 15 degrees below zero. The wind flow pattern in mid-troposphere at this time continued to swing southward around the western trough, then flow northeastward to travel around the northern portion of the ridge.
The 300 mb chart that depicts the weather in the upper troposphere also has a similar 300 mb pressure surface topography and flow pattern as found in mid troposphere. A trough of lower heights (with the lowest altitude of 8780 meters at Boise) appears over the Great Basin with the coldest air and a ridge of higher heights (with the highest altitude of 9550 meters over Key West) in the Southeast with the warmest air. A wavelike pattern continues, with an equatorward excursion of the upper tropospheric flow in the west and a polarward excursion in the east. Winds are strongest at this level, with winds over Wyoming reaching 100 knots (nautical miles per hour).

YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- The lowest temperature on Wednesday was 8 degrees at Stanley, ID and Bozeman, MT. Wednesday's high was 88 degrees at Wink, TX.

ALASKAN WEATHER -- The arctic high pressure system that brought cold air across northern Alaska earlier in the week began to recede from the state by Wednesday. Partly cloudy to clear skies remained over interior Alaska, and over the southern portion of the Panhandle.

A large storm system that moved northeastward into the Bering Sea was spreading clouds across much of southwestern Alaska, to include the Aleutians, the Pribilofs, the Alaska Peninsula and Kodiak Island. As of late Wednesday afternoon, the low pressure center was located near Dutch Harbor, with an occluded front that stretched northeastward across Bristol Bay, before turning southeast toward a point of occlusion located just to the south of the Alaska Peninsula. A warm front extended eastward across the Gulf of Alaska, while a cold front continued southward over the North Pacific. Snow fell at Healy, McGrath, Bethel and St. Paul. In the warmer air, rain fell over Kodiak Island and along portions of the central and northern Panhandle. Strong winds also accompanied this system, with gusts reaching 41 mph at Cold Bay, 39 mph at St. Paul and to 37 mph at Dutch Harbor .

Low clouds were also reported along coastal regions of western and northwestern Alaska. Windy conditions were also reported across interior and northwest Alaska, with Gambell having gusts to 37 mph and Point Hope gusts to 30 mph.

The state's lowest overnight temperature as of Wednesday was 44 degrees below zero at Deadhorse and Prudhoe Bay. The midafternoon high was 48 degrees at Klawok.

HAWAIIAN WEATHER -- The intensity of the gusty trade winds across the islands diminished slightly on Wednesday as the ridge of high pressure to the north of Hawaii weakened. Rainfall also decreased, and was confined more to the windward slopes of the islands. On Wednesday evening, gale warnings that had been in effect for the Alenuihaha Channel were canceled. Small craft advisories remained in effect for state waters.

APRIL IS TSUNAMI AWARENESS MONTH -- According to a recent NOAA (National Oceanic and Atmospheric Administration) Press Release, activities have been scheduled during April to educate the public in Hawaii, Alaska, California, Oregon and Washington State as to the potential risk associated with a tsunami. The tsunami, often times incorrectly called a "tidal wave", is generated by underwater earthquakes or landslides, and can cause much loss of life, especially along the coasts of the five participating states. On 1 April 1946, a tsunami generated by an earthquake in the Aleutians caused 173 deaths in Hawaii. On 27 March 1964, the Great Alaskan Earthquake produced a major fast moving tsunami that crossed the entire Pacific, inflicting damage.

For more information, consult the NOAA Tsunami Awareness Month Press Release.

THE UPPER AIR CHARTS -- For a more complete look at features of various upper air charts available on the Online Weather Homepage, see the optional Thursday Supplemental Information.

HISTORICAL WEATHER EVENTS - 1 April

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

...1786...A heavy snowstorm hit, bringing 12 inches from New Jersey to New Hampshire and prolonging winter into spring. This strong storm caused gale force winds and high tides. Five piers of the Charles Bridge were destroyed at Boston, MA. (Intellicast)
...1807...The famous "1807 spring storm" buried interior New England in snow and caused a great tide along the coast. Danville, VT received 30 inches of new snow, bringing their snow cover amount to 60 inches. (Intellicast)
...1912...A tornado with incredible velocity ripped into downtown Houston, TX breaking the water table and giving the city its first natural waterspout. (The Weather Channel)
...1923...Residents in the eastern U.S. awoke on "April Fool's Day" to bitterly cold temperatures. The mercury plunged to -34 degrees at Bergland, MI and to 16 degrees in Georgia. (David Ludlum)
...1987...Forty-five cities across the southeastern U.S. reported record low temperatures for the date. Lows of 37 degrees at Apalachicola, FL, 34 degrees at Jacksonville, FL, 30 degrees at Macon, GA, and 22 degrees at Knoxville, TN, were records for April. (The National Weather Summary)
A tornado touched down briefly during a snow squall on the south shore of White Fish Bay (six miles northwest of Bay Mills, MI). A mobile home was unroofed and insulation was sucked from its walls. (The Weather Channel)
...1988...A powerful spring storm produced 34 inches of snow at Rye, CO, 22 inches at Timpas, OK, 19 inches at Sharon Springs, KS, and up to 35 inches in New Mexico. Severe thunderstorms associated with the same storm spawned a tornado which caused 2.5 million dollars damage at East Mountain, TX. (The National Weather Summary) (Storm Data)
...1989...Up to six inches of snow blanketed the Adirondacks of eastern New York State and the Saint Lawrence Valley of Vermont. Up to a foot of snow blanketed the Colorado Rockies. (Storm Data) (The National Weather Summary)
...1990...Thunderstorms produced severe weather in Texas, from southern Arkansas and northern Louisiana to southern Georgia, and from northern South Carolina to the Upper Ohio Valley during the day and evening. Thunderstorms spawned a tornado at Evergreen, AL, and there were more than eighty reports of large hail and damaging winds. Thunderstorms produced baseball size hail north of Bastrop, LA, and produced damaging winds which injured one person west of Meridian, MS. (The National Weather Summary) (Storm Data)