ONLINE DAILY WEATHER SUMMARY

Friday, 2 April 1999



WINTRY WEATHER ACROSS THE NORTHERN PLAINS -- Even though the calendar says spring, a variety of winter-like precipitation forms to include snow, ice pellets (sleet), freezing rain and freezing drizzle accompanied a winter storm that was moving through the northern Plains. As of late Thursday night a low pressure system was situated over western Minnesota. A warm front extended eastward from the low into northern Wisconsin where it became a stationary front that eventually reached southern New England. A cold front trailed southward and then southwestward across the Plains, to link with a warm front associated with another winter storm system in the Colorado Rockies.

This northern storm system had developed over Wyoming and moved across the Dakotas on Thursday. Heavy snowfall rates were accompanied by thundersnow -- a convective situation where thunder is heard during a snowstorm. More than a foot of new snow fell in the Black Hills in western South Dakota. Strong winds accompanied the snow, causing a reduction of visibility to blizzard conditions from the Black Hills to central North Dakota. Blizzard warnings continued until late Thursday night in eastern North Dakota. To the south and east of the storm system, freezing rain and ice pellets were reported as warm air drawn northward into the system was lifted over the colder air near the surface. As of late Thursday night, winter weather advisories for a combination of ice pellets and freezing rain or freezing drizzle were in effect for northern Minnesota and portions of the Dakotas.

This storm system is expected to move eastward, positioned near the Twin Cities by Friday morning. Much of the precipitation should have moved northward into southern Canada, except for some freezing precipitation that could remain across northern Minnesota from the Lake of the Woods and the Arrowhead eastward to Michigan's Upper Peninsula.

SPRINGTIME IN THE ROCKIES? -- Another winter storm system was producing heavy snows across the central and southern Rockies on Thursday night. At that time this complex storm system contained several low pressure centers, with one center located in southeastern Colorado, a second low pressure center in western Colorado and a third low center in northern Arizona. These low pressure centers were situated along a frontal zone that separated warm air over the southern Plains to the south and east of the storm system from colder air over the northern Rockies to the north and west of the system.

Snow continued to fall across the Rockies, from southern Montana and neighboring Idaho south to northern New Mexico and west to northern Arizona. Between 8 and 16 inches of snow had fallen over the San Juan Mountains in southwest Colorado by late Thursday afternoon.

By sunrise on Friday, the storm system should continue moving southeastward into the Plains. One low center should be located in the Texas Panhandle, while one of the other low centers should remain over the Four Corners. A wide area should expect snow. A variety of snow advisories and winter storm warnings were in effect across Colorado and New Mexico where some locations could have an additional 16 inches. Heavy snow warnings were posted for the higher elevations of the Mogollon Rim through central Arizona where as much as 6 inches of additional accumulation was expected. To the east, a slight risk of thunderstorms reaching severe limits is possible across the Plains from west Texas to southern Iowa.

PLEASANT WEATHER RETURNS TO THE EAST -- Many areas along the Eastern Seaboard had light rainfall on Thursday morning. Some locations in the Appalachians between Georgia and the Virginias had between one half to three quarters of an inch of rain. Later in the day, most of the rain moved off the coast. Thunderstorms in the Southeast produced damaging high winds that gusted to 60 mph in South Carolina and in Florida. Farther westward, southerly winds across the southern Plains and the Midwest brought another day of unseasonably warm conditions.

With clear skies, weak winds and plenty of low level moisture, dense fog was beginning to form in many areas of the East and Southeast on Thursday night. As a result, dense fog advisories were issued for portions of Pennsylvania, Kentucky, Alabama, Georgia and Florida into Friday morning.

CHILLY WEATHER FOUND ACROSS NORTHWEST -- A pool of cool air continued to reside along the West Coast. A weak region of high pressure also produced dry conditions and relatively cloud-free skies across the Pacific Northwest. As a result, record low temperatures were set on Thursday morning at Quillayute/Forks, WA (23 degrees) and in California at Eureka (32 degrees) and Downtown San Francisco (42 degrees).

UPPER AIR WEATHER CONDITIONS -- The 500 mb and 300 mb upper air charts for 00Z Friday both reveal similar types of topography and wind flow patterns. For both charts, representing the mid and upper troposphere, respectively, a cold pool of air in the West has produced a height trough, where the height of each pressure surface remains closer to sea-level than elsewhere. On the other hand, warm tropospheric air to the east of the Rockies created a height ridge on the two pressure surfaces where these surfaces stand higher above sea-level. As a result of this topography, the prevailing westerly mid-latitude winds aloft that enter the country would be deflected to the south around the trough over the Intermountain West, then proceed across the Plains as southwest winds, before passing to the north of the East Coast ridge.

At 300 mb, a level where the strongest winds typically are located during the winter, the winds circulating in a counterclockwise fashion abut the upper level trough reached speeds between 60 to 110 knots. The pattern of strong winds at this upper tropospheric level provides a means for intensifying and maintaining the surface low pressure features over the Rockies.

YESTERDAY'S TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Thursday was 9 degrees at Truckee, CA, while the day's high was 89 degrees at Daytona Beach, FL and Lajitas, TX.

ALASKAN WEATHER -- A large complex storm system that moved across southwest Alaska spread clouds across much of the state on Thursday. One low pressure center was situated over the Yukon Valley with a front that trailed southward to another low pressure center on the north Gulf coast near the Kenai Peninsula. The front continued southward into the Gulf of Alaska. In the vicinity of this front, snow fell at Cordova, mixed rain and snow was reported at Yakutat, while warm air in the southeast meant that the Panhandle had rain. To the west of the low, snow fell at St. Paul , King Salmon and at Bethel. Winds along the front were gusty, with Seward having gusts to 41 mph and Anchorage to 30 mph. Farther to the east, Juneau and Skagway had gusts to 46 mph and Yakutat to 45 mph. Strong northerly winds were found to the west of the low pressure system. Cold Bay reported gusts to 46 mph and Dutch Harbor had gusts to 40 mph. Other locations across southwest Alaska and the Pribilofs had winds gusting to between 30 and 40 mph.

An east-west oriented stationary front situated to the north of the storm system separated arctic air to the north from more mild air to the south. Across northern Alaska to the north of the front, winds gusted to 51 mph at Point Hope, while at Gambell winds gusted to 38 mph and at Barrow, 21 mph.

On Thursday the lowest overnight temperature in the state was 36 degrees below zero at Deadhorse and Prudhoe Bay, while the highest temperature as of midafternoon was 52 degrees at Elmendorf AFB.

HAWAIIAN WEATHER -- A ridge of high pressure located to the north-northeast of Hawaii on Thursday afternoon helped maintain brisk northeast trade winds across the islands. Some trade showers continued across the islands, especially on the windward slopes of the Big Island and Maui. Fair weather was found elsewhere. The trade winds are expected to weaken with an increased chance of precipitation over the weekend as the high pressure cell moves away from the islands and a storm system from midlatitudes passes close to the islands. Small craft advisories remained in effect for state waters.

A TIMELY REMINDER -- Daylight Saving Time will go into effect this coming Sunday morning for essentially the entire nation -- the exceptions include Arizona, Hawaii, Puerto Rico and the eastern time zone sections of Indiana. These changes have been mandated by the U.S. Congress. In other words, following the old adage of "spring ahead, fall behind", you will need to turn your clocks ahead by one hour to conform with the local time observance.

What does this time change mean to you (other than later sunsets)? Contrary to a popular belief that has surfaced at times, the change from Standard to Daylight Saving Time does not add an extra hour of daylight to the day nor does it affect weather patterns. While the weather will not change because of the time change, the times when you will be able to obtain weather charts will now be one hour later. The reason is that the National Weather Service operates on "Z time" (variously called Greenwich Mean Time or Universal Coordinated Time) which does not observe Daylight Saving Time, and the charts are still produced and transmitted at the same Z time.


HISTORICAL WEATHER EVENTS - 2 April

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

3 April

4 April


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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological Society.