MORE WINTRY WEATHER FOR THE MIDWEST -- A new storm system moving across the Plains was spreading a wintry mix of rain, freezing rain and snow across the Upper Midwest on Wednesday. The low pressure system that formed over the lee slopes of the Rockies in southeastern Colorado and northeastern New Mexico on Tuesday moved to the Missouri Valley near Omaha, NE by Wednesday night. A cold front that moved southward across the northern Plains merged with this system. As a result, a cold front extended from one low pressure center in Ontario near James Bay to northwest Iowa in the vicinity of the low pressure system that had developed in Colorado. A cold front trailed southwestward from this low to southeast New Mexico.
The low pressure system over the Missouri Valley was accompanied on the north (or cold side) by a band of snow that stretched from eastern Nebraska and southeastern South Dakota across southern Minnesota to west central Wisconsin. Some localized regions of rain and freezing rain fell to the south and east of the storm system in slightly warmer air. Several inches of snow had accumulated.
Strong northerly and northwesterly winds swept across the Northern Plains in the wake of this storm system. A tight pressure gradient was detected on the surface weather maps of Wednesday evening.
This storm is expected to continue a track to the east-northeast, with the low pressure center reaching southwest Wisconsin by Thursday morning and to Lake Huron by evening. A variety of snow and winter weather advisories were in effect through Thursday morning for an area that extends along the storm track from northeastern Nebraska across southeastern South Dakota, northern Iowa, southern Minnesota into western Wisconsin. As much as 6 inches could fall in some locations. Winds shifting to northwest and increasing in speed could cause some blowing and drifting of the snow, along with reduced wind-chill equivalent temperatures. Snow advisories were posted for those counties in Michigan's Upper Peninsula that border on Lake Superior, in anticipation of the lake-enhanced snowfall on northerly winds feeding into the storm system as it passes to the south. Accumulations of between 4 to 8 inches are anticipated through Thursday.
A SLOW DEPARTURE -- The previous storm system that brought wintry weather to the Midwest continued to make its presence felt across New England on Wednesday night. At that time, the low pressure center was located over the Gulf of St. Lawrence. This system continued to produce northwesterly winds and some precipitation across northern New England.
The low should continue to move to the northeast, so the precipitation should have dissipated over northern Maine by Thursday morning. However, gale warnings remained in effect for a portion of the New England coast running from Merrimack River, MA to Eastport, ME.
WET WEATHER ALONG THE GULF COAST -- An area of low pressure along the southern Texas Gulf Coast near Corpus Christi on Wednesday night produced widespread rain across central Texas.
This low pressure system and accompanying rain should move eastward along the Gulf coast on Thursday. By morning the low pressure center should be situated near Galveston, TX and by evening it should be near Meridian in eastern Mississippi. Between 0.25 and 1.5 inches of rain are forecast to fall in the 24 hours ending Thursday evening over the central Gulf Coast, extending northeastward over the lower Mississippi Valley into the Tennessee Valley.
THE CHILLY WEATHER CONTINUES -- Many locations across the country experienced another unseasonably cold day. Afternoon high temperatures on Wednesday were as much as 20 degrees below the long-term climatological average high over the Rockies. Earlier, record low temperatures for the date were tied at the California communities of Cuyama (21 degrees) and Bakersfield (30 degrees).
On Wednesday night, frost advisories were posted for portions of the San Joaquin Valley of California. Along the East Coast, a variety of frost and freeze warnings for eastern North Carolina and for coastal portions of South Carolina, extending into adjacent counties of Georgia.
UNSETTLED WEATHER ALONG THE WEST COAST -- A weakening storm system located off the Oregon coast was responsible for some widely scattered rain along the California coast from near Eureka south to Santa Barbara. A wind advisory was in effect for the coast and mountains near Santa Barbara. By Thursday morning, the precipitation is expected to dissipate.
UPPER AIR -- The 500 mb and 300 mb constant pressure charts for 00Z Thursday contain meridional flow patterns across the West, with large excursions of the winds to the north and south during their flow across the continent. A large trough of lower heights extends from western Ontario southwestward to Colorado. Winds entering the West Coast from off the Pacific are deflected to the south and even southwest before curving around the southern flank of the upper level trough. Southwesterly winds then progress across the nation's midsection to a height ridge over the eastern Great Lakes.
TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 10 degrees below zero at Big Piney, Lander, Riverton and Shoshoni, WY, while the Wednesday afternoon highest temperature was 81 degrees at Miami, Opa Locka and Pembroke Pines, FL.
ALASKAN WEATHER -- A large storm over the Bering Sea and the eastern Aleutians was responsible for cloudy, wet and windy weather across western Alaska on Wednesday afternoon. The storm system consisted of two low pressure centers along with associated frontal system. One low pressure center was located near St. Paul Island in the eastern Bering Sea and a second low center was situated near Cold Bay on the Alaska Peninsula. An occluded front extended southeastward across the Alaska Peninsula. High pressure located over southeast Alaska helped build a tight pressure gradient across southern Alaska. As a result, high winds from the southeast were found across southwest Alaska. Togiak on Bristol Bay had gusts to 55 mph and those at Mekoryuk on Nunivak Island to 48 mph. On Tuesday night Cold Bay had a peak wind gust to 56 mph during frontal passage, along with 1.65 inches of rain in the 24 hours ending on Wednesday afternoon. The broad flow of southwesterly winds to the east of the storm system spread relatively warm air across much of Alaska. The northern periphery of this warm air was a stationary front that stretched along the Arctic coast.
The lowest temperature in Alaska on Wednesday morning was 15 degrees below zero at Arctic Village. The highest statewide temperature as of Wednesday afternoon was 46 degrees at Klawock.
HAWAIIAN WEATHER -- Moderate northeast trade winds with speeds ranging from 10 to 30 mph continued across most of the islands on Wednesday afternoon as a high pressure system remained far to the northeast of Hawaii. Showers and some isolated thunderstorms formed and moved across the Big Island and the eastern portion of Maui. Some clouds were found over the other islands, with negligible precipitation. A cold front located approximately 600 miles to the northwest of Kauai was moving toward the islands and could reach the 50th State late Friday. With strong trade winds, small craft advisories were continued for state waters. Since ocean surf is expected to range between 10 to 15 feet, high surf advisories were posted for the northwest shores of the islands.
A METEOR SHOWER OR STORM? -- Astronomers predict that within the next two days the earth should experience the Leonid meteor showers. The Leonid meteor shower usually occurs at this time of year, with any hourly rate that typically was between 10 to 15 meteors per hour. However, two years ago the comet Tempel-Tuttle, the parent comet of the Leonid meteor swarm, passed through the inner solar system after completing a 33 year orbit. As a result, as the earth passes through the tail of the comet, we could experience a meteor storm with as many as one hundred meteors per hour resulting. While the storm would pose little threat to residents of the earth, spacecraft could be in jeopardy as the meteor swarm passes. Many of the meteor particles are smaller than the size of sand grains and they travel at more than 155,000 mph. These projectiles could damage or destroy sensitive portions of the orbiting satellites, either by direct collision or by generation of electrostatic discharges. Some precautions have been taken to reduce the threat on some satellites operated by NASA. On Saturday morning, NASA plans to launch a camera-equipped balloon into the stratosphere to an altitude of 100,000 feet and then offer live pictures of the latter part of the meteor shower on the Internet. This will be the third year that a NASA-sponsored balloon is launched. Additional information can be obtained from Science@NASA.
Peak viewing in eastern North America is about 0750 UTC on Friday and Saturday. The moon is near last quarter, so viewing may be affected. If the skies are clear and dark, look toward the east early tomorrow morning and again on Saturday morning. The Leonid meteors should disperse across your local sky as the radiant point near the constellation Leo rises in the southeast.
Most of us would like to know what the weather will be for many reasons. We would like to know what to wear to an outdoor sporting event, or we may need to take appropriate action to save ourselves from potential severe weather. For centuries, humans developed various means for forecasting, including the rich weather lore that may or may not involve sound physical rationales. A major focus in modern meteorology entails the development of methodologies to make accurate forecasts of future weather events using proven scientific methods.
So how can we make a reasonable scientific weather forecast? We will consider just the next several days, since forecasts for more than several days are considered to be outlooks of general trends. Obviously, the easiest method would be to consult the local forecast prepared by the National Weather Service. Their forecasts are based upon an array of various "numerical weather prediction" models that are run on computers using weather data from surface weather observation stations, radiosondes and weather satellites.
If we were not able to receive a forecast, we could make a reasonable forecast. One method would be by "persistence", which assumes that the weather would remain the same or persist throughout the forecast period. In other words, if you step out and observe sunny skies and mild temperatures, you would make a forecast that these conditions would continue for the next hour or two. Often times this type of forecast would be reasonable for a short time, particularly if a large high pressure cell is nearby. The accuracy of this method decays rapidly with time.
Another forecast method would involve "climatology", where the forecast is based upon some long term climatological average. In other words, you would forecast tomorrow's high temperature as being the same as the "normal" high temperature for tomorrow. This type of forecast may fail if an extremely cold or warm air mass moves into the your region.
We could also use single station forecasts, by watching the sequence of weather that evolves in combination with looking at the current weather map. We have discussed how you can locate where the low (or high) pressure cell would be relative to you by facing downwind. Looking at the current weather map helps pinpoint the positions. We can also refine our forecast skills by looking for changes in the wind direction, cloud types, air pressure and air temperature over several hours, especially if a mid-latitude cyclone were approaching. Using your WeatherCycler or the description on pages 184-185 of Part A of the DataStreme Study Guide, you determine whether you will be on the warm side or cold side of the storm. In addition, you can look at a sequence of surface weather maps and attempt to extrapolate the movement of the weather systems that would cross your area.
For a description of how to read and interpret the Forecast charts on the DataStreme Homepage, you can read the optional Thursday Supplemental Information.
To be submitted on the lines for Thursday on the Study Guide, Part B, Applications', Week 10 Chapter Progress Response Form, under section B. Daily Summary.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast