ANOTHER STORM APPROACHES THE NORTHWEST -- A storm system that was located approximately 350 miles to the west of the mouth of the Columbia River was making its presence felt across western Washington and Oregon. Many locations were reporting strong southerly winds along with some rain. Wind gusts to 80 mph had been reported at the 5000 foot elevation near Alpental, WA. Southerly winds in advance of the next storm system helped produce record high temperatures in Oregon at Salem (68 degrees), Portland (67 degrees), Eugene (67 degrees) and McMinnville (66 degrees) and in Washington at Yakima (65 degrees) and Ellensburg (62 degrees).
The rain accompanying this new storm system quickly followed widespread heavy rains associated with a cold front that had made landfall on the Olympic Peninsula on Tuesday evening. This precipitation continued into Wednesday. By late afternoon record rainfall totals had been established at several sites in Washington to include Olympia (3.63 inches), Seattle (2.59 inches) and Hoquiam (1.79 inches). The heavy rains in the Seattle area produced mudslides that caused some damage and disrupted traffic. With streams reaching near bankfull, flood warnings were posted for several rivers in western Oregon and Washington State.
The low pressure center is expected to move to the northeast toward Vancouver Island while the cold front trailing southward from the low should reach the Washington and Oregon coasts during the midday on Thursday. A high wind warning was continued for the coastal headlands of Oregon through Thursday morning. Southerly winds ahead of the cold front could produce 45 mph winds with gusts to 65 mph. High wind warnings also covered coastal Washington to include the area surrounding Puget Sound, where southeast winds could have gusts to 60 mph. Winds could gust to 100 mph on exposed ridge tops of the Washington Cascades and Olympic Peninsula at elevations above 5000 feet. Storm warnings were posted along the Washington coast from Cape Flattery to Cape Shoalwater, while gale warnings were continued southward from Cape Shoalwater to Cape Mendocino, CA. Heavy surf advisories were also in effect along the Pacific coast from Cape Flattery, WA south to Point St. George, CA.
Nearly 3 inches of precipitation are forecast to fall by Thursday evening across the Olympic Peninsula, with amounts ranging from 1 to 2 inches along the western slopes of the Washington Cascades. With snow levels relatively high because of the warm air, most of the precipitation should fall as rain. Once the cold front passes, some of the precipitation could fall as snow as the snow levels fall.
SEVERE WEATHER ACROSS TEXAS -- A weak trough of low pressure located over New Mexico, west Texas and the Mexican state of Chihuahua helped provide an environment favorable for the development of strong to severe thunderstorms over Texas on Wednesday. Southeasterly winds brought warm and humid Gulf air across the Lone Star State. Some of the thunderstorms that developed across the state turned severe. A tornado that remained on the ground for only a brief time was reported near Lubbock on Wednesday morning. Other thunderstorms dropped large hail with diameters up to one inch across the Rio Grande valley near Big Bend National Park, near Corpus Christi and to the north of Houston. Severe thunderstorms were continuing across southern Texas to the west of San Antonio as of midnight local time.
Heavy rains also accompanied the thunderstorms. Based upon Doppler radar estimates, up to 8 inches of rain fell during a three hour span late Wednesday night in several counties between San Antonio and Corpus Christi. Several streams had flash flood warnings. Widespread rainshowers and thunderstorms are expected to continue across a large portion of Texas through Thursday. Nearly two inches of rain were expected to fall across central Texas during the 24 hours ending Thursday evening. Consequently, flash flood watches were in effect for southern and western Texas through Thursday afternoon. A slight risk of severe thunderstorms was expected to continue across South Texas into Thursday morning.
While rain is expected across Texas, snow could fall over southern New Mexico. A snow advisory was posted for the Sacramento Mountains of southern New Mexico as 3 to 5 inches could fall by early Thursday morning at elevations above 8000 feet. Snowbursts could accompany isolated thunderstorms.
WET WEATHER CONTINUES ACROSS FLORIDA -- A large area of rain was found extending northward from the vicinity of a low pressure center located along Florida's Atlantic Coast near Cape Canaveral. The rain has been fairly heavy across the Florida Peninsula, with Daytona Beach (4.09 inches) and Melbourne (2.72 inches) reporting record daily rainfall totals.
The low pressure center is expected to remain relatively stationary through Thursday evening. Relatively heavy rain associated with this system is expected to continue. As much as 1.2 inches of rain is expected along the coast of northern Florida and southeastern Georgia during the 24 hours ending on Thursday evening. A flash flood watch was posted for coastal counties in northern Florida and in southeastern Georgia.
In addition to the heavy rains, a relatively tight pressure gradient exists between high pressure over the Carolinas and the low pressure center along the Florida coast. As a result, relatively strong onshore easterly winds have persisted for a sufficient length of time to pile ocean water against the coastline. Heavy surf advisories were continued along the Atlantic coast from Altamaha Sound GA to South Santee River, SC.
MORE RECORD WARMTH -- Unseasonably warm weather continued across a large portion of the country on Wednesday extending from the Pacific Northwest to the Great Lakes. The largest temperature departures were found across the northern and central Plains where highs were 25 to 30 degrees above the averages for mid November. Record high temperatures were reached at Norfolk, NE (72 degrees) and Marquette, MI (59 degrees). In addition, numerous record high minimum temperatures were tied or exceeded in Kansas at Salina (60 degrees) and Russell (58 degrees); in Iowa at Des Moines (59 degrees); in Wisconsin at La Crosse (55 degrees) and in Minnesota at Minneapolis-St. Paul (52 degrees) and Duluth (49 degrees).
UPPER AIR -- The mid-tropospheric 500 mb constant pressure chart and the upper-tropospheric 300 mb chart for 00Z Thursday both reveal an essentially cut-off low over the Southwest. This feature can be identified by a set of closed height contours and a counterclockwise circulation regime that appears detached from the flow pattern to the north along the Canadian border. This cold pool of air that forms this height trough is also associated with the trough of low pressure at the surface that produced the severe weather in Texas and could generate snow in New Mexico. To the north, the winds at both levels are essentially zonal, or they move primarily from west to east with little north-south deviation.
TEMPERATURE EXTREMES IN THE CONTINENTAL U.S. -- Wednesday morning's lowest temperature was 15 degrees at Houlton, ME, while the Wednesday afternoon highest temperature was 86 degrees at Simi Valley, CA.
ALASKAN WEATHER -- Arctic air remained in control of the weather across much of interior Alaska north of a stationary front that essentially extended eastward along the Alaska Peninsula and along the Gulf coast of southern Alaska to northwest British Columbia. Subzero temperatures were found along the North Slope and northwest Alaska at midday, while single digit temperatures were reported across the interior. Snow was reported at Nuiqsut and Wainwright on the North Slope. A storm was located over the northern Gulf of Alaska south of Prince William Sound. Rainshowers were reported across southeast Alaska. Haines Customs reported 6.3 inches of new snow. A relatively tight pressure gradient developed over the Gulf Coast between high pressure in Far East Russia and the Gulf low, resulting in strong winds. With northwest winds forecasted to gust to 70 mph, a high wind warning was posted for Kodiak Island. Another storm system was located over the western Bering Sea with an occluded front that stretched across the central Aleutians.
The lowest temperature in Alaska on Wednesday morning was 22 degrees below zero at Gulkana. The highest statewide temperature as of Wednesday afternoon was 48 degrees at Ketchikan and Metlakatla.
HAWAIIAN WEATHER -- The normally persistent northeast trades were replaced by light and variable winds on Wednesday as a ridge of high pressure approached the Aloha State from the north. Relatively cloud-free skies prevailed across the islands except for Maui and the Big Island, where some clouds and light showers were reported. Since the ridge is expected to stall near Kauai, weak winds along with relatively quiet weather, warm, sunny days and clear, cool nights, is expected. The cold front located several hundred miles to the north of the islands is not anticipated to reach the islands since it should stall and dissipate before reaching the islands.
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