WELCOME TO DATASTREME - This Daily Summary file will describe the current weather pattern across the United States. The Tuesday and Thursday files will also contain the "Concept of the Day" with a question to be answered on the weekly Chapter Response Form. Additional Supplemental Information files will provide optional background material.
The following discussion is based upon the major weather features appearing on Monday night's surface weather maps:
FAY REMAINS A FACTOR -- After developing ten days earlier along the coast of the Dominican Republic, Tropical Depression Fay continued to remain an identifiable system on Monday evening. At that time, the center of Tropical Depression Fay was located near Meridian in east-central Mississippi. Maximum sustained near surface winds were approximately 25 mph, with some higher speeds reported in wind gusts. The forward speed of the system was at 5 mph to the northeast. The central minimum pressure was 1003 millibars (29.62 inches of mercury).
The system remained a prolific rainmaker as the counterclockwise circulation around the center of Fay brought a deep layer of humid and unstable tropical air northward into the sections of the Southeast located to the east of the depression's center. Daily maximum precipitation totals for the date were established on Monday in Alabama at Mobile (4.73 inches) Birmingham (2.63 inches) and Huntsville (2.19 inches); in Mississippi at Meridian (1.90 inches) and in South Carolina at Columbia (1.96 inches) and Florence (1.50 inches). The humid air that was carried northward was sufficiently unstable that daytime heating resulted in additional destabilization to permit development of thunderstorms. Some of the thunderstorms became severe across the Southeast on Monday, spawning tornadoes and generating damaging straight-line winds. As many as seven unconfirmed tornadoes were reported across Alabama, Georgia and the western Florida Panhandle during the morning, afternoon and early evening. Some damage was reported with several of the tornadoes. Trees and power lines were downed by thunderstorm winds in Alabama. Several thunderstorms continued across Alabama and the western Florida Panhandle into the late evening.
Fay was forecast to continue traveling to the northeast on Tuesday, with some increase in speed as it travels across northwest Alabama. Gradual weakening was anticipated. Between three to six inches of additional rain could be generated by Fay over a large area of the Southeast, stretching from northern Alabama northeastward to southwestern Virginia. Some of the largest totals could occur in the mountains of eastern Tennessee and the western Carolinas. Some of the region has been under an extended drought. Since the rainfall rates would be relatively high, flash flood watches remained in effect across much of Alabama, Georgia and the Florida Panhandle, along with sections of eastern Tennessee and the western Carolinas. With several streams at or above flood stage, flood warnings were in effect for southern sections of Alabama and Georgia, along with northern Florida. Some of the thunderstorms could also spawn tornadoes across eastern Alabama, western Georgia and the Florida Panhandle.
A CHILLY START -- A large high pressure system that had origins in Canada drifted eastward across the western Great Lakes on Monday, accompanied by cool and dry air. As of Monday evening, the center of this high pressure system was located over eastern Lake Superior. However, its influence extended as far eastward as New England, as far southward as the Ohio Valley and as far westward as the Plains, resulting in pleasant, dry and tranquil weather. A clockwise circulation around the high pressure center was readily apparent on Monday evening's surface weather analysis charts. To the east of the high, winds were out of the north or northwest across the eastern Great Lakes and sections of Upstate New York and New England. Winds across the Ohio Valley south of the center were from the northeast, while winds across the Upper Mississippi Valley and the northern Plains on the western flank of the high were from the south and southeast. Near the center of the high, calm conditions or light and variable winds were found.
The high pressure system brought an end to the growing season for some places across northern Minnesota and Wisconsin as nighttime temperatures dropped to near or below the freezing point. The cool and dry air mass accompanying this system, coupled with the weak winds and clear skies near the center of the high were ideal ingredients for vigorous cooling due to radiation out to space with little mixing of warm air. In Wisconsin daily low temperature records were either tied or broken on Monday morning at Lakewood (29 degrees), Minocqua (31 degrees), Merrill (32 degrees), Florence (34 degrees), Rhinelander (34 degrees) and Eau Claire (40 degrees).
The center of the high was forecast to drift eastward across Georgian Bay and into sections of eastern Ontario on Tuesday. As the high moves to the east, winds from the south should bring in warmer and slightly more humid air to sections of Minnesota and Wisconsin, keeping nighttime temperatures higher than on Sunday night and early Monday. However, the cold air spreading across the eastern Lakes and the Adirondacks of Upstate New York had resulted in temperatures late Monday night for that region to range from 10 to 17 Fahrenheit degrees lower than 24 hours previously. This region could expect some patchy frost early Tuesday.
HOT IN SECTIONS OF THE WEST -- Sections of the West, extending from the Plains of Montana southward into the Great Basin of Utah experienced unseasonably warm weather on Monday. Daily high temperatures were either tied or broken in Montana at Miles City (103 degrees), Billings (103 degrees), Bozeman-Belgrade (102 degrees), Lewiston (99 degrees) and Dillon (93 degrees) and in Utah at Utah Test Range (99 degrees) and Coalville (95 degrees).
The unseasonably warm conditions across the northern high Plains, the northern Rockies and the Great Basin resulted from a ridge of high pressure that developed ahead of a strong cold front that was moving across the Northwest.
The unseasonably warm weather was forecast to be replaced by cooler air as the cold front moves eastward across the northern Plains on Tuesday. Windy conditions were expected to accompany the cold frontal passage. The dry weather that the region has experienced along with the strong and gusty winds accompanying the cold front was expected to cause dangerous wildfire weather conditions. Therefore, red flag warnings were issued across much of south central Montana and western Wyoming effective through Tuesday evening due to winds gusting to 50 mph and low relative humidity readings.
CHILLY AIR ROLLS INTO THE NORTHWEST -- A cold front that had moved onshore along the coast of Washington State late Sunday continued to push eastward across the interior Northwest on Monday, accompanied by rain and markedly cooler weather. As of Monday evening, the cold front trailed southwestward from a low pressure center over Saskatchewan across northwest Montana and northern Idaho into southern Oregon and northern California. Scattered rainshowers and several isolated thunderstorms were moving eastward from eastern Washington across the Idaho Panhandle into western Montana as winds from the west were bringing humid air from the eastern North Pacific into the region. The presence of the northern Rockies contributed to the precipitation as the air from the Pacific was being forced to rise above the mountains. The air following behind the cold front was distinctly colder than the air being replaced. Monday evening temperatures across interior sections of Oregon, Washington, Idaho and western Montana were 10 to 18 Fahrenheit degrees lower than at the same hour on Sunday evening.
The cold front was expected to continue traveling eastward across the Rockies and out onto the adjacent high Plains on Tuesday. A ridge of high pressure located off the Oregon and Washington coast was expected to build eastward across the Northwest, causing a return to cloud-free-skies. The cold air along with clearing skies behind the front could result in nighttime temperatures across the interior Northwest to fall to near the freezing point by Tuesday morning. Therefore, frost advisories were posted across a large section of south central Oregon and adjacent sections of northeastern California.
FLOODING IN THE DESERT SOUTHWEST -- Humid air was beginning to flow northward into southern sections of New Mexico, Arizona and California. This flow of humid air was ahead of Tropical Storm Julio that was traveling north across Mexico's Baja California and toward the Gulf of California (see "Eye on Tropics" section below). Numerous thunderstorms continued across the typically arid areas of Arizona from the Phoenix metropolitan area westward to Needles and Blythe in southeast California. Some Arizona locations received up to one half inch of rain, which can be considered excessive. Flooding was reported in some locations in western sections of Arizona.
Flash flood watches were continued into Tuesday for sections of Arizona and California, as humid air from Mexico should result in afternoon thunderstorms across the region.
TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 27 degrees (Fahrenheit) at Embarrass, MN, while Monday's highest temperature was 121 degrees at Death Valley, CA.
ALASKAN WEATHER -- A broad area of low pressure with multiple low-pressure centers was located over eastern Alaska and northwestern Canada, resulting in cloudy skies across south central and southeastern sections of the 49th State on Monday. A trough of low pressure located across the northeastern Gulf of Alaska was responsible for light rain and fog along with gusty winds across the southeast Panhandle. High pressure located across northern Alaska helped produced partly cloudy skies across sections of the north central interior and along the western coast. Clouds remained across northwestern Alaska, remnants of a cold front that had moved across the region on Sunday before dissipating.
The state's lowest temperature on Monday morning was 28 degrees at Wainwright. The highest temperature across Alaska as of midafternoon on Monday was 68 degrees at Bethel.
HAWAIIAN WEATHER -- A strong ridge of high pressure extending across the North Pacific within 1000 miles of the Hawaiian Islands maintained typical trade wind weather across the Aloha State on Monday. This high-pressure ridge was drifting southward, resulting in a slight increase in the moderate easterly trade winds across the islands. These winds from the east are the typical prevailing wind regime across the islands and the subtropical ocean basins due to the clockwise circulation emanating out of the large high pressure cells usually located farther to the north. Winds near the summit of the Big Island's Mauna Kea volcanic peak had speeds above 30 mph. The trade wind weather across Hawaii consists of relatively cloud-free skies except for some scattered clouds and isolated light rainshowers that are embedded in the trade wind flow. Most of the trade wind showers are found along the windward (east-facing) slopes of the mountains that form the islands. Some showers upstream of the islands should approach the Big Island on Tuesday.
A wind advisory remained in effect into early Tuesday morning for Maui's Haleakala summit and the volcanic summits of the Big Island. A small craft advisory was continued through late Tuesday afternoon for the Pailolo and Alenuihaha Channels, Maui's Maalaea Bay and the coastal waters southeast of the Big Island.
PUERTO RICO/US VIRGIN ISLANDS WEATHER -- Skies remained mostly cloudy across Puerto Rico, Vieques, Culebra and the Virgin Islands late Monday night because of the circulation around Tropical Storm Gustav (see following "Eye on Tropics" section). Some rivers in Puerto Rico had risen to above flood stage due to the excessive rainfall rates. The lighter rainfall totals were found across the Virgin Islands. Most of the rainshowers and isolated thunderstorms that had been over the islands earlier in the evening had moved northward, with some light showers remaining over eastern Puerto Rico during the late night hours. The majority of the precipitation was detected over the offshore waters of the Atlantic north of the islands. With Tropical Storm Gustav located south of Haiti, winds across Puerto Rico and the Virgin Islands were light and from the southeast to east-southeast. While Gustav was expected to travel away from the region, the flow of humid and unstable tropical air from the southeast should produce some locally heavy rainshowers and thunderstorms that could travel northward across the islands into Tuesday.
EYE ON THE TROPICS -- The area of low pressure located south of Puerto Rico on Sunday night intensified into a tropical depression on Monday morning and into Tropical Storm Gustav by midday. This new tropical storm was the seventh named tropical cyclone (low-pressure system with an intensity of a tropical storm or hurricane) of the 2008 North Atlantic hurricane season. As of late Monday night, Tropical Storm Gustav had maximum sustained surface winds of 70 mph as the center was located 150 miles south-southeast of Port-au-Prince, Haiti. Movement of this storm was to the northwest at 12 mph. Gustav was expected to intensify into a hurricane early Tuesday as maximum sustained winds could reach 74 mph. The projected track of Gustav would bring it near the coast of Haiti by Tuesday afternoon. Consequently, hurricane warnings were in effect along the southern coast of Hispaniola. In addition to strong winds coastal storm surge flooding was anticipated to range between two to four feet above normal tide levels as the strong winds push the water toward the coast in what is known as "storm surge." Rainfall totals could range from five to seven inches across Hispaniola, with some mountain locations possibly receiving up to 25 inches. Thus, life-threatening flash floods and mudslides were possible. Gustav could pose problems for US interests later this week.
In the eastern North Pacific basin, Tropical Storm Julio, continued to travel to the north-northwest along Mexico's Baja California Peninsula as a minimal tropical storm on Monday. (Note: The red-winged symbol appearing over Baja California on the accompanying fronts-satellite insert is the official symbol for a tropical storm.) As of Monday evening, Julio weakened to a tropical depression as maximum sustained surface winds fell to 35 mph, below the 40-mph threshold for tropical storm intensity. The center of Tropical Depression Julio was located approximately 55 miles north-northwest of Santa Rosalia, Mexico, as it was moving to the north-northwest at 7 mph. Thus, the Mexican government discontinued all warnings for the Baja Peninsula and for the southwestern coast of mainland Mexico. Julio was expected to move over the northern Gulf of California on Tuesday, with continued gradual weakening. Up to six inches of rain could fall in some locations on the Baja.
REPORTS FROM THE FIELD -- If you experience some interesting weather phenomenon that you would like to share with other DataStreme participants as a "Report from the Field", please email your message to the address below.
You will find that all DataStreme Atmosphere meteorological maps and charts are labeled with numbers followed with a "Z", such as 00 Z, 12Z, 1915Z, etc. These labels indicate the time of observation in Universal Coordinated Time (UTC). The UTC or "Z" time is used because weather observations must be taken at the same time everywhere to accurately represent the state of the atmosphere. But how can you tell from the reported Z time when the observations were made where you live?
Z time is the time along the Prime Meridian, 0 (zero) degrees longitude. Life would be easy if you lived in England because your local time and Z time are the same. But what about where you live? For example, if you are looking at today's 12Z weather map, what time was it in your time zone?
Because you live in the U.S. and the earth rotates toward the east, your local time will be earlier than the local time at the Prime Meridian -- that is, the sun rises in England hours before it does in the U.S. Presently, many of us observe Daylight Saving Time. Therefore, 12Z (noon in England) would be 8 AM Eastern (4 hours earlier than local time in England), 7 AM Central (5 hours earlier), 6 AM Mountain (6 hours earlier), and 5 AM Pacific time (7 hours earlier). However, UTC time does not change seasonally. So when the entire country reverts to Standard Time in early November for the winter season (2 November 2008) and we set our own clocks back one hour, 12Z would then become 7 AM Eastern (5 hours earlier than local time in England).
A table of time conversions for the U.S. is listed in the DataStreme Atmosphere website User's Guide. For additional Z-time explanation, call up Tuesday's optional Supplemental Information.
To be submitted on the lines for Tuesday on the Investigations Manual, Chapter 1 Progress Response Form, under section B. Daily Summary (found in Week 1 section of the Investigations Manual and also on DataStreme Atmosphere website).
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
Return to DataStreme Atmosphere website
Prepared by Edward J. Hopkins, Ph.D., email
mailto:hopkins@meteor.wisc.edu
© Copyright, 2008, The American Meteorological Society.