WELCOME BACK: Procedure continued from STUDY GUIDE.
At the end of last week, a cool air mass progressed into the north-central US from central Canada bringing dramatically cooler temperatures to the region. Farther to the west, from the Rockies out onto the Plains, a broad area of low pressure brought precipitation. Finally, Tropical Storm Gabrielle was crossing Florida accompanied by heavy rains. Details of these events are given in the Monday Daily Weather Summary for 17 September 2001.
The electronically delivered weather maps used in this course typically have greater detail than those seen on television or in newspapers. Image 1, Isobars, Fronts, Radar, & Data, is the Friday 12Z 14 SEP 2001 (8 AM EDT, 7 AM CDT, etc.) surface map. It depicts weather conditions across the country at that time. The center of high pressure was located along the US-Canadian border just west of Lake Superior. The wind directions around the High showed the wind flow to be [(clockwise) (counterclockwise)] and [(inward) (outward)]. This [(is) (is not)] consistent with the hand-twist model of Activity 1A.
While incompletely shown, the pattern of isobar values in the Gulf of Mexico to the western coast of Florida, indicated a center of [(high) (low)] pressure. The eastern Gulf just southwest of Tampa was the location of Tropical Storm Gabrielle at that time. The winds shown at Tampa, midway along the west FL coast, and at Key West, the most southerly station, [(are) (are not)] consistent with the counterclockwise and inward pattern of a [(High) (Low)].
The heavy line with triangles (blue on-screen) that curves from the Canadian Maritime Provinces in the northeast corner of the map around to western Kansas marks the position of a [(cold) (warm) (stationary)] front. This front was the leading edge of the cold air mass whose center was marked by the High. The triangle symbols along the front show that the cooler air mass was moving generally toward the [(southeast) (northwest)].
The frontal system (red on-screen) from western Kansas to the Low in southeastern Wyoming was shown as a [(cold) (warm) (stationary)] front. The half-circle symbols show the front was advancing generally toward the [(northwest) (northeast)]. Finally, the portion of the frontal system from the Wyoming Low to western Montana (alternating blue triangle and red half-circle segments on-screen) was shown as a [(cold) (warm) (stationary)] front. A stationary front also was positioned eastward from northern Florida into the Atlantic.
At map time, Jackson, Mississippi, had a temperature of 68 degrees F, and a dewpoint of [(67) (69)] degrees F. The winds were generally [(from the northeast at 10 knots) (calm)], and the air pressure corrected to sea level was [(1167.0) (1016.7)] mb. The sky was [(clear) (overcast)]. The solid and broken horizontal lines in the "9 o'clock" position indicate that the weather condition reported was fog.
Indianapolis, Indiana, with a temperature of 50 degrees F and dewpoint 48, was [(partly cloudy) (overcast)] with 10 knot winds from the [(southwest) (northeast)]. The map shows Indianapolis to be behind the cold front. The air at Indianapolis was [(colder) (warmer)] than the air at Jackson, in advance of the approaching cold front.
Current weather symbols (9 o'clock position of the station model) for
the following stations were:
Atlanta, Georgia ("8" on side) _______________________
San Diego, California (broken line over solid line) _______________________
[For a complete listing of the weather symbols, see the Homepage User's
Guide.]
Brownsville, Texas (southernmost station), had a broken line over solid line in the current weather position of its station model, represents the condition of [(snow) (fog)]. The temperature at Brownsville is 75 degrees and the dewpoint is _____ °F. The equal temperature and dewpoint values mean the air at Brownsville was probably saturated producing this weather condition.
Precipitation on surface weather maps is denoted by reports from National Weather Service radar sites. Radar can survey the sky beyond their horizons for a more complete picture than may be sensed at the stations alone. On surface maps, the intensity of the radar echoes, which is related to the intensity of the precipitation, is shown by shadings using the scale at the lower left. The shaded areas on the 12Z 14 SEP 2001 map show precipitation probably was occurring:
Precipitation across the New York City area hampered rescue operations in Manhattan that morning and dampened the visit of President Bush to the scene. Elsewhere rains from Gabrielle ranged up to 11 inches in spots.
Refer back to the surface weather map of Activity 1A for 00Z 03 SEP 2001. Additional weather symbols are shown on that map. Two dots at Little Rock, Arkansas indicates the weather conditions at Little Rock at that time was [(snow) (rain) (fog)]. New Orleans, Louisiana, in southeastern LA, had [(haze) (thunderstorms)].
Image 2 is the Monday 12Z 17 SEP 2001 surface map. The cool air mass located in the northern US and central Canada on the Image 1 map of 12Z 14 SEP 2001 had moved to the East Coast. Compared to the central pressure value of Image 1 (1035 mb) on the 14th, the central pressure of the air mass on the 17th is [(higher) (lower)].
Conditions as shown by the station model at Charleston, South Carolina, were: temperature 58 °F, dewpoint _____ °F, pressure 1019.8 mb, sky conditions: [(clear) (overcast)], winds from the north-northeast at 5 knots. Three days earlier at 12Z on the 14th (Image 1) the temperature at Charleston was 69 °F. Charleston's temperature [(rose) (fell)] over the weekend as a result of the influence of the air mass.
The central US precipitation continued to move eastward and a new air mass was poised to enter the US from Canada. Generally fair and cool weather was over the eastern US.
Displaying a sequence of recent surface weather maps ending with the current map in your classroom can show the movement of "weather makers" (high and low pressure centers and fronts) and the changes in atmospheric conditions at your location over time resulting from their movements. Practice looking for connections between weather changes depicted on the map sequence and predict local weather for the next half day or so.
The National Weather Service provides information of current weather conditions especially highlighting threatening and/or severe weather, via their http://iwin.nws.noaa.gov/iwin/iwdspg1.html page. Choosing a state will show the weather reporting sites in that state, which may be useful to locate the stations, as well as obtain the current observations and forecast conditions. You may wish to note or "bookmark/favorite places" this site for future reference.
Hold this activity until you have completed all applications for this week. Instructions for faxing your LIT mentor will appear at the end of this week's Activity B.
Return to DataStreme Homepage
URL: datastreme/learn/a_act.html
©Copyright, 2001, American Meteorological Society