CWS 8B

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UPPER-AIR WEATHER MAPS

Do Now:

Print this file.
Print the associated Curr= ent Weather Studies B Image 1 and Image 2 Files.
Print the Daily Summary and/or Supplemental Information Files, if directed by your instructor.=

To Complete Investigation:

Reference: Chapter 8 in t= he Weather Studies textbook.
Complete Investigation 8B= in the Weather Studies Investigations Manual as directed by your instructor.
Complete this Wednesday online-delivered Current Weather Studies 8B activity if directed by yo= ur instructor.

Image 1 is the surface weather map (Isobars, Fronts, Rada= r & Data) for 00Z 28 OCT 2009, Tuesday evening. The storm system that was= in the center of the U.= S. on Monday had moved eastward. Its southern frontal boundary became the syst= em that was bringing the precipitation to the eastern U.S. on the Image 1 map. One low-pressure center that developed along the frontal boundary is shown cent= ered east of Delaware<= /st1:State>. Another low-pressure center is shown in west-central Tennessee with an occluded front extending southward to the Alabama Gulf coast where it meets a warm= front that stretches northeastward toward the Atlantic Low and a short cold front/stationary front extending across the Gulf of = Mexico. The connection of the occluded, warm and cold fronts at the coast is the triple point, which is often found associated with mature midlatitude cyclones. A second extensive frontal system is found over the west-central = U.S. stretched from a Low center along the= North Dakota-Canada border to southwestern Arizona. This system had been approaching the West Coast on Monday. Details of the <= span class=3DGramE>weather associated with these features can be found in= the Wednesday, 28 October, Daily Weather Summary.

1= . The circulation pattern around each of the storms' centers marked by the three = Ls in the Atlantic, Tennessee and North Dakota is generally [(counter= clockwise and inward)(clockwise and outward)] as given by t= he hand-twist model. These circulation patterns are opposite that around the <= b>H along the Texas Gulf Coast.

2= . Observe the weather conditions at stations in the warm sector of the Southeastern Low between the cold front extending into the Gulf and the warm front across Florida and Georgia to the South Carolina coast. The wind directi= ons and temperature pattern in this region indicates that [(warm)(cold)] air was flowing northward, overrunning the warm front.

3= .      Additionally, the winds and dewpoints indicate that there = [(was)(was not)] considerable flow of moi= st air northward into the storm circulation. This was moisture advection, a necess= ary ingredient for the thunderstorms and widespread precipitation.

4= .      The majority of the widespread precipitation in the eastern U.S. wa= s found generally [(between the Low centers)(<= /span>along the warm, occluded and cold fronts)].

5= .      The largest continuous area of precipitation associated with the western Low and frontal system was located [(north of the Dakota Low center)(along the cold front)].

6= .      Observe the pressure gradients and wind speeds across the map associated with both storm systems. In the western U.S. compare the northern California to north= ern Arizona area with that across Texas. This is typified by the winds a= t Las Vegas, NV (fr= om the north at 25 kts) and San Antonio (from the south at 5 kts). Higher wind speeds were generally associated wi= th the stronger pressure gradient as depicted by [(closely)(widely)] - spaced isobar lines in = that area.

Image 2 is the 500-mb constant-pressure map for 00Z 28 OCT 2009. These were t= he upper-air conditions over the coterminous U= .S. and adjacent areas of Canada and Mexico at the same time as the conditions shown on the Image 1 surface map.= The 500-mb conditions are those in the middle troposphere associated with the surface conditions, including the storm systems that dominate the surface m= ap. Weather systems extend well into the troposphere and a three-dimensional understanding of them is necessary for accurate predictions.

Maps of upper-atmospheric conditions are made twice each day at 00Z and = 12Z, and are based on rawinsonde reports. Those disp= layed on the course website are from the radiosondes launched from about 70 stations across the continental U.S. and Canada/Mexico areas. On an upper-air map, the temperature, dewpoint, height and wind data from a station's rawinsonde report at that pressure are plotted around each station location (at the forward end of the wind arrow) in an upper-air station model format, as discussed earlier in this Investigation and the User's Guide, linked from the Extras section of the course website.

7= .      On the Image 2, 500-mb map, the plotted report for Riverton, in west-central Wyoming, shows that at 500 mb over the station,= the temperature was [(–18)(–27)(<= u>–30)] °C.

8= .      The dewpoint at 500 mb = over Riverton was [(–22)(–30)(–36)] °C.

9= .      Recalling that the heights plotted at individual stations on 500-mb maps are in te= ns of meters (add a 0 to the three plotted digits), the height at which= 500 mb occurred over Riverton was [(5810)(5600)(5420)] meters.=

1= 0. The w= ind at Riverton was from the south at about [(20)(45)(70)] knots. [Note: When winds of 50 knots or greater are reported, a pennant = is used on the station's wind shaft for a 50-kt increment along with the usual long and short "feathers".]

1= 1. The following data were from a radiosonde report at another station's 500-mb level at 00Z 28 OCT 2009 —
Height (m): 5680, temperature (°C): –12.3, d= ewpoint (°C): –15.5, wind direction (deg. from N): 205 (i.e. SSW), wind speed (kts): 67.
Examining the stations plotted on the 500-mb map in Image 2 shows this stat= ion to be [(Dodge City,= KS)(Nashville, TN)]. Current radiosonde reports containing upper air= data can be found from the Upper Air section, "Upper Air Data - Text" on the course website.

1= 2. The p= attern of 500-mb heights (heights above sea level where the air pressure is 500 mb as found by the radiosondes at that time) can be shown by contour lines. To better visualize the contour pattern plotted by the computer on the Image 2 map, highlight the 5580-m contour by tracing over it. [The 5580-m contour curves from central California southeastward to = Arizona and then generally northeastward across Lake Superior and finally over Maine.]

The contour pattern of the 500-mb map has = [(only a deep trough in the western U.S.)(only a ridge near the U.S. Ea= st Coast)(both a western trough and an easte= rn ridge)]. There are also localized trough-like curvatures in the flow over the Mississippi Valley associated with the Tennessee surface Low referred to as a "short wave".

1= 3. The I= mage 2, 500-mb map also shows that, where contour lines are relatively close, su= ch as along the West Coast and over the southern U.S., wind speeds are [(slower)(faster)]. This principle corresponds to that of the spacing of isobars and wind speed= s on surface maps.

1= 4. At up= per levels, the wind directions are also related to the contours. That is, where winds are relatively fast, the winds are generally [("paralle= l" to the contours)(directed across t= he contours at large angles)]. The absence of friction at upper le= vels means that flow is controlled mainly by the pressure gradient and Coriolis forces. Therefore winds are generally along = the contours on upper level maps as opposed to the inward circulations with Lows and outward with Highs seen on surface maps.

1= 5. Using= the station values as well as the contour pattern, compare the heights at Riverton, WY in t= he west to those of Pittsburgh, PA in the east. At comparable latitude= s, the 500-mb heights were relatively [(lower= )(higher)] over Riverton compared to those over Pittsburgh.

1= 6. Also compare the temperatures for these stations. The 500-mb temperatures are relatively [(lower)(highe= r)] over Riverton compared to Pitt= sburgh. The relation of column temperatures to heights of pressure surfaces was examined using conceptual "pressure blocks" in Investigation 5B. =

1= 7. The direction of movement of surface low-pressure centers can often be anticipa= ted from the 500-mb wind flow directions over their locations. Using the general wind directions at 500 mb over Tennessee and No= rth Dakota as guides, one could predict the movement of those surface Lows in t= he next day or so as being toward the [(southeast)(= northeast)(northwest)(southwest)].

Middle and upper tropospheric conditions are inextricably linked with the surface weather features. They are involved in= the development and movement of weather systems over the Earth. We will consider these relationships along with upper tropospheric maps and conditions in Current Weather Studies 9A.

If directed by your instructor, place the answers to Investigation 8B and Current Weather Studies 8B on the B Answer Form linked from the AMS Weather Studies website.

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