Note: Next week, 15 - 19 March 2010, willbe Break Week for theDataStreme Atmosphere course's spring semester. These Week 6 CurrentWeatherStudies investigations will be left on the course website during theweek. Allmeteorological files will continue to be updated. Weekly Weather andClimateNews and Daily Weather Summaries will be new.
In the Monday, Current Weather Studies (CWS) 6A, we examined awinter storm that brought precipitation to southernCalifornia. San Diego was receiving rain ahead of a landfalling frontalsystem. Here we willfurther consider where vertical air motions associated with the passageof a front were depicted on a Stüve diagram.
Image 1 is the surface weather map for 00Z 10 MAR 2010, Tuesday evening. Atthat time a sprawling storm system was circulating across the centralU.S. Heavy rainsand some snow were affecting regions about the system. Following thatsystem was another frontal system shown in two parts from eastern Idahoto northern Mexico that brought more scattered rain and snow tothe Intermountain West. This pair of fronts was the system that hadcome ashore from thePacific earlier and was examined Monday. And another frontal system wasalong the northernCalifornia to Washington state coasts ready to make its entrance. Fordetails, see the Wednesday, 10 March 2010 Daily Weather Summary. Wewill take a look at the atmospheric conditions over Salt Lake City,Utah that accompanied the frontal system there.
The surface temperature at Salt Lake City was 44°F and the dewpoint was 35 °F. Therefore, the surface airat SaltLake City [(was)(wasnot)] saturated.
Based on the station model sky cover and the radar echoshadings ofprecipitation shown around the Salt Lake City area, clouds[(were)(werenot)] present somewhere above thesurface.
Therefore, we can be confident that saturated air[(was)(wasnot)] present above the surfaceover the Salt Lake City area.
Salt Lake City in the Great Basin region is surrounded bymountains so wind patterns would often provide orographic lifting ofthe air in the area.Also, the Image 1 weather map shows a [(high-pressuresystem)(coldfront)] had just passed Salt Lake City.Bothof these mechanisms were providing lifting of the air overSalt Lake City.
With both lifting mechanisms for the air overthe SaltLake City area, we can be reasonably sure that[(rising)(sinking)]vertical motions occurred abovethe surface.
Image 2is the Stüve diagram fromthe Salt Lake City (SLC) rawinsonde observation at 0000Z 10 MAR 2010,the sametime asthe Image 1 surface map. Note that the lowest pressurelevel shown forthe temperature and dewpoint profiles in Salt Lake City is at about 860mb. This is the stationpressure, that measured by a barometer of the air above that elevation.The surface elevation of the rawinsonde station in Salt LakeCityis 1289 meters (4228 feet). The Image 1 map's decoded surfaceair pressure, 1004.0 mb, is the sea-levelpressure reading, the station pressure corrected towhat it would be at sea level!
The temperature and dewpoint profiles from thesurface in Salt Lake City up to about 800 mb show that the air[(was)(wasnot)] saturated.
The temperaturesand dewpointswere approximately equal from about 800 mb to about 640 mb. This nearequality as described in the Monday Current Weather Studies 6A means it[(was)(wasnot)] likely that cloud conditions werepresent in that layer.
From about 860 mb to 800 mb, the temperature profile wasparallel to theadjacent [(straight, solid, green dry)(curved,dashed, bluesaturated)] adiabatic lapse rate lineprinted on the diagram.
From about 800 mb to about 640 mb, the temperature anddewpoint profiles curved approximately "parallel" to theadjacent [(straight, solid, greendry)(curved,dashed, bluesaturated)] adiabatic lapse rateline printed on the diagram.
The following values come from the rawinsonde text data(not shown). Over Salt Lake City, 861 mb (surface) occurred at 1289 mwhere the temperature was 6.6 °C and 793 mb was at 1953 m where thetemperature was 0 °C.Therefore, the temperature difference between those levels was 6.6 C°over an altitude change of 669 m. The temperature lapse rate wastherefore an equivalent 9.87 C° per kilometer. This lapse rate value [(was)(wasnot)] essentially the same as thetheoretical9.86 C° per kilometer. Unsaturated rising air really does follow anadiabatic process!
Additionally, at the top the identified cloud layerover Salt Lake City the temperature was -11.1 °C at 639 mb(3658 m). The temperature difference between the 793-mb cloud base andthe 639-mb cloud top was 11.1 C° over an altitude change of 1705 m. Thetemperature lapse rate was therefore an equivalent 6.5 C° perkilometer. This value [(was)(wasnot)] reasonably consistent with theaverage6 C° per kilometer for clouds. Saturated rising air also really doesfollow an adiabatic process!
As another example of temperature changes associated with astorm system,you might review the Stüve (Figure 4) that accompanies the Applicationsportion of Investigation 6B of the Weather StudiesInvestigationsManual.
Stüve diagrams of actual observations confirm that verticalatmospheric motions do follow the theories! Call up these Stüves asdramatic weather changes affect your area. Weather systems (Highs,Lows,fronts) force air to move vertically causing accompanying temperaturechanges.Flow forced over higher and lower elevations, particularly in thewesternU.S. also drives atmospheric temperature patterns.
Record your responses to items in CWS Activities 6A and 6B ontheCWS Answer Form fortransmission to your coursementor.
Instructions for Communications with Mentor:
After completing this week's applications, transmit the following workto yourLIT mentor by Monday, 15 March 2010, or as coordinated with yourmentor:
Return to DataStremeAtmosphere website
©Copyright, 2010, American Meteorological Society
