Synoptic-Scale Flow and Valley Cold Pool Evolution in the Western United States

Heather Dawn Reeves NOAA/National Severe Storms Laboratory, Norman, Oklahoma

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David J. Stensrud NOAA/National Severe Storms Laboratory, Norman, Oklahoma

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Abstract

Valley cold pools (VCPs), which are trapped, cold layers of air at the bottoms of basins or valleys, pose a significant problem for forecasters because they can lead to several forms of difficult-to-forecast and hazardous weather such as fog, freezing rain, or poor air quality. Numerical models have historically failed to routinely provide accurate guidance on the formation and demise of VCPs, making the forecast problem more challenging. In some case studies of persistent wintertime VCPs, there is a connection between the movement of upper-level waves and the timing of VCP formation and decay. Herein, a 3-yr climatology of persistent wintertime VCPs for five valleys and basins in the western United States is performed to see how often VCP formation and decay coincides with synoptic-scale (∼200–2000 km) wave motions. Valley cold pools are found to form most frequently as an upper-level ridge approaches the western United States and in response to strong midlevel warming. The VCPs usually last as long as the ridge is over the area and usually only end when a trough, and its associated midlevel cooling, move over the western United States. In fact, VCP strength appears to be almost entirely dictated by midlevel temperature changes, which suggests large-scale forcing is dominant for this type of VCP most of the time.

Corresponding author address: Heather Dawn Reeves, DOC/NOAA/OAR/National Severe Storms Laboratory, 120 David L. Boren Blvd., Ste. 2401, Norman, OK 73072-7319. Email: heather.reeves@noaa.gov

Abstract

Valley cold pools (VCPs), which are trapped, cold layers of air at the bottoms of basins or valleys, pose a significant problem for forecasters because they can lead to several forms of difficult-to-forecast and hazardous weather such as fog, freezing rain, or poor air quality. Numerical models have historically failed to routinely provide accurate guidance on the formation and demise of VCPs, making the forecast problem more challenging. In some case studies of persistent wintertime VCPs, there is a connection between the movement of upper-level waves and the timing of VCP formation and decay. Herein, a 3-yr climatology of persistent wintertime VCPs for five valleys and basins in the western United States is performed to see how often VCP formation and decay coincides with synoptic-scale (∼200–2000 km) wave motions. Valley cold pools are found to form most frequently as an upper-level ridge approaches the western United States and in response to strong midlevel warming. The VCPs usually last as long as the ridge is over the area and usually only end when a trough, and its associated midlevel cooling, move over the western United States. In fact, VCP strength appears to be almost entirely dictated by midlevel temperature changes, which suggests large-scale forcing is dominant for this type of VCP most of the time.

Corresponding author address: Heather Dawn Reeves, DOC/NOAA/OAR/National Severe Storms Laboratory, 120 David L. Boren Blvd., Ste. 2401, Norman, OK 73072-7319. Email: heather.reeves@noaa.gov

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  • Bader, D. C., and McKee T. B. , 1985: Effect of shear, stability and valley characteristics on the destruction of temperature inversions. J. Climate Appl. Meteor., 24 , 822832.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Banta, R., and Cotton W. R. , 1981: An analysis of the structure of local wind systems in a broad mountain basin. J. Appl. Meteor., 20 , 12551266.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Benjamin, S. G., 1989: An isentropic mesoα-scale analysis system and its sensitivity to aircraft and surface observations. Mon. Wea. Rev., 117 , 15861603.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Billings, B. J., Grubišić V. , and Borys R. D. , 2006: Maintenance of a mountain valley cold pool: A numerical study. Mon. Wea. Rev., 134 , 22662278.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Cheng, W. Y. Y., and Steenburgh W. J. , 2007: Strengths and weaknesses of MOS, running-mean bias removal, and Kalman filter techniques for improving model forecasts over the western United States. Wea. Forecasting, 22 , 13041318.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Fast, J. D., Zhong S. , and Whiteman C. D. , 1996: Boundary layer evolution within a canyonland basin. Part II: Numerical simulations of nocturnal flows and heat budgets. J. Appl. Meteor., 35 , 21622178.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hart, K. A., Steenburgh W. J. , Onton D. J. , and Siffert A. J. , 2004: An evaluation of mesoscale-model-based model output statistics (MOS) during the 2002 Olympic and Paralympic Winter Games. Wea. Forecasting, 19 , 200218.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hart, K. A., Steenburgh W. J. , and Onton D. J. , 2005: Model forecast improvements with decreased horizontal grid spacing over finescale intermountain orography during the 2002 Olympic Winter Games. Wea. Forecasting, 20 , 558576.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hill, C. D., 1993: Forecast problems in the western region of the National Weather Service: An overview. Wea. Forecasting, 8 , 158165.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hoggarth, A. M., Reeves H. D. , and Lin Y-L. , 2006: Formation and maintenance mechanisms of the stable layer over the Po Valley during MAP IOP-8. Mon. Wea. Rev., 134 , 33363354.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee, T. J., Pielke R. A. , Kessler R. C. , and Weaver J. , 1989: Influence of cold pools downstream of mountain barriers on downslope winds and flushing. Mon. Wea. Rev., 117 , 20412058.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lenschow, D. H., Stankov B. B. , and Mahrt L. , 1979: The rapid morning boundary-layer transition. J. Atmos. Sci., 36 , 21082124.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mayr, G. J., and McKee T. B. , 1995: Observations of the evolution of orogenic blocking. Mon. Wea. Rev., 123 , 14471464.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pataki, D. E., Tyler B. J. , Peterson R. E. , Nair A. P. , Steenburgh W. J. , and Pardyjak E. R. , 2005: Can carbon dioxide be used as a tracer of urban atmospheric transport? J. Geophys. Res., 110 , D15102. doi:10.1029/2004JD005723.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Petkovsek, Z., 1992: Turbulent dissipation of cold air like in a basin. Meteor. Atmos. Phys., 47 , 237245.

  • Reeves, H. D., and Lin Y-L. , 2006: Effect of stable layer formation over the Po Valley on the development of convection during MAP IOP-8. J. Atmos. Sci., 63 , 25672584.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rex, D. F., 1950: Blocking action in the middle troposphere and its effect upon regional climate. Part I: An aerological study of blocking action. Tellus, 2 , 275301.

    • Search Google Scholar
    • Export Citation
  • Savoie, M. H., and McKee T. B. , 1995: The role of wintertime radiation in maintaining and destroying stable layers. Theor. Appl. Climatol., 52 , 4354.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Smith, R., and Coauthors, 1997: Local and remote effects of mountains on weather: Research needs and opportunities. Bull. Amer. Meteor. Soc., 78 , 877892.

    • Search Google Scholar
    • Export Citation
  • Struthwolf, M., 2005: An evaluation of fog forecasting tools for a fog event and non-event at Salt Lake City International Airport. NWS Tech. Attach. 05-05, 24 pp. [Available online at http://www.wrh.noaa.gov/wrh/05TAs/ta0505.pdf].

    • Search Google Scholar
    • Export Citation
  • Vrhovec, T., 1991: A cold air lake formation in a basin: A simulation with a mesoscale numerical model. Meteor. Atmos. Phys., 8 , 9199.

    • Search Google Scholar
    • Export Citation
  • Vrhovec, T., and Hrabar A. , 1996: Numerical simulations of dissipation of dry temperature inversions in basins. Geofizika, 13 , 8196.

  • Whiteman, C. D., 1982: Breakup of temperature inversions in deep mountain valleys: Part I. Observations. J. Appl. Meteor., 21 , 270289.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Whiteman, C. D., and McKee T. B. , 1982: Breakup of temperature inversions in deep mountain valleys: Part II. Thermodynamic model. J. Appl. Meteor., 21 , 290302.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Whiteman, C. D., Bian X. , and Zhong S. , 1999: Wintertime evolution of the temperature inversion in the Colorado Plateau basin. J. Appl. Meteor., 38 , 11031117.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Whiteman, C. D., Zhong S. , Shaw W. J. , Hubbe J. M. , Bian X. , and Mittelstadt J. , 2001: Cold pools in the Columbia Basin. Wea. Forecasting, 16 , 432447.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wolyn, P. G., and McKee T. B. , 1989: Deep stable layers in the intermountain western United States. Mon. Wea. Rev., 117 , 461472.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zängl, G., 2002: Improved method for computing horizontal diffusion in a sigma-coordinate model and its application to simulations over mountainous topography. Mon. Wea. Rev., 130 , 14231432.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zängl, G., 2003: The impact of upstream blocking, drainage flow, and the geostrophic pressure gradient on the persistence of cold-air pools. Quart. J. Roy. Meteor. Soc., 129 , 117137.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zängl, G., 2005a: Formation of extreme cold-air pools in elevated sinkholes: An idealized numerical process study. Mon. Wea. Rev., 133 , 925941.

  • Zängl, G., 2005b: Wintertime cold-air pools in the Bavarian Danube Valley basin: Data analysis and idealized numerical simulations. J. Appl. Meteor., 44 , 19501971.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zhong, S., Whiteman C. D. , Bian X. , Shaw W. J. , and Hubbe J. M. , 2001: Meteorological processes affecting the evolution of a wintertime cold air pool in the Columbia Basin. Mon. Wea. Rev., 129 , 26002613.

    • Crossref
    • Search Google Scholar
    • Export Citation
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