Unexpected Warming Induced by Foehn Winds in the Lee of the Smoky Mountains

David M. Gaffin National Weather Service, Morristown, Tennessee

Search for other papers by David M. Gaffin in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

On 2 January 1999, a southeasterly foehn wind produced a narrow band of temperatures up to 10°C (18°F) warmer than the surrounding area in the central Great Tennessee Valley on the northwest side of the Smoky Mountains. This particular event was interesting in comparison with other documented foehn wind events in that the dewpoint temperature rose substantially along with the actual temperature, resulting in little change in the observed surface relative humidity. A relatively warm and nearly saturated 850-hPa air mass around the highest ridges of the Smoky Mountains was found to be the source of the adiabatically compressed air observed on the northwest side of the Smoky Mountains. The observed foehn winds across the central Great Tennessee Valley were not unusually strong during the afternoon, with surface wind gusts reaching 13 m s−1 (26 kt). However, mountain waves may have been associated with the foehn winds on 2 January 1999, because a strong surface pressure gradient was in place across the mountain range, winds in excess of 15 m s−1 (30 kt) were observed in a stable layer at 850 hPa blowing nearly perpendicular to the highest Smoky Mountain ridges, and favorable vertical wind and terrain profiles were present. Any mountain wave activity likely remained close to the mountains away from any of the observation stations in the Great Tennessee Valley. Also, high relative humidity levels (>70%) throughout much of the boundary layer near the Great Tennessee Valley may have reduced the strength of the foehn winds.

Corresponding author address: David M. Gaffin, National Weather Service, 5974 Commerce Blvd., Morristown, TN 37814. Email: david.gaffin@noaa.gov

Abstract

On 2 January 1999, a southeasterly foehn wind produced a narrow band of temperatures up to 10°C (18°F) warmer than the surrounding area in the central Great Tennessee Valley on the northwest side of the Smoky Mountains. This particular event was interesting in comparison with other documented foehn wind events in that the dewpoint temperature rose substantially along with the actual temperature, resulting in little change in the observed surface relative humidity. A relatively warm and nearly saturated 850-hPa air mass around the highest ridges of the Smoky Mountains was found to be the source of the adiabatically compressed air observed on the northwest side of the Smoky Mountains. The observed foehn winds across the central Great Tennessee Valley were not unusually strong during the afternoon, with surface wind gusts reaching 13 m s−1 (26 kt). However, mountain waves may have been associated with the foehn winds on 2 January 1999, because a strong surface pressure gradient was in place across the mountain range, winds in excess of 15 m s−1 (30 kt) were observed in a stable layer at 850 hPa blowing nearly perpendicular to the highest Smoky Mountain ridges, and favorable vertical wind and terrain profiles were present. Any mountain wave activity likely remained close to the mountains away from any of the observation stations in the Great Tennessee Valley. Also, high relative humidity levels (>70%) throughout much of the boundary layer near the Great Tennessee Valley may have reduced the strength of the foehn winds.

Corresponding author address: David M. Gaffin, National Weather Service, 5974 Commerce Blvd., Morristown, TN 37814. Email: david.gaffin@noaa.gov

Save
  • Blier, W., 1998: The Sundowner winds of Santa Barbara, California. Wea. Forecasting, 13 , 702716.

  • Burroughs, L. D., 1987: Development of forecast guidance for Santa Ana conditions. Natl. Wea. Dig., 12 , 411.

  • Colson, D., 1954: Meteorological problems in forecasting mountain waves. Bull. Amer. Meteor. Soc., 35 , 363371.

  • Durran, D. R., and Klemp J. B. , 1983: A compressible model for the simulation of moist mountain waves. Mon. Wea. Rev., 111 , 23412361.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Klemp, J. B., and Lilly D. K. , 1975: The dynamics of wave-induced downslope winds. J. Atmos. Sci., 32 , 320339.

  • Lessard, A. G., 1988: The Santa Ana winds of southern California. Weatherwise, 41 , 100104.

  • Lilly, D. K., and Klemp J. B. , 1979: The effects of terrain shape on nonlinear hydrostatic mountain waves. J. Fluid Mech., 95 , 241261.

  • Nkemdirim, L. C., 1986: Chinooks in southern Alberta: Some distinguishing nocturnal features. J. Climatol., 6 , 593603.

  • Oard, M. J., 1993: A method for predicting chinook winds east of the Montana Rockies. Wea. Forecasting, 8 , 166180.

  • Queney, P., Corby G. , Gerbier N. , Koschmieder H. , and Zierep J. , 1960: The airflow over mountains. WMO Tech. Note 34, 135 pp. [Available from World Meteorological Organization, P.O. Box 2300, CH-1211 Geneva 2, Switzerland.].

    • Search Google Scholar
    • Export Citation
  • Ryan, G., and Burch L. E. , 1992: An analysis of Sundowner winds: A California downslope wind event. Preprints, Sixth Conf. on Mountain Meteorology, Portland, OR, Amer. Meteor. Soc., 64–67.

    • Search Google Scholar
    • Export Citation
  • Scorer, R., 1949: Theory of waves in the lee of mountains. Quart. J. Roy. Meteor. Soc., 75 , 4156.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 558 101 2
PDF Downloads 189 48 0