Analysis of Valley Inversion Structure Using Radiosonde, Radar Profiler and Mountain Mesonet Data

1
Analysis of Valley Inversion Structure Using
Radiosonde, Radar Profiler and Mountain Mesonet
Data
Eleventh Annual Workshop on Weather Prediction in
the Intermountain West 4 Nov 2004 University
of Utah, Salt Lake City, UT
Temporal evolution of boundary layer
thermodynamic structure in mountainous terrain
can be strongly influenced by air drainage
patterns, topographic shading, orographic
enhancement of cloudiness, and stability
conditions induced by pooling of cold air. This
paper demonstrates the value of surface-based
mesonet stations at multiple elevations in areas
where these processes impact other important
meteorological processes such as cloud
microphysics, snowfall intensity and air
pollution.
Melanie A. Wetzel and Randolph D. Borys
Storm Peak Laboratory / Division of Atmospheric
Sciences Desert Research Institute
Fig. 12. NCAR Integrated Sounding System
providing radar wind profiles and radiosonde
launches at the base of the mountain range.
The Park Range in northwest Colorado (Fig. 1)
benefits from a meso-network of several
meteorological monitoring stations (Fig. 2)
operated by the Steamboat Ski and Resort
Corporation (SSRC) at a range of elevations (Fig.
3). Additional monitoring is conducted by the
Desert Research Institute (DRI) Storm Peak
Laboratory at ridge-top (Fig. 4 Fig. 5). DRI
scientists and collaborators from the National
Weather Service (NWS) and the National Center for
Atmospheric Research (NCAR) have also carried out
research programs with radar wind profiler and
radiosonde launches that facilitate analysis of
time series of the surface mesonet data.
Fig. 11. NCAR MAPR time series profiles
indicating wind velocities and radar backscatter
intensity for 16 Feb 2002 during a period of
valley inversion conditions.
Elevational mesonet profiles complement
radiosonde (Fig. 10) and profiler (Fig. 11, Fig.
12) data for study of valley inversion
development and breakup. Fig. 13 depicts the
arrival of a front near 20 UT on 17 Feb that
interrupts the diurnal inversion cycle (at 13 MST
in Fig. 14). However, the initial air mass
influx only produces a precipitation signature in
the upper zone of the ridge for the first several
hours (Fig. 15) and this is evidenced by low RH
for mesonet stations below 2700 m until after
midnight MST (Fig. 16).
Fig. 1. Park Range near Steamboat Springs in
northwest Colorado with orographic cap cloud at
ridge top.
Fig. 3. Ski lift building showing location of
one of the mesonet sites (pole above top of roof).
Fig. 13. NCAR MAPR time series profiles
indicating wind velocities and radar backscatter
intensity for 17 Feb 2002.
Fig. 14. Time series of air temperature from
elevational mesonet measurements.

Fig. 2. Mesonet instruments provide air
temperature, humidity and wind velocity and data
are transmitted by radio.
Fig. 6. Time series of air temperature obtained
from sites at multiple elevations during 11-14
January 2002.

Fig. 10. Thermodynamic and wind speed component
profiles from radiosonde profile of 2328 UT on 17
Feb 2004.
Fig. 7. Time series of relative humidity
obtained from sites at multiple elevations during
11-14 January 2002.
Time series of surface air temperature (Fig. 6)
and relative humidity (Fig. 7) provide
quantitative information on the evolution in the
depth and magnitude of nocturnal cooling during a
valley inversion period, with an abrupt
transition in the temperature trend at 21 UTC on
12 January. The relative humidity time series
indicates that cloud base after this time is
located near 2500m, and that cloud layer
temperatures are 9 to 15 C between cloud base
and ridge top, providing ideal conditions for
snow growth. Comparisons of temperatures (Fig.
8) and humidity values (Fig. 9) at mesonet sites
to radiosonde profile data at the same elevations
and time show differences during periods of rapid
surface warming (11 Jan) but more correspondence
during well-mixed conditions (13 Jan).

Fig. 15. NCAR MAPR time series profiles
indicating wind velocities and precipitation
backscatter intensity for 18 Feb 2002.
Fig. 4. Measurements at the Storm Peak Lab and
mesonet sites help to identify the presence of
cloud.
Fig. 16. Time series of relative humidity from
elevational mesonet measurements.
Fig. 5. Fog and stratus are commonly restricted
to lower elevations due to a valley inversion and
availability of moisture from prior precipitation.
The authors acknowledge the collaboration of
scientists from NCAR and DRI in the research
programs that provided the data described here,
and grant support from NSF and NOAA. Logistical
assistance from the Steamboat Ski and Resort
Corporation is greatly appreciated. DRI is an
equal opportunity service provider and employer
and is a permittee of the Medicine-Bow and Routt
National Forests for the Storm Peak Laboratory.
Fig. 9. Vertical profiles of relative humidity
obtained from radiosonde soundings (SND) and
mesonet (SFC).
Fig. 8. Vertical profiles of air temperature
obtained from radiosonde soundings (SND) and
mesonet (SFC).
Project funding from NOAA
and NSF through University of Alaska
International Arctic Research Consortium
additional support from the USDA UV-B Program
Office.