Overview

Being able to use weather observations to determine the freezing level and estimate the snow level can help you find snow and avoid skiing in a garbage bag all day. While this is especially true in coastal mountain ranges like the Cascades of the northwest United States and the Coast Range of British Columbia, even the Wasatch see rain in warm storms. At the conclusion of this learning activity, you will be able to access temperature observations from ski areas, determine the freezing level, and estimate the snow level.

Instructions

Utilize the information located in the Scenario, Key Concepts, and Resources to answer the questions located in this activity. You may refer to your textbook and notes to help you work through the assigned questions if desired. You will have two attempts to complete this activity. The highest grade will automatically be recorded. Once you have submitted your activity for a second time, you will be able to see the correct answers. Discuss with your instructor if you have questions about your answers or feedback. Important: To answer the questions in this assignment, use the data on the map in the resources section and not the weather observation links for live data from the ski resorts. The links for live data from the ski resorts is provided so that you can access that data for your skiing and recreation planning.

Activity is due Sunday, by 11:59 p.m. MT

Submission and Assessment Guidelines

You will complete the quiz associated with this scenario within Canvas. For help on how to take a quiz in Canvas, review How do I take a quiz.
This learning activity is worth 10 points toward your final grade.

Scenario

It's a holiday weekend and it's raining in Salt Lake City. You don't want to ski in the rain. How can you figure out where the snow level is and where to ski to avoid the rain?

Key Concepts

a. The melting layer, freezing level, and snow level

During warmer winter storms, snow at higher altitudes transitions to rain as it falls through the melting layer, which is also referred to as the transition zone. As depicted in Figure 1, falling precipitation is in the form of snow above the freezing level where the temperature is 32˚F/0˚C. Below the freezing level, temperatures are above freezing and the falling snow begins to melt, transitioning to wet snow, then slush, and finally rain. Because the snow has different shapes and sizes and some snow crystals can survive longer than others, it can result in a mixture of wet snow, slush, and rain in the lower portion of the melting layer. Often, the freezing level is lower and the melting layer deeper near the mountains than over the surrounding lowlands as illustrated in Figure 1. This is due to the "ice-cube effect." Snowfall rates are often higher over the mountains, which cools the atmosphere more than upstream — similar to adding more ice cubes to a drink.

Schematic depiction of the melting layer Figure 1. Schematic depiction of the freezing level, melting layer, and snow level over and near a mountain. From Steenburgh (2014).

Surprisingly, there is no clear definition of the snow level. The level at which snow changes to rain isn't quite right because that change happens through a layer rather than at a level. Some prefer the level at which snow accumulates on the ground (sometimes referred to as the snow line). This makes sense, but that level can be different depending on the surface (for example, asphalt or grass), and precipitation is often in the form of snow slightly below this level - it just doesn't stick.

Since we're interested in skiing, we will define snow level as the level at which snow is accumulating on the ground or vegetation. See Figure 2 for an example.

Figure 2. Photo of the snow level/snow line on a mountainside.

b. Estimating freezing level

Many ski areas provide real-time temperature observations that can be used to estimate the freezing level and the melting level. Sometimes you get lucky and one of the observing sites is 32˚F/0˚C, which tells you right where the freezing level is. More often you need to find a station above the freezing level (with a temperature less than 32˚F) and a station below the freezing level (with a temperature above 32˚F) and estimate where the freezing level is between them.

For example, suppose there are weather stations at 7,000 and 8,000 feet with temperatures of 34˚F and 30˚F, respectively. The freezing level is between them, but at what elevation?

To determine the elevation, first, calculate the rate of change of temperature with an altitude between the stations. This is known as the lapse rate.

LapseRate = (LowerAltitudeStationTemp - HigherAltitudeStationTemp) / (HigherAltitudeStationElev - LowerAltitudeStationElev)

In this case:

Lapse rate = (34˚F - 30˚F)/(8,000 feet - 7,000 feet) = 4˚F/1,000 ft = .004˚F/feet

This means that the temperature decreases 4˚F per 1,000 feet increase in elevation, or .004˚F per foot increase in elevation.

Using the lapse rate, the elevation of the freezing level can be calculated from

FreezingLevelElev = LowerAltitudeStationElev + ((LowerAltitudeStationTemp - 32˚F) / Lapse Rate)

In this case:

Elevation freezing level = 7,000 feet + ((34˚F - 32˚F) / .004˚F/feet) = 7,500 feet

c. Estimating snow level

Unfortunately, there isn't an exact relationship between freezing level and snow level. In addition to the height of the freezing level, the snow level also depends on the lapse rate, the relative humidity, and the shape and size of the snow crystals. Complications are also introduced if an inversion is present in which temperature increases instead of decreases with height.

A rule of thumb, based roughly on the average distance the snow level lies below the freezing level, is to assume the snow level is 1,000 feet below the freezing level. So, for the previous example:

Snow level = Freezing level - 1,000 feet = 7,500 feet - 1,000 feet = 6,500 feet

You can use this assumption for this lab and as a guess in practice, but recognize there can be variations depending on the conditions.

d. Weather observations

Prior to a ski day, you can use online ski area weather observations combined with the methods above to estimate the current snow level (although it should be noted that this snow level can change with time and we'll deal with forecasting later in the class). For example, real-time observations from Utah ski resorts can be accessed from the links provided at the end of the Key Concepts section (but may not be available outside of the ski season and are sometimes missing during the ski season), which we provide for your future use. Most of these stations are operated by the resorts, but SNOTEL stations are operated by the Natural Resources and Conservation Service. The measurements collected vary by station, but most (but not quite all) report temperature.

Alta
Base (ATB)
Collins (CLN)
Top of Collins (ALT)
Mt. Baldy Summit (AMB)

Snowbird
SNOTEL near Gad Restaurant (SBDU1)
Hidden Peak (HDP)

Solitude
Base (SOLBS)
Moonbeam (SOLMB)
Apex (SOLAP)
Powderhorn (SOL)
Summit (SOLSM)
Honeycomb Peak (SOLHP)

Brighton
SNOTEL at base (BRIU1)
Crest (BRC)
Great Western (BRW)

Park City Mountain Resort-Mountain Village
Base (PCB)
Eagle (PCS)
Payday (PCPD)
Crescent (PCR)
King Con (PKK)
Bonanza (PCZ)
Silverlode Bottom (PCH)
Silverlode Top (PCSL)
Pinecone (PCPCN)
Summit (PCT)
Jupiter (PKC)
SNOTEL in Thaynes Canyon (THCU1)

Park City Mountain Resort-Canyons Village
Lookout (CLK)
Condor (CCD)
Daybreak (CDYBK)
Dreamscape(CDSUT)
9990 (C99)

Deer Valley
Deer Crest Gondola (DVG)
Burns (DVE)
Bald Eagle (DVB)
Ruby (SNV)
Ontario (DVO)
Mount Baldy (MBY)
Empire Peak (EMPUT)

Snowbasin
Base (SBE)
Strawberry Base (SB1)
Middle Bowl (SNI)
Wildcat (SWI)
Shooting Star (SSS)
Boardwalk (SBBWK)
Strawberry Tower 15 (SBT15)
John Paul (SBW)
Strawberry Top (SB2)
Allens Peak (SBB)
Ogden Peak (OGP)

Powder Mountain
Powder Mountain (UTPWD)
Powder Mountain 2 (UTPW2)
Mary's Lift (UTPW4)
James Peak (UTPW3)

Sundance
Mid Mountain (SNM)
Arrowhead Summit (SND)

Resources

For this activity, we will evaluate the snow level during a relatively warm storm period on Martin Luther King Day 2011. Imagine you wake up that morning in Salt Lake City and its raining. Should you get excited to drive up to your favorite resort or hit the snooze button for more sleep?

This map shows temperature observations at 7 AM that morning from ski resorts in the central Wasatch (Click here for a larger image). The elevations of the observing sites are listed in the upper left corner of the map. Using these observations and elevations, answer the questions that follow.

Map with temperature observations on MLK weekend 2011 Figure 1. Surface temperatures at 7 AM MST 17 January 2011.

Citations

Key Concepts:

- - Weather Conditions for ATB
    - Citation: MesoWest. (n.d.). Weather conditions for ATB. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=ATB
  - Weather Conditions for CLN
    - Citation:MesoWest. (n.d.). Weather conditions for CLN. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=cln
  - Weather Conditions for ALT
    - Citation: MesoWest. (n.d.). Weather conditions for ALT. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=alt
  - Weather Conditions for AMB
    - Citation: MesoWest. (n.d.). Weather conditions for AMB. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=amb
  - Weather Conditions for SBDU1
    - Citation: MesoWest. (n.d.). Weather conditions for SBDU1. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SBDU1
  - Weather Conditions for HDP
    - Citation: MesoWest. (n.d.). Weather conditions for HDP. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=HDP
  - Weather Conditions for SOLBS
    - Citation: MesoWest. (n.d.). Weather conditions for SOLBS. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SOLBS
  - Weather Conditions for SOLMB
    - Citation: MesoWest. (n.d.). Weather conditions for SOLMB. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SOLMB
  - Weather Conditions for SOLAP
    - Citation: MesoWest. (n.d.). Weather conditions for SOLAP. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SOLAP
  - Weather Conditions for SOL
    - Citation: MesoWest. (n.d.). Weather conditions for SOL. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SOL
  - Weather Conditions for SOLSM
    - Citation: MesoWest. (n.d.). Weather conditions for SOLSM. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SOLSM
  - Weather Conditions for SOLHP
    - Citation: MesoWest. (n.d.). Weather conditions for SOLHP. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SOLHP
  - Weather Conditions for BRIU1
    - Citation: MesoWest. (n.d.). Weather conditions for BRIU1. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=BRIU1
  - Weather Conditions for BRC
    - Citation: MesoWest. (n.d.). Weather conditions for BRC. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=BRC
  - Weather Conditions for BRW
    - Citation: MesoWest. (n.d.). Weather conditions for BRW. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=BRW
  - Weather Conditions for PCB
    - Citation: MesoWest. (n.d.). Weather conditions for PCB. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCB
  - Weather Conditions for PCS
    - Citation: MesoWest. (n.d.). Weather conditions for PCS. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCS
  - Weather Conditions for PCPD
    - Citation: MesoWest. (n.d.). Weather conditions for PCPD. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCPD
  - Weather Conditions for PCR
    - Citation: MesoWest. (n.d.). Weather conditions for PCR. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCR
  - Weather Conditions for PKK
    - Citation: MesoWest. (n.d.). Weather conditions for PKK. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PKK
  - Weather Conditions for PCZ
    - Citation: MesoWest. (n.d.). Weather conditions for PCZ. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCZ
  - Weather Conditions for PCH
    - Citation: MesoWest. (n.d.). Weather conditions for PCH. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCH
  - Weather Conditions for PCSL
    - Citation: MesoWest. (n.d.). Weather conditions for PCSL. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCSL
  - Weather Conditions for PCPCN
    - Citation: MesoWest. (n.d.). Weather conditions for PCPCN. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCPCN
  - Weather Conditions for PCT
    - Citation: MesoWest. (n.d.). Weather Conditions for PCT. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PCT
  - Weather Conditions for PKC
    - Citation: MesoWest. (n.d.). Weather conditions for PKC. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=PKC
  - Weather Conditions for THCU1
    - Citation: MesoWest. (n.d.). Weather conditions for THCU1. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=THCU1
  - Weather Conditions for CLK
    - Citation: MesoWest. (n.d.). Weather conditions for CLK. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=CLK
  - Weather Conditions for CCD
    - Citation: MesoWest. (n.d.). Weather conditions for CCD. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=CCD
  - Weather Conditions for CDYBK
    - Citation: MesoWest. (n.d.). Weather conditions for CDYBK. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=CDYBK
  - Weather Conditions for CDSUT
    - Citation: MesoWest. (n.d.). Weather conditions for CDSUT. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=CDSUT
  - Weather Conditions for C99
    - Citation: MesoWest. (n.d.). Weather conditions for C99. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=C99
  - Weather Conditions for DVG
    - Citation: MesoWest. (n.d.). Weather conditions for DVG. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=DVG
  - Weather Conditions for DVE
    - Citation: MesoWest. (n.d.). Weather conditions for DVE. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=DVE
  - Weather Conditions for DVB
    - Citation: MesoWest. (n.d.). Weather conditions for DVB. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=DVB
  - Weather Conditions for SNV
    - Citation: MesoWest. (n.d.). Weather conditions for SNV. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SNV
  - Weather Conditions for DVO
    - Citation: MesoWest. (n.d.). Weather conditions for DVO. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=DVO
  - Weather Conditions for MBY
    - Citation: MesoWest. (n.d.). Weather conditions for MBY. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=MBY
  - Weather Conditions for EMPUT
    - Citation: MesoWest. (n.d.). Weather conditions for EMPUT. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=EMPUT
  - Weather Conditions for SBE
    - Citation: MesoWest. (n.d.). Weather conditions for SBE. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SBE
  - Weather Conditions for SBI
    - Citation: MesoWest. (n.d.). Weather conditions for SBI. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SB1
  - Weather Conditions for SNI
    - Citation: MesoWest. (n.d.). Weather conditions for SNI. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SNI
  - Weather Conditions for SWI
    - Citation: MesoWest. (n.d.). Weather conditions for SWI. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SWI
  - Weather Conditions for SSS
    - Citation: MesoWest. (n.d.). Weather conditions for SSS. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SSS
  - Weather Conditions for SBBWK
    - Citation: MesoWest. (n.d.). Weather conditions for SBBWK. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SBBWK
  - Weather Conditions for SBT15
    - Citation: MesoWest. (n.d.). Weather conditions for SBT15. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SBT15
  - Weather Conditions for SBW
    - Citation: MesoWest. (n.d.). Weather conditions for SBW. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SBW
  - Weather Conditions for SB2
    - Citation: MesoWest. (n.d.). Weather conditions for SB2. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SB2
  - Weather Conditions for SBB
    - Citation: MesoWest. (n.d.). Weather conditions for SBB. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SBB
  - Weather Conditions for OGP
    - Citation: MesoWest. (n.d.). Weather conditions for OGP. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=OGP
  - Weather Conditions for UTPWD
    - Citation: MesoWest. (n.d.). Weather conditions for UTPWD. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=UTPWD
  - Weather Conditions for UTPW2
    - Citation: MesoWest. (n.d.). Weather conditions for UTPW2. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=UTPW2
  - Weather Conditions for UTPW4
    - Citation: MesoWest. (n.d.). Weather conditions for UTPW4. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=UTPW4
  - Weather Conditions for UTPW3
    - Citation: MesoWest. (n.d.). Weather conditions for UTPW3. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=UTPW3
  - Weather Conditions for SNM
    - Citation: MesoWest. (n.d.). Weather conditions for SNM. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SNM
  - Weather Conditions for SND
    - Citation: MesoWest. (n.d.). Weather conditions for SND. University of Utah. https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=SND

Images:

Key Concepts

- Figure 1. Schematic depiction of the freezing level, melting layer, and snow level over and near a mountain
  - Citation: Steenburgh, J. (2014). Secrets of the greatest snow on earth: Weather, climate change, and finding deep powder in Utah’s Wasatch Mountains and around the world. Utah State University Press.
- Figure 2. Photo of the snow level/snow line on a mountainside
  - Citation: Sautter, J. (n.d.).

Resources:

- Figure 1. Surface Temperature (°F) 07MST17Jan2011
  - Citation: MesoWest Surface Observations via Cooperative Networks and Providers. Topo: © OpenStreetMap Mitwirkende, SRTM | Kartendarstellung: © OpenTopoMap (CC-BY-SA)