Frequently Asked Questions
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How much computational resources are required to run the analysis and forecasting system?
The forecast system requires 5120 cores on NCAR's Yellowstone supercomputer for approximately 4-hrs.
Do we plan to produce 12Z initialized ensemble forecasts?
We are exploring the possibility of initializing 12Z forecasts during Spring 2016, given the availability of additional computing time.
Are the data freely available for use to external collaborators?
Yes, subject to UCAR's terms and conditions. Send us an email.
What is parcel Bmin?
Bmin represents the buoyancy minimum experienced by an air parcel lifted from a specified height. The graphics on this site use an air parcel lifted from the surface. More information on its development and utility can be found in Trier et al. (2014).
How are the simulated satellite products created?
The simulated satellite product is derived from the Community Radiative Transfer Model (CRTM) embedded inside the UPP.
How is precipitation type determined?
Precipitation type is computed using the AFWA precipitation type diagnostics package in WRFV3.6.1. The full documentation for this package can be found here. Precipitation type is determined independently from the microphysics scheme using a top-down approach as summarized below:

For each vertical grid column, do the following:
  1. Modify the 2-m temperature by adding the shortwave radiation (W m-2) divided by 100.
  2. If the modified 2-meter temperature is > 2C, set type to rain.
  3. Check the vertical profile to find highest cloud temperature (RH < 80%). If a cloud is found, but below it a dry (RH < 70%) layer is found, reset and keep checking.
  4. If the cloud top temperature is < -9C, set type to snow. Otherwise, set to rain.
  5. Check the vertical profile that the rain or snow is falling through:
    1. If snow or ice pellets falls through a melting layer, integrate total melting energy.
    2. If the integrated energy is > 50 J kg-1, then set type to rain.
    3. If the integrated energy is between 25-100% of 50 J kg-1, and it subsequently falls through a sub-freezing layer, assume it partially melted and then re- froze into an ice pellet. Reset melting energy to zero.
    4. If as rain falls it encounters a temperature < -9C, set type to ice pellets.
    5. Keep running these checks all the way to the ground and adjust types accordingly.
    6. Once it gets to the ground, rain becomes freezing rain if the modified 2 meter temperature is < 0C.
At grid points where the precipitation type is determined to be snow, the liquid-equivalent precipitation amount is converted to a snowfall total via a snowfall ratio that depends on the surface temperature via the following equation: (Snowfall ratio = 5.0*(278.15K - modified 2m temp[K]) ^ 0.4)

This produces a snowfall ratio of 10:1 near 0C, 15:1 near -11C, and 20:1 near -27C. This is an obvious simplification, as snow crystals form above the surface in a potentially different thermodynamic environment. In cases where temperatures in the snow growth region are between -12C and -18C, snowfall ratios could easily exceed 20:1. Keep this in mind when examining the snowfall accumulation graphics on this site.

This algorithm tends to produce freezing rain immediately downwind of high terrain, when the actual precipitation type is likely to be snow. This is due to the way in which the highest cloud temperature is determined as described above. We will be investigating this issue during the winter of 2015-2016.
How are the 24-hour smoothed severe weather probabilities produced?
The severe weather probabilities are produced following a method described in Schwartz et al. (2015), which is based on a method proposed by Sobash et al. (2011). Briefly, the probabilities use diagnostic fields that represent the intensity and behavior of convection to identify locations where severe weather may occur, by selecting thresholds that approximately match the frequency thresholds for observed severe weather. These locations are smoothed to account for location and timing errors to produce a 24-hour severe weather guidance product.
Where can I find more information about the model configuration?
Some aspects of the model configuration is documented on our "About" page. Additional documentation is provided in Schwartz et al. (2015).