MOS Expanded Change Logs (2008-Present)

January 13, 2016

Upgrades to NAM MOS

MDL and NCEP will be implementing several updates to the NAM MOS guidance Wednesday, January 13, beginning with NCEP's 1200 UTC product cycle. The following are some highlights:

  • New cool season forecast equations are being introduced for probabilistic and categorical precipitation type. These forecasts will now appear in the NAM MOS bulletins for the first time. This will result in the addition of three new lines to the bulletin, labeled "POZ", "POS", and "TYP". Respectively, these lines will contain probabilistic forecasts of the occurrence of freezing precipitation and snow, as well as a categorical forecast for the most likely precipitation type. With this change, the format of the NAM MOS bulletins will now match that of the short-range GFS MOS.
  • While the above guidance is new to the bulletins, MDL has been producing experimental NAM MOS precipitation type forecasts in support of Eastern Region winter weather operations for some time. These equations have been updated to include output from the newest version of the NAM (v3.1) which became operational in August 2014.
  • The forecast equations for the probability of thunderstorm occurrence and the probability of severe weather have been updated to include data from the newest version of NAM. Also, thunderstorm probability forecasts now will be available for sites in Alaska for the first time. Accordingly, this will result in the addition of two lines to the NAM MOS bulletins for Alaskan sites. These lines will be labeled "T06" and "T12" for the 6-h and 12-h thunderstorm probabilities, respectively.
  • Updated NAM MOS forecast equations for categorical snowfall amount will be implemented. The dependent sample for these equations has been updated to include output from more recent versions of the model. They replace the currently-operational system, which is dependent solely on output from the older, eta-coordinate model.

Once again, these updates are scheduled for implementation beginning with the 1200 UTC cycle on January13, 2016. For additional details regarding the NAM MOS updates, please see the Technical Implementation Notice: