Frequently Asked Questions
Q: What is "Predominant Weather"?
A: Predominant Weather (Wx) is the expected weather (precipitating or non-precipitating) valid at the indicated hour. The weather element includes type, probability, and intensity information.
Q: What images are available?
A: Current images and example images are both available.
Q: What GMOS elements are used to make weather?
For more information on GMOS, visit the Statistical Modeling Branch webpage. To view selected 2.5 km GMOS elements, click on the links in the table above or visit the GMOS Experimental 2.5km Grids webpage. To view Alaska GMOS elements, click on the links in the table above or visit the GMOS Experimental Alaska Grids webpage.
Q: What are Precipitation Potential Index and the other potential indices?
A: Precipitation Potential Index (PPI) is a means to show confidence as to the location of precipitation at each forecast time across the forecast area. It is defined as "Floating PoP12" in NWS Instruction 10-201 [PDF] as an internal index from which a PoP12 for any 12-hour period can be derived by taking the maximum PPI within the desired period. PPI supports the generation of Predominant Weather. This concept is additionally applied to freezing precipitation, frozen precipitation, liquid precipitation, thunderstorms, and severe thunderstorms. The following thresholds are used to translate potential index into probability categories:
Q: Why aren't fog, haze, smoke, etc. present in the MOS weather grid?
A: GMOS weather does not yet include obstruction to vision or visibility information. These may be added in the future. Drizzle and freezing drizzle are also not available in the current version.
Q: How often does this page update?
A: Each page updates twice a day. The updates occur after the valid time for the final projection (192 hours from original start time) has been reached for the corresponding Gridded MOS run. Images for 00Z will update around 2:15 AM EDT and 2:15 PM EDT for 12Z cycle. For the GMOS Weather pages, images are produced for every 3 hours from 6 to 192 hours out from the original GMOS run. For the GMOS/NDFD Comparison pages, images are produced for every 3 hours from 6 to 72 hours and every 6 hours from 72 to 168 hours out from the 00Z cycle.
Q: Why aren't the products on your website always the most up-to-date?