AN IMPORTANT NOTE TO CIP AND FIP USERS ---------------------------------------- CIP and FIP users should be aware that icing conditions sometimes change rapidly in time and space. CIP and FIP flight level and cross-section plots may not be able to capture rapid changes and/or small-scale differences in icing. They also will not capture all occurrences of icing. Users are advised to look at several of the icing plots to assess the icing situation along their route. Flight route cross-sections show icing within ~60km of a straight line route, and icing conditions may be significantly different just beyond this +/-60km window. Flight level plots show the icing that is expected at that altitude, and icing conditions may be significantly different at altitudes just above and below these heights. Horizontal and vertical cross-sections of CIP output ----------------------------------------------------- Since CIP is a 3-D depiction of the icing, SLD, and icing type that exists in the atmosphere, one can slice and dice it in many ways to get a feel for what the icing really looks like at a given altitude or along a given flight path. Horizontal cross-sections of CIP output are made at 3000 foot intervals. The icing value for each altitude (e.g. 9000 feet) is found by examining the column of CIP output at each horizonatal grid point (e.g. a column of data over Cleveland, Ohio), looking for the two grid points which surround that altitude (e.g. 8871 and 9215 feet) and calculating a weighted average icing, SLD, and icing type value for the altitude of interest (9000 feet). Pilot reports shown on these cross sections are for 1000 feet either side of the level in question (e.g. icing PIREPs for 8000 to 10000 foot range will be shown on the 9000 foot MSL horizontal cross-section). Vertical cross-sections of CIP output are made in straight lines from one airport to another (e.g. Chicago to Denver). The flight route is broken into approximately 20km "chunks." At the location of each chunk, a column of CIP values will be calculated. The algorithm will look in an approximately 80km radius around the location of interest, looking for data from nearby gridpoints. In 1000 foot altitude blocks (e.g. 1000 to 2000 feet MSL), the algorithm will look at all datapoints within the 80km radius that are in the altitude range, and calculate the maximum icing and SLD value. This maximum value from the nearby gridpoints will be assigned as the value for the 1000 foot altitude block in question. After all 1000 foot blocks have been calculated at a given location (chunk), the algrithm moves on to the next "chunk", approximately 20km away, and goes through the same process. Eventually, icing and SLD values are calculated at all altitudes and locations between the two airports, and a vertical cross-section can be drawn. Pilot reports of icing shown on these cross-sections are those which were found within 80km either side of the cross section. Pilot reports are plotted in the following manner: -------------------------------------------------- Icing types: R=rime X=mixed C=clear/glaze U=unknown type Icing severities: small font = trace, trace-to-light, and light icing medium font = light-to-moderate and moderate icing large font = moderate-to-severe, heavy, and severe icing The PIREP is plotted at the altitude for which icing was reported. If multiple icing altitudes were reported (e.g. 5000 to 9000 feet), then the symbol is plotted every 2000 feet, beginning at the lowest altitude (e.g. at 5000, 7000, and 9000 feet). The 2000 foot interval is chosen to provide a maximum amount of information, while attempting to minimize clutter. On national and regional PIREP plots, both color and font size are used to indicate icing severity. A color scale is given at the bottom of each plot. For PIREPs with at least light-to-moderate severity icing, the aircraft type is given above and to the right of the type symbol, while the icing altitudes (in 100s of feet) are given to the right (top altitude) and below and to the right (base altitude).