Tutorial on the "Current Icing Potential (CIP)" (formerly known as IIDA)

The Current Icing Potential (CIP) product combines sensor and numerical model data to provide a three-dimensional diagnosis of the icing environment. Currently CIP output consists of a likelihood field ranging from 0 (no icing) to 100 (certain icing). While this is not yet calibrated as a true probability value, CIP has value in pointing out real differences in the likelihood of encountering icing at a given location.

   CIP depicts both "all" icing and "SLD" (supercooled large droplet) icing conditions. SLD icing conditions are characterized by water drops larger than 50 micrometers (diameter) which includes freezing drizzle and freezing rain aloft. These conditions are outside the icing certification envelopes (FAR Part 25 Appendix C) and have been demonstrated to be a particularly hazardous condition to some aircraft. Thus the information can be valuable for flight planning.

   CIP is output on a grid with pixels every 40 km at 1000-foot vertical intervals. ADDS displays every third level except on the Flight Path Tool which provides access to all levels. To retrieve a CIP graphic on ADDS, simply choose either the "All icing" or "SLD" radio button, then click on the desired altitude. Besides the individual levels, you can select a composite (maximum value of all altitudes), the bases (lowest icing altitude), or tops (highest icing altitude). The latter two choices display the altitude of icing in hundreds of feet above mean sea level. For all graphics except "bases" and "tops", the scale is from 0 to 100 using cool to warm colours with warmer colours indicating higher icing likelihood. Pilot reports (PIREPs) of icing are overlaid on the single-level graphics (legend found at the bottom of each graphic) if within 1500 feet vertically and 75 minutes temporally. On the composite graphic, PIREPs are for all altitudes. Regions shown in white indicate zero icing potential according to this product. On the SLD graphics, regions shown in grey indicate an icing threat (note these regions are coloured in the all icing graphic) but the SLD potential is indeterminate.
 
Example event: 21 Feb 2002
 

On 21 Feb 2002, a surface low-pressure system existed in the Great Lakes region. Aircraft icing conditions accompanied the storm in widespread stratus clouds behind a cold front. A series of graphics created from CIP data at 1400 UTC is shown on the right. The thumbnail graphics show the Great Lakes region of the U.S. whereas clicking on the graphic reveals coverage for the entire CIP domain along with PIREPs of icing overlaid from this particular event.

   Note the yellow, orange, and red colours found in northern Ohio and Indiana. These colours denote the highest potential for icing whereas the "cooler" hues of green and blue denote a lower icing potential (see the full graphic for the scale). It is worth repeating here: the icing potential scale conveys the potential or likelihood for icing but is not an absolute probability scale from a statistical standpoint. No information is provided as to the severity of icing and none should be inferred. Future versions of this product will predict severity. On this day, the graphics show the greatest icing potential at flight levels 030, 060, and 090 while the potential rapidly decreases above FL120 because the top of the clouds is found near FL120. (Graphics above FL120 omitted.)

   For a single quick overview of icing threat, you can view the graphic labelled Composite. This composite graphic displays the maximum icing potential at any vertical level (FL001 to FL300) and provides a quick mechanism to see if icing exists in a given location before proceeding to locate the icing potential vertically. Besides clicking on subsequent individual levels, locating the vertical extent of icing threat is aided by the bases and tops graphics. A threshold minimum value of 15 is used to locate the base and top at every grid point displayed. In other words, the lowest flight level with a CIP value greater than or equal to 15 is displayed as the "base" while the highest flight level with CIP value greater than or equal to 15 qualifies as "top." Keep in mind the graphics displayed here are from an event in the past. Utilize the realtime ADDS graphics of CIP from the Icing tab above for current data.

   In order to gain confidence using the product, view the locations of actual pilot reports of icing overlaid on the CIP graphics. For the event shown here, click the thumbnail image for a larger view that also includes the PIREPs. Negative icing PIREPs should appear primarily in regions coloured white while positive reports should appear in coloured regions with a majority of PIREPs appearing in the warmer hues (yellow, orange, red). The PIREPs are plotted within 1500 vertical feet of the advertised level and within the past 75 minutes since issuance of the icing product. So, in the example here at FL090, the PIREPs displayed are between FL075 and FL105 and between 1300 and 1415 UTC.

   In the discussion above, emphasis was placed on one component of CIP, referred to as "all" or "total" icing. Another component of CIP is the "SLD" (Supercooled Large Drop) icing product. The final graphic found to the lower right is a plot of the SLD icing at FL060 for this event. This graphic shows potential for large droplet icing in central Ohio. As stated above, SLD icing may be particularly hazardous to some aircraft. Regions coloured gray have icing potential as found in the "all" component but the SLD potential is indeterminate.

   As part of the development work behind the CIP product, researchers from NCAR and NASA purposefully fly into known icing conditions. This event was chosen because a team of researchers flew into the clouds and icing conditions in the area around Cleveland, OH on this day. Two photos of the ice accretion accumulated on the NASA Glenn Research Centre Twin Otter aircraft are shown below after flying between FL040 and FL070 south of Cleveland. Note the large build-up of ice on the leading edge of the wing. Photo credit: NASA Glenn Research Centre.

 


 

CIP graphic for FL030
CIP graphic for FL060

CIP graphic for FL090

CIP graphic for FL120

CIP composite graphic

CIP bases graphic

CIP tops graphic

CIP SLD graphic for FL060