Page 35 - Volume 15 Number 2

ND
W HLF...OVC030 LYRD 140. TIL 00Z ISOL -SHSN. OTLK...MVFR CIG.
NERN...OVC020 TOP 120. OTLK... IFR CIG. SE...OVC030 TOP 100. OTLK... MVFR CIG.
However, given the actual variability of tops in North Dakota on this day, you wouldn’t be very happy with this forecast. In fact, actual tops near Bismarck in south- central North Dakota were layered to nearly 20,000 feet during this forecast period and tops near Fargo in eastern North Dakota were about 4,000 feet.
Forget Echo Tops (ET)
I know some pilots are often tempted to use echo top heights as a way to determine the height of the cloud tops. In addition to composite reflectivity, echo top height is also a volume product generated by the same NWS WSR-88D NEXRAD Doppler radars throughout the United States and is made available using the new RIDGE2 radar display (radar.srh.noaa.gov/).
Regardless if this product is displayed on your laptop computer at home or on your cockpit display courtesy of a datalink satellite weather broadcast, echo tops heights are not cloud tops and should never be used as such. They are strictly used by forecasters to identify the most significant storms by locating the highest echo regions. Stronger updrafts are seen in regions where the highest echo tops are located.
So if you are interested in knowing the top of the precipitation core in a thunderstorm then echo tops are useful. Otherwise, forget about using it to determine the tops of a stratus deck that formed downwind of the Great Lakes; you’ll be sorely disappointed 99 percent of the time.
Air Traffic Control
Probably the most underutilized resource is air traffic controllers. If you are looking for an up-to-the- minute report of the tops before you depart, why not ask ATC? They may not have an immediate answer, but
FEBRUARY 2011
depending on their workload and if there’s traffic in the area of concern, they can often query a pilot or two that’s flying above the soup to get a tops report for you.
Miscellaneous Products
AIRMET Zulu and guidance such as the Current Icing Product (CIP) or Forecast Icing Product (FIP) available on ADDS (aviationweather.gov/ adds/icing/icing_nav.php) can also help identify the tops during the cold season. In many situations the icing tops can often equate to the cloud tops when the cloud top temperature is below 0 degrees Celsius.
FIP strictly uses the temperature- dewpoint profile from the RUC model, so its solution will be similar to using forecast soundings. CIP, on the other hand, uses several of the same weather products to include a two-hour RUC model forecast, the same infrared and visible satellite images as mentioned earlier and our much needed PIREPs to determine the icing threat. Even so, CIP also suffers from uncertainty and the top of the icing layer is not necessarily presented as a crisp and clean break.
I’m sure you remember a discussion with your instructor about over-relying on one single instrument while in IMC. When that instrument fails, you may get burned. Similarly, when determining cloud tops you should always arrive at an answer from using multiple sources as discussed here. Don’t put your faith in one single weather product. Every single-source weather product has its limitations, including pilot reports. You’ll get your highest quality answers when all o•f the weather guidance is conflated into one clear estimate of the tops. T&T
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Scott Dennstaedt is a CFI and former NWS meteorologist based in Fort Mill, S.C. To learn more about aviation weather, visit his Web site at http://avwx- workshops.com.
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