AOPA Pilot Magazine - January 2024 - 91

Level
Approximate height
(in millibars)
1000 mb
925 mb
850 mb
700 mb
500 mb
300 mb
we can work to navigate around thunderstorms,
but icing layers are much more
of a challenge. Frankly, I'm scared of
ice in a small aircraft. I never execute a
cross-country trip in my Mooney M20J
during the cooler months without looking
at icing potential along my route
above sea-level
(in feet)
300 ft
2,500 ft
5,000 ft
10,000 ft
18,000 ft
30,000 ft
several times the day before and right up
to the time of my trip. The good news is
we have very good resources to help us
with our flight planning during the cool
season. The more conventional data
source is the Aviation Weather Center
(aviationweather.gov) and our FAA
weather briefings. The Aviation Weather
Center provides a new interactive tool
that allows pilots to visualize forecast
icing levels and pilot reports. Imagery
from aviationweather.gov is also available
within many electronic flight bags
including ForeFlight and Garmin Pilot.
The icing analysis and probability chart
helps determine the chance for icing
with user-selectable altitudes. These are
great tools for the near term, but what
about a trip several days from now?
Let's now venture beyond the briefing
and look at some nonconventional
sources for weather data. One of my
favorite sites is pivotalweather.com. The
free weather data site has a variety of
forecast models to peak into the future
weather. One of my favorites for shortterm
forecasting is the High Resolution
Rapid Refresh Model (HRRR). The
model goes out 48 hours. You simply
click on the pivotalweather.com map how
many hours out from model initialization
you want to examine.
Once selected, one of the handy features
on pivotalweather.com is the ability
to click inside the map and pull up a
Skew-T chart for the location you wish to
query. With this rather complex-looking
chart, you might think this is something
reserved for weather geeks. It is not, and
is probably easier to understand than you
think. I will keep it to the point and specific
about icing in this article, but you
can also forecast cloud layers and severe
weather using these tools.
On the Skew-T, the left scale is the
altitude in millibars and the scale at
the bottom is temperature in Celsius.
Look for the zero degree line or freezing
line. That's important. You will also
notice a green and red line. The red line
is the temperature at each layer of the
atmosphere while the green line is the
dewpoint temperature. It is where these
two lines come together that clouds form.
If you see the two lines converge to the
left of the zero degree line, this is where
you likely have clouds with the temperatures
below freezing. Guess what? This is
where icing could be troublesome.
In the included example, you can see
The HRRR derived Skew-T from pivitolweather.com (top) and icing forecast from
aviationweather.gov (above).
the circled area where icing would be
most likely.
AOPA PILOT / January 2024
91

http://www.aviationweather.gov http://www.pivotalweather.com http://www.pivotalweather.com http://www.pivotalweather.com http://www.aviationweather.gov http://www.pivitolweather.com http://www.aviationweather.gov

AOPA Pilot Magazine - January 2024

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