Summer Weather Information For Pilots

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When the blustery winds of winter finally die down and the warm sunshine starts breaking through, flying a general aviation aircraft is an enjoyable way to travel. Even as nice as summertime travel is, it is not without its unique concerns. The pilot should be aware of special summer weather conditions.
Thunderstorms
Information applies to the northern hemisphere
1. Avoid cells by 20 miles--this means having 40 miles between two cells.
2. Provide extra distance from cells moving at 20 knots or greater and the cell at the south end of a line of storms. This cell does not have to compete for moisture with other cells so it has an abundant "fuel" supply to generate turbulence.
3. Surface dew point and temperature are a good indicator of storm severity. Thunderstorms forming over an area where the dew point is 50 F or higher with more than a 30 degree spread

between temperature and dew point indicate a potential for extremely strong storms.
4. If flying a radar-equipped aircraft, learn to use the antenna tilt feature effectively to identify tops of the moisture and to determine if rain is so heavy that it is attenuating the radar beam. Cells shapes and rain gradients provide key information on the hazards of storms. Many commercial training courses are available for instruction in use of weather radars. Remember, radar is for avoiding, not penetrating, storms.
5. Storm hazards are linked to the overall instability of the atmosphere. Check the convective outlook, or "AC Note" as it's referred to, which categorizes the thunderstorm risk in a warning area as "slight," "moderate," or "high." Use extreme caution when flying in the warning area, especially where the risk is moderate or high. The "AC Note" is accessed by FSS briefers with the command: RQ MKC AC on request. DUATS provides this in the "Severe Weather Warning" section.
6. Check the winds at 18,000 feet (500 milibar level). If they are southwesterly, you can expect storms to form.
7. Consider flying in the morning before the afternoon heat can trigger storms.
8. Consider delaying takeoff when a cell is closer than 20 miles to the departure airport.
DENSITY ALTITUDE
1. Always check density altitude against aircraft performance figures. Density altitude is pressure altitude (the altitude read from the altimeter when 29.92 inches set) corrected for nonstandard temperature.
2. When departing a high density altitude airport in a non-turbocharged aircraft, be sure to LEAN THE MIXTURE, according to the pilot's operating handbook. A temperature of 105 F at sea level means a density altitude of 3,000 feet, and proper leaning is important.
3. If you're flying with a full load from a short field with high density altitude, it may be safer to take passengers and payload in two trips to a nearby airport with longer runways. Then fully load the aircraft and depart on course. Be sure to stay within the aircraft's performance capabilities and your personal minimums for an extra margin of safety.
4. Multi-engine pilots should consider the obstacles in the departure path against aircraft climb gradient on one engine. Climb gradient is the altitude gained per horizontal distance traveled. Should an engine failure occur at rotation, a Beech Baron, for example, requires a ground roll of 3,760 feet but a total distance of 9,400 feet to clear a 50 foot obstacle. This is for a pressure altitude of 5,700 feet with temperature 9 C above standard.
5. Single engine service ceiling should also be considered for en route planning purposes. Can your multi-engine aircraft maintain the minimum en route altitude if IFR, or a safe altitude if VFR, should an engine failure occur? Select a course that allows suitable airports along the route.
GENERAL
1. Summer haze can reduce flight visibilities to almost zero, even when ground visibility is 3 miles. When flying over bodies of water (lakes, bays) haze can obscure the horizon, and pilots should be ready to fly by instruments. This can pose serious problems for students and low-time private pilots. The haze also makes clouds, thunderstorms, and other aircraft difficult to see.
2. Summer flights over the southwestern U.S. desert at low altitudes during the afternoon can encounter severe turbulence from rising thermals. Flights will be smoother in the morning.
3. When crossing a ridge at or near the aircraft's service ceiling, pilots tend to pitch-up to stay above rising terrain. If a turn back is attempted with airspeed near stall, the increased load factor imposed by the turn can cause a stall/spin accident. Approach all ridges at a 45 degree angle with at least 2,000 feet of terrain clearance to facilitate a turn back.
4. When weight is not a factor for the next flight, fill the tanks right after landing. The high humidity of summer can cause moisture to form in fuel tanks as they cool.
5. Don't forget to take care of the most important part of the aircraft--the pilot. Bring some water along on trips to avoid dehydration.
Summer brings great opportunities for a GA aircraft with trips for vacation travel to just plain "fun flying." Keep summer's special risks in mind when flying, stay cool and enjoy the great weather!



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