Temperature Dew point spread?

Vance

Gyroplane CFI
Staff member
Joined
Oct 30, 2003
Messages
18,357
Location
Santa Maria, California
Aircraft
Givens Predator
Total Flight Time
2600+ in rotorcraft
It is 8:10 Sunday and we are about to go flying.

I checked ATIS and the temperature was 11 and the dew point was 11.

What does this mean to our flying?

It was my understanding that if the spread is less than 3 degrees that fog was likely.

It is clear and beautiful after the storm.

Thank you, Vance
 
Vance: When the temperature and dewpoint meet , its at 100% humidity.


Heres an interesting calculator for punching in temp, humidity...altitude, etc to calculate density altitude and real performance.


http://wahiduddin.net/calc/calc_da.htm
Stan
 
If the temperature and dew point are within two degrees celcius, fog has the potential to form.

If the wind is calm or more than five knots the fog will not form.

If the wind is calm, the fog will not be stirred into existence.

If the wind is more than five knots, the wind will blow the fog away before it can form.
 
Thank you Stan,

I have come to believe it is a mistake.

It is 64 degrees F in Nipomo.

Thank you for the chart.

Thank you for the quick response Jeff.

I knew you would have the answer.

I suspect that I will need to be mindful of carburetor ice.

We are off to fly!

Thank you, Vance
 
Vance if the temp/dew point spread is close fog can form if the winds are calm or light. What I look for is what is the time of day I plan to fly. If the spread is close but, it is 10 am , you know it will warm up. The closer you get to evening and a temp drop, fog will be more of a possibility. What you need to watch is where the temps are. If the temp is below the dew point then you might want to wait. As the temp increases and reaches the dew point, the fog may form. Since you are near the ocean, you can probably see the fog coming in. The fog that is usually formed by temp/dew point influence for our area is in the valleys.
 
Vance,

Temperature and dewpoint, like wind, has pockets. The good thing about fog, is that you can see it. The bad thing is that 5 minutes can make all the difference for the formation of fog. I get nervous about finding fog when my destination has a projected temperature/dewpoint within 3 degrees of my arrival if the temperature is dropping. Wind or no wind.

*JC*
 
Thank you Bob,

I used to believe that fog moved in from the Ocean. I can watch a wall of it moving across the valley sometimes.

I am coming to understand that it can form under the proper conditions and this is a very different understanding. It will often be clear here at 4:00 am and foggy by 6:00 am with no apparent movement.

I do not want to get trapped by the fog so I am trying to understand it.

I did not realize that the temperature could be below the dew point.

I will learn more about it.

Thank you, Vance.
 
Thank you Jon,

That was my rule also. 3 degrees spread in the morning was ok, 3 degrees spread in the evening evoked caution.

The conditions were very strange Sunday with pockets of fog in some of the valleys but generally clear.

The pattern I have come to expect is the fog moving across the Valley from the ocean.

I can see that I need to learn more.

Thank you, Vance
 
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