Re: [weewx-user] Fog detection?

[storm...@gmail.com]

In general, the possibility of fog developing is when the dewpoint spread 
is less then  5 degrees F.

On Tuesday, August 31, 2021 at 6:02:58 PM UTC-4 n0...@n0nb.us wrote:

> * On 2021 31 Aug 14:35 -0500, František Slimařík wrote:
> > 
> > Hi all,
> > 
> > I got question for hardcore meteorologists here. Is it possible to 
> detect 
> > fog based on classic meassured values like temperature, humidity, 
> preasure, 
> > etc?
> > Logically I would say fog appears when dew point equals current 
> > temeperature but I guess it will not be so easy. Fogs didn't appear here 
> > this year in my locality so I am waiting for autumn to start with 
> > observations.
>
> I'm certainly no meteorologist!
>
> It seems we've had more foggy mornings this summer than in years past.
> Humidity has certainly been high with only a handful of stretches with
> more than a day below 50% relative humidity.
>
> Many times it seems as though warm air over cooler moist ground is
> necessary for its formation. I don't think this is a temperature
> inversion, as such, but they also seem to sometimes be quite localized
> and are related to some interesting effects.
>
> I along with other radio amateurs and possibly Greg find the effects of
> these weather phenomena on VHF and UHF radio propagation interesting.
>
> - Nate
>
> -- 
> "The optimist proclaims that we live in the best of all
> possible worlds. The pessimist fears this is true."
> Web: https://www.n0nb.us
> Projects: https://github.com/N0NB
> GPG fingerprint: 82D6 4F6B 0E67 CD41 F689 BBA6 FB2C 5130 D55A 8819
>
>

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Re: [weewx-user] Fog detection?

[Nate Bargmann]

* On 2021 31 Aug 14:35 -0500, František Slimařík wrote:
> 
> Hi all,
> 
> I got question for hardcore meteorologists here. Is it possible to detect 
> fog based on classic meassured values like temperature, humidity, preasure, 
> etc?
> Logically I would say fog appears when dew point equals current 
> temeperature but I guess it will not be so easy. Fogs didn't appear here 
> this year in my locality so I am waiting for autumn to start with 
> observations.

I'm certainly no meteorologist!

It seems we've had more foggy mornings this summer than in years past.
Humidity has certainly been high with only a handful of stretches with
more than a day below 50% relative humidity.

Many times it seems as though warm air over cooler moist ground is
necessary for its formation.  I don't think this is a temperature
inversion, as such, but they also seem to sometimes be quite localized
and are related to some interesting effects.

I along with other radio amateurs and possibly Greg find the effects of
these weather phenomena on VHF and UHF radio propagation interesting.

- Nate

-- 
"The optimist proclaims that we live in the best of all
possible worlds.  The pessimist fears this is true."
Web: https://www.n0nb.us
Projects: https://github.com/N0NB
GPG fingerprint: 82D6 4F6B 0E67 CD41 F689 BBA6 FB2C 5130 D55A 8819

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Re: [weewx-user] Fog detection?

[Doug Jenkins]

I wonder if you take cloud base and the humidity values to determine if you
have fog. If the cloud base is low and you have high humidity, then one
could speculate that fog is imminent.

Any meteorologists can weigh in?



On Tue, Aug 31, 2021, 4:19 PM Greg Troxel  wrote:

>
> František Slimařík  writes:
>
> > I got question for hardcore meteorologists here. Is it possible to
> detect
> > fog based on classic meassured values like temperature, humidity,
> preasure,
> > etc?
> > Logically I would say fog appears when dew point equals current
> > temeperature but I guess it will not be so easy. Fogs didn't appear here
> > this year in my locality so I am waiting for autumn to start with
> > observations.
>
> Good question, but my impression is that it is really difficult to
> measure humidity above 95%.   I more or less have the impression that
> fog happens when temp/dewpoint are about the same and the temperature
> falls.
>
> I think you need a fog sensor that actually measures impaired light
> transmission.  Surely there is a norm for measuring that already.   I
> need one too, right after I build a seismograph.
>
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> .
>

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Fwd: [weewx-user] Fog detection?

[VE4PER / Andy]

per request

 Forwarded Message 
Subject:Re: [weewx-user] Fog detection?
Date:   Tue, 31 Aug 2021 15:26:46 -0500
From:   VE4PER / Andy 
To: Greg Troxel 



I think the sensor is referred to as transmissometer; usually in pro 
unattended observer stations that is used and also a similar ceilometer 
for cloud heights


On 2021-08-31 3:19 p.m., Greg Troxel wrote:

František Slimařík  writes:


I got question for hardcore meteorologists here. Is it possible to detect
fog based on classic meassured values like temperature, humidity, 
preasure,

etc?
Logically I would say fog appears when dew point equals current
temeperature but I guess it will not be so easy. Fogs didn't appear here
this year in my locality so I am waiting for autumn to start with
observations.

Good question, but my impression is that it is really difficult to
measure humidity above 95%. I more or less have the impression that
fog happens when temp/dewpoint are about the same and the temperature
falls.

I think you need a fog sensor that actually measures impaired light
transmission. Surely there is a norm for measuring that already. I
need one too, right after I build a seismograph.



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Re: [weewx-user] Fog detection?

[Greg Troxel]

František Slimařík  writes:

> I got question for hardcore meteorologists here. Is it possible to detect 
> fog based on classic meassured values like temperature, humidity, preasure, 
> etc?
> Logically I would say fog appears when dew point equals current 
> temeperature but I guess it will not be so easy. Fogs didn't appear here 
> this year in my locality so I am waiting for autumn to start with 
> observations.

Good question, but my impression is that it is really difficult to
measure humidity above 95%.   I more or less have the impression that
fog happens when temp/dewpoint are about the same and the temperature
falls.

I think you need a fog sensor that actually measures impaired light
transmission.  Surely there is a norm for measuring that already.   I
need one too, right after I build a seismograph.

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Re: [weewx-user] Fog detection?

[DR]

I wonder what the official textbook answer might be, if there is one.


I for one have seen pockets of fog over roads and in low lying areas 
where micro climate is very close to each other but clearly particulate 
or radiative cooling or something makes fog form and 40 feet away there 
isn't any (yet).


How much particulate matter make fog more likely, like clouds to some 
degree?


I know that some programs (like Weather Display) will indicate FOG in 
the conditions visual, but it isn't there, frequently.  I think it says 
is is possible, but not a sure thing.



Vaisala makes a gizmo that I think for aviation is called RVR (Runway 
Visual Range) that uses a light source and a receiver mounted at an 
angle to each other yet only a few feet at most apart, and it does a 
pretty good job of telling if the conditions are hazy but not sure if 
there is a light or heavy fog output in its data stream.


Great question.  I hope others with experience or training can chime in.


On 8/31/2021 2:35 PM, František Slimařík wrote:


Hi all,

I got question for hardcore meteorologists here. Is it possible to 
detect fog based on classic meassured values like temperature, 
humidity, preasure, etc?
Logically I would say fog appears when dew point equals current 
temeperature but I guess it will not be so easy. Fogs didn't appear 
here this year in my locality so I am waiting for autumn to start with 
observations.


Thanks for hints
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[weewx-user] Fog detection?

[František Slimařík]

Hi all,

I got question for hardcore meteorologists here. Is it possible to detect 
fog based on classic meassured values like temperature, humidity, preasure, 
etc?
Logically I would say fog appears when dew point equals current 
temeperature but I guess it will not be so easy. Fogs didn't appear here 
this year in my locality so I am waiting for autumn to start with 
observations.

Thanks for hints

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