[wxqc] Vantage-Pro Dew Point Calibration Question

[Lance]

Hi Evan

Interesting idea about the fan aspiration. I too have a 24hr fan 
aspirated unit. If the air weren't fully saturated across a large area, 
the movement of air across the sensor in pockets of varying levels, 
might not ever allow the sensor to achieve 100%. As Steve mentioned, he 
had extreme fog for an extended period before reporting 100%.
It sure would be nice to have a remote on/off switch for that fan, it 
would be interesting to see if there is really any difference.

Lance
CW1020
www.mountainbase.com

Evan Bookbinder wrote:
> In the ASOS realm, if the visibility is 6 miles or less, HZ or BR will 
> be appended to the observation. ASOS cannot determine smoke and does not 
> discriminate visibility reduction purely based on precipitation 
> intensity (heavy rain or snow).
>
> BR (mist -- visibility reduced by water vapor/droplets) will be used 
> when the dewpoint depression is 5F or less and HZ (Haze -- visibility 
> reduced by particulates) will be used for dewpoint depressions of 6F or 
> above. FG (dense fog) will be used when visibilities of 1/2SM or less 
> are observed.
>
> Personally, I have never seen my RH sensor go above 95%, even in 0SM 
> visibility in fog last Tuesday (our first fog event in over a year). I 
> think part of the problem may be the fan aspirator which is inducing a 
> circulation although the air in a radiation fog event is typically dead 
> calm -- but since my dwpt/RH are almost always within 1F/1% of the 
> nearby ASOS, I haven't considered it a problem. Some other 
> manufacturers' humidity sensors are FAR less stringent and won't even 
> report values below 20% or above 90%.
>
> Evan
>
>
>
> Dave Helms wrote:
>   
>> In METAR reporting procedures, the general rule is you can report fog as 
>> "present weather" (e.g. restricting horizontal visibility to less than 7 
>> miles) with dew point depressions as great as 7 F degrees. As you found, 
>> it is not uncommon to observe fog where complete saturation is not 
>> reached.   I poked around hoping to find some statistics from an ASOS 
>> station on the frequency fog (types BR, MI, and FG) is reported as a 
>> function dew point depression and/or RH, but didn't find a source.  Any, 
>> no big deal to have fog and not fully saturate.  Then again, you should 
>> watch to see if your humidity sensor can saturate at all or too much as 
>> a potential problems.
>>
>> Dave
>> CW0351
>>
>> Steve Hatchett wrote:
>>
>>   
>>     
>>> We had a fog event that lasted quite a few days. It was extremely foggy, and
>>> everything was dripping wet. I was convinced it could get no foggier or more
>>> saturated than it was. But my VP2 refused to go above 99%. I was somewhat
>>> disappointed, and literally on the verge of bumping the calibration up by a
>>> percent when it proceeded to get even foggier and more saturated than I
>>> thought possible and the station began reporting 100% humidity. It stayed
>>> that way for several hours until a system moved through and ended the
>>> inversion. Now I'm glad I didn't do the calibration adjustment.
>>>
>>> Steve
>>>
>>>  
>>>
>>>     
>>>       
>>>> -----Original Message-----
>>>> From: Keith Miller [mailto:kdmiller at oldsgmail.com]
>>>> Sent: Tuesday, November 14, 2006 11:49 PM
>>>> To: lwood at mountainbase.com; 'Discussion of weather data quality issues'
>>>> Subject: Re: [wxqc] Vantage-Pro Dew Point Calibration Question
>>>>
>>>>    
>>>>
>>>>       
>>>>         
>>>>> -----Original Message-----
>>>>> From: wxqc-bounces at lists.gladstonefamily.net
>>>>> [mailto:wxqc-bounces at lists.gladstonefamily.net]On Behalf Of Lance
>>>>> Sent: Wednesday, November 15, 2006 1:34 AM
>>>>> To: wxqc at lists.gladstonefamily.net
>>>>> Subject: Re: [wxqc] Vantage-Pro Dew Point Calibration Question
>>>>>
>>>>>
>>>>>      
>>>>>
>>>>> I have a question for the group.  Can you be socked in with
>>>>> fog and not have 100% humidity? I have never seen it on my station,
>>>>> maybe 98%. I am already getting hit for being too high and don't
>>>>> want to adjust it up.
>>>>>      
>>>>>
>>>>>         
>>>>>           
>>>> I've seen 100% http://weather.stadhaugh.com/record.php Although,
>>>> typically, I see 98% or 99% during a rainfall event...
>>>>
>>>>
>>>> Keith
>>>> --
>>>> CW5250 => http://weather.stadhaugh.com
>>>>
>>>>
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