[wxqc] Vantage-Pro Dew Point Calibration Question

[Dave Helms]

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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