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<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff
size=2>Yep, the fog you describe should give you 100% RH (temp and dew
point same) nearly every time. But, having fog doesn't mean you
will have 100% RH. Sometimes there is a small layer near the surface that
is not quite saturated yet the horizontal visibility can be very
low. Its an old rule of thumb that you never code fog in an
aviation weather (METAR) observation with dew point depression greater than 7 F
(quiz for tonight, who knows what an AXXX bulletin is?), which is to
say, you can get fog with temp/dew point depressions anywhere from 0 to 7 F
degrees. </FONT></SPAN></DIV>
<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff size=2>On the
Honeywell accuracy of 2%, I'm a bit skeptical. That kind of accuracy is
typically reached by research quality hygrometers. I think most
sensor manufacturers won't claim accuracies better than 5%, and that is a
stretch as most hygrometer's performance will "drift" (degrade) over time.
</FONT></SPAN></DIV>
<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff
size=2>Looking over your station reports, you track very well with KILM with
temp and dew point so you are doing very well.</FONT></SPAN></DIV>
<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff
size=2>DaveH</FONT></SPAN></DIV>
<DIV><SPAN class=845295904-01042005><FONT face=Arial color=#0000ff
size=2>CW0351</FONT></SPAN></DIV>
<DIV><FONT face=Tahoma><FONT size=2><SPAN class=845295904-01042005><FONT
face=Arial color=#0000ff> </FONT></SPAN></FONT></DIV>
<DIV><FONT size=2><SPAN class=845295904-01042005> </SPAN>-----Original
Message-----<BR><B>From:</B> wxqc-bounces@lists.gladstonefamily.net
[mailto:wxqc-bounces@lists.gladstonefamily.net]<B>On Behalf Of
</B>Bob<BR><B>Sent:</B> Thursday, March 31, 2005 10:23 PM<BR><B>To:</B>
wxqc@lists.gladstonefamily.net<BR><B>Subject:</B> [wxqc] Fog, Dew Point, and
RH<BR><BR></DIV></FONT></FONT>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<DIV><SPAN class=164475802-01042005><FONT face=Arial size=2>If we are in a
heavy fog, am I incorrect in believing that the RH is 100%? As I look at my QC
data for Today, I note that I am supposedly in error from 05:00 -
10:00 for reporting a dew point pretty close to ambient temperature - ie;
100% humidity. During that time period, the entire area, including the weather
service was under an extremely dense fog. <A
href="http://weather.gladstonefamily.net/cgi-bin/wxqchart.pl?date=20050401&site=C3321">http://weather.gladstonefamily.net/cgi-bin/wxqchart.pl?date=20050401&site=C3321</A></FONT></SPAN></DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial size=2>And the
surrounding stations are reporting similar data....</FONT></SPAN></DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial size=2><A
href="http://www.srh.noaa.gov/data/obhistory/KILM.html">http://www.srh.noaa.gov/data/obhistory/KILM.html</A></FONT></SPAN></DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial size=2><A
href="http://www.srh.noaa.gov/data/obhistory/KLBT.html">http://www.srh.noaa.gov/data/obhistory/KLBT.html</A></FONT></SPAN></DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial size=2><A
href="http://www.srh.noaa.gov/data/obhistory/KFAY.html">http://www.srh.noaa.gov/data/obhistory/KFAY.html</A></FONT></SPAN></DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial size=2>I have three
temperature sensors, and a Honeywell HIH 3610 humidity sensor in a fan
aspirated tube with an intake 5 feet off the grass. The temperature sensors
all read within .2 degrees F, and previously been verified accurate accurate
within .3 degrees F at 32 F, and 212 F, I'm not likely to be reporting
incorrect temperature. The Honeywell humidity sensor has a claimed
accuracy of 2% Rh. </FONT></SPAN></DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=164475802-01042005><FONT face=Arial size=2>SO..... If we are
experiencing "can't see two feet in front of you" fog, should I not be
reporting ambient temp = RH?</FONT></SPAN></DIV></BLOCKQUOTE></BODY></HTML>