<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Since I've been recommending for years web sources such as the
Weather Underground for those wanting site-specific weather data ,
it behooves me to know how reliable are such data? It's difficult
to answer that question in the absolute sense because there are no
incontrovertible sources against which to compare. However, I did
the next best thing, which is to compare the data against that from
a nearby major weather station and then look to see whether the
differences make sense according to general understanding of terrain
factors and urban microclimate variations.
<div class="moz-forward-container">
<div class="moz-forward-container">
<div class="moz-forward-container">
<div class="moz-forward-container">
<div class="moz-forward-container">
<p>This comparison was not done in a vacuum, but in
response to a client who wanted weather data for a site
in Portland Oregon, with a particular interest on the
amount of rainfall. The map below shows the site of
interest (red teardrop) and the NSW station at the
Portland Airport 4.5 miles away. The Weather
Underground station PORTL437 is located about 0.5 miles
to the east of the site equidistant on the other side of
the MLKing Blvd.</p>
<p>I'll let the plots in my reply to the client speak for
themselves, but my general feeling is that the WU data
looked quite consistent with the airport data, and that
the differences are quite understandable, e.g., the
reduced wind speeds and the lack of correlation in the
wind direction, since the airport station is in a flat
open area next to the Columbia River, while the WU
station is in a urban residential area 4-5 miles away.</p>
<p>I'm still withholding judgement whether the 60%
difference in the recorded rainfall is real, a result of
the placement of the WU station, or a defect in the
measurement protocol. Come to think of it, I don't know
how these automated weather stations record rainfall
(liquid precipitation to be technically correct). I can
only think of a rain gauge that's manually recorded and
maintained.</p>
<p>Joe<br>
</p>
<div class="moz-forward-container"><img
moz-do-not-send="false"
src="cid:part1.98DE1754.CDAEE17A@whiteboxtechnologies.com"
alt="" class="" height="720" width="960"><br>
<br>
-------- Forwarded Message --------
<table class="moz-email-headers-table" cellspacing="0"
cellpadding="0" border="0">
<tbody>
<tr>
<th nowrap="nowrap" valign="BASELINE"
align="RIGHT">Subject: </th>
<td>Re: Weather data for Portland with monthly
updates</td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE"
align="RIGHT">Date: </th>
<td>Fri, 23 Feb 2018 16:27:07 -0800</td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE"
align="RIGHT">From: </th>
<td>Joe Huang <a class="moz-txt-link-rfc2396E"
href="mailto:yjhuang@whiteboxtechnologies.com"
moz-do-not-send="true"><yjhuang@whiteboxtechnologies.com></a></td>
</tr>
<tr>
<th nowrap="nowrap" valign="BASELINE"
align="RIGHT">To: </th>
<td>XXXX</td>
</tr>
</tbody>
</table>
<br>
<br>
<meta http-equiv="Content-Type" content="text/html;
charset=utf-8">
<p>XXXX,</p>
<p>Attached are both weather files for the ISD station
at the Portland Airport (OR_PORTLAND-IAP_726980_18)
and the Weather Underground site KORPORTL437
(OR_WU_PORTL437_18). The data are available through
Feb. 22 for the ISD station and through Feb. 23 for
the WU station.<br>
</p>
<p>Out of curiosity, I compared the data between the two
files (see below). The dry-bulb and dewpoint
temperatures are very well correlated, so that I find
the hourly variations to be credible and reflecting
microclimate differences. The wind speeds are about
three times higher at the airport, which is also
believable, while there is no correlation in the wind
direction. The rainfall amount also differs, with the
airport reporting 60 % more than at the PORTL437
Weather Underground station. <br>
</p>
<img moz-do-not-send="false"
src="cid:part3.2B9471B3.EBCF968E@whiteboxtechnologies.com"
alt="" class="" height="720" width="960"><img
moz-do-not-send="false"
src="cid:part4.D9CCD60C.AD8562A1@whiteboxtechnologies.com"
alt="" class="" height="720" width="960"><br>
<pre class="moz-signature" cols="90">Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
<a class="moz-txt-link-abbreviated" href="mailto:yjhuang@whiteboxtechnologies.com" moz-do-not-send="true">yjhuang@whiteboxtechnologies.com</a>
</pre>
<a class="moz-txt-link-freetext"
href="http://weather.whiteboxtechnologies.com"
moz-do-not-send="true">http://weather.whiteboxtechnologies.com</a>
for simulation-ready weather data (o) (925)388-0265 (c)
(510)928-2683 "building energy simulations at your
fingertips" <br>
<div class="moz-cite-prefix">On 2/19/2018 12:39 PM, XXXX
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CA+bb+RigW+h9WdD2zOSuzrj604o0N_uGF-d2_0oh_vrOzzv0kw@mail.gmail.com">
<div dir="ltr">Joe,
<div><br>
</div>
<div>Yeah, the precipitation data as well as
relative humidity is crucial to my study so that's
why I am a bit concerned. If you are willing to
separate out ISD and WU that would be great
because I could compare the two and see if the
problem is just isolated to precipitation. It did
seem like weather underground's RH and temp. data
were what I expected so I was planning on sticking
with that. I would like to see how weather
underground's wind data compares to ISD because
driving rain has some importance me. Thanks for
the info on the NOAA data. </div>
<div><br>
</div>
<div>XXXX</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Feb 19, 2018 at
12:41 PM, Joe Huang <span dir="ltr"><<a
href="mailto:yjhuang@whiteboxtechnologies.com"
target="_blank" moz-do-not-send="true">yjhuang@whiteboxtechnologies.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0
0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>XXXX,</p>
<p>OK. Will do. However, I wouldn't go as far
as you in dismissing the WU data simply
because the rain measurements differ from
other sources. For one, I'm not sure what
mechanisms are used in the automatic weather
stations such as the WU stations to measure
rainfall. It could be that the measurement
method is unreliable, or it could mean that
there is that amount of difference due to
other factors - shielding, microclimate
variations, what not. Are the rainfall
measurements of primary importance to you? I
could give you both ( ISD and WU) if you're
interested, no difference in price. Also, I
don't think of the ISD data as NOAA data,
since the weather station is a NWS station
and the only way NOAA is involved is that
the NCDC/NCEI that maintains the ISD has now
moved from the Dept. of Commerce to NOAA.</p>
<p>Joe<br>
</p>
<pre class="m_-8268520906411674597moz-signature" cols="90">Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
<a class="m_-8268520906411674597moz-txt-link-abbreviated" href="mailto:yjhuang@whiteboxtechnologies.com" target="_blank" moz-do-not-send="true">yjhuang@whiteboxtechnologies.<wbr>com</a>
<a class="m_-8268520906411674597moz-txt-link-freetext" href="http://weather.whiteboxtechnologies.com" target="_blank" moz-do-not-send="true">http://weather.<wbr>whiteboxtechnologies.com</a> for simulation-ready weather data
(o) <a href="tel:%28925%29%20388-0265" value="+19253880265" target="_blank" moz-do-not-send="true">(925)388-0265</a>
(c) <a href="tel:%28510%29%20928-2683" value="+15109282683" target="_blank" moz-do-not-send="true">(510)928-2683</a>
"building energy simulations at your fingertips"
</pre>
<div
class="m_-8268520906411674597moz-cite-prefix">On
2/19/2018 8:23 AM, XXXX wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi Joe,
<div><br>
</div>
<div>Can you send me another monthly
weather update for OR_WU_PORTL437_17
(All of 2017 + January 2018)? I would
actually like to switch to NOAA data for
this weather file because of the
precipitation discrepancy we had
discussed earlier. I had originally
chosen weather underground because I
thought it would give a bit better
resolution for the Portland area but it
seems maybe there is some error at this
location. </div>
<div><br>
</div>
<div>Thanks, </div>
<div><br>
</div>
XXXX</div>
</blockquote>
</div>
</blockquote>
</div>
</div>
</blockquote>
<br>
</div>
</div>
</div>
</div>
</div>
</div>
</body>
</html>