Retaining value of a Global variable

Hi,

I have a global variable defined at the top of my stylesheet. When I try to use 
it subsequently it gets reinitialized. Here's the code.

 <xsl:variable name="whead" select="'No'" />

<xsl:template match="/newsletter">
.
.
      <xsl:apply-templates select="content/article" mode="proc_webcastheader" 
/>.

</xsl:template>

<xsl:template match="article" mode="proc_webcastheader">
<xsl:variable name="artclass" 
select="normalize-space(metadata/article-classification/.)" />
<xsl:if test="contains($artclass,'Biz-Webcast')">
          <p><xsl:value-of disable-output-escaping="yes" select="$whead"/></p>
          <IMG 
src="http://www.sas.com/subscriptions/images/hdr_webcast.gif";></IMG>
          <xsl:variable name="whead" select="'Yes'" />
          <p><xsl:value-of disable-output-escaping="yes" select="$whead"/></p>
</xsl:if>
</xsl:template>


In the second template when I print whead before the <img> it shows 'No' for 
all articles even if I set it to 'Yes' after the <img>. Any clues on how to 
retain the value of the variable?

Thanks
Vivek