X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 03 Aug 2008 14:48:03 -0400 Message-ID: X-Original-Return-Path: Received: from web82707.mail.mud.yahoo.com ([68.142.201.88] verified) by logan.com (CommuniGate Pro SMTP 5.2.5) with SMTP id 3053977 for lml@lancaironline.net; Sun, 03 Aug 2008 10:53:45 -0400 Received: (qmail 60463 invoked by uid 60001); 3 Aug 2008 14:53:44 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Received:X-Mailer:Date:From:Subject:To:MIME-Version:Content-Type:Message-ID; b=mllTGWP64f3BE28PB5n42pmFrqYOonN5b9Shc2iirtt1Qo586HkZ6V5qEYb5T4OM9+EarA9qiZqGQgfGj8cMN+eVkULOB3iong+ILGAOkcpaHy4+P0fLhZLYhkjtDeMyjeeBMsuZWmWA1lxiNVpScr7CHKlyv+yqG4yV1jeQHBs=; Received: from [75.16.254.57] by web82707.mail.mud.yahoo.com via HTTP; Sun, 03 Aug 2008 07:53:44 PDT X-Mailer: YahooMailRC/1042.40 YahooMailWebService/0.7.218 X-Original-Date: Sun, 3 Aug 2008 07:53:44 -0700 (PDT) From: Earl Schroeder Subject: Re: [LML] Re: Garmin 496 NEXRAD False Echoes X-Original-To: Lancair Mailing List MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-676140876-1217775224=:60372" X-Original-Message-ID: <271822.60372.qm@web82707.mail.mud.yahoo.com> --0-676140876-1217775224=:60372 Content-Type: text/plain; charset=us-ascii I can verify Luke's comments. My return trip from Oshkosh yesterday showed 'heavy' precip just West of my path near the Indiana Illinois border. My route was just East of that area and I had my hand up to block the sun shining in my face to get a clearer look to the West to see that there was in fact NO rain and very few low clouds [sort of fog stuff]. As each update painted, the red, yellow, green nexrad display went away. This was at 0800 CDT. On similar note, I've seen XM depict NO clouds in the morning hours while flying over a solid overcast for hours. The IR representation can be misleading. As noted always check the ground stations for confirmation. Earl ----- Original Message ---- From: "lalcorn@natca.net" To: lml@lancaironline.net Sent: Saturday, August 2, 2008 5:50:25 PM Subject: [LML] Re: Garmin 496 NEXRAD False Echoes If it was in the morning, what you are seeing is a temperature inversion. The XM is still only as good as the NEXRAD sites it is coming from and NEXRAD is 30 year old technology. In the morning a temperature inversion will show as anything from small dots, to large areas of heavy precip, just depending on where the inversion is in respect to the antenna. If you know where the nexrad sites are, that will help you determine if it is and TI. Always cross check nexrad data with metars, and satellite data. Luke Alcorn -- For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html --0-676140876-1217775224=:60372 Content-Type: text/html; charset=us-ascii

I can verify Luke's comments. My return trip from Oshkosh yesterday showed 'heavy' precip just West of my path near the Indiana Illinois border. My route was just East of that area and I had my hand up to block the sun shining in my face to get a clearer look to the West to see that there was in fact NO rain and very few low clouds [sort of fog stuff]. As each update painted, the red, yellow, green nexrad display went away.

This was at 0800 CDT. On similar note, I've seen XM depict NO clouds in the morning hours while flying over a solid overcast for hours. The IR representation can be misleading. As noted always check the ground stations for confirmation. Earl

----- Original Message ----
From: "lalcorn@natca.net" <lalcorn@natca.net>
To: lml@lancaironline.net
Sent: Saturday, August 2, 2008 5:50:25 PM
Subject: [LML] Re: Garmin 496 NEXRAD False Echoes

If it was in the morning, what you are seeing is a temperature inversion. The XM is still only as good as the NEXRAD sites it is coming from and NEXRAD is 30 year old technology. In the morning a temperature inversion will show as anything from small dots, to large areas of heavy precip, just depending on where the inversion is in respect to the antenna. If you know where the nexrad sites are, that will help you determine if it is and TI. Always cross check nexrad data with metars, and satellite data.
Luke Alcorn

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