So, to roll up all the findings so far...
The Sensor Data Packet (SDP) is not
encrypted, and contains "display values" in most of the fields. This means they are not the usual integers, long words, double precision numbers one usually finds in telemetry packets. The values are (usually) the actual digits in hexadecimal format that appear on your LCD screen. So if you screen says "98" then the corresponding value in the SDP data will be 0x98. Decimal points are not found in the SDP, since all screen values use a fixed DP. Dates and times are stored as "display values" too: 13 12 29 02 06 (in hex) is 2013 December 29th at 02:06 in the morning. Note the Y3K problem with this format
The SDP contains a lot of historical min/max values, paired with the date/time of the event. That is the major reason the packet is so large (192 bytes).
What do you need to do to read/store your own weather data? Here are two different methodologies:For legal reasons, I strongly advocate the second approach. Simulate the Lacrosse server
Create a DNS server to fake out the GW into using your own local server instead of theirs. The GW can be reprogrammed to use a static IP address on your LAN, and look for the DNS server at an address of your choice (your own PC). Redirect the GW to use your own HTML server instead of theirs.
Create an HTML server to handshake with the GW, so that it thinks it is talking to the real one. You may need to capture the magic numbers that are exchanged during the registration process or simply mimic the normal chit-chat the GW does with the real server. This new server should parse the SDP packets and store the data to a database.
Next, you need some sort of viewer program to watch the DB in real-time. This is optional and probably only useful if you only want to watch your historical data at your house. I suppose you could expose your DB server on a public IP and watch your data with a client/server app remotely. A web server/browser would be simpler and platform agnostic...
A second way to read/manage your own data, but only if you pay Lacrosse to show it on their server would be to snoop the SDP packets going to their server, parse them and store them locally in a database. If you are a good programmer, there are libraries available to create your own WinPCap-compatible app to snoop the SDP packets I mentioned. Parsing the SDP contents is relatively simple. Next you would have to write some sort of viewer program to watch your historical data (see above). Using Wireshark works for snooping, but it is a royal PITA to get usable data out of it. I strongly recommend using an integrated snooper/parser/database updater solution. Oh yeah - you need to acquire an old-school "hub", not to be confused with a "switch" or "router". You need one of the now-obsolete CAT-5 hubs to snoop on the GW traffic. There are lots of them on eBay (where I just bought mine). They run $20-$30 USD. Warning: many do not come with a power supply. Make sure the hub ships with one if you are not technically savvy enough to cobble one together. Mine arrived sans power cube. Luckily, I had one in my junk box that worked.