I would think it's usually quite the opposite as well, during summer copper will expand and will usually see your SNR drop a little.
Not to hijack this thread or anything, but I have two DSL lines at home bonded over a small cisco router and one of them syncs at 3008/800 and other 3008/512, go figure, I'm unable to get it to sync at 800 even though the lines are coming in the same loop.
gw#show dsl int atm0/0
ATM0/0
Alcatel 20150 chipset information
ATU-R (DS)ATU-C (US)
Modem Status: Showtime (DMTDSL_SHOWTIME)
DSL Mode: ITU G.992.1 (G.DMT) Annex A
ITU STD NUM: 0x01 0x1
Vendor ID: 'ALCB' 'ALCB'
Vendor Specific: 0x0000 0x0000
Vendor Country: 0x00 0x0F
Capacity Used: 81% 92%
Noise Margin: 6.5 dB 8.0 dB
Output Power: 20.0 dBm 12.0 dBm
Attenuation: 51.5 dB 31.5 dB
Defect Status: None None
Last Fail Code: None
Selftest Result: 0x00
Subfunction: 0x15
Interrupts: 7977 (0 spurious)
PHY Access Err: 0
Activations: 7
LED Status: ON
LED On Time: 100
LED Off Time: 100
Init FW: embedded
Operation FW: embedded
SW Version: 3.8131
FW Version: 0x1A04
InterleaveFastInterleaveFast
Speed (kbps): 0 3008 0 800
gw#show dsl int atm0/1
ATM0/1
Alcatel 20150 chipset information
ATU-R (DS)ATU-C (US)
Modem Status: Showtime (DMTDSL_SHOWTIME)
DSL Mode: ITU G.992.1 (G.DMT) Annex A
ITU STD NUM: 0x01 0x1
Vendor ID: 'ALCB' 'ALCB'
Vendor Specific: 0x0000 0x0000
Vendor Country: 0x00 0x0F
Capacity Used: 92% 67%
Noise Margin: 4.5 dB 15.0 dB
Output Power: 19.5 dBm 12.0 dBm
Attenuation: 50.0 dB 31.5 dB
Defect Status: None None
Last Fail Code: None
Selftest Result: 0x00
Subfunction: 0x15
Interrupts: 4021 (0 spurious)
PHY Access Err: 0
Activations: 8
LED Status: ON
LED On Time: 100
LED Off Time: 100
Init FW: embedded
Operation FW: embedded
SW Version: 3.8131
FW Version: 0x1A04
InterleaveFastInterleaveFast
Speed (kbps): 0 3008 0 512
