Download Crash Reporter from Cydia. Scroll down to the Springboard log and open it. Crash Reporter will give a likely cause. In most cases it will be correct.
Thanks. I downloaded the app and it does capture a springboard crash log. However, it doesn't list anything under the "suspects" headings.
Here's the log of the thread that crashed. It looks like it's erroring on an http request, not that it means much to me. Perhaps my lockscreen is requesting weather updates while the phone is in sleep mode and not connected to the internet?
Thread 4 Crashed:
0 WebCore 0x33eb4ec2 0x33cbc000 + 2068162 // WebCore:

ocumentThreadableLoader::cancel() + 0x1a
1 WebCore 0x33e03a9e 0x33cbc000 + 1342110 // WebCore::XMLHttpRequest::internalAbort() + 0x1e
2 WebCore 0x341b21fc 0x33cbc000 + 5202428 // WebCore::XMLHttpRequest::networkError() + 0x130
3 WebCore 0x341b2276 0x33cbc000 + 5202550 // non-virtual thunk to WebCore::XMLHttpRequest::didFail(WebCore::ResourceError const&) + 0x3a
4 WebCore 0x33eb4d9c 0x33cbc000 + 2067868 // non-virtual thunk to WebCore:

ocumentThreadableLoader::didFail(WebCore::SubresourceLoader*, WebCore::ResourceError const&) + 0x8
5 WebCore 0x341443e2 0x33cbc000 + 4752354 // WebCore::SubresourceLoader::didFail(WebCore::ResourceError const&) + 0x22
6 WebCore 0x34121716 0x33cbc000 + 4609814 // WebCore::ResourceLoader::didFail(WebCore::ResourceHandle*, WebCore::ResourceError const&) + 0x1e
7 WebCore 0x3411dd58 0x33cbc000 + 4595032 // -[WebCoreResourceHandleAsDelegate connection:didFailWithError:] + 0x1dc
8 Foundation 0x3148ff12 0x31450000 + 261906 // -[NSURLConnectionDelegateProxy connection:didFailWithError:] + 0x22
9 Foundation 0x3148fbb2 0x31450000 + 261042 // -[NSURLConnection(NSURLConnectionReallyInternal) sendDidFail:] + 0x82
10 Foundation 0x3148faec 0x31450000 + 260844 // _NSURLConnectionDidFail + 0x50
11 CFNetwork 0x35274a54 0x351db000 + 629332 // URLConnectionClient::_clientDidFailWithError(__CFError*, URLConnectionClient::ClientConnectionEventQueue*) + 0x1a0
12 CFNetwork 0x351dfbe0 0x351db000 + 19424 // URLConnectionClient::ClientConnectionEventQueue:

rocessAllEventsAndConsumePayload(XConnectionEventInfo<XClientEvent, XClientEventParams>*, long) + 0xd0
13 CFNetwork 0x351dfa60 0x351db000 + 19040 // URLConnectionClient:

rocessEvents() + 0x40
14 CFNetwork 0x351dfa12 0x351db000 + 18962 // URLConnection::multiplexerClientPerform(RunLoopMultiplexer*) + 0x1e
15 CFNetwork 0x351df990 0x351db000 + 18832 // MultiplexerSource:

erform() + 0x78
16 CFNetwork 0x351df90e 0x351db000 + 18702 // MultiplexerSource::_perform(void*) + 0x2
17 CoreFoundation 0x3097ba86 0x3090a000 + 465542 // __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 0x6
18 CoreFoundation 0x3097d768 0x3090a000 + 472936 // __CFRunLoopDoSources0 + 0x178
19 CoreFoundation 0x3097e504 0x3090a000 + 476420 // __CFRunLoopRun + 0xe0
20 CoreFoundation 0x309278e4 0x3090a000 + 121060 // CFRunLoopRunSpecific + 0xe0
21 CoreFoundation 0x309277ec 0x3090a000 + 120812 // CFRunLoopRunInMode + 0x34
22 WebCore 0x33cbf056 0x33cbc000 + 12374 // __ZL12RunWebThreadPv + 0x16a
23 libSystem.B.dylib 0x31292986 0x31218000 + 502150 // _pthread_start + 0xf2
24 libSystem.B.dylib 0x312880e4 0x31218000 + 458980 // thread_start + 0x0