DCS99 - Preflight we have links to worldwide weather. Sat, IR Sat, radar(if radar coverage), forecast hazardous wx areas, PIREPS, etc, etc.
Enroute - In ACARS coverage we can get current and forecast weather. Selecting 'area weather' for a specific airport gives us the current weather for several nearby airports.
Enroute - Dispatch has an automated system that sends SIGMETS/AIRMETS to aircraft in the same ATC center's airspace and the adjacent center's airspace. Eg. if you're in NYC Center you'll get warnings for Toronto, BOS, and Washington Center.
We have the capability to send text messages to dispatch while in ACARS coverage.
Dispatch will ususally send us updated information about the location of lines of weather or weather at destinations or alternates. Usually, but not guaranteed. Sometimes it takes a direct request for information to generate a response.
Based on the flight diverting, along with holding with significant weather in the area, our dispatch system would have been in contact with a flight in similar circumstances. Typically prior to the divert decision.
It's been my experience, and practice, to have early engagement with dispatch - "in the event we go around our plan is ABC. Do you agree?"(or similar type communication). Once the decision to divert is made the only contact dispatch would need to make is if the preplanned divert is no longer appropriate.
The workload is very high during a divert, especially in congested airspace. Having an agreed upon plan prior to the divert is important. However, sometimes circumstances require last minute, unplanned, diverts - "that's what you get the big bucks for" (US pilot phrase)
