Any weather that interferes with the signal between the dish and the satellite (the satellite is in space) may cause an outage. The weather can be in your area or in the area where your gateway is, and there is not much you can do but be patient. This type of thing happens with satellite internet.
Any moisture has an effect. The radio signal to/from the satellite is approximately 20GHz over a 22k mile path. Any kind of moisture in that path will attenuate the signal through diffraction. Heavy rain or snow will attenuate it the most (I can probably find the formula somewhere if I dig enough), but I'm not sure which is worse, rain or snow. High humidity and fog not as much, but it will attenuate it some.
What it means to us is that any kind of precip that's enough to drop the signal quality below 40 or 30 will essentially render the path useless. High Humidity might drop it only 10-20 points below what you normally see, and a mild rain might drop it between 20-40 quality points (signal quality actually being an inverse measurement of bit error rate).
Not all rainstorms will knock it out completely, but it mostly depends on where all the water is. For example, if the storm is coming up from the South, it might have more of an impact well before it even hits you than when it's coming down buckets over your house. Again, this is mainly because all of the moisture is concentrated between you and the satellite.
Ice on the dish will also affect it, but not mainly due to attenuation. There will be some attentuation at the point where the signal bounces off the dish to/from the feed horn. However, the main issue there is that it makes the surface irregular and diffuses the signal instead of focusing it on/from the transceiver.
Another thing you have to consider is foliage in and around the dish. If the rain or snow is enough to weigh any branches into the dish's field of view, they can either block or reflect the transmitted signal back into the transceiver. If it's reflected, it will create a real nasty standing wave pattern, and cause a lot of data errors, possibly even confuse the system.
So, in short... there are a lot of factors. Sorry it's not a real simple answer to a seemingly simple question.
Ten hours? It may very well be the slushy frozen stuff you mentioned on your dish. In my experience, that type of precipitation on a dish is the worst. I can have three or four inches of fluffy snow on my dish and it's fine, yet get a quarter inch of that wet, slushy stuff and it's lights out, so to speak. And if it freezes on the dish, it can be even worse. I live just south of Buffalo, so I get a LOT of snow, but I'll take the snow any day over that slush. Luckily, my dish is a pole install so I can clean it off fairly easily.
Edit: If your dish is clean, but you still don't have service, you should probably call customer service. Just in case you need it, the customer service number for business plan members is 800-347-3272.
Have you checked your System Control Center? If you go here, what is the Satellite Receive Signal Strength showing in the WAN Info box (on bottom left)? Also, near the top of the page, what is the State Code you are seeing in the System Summary box?
It's a good idea to bookmark the System Control Center so that if/when you have an issue you may be able to get an idea of what's going on. The System Status and System Information buttons at the top of the page are you how navigate to the two other important pages, including the one that contains the info asked for above, and the Home button on the left is to get back to the main page.
BTW, there was a widespread service disruption that started on Sept. 2nd and went through Sept. 4th. You may have been affected by this. They gave 3GB of data tokens to all those that were affected by this outage. I only mention it as it may be one of the service outages you're remembering over the last six months.
I think cleaning the dish is not suggested because you could inadvertently harm the radio. I'm sure someone will chime in with more info about this.
I wouldn't clean it, and mine gets a nasty black on it this time of year. Usually the ice and snow of winter cleans it off naturally.
Speaking of ice... I will lightly scrape it and clear any snow buildup, as that could be a problem. When you scrape it, you just need to make sure it's not so rough as to throw it out of alignment. If that happens then you need a tech call to come realign it.
I've always had my dishes pole mounted for this very reason. Takes less than 5' to clear the HN and DTV dishes from any snowy buildup.
When I clean mine I only ever either brush snow off of it, or pour cool water over it to melt the ice buildup, but not warm water so as to not warp the dish. Where I live if I didn't do so the snow and/or ice could be on there for days. I never do anything more invasive than that, though. The rain and/or melting snow/ice keeps it clean enough otherwise. I never touch the radio itself.
Again, though, mine's a pole mount, so it's very easy to get to. Were it on the roof I would only be worrying about snow buildup, and cleaning it in a different way. My folks have a long brush that they use to clean their two dishes of snow during the winter, as they're mounted on their garage roof. It's just a round "Webster" duster brush screwed onto a telescopic 15' Christmas light hanging pole. They got lucky with the threads being the same.