Right now the weather radar shows the precipitation almost comically stopping at the Canadian border, except for Michigan and some smaller patches out west. But not compared to the populated sections of 5 provinces simultaneously getting almost fully blanketed.
Am I missing something?
In the winter, snow piles up in the mountains. In the spring, the snow melts and water flows into the reservoirs. We use the water from the reservoirs for the rest of the year.
this year, we had a really extreme heat wave right at the beginning of spring. Most of the snow melted so there is not much left. It seems like that water should now be in the reservoirs ready to use. Why the panic over a thin snowpack?
Here in Oregon, the problem is that reservoirs were not designed to hold all the precipitation as water all at once. When precipitation falls all as rain and not as some snow, the only thing the water managers can do is let the excess rain flow out of the reservoirs through the spillways. And there is no melting snow pack to replace it later in the dry season.
California seems to have enough reservoir capacity to hold several years worth of water. It was built a long time ago. The population has gone up and the droughts have gotten longer. It may be time for more but this year is looking okay.
And in Colorado, they had a “snow drought” this past winter, which is now leading to concerns about water shortages.
Even in California things are well below normal. UCSD tracks this and has a handy graph you can look at. If this doesn’t load inline, you can see it here: https://cw3e.ucsd.edu/water_storage_tracking/
https://cw3e.ucsd.edu/images/Reservoirs_Snow/Sierra_Reservoirs_Snow_Storage.png
The TLDR is even with the reservoirs holding more water than normal, it’s not even close to enough to account for the lack of water being held in the snow pack for later this year. Also, what’s currently in the reservoir is vulnerable to evaporation (which snow obviously would not be until after it normally melts) which will further exacerbate the problem as we move into summer.
The picture is much much worse when you move into the colorado basin. I’m not aware of a reservoir + snowpack graph for it (if anyone knows of one please link), but you can see from their current capacity as of April 1 that the two big reservoirs are already below normal and there are places where the snowpack is already completely gone.
To further demonstrate that the water levels are already abnormally low, and not sitting on a bunch of pre-melted snowpack, here is firmer data for Lake Powell. Specifically I’d like to call attention to the bottom of the page pertaining to boat launch conditions: most of the launch ramps are already high and dry. They wouldn’t build launch ramps in places that could only be accessed during years of good rainfall.
I like the last line on that launch ramp table:
Blue Notch is unknown and really just shoreline launching at whatever point feels good. No minimum given except amount of courage it takes to reach this launch.
Correcting myself from above. I was just watching Daniel Swain’s virtual office hours video from earlier today and it directly contradicted me 
(~36:36) So again, is this the worst situation we’ve ever seen in California? No. Very, very far from it. There are no major water supply concerns in California this year, at least from a climate perspective. But in the broader West, it is a very different story in the Colorado Basin.
This is from here, but it won’t let me link directly for whatever reason in the usual way. Throws an error about embedding media (maybe because it’s a “live” video 
) https://www.youtube.com/live/SIRF3D4-ccs
Speculation, but presumably the recent week of unusual rain/thunderstorms plus some actual snowfall is helping to ameliorate the shortfall in snow pack from the March heat wave? Anyway, your info was more correct than mine for this state.
Embedding YouTube vids (any YT vid) requires a special technique to get around a bug in Discourse. Easy once you’ve been given the secret, but baffling until then.
See
Is that a new bug? I was able to link one just fine in the OP - that’s why I assumed it was something particular to this video
Nope, it’s been an issue for a couple of years, IIRC.