When this Christmas storm first appeared on the models a few days ago, I was hopeful that it would finally snap our five year streak of Grinch storms on or near Christmas, and until last night, it looked like that would be the case. However, meteorology loves to throw curveballs at us, and quite a bit of the overnight guidance came further west with our low pressure system for Monday, making the net result a rain storm for a lot of the state. Whether this trend is real or not remains to be seen, and there are still two days for it to go back the other way, but if you're a snow lover hoping for a White Christmas, the trend is not your friend in this case. Nonetheless, we will still see some snow across at least part of the state, and so a snowmap and discussion is in order.
Models and Trends
Since yesterday, we've clearly seen a trend towards later development of the secondary coastal low, which means that there is less time for cold air to get wrapped up in the system and the boundary layers warm above freezing as a result. This is shown well by looking at the last couple of NAM runs - you can see the center of the system jump quite a bit NW and the net result go from primarily a snowstorm to primarily a rainstorm.
While most of the guidance follows the NW trend shown here on the NAM, the Euro is the exception and actually ticked a hair colder last night, which would allow for a mostly snow event across the region. Because of it's earlier development of the coastal, it allows the northeastern portion of our forecast area to get into the band of inverted trough snows that are otherwise forecast to be to our north and actually jackpots that area with 6"+. Unfortunately, that solution is currently an outlier and I am hesitant to give it too much weight considering the trends, but the Euro is a good model with thermal profiles as well as being one of the most reliable pieces of guidance in general, so I feel like I have to give it at least some weight in the forecast. Therefore, will go with a 70/30 blend of the consensus model forecast excluding the Euro at 70% and the Euro at 30%. That blend gives us the snowmap below.
Forecast & Timing
Here is our snow forecast for this event.
The rest of the state makes up the battleground zone where this is a tricky forecast. On the Euro, we see mostly if not all snow here, whereas on the rest of the guidance it is a messy rain/snow mix for most of the event or just plain rain, and snow accumulations would likely be minimal at best. I do think that we might see things go a bit colder as we do have some high pressure in play to our north that is often under modeled, and so have gone with a 1-3" forecast here, but that will probably be a messy 1-3". The next couple of model cycles will tell us a lot about the fate of this zone - should we see the warm trend continue, we can probably get rid of this zone and lump this area in with the rain to the southeast, but I'm not ready to go there quite yet. We'll see where the guidance is at tomorrow and if needed we can update then.
As far as timing goes, looks like precipitation comes in after midnight Monday and should be out of the state by 10 AM or so at the latest, even earlier in western areas.
Here is the SCW Impact Scale for this event.
We'll be back tomorrow afternoon with a final update on this system, until then, stay safe out there today with the freezing rain and thank you for reading SCW!