|Thursday night-Friday snow forecast|
|Weekend snow forecast|
So by Sunday afternoon temperatures will warm significantly as the warmth associated with the sub-tropical moisture continues its northeastward surge. Snow levels will rise to 4000' or higher over the entire Inland Northwest. This will translate to melting snow over most of these valley locations. The big question is can we melt what falls? That depends on how much accumulates over these locations. The warming will be accompanied by breezy conditions which will help melt the snow especially when the dewpoint temperature and nighttime lows rise above freezing. And that's what we are expecting as of our latest forecasts. Here's a look at the high-temperature forecast for Sunday.
So based on the current forecast the only valley locations which stand a chance of snow before Christmas Eve would be near the Canadian Border, Cascades, or Waterville Plateau. How about the remainder of the region? Well, as we talked about in our last blog entry we are expecting a big pattern change, right around Christmas Eve. That's still true. Our mild west-southwest flow of late will take a decided cooler turn to the northwest. Here's what the upper-level pattern is going to look like (at least something like it anyway). The wind flow will be parallel to the yellow height lines. That means our flow will be riding through the Gulf of Alaska before it moves into the Inland Northwest. Meanwhile, the remnants of the weekend moisture stream will get hung up somewhere over the Pacific Northwest. The big question is where is that going to happen? Most likely it will occur immediately downstream or east of the kink in the yellow lines. In the picture below that suggests somewhere over the southern third of Washington and northern Oregon.
So is there good model agreement in where that kink is going to form? That is the key to this forecast. As of the latest model runs, consensus is growing. Here's a look at four various model runs all looking at the afternoon hours of Christmas Eve. We have placed the precipitation forecast on top of the 500 mb yellow height lines. Notice, they all show a similar kink in the height lines or flow, however they vary on how far north to place it based on a trailing low-pressure system dropping through BC. The model in the lower right is the farthest north of the solutions due to the strength of the low (circular height line) over southern British Columbia. This places the band of heaviest precipitation (blue and purple shading) over the Idaho Panhandle and the eastern quarter of Washington. Meanwhile, the other solutions are not depicting a closed low and hence drive the moisture plume farther south. The further south solutions have become more common and are beginning to raise our confidence for locations near the Oregon/Washington border such as Lewiston, Pullman, and Ritzville seeing the best chances of precipitation. However, even in those locations temperatures may remain just a little too warm for snow.
So to answer our original question. Are the chances for a White Christmas improving? For locations such as Mazama, Republic, or Plain the answer is a decided yes. For Lewiston or Pullman the answer is a maybe. Folks in Spokane, Couer d'Alene, Moses Lake, or Wenatchee the odds are not great. Of course, Christmas eve is still a week away and much can change between now and then. So stay tuned and maybe just maybe the yellow kink will decide to set up over the entire Inland Northwest resulting in a White Christmas for all.
|Sunday high-temperature forecast|
|500 mb pattern for Christmas Eve|