Vacation Extra: White Christmas?

December 23, 2007

Dscf0028 I just took a very close look at the weather maps (while relaxing at home).  Someone today said "how about that white Christmas coming?".  I replied something like "that’s pretty unlikely, where did you hear that?", even though I only had a brief look at weather information the last couple of days and have seen no TV weather reports since Wednesday night.  Funny how sometimes we just spout off with very little information to back it up.  By the way, that’s my daughter Ariel getting a nice bite of snow up on Larch Mountain road Friday morning.  There was about 10" of snow at 2,000′!  Pretty impressive depth, and it’s really hard to sled off the edge of the road and into the ditch…but Daddy did some rearranging of the snow and the kids were happy in the end.

Okay, so what about snow?  Here are my thoughts, which are actually quite similar to the NWS forecast…I must be getting old and conservative, or they are much better than they were 15 years ago…most likely the latter.

TONIGHT:  No, it’s pouring right now with a cold front getting close.  By the way, I think I’ll crack 10" in my monthly rain total at home tonight.  A wet month.

CHRISTMAS EVE (Day or Night):  Very unlikely below 1,500′.  By the time the coldest air arrives tomorrow evening, we’re getting very dry.  Similar to what we saw Saturday.  I think it’s going to be very tough to get snow even at my home (at 1,000′ in the Cascade Foothills).

CHRISTMAS DAY:  Very unlikely below 1,000′.  Why?  We’ve seen exactly the same thing several times this season.  Cold overnight airmass, then a front moves in middle of the day or afternoon with precipitation.  At the same time low level wind is southerly (mainly above the surface, pretty calm down where we live.  Both NAM and GFS say slightly too warm.  MM5-GFS X-Section shows it quite well, as does the meteogram.  I would say the Gorge (east of Multnomah Falls), and areas well above 1,000′ west of the Cascades will see a white Christmas afternoon.  But I’d put the chance of sticking snow in Portland metro area anytime Christmas Day (8am-Midnight) is maybe 10-20%.  The reason I don’t see anything in the evening is that strong onshore flow develops around sunset.  At that point, and until colder air arrives Wednesday daybreak or so…forget about snow below 1,500-2,000′.

WEDNESDAY:  Possible below 1,000′ if the moisture holds up, but it’ll be tough to get snow down below that elevation.  And it’s still only maybe a 20-30% chance of sticking snow in the city.  It would only be showers, and most likely our high makes it up to 39-42 degrees in the city.  By the time it cools off in the city in the evening, we’re drying out again.  But this is probably the best chance for some widespread snow on the hilltops.

THURSDAY:  We do it all again with another system moving in over cooler air.  This one is slightly warmer than Christmas Day, so snow stays well above 1,000′.

So to sum things up…I don’t see a GOOD chance for snow in the lowest elevations (I-5 Corridor below 1,000′) the next few days. That said…lots of spots in the hills will have at least a dusting, maybe more than once, and almost all of us should at least see some snow in the air. Of course this is based on what I see as of Sunday evening.  If we get an area of low pressure that develops to our south, or a very organized system develops in the cold air Wednesday, that’s a different story..Mark Nelsen

Back to Christmas now…