I'm not at work today, busy getting all the snow preps done! Just kidding, I left my snow shovel at work for a promo shoot. I've been confident I won't need it tomorrow morning, even at 1,000'. I don't shovel an inch or so...
This little "event" coming up late tonight and tomorrow morning has been solid forecast-wise for four days! Nothing has changed in either models or our thinking. The previous post is still valid.
- We will all wake up (west of the Cascades) to rain or a mix of snow/rain at the lowest elevations. Precipitation arrives sometime after 3am...timing has moved up a bit.
- If you live near/above 1,000', there's a decent chance you get at least a dusting on the ground. If you live below 1,000' IN THE METRO AREA, I'd be surprised if anything sticks. The "1,000 ft" is an approximation, we can't actually forecast snow level with precision more than 500-1,000'. See rant below...
- Whatever happens will be done by noon, then temps rise a few degrees (up to around 40 or so) and steady rain changes to light afternoon showers. Nothing interesting happens the 2nd half of the day
- If you live in the lowest elevations (90% of us), your life should continue as normal tomorrow. Except for that COVID thing, but you know what I mean. Normal for these times.
- If you live well above 1,000' (like 1,500' or higher), you'll have some nice snow to enjoy tomorrow! Probably 1-4" up there. This includes northern Clark County foothills, the hills above Scappoose and St. Helens, and above Kalama, Longview etc...
This graphic summarizes it well
Tomorrow night and Monday we'll see very light showers; could be mixed at times, but leftover wet roads freezing in a few spots Monday morning MIGHT be a bigger issue. I'll tackle that tomorrow
SOME OTHER INFO
Latest ECMWF snow forecast looks the same as it has for the past few days
This will be the first test of IBM's 4km (higher resolution) GRAF model for us. Actually it nailed the 1/2" last March, but this is the longer range version (to 3 days) that came out last summer. It says "FORGET IT" in the lowest elevations.
The "reliable for the past 20+ years" WRF-GFS (UW) is reasonable...a bit of snow most areas above 1,000'. But all lowest elevations...forget it. I've noticed it tends to "over snow" these marginal events. So we'll see if hills around Happy Valley and central Clark county picks up measurable snow... This is the highest resolution model we have for our area. 1.33km! This means grid spacing is so tight that the model's terrain includes features not seen in coarser resolutions. You can see Chehalem Mtn, the West Hills, outer SE metro area buttes, and south Salem hills. Note this one can also clearly "see" the Gorge. Little or no snow on I-84 in the Gorge tomorrow.
Just taking a look at the text data from ECMWF says we're coolest before midnight with the partly cloudy skies we're seeing now, then a light southerly breeze plus cloud cover means temps actually rise a bit toward sunrise. Precipitation is quite light on this model as well. Only .10 to .20" by noon, that's not going to drag the snow level down very far. NOTE THAT TYPICALLY THE -3 to -4 850mb temps would mean a sticking snow level up around 2,000'. We're lucky to see sticking snow below that elevation briefly tomorrow morning.
WE CAN'T FORECAST SNOW LEVELS IN 100' INCREMENTS
You may remember my rant about snow level forecasting in the past. I cringed when the NWS folks issued a Winter Weather Advisory for elevations ABOVE 700' in the metro area for Sunday. I have no problem with NWS; they all work hard and do a great job. But when is the last time you heard a Mt. Hood snow forecast of "3,700' tomorrow". Or "expect a 4,300' snow level dropping to 2,700' late this evening". We don't, and shouldn't in this case either. That's because snow level is also highly dependent on precipitation intensity. Heavier precipitation = lower snow levels generally. So don't read the Winter Weather Advisory as "you won't get sticking snow at 600' but will at 800 ft". Instead, I wouldn't be surprised if some neighborhood gets sticking snow (somewhere) to 500' Sunday morning, but somewhere else you get nothing at 1,000'. That's why I use the "near and above 1,000 ft." terminology.
So insert your eyeroll here and "oh geez, Mark is throwing a fit about THIS again?" One example below is from a blog post in 2016. Setup was a bit different, but same issue
We're doing people a disservice by implying we have more accuracy than we do.
This morning is a perfect example of why forecasters (and the NWS) shouldn't be forecasting snow level in increments below 1,000' in a snow shower pattern. A snapshot at 8:30am: Staley's Jct. on U.S. 26 west of Banks...elevation 200 feet. A snowy road and maybe a half inch on the ground:
At the SAME ELEVATION, but 15 miles east on the west side of Beaverton...all bare and wet with no snow in sight:
Then over on the eastside of the metro area just above Sandy...at 1,200'. NO SNOW. The white stuff is left over from yesterday's hail/graupel showers.
So what was the "snow level" at 9am??? Under the heavy showers it was near sea level, where very little precipitation fell it was higher, up around 1,500'.
Alright, I'll be on TV tomorrow evening at 5/10/11pm, taking a close look at Monday and Tuesday. Likely a couple more "near misses" for those days.
Chief Meteorologist Mark Nelsen