I feel like it’s time for one of those "sample" tests. The ones that don’t really count, but you take them to see how your skills are coming along. Why the heck am I wound up about snow or a surprise snowstorm in Portland, Oregon on March 28th??? That thought actually makes the forecasting easier, thinking that 7 days from now we could hit 75 or 80 degrees (first week of April). But, back to reality.
Very complex and messy forecast with a high potential for being wrong some areas and right on others in the morning. So the 00z runs are out and STILL in some reasonable disagreement tonight. Both GFS and NAM take a low across Southern Oregon tomorrow, of course the NAM continues to be significantly deeper. But there is a 2nd, weaker low that approaches the Washington Coast at the same time late tonight and tomorrow. In reality it’s almost more like a negative tilt front with a wind swith line from easterly to gusty westerly. It passes through the metro area about midday tomorrow. From now until midday, we have light or calm wind. No significant east or southerly wind (plus there is no cold air to our east in late March, so the easterly wouldn’t help anyway). A cold atmosphere modifies only slightly the next 12 hours, so all we need is steady, heavy precipitation to drag a very wet snow level down to sea level in the first few hours of daylight. The MM5-GFS is more impressive with precipitation, bringing snow down to the Valley floor, the NAM a bit slower, which would say no snow anywhere below 1,000′. I’m leaning more towards the GFS with it’s track record. You see my forecast above, it applies to all areas West of the Cascades, including the Coastline, in Northwest Oregon and S.W. Washington.
As I’ve mentioned in the last few months, I’m done with that 200′, 500′, 700′ snow level crap that was so useless this winter for many. I just think we’ll have heavy, wet snowflakes from 5-9am, with some sticking possible, but temps bottoming out near 35 in the city and 32 at the top of the West Hills. The North Coast is in a very interesting spot with light morning wind and even heavier precip. right under the front. Could it be a widespread 2-4" even to the beaches out there? Tough call. If the northern low is slightly too strong, then a weak onshore breeze will be present all night and through the heavy precip. No snow in that case. But I’ll stick with the Trace-1" forecast out there in the end.
Saturday and Sunday look far more showery, so it should be like this morning, with random spots each morning getting a dusting. Amazing how strong the sun is. An airmass cold enough to bring a dusting to the lowest elevations at night, but a high of 50 by late afternoon, then back to snow the next night. What a battle between solar insolation and the very cold upper-level airmass. If today was a winter day, we would have had a 38-40 degree high at PDX, even with the sun.
A bit more reasonable next week with temps recovering to near normal…which is about 58 for the first few days of April in Portland…Mark Nelsen