February 22, 2007

Things are going about as expected.  Assuming the heavy band of rain/snow coming off the Coast Range right now holds together, we should see sticking snow down to 1,000′ or a little under in the next 2 hours.  At 11:20pm the edge of the precipitation has made it to the edge of Hillsboro, so maybe this really is going to hold together.  No changes to previous discussion…uh-oh, I promised myself I would never say that in the blog.
Okay, one more look at the long range shows somewhat confused models.  But I just checked the brand new 00z ECMWF.  It is similar to the GFS (a bit colder than it’s earlier run).  Apparently we are going to mess around with low-elevation snow chances again the early-middle of next week.  No warmup for at least another week…Mark

Fun Thursday Evening

February 22, 2007

I’m posting early today since I have a few extra moments, and I think any interesting weather tonight will occur about the time I usually post.

Impressive agreement this afternoon between satellite imagery, UW-MM5 mesoscale model, and our own RPM-WRF model here at the station.  I just spent the last hour or so staring at precip forecasts, isobars, low level cloud animations etc… It appears that the coldest air of our little cool spell is just offshore.  It shows up quite well as a sharp trough with heavier showers halfway between the Coastline and 130W longitude.   I notice that Buoy #46005 has been right at 40 degrees all day (plus or minus 1 degree).  That’s cold considering it’s sitting on top of a 50 degree ocean!  That also tells me snow showers are probably at least mixing in with the rain down to sea level in that airmass.  The sharp trough moves onto the coastline around 7pm and into the metro area around newstime tonight.  Our model here paints it as snow with temperatures quickly dropping to around 36 at the valley floor as it passes through.  I expect widespread rain/snow mixed with some areas of all snow if the showers are heavy enough.  This should drop at least a dusting to just below 1000′.  I think it’s unlikely we will see a dusting below 500’…but we all know that unexpected heavy showers could push the snow level lower.  That was the good news in the model agreement.  The bad news is that both the 4km-MM5 and our model show it as just one line of showers from 10pm-Midnight.  Then the only leftover showers are over the Coast Range and west slopes of the Cascades.  This would make sense because the flow is WNW behind the passing trough, which would tend to rain shadow the valleys with lighter showers.  This has happened several times this winter already.  So I bet we wake up to 36 degrees and partly cloudy skies tomorrow morning with just a snow shower here or there.  I really doubt we’ll get sticking snow in the city of Portland overnight…but we can always hope right?  If you live at or above 1000′ I would expect a dusting to 2" during the 10pm-Midnight snow showers.
Just partly cloudy with light showers tomorrow and then it’s on to very wet and windy Saturday/Sunday with the snow level both days above 2000′.  More later…Mark