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

Cold and Colder

February 21, 2007

Snapshot_23A slightly earlier post tonight since I got my graphics all finished.  Lots of weather to talk about eh?  In the short term…nice plume of moisture moving north out of California bringing rain and snow north all over Oregon.  A good snowstorm in progress across the southern 1/2 of the state.  6" reported from Ray Nelson in Christmas Valley (rare for that dry desert location, no relation either).  This is a wave on the back of yesterday’s front.  It moves off to the northeast after daybreak.  Then we wait for a very visible trough out around 130 West to move inland tomorrow night.  Our RPM model here pushes the snow level below 1000′ tomorrow night.  Looks like a guaranteed dusting to 1000′ and possibly a bit lower too.  As we know, precipitation intensity is most important, but I wouldn’t be surprised to see a dusting by Friday morning everywhere above 500′.  Then a quiet Friday.
A strong westerly jet punches into the Northwest Saturday and Sunday, slamming the mountains with heavy snow…probably 2 or 3 feet again.  Snow levels both days stay above 2,000′.
Then the coldest airmass yet moves inland Monday with cold showers.  Depending on the setup, this could produce sticking snow below 1000′.  Each model run from every model has been a bit different.   Seems to me that the GFS is heading more towards the ECMWF the last few runs.  By that I mean much more digging of an offshore trough into California Monday-Wednesday next week.  So my 7 Day forecast is based on that…drying us out after Monday.  That could easily be wrong of course…but I can always change later…Mark

Cold & Wet, Or Snowy

February 20, 2007

Snapshot_27The humiliation in tonight’s 10pm show is now over so that’s good.  I refer to our attempts at Karaoke around 10:29pm.  But let’s move on…cold onshore flow continues this evening behind a strong cold front that moved inland this morning.  The strong westerly flow turns light southerly by this time tomorrow evening.  That’s not a good pattern for significant moisture in the Cascades and we usually only get light showers in the Valleys with this setup too.  The top of our tower at 1800′ is about 33 degrees at 11pm, so the snow level must be just below 2000′.  It should drop to close to 1000′ overnight, although showers will taper off too.  So tough to get snow much below 1500′.  A more organized system in the south or southwest flow  tomorrow night brings some steady precip back over us.  Once again snow may fall close to 1000′  at that point.  Just light showers again Thursday and Friday as we wait for several very wet and cold storms for Saturday-Monday.   ECMWF & GFS say the back side of these systems will be slightly colder than today’s airmass.  850mb. temps bottom out somewhere around -7 or -8 deg. Celsius.  IF moisture lines up just right, this could produce sticking snow below 1000′ in late February, but everything has to be just right.  There is no sign of cold/dry arctic air moving into the Northwest and interacting with the moisture to produce snow down to sea level.  I do notice that after Wednesday models to warm us up to more reasonable early March temperatures…Mark

Cold & Snowy

February 19, 2007

Snapshot_25Sorry about the delay in posting this evening.  I had a crisis when I realized Battlestar Galactica didn’t come on at it’s normal time for recording tonight.  But, it’s on tomorrow night…whew!  I’m too cheap to pay for the channel at home so I record it here.  But that’s WAY too much information about my personal viewing habits. 
Long range models last week showed a substantial change to our dry winter weather pattern and apparently they were correct in showing this change.  A cold flow from the west and northwest will dominate our weather through the end of the month (next Wednesday) at least.  Twice between now and early next week we get a very strong westerly jet punching right into the Northwest.  This is a perfect setup for 2 feet of snow in the Cascades each time.  Add in the lighter snowfall inbetween and the middle of next week?  You get 5-7′ of snow by the end of the month.  This could make up all the snowpack we’ve been missing since mid-January.
So the big question…how low will it snow in the next 10 days?  The lowest 850mb temps on BOTH the GFS and ECMWF is -7 deg.C.  That can bring snow to 1000′ this time of year, possibly lower IF everything works out just right.  New 00z GFS has a -8 deg. the early part of next week.  Assuming that’s a bit cold, as the GFS usually is that far out, I’m guessing no snow in Portland.  Something to watch daily though.  Those of you at or above 1000′ have a very good chance of flirting with snow at times over the next 10 days…Mark

Active Weather Returns

February 16, 2007

A brief break tonight through tomorrow, then it’s back to the wet stuff tomorrow evening through next week.  A large and cold upper-level trough will gradually approach the West Coast Monday and Tuesday and then move overhead Wednesday.  Looks like lowest snow levels on Wednesday will be below 2,000′, possibly as low as 1,000′ at some point between Wednesday AM and Thursday AM.   Then more westerly flow and troughs follow after that.  February is going to end colder and wetter than it began.  Of course we CAN still see snow in the last 10 days of February (remember last March?), but you have to get 850mb. temps down to -6 or preferably below.  500-1000mb thicknesses must get down to 522dm or less as well.  I DON’T see any cold arctic air or a windstorm setup in the next 7 days.  So I plan to pull the mulch off of my plants tomorrow during the very brief dry spell…Mark

Wet & Windy

February 14, 2007

Snapshot_24Nice slug of subtropical moisture sitting offshore and stretching well off to the southwest.  This means a good 24-36 hours of  heavy rain in the mountains (Timberline and Mt. Hood Meadows are already above freezing at 5,500’+), and light-moderate rain here in the lowlands.  The strong orographic component to the flow should squeeze more than 3 times the valley rainfall totals down over the mountains.  As I pointed out at 11pm, this is good news in February because reservoirs begin holding back water here in the Northwest.   The break between the warm wet system Thursday and a much colder system Sunday has narrowed a bit.  It’s definitely a one day warmup for Saturday.  Onshore flow and 850mb temps to -4 Sunday should bring snow down to 2,000′.  This ushers in a cool & wet pattern for next week.  So make your outdoor plans for Saturday because every other day of the next 7 looks at least showery, if not quite wet…Mark