One last “Snow Day”

February 28, 2007

Snapshot_29One last tough forecast as we wrap up meteorological winter tonight.  Cold showers still streaming onshore this evening.  We are now in the coldest airmass of this cold/wet episode.  850mb temps bottom out around -8 deg. C. in the next few hours and then rise to -4 or so by tomorrow afternoon.  A line of showers moved over southern Columbia county and Clark County for an hour or so this evening, giving a nice dusting in those spots.  With such a cold airmass overhead, any other significant showers overnight should drop a dusting or more.  I see the top of our transmission tower in the West Hills (it’s the one that’s farthest north in that array up there) is down below 29 degrees at 1800′.  That’s cold!
So we have colder air, but less moisture the next 10 hours, compared to this morning.
With that in mind, I figure a trace to 1" anywhere in the metro area is a good bet.  A bit of melting snow that freezes on roads can make a mess as well.
Overrunning slightly warmer air tomorrow midday-afternoon should give us more stratiform rainfall (solid light rain).  The snow level will be very slow to rise, so unless we get heavy precip, I think most likely we’ll see an inch or more 1,000′ or so and maybe 2-3" up above 1,500′ by late tomorrow before the snow level finally reaches 2000′ by tomorrow evening.
A building upper-level ridge Friday brings us plenty of warmer rain, then the ridge shoves the rain north of us later Saturday and Sunday.  The 00z GFS has some light precip over us Sunday, but that is unlikely with such a strong ridge.  +6 deg. 850mb temps in early March CAN send temps well into the 60’s.  Assuming we get to at least partly cloudy skies, 63 shouldn’t be too hard to hit.  Hard to believe after the cold temps lately, but it’s a bit overdue…Mark


Snow Totals II

February 27, 2007

Okay, this may be the last of the season…you know the rules.

Snow accumulated on the ground only in this post…no weather discussion here, do that below.

1.  Depth
2.  Location
3.  Elevation if you know it


Another Tough Forecast

February 27, 2007

Snapshot_28Once again, a break this evening as we wait for another surge of moisture to move onshore.  Today’s heavy showers were concentrated on the west side of the metro area.  I notice Council Crest at 1000′ had 2.5", but Welches at 1400′ had nothing.  If you want snow, it doesn’t help if you have cold enough air but not enough moisture.  The airmass overhead cools in the next 24 hours, but I’m a bit concerned that we may not get enough moisture for metro area snow tomorrow.  To get snow in Portland, we need to see good steady precipitation before 10-11am.  Since it’s the last day of February, temperatures rise each afternoon with the increasing insolation (warmth from the sun).  MM5 and our model here both have a nice band of snow moving over us right at daybreak.  This is what I’m pinning hopes on for tomorrow.  I think this could be our last flirtation with snow for the season.  It looks like showers taper off tomorrow evening with drier conditions Thursday morning.  The steady precipitation that arrives Thursday afternoon does so with an increasing southerly wind, so the snow level will quickly lift up to around 2000′.
Longer range maps have some ridging and drying over us this weekend.  The best chance for dry weather will be Sunday.  It is early March so 60 degree temperatures shouldn’t be hard to hit…Mark


The Morning Letdown

February 27, 2007

Models were partly right, but more important, partly wrong.  Surface low is sitting right near Tillamook/Seaside at 9am.  That’s farther north than expected, so milder southerly wind has arrive in the interior as far north as Clark County.  That boosted temperatures up after midnight.  I expected the low to track closer to Newport, keeping the south wind out of the metro area and northern Willamette Valley.  Looks like sticking snow is mainly above 500′ at this hour and probably won’t go any lower with slight daytime heating.  Precipitation forecast was about right with heavier precip holding off until 8am or so.  Atmosphere overhead is quite cold with the freezing level not much above 1000′, so a cold snow/rain day in the metro area.  Freeways and main roads below 500′ should remain clear but several inches of snow closer to 1000′ and up are likely…Mark


Snow Totals

February 26, 2007

Hopefully for the last time this season:
1.  Only put measured snow totals in this post please.  Continue weather discussion below
2.  Depth, Location, Elevation IF you know it.
3.  No "no snow here" comments please.


More Overnight Snow?

February 26, 2007

That was a fun little 1/2 hour snowstorm that moved through the metro area between 7-8pm.  Proves that precipitation intensity is often more important than the actual freezing level.  We watched the Sylvan ODOT camera (at 700′) for about 15 minutes and it went from bare to at least 1/2 inch with a snow-covered road in just that time.  Once the showers moved off to the north the roadway melted nicely.  Now it’s going to be dry until sometime late tonight.  With any clearing there will be quite a bit of ice on the roadways.
Quite a tricky forecast for the next 18 hours or so.  Beautiful wrapped up surface low has suddenly deepended west of Newport and at 8:30pm is out around 128W.  I noticed earlier today as the low passed near Buoy 46005, temperatures on the buoy dropped to the 36-38 degree range.  That is very cold for sitting on a little floating buoy in the middle of a 50 degree ocean. 
Both versions of the MM5 model now move the low a bit farther north as it moves inland tomorrow morning/midday.  They move it directly over Portland!  They also agree on a pretty good slug of precipitation beginning by 5-6 am at the latest, maybe by 3am.  If so, this could easily be snow since we have cool easterly flow moving out of the Gorge as the low approaches.  IF everything was perfect, we could get a 3-5" wet/heavy snowfall out of this for the morning commute down to the valley floor.  BUT, it looks slightly too warm for that.  So two thoughts stick out in my mind.
1.  With the low track farther north, sea-level or valley-floor snow is unlikely south of Portland and south of Tillamook.  Looks like Astoria-Tillamook and Longview-Portland is the most likely spot for significant snow down to the lowest elevations. Apparently this is the winter for coastal snowfall.
2.  That said, it is a bit warmer than I would like to see at the lowest levels to call for a snow storm in Portland.  And by that I mean by maybe only 2-3 degrees too warm.  It’s going to be close!

So….
-Trace-2" possible at the lowest elevations from Chehalis to Wilsonville AND Tillamook north to Long Beach Peninsula
-2-3" on the hills above 500′ and possibly at the coastline if the precip is heavy enough.
-3-5" up around 1000′ or higher.
-It’s quite possible that we have a messy morning commute coming.  A few inches at/above 500′ affects quite a few people.

Once the precip lets up around midday tomorrow, temps should rise up to the lower 40’s.  Then with stronger onshore flow Wednesday and Thursday AM, it’s unlikely that we’ll see significant snow to such a low elevation.  I think it’s possible this will be our last good threat for snow this season, since next week should be quite a bit milder…Mark


Friday Night Quickie

February 23, 2007

Snapshot_26A short post tonight since I got behind in the weather center for several reasons.  There is lots of cold air to the north, but I don’t see any map that shows a sudden plunge of arctic air into the Northwest.  Just more of the cold and wet weather.  I took most of the snowflakes out of the 7 Day forecast because of a persistent backing off of cold 850mb temps as we head into early March.  At one point it was supposed to be -7 deg. Monday and Tuesday and now GFS doesn’t show that, pushing that cold air back to later in the week.  A lot of rain and lots of mountain snow this weekend.  Enjoy some popcorn, movies, and fire up the fireplace or woodstove this weekend…Mark


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