Rainy & Windy

December 29, 2008

Snapshot  My driveway was finally passable by 4×4 transportation today, that was after my wife and I did 3 stints shoveling out the last 200' over the weekend.  I even have 2 blisters to prove it…pretty cool eh?  I figure another 2 days of melting should allow a 2 wheel drive to go at least downhill, another day or two to get back up.  Life will be good again!  The warm rain over the weekend was amazingly effective at getting rid of the snow.  Here at the station in Beaverton there is no snow left on the ground.  I had 26" which is now down to around 6" at home.

The graphic is one I've shown on our various shows tonight (I've done 3 of 5 so far).  It makes a point;  just because you have a big snowpack in the mountains doesn't mean a flood is coming.  Thick snowpack is just one ingredient for a flood.  Last year there was twice as much in the Coast Range at two different times during the winter.  In fact the 2nd time there was 35" of snow water equivalent on Saddle Mtn. west of Forest Grove was at the end of April!  No flood because we never had heavy, warm rains on top of the snow.  We don't see that coming anytime soon either.  Lots of weather systems the next 10 days, but the freezing level jumps up and down with each cold and warm front.  We can use lots of rain because our monthly total is only about 1/2 of average, continuing a trend that began in January.  I'm shooting from the hip here, but I think August was the only month this year with above average rainfall.

None of the systems this week appear to have the correct positioning or strength to give us a windstorm in the Valley.  The Thursday night-Friday system has been taunting us for a few model runs.  The latest 00z run of the WRF-GFS would give us 15-17 millibars EUG-OLM pressure gradient for a very windy night, but probably no gusts above 50 mph.  It has the low center getting close to 960 mb. as it moves inland over central Vancouver Island, a bit too far north for a big storm here.

Okay, time to move on…got to get a few graphics organized for the 10pm show…Mark Nelsen

White Christmas!

December 25, 2008

Snapshot Merry Christmas!  Here we are again…it's Christmas in Portland and it snowed…who would have thought it could happen in two back to back years!

That nice little band of solid snow that dropped through the Portland Metro area this afternoon dropped anywhere from 1/2" to 4".  Officially .8" fell at the NWS office on NE 122nd Ave.  There is still 10" on the ground there, and 5" at PDX.  That 5" at PDX still blows away any previous snow on the ground measurements for Dec. 25th.  The next largest amount was a trace.  So now you can once again tell your kids about the White Christmas of 2008.  Oh, and now it's the 2nd snowiest month in PDX snow history, outranked only by January of 1950.

I didn't work yesterday, but when I left Tuesday night, I expected 1-3" of snow Christmas Eve morning before an afternoon warm up.  Others were very skeptical, but the south wind did the trick again, pushing PDX to 39.

It also appeared a surface low would come quite close to us on it's way SE for today.  That did happen, although the low center was farther offshore.  We still had one nice wrap-around band come through the area this afternoon which pretty much saved it from being a forecast bust.  I had figured maybe 2-4", which was high for most of us.

So now it's on the westerly flow after leftover snow showers tonight.  The flow through the Columbia River Gorge is light westerly right now, so we'll have no problem warming the airmass tomorrow for a quick changeover to afternoon rain.  Yes, we'll see a mix just about anywhere in the morning, but then it's on to a cold Friday afternoon rain.  Increasing southerly wind with a warm front tomorrow evening actually pushes our temperature up and by Saturday AM we may be well into the 40s.  Oh man…I can't imagine what kind of noise that snow on the metal roof will make when it slides off.  I'll try not to stand under it.  That's if I don't get speared by the 4 ft. icicles hanging off the gutters…apparently I need to get better insulation in my attic because my snow was melting on the roof pretty well yesterday even with a temp in the mid 20s.

Speaking of the home front…I got an additional 3" yesterday morning, then 6" again from yesterday afternoon through this afternoon.  That brings the snow depth to an amazing 26"!  I have never lived in a place that had so much snow on the ground.  My winter total (the last 11 days) is up to 42.5".  Now if we could just do the same thing again the last week of January AFTER I buy some sort of snow blower, that'll be cool.  But for now it's back to lots of rain and south wind.  We'll keep a close eye on developing low pressure systems…hopefully no big windstorms on the way…Mark Nelsen

Snow Totals Ver 5.0: Christmas Edition

December 24, 2008

Really, this should be it this time around! It's getting a bit ridiculous. Looks like everyone gets some between now and Christmas afternoon. Put in your snow totals on this post through Christmas.

1.  New Snow (starting Christmas Eve morning, Wednesday)

2. Total snowdepth

3. Location

No other comments or discussion in this post please.  Keep discussing weather in other posts.

Between Snow Storms Today

December 23, 2008

DSCF0012 I was a bit negligent in posting yesterday…probably due to exhaustion and the fact that forecast-wise there wasn't much to talk about for today.  The other is that I REALLY wanted to get home due to generator issues and other things (2 kids stuck in a house alone with my wife).  So at midnight I made it down my rural road which had one lane plowed with 3 foot berms on each side.  I get to my driveway and…nowhere to park!  My wife had left the snow shovel, so at midnight I spent 30 minutes digging through the (relatively light) snow, just enough to nuzzle the SUV into a little parking spot.  Then it was a 500 ft. trudge through about 2 feet of snow in the pitch dark, stumbling into the powder, in jeans and hanging onto bananas and a bottle of wine.  You can imagine the scene.  No electricity at home and the family was camped out by the woodstove all asleep like it's Christmas Eve!  To make this long story short, the power just came back on and internet access is restored.  I am just amazed at the snow depth.  I still have 21" on the ground about 2 miles east of Corbett at 1,000' elevation…I don't get much drifting here because of very little wind, so I assume that there must have been 22-24" before it compacted the last 24 hours.  That includes 13" on top of the thin ice layer Sunday too.  You see the picture…that's my dog;  the Prius is on the left and the Odyssey minivan is on the right.  They won't move for a long time!  I'll put some other pictures in the viewer photos on the sidebar.

I haven't spent the usual enormous amount of time staring at maps today, but enough to confirm what I was already thinking, with a few changes…

Offshore flow continues tonight and early tomorrow ahead of an approaching weather system…keeping us relatively cold through morning.  I see temps are approaching freezing in spots at 1pm, so that forecast is looking good.  I doubt we'll see a dramatic drop tonight, just staying in the mid-upper 20s.  That sets us up for some snow in the morning as precipitation from the approaching California storm merges with the cold front coming in from the northwest.  Last night I said 2-4" and at this point that seems a bit high, considering that the freezing level should rise to about 1,500' from 4pm tomorrow through early morning Christmas Day, and the heavier precip comes with that slight warming.  Maybe 1-3" is a better bet.  Christmas Eve itself (tomorrow evening), should be a bit sloppy with a rain/snow mix due to a good southerly wind blowing up the Valley.  Not exactly a real warm wind, but enough to change those of us below 1,000' to that sloppy mix.

Then the fun returns Christmas Day itself.  Looks like a surface low slides right over the top of us or just to the south during the morning hours, turning our surface wind easterly again (cold), then light north by late in the day.  There is a good burst of precipitation at the same time…SO…I think Christmas Morning we'll probably see widespread 2-4" snowfall, with some spots up to 6" if we stay chilly enough.  Maybe Steve Pierce can confirm, but I don't think we've ever seen such a White Christmas! 

I think the higher elevations and Columbia River Gorge could see another foot of snow from tomorrow morning through Christmas night!  Down here in the metro area I see snow, then rain/snow mix or all rain, then more fresh snow Christmas Day.

I didn't look too far beyond Christmas since I spent the morning shoveling, BUT, it's obvious there is going to be a quick change to mild and wet westerly flow late Friday and the weekend.  50 degrees isn't too far away for those of you tired of the snow…

9pm Update:  This will be brief, since I need to get organized for the 10pm show, but I see precipitation is moving in quickly this evening.  Some below have mentioned the KPTV tower temp is above freezing at the top.  Yes, but just barely and the dewpoint at that elevation is below zero.  That means evaporational cooling should drop temps down below freezing at that elevation soon after the precipitation starts falling.

Just looked at 00z maps…there seems to be a slight northward trend in the 00z WRF-GFS and 00z MM5-NAM in the low pressure center location for Christmas Day.  The 00z NAM would give us no snow, but the 00z WRF still could.  Just another wrinkle in the forecast. 

What continues to be very clear in the longer range is that the snow threat ends Friday.  After that it's back to wild, wet, and warm Pacific weather systems.  Enjoy the snow while it lasts!

Mark Nelsen

The Snow Keeps Coming

December 21, 2008

For those of you that have been waiting years, and agonizing about it on this blog…apparently the last few days have been make up time for our snowfall.  The National Weather Service here in Portland has recorded 11.5″ of snowfall for the month now, making it the snowiest December since 1968.  And I don’t think we’re done yet!  There was 7″ at the forecast office yesterday, 2″ today, and 2.5″ on three other days earlier this week.  Didn’t I say the good times were going to continue?

I wish we wouldn’t have gone for some warming west side today.  ONCE AGAIN, even the mesoscale models were heavy on the southerly wind.  They never showed a dramatic warmup, but they were also clueless on the Valley wind.  At least we caught the change quickly and called for things to stay cold down the Valley today in our morning shows.  That is an improvement over 2004 when we tried for a dramatic warming 3 days in a row!

This is the only situation in my forecast career where a silver thaw turned back into at white freeze.  Colder air aloft moved overhead with that band of heavy precipitation this afternoon, changing our freezing rain back to snow.  As the nice looking surface low west of Newport shifts inland tonight, this keeps the easterly flow going over us through tomorrow morning, so the whole column of air overhead stays below freezing.  There should be good lifting on the north side of the low and models show a nice burst of heavy showers around 4-10am in Northwest Oregon.  That’s why I’m forecasting more snow late tonight over the area.  The south edge of the cold air has been lingering down around Salem all day, and there’s no reason that won’t continue until morning too.  We will transition from a “Gorge” event to just plain cold atmosphere during the day tomorrow, so the east wind goes light, and everyone should warm up a bit.  But since we’re going from bitterly cold air from the east to just plain cold air drifting down from the nroth, it’s going to be tough to get above freezing with all this snow cover around.  By the way, let’s hope for some brief clearing tomorrow night.  Think of the low temperature possibilities with light wind, heavy snow cover, and clearing!  We don’t get that opportunity much here in the metro area.

Now it’s on to the Christmas Eve system.  We are going to go from cold enough to snow at sea level to cold enough to snow at 1,000-1,500′ by afternoon, so I expect some pretty good accumulation in the morning, changing to rain/snow mix in the afternoon.  Those of you at/above 1,000′ will have a lot more snow just in time for Christmas Day.  The reason I think it’ll warm up (some) Wednesday is that we get a strong low pressure system moving by directly to our north.  Nice southerly wind again…not quite as strong as last Wednesday, but similar.  Even with the snow cover on the ground, I doubt it’ll be tough to get up to 38 in the city.  Cold air behind the system gives us a good chance for snow showers Christmas Day, mixed with rain in the lowest elevations (maybe).

Storm Day is Here

December 20, 2008

8:30am: I slept horribly last night…going to bed close to 1am and waking up around 5:45am…too ramped up about the snow moving in.

The good news is that everything is most definitely proceeding according to plan with one small hitch; the steady snow has arrived a bit earlier than I expected.  This is going to mess up some of people’s plans to get errands done in the 1st half of the day.  Of course for those who have become used to driving on snow the last few days, it’s not a big deal.

Cold air is pouring out of the Gorge now, pressure gradient from PDX-DLS is up to -6.5 already, with peak gusts approaching 50 mph at Corbett.  The edge of the low level cold/dry airmass is between Salem and an Aurora/McMinnville line.  That should make it just about to Salem, but not any farther at it’s maximum southward point this afternoon.  Temps are a bit colder than I expected this early, and I see The Dalles continues to see a drop temp and dewpoint…very good signs.  The east side of the Metro area should be down to around 20 by sunset or this evening.  Enjoy the snow.

8:30pm:  Now THIS is a snow storm!  It appears to me that this may be our biggest snow storm since the early 1990s.  For sure it’s the best for such a wide part of the Portland/Vancouver Metro area.  As of this time, I see new snow totals from 6-11″ widespread across the area.  Looks like another couple inches are possible before we make the switch to ice pellets or freezing rain between 10pm and 1am.  That warm air surges in behind a ront during that time.  Then precipitation tapers off after that time until a secondary front races onshore around midday.  Whoever hasn’t risen above freezing by that time (at least the entire are east of the West Hills), will see a good coating of glaze ice with freezing rain.  That secondary surge will give the Central/Eastern Gorge more snow where the cold air is thicker.  Speaking of cold air, models have handled the situation really well, including the solid surge of cold, dry arctic air down through the Gorge and all the way to Salem.  I was worried about 1pm that Salem wouldn’t see snow, but now the north side of Salem has about 4″ snow while the south side has very little.  Pressure gradient from PDX-DLS is now over 14 millibars…I really like the peak gust of 67 mph and temp of 12 degrees at Corbett.  That gives a windchill below -10!

11:00pm:  Okay, all done for the day, just in time for widespread reports of freezing rain and ice pellets.  Clearly the warm air is moving in just as scheduled overhead.  However, the cold air at the surface streaming through the Gorge is the coldest we have seen.  It’s going to be tough to get rid of it!  If I get up in the morning and it’s not 40 or 45 at Salem and 40 at McMinnville, that’s a problem…Mark Nelsen

Best Storm in 5 Years

December 19, 2008

Not much has changed forecast-wise in the last 24 hours.  What HAS changed is our confidence that there is going to be a major snow/ice storm here in the Portland/Vancouver Metro area and Columbia River Gorge starting tomorrow afternoon and continuing through Sunday PM.  Here are my bullet points:

1.  Drew and I just compared several different model runs compared to 12 hours previous…no change.  That means there is no “warming” trend showing up on models, or for that matter a farther north triple-point on the frontal system moving in.  That’s the point where the warm/cold fronts join up.

2. The cold arctic air that’s moving down the east side of the Cascades this evening gets sucked through the Gorge as the low pressure approaches.  WRF-GFS says 14 millibars through the Gorge.  Considering the cold airmass, I think gusts 70-80 mph EAST of Troutdale/Gresham in the Corbett/Multnomah Falls are likely tomorrow night.  Gusts to 50 mph are likely anywhere east of I-205.  The potential is still there for a downslope wind event in the Clark County foothills, we’ve historically seen damaging wind in an event like this out there.  Maybe gusts to 60 mph in the evening.  The combination of rapidly increasing east wind + falling precipitation (evaporative cooling) means temps likely fall well down into the 20s by sunset.  Maybe into the upper teens near the Gorge.

3.  The snow isn’t going to last long from Salem south down the Valley.  IF models are overdone in the weak southerly gradient, we could see freezing rain during the transition down there, otherwise it’s 2-4″ and then a change to rain down there late tomorrow evening.

4.  Transition from snow to ice pellets or freezing rain here occurs during the night tomorrow night.  I figure there is enough precip. to hit at least 6″ in most of the metro area (and Longview!) by that time.  Precipitation from Multnomah Falls east into the Gorge will be all snow through the entire event.  That means Cascade Locks/Stevenson/Hood River could see 20-30″ total as the moist Pacific airmass rides up and over the cold dome locked into the eastern end of the Gorge.  The Portland metro area stays with freezing rain all day Sunday.  That may be bad news from the central/eastside with significant glazing on power lines and trees.

5.  Sunday the surface high eastside weakens eastside, but we stay below freezing from the West Hills east.  I wouldn’t be surprised if it’s 45 degrees at Wilsonville, and Hillsboro Sunday afternoon, while it’s 28-30 out at PDX and Troutdale.  That’s optimistic.  If models are overdoing the southerly gradient, we just stay near/below freezing all areas north of Wilsonville.

Looking beyond Sunday PM:

This is the only time in a silver thaw situation where we don’t REALLY warm up.  The surface low throws some warm air at us, then decides to slide by off to the south Sunday night and Monday!  This is a good setup to continue drawing cold air out of the Gorge.  So it’s quite possible it never really gets above freezing on the east side of the metro area until Monday afternoon. 

After Monday…I have a headache.  I don’t want to think about it.  We’re going to stay in a generally cool pattern, although without arctic air.  For those of you in the Gorge, it may be tough to get rid of that 3 feet of snow that’s on the ground by Christmas Eve!