luterra

2" snow on top of ~0.05" ice in Corvallis, still big flakes falling and no return to ZR.  This is our first "real" ground-whitening snowfall of the season; the first in December was mostly sleet and Wednesday brought about a half inch.

Temp steady at 28, dp 26.  Marys Peak at 4100 ft also reporting 28 dp 27 - fairly isothermal lower atmosphere at present.

Silly RPM. Sends temps into the 40s with a raging east wind. 

 

 

http://www.cascadeaccess.com/~mnelsen/web_RPM_12z_Text_PDX.jpg

Seems extreme, though one thing to keep in mind is that the source of the east wind will be warming substantially over the next days, from 0-10 now up into the 20-30 range.  No real reload of the cold pool east of the Cascades until Thurs-Fri, so any midweek snow/ice events - at least in the Portland area - will be more marginal/bust-prone...

Aside from the immediate coast there are no above-freezing observations north of Eugene right now, at any elevation.

Snow mixing in with sleet in Corvallis now, temp 27.6 down from 28.3 before precip started, DP 25 up from 22.

More sleet than ZR in Corvallis right now, creating a textured ice surface that is a little better for traction than straight glare ice.

Well in a freezing rain scenario I'd argue that more warming would occur via latent heat release at the surface during the freezing/accretion process than via diffusive transfer. But yes, heavier precipitation can warm the surface boundary layer more effectively via diffusive transfer than drizzle or light precipitation.

That makes sense.

Heat of vaporization 2260 J/g

Heat of fusion 334 J/g

Heat released by cooling 7C: 4.2 J/g-C * 7C = 29.4 J/g

Which is to say that for a given precipitation rate:

--wetbulb cooling is roughly tenfold stronger than ice-accretion warming, and

--ice-accretion warming is roughly tenfold stronger than direct heat transfer by warm raindrops.

So, to answer my own question, warm raindrops don't seem to matter much...though steady rain at 31 degrees in a saturated atmosphere should tend to warm the surface to the freezing point in the absence of advection.

Here's a question for the physicists - Phil?

Is the heat transport by liquid precipitation ever a significant mechanism for warming the lower atmosphere?

When precipitation begins, the lower atmosphere cools by evaporative (wet-bulb) cooling until saturation or near-saturation limits evaporation.  After that any temperature change is assumed to occur via advection.

For my location Sunday morning the GFS is showing freezing rain with 850 temps of 5-7C, near surface temps of around -1C, and light surface wind.  We shall see if this verifies; my intuition tells me those warm raindrops will start bringing warmth down with them...

Marys Peak @ 4000 ft in the coast range just dropped to 19 degrees (-7C).  Current modeled temps are -3C at 925mb and -1C at 850mb.  Upslope effect, more or less consistent with adiabatic lapse rate from our 29F in the valley.

Hoping this means the cold air is deeper than modeled, more snow, less ice...

A line of clearing is actually working up the valley. EUG down to 28 on the hour, dp has dropped to 23 there. Down to 23 here under starry skies. 

Dropped from 33 to 27.5 here when the skies cleared with no wind, now bouncing back up again as a light breeze returns.  Dew point 25 and falling, sky still mostly clear.

Having a hard time getting down to freezing here tonight, holding at 33 with 27 DP and no wind in Corvallis.  WSW could bust, though there will probably be some wet bulb cooling with the onset of precip that will make some ice.

Some serious disagreement between the GFS ensembles and the CPC outlooks in the 8-14 day period.

http://old.wetterzentrale.de/pics/MT8_Portland_Oregon_USA_ens.png

http://www.cpc.ncep.noaa.gov/products/predictions/814day/814temp.new.gif

8-14 DAY OUTLOOK FOR DEC 13 - 19 2016   DURING THE 8-14 DAY PERIOD, MODEL AGREEMENT REMAINS GOOD, ALTHOUGH  DISCREPANCIES GROW COMPARED TO THE 6-10 DAY PERIOD. A BLOCKING STRUCTURE IS  STILL PREDICTED OVER THE CENTRAL PACIFIC WITH TROUGHING NEAR HAWAII AND RIDGING  OVER THE BERING SEA. TROUGHING IS PREDICTED OVER CENTRAL CANADA. THE MODELS  DISAGREE ON THE SOUTHERN EXTENT OF THE TROUGHING, WITH THE EUROPEAN ENSEMBLE  MEAN DROPPING HEIGHTS OVER THE SOUTHEAST CONUS AND RAISING 500-HPA HEIGHTS OVER  THE WESTERN CONUS. THE GFS MAINTAINS A BROAD TROUGH OVER MUCH OF THE CONUS WITH  ONLY A MODERATE RAISING OF HEIGHTS FROM THE 6-10 DAY PERIOD. THE CANADIAN  ENSEMBLE MEAN DRAMATICALLY RAISES HEIGHTS OVER THE WESTERN CONUS. THE 500-HPA  MANUAL BLEND INCORPORATES THE EUROPEAN ENSEMBLE AND THE GFS BASED SOLUTIONS. 

NWS may have overestimated the winds, but they have been underestimating the rainfall at least here in the Willamette Valley.  Corvallis up to 5.7" since last Thursday and 8.7" on the month.  If this were not the first storm of the season, we would be looking at flooding problems.

Pressure rise with squall was temporary here in Corvallis, dropped back to 29.29" and still at minimum though beginning to tick upward.

Impressive squall just moved through the Corvallis area (11:50a) with brief but intense winds, rapid pressure rise.  Gust 38 mph at Corvallis airport, 102 mph on Marys Peak.  Suspect this may be our peak winds with this event.  Not a historic storm by any means but still the strongest of this series.  Power flickered but still on.

I am up to 6.75" rain in October.

1.85" so far today in Corvallis. Drove up Marys Peak after work to experience the storm and managed be there for the strongest gust, and also strongest wind I have personally experienced, 92 mph at 6:15 pm.

This winter has featured more sunshine than any PNW winter I can remember.  We have had a few fogged-in inversion days, but even our inversions have been sunnier than years past.  Today felt like April with 50 degrees, bright sunshine with occasional showers and rainbows.

My father moved to Oregon from Minnesota in November.  He wasn't sure he could handle the gray.  Turns out it has been almost as sunny as back home, not to mention substantially warmer.  And when the inversion fog happens, there's always the option to take a day trip up Marys Peak or to the coast where it's 60 degrees. 

No snow so far, granted, but all in all one of the more enjoyable PNW winters I have experienced.  Just a counter-perspective to all of the depression on here of late.

The new GFS seems to be able to predict Willamette Valley inversions, while the old one kept spitting out 55-degree highs under ridges.  Some progress at least...

I still haven't heard a good explanation for why our average daily temps bottom out so early in the season - especially in spite of all the 850mb seasonal lag - nor why our cold snaps start to trend rapidly milder after Groundhog Day.

 

Yes it is the case that January used to be the coldest calendar month.  Is the recent shift to December more of a "luck of the draw" as far as when we get our arctic blasts and inversions - or is climate change (either natural or human) somehow tweaking the shape of our seasonal temperature curve (as opposed to merely shifting the whole curve up or down)?

I'll give it a shot...this is based on physical reasoning without looking at long term historical ridge/trough placement so could be wrong.

The land cools more quickly than the ocean in the fall.  Since cold air is denser than warm air this creates a tendency toward higher pressure inland.  In December this pressure difference is more frequently sufficient to overwhelm the prevailing westerlies, generating periods of low-level offshore flow.  From November through mid-February, offshore flow brings significantly colder weather than onshore flow, so it perhaps not surprising that December and January are the coldest months at the surface.  The sun angle contributes as well of course, especially as high pressure regimes may average 10-15 degrees colder than they "should" be if inversions set in.

At some point around Feb. 15, the land has started to warm while the ocean is just reaching its coldest temperature of the season.  This tips the balance in favor of neutral pressure gradients or offshore highs, both of which favor onshore flow.  With the upper level temps tracking ocean temps, 850 mb temperatures frequently drop into the -2 to -6 range bringing plenty of mountain snow while the valleys see warmer average temps than Dec. and Jan. since early-spring maritime air is warmer than mid-winter continental air.

Had six trees down across our road, and power lines hanging at eye level in two places.  Unfortunately the car is trapped in until the power crews make it out there - hopefully later today.

Up to 39 with sun peeking through.  Trees releasing their snow and ice loads.

How is your hot tub heated if you lost power? It can be a mess with heavy ice.

Wood-fired hot tub.  Kept it hot all through the winter storm.

Waiting for the warm up still west of Philomath in the woods. Lost power at 6 last night in heavy freezing rain. Eerie to sit in the hot tub listening to mature Douglas firs crashing down every few minutes without a breath of wind. Still hearing the occasional crash this morning. Tree just missed our house and car, so far no property damage.

Got about a quarter inch of ice accumulation at our place W of Philomath.  Up to 33 now and am thinking we will stay above freezing from here on out.  Could still be surprised.

Semi-freezing rain west of Philomath.  Temp of 31 degrees.  Not accumulating substantially on elevated surfaces.  Liquid puddles forming over hard snow crust.

I'm not sure I'm buying the all-day ice idea that both the NWS and KMartin are supporting for the south valley.  Every one of these systems has warmed us a few degrees, from 20 up to 27 yesterday and from 26 up to 31 today.  It's true that we won't have much in the way of southerly flow to scour out the cold air, but we won't have much in the way of northerly flow either.  We only have two degrees to go, and diurnal heating ought to do the trick.  If I had to guess I would say EUG and Corvallis should be above freezing by noon tomorrow.  PDX and areas under gorge influence, or areas farther north, could well see a real ice storm.