A Cold New Year

December 30, 2010

Temps have dropped like the proverbial rock tonight…PDX had it’s coldest December temp (way overdue) of 28 this morning, then dropped to 26 briefly this evening before a patch of low clouds moved in around 10pm.  I’m confident they’ll pass on and PDX should be in the mid 20s around daybreak.

Easterly pressure gradient just now picking up through the Gorge as a surge of drier and colder air arrived at the east end a few hours ago.  East wind starts blowing in the usual spots the next few hours, then spreads out into most of the Metro area by midday Friday.  The result is actually WARMER afternoon temps the next few days due to better mixing.   Today we had a thin layer of cold air held in by the low clouds; thus the highs only right around freezing.  The east wind is only breezy out in Corbett and the hills above Washougal right now, but it should be cranking the rest of the weekend, and until further notice for that matter.  Split flow or ridging or the Pacific Northwest is going to be dominant through the middle of next week.  Except for the wind and chilly temps, I don’t see any real interesting weather through at least Tuesday.

Just for fun…anyone notice today’s record low maximum?  On this date in 1968 the HIGH temperature at PDX was 14 degrees…the coldest high temperature ever recorded at that location.  The low was 8, it snowed lightly all day, and the east wind was raging.  Can you imagine?  I wasn’t around, in fact I was somewhere between conception and birth.  My parents have mentioned over the years the harsh winter that year that ruined so many fruit trees on their Hood River farm.

Have a safe and Happy New Year.  I’ll be back at work Monday.

Chief Meteorologist Mark Nelsen


2010 Year End Stats

December 30, 2010

Tyler Mode suggested we have a year-end stats post…of course a good idea since it appears no more precipitation will fall in the next 30 hours or so.

How about this:

1. Location

2. Rainfall for 2010

3. Extreme High/Low

4.  Anything else you want to add.

KEEP DISCUSSION OF CURRENT WEATHER ON THE OTHER POSTS PLEASE


Wednesday AM Update

December 29, 2010

Whew…for once things went about as planned overnight, with some of the lowest elevations seeing very light amounts under the heavier showers, and lots of snow in the eastern suburbs up in the hills.  We forecast a low of 34 at PDX, and I was unsure if we’d make it there around midnight, but somehow it did. 

I woke up to 4″+ snow on the ground and it was blowing off the roof during a gust.  Briefly freaked out, thinking it was a forecasting disaster, but then quickly realized it was only up at this elevation.  I think the ZERO to TRACE in the lowest elevations covered it well.  Should have gone a bit higher in the hills eastside though.

Showers taper off today with plenty of sunbreaks inbetween, still a dusting possible overnight tonight anywhere, but the big story is on to chilly weather and really cold east wind New Year’s Eve and Day.  Brrr!

Chief Meteorologist Mark Nelsen


Snow Reports: Your Numbers

December 29, 2010

This post for one subject…tell us how much snow you have:

1.  AMOUNT

2. LOCATION

3. ELEVATION (IF YOU KNOW IT)

Keep all other discussion on other posts please.


Tonight/Tomorrow Snow Outlook

December 28, 2010

Here is what I’m going with this evening (from our Facebook page this afternoon):

SNOW FORECAST FOR LOWEST ELEVATIONS
Steady rain changes to mainly heavy/wet snow after 8pm, could see brief sticking snow in the hills and east of I-205. Unlikely to affect traffic, except up around 1,000′ and far east side (Gresham, Estacada, Damascus, Camas, Battle Ground).
Snow showers off/on Wednesday……ZERO to TRACE accumulations.

SNOW FORECAST FOR HILLY AREAS UP NEAR 1,000′
This includes upper West Hills, Mt. Scott, hills around Gresham etc…
Rain changes to snow late this evening, could stick with a TRACE-1″ towards 10pm-Midnight. Then snow showers tomorrow with TRACE-1″ additional snowfall. No big traffic issues, but definitely so…me snow on roads for AM Commute up around 1,000′.

SNOW FORECAST FOR 1,000’+
This includes highest spot or two in West Hills, Sandy, Northern Clark County Hills etc…
Rain to Snow later this evening…1-3″ on ground by daybreak. Snow showers with another TRACE-1″ during the day tomorrow. Total 1-4″. Above 1,500′ up to 5″ is possible.

But here’s a big issue.  Anything after midnight and through noon will be showery, so I could easily see one spot getting an inch near sea level, while 5 miles away the same elevation gets nothing!  Another reason not to go with the 500′, 750′, 800′ wording that seems to be so popular nowadays…

Chief Meteorologist Mark Nelsen


Tuesday AM Update

December 28, 2010

In a hurry this morning to get a few things done before heading to work…I can tell it’ll be a long day.  Three things pop out:

1.  Snow sometime after 7pm this evening to all areas above 1,000′, probably lower than that far east side of metro area.

Situation this evening is very similar to what occurred November 17th: http://fox12weather.wordpress.com/2010/11/17/a-crazy-weather-night/  This should be fun to watch.

Steady, heavy precipitation as a wave passes by and colder air comes surging in at the surface from the northwest.  In fact no southerly wind but a light north-northwest wind.  Our RPM model shows a changeover to mostly snow in the air even at the lowest elevations, and sticking for sure on the hills.  In this pattern the foothills of the Cascades (and east Valley) are/is favored.  It may even stick in Gresham, Troudale, Camas, Estacada.  Less likely over in the Tualatin Valley as things dry out.  Prime time seems to be 7pm-Midnight.  I can already feel the news freakout…praying that it holds off until 9pm or so.

2.  Precipitation is very close Thursday morning, closer than in previous model runs…could be a dusting?

3.  GFS is swinging dry over the weekend like ECMWF now, we can leave the precipitation out of the forecast.

Chief Meteorologist Mark Nelsen


Monday PM Update

December 27, 2010

Will there be enough, or any, snow to go sledding on Wednesday morning here in the lowest elevations?  Seems unlikely right now, I’d give it about a 20% chance fo “sleddable” snow here in the Valley.  It IS a tough forecast the next few days. 

Apparently we’re back to the usual “will the moisture and colder air mix it up just right” game for the first time this season.  In November we had an amazingly cold blast of air come in from the north and northwest…remember how easily we changed to snow and then a hard freeze overnight that Tuesday?  Then a few times this month we’ve had chilly air in place and moisture arrive over the top of it.  Evaporative cooling dropped temps down enough to bring at least the sight of snowflakes into the city with those. 

But this will be the first time this year (I think) that we’ve been close to snow with the cold instability showers behind a cold front.  And those of you who’ve been on the blog for several years know how frustrating it is to get decent showers coming in from the northwest.  Often the Coast Range eats up a good chunk of the moisture.   The biggest issue is that the cold air in this case is travelling over about 2,000 miles of mild Pacific Ocean water before it gets here…really tough to get snow to sea level in these situations for that reason alone.

Not much happening in the next 24 hours as a juicy cold front sits over us.  A 2nd wave renews the rainfall tomorrow afternoon and evening.  Our 18z RPM had shown steady and heavy precipitation lingering with that wave until the middle of the night tomorrow night as the snow level lowered dramatically.  The 00z version doesn’t show that…it just shuts down the precipitation after 8pm or so.

Our best chance for lower elevation snow will probably be late tomorrow night or early Wednesday morning as the cold upper-level trough slides through.  Models (and satellite) show a vigorous batch of showers passing overhead between midnight and 8am.  I think that guarantees a decent 1-3″ at/above 1,000′, and maybe something all the way down to sea level if the precipitation is heavy enough.  In our favor is no mild southwest wind.  So I’ll say zero to a trace at the lowest elevations, but 1-3″ at/above 1,000′. 

As I’ve mentioned numerous times, the elevation distinctions are approximate, especially with the showery nature of the precipitation coming through.

During the day Wednesday, with sunbreaks and lighter precipitation, temps should rise to around 40 degrees or so.

Thursday morning COULD be interesting, but the mesoscale models keep the moisture to our south as a wave slides down the Coast.   The much lower resolution GFS has precipitation over us, but since we’re at the edge of the precip…we’d be arguing over grid points on that one.  Either way generally dry from Wednesday evening through sometime early next week.  Colder too as higher pressure settles east of the Cascades beginning Thursday.  Not a big blast by any means, but seasonably chilly for late December or early January.

One other weather forecasting issue:  New Year’s Eve and/or New Year’s Day.  GFS has been very insistent in pushing a weak system through the developing ridge overhead.  The system holds together far more on this model than others.  The ECMWF has a full-on split and takes all precipitation to our south.  If the GFS verifies, we would probably have some snow on New Year’s Eve.  At least a trace, maybe 1-2″?  The GFS would also warm things back up to normal quicly either Saturday or Sunday…warmer at least than our 7 Day shows.  I’ve left the forecast dry, hoping for a change on either the 00z ECMWF of 12z GFS.

Chief Meteorologist Mark Nelsen


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