Slow Weekend

December 29, 2006

Things are looking real slow the next 3 days weatherwise.  Several weak systems move into our West Coast ridge and die a slow death.  Today’s system was amazingly well predicted by models.  Our RPM showed solid rain on the coast late this morning, then brief rain in the western valleys and no rain making it to the Cascades.  Radar loops this afternoon showed exactly that scenario occurring.  It knocked down the easterly pressure gradient from around 11millibars PDX-DLS to only 2 mb.  That gradient should recover to 6-8 mb. again tonight/tomorrow, so the wind will make a recovery, but only in the usual "Gorge-influenced" spots.
2 obvious changes in long-range maps tonight:

1.  Back to active westerly flow along with fast moving waves/troughs…good system comes through Wednesday.
2.  Chilly trough slides into Northwest (and out again quickly) Thursday.  850mb temps on all models briefly dip to -6 or -7.  Most likely a hilltop snow event with strong onshore flow, definitely not a widespread snow producer at sea level.
3.  Wait, I only said two but I thought of another.  Long range GFS in 12-16 day period has tried to send some sort of very cold air our way in the last 3 runs.  This is way out in la-la-land of course but bears watching.  I DID notice that 00z Canadian dumps the cold air out over the Pacific at 10 days instead of down towards us.
Mark


Downslope Wind

December 28, 2006

It’s a windy night across the metro area as our Gorge easterly wind appears to have started as a downslope wind event instead.  Massive increase in gradient this evening to around 10 millibars PDX-DLS.  That was well forecast by models.  But the sure signs of easterly downslope wind are (in my book):  1) I have east wind at my home east of Corbett, that only happens with downslope wind, usually my "east" wind comes around a hill from the northwest.  2) Brightwood has a gusty east wind.  3) Our rooftop sensor just recorded a gust to 34 mph at 10:45pm.  We only get strong east wind at KPTV at Cornell & Hwy. 26 with the downslope winds.  4)  Dewpoints lower at HIO, VUO, PDX than TTD.  If the cold/dry air was only coming out of the Gorge dewpoints shouldn’t get drier as you get AWAY from the Gorge should it?

System approaching may hang together enough for light precip west of the Cascades tomorrow…maybe not, tough call.

Splitting/ridge pattern holds through at least Sunday.  Some models have precip in here by Monday (ECMWF), but new 00z GFS is dry until Wednesday!  I’ll leave any changes to the 7 Day for Drew in the morning.   Or I could just write "Long Term…no Changes" for my NWS friends.  If the Thursday-Friday chilly 850mb temps hold in future model runs it will be cooler than what my 7 Day shows too…Mark


Back to Sun & Wind

December 27, 2006

Rain/snow showers now all finished across the region after dropping sticking snow in spots down to around 1000′.  I had just a trace at 1000′…everything was just a bit white.  Looks like the coldest metro airport temps got was 36 or 37 when the coldest showers passed through around 3-4am.

High pressure at the surface builds directly overhead through tomorrow morning, so a calm wind start to the day with plenty of icy fog.  High then builds quickly eastside tomorrow afternoon/evening.  I notice the MM5 develops a strong gradient through the Gorge between 4-10pm tomorrow evening/night.  10 millibars by Friday morning at least!  Plenty of chilly air too so Friday is going to feel like winter with gusty east wind and highs only around 40 on the eastside of town.  Friday through Sunday should be good for frozen waterfalls in the Gorge too as highs near river level only get up to around 35 degrees at best.  That east wind will be gusting to 60-70 mph Friday in the usual spots out there too…brrr!

Weak system falls apart Friday afternoon as it passes overhead.  A 2nd storm New Year’s eve does the same.  If you look back over the last 4-6 runs of the GFS, it’s obvious the rain keeps getting pushed back in time, as models seem to be slow catching onto a developing split-flow/dry ridge pattern.  I’m not sure if this is a long term trend or just a 5-7 day break from the stormy weather…time will tell.  Stay warm!…Mark


Much Drier Forecast

December 26, 2006

Elongated surface low appears to be just about right over the Coastline at 7:30pm…kind of hard to find on the satellite picture, but the buoy just off of Astoria has gusty north wind now, so it’s on the land side of that.

As the low moves inland we should all (Coast to Central Oregon) see a good burst of west or northwest wind by daylight at the latest, more likely around midnight in the metro area.  Then temps drop quickly with a much cooler airmass filling in behind.  Showers last until just after daybreak and then that should be it.  Most likely the metro area will be mainly dry after 8am according to our model here and the UW-MM5.  Just leftover showers over the west slopes of the Cascades after that.  Cross-sections and other model info seem to keep sticking snow above 1,500′ late tonight and in the morning, so I doubt anyone in the metro area will see snow.

GFS & ECMWF are definitely heading towards splitting/ridging in the 7-10 day period.  Models (especially GFS) tend to try and send weak systems through the ridge too easily, so I’ve taken rain out of the forecast.  Looks like late Friday/Saturday morning and New Year’s Day may be close, but I’m betting we’ll stay dry.  Lots of east wind and cool temperatures the next week as well, especially since we lock in cool air at the surface that moves in tomorrow east of the Cascades…Mark


Christmas Night Rain

December 25, 2006

Back to work this evening, plenty of weather on the maps for us to look at, but it generally comes down to more wet & cool weather for regular folks.  Only the weather geeks find much interesting within the next week or so…

2 things I learned while on a very relaxing vacation at home:
1.  Get a generator if you live in the woods and don’t want to shuttle frozen foods across town everytime the power goes out or bucket water from the hot tub to flush the toilets.
2.  Chutes & Ladder is the MOST frustrating game I’ve played with my little kids, it never ends!  Candyland is boring but more satisfying in the end with a good conclusion.

Wavy frontal band pushing back north over us this evening after staying to the south most of the day.   Radar looks impressive but amounts are pretty small.  Looks like a wave just offshore moves inland tonight to our south.  A much stronger wave our around 138W/40N is forecast to more or less move inland right over NW Oregon tomorrow evening/night.  Not a wind issue really, except easterly wind should pick up over the metro area in the next 12 hours.  No source of cold or dry air to the east, so no chance for freezing rain or snow even in the west end of the Gorge.  Maybe above 500-1000′ east end of the Gorge in Hood River Valley and above The Dalles tonight/tomorrow AM.  After the low passes overhead, and by the way it’s a funny-looking elongated thing, it’s a quick switch to a pretty strong NW wind behind it later tomorrow night and Wednesday morning.  This caught my eye earlier today for a possible lower-than-expected snow event Wednesday morning, but 00z models (including MM5-UW) don’t impress me.  I doubt we’ll see sticking snow below 1,500′.  Colder air settles in Wednesday evening, but by then it’s dry.  So I threw a snowflake into the 7 Day forecast, but that was to indicate some snow in the air, not sticking in the metro area.
High pressure develops eastside Thursday and Friday and one thing I notice is the airmass really dries out.  Dewpoints drop pretty dramatically, especially later Thursday and Friday with east wind, so a cooldown even with a lot of sunshine.
Disagreement on next system, either later Friday or Saturday is most likely.  Could be a Gorge snow or freezing rain producer, but not in the metro area.
I don’t see a sign of arctic air on any weathermap, which is a bit rare (especially with GFS) for the coldest time of year.  Off/on systems and some "splittiness" at times though…Mark


Midweek Vacation Extra

December 20, 2006

Here is a note I sent to a few weather friends last night around 10pm…Too bad I didn’t take the time to put it on the blog too, but hey, I’m on vacation this week.

———————————————————————

I”ve been out of the loop, trying to forget weather for a week while off.  But I just looked at 12z and 00z info and I don’t see how the metro area could get freezing rain tomorrow.

 
1.  Very little moisture at first.
2.  Airmass coming through the Gorge is barely cold enough to get freezing rain to Troutdale.  Corbett is 30 this evening with a dewpoint in mid-upper 20′s.  It needs to be 28 or less there as the precip starts to get freezing rain into Troutdale, at least that’s what I’ve noticed in the past.
 
I’d say 33 for at low at PDX tonight, but a quick rise to 35 when precip starts at midday (00z ETA doesn’t have it here until afternoon).
 
I think this will be a bust.  Just doesn’t look cold enough with precip even arriving at the right time…okay maybe a pocket or two if precip arrives before 10am, but freezing rain needs a sustained inflow of cold/dry air to continue more than an hour, and I don’t see that anywhere other than Troutdale east…
 
Mark

Windstorm in 24 hours!

December 13, 2006

Okay here are my thoughts on wind tomorrow night:

1.  Models all seem to like a landfall somewhere between C. Vancouver Island and NW Washington Coastline.
2.  Taking the GFS/NAM at face value, I would figure maybe gusts to 50-55 mph at PDX and in metro area…hardly a major windstorm, but a nice little winter windstorm.

But once again the MM5-GFS is very insistent on a strong bent-back occlusion swinging through in the late evening or midnight.  The new 00z version even seems to develop a 2nd surface low that skirts around the south side of the Olympics, almost like a "dumbelling" around the initial low.  That really tightens the gradient.  I counted 15 mb PDX-OLM and 23 EUG-OLM.  This is major windstorm material, especially considering the 1000-2000′ wind is forecast to be 60-70 kts.  IF that wind surfaces gusts to 70 mph are likely from PDX north.  I say PDX north because of the tightest gradient up north.  That’s why I leaned heavily on that during the 10pm weathercast.
For those of you on the coast, the southwest wind that comes surging in behind the occlusion is amazing.  MM5 once again shows 60kts sustained surface wind slamming the coastline.  Wow…One other reason is that the whole surface low/bent-back occlusion is moving at 50 mph, which is great for a quick hit of strong wind.
On the negative side, I am worried a bit by the weak surface wind forecast on the same MM5.  Only 20-30kts in the valley even though it’s far stronger just a couple thousand feet above.  Hopefully the model doesn’t know something I don’t.  I’d hate to see gusts to only 45 mph after such a big anticipation of the event.

As for snow, I pretty much covered that at 10:45.  Not real impressed with precip on MM5 for Saturday or Sunday.   Earlier runs had a surface low moving up to mouth of the Columbia, but 00z models a bit sketchy on that.  I feel it’s going to be a pretty quiet weather weekend with snow showers mainly in the hills on Saturday only.  My high temps at PDX may even be 2-4 degrees too cold if we get much sunshine.
Back to mild rain next week..Mark

 


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