good chance for some arctic air to pay WWA a visit

Some interesting features in the jet stream are on deck for this weekend and early next week which will invite some arctic air into the Puget Sound lowlands / WWA.

The perpetual west coast ridge and central/east coast US trough continue to hold fast, but some changes in the upper-level pattern over Russia will begin to affect things downstream leading to a retrograde of the amplified pattern.  The cold arctic air has continually been sliding just east of us on the other side of the Rockies but it looks to reach WA this time as the trough retrogrades and a positively tilted short wave provides the offshore oomph aloft to help push the arctic air west.







The strong polar jet over eastern Russia is beginning to split into a northerly and southerly branch (a sign of spring). The ensembles all have the northern branch, with a strong embedded 150+knot jetlet, take a trip over Alaska and dive south along the west coast. This feature helps retrograde the North American trough and supports a positive tilt short wave impacting WA Friday ....  all ensemble support this feature, although the magnitude and timing is slightly different from run to run.





Friday night there is high probability that an arctic front will pass south through the Fraser river gap. Moderate chilly winds will arrive Friday night but last only a day or so.... the air won't be that cold, but there is possibly a chance for a flurry or two Friday night around Skagit/Island counties and possibly along the northeast  of the Olympic peninsula.

A second short-wave arrives Monday night and may be more interesting ... several of the ensemble runs and the ECMWF support a quick pulse of arctic air.. a bit colder and a bit more lift/moisture than the first feature.  However, ensemble spread is higher for this feature.

Both of these features are rather weak for an 'arctic blast' event and are quick lived ... the air won't be that cold (it's almost March!) and the pressure gradients aren't too extreme. However, both could result in a period of gusty winds in the NW interior especially in W Whatcom County, and possibly some light snow along the frontal boundaries and north Olympic peninsula.

weather for coming week - wow...

 The next week looks to be dry and warm as the persistent ridge continues to hold firm to the west coast. Conditions will be quite spring-like early and mid week followed by a chance of light rain early in the week.

The ridge amps up Tuesday - Wednesday with thicknesses approaching 560 dm (shown below)!
This is some very warm air for this time of year and will result in surface temps possibly in the 60s (record highs) this week.

 

forecast for Timberline Lodge Feb. 16 - 22nd.

Hi, a friend has asked for a quick forecast for Timberline Lodge on Mt. Hood from Feb. 16-22nd for an upcoming possible ski vacation.... decided to post my forecast here:

First, the forecast is for the ~9-15 day range (216-360 hour) range ... deterministic forecasts at this range will tend to have high uncertainty, so the best approach is a probabilistic forecast based on the ensembles. But, it would also be useful to take a look at the preceding weather to get a feel for the snow.

First, let's take a look at the GFS and ECMWF operational runs for this period:




Both the GFS (7-day shown above) and ECMWF insist a pretty solid ridge will dominate the west coast after our quick brush with the 'wind-storm' on Monday.... looks really bad for snow as we dry out and upper-level temps approach summer-like levels.... snow levels look to reach 10k+ ft. and stay that way the entire week before we reach the timeframe of the ski trip.... sorry!

Both models continue to keep the ridge frozen along the west coast through the 9-12 day range. GFS MOS keeps temps and snow-levels high the entire time also

Now, let's look at the GFS ensemble (below): at ~216 hours almost all the models support the strong west-coast ridge (and model spread was fairly low up to this point). Only 1 member shows a flatter ridge, but still with pretty warm upper-level temps. A few embedded short-waves occur sporadically in the 190-220 hr range, but too warm and too far north to really help with the snow situation.


http://mp1.met.psu.edu/~fxg1/ENSPRS_12z/ensloop.html#picture

From 216-240 hrs, the solutions begin to diverge from each other radically. The strength and position of strong surface and upper-level Lows in both the Gulf of Alaska (GOA) and along the East coast varies... these beasts ultimately have a lot of influence on the change in upper-level patterns at this point, so predictability remains low after 220 hrs. 

A number of the runs in the 220-300 hr range bring the GOA Low further west, helping to flatten out the ridge and lower thicknesses. A few of these really take off and build a positively-tilted trough which would possibly be great for snow levels and Mt. Hood snow... but these are the outliers. About half the runs are favorable for Mt. Hood snow in the ~300-360hr range. The other half provide a random assortment of various amplitudes of ridging.  Uncertainty is really too high to get a good picture of the wx over this period, though the odds say that conditions will be improving over  those of the 150-200 hr range.




The CPC supports the above-normal temps also:



In conclusion, the snow looks pretty crappy at the beginning of the 'ski vacation' period.  There are fairly good odds that things may improve near the weekend of Feb. 21-22nd, but it is just as likely that they will not.

Sorry!  This has been a pretty poor winter for west coast mountain snow so far.

 the 'atmospheric right hook' has hit us hard the past 48 hours --- a strong jet stream supporting the advection of a lot of moisture into our area. Right now, things are primed for continued heavy rain and storm development:  lots of warm/wet air arriving from the south, strong jet streaks, and a very cold chunk of arctic air just sitting north of us.

 

These conditions are ripe for developing a strong Low right off the coast, as the models predict will occur Sunday night into Monday... though not quite a 'meteorological bomb' event, and not quite aimed along the 'sweet spot' track for Puget Sound windstorms, the storm will pack a punch to the Oregon and Washington coasts.  The storm forms rapidly Sunday, supported by 140-knot jet-induced divergence aloft. The storm drops into the 980s before beginning to fill on Monday as it rides up the Oregon and WA coasts.  The storm is still a few days out and the storm track isn't 'set in stone' given that quasi-explosive cyclogenesis can pull some tricks on its own.