Mallow Posted January 8, 2011 Share Posted January 8, 2011 There will be a significant snow event in Western Washington and Oregon next week, starting around Wednesday-ish. The overall pattern, consistent across all models/ensembles, is for the cold northern jet to converge with the moist southern jet right over the Pacific Northwest. The devil is in the details. Several low pressure systems are expected to form over the Pacific and track eastward into Washington and Oregon. Very cold air is in place in BC, and cold air is also in place throughout the Pacific Northwest, including (crucially) east of the Cascades. As the first low approaches, it throws moisture over the cold airmass in place. 850mb temperatures start well below 0C, and surface flow is out of the north in Seattle and east in Portland. Therefore, the precipitation will begin as snow everywhere. As the series of lows quickly progresses eastward, some of the waves will develop more than others. One such wave, expected to arrive on Thursday, is forecast by many models to travel further north, almost directly over Seattle. If that occurs, 850mb temperatures will warm well above 0C in Portland in the southern sector of the low. A transition to freezing rain (while winds are still easterly out of the Gorge), followed by rain, is likely in Portland in that case. This is currently the favored solution, shown by the 00z Canadian, 00z and 12z Euro, 18z GFS, and almost all GFS ensemble means. However, the 12z Canadian, 00z, 06z, and 12z operational GFS all have a slightly different solution, with the low forecast to track over Portland instead of over Seattle. In this case, 850s would approach, and maybe briefly exceed, 0C, at the warmest part of the storm. In the former (more likely) case, Seattle would see upwards of a foot of snow in the Wednesday-Thursday time period. Portland would receive about 6 to 10 inches of snow, before transitioning to freezing rain. We would then get a quarter inch or so of freezing rain before going over to all rain. Finally, about 12 to 18 hours later, we'd transition back to snow on the backside of the low, but with not much if any precipitation left. In the latter (less likely) case, Seattle would see generally 5 to 9 inches of snow Wednesday-Thursday. Portland would receive over a foot of snow, changing to ice for maybe 6 to 12 hours (with ice accumulations of perhaps up to a half inch), then back to snow with little additional accumulations. Then, we get a brief break before the next system approaches. Models are still all over the place with this one, but solutions range from another quick snow-to-rain transition for both Portland and Seattle, to all snow if the low tracks to the south. Significant additional accumulations are possible with this next batch of surface lows, but there's still a lot of uncertainty about these. Link to comment Share on other sites More sharing options...
turtlehurricane Posted January 8, 2011 Share Posted January 8, 2011 Thanks for the synopsis, this will be a fun one to watch! Link to comment Share on other sites More sharing options...
Indystorm Posted January 8, 2011 Share Posted January 8, 2011 As I am watching the playoff football game now it is hard to believe Seattle could see a foot of snow in a few days. Link to comment Share on other sites More sharing options...
Mallow Posted January 9, 2011 Author Share Posted January 9, 2011 The 18z GFS ensembles are the worst case scenario for Portland. A brief overrunning snowstorm, followed by a quick transition to rain that never goes back to snow. Link to comment Share on other sites More sharing options...
turtlehurricane Posted January 9, 2011 Share Posted January 9, 2011 The 18z GFS ensembles are the worst case scenario for Portland. A brief overrunning snowstorm, followed by a quick transition to rain that never goes back to snow. We are in the mid-range of the models now so I wouldn't put too much into it. All the energy associated with the system is out over open waters and not being observed well. I've noticed that with almost every storm Madison has gotten this year. Link to comment Share on other sites More sharing options...
Mallow Posted January 9, 2011 Author Share Posted January 9, 2011 Unfortunately, it is now looking likely that the 18z ensembles were right. Link to comment Share on other sites More sharing options...
thewxmann Posted January 10, 2011 Share Posted January 10, 2011 Unfortunately, it is now looking likely that the 18z ensembles were right. yeah, the models really went downhill fast. Link to comment Share on other sites More sharing options...
Mallow Posted January 10, 2011 Author Share Posted January 10, 2011 Bust of epic proportions. I haven't seen one this bad in a long time. Sure I expected things to trend north (worse), but not this bad. Now we may get only an inch of snow (if any!?) before changing over to freezing rain and rain. And the ensembles have gone to crap in the medium range as well. All is wrong in the world of weather! So, with that said... Go Ducks! Link to comment Share on other sites More sharing options...
baroclinic_instability Posted January 10, 2011 Share Posted January 10, 2011 Bust of epic proportions. I haven't seen one this bad in a long time. Sure I expected things to trend north (worse), but not this bad. Now we may get only an inch of snow (if any!?) before changing over to freezing rain and rain. And the ensembles have gone to crap in the medium range as well. All is wrong in the world of weather! So, with that said... Go Ducks! Hey don't worry, the Arctic outbreak was a massive bust too! Link to comment Share on other sites More sharing options...
LizardMafia Posted January 10, 2011 Share Posted January 10, 2011 Bust of epic proportions. I haven't seen one this bad in a long time. Sure I expected things to trend north (worse), but not this bad. Now we may get only an inch of snow (if any!?) before changing over to freezing rain and rain. And the ensembles have gone to crap in the medium range as well. All is wrong in the world of weather! So, with that said... Go Ducks! Good'ol typical Oregon winter.. Think your going to get some snow, only to end up with some liquid sunshine.. ..and yes Go Ducks! Link to comment Share on other sites More sharing options...
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