Waiting - for Christmas, for snow.  One we are sure of, the other, well, let’s give it a try.  Challenging forecast to ramble through, so better fill that Mug.  Ready?  

 

Mild conditions across much of the PNW will yield to a much colder, typical December pattern soon.  It will happen in stages.  First, to the relief of many in NW WA & BC, the incessant rains have let up, yielding time to repair, replace, rebuild.  That said, a weak system will move onshore Saturday, ushering in some precip, mainly north of Portland.  As that Low moves SE, colder air will fill in, setting up the chance for snow above 1,000 ft, and a snow/rain mix at the surface north of Seattle.  It will continue mild over Oregon.

 

The next, much stronger storm, will arrive from the NW by Monday morning.  This Low will generate a fair amount of rain & wind for WA & OR; the Coastal Mountains of Canada will likely get a good shot of snow.  By Tue, it will dry out during daylight hours.  

 

Second stage, in a manner of speaking, starts overnight Tue - this one will drop the freezing level rather low, esp over western WA, so expect snow showers mixing down to 1,000 ft by Wed night, and even though showers will diminish by Thu, the freezing level may drop lower still.  Portions of western WA could get some snow in the foothills, although the ground will not be frozen to hold very long.  A weak trough may arrive Thu night Dec 9, drawing in more cold air and dropping snow levels to sea level or very near so in many west side locations, esp north of Portland (or even Salem).  Not a lot of moisture with this disturbance, so rain/snow mixed at the surface will be light on Fri Dec 10; should be all snow in any showers north of Chehalis.  If not foggy in your location, a hard frost is likely Saturday morning, the 11th.  

 

Third stage.  Pooled, cold air over the Gulf of Alaska will sag south even more by Monday Dec 13.  The transition could be Sunday the 12th, with increasing chance for rain as a surface Low moves south along the coastal waters.  If the Low turns inland early (as some model runs suggest), the air mass will be cold enough for very low elevation snow, esp western WA; a few model runs track the Low farther south into the San Francisco area, keeping much of the PNW on the narrow, warmer edge of the broad upper level Low for an extra day or two.  We’ll see.  Rain and showers will persist on/off through Tue Dec 14.  

 

Middle-to-end of the week, Dec 15-17:  Fourth stage: heavy rain over central/southern OR as another push of cold air arrives from the NW.  This one may have the needed cold air aloft to spark SNOW at all elevations from Eugene north.  If not, snow will be everywhere on one’s path west, south, north or east over any terrain over 500-1,000 ft.  Chain time.  A weak series of fronts may push in from the NW, each with enough cold air support to threaten low level snow or rain/snow mixed for all areas west of the Cascades as the week ends.  

 

The weekend of Dec 18,19 is trending chilly, with snow or rain/snow mixed depending on elevation.  Precipitation could be heavy at times, which could drive snow down to the surface periodically.  

 

Second Cup: Various global weather models have been struggling on a consistent solution for the Dec 12-19 period, as we have noted here for several forecasts.  Anyway, we must report that the overall pattern remains on a trend for COLDER air to begin arriving into the PNW from the NW over the eastern Pacific (not from our usual ‘Arctic outflows’ out of the Fraser Gap or Columbia River Gorge).  Snow at the surface in the PNW requires quite a few atmospheric attributes to align just right — a few of these do properly align during the period in question.  We usually lack moisture when the air aloft is cold enough for snow.  The cycle discussed here is right on the edge of ‘cold enough’ while also having plenty of moisture.  We recall December 2008 when a similar combination was charting - and verified.  Will December 2021 be a repeat?  Close call for now.

 

For our California Patrons - heavy rain and surprisingly low elevation snow is possible during the period discussed above.  Be safe!

 

Our quip today reminds us that forecasting is always tough, even for the best of us:  “The phonograph is not of any commercial value.” -Thomas Edison, 1915.

 

 

That’s right, 'The White’ (our affectionately coined term for SNOW) is looking probable for the PNW later in December.  While others may brush aside atypical patterns that extended-range models project, The Weather Café®️ doesn’t hesitate to give Patrons the heads-up and the preparation time needed to get ready for unusual weather events.  Snow, at the surface west side of the Cascades, is, indeed, one of those unusual events worthy of preparation (and fun anticipation, for many).  So, Mug up, Patron.

 

The flooding situation up in NW WA and BC will continue to dominate everything through Wed night this week.  Later Wed, colder air aloft will help ‘hold’ some of the excessive precipitation in the mountains as snow, but still, record breaking rains have sent several rivers above flood stage, yet again.  It will dry out up north late week, as temperatures begin to lower several degrees, esp by the Dec 4,5 weekend .  

 

For a few days this week there will be a ‘zonal’ west-to-east flow of the ‘jet stream' with cooler air over WA (from roughly north of Chehalis) and mild air over OR.  That same flow will train moisture into the far NW, as noted, and keep OR & southern ID on the mild, DRY side.

 

Model runs have generally settled on the first weekend of Dec being relatively dry, as the pattern mentioned above continues.  By late Sunday or early Monday, a relatively strong ‘warm’ storm will move onshore north of Vancouver Island, ushering in a warm southerly WIND and wide-spread rain (freezing level jumps again).  Breezy, showery early Tue Dec 7 - Pearl Harbor Day - then a brief stop in the precipitation late Tue & Wed next week.

 

Now, the interesting transition.  High pressure ridge over the western Alaska (cold up there, with temps in the -35 to -42 degrees F recently), will begin to chill down the air mass over the Gulf of Alaska.  The resulting broad cold trough is modeled to begin approaching the PNW overnight Wed Dec 8.  Current model solutions continue that cold movement all the way south over WA, OR and northern CA as the week of Dec 6-9 ends.  Heavy rain, WIND and a rapidly lowering freezing level will be in play for the PNW.  In fact, by Fri the 10th, the air aloft over from NW OR north looks to turn cold enough for surface snow, esp north of Portland.  If not at the surface, then as least just a few hundred feet above sea level.  Have winter travel gear ready.  Rain over southern OR & northern CA could be quite heavy.  

 

Another pair of powerful Pacific storms may arrive from the NW on Sat/Sun and Sunday night Dec 12.  Initially, southern winds will lift the freezing level for plenty surface RAIN & mountain snow, before turning colder again, with a decent combo of moisture & temperature on the backside of the second storm to drive snow down to near, or at, sea level in many places from Eugene north.  It will be a very windy weekend, as well.  Blizzard conditions for all mountain pass travel.

 

Snow showers, if the whole pattern mentioned above verifies, will continue into Tue night, Dec 14.  Some models solutions set up a strong winter temp outflow from the Fraser Gap and Columbia River Gorge by mid-week.  Any snow is likely to hang around for a few days.  

 

Second Cup:  of course, all of the above is simply a model projection.  However, a cold, possibly surface-snow-pattern has been popping up on the wx models for quite some time now.  A few model runs build a mild High pressure ridge over the west coast, keeping the cold event away from much of the PNW for an extra few days, but none remove ‘The White’ threat completely in the time-frame of Dec 12-15.  Patrons know that over the past 27 years, these long-range projections have been accurate enough to warrant preparations, just in case.  We’ll be a few days closer to said events by our next Mug here, so stay tuned.

 

From an actual Church Bulletin: “On Sunday, a special collection will be taken to help defray the expense of the new carpet.  All those wishing to do something on the carpet, come forward and get a piece of paper."

 

 

Lots of rain will continue to fall over the far NW corner of the PNW; trending drier for the rest.  Let’s go through the latest outlook.

 

From now until late Tue Nov 30, rain & showers will be almost continuous for portions of Vancouver Is, southern BC and the NW corner of WA.  Heed Nat’l Wx Service alerts as to flooding issues.  For SW WA, OR and ID, additional precip is charting for Saturday & early Monday.  Fog & dry conditions are likely to develop by Tue, excluding the far NW.

 

Ponder Points.  Here’s where the models begin to chart a mixed message (happening frequently this fall, for sure) - 

   1st scenario: generally dry and gradually cooler conditions for Wed Dec 1 through the end of next week.  Maybe some showers over the weekend of Dec 4,5, with a N-NE wind developing as cold High Pressure dome drops deep into the heartland, east of the Rockies.  Mild-to-warm (esp for OR) Sunday & Mon, Dec 5,6 before it turns colder with snow teasing Patrons north of Bellingham by Dec 9th.

   2nd scenario: coldest air of the season begins to drop into the PNW, with increasing chance for low level SNOW during the weekend of Dec 4,5.  A Low develops over northern CA, drawing 'snow-cold' air over OR & WA for snow showers becoming likely at the surface.  Ground may not be frozen yet, so accumulations may delay; cold Fraser Gap outflow - strong wind - could set up sometime that weekend, too.  (The pattern for Dec 4-12, 2021 has similarities to that of our very snowy Dec 2008.) Cold wx for much of CA, too, with the 2nd scenario.

 

Overall, both solutions do project our weather turning colder with very low snow levels as the week of Dec 13 gets under way.  

 

La Nina.  We are in a rather COLD La Nina pattern.  The image below (as of Nov 23, 2021) illustrates the cold (blue color) sea surface temperatures from the west coast of South America on east across the central tropical Pacific.  The Pacific Ocean offshore of the PNW is also running colder than average.  This is our second fall/winter with a La Nina pattern in place.  Yes, back-to-back La Nina winters do happen, as this will be the 6th time since 1999.  While not a certainty every time, La Nina winters generally produce more low level snowfall and above average precipitation in the PNW.  As the chart below indicates sea surface temps in the ‘middle’ of the tropical Pacific 0.75 - 2.0 degrees C colder than average.  We’ll see how all this plays out over the next 3 months. For now, be prepared for the chance for low elevation SNOW as the month of December gets underway.  It is probable. 

 

 

 

 

 

 

-Rufus

 

 

 

 

Early Sunday post because the coast is calling - we’ll be spending a few days at the beach before Thanksgiving.  Update, per usual, on Black Friday.  For now, here’s the latest outlook.

 

Weak system arrives later on Monday (north to south), bringing onshore a bit of rain or showers.  By Tue afternoon, partial clearing and morning fog will return in the usual places.  Dry, foggy Wed.  

 

Thanksgiving:  the next system will be the beginning of another rather extended WET cycle, with moderate-to-heavy rain.  It all begins in the north Wed night, as a moisture laden front moves onshore.  Western WA & BC first on Thanksgiving Day, then the system will drape over OR, as well, overnight Thanksgiving.  Black Friday will be a wet Friday to start, drying down by late afternoon.  Don’t put the rain gear away quite yet.  More rain hits Vancouver Is & NW WA by sunrise on Saturday, and making its way into OR by Sunday morning.  This system should not be quite as wet as the Thanksgiving storm.  Still, more rain where is really isn’t wanted at this time.

 

A short break in the action for early the week after Thanksgiving, but the rain returns first to the northern half of Vancouver Is Monday night, and spreads to all the PNW by sometime on Tue, Nov 30.  This storm will be a drencher - from northern CA to BC.  Fortunately for BC, much of the precip will be ‘held’ as snow in the mountains.  Good placement.  WET Wed Dec 1.  A powerful Pacific storm will rapidly move in overnight Wed, bringing WIND (!) and heavy rain Wed night through Thu Dec 2.  Early yet, but models charts a Low pressure center of 974-978 mb making landfall over Vancouver Is sometime Thu night.  If verified, damaging WIND will be likely over some portion of the PNW Thu night.  Freezing levels drop Fri morning after the strong cold front passes.  Frosty Sat Dec 4, if the sky clears in your area.  

 

What was earlier modeled to be cold, low-snow-pattern for the first weekend of Dec may be delayed, as models are mixed - could be wet and mild, with plenty of wind that weekend, or continue to the colder wet side, with snow levels falling through the weekend, on into the following week. 

 

Bottom line - early Dec should be chilly, with mountain snow and the chance for snow at the lowest elevations of the season.   For now, the parameters we discussed last time are still showing on the charts for early December — 'snow cold' air mass over the Gulf of Alaska & eastern AK & the Yukon, setting up strong Pacific storms for the PNW, along with colder conditions as the month unfolds.   It will be interesting to watch what actually develops. (We postponed the La Nina discussion until Fri.)

 

 

 

A pleasant weather weekend ahead, which is good news for cleanup & repairs from the flooding in the northern areas of the PNW.  Grab your morning beverage.

 

The break in rainfall will last through this weekend; Sunday will be the warmest, with plenty of sunshine after a possible frosty morning in many locations.  The next damp system is not due until later on Monday.  Even then, it will not be a heavy rain producer.  In fact, it could be more of a cloudy pattern, than one with lots of precip.  The weak Low will move into CA, ushering in some clouds & showers for the Golden State on Tue.  We can expect our weather to begin drying out dry on Tue, from north to south, as the Low drifts over CA.  There will be a wetter front moving into the PNW late Wed on into Thanksgiving.  Higher amounts of precip will fall over the NW corner of WA & Vancouver Is.  Showers on Black Friday.

 

The post-Thanksgiving weekend is trending moderately wet & breezy yet again, as another front sweeps in on Sat.  Similar to the previous front, the heaviest precip will be north of OR.  Timing may vary somewhat, as model projections have been indicating a VERY WET pattern returning to the PNW after Thanksgiving.  Some solutions brought back heavy rain during that weekend, others hold it off until during the week after Thanksgiving.  Either way, the relatively ‘calm’ weather in store for the PNW over the next 7 days will be appreciated & needed given the extended outlook.  

 

As November ends and December begins (week of Nov 29 - Dec 3), we may be in for heavy rainfall, WIND and the coldest storm fronts of the season, to date.  Each very wet front that arrives that week will progressively be colder & colder.  In fact, by the end of that week, the PNW could be seeing 'The White' in many low elevation locations, even teasing valley floors.  “There you go again”, some Patrons may be thinking.  Well, there is that possibility.  Sip on.

 

Ponder Point:  By late November, we see indications that a COLD High pressure dome may begin moving from NE Siberian on over Alaska and the Yukon. Will the high pressure increase to our ‘trigger’ range of 1040+ mb?  We’ll see.  Anyway, this cold air mass is charting to drop temps over the Gulf of Alaska and the interior (winter pattern), with subsequent support for strong Pacific storms over the PNW.  Each of those storms may bring colder air over our region.  This is similar to Dec 2008, if it actually develops.  For now, this is merely a projection, but one that could present low elevation snowfall that so many mention as an attribute of a strong La Nina winter in the PNW.  We are, indeed, in a cold La Nina pattern (we’ll present details on Monday).

 

Beforehand, the wet week after Thanksgiving will be quite wet, but with one key benefit relative to last week’s horrible flooding - the lowering freezing level will “hold” much of the precipitation in the mountains as snow.  (The freezing level was well over 8,000 ft in the last major rain event.)

 

The weekend of Dec 4,5 is trending either very WET with snow lowering to the footlhills, or generally wet with snow/rain mixed at the surface, turning to all snow late Sunday the 5th (esp over much of western WA).  Review the Ponder Point above as to why.  It will be interesting to see what  Nature actually does.