Thursday, October 22, 2015

The atmospheric rain switch is about be flipped

It happens nearly every year.  We enjoy a beautiful and generally dry summer--climatologically one of the driest in the nation.

September is usually sunny and mild, with a few rainy periods that aren't too much of a nuisance.

Then, the first part of October brings cooling, but is often quite mild and not that wet.

But then something happens.  The Northwest rain switch is flipped, and sometime in late October or early November we transition to our wettest, windiest weather.


The worst week of the year?  Amazingly, the last week of November.

It is truly remarkable how quickly our region's weather degrades;  almost like going off the proverbial weather cliff.

And folks, if the weather models are correct, it is going to happen in about a week.

But before I tell you about your sodden fate, let's look at climatology, in this case at Seattle Tacoma Airport.  Here is the probability of getting .01 inch in a day.  Very low during the summer, rising to about 40% in early October, but there there is the major ramp up to roughly 65% during the first week of November. From then on into March we are doomed to moisture almost every day.


But that is light rain.   What about the change of getting say, .5 inches, over a week? (see below)  A huge ramp up between mid-October and the first week of November to about 75%.  Ouch.  And we stay up there for a while.


So, after softening you up with climatology, let me show you some precipitaton forecasts from the National Weather Service GFS model.  During the next few days (through Sunday early AM), we will get virtually nothing, as shown by the cumulative rain during that period.   So enjoy your Saturday!

But prepare yourself.  Here is the forecast for the next 360 h (15 days). Orange is over 5 inches...and that is what is forecast over western Oregon and Washington.  Even northern CA gets rain.


 Now this is just one model and one forecast.  What about the forecast from the many-model NAEFS North American ensemble system?  (see below) The second panel is precipitation. The "whisker" shows you the range of precipitation amount for all the models and horizontal bar gives the median amount.  Rain turns on around Oct 28th. The bottom panel shows cloud coverage greatly increases at the same and the panel above that is wind, which also increases.   Rainy, windy, and cloudy.  Sounds like typical Seattle winter weather.


So enjoy the last week of pleasant, mild, perfect fall weather.  Take your last major hike on Saturday. The models don't think it will last, El Nino or not.  During the next two week we should be making the transition to Northwest winter, first with light rain and then the heavier stuff in early November.

Our weather reckoning is coming.  And the switch is about to be flipped.






22 comments:

Becky said...

Yay!!! Bring on the rain.

granitix said...

I'll roll out the grey carpet for it! Just please don't be like 2001 where every forecast was dry thru day 7 then turning wet by day 10.. that forecast busted for months on end. Climo kept pushing models back to the wet side but the atmosphere refused to play along.

Mark said...

A little forecasting competition between the NWS and Cliff. Will it be a cliff hanger? I'm hoping Cliff is right but granitix has seen this pattern before.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT THU OCT 22 2015

.LONG TERM...
THE ECMWF WAS THE MODEL OF PREFERENCE. AN UPPER LEVEL RIDGE WILL
DOMINATE THE WEATHER PATTERN OVER THE AREA DURING MUCH OF THIS
PERIOD. ANOTHER LOW PRESSURE SYSTEM WILL APPROACH THE REGION ON
WED. HOWEVER...A SPLIT FLOW REGIME WILL PERSIST...WITH THE
SOUTHERN BRANCH OF THE JET STREAM BEING THE MOST ACTIVE. THIS IS
A TYPICAL PATTERN DURING EL NINO EPISODES. THEREFORE...LOOK FOR A
STRONG UPPER LOW TO HEAD TOWARDS CA. THIS WILL PLACE THE PACIFIC
NORTHWEST /ONCE AGAIN/ UNDER THE MUCH WEAKER NORTHERN STREAM. FOR
THIS REASON...HAVE CHOSEN TO CUT BACK POPS FOR WED AND THU. AT
THIS TIME...IT LOOKS LIKE THE BEST CHANCE OF RAIN WILL BE ON THE
COAST. TEMPS ARE FORECAST TO BE ABOVE NORMAL.

Kenna Wickman said...

I need a low Nehalem River level in NW Oregon for some fieldwork November 6-9. So far so good. Cliff, will the rains we get cause any major changes in streamflow or will it be a gradual ramp-up? I am hoping the models are wrong and we stay dry for a week longer.

gs said...

Jeff Renner can save you! Tell him to keep pushing the 'good weather' button!

https://www.youtube.com/watch?v=0ryHqoer8mo

John Marshall said...

Our annual tithe which pays for the perfection we enjoy the rest of the year. Daily rain, wind and cold, accompanied by the loss of daylight culminating in the deep darkness of the winter solstice.

A good time for a retired guy like me to turn on all the lights, stoke the fire, and curl up on the rug before the fire with the dogs to enjoy the warmth. My pack of Labradors, who normally love water and cold, suddenly become house dogs for a couple of months.

That said, first snow at our house (elevated location on the OlyPenfd and prone to snow) is the signal that we're shifting into the good part of winter. Dogs want to be out again and so do I. Rarely before Christmas.

But from now to then, we have to endure and think happy thoughts about aquifer replenishment. Or whatever.

Ashley said...

Cliff: Could you include the web links for some of the model results you report? I can't seem to find the Environment Canada NAESF model runs on their web site.

Thanks!

MBeebe said...

Dr. Mass,

Could you talk a little about the hurricane in Mexico? Is it as apocalyptic as all the new organizations are saying?

-- Mike Beebe

NWBlogger said...

Yeah the hurricane is being described as off the C harts severe.

MNS said...

+1 to hearing your hurricane perspective, Cliff. I bet you're already working on it, but yours was literally the first resource I turned to as soon as I heard all the hype in order to get a data-driven perspective.

soaringbrain said...

What caused such an intense hurricane?

Westside guy said...

Bring it on!

tracksdc89 said...

THANK GOD!! I was literally just thinking how long it has been since our last meaningful rainfall (not to mention seeing sprinklers in action) and thought "hopefully Cliff's blog has some iota of an idea when 'the rainy season' will actually get going." Looks like we'll have to chalk up another "below-normal" precip month (October). Not counting August, how many below-normal months in a row would that be?

tracksdc89 said...

Yes, interesting considering the above map is also from the NWS.. and the NWS VERY RARELY editorializes in its forecasts, but here they do: "once again". That is worrisome....

Mike said...

Please take the rain! It's been sooo wet in South East Alaska this year. I miss the sun. The storm track does start shifting south this time of year and we get drier. Last winter that did not happen and tons of rain was the result. I could use the rain break!

Bob said...

Hole-punch cloud heaven over the west coast today...

http://lance-modis.eosdis.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2015296190000-2015296190500.250m.jpg

(large file)

John McBride said...

I grew up on a small farm east of Seattle and just north of Issaquah. From November to March, and sometimes through April, we had the rains, sometimes for days on end. And that's not an exaggeration. To the south were Tiger and Squak Mtns, and across Issaquah valley, to the west, southwest, was the long, high profile of Cougar Mtn. The storms used to roll over those mtns like waves. We could watch the rain curtains sweep down them and up and across us. There were more than a few times when the rain gauge would have several inches of rain, and plenty when it would collect 4 over a 24 hour period. The low pastures would turn into ponds and, if we were lucky, and a cold spell came sweeping in, the ponds would be turned from duck and geese paradise into skating rinks. A lot of northwesterners get worn out by our winters. Not me. I love the weather here. We drink the Tolt and Cedar, we ski on the Pacific Ocean, and our blood is the rain.

Thank God it's rain season again.

Cliff, a quick diversion: I'm perplexed by reports that describe Patricia as the most powerful storm ever, and that go on to talk about it being the 2nd or 3rd most powerful hurricane recorded. I know, and you know, it's one, or the other. The question is, just what exactly are the parameters of their determination? Your blog, your topics, but if you're inclined, I know you can enlighten us amateurs with inquiring minds. Thanks.

Gpacharlie said...

The competition will be a "Cliffhanger"

Betty Levitin said...

"The "whisker" shows you the range of precipitation amount for all the models and horizontal bar gives the median amount." Horizontal or vertical bar?

lhsouthern said...

Hopefully it will be cold rain not pea soup

Yasmine Galenorn said...

Am SO glad it's rainy season again. I hated this summer--I love the rain and the gloom here. But hoping it will be cold this winter, by some stroke of luck (El Nino or not)...the bugs are out of control thanks to the warm winter last year.

Ansel said...

I was hoping for a few sunbreaks as you hinted at on KPLU on Friday. Instead I went up Sulphur Mountain (up the Suiattle River)and got snowed on- for about ten minutes it was almost a blizzard. There was rain below 6000 few, if only a little.