Impressive early-season atmospheric river in NorCal & Pacific Northwest; some early thoughts on coming rainy season

Filed in Uncategorized by on October 11, 2016 2,760 Comments

Remnants of Typhoon Songda to bring powerful Pacific NW storm

Infrared satellite imagery showing category 4 Super Typhoon Songda over the West Pacific. (NOAA SSD)

Infrared satellite imagery showing category 4 Super Typhoon Songda over the West Pacific. (NOAA SSD)

Much of the West Coast of North America is about to experience a rather impressive, prolonged period of stormy conditions over the next 7-10 days. Multiple intense and high-impact storms are likely to affect coastal areas from southern British Columbia to the northernmost reaches of California, with more modest rain and wind likely as far south as the Bay Area. As is often the case during autumn storm events, there will be a fairly sharp north-south rainfall gradient across California over the coming week–with the far North Coast potentially seeing upward of a foot of rainfall while the SoCal metros (including Los Angeles and San Diego) receive little if any precipitation.

 

Minor weather tangent: West Pacific tropical remnants & West Coast storms
This unusual (but certainly not unprecedented) burst of autumn storminess can largely be attributed to the injection of moisture and energy into the Pacific storm track by present Super Typhoon Songda. Tropical cyclones in the warm West Pacific can occasionally “recurve” from their predominantly east-to-west trajectory, veering northward and then eventually eastward as they approach the active west-to-east storm track region and associated upper-atmospheric jet stream. Such recurving cyclones can affect West Coast weather via one or both of two possible mechanisms–either by strengthening and “extending” the East Asian jet stream further eastward over the North Pacific basin or less commonly by transitioning into a “hybrid” extratropical cyclone and arriving largely intact (but in weaker form) in the Pacific Northwest. In the present case, it appears that Songda will do a little of both–strengthening the overall storm track and persisting as a powerful remnant surface low as it treks eastward across the Pacific.

The path of Typhoon Songda's remnant surface low can be traced for thousands of miles across the Pacific! NCEP via tropicaltidbits.com

The path of Typhoon Songda’s remnant surface low can be traced for thousands of miles across the Pacific! NCEP via tropicaltidbits.com

It might be a bit surprising to learn that former West Pacific typhoons can have such a profound influence upon West Coast weather. But history suggests that there is a relatively narrow window in autumn–mostly during the month of October–when a rare confluence of events can produce truly extreme storm conditions. One of the most significant California events of this kind in recent memory occurred in October 2009, when the remnants of Typhoon Melor re-intensified as an extratropical cyclone off the coast of Northern California and brought extraordinary rainfall and damaging winds to a wide region. But even the 2009 event pales in comparison to the incredibly destructive Columbus Day Storm of 1962, which drew its energy from the remnants of former Typhoon Freda. The so-called “Storm King” brought winds well in excess of 120 mph to much of coastal Oregon and near-hurricane force winds from the California border to Vancouver, BC–an event that would be even more disastrous today, given the large increase in population and human infrastructure that has occurred in that region since 1962. Fortunately, as disruptive as the upcoming event may be in Washington and Oregon, nothing even close to the magnitude of the 1962 event is anticipated.

 

California impacts: Very wet and rather windy north; SoCal misses out (again)

7-day ensemble mean accumulated precipitation totals from GFS, showing a range from 7-10 inches along the North Coast to less than a 0.25 inches in SoCal. (NCEP via tropicaltidbits.com)

7-day ensemble mean accumulated precipitation totals from GFS, showing a range from 7-10 inches along the North Coast to less than a 0.25 inches in SoCal. (NCEP via tropicaltidbits.com)

Northern California will probably see some hefty rainfall accumulations over the next 7 days as a series of storms take aim at the west coast. While the heaviest rainfall and strongest winds with the upcoming storm series will be focused at the Pacific Northwest, the northern third of California will experience periods of intense precipitation and strong winds through the next 5-7 days. In fact, a very impressive atmospheric river associated with the remnant moisture plume from Songda will extend clear across the Pacific Ocean by Thursday. Recent atmospheric model forecasts suggest that the amount of atmospheric water vapor transport during that portion of the event could exceed record values for the month of October over most of NorCal–a striking statistic, although it’s worth noting that October records are considerably lower than those during our peak rainy season from November-March. Moderate to heavy rainfall may occur as far south as the Bay Area, and light rainfall somewhat further south than that. There is a chance of some light rain in southern California, but at the moment it does not appear that areas from Los Angeles southward will see appreciable rainfall.

GFS simulation depicting remarkably elongated atmospheric river stretching from the Pacific Ocean near Japan to the far eastern Pacific near California. (Scripps)

GFS simulation depicting remarkably elongated atmospheric river stretching from the Pacific Ocean near Japan to the far eastern Pacific near California. (Scripps)

Winds will be strong and gusty in NorCal, especially along the North Coast. But, for the most part, the more damaging conditions will likely remain north over Oregon and Washington–where gusts in excess of 70-80 mph are entirely possible.
Rainfall of the magnitude that is expected to fall along the North Coast could lead to some flooding problems, especially since the first round of intense rainfall will be followed by another later in the weekend. Further south, it’s likely that even relatively heavy precipitation will be absorbed by the extremely dry soils without too much trouble. “Season ending” rainfall–enough to dramatically reduce wildfire risk–will likely occur this week over most of Northern California. Rainfall in central California will probably be enough to temporarily reduce fire risk, although the southern 2/3 of the state likely won’t see season-ending rains in the next 10 days. All told, this series of early-season systems will likely bring more benefits than hazards to drought-stricken California.

 

Latest thoughts on the coming winter: another north-south split?

The NMME is suggesting a north-south precipitation split is possible in California this winter, with dry conditions possible statewide later in the season. (NMME/CPC)

The NMME is suggesting a north-south precipitation split is possible in California this winter, with dry conditions possible statewide later in the season. (NMME/CPC)

Despite the promising start to the rainy season this week across NorCal, longer-term signs for the coming winter are decidedly mixed. La Niña conditions are no longer officially expected to occur, but the East Pacific nonetheless remains marginally cool, and a vast swath of the North Pacific from the western tropics to the northeastern extratropics remains exceptionally warm. The most recent forecast from the North American Multi-Model Ensemble (NMME) is suggesting that persistent West Coast ridging may return this winter–but not necessarily to the total impediment of NorCal precipitation. Interestingly, the multi-model ensemble is hinting that last year’s north-south wet-dry split could continue, along with relatively warm conditions–with SoCal remaining fairly dry and NorCal remaining a bit more of a wildcard (could be wet or dry, depending on how persistent the ridging ultimately becomes). With the ever-present caveat that accurate seasonal forecasts for the West Coast remain elusive, it will be interesting to see if the general spatial patterns showing up in these long-range model simulations ultimately come to pass. Stay tuned!

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  • craig(Big Sur/Carmel Valley)

    Good potential for widespread convection/thunderstorms in the pre-frontal zone off the s-central CA coast ahead of our next system IMHO. https://uploads.disquscdn.com/images/ba97a546eb529f4235af84d5083e6f66b985868a64472282ab1637a7198cacdd.gif

    • SoCal Al (El Monte-SGV)

      Oxnard seems to be coming around to that idea. Hopefully, we all can get on the action this time:

      .SHORT TERM…(Tngt-FRI)

      The upper level low pressure system lifts well north of our region during this time frame, but the 90kt southerly jet slides across southwest California overnight. Very deep precipitable water values are expected with this system approaching 1.6 inches along the coast which is near historical records for this time of year. Model data suggests 3-hour rain amounts around 1 inch and there will be MUCAPE values over 400 j/kg with strong forcing along the cold front Thursday night. This leads us to believe there will be period of moderate rain showers with embedded heavy downpours associated with thunderstorms.

      • craig(Big Sur/Carmel Valley)

        We could see some serious gully washers outta this especially if thunderstorms develop in lines and train sw to ne over the coast and coast ranges.

        • SoCal Al (El Monte-SGV)

          For sure, especially with historical 1.6 inch PW’s and being on the left front quad of the 90kt jet…..wow!

          • craig(Big Sur/Carmel Valley)

            That is amazing…and rare, wow. I remember a storm in Oct 1987(or 1988) that was similar to the way this next storm appears to be setting up with the jet dynamics and a draw from a remnant tropical system. That storm produced a night long thunderstorm event and 4 inches of rain in the Big Sur area.

    • Looks like NCEP added some color to help this one model. 🙂

  • Thor

    The sun is starting to break through in Marin. It stopped raining about an hour ago. 24hr totals ending an hour ago (2pm) are pretty impressive. 2.87 for Mt Tam, 1.93 near me…and yet San Francisco barely a .10 of an inch not even 20 miles away. http://www.cnrfc.noaa.gov/county_precipMaps.php?group=marin&hour=24

    Not a bad way to start the week especially with more on the way.

    • SoCalWXwatcher

      ”Forecast models are not all that good in handling tropical moisture influx in this part of the world. So no doubt they will be playing catch up as time gets closer and the timing becomes more clear.”

      ^Part of the reason I think the forecasted rain totals for SoCal are probably underestimates.

      ”Height Rises to provide warmer days and a bit of a break in the wind”

      ^ I can picture Beavis & Butthead having fun with that quote.

      • RunningSprings6250

        Hehe hehehehe hehe hehe hehe

      • DelMarSD

        Agreed. December 2014 was one such instance. Post frontal thunderstorms interacting with copious moisture led to huge amounts of rain falling in San Diego. The total was 4.5 inches for December 2014.

        • SoCalWXwatcher

          I remember that storm well. NWS Simply could not anticipate how much enhancement would take place from the subtropical “slug” of moisture coming up from West of Baja.

          • SoSoCal

            Fingers crossed that happens down here in South San Diego. The anticipation is fun, in any case.

      • SoCal Al (El Monte-SGV)

        Butthead: Huh huh huh…..he said. “break in the wind”…huh huh.

        Beavis: Oh yeah….heh heh heh……..”poop”… heh heh heh.

      • About all the NWS can do is broad brush it. It then it all falls in one area.

  • 961ElNino

    The people working out of the San Diego office are really downplaying the Thursday/Friday storm…

    • RunningSprings6250

      They’re being realistic with the trend towards the goods being delivered mostly north of LA county. Still forecasting up to 1.5″ here in the mountains and San Diego only forecast TR-.03″…who knows though…

      • 961ElNino

        Yeah after the botched forecast they gave with the Sunday/Monday storm I will wait and see ?

    • SoCal Al (El Monte-SGV)

      I believe Oxnard and SD offices did a “swap” of personnel for training purposes.

    • weathergeek100

      Well, it certainly doesn’t look bright for san diego county…..as the models are showing.

    • Tyler Price (Van Nuys)

      NWS Oxnard/LA are is still calling for
      Widespread .50-1.0 inch rain totals.. I think IMO there will be several
      Metro locations that report
      Over an inch. Valleys/foothills could easily pull off 2 inches.

      • SlashTurn (Santa Barbara)

        Santa Monica Mts should do very well with this flow.

      • RunningSprings6250

        Which means back to normal! Yay!

  • SoCalWXwatcher
    • RunningSprings6250

      I like that green blob over me with a direct connect to Seymour.

    • I pick this model as the winner.

      • Yanet Garcia (NYC, USA)

        I am first runner up!

  • Barney

    Mt. Shasta is having one helluvah an October: http://forecast.weather.gov/MapClick.php?lat=41.4093&lon=-122.195#.WA_0Vy0rKM8

    And the north coast is about to get nailed yet again. I’d love to see some monthly totals for say, from Mendocino to Crescent City or so.

    • thebigweasel

      We are indeed. I’m back in McCloud briefly, and we’re closing in on ten inches for the season. The forecast suggests we could be at 25 or even 30% of our annual average by November 1st, which is usually when our wet season begins.
      It’s a jarring change from Santa Barbara, which is so dry even the eucalypts are starting to die. I did a hike around the botanic gardens with my wife the other day, and it was jarring. It’s usually pretty dissicated this time of year, but even the desert area was showing signs of stress.
      I’m heading back down Thursday, and hopefully I can bring some of the rain with me. The forecast is optimistic–1-3″ for SB over the next week. Let’s hope. We got .2″ last week, and you could just about hear the vegetation exhale…

      • RandomTreeInSB

        Did a hike at Stevens park last weekend, I noticed even some old oaks are dying.

      • SlashTurn (Santa Barbara)

        You’d be surprised how resilient this land (Santa Barbara) is. Yes, many non native (and native) species are dying off, but these coastal live oak riparian front range canyons have been through these cycles for long periods before and will survive and thrive into the future. We are due for a good wet cycle…

        My concern is humans and the unsustainable habits of pumping groundwater for the irrational growth of populations in the region.

        • SoCal Al (El Monte-SGV)

          I used to fish Lake Cachuma a couple times a year and it’s so sad to see the water levels now. I read an article which said it’s at 15% (?). Such a terrific place to camp and fish, just hope we get a AR pointed right at Santa Barbara and Lake Cachuma, of course without the hazards that go with heavy rain.

    • Boiio

      Glacier food!

    • CHeden

      See my post above.

  • rob b-Truckee/East Bay

    Some fun facts about rain in Halloween from Jan Null

    https://twitter.com/ggweather/status/791071799400239104

  • Tyler Price (Van Nuys)

    One things for certain in my opinion: thunderstorms ? will be numerous, even more so than the last. Better dynamics, surface low and upper-level low involved, very high PWATS will get entrained into all of CA, CAPE will be higher along with Lifted Indexes being lower.. SLO will probably be the bullseye for the center of the “firehose”. High PWATS will sweep through all of SoCal though there after.. so even if SoCal doesn’t get prolonged rain.. I believe that IMO there WILL be a prolonged period of showers and thunderstorms happening in SoCal with convective skies above. ????? The winds will make it even funner! I bet it will feel more like Florida for a day than California.. AFAIK there won’t be any dry air in the lower levels to battle with a moisture laden atmosphere from top to bottom (850-700 mb and up! To 500 mb) probably because the surface low will help to steer lower level moisture up from the sub-tropics.. & tropics?? Hurricane Seymour is now a category 4! Hoping it picks up some forward speed and starts it’s northward plunge with full speed ahead! It’s slowed down a wee bit for the time being probably because it’s become larger in size and intensity.. anyways I’m rambling on this is my analysis though.. hope it makes sense! 😉 Here’s some
    Images I’ve attatched to piece it all together.. 850 mb RH along with 850 mb PWATS which shows even 1-1.5 inch PWATS, & last, but not least! 500 mb RH which clearly shows abundant warm moist air getting pulled into all of CA much more so than the 850 mb graph near the surface. 500 mb RH is confirming the idea that a lot of moisture is still going to get pulled into the closed upper-level low from Seymour! 🙂 anyways can’t wait to see how this all unfolds! So happy that weather has begun to get exiting again finally! ??????? https://uploads.disquscdn.com/images/6694c6d5a4e7cde07d427d8a229082c2d2c645f65b1c8ee68a4ae430904d6d5b.png https://uploads.disquscdn.com/images/e826954a8e89a9c0495688e9d6074f1b7e66ac7fe365408b08b2bafcc76c33a9.png https://uploads.disquscdn.com/images/5590e85cf161ddb562630f38fdba194f83817f96f905a7b0efbe68c31e7b37b5.png https://uploads.disquscdn.com/images/a8f29b56c923664e52bb1b33544c43b1a13f35bd659eb0d74577793b1995a6aa.png https://uploads.disquscdn.com/images/10a6a19c13dbea5c005dde968d5a028fa6db0e7b9afa3a5b1894ae6200fe8a77.png https://uploads.disquscdn.com/images/e3b5be2c4aa4f5224400217a6fd83a7708f4b4d4bb63d88382af24638a2383f1.png https://uploads.disquscdn.com/images/23286b439faeedefbfb1df0713be6d34865175707ab9cc560e652c395e496af3.png

    • Tyler Price (Van Nuys)

      Forgot to attatch hurricane syemours new track and intensity.. GO Seymour! GO! Full speed ahead!! If the surface low becomes a little stronger it will help to increase syemours forward speed IMO. https://uploads.disquscdn.com/images/bd35358baa2b5c6e2a549477c2277b483cbf8cf8d45301df80ad3b93ba8d80dc.png

      • SoSoCal

        Enjoyed your post! Hope this over-performs for SD County. NWS doesn’t sound too optimistic. They did mention 1.4PWATS in the last update so this could get interesting. 🙂

        • DelMarSD

          Yeah, moisture doesn’t seem to be the problem. I just hope some of the better dynamics make it this far south.

    • CHeden

      Nice synopsis, Tyler! Hope the convection yer mentioning comes down as you’ve projected.

    • You did all of this on your ? ? ? ?

  • Boiio

    What was supposed to be a .25-.5″ storm ended up dropping 2.93″ here is San Rafael! I think we were in the sweet spot when the front stalled last night. We now have a really good chance of finishing the month of October with 25% of our annual rainfall already in the bucket. At this pace the MMWD reservoirs will be spilling by Thanksgiving!

  • CHeden

    Some pretty impressive 30-day rain totals in NorCal. Most of the key watersheds did really well.
    https://uploads.disquscdn.com/images/c6a0a306b8a268adcd51fda6cfb870f9d65e51da7f09cd845844c5bd4b49cdd2.jpg

    • Barney

      Great graph, thanks.

      And more to come over the next several days.

    • Bombillo1

      Big Bend is now at 12.15 for October, and counting.

  • SlashTurn (Santa Barbara)

    GFS operational runs have been (to me) remarkably consistent this transitional (summer-fall) period. Not deviating much from its course. I’m impressed.

    Although the trough is much more to the west right now and lacks the subtropical influence, this frame was from a run on 10/14…For the past few years it has been rare to see this uniform character, even in the middle of winter…

    https://uploads.disquscdn.com/images/966b22b4711ba0f95b57e0e554dde9236edeb95aa4e16a13b6ff226fa66b412f.jpg

    • Barney

      I agree, so far so good this year. But I’m jaded and I inwardly scoff on a daily basis at the daily runs. But again, they have been very impressive the past few weeks.

      • FolsomPrisonBlues

        I think we have all been conditioned to accept the worst by now. Hoping this trend continues though.

  • Dan the Weatherman

    0.45″ fell here in Orange with the Sunday / Monday storm. I thought that with the duration of the event and the brief heavy showers, the total would have been a bit more. This is a good amount for an October storm, though, and I am really looking forward to more rain later this week!

  • Powerful winter storms of 2016

    seeing all this rain early is grate news but what would be more good news is when we start getting some colder storms with snow down too 4000 too 5000ft and not snow above 7,000 too 9,000ft i would like too see us start building some snow pack in the mts

    • Barney

      I think we will start building on Sunday.

      • FolsomPrisonBlues

        Agreed. I know it is possible to get lower altitude snow, but we are still only in the middle of fall. This storm coming over the weekend though looks deliciously cold!