It’s late September and still no sign of a soaking rain ahead; but how unusual is that?

The sunshine and warm (not hot!) temperatures have been nice this month.

Blog Almanac
Blog Almanac(kptv)

But now it’s getting a bit weird. Where’s the rain? So far only .05″ rain in Portland, but take a look at how wet our recent Septembers have been

(kptv)

Most of the region has been relatively dry, but the southern half of Oregon HAS seen a nice soaking the past 3-4 days due to an upper level low sending clouds/rain through California and a bit farther north. Look at the areas that have picked up at least 1/2″ the last 3 days

72 hour rain totals
72 hour rain totals(NOAA)

Now in most years the bulk of our first soaking falls in the 2nd half of the month. Take a look at the increase in rain chances as we go from August to November. A bump up in mid-September with about a 30% chance that any one day at mid-month will give us measurable rain. Then you see a 2nd jump in late October. By November we are IN the rainy season with a peak occurring in late November and early December. During that time about 70% of days (on average) will feature measurable rain; a drastic change from that 5-6% chance in early August!

(kptv)

Another way to look at this is: WHEN DO WE GET OUR FIRST “SOAKING” OF THE SEASON?

Let’s consider 1/2″ rain our first soaking at PDX. Notice in the graphic below that in many years it happens in mid-September. For some reason September 17th/18th has been popular lately! Not this year of course. Back in 2012 and 2011 (not on the graphic) there was no soaking until early October. In fact in just under 1 in 5 years that happens. So although it’s not unheard of to wait until October for real rain, it IS not a common occurrence. Then, every couple of decades, the rains REALLY hold off. By that I mean in 4 years (since 1940), Portland didn’t pick up 1/2″ rain until the 2nd half of October. I remember 1987…no soaking until Halloween and the days following. So I suppose the good news is that the rain ALWAYS arrives at some point; it always has by Halloween at the latest.

(kptv)

WHAT’S AHEAD?

The big message I’m seeing on all our modeling is that there’s no soaking in sight; at least through the end of September. Looking at the big picture, this loop of 500mb heights goes from now through the first day or so of October. It’s the 5 day average anomaly…warm colors are higher than normal and cool colors show below normal heights. Notice ridging is dominant along the West Coast through the 5 day period ending around the 3rd of October. That’s about 12 days out in time

(kptv)

If we just take a look at 3 different ensemble forecasts (many runs of the same model), the GFS, GEM, & ECMWF models all have a similar theme…much drier than normal through October 1st. The ensemble averages all give us 1/2″ or less rain through the rest of September (a week from Friday)

THE BIG MESSAGE?

This is one of those unusual years where you need to keep watering through all of September. Many years you can stop earlier in the month, but not this year. Luckily, even in drier years, plants/lawns stop using much water in October as temperatures cool. In much of the region the official irrigation season ends October 1st too.

42 Responses to It’s late September and still no sign of a soaking rain ahead; but how unusual is that?

  1. JERAT416 says:

    I’m calling it already, rain bust. Nobody in the metro area (other than cascade foothills or coast range ) gets over 0.04 inches. I’m tired of being disappointed, so I’ll be cynical instead.

    • Joshua Lake Oswego says:

      There is certainly good bust potential. It’s a weak sauce low swinging in. I’m betting that Eugene to Salem ends up scoring the most in the valley. There is a possibility that some spots could get a soaking. I would gladly take a widespread .25’’. Our vegetation and wildlife need a drink very badly.

      • JERAT416 says:

        If I could control three weather, I would have given the entire west coast a good soaking over several days early this month then just had another month of 70-75 degrees sunny days.

  2. Roland Derksen says:

    After the last really dry September in 2012, we had a warm dry start to October as well through the first several days, before the skies opened after the 9th, and we ended up with 7.90 inches. Perhaps it will be similar this time.

  3. Opie says:

    “The record warmest September at PDX is 68.0, set in 2014. Projecting out, based on this morning’s Weather.com forecast, this September will be 69.6.”

    I posted this on the 23rd, but coincidentally came up with the very same same number this morning.

  4. tim says:

    Models are trending wetter for Portland and dryer for Seattle now with Wednesday system, injoy the wash out.

    • X says:

      Maybe you’ll enjoy the rain for once instead of the state burning down and families fleeing smoke? Is that too hard to ask?

  5. Joshua Lake Oswego says:

    Amongst the sea of amazing warmth and dryness facts of late:

    No high temp below 70 degrees for 98 days.

    Not been below 50 degrees for 127 days.

    <.25’’ of rain in the past 99 day.

    58 out of the last 63 days have been warmer than normal including a streak of 40 in a row.

    Hottest week ever in July, hottest month ever in August, hottest September ever…

    I’m sure I’m missing some.

    • tim says:

      More heat this weekend!, how warm will October be 2014 and 2015 are the warmest on record can we beat that? well see.

    • tim says:

      Josh your outside Portland metro so it should be cooler at night were your at right?. It’s cooler at my house then downtown Seattle most nights because I live in the suburbs.

      • Joshua Lake Oswego says:

        I’m only about 10 miles south of downtown Portland. Lots of tree cover here. I am usually a bit cooler than the PDX station for lows. Much cooler for highs many days. Sometimes 6-8 degrees cooler.

        I have had a few nights in the 40s and a few highs below 70.

  6. WEATHERDAN says:

    Amazingly warm 16 day outlook. Also very dry. Outstanding. Peace.

    • Joshua Lake Oswego says:

      So outstanding. Amongst many other ill-effects, it’s awesome that our native flora is dying en masse due to incessant warmth and dryness.

      • Joshua Lake Oswego says:

        On another note, Wednesday into Thursday is trending wetter for Portland. The problem is that it is still 48+ hours away and with such a narrowly focused bullseye, it almost certainly won’t end up being Portland.

  7. tim says:

    Looking at the models they have back off on the intensity of the systems from previous runs for the first week of October so maybe In November they’ll be more robust.

    • Joshua Lake Oswego says:

      Long range GFS is pretty sexy, albeit very unlikely to verify.

    • Timenators says:

      I remember living in Sherwood(just moved to Redmond, OR in Oct last year) and it was like someone flipped a switch (nice fall weather to RAIN) anytime between October 15th and November 1st. You could almost set your clock by it. No reason to think otherwise at this point

  8. Opie says:

    “With 6:34 to play in Pullman, Washington State held a 34-22 lead on Oregon and it looked like it was time to label the Cougars as full-blown contenders in the Pac-12.”
    At which point I turned off the TV in disgust.

    “Five minutes and 33 seconds later, Oregon was up 44-34.” 🤪

    (Ok, back to weather)

  9. WEATHERDAN says:

    Freezing Level over 14K today another beautiful warm September day is at hand. Peace.

  10. Roland Derksen says:

    I sure overestimated how much rain I was going to get yesterday: only 0.01 inches instead of my guess of 0.40 inches. Oh well, we have one more chance next week on Wednesday or Thursday to see something come down. If not, this will become my 3rd driest September. Meanwhile we’re in a Category 4 drought.

  11. tim says:

    There appears to be a pattern change first week of October but we seen this before for most of September and it ended up being a bust, well see.

  12. Opie says:

    The record warmest September at PDX is 68.0, set in 2014. Projecting out, based on this morning’s Weather.com forecast, this September will be 69.6.

  13. Roland Derksen says:

    The Chance of precipitation here tomorrow is fluctuating- a couple of days before we were forecasted “periods of rain”, then more recently ” a 40% chance of showers” , now it’s up to 60%.

    • Roland Derksen says:

      Just a light shower here before sunrise, nothing else since. Our next chance for any precipitation appears to be the following Thursday- so there’s still a chance this September will be my 3rd driest after 1975 and 1993.

  14. WEATHERDAN says:

    Really cold at Newport today NWS has it at -35!. Also what Rod Hill put on his Noon news report. Don’t these guys check what they put on their graphics? Peace.

  15. Bethany250ft says:

    Hurricane Fiona

  16. tim says:

    Key word is some the problem with models is they break down the ridge too soon and over estimate precipitation amounts, I’m not expecting a pattern change until all models agree a 100% we are also due for a dry October in western Wa as well it’s been years.

  17. Timenators says:

    Based on some models (our buddy GFS) rain and snow in mountains chances increase end of Sept/1st week of Oct

  18. tim says:

    Record highs are out of reach unless models trend warmer.

  19. tim says:

    Another nice warm up nextweek the summer that keeps giving.

  20. Roland Derksen says:

    I’ve seen some wetter than normal Septembers here in recent years, especially last year. So I’m not complaining.

  21. OC550 says:

    Thanks as always for an informative post Mark. To keep perspective, we didn’t need to start watering until late June due to the wet spring. So I guess watering into Fall is just keeping the balance. Glad to see Southern Oregon picking up some rain lately. They always seem to need it.

  22. Late September, early morning lawn watering check list: hot coffee; puffy jacket; flashlight; warm socks. Be sure heat is on in the house before stepping outside as you will want to warm up when you are finished. But I will follow Mr. Nelsen’s wise advise and continue with irrigation duties until further notice!

  23. JohnD says:

    Thank you Mark. Interesting stuff—as always. Guess I’d better pull the garden hose back out!

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