Amazing Dewpoints!

Only a weather geek can get pumped about some incredibly high dewpoints…but even regular folks can understand how amazingly humid it has been the last 24 hours in the Pacific Northwest.  Sure, it was humid a couple weeks ago, which was very unusual for mid September. 

But now even worse?  Check out some of the dewpoints this evening (a direct measure of the amount of water vapor in the air).  As of 9pm many areas are hitting their highest of this warm season so far.  PDX has hit 67 (not to wildly high), but Scappoose-68, Olympia-69, Tillamook-72!, Lincoln City-71, Vancouver-67, Troutdale/Hillsboro-66, Hood River-66 (very rare).  I could swear such high humidity/dewpoints have become more common the last 4-5 years, but don’t have any hard facts to back it up.  That would take a lot of searching through weather records.  I can say that I looked through the last 6 summers at PDX and only last summer (2009) for a few hours did we hit a dewpoint of 67 & 68 at the end of the heat wave.  The closest to that was a dewpoint of 70-72 during that extremely humid event late July 2006.  So it’s fair to say that this is one of the 3 most humid periods in the last 6 years.

You can see the reason and source for the tropical moisture on this precipitable water loop…I found this on Cliff Mass’s blog:

Looking ahead, some really nice weather on tap for the rest of the week.  For starters, the passage of a wind shift line/cold front tomorrow evening brings the wind around to the north, pushing the deep tropical moisture out of here.  That spells a sharp end of our “sweaty spell”.  Model cross-sections show it really well as well as MOS data.  The the northerly wind turns northeast and easterly Wednesday afternoon through Thursday.  Dewpoints may drop into the 40s as the atmosphere warms up again.  So the last two days of the month should give us a very typical late September warm spell.  Overnight lows should drop down to around 50 in the city as well.

A weak system moves through our warm ridge Friday, but then it rebounds Saturday and Sunday for a nice weekend.  No sign of stormy weather in sight (the first few days of October).

By the way, I should point out that at Kona and Lihue, afternoon temperatures were about the same at PDX, but just slightly more humid, so in the end we WERE much the same as the Hawaiian Islands today!

Chief Meteorologist Mark Nelsen

93 Responses to Amazing Dewpoints!

  1. Karl Bonner says:

    Final message. I’m curious as to whether our current heat wave would have been even hotter without all the humidity, at least during the day. Or would a dry airmass necessarily be slightly cooler aloft than a humid subtropical one?

    I bet this would have gotten us to 90 with drier air and more offshore flow, maybe even 92!

  2. Rob "Wrath" S.E. Portland says:

    Did anyone see tonight’s 00z!? 😮

  3. Rob "Wrath" S.E. Portland says:

    My Fall and Winter Predictions

    Wind Storm: Yes, 2. October 24th and November 19th
    Peak Gust: 62mph
    First Freeze: November 2nd
    First Snowfall: November 30th
    Snowfalls: 9
    Total snow: 33.9″
    Coldest Temp: 7
    Zoomed Water Vapor Maps: 73
    Snowmen built: 2
    Freezing rain days: 4
    # of times I suggest a Low Pressure Center might deviate from its course within 18 hours of landfall: 7,109

    • Boydo3 500' North Albany says:

      That’s good, Rob! And generous too!
      My early guess is…
      No windstorm before Thanksgiving but maybe around then.
      Snow shows up on the surface after Christmas but in the low hills many times before. We get more snow in the valley than Portland this year.
      Flooding will occur after New Years when our first big low level snows get pounded by a pineapple express.
      Another windstorm around Super Bowl Sunday.
      Coldest temps will be early to mid Feb. Low teens or single digits at night for 10 days. And of course the classic transition of snow, freezing rain to rain and another round of flooding. Late February and early March will be raw but late March will kick in nice for a fine spring!
      That’s my official guess! Print it or quote it only giving full credit to Boydo. 😉

    • Karl Bonner says:

      Boydo: “More snow in the valley than Portland this year.” So you’re saying that it will get snowier as you head south down I-5?

      I guess it’s possible: there are an extra 300-500 feet of elevation down near Eugene/Springfield, but at the same time, it’s an extra hundred miles south. But then again, Grants Pass gets a fair amount of snow and it’s less than 900 feet up. Not sure if the snow down there is due to cold air pooling or if the snow levels in southern Oregon really are no higher than they are north.

      The South Valley gets a lot of inversions but usually they get scoured out before the precip arrives. On the other hand, the East (and Central) Gorge are sheltered at the surface from the southerly and westerly winds during winter storms so moderately cold air can get trapped down to low elevations. I imagine that if the mountains to the west and south of Eugene were taller, the South Valley would get a lot more frozen precip. How much higher the mountains would have to be is uncertain, but I bet even 1000 feet extra would make a significant difference and cause at least a mild “Pineapple Shadow.” There, I just coined a new weather phrase!

    • PaulB/Eugene says:

      Windstorms: 2 with wind gusts >50mph somewhere in valley…strongest winds to the N…Eugene peak gust 52mph, PDX 60 mph. First windstorm second week of Nov, second in February (the first one is the stronger one)…storm similar to Hood Canal storm…not Nov 81

      First freeze in PDX: Nov 20

      First measurable snow in PDX: Dec 20

      Cold wave between Jan 7 and Jan 21, then early March 2 day cold snap.

      Lowest high temp @ PDX 18
      Lowest high temp @ EUG 20
      Lowest temp @ PDX 10
      Lowest temp @ EUG 2

      Snowfall: PDX: Nov: 0; Dec: 1″, Jan 8″, Feb 0″, Mar 2″, total 11″ in 5 snow days
      EUG: Nov: 0; Dec: Trace, Jan 12″, Feb 0″, Mar 0″: total 12″ in 3 snow days
      Seattle: Nov: 0, Dec 2″, Jan 10″, Feb 0″, Mar 5″ in 6 snow days
      2 day ice storm in PDX in Jan
      Bend with most snow since 92-93

      Peak snowpack at Government Camp: 146″ in March

      Rain: Dry Oct. Dry 1st week of Nov.

    • Karl Bonner says:

      My reply:

      Wind Storm: At least two but very possibly more. I suspect that if we get a lot of them, at least half will happen before December 15.

      Peak Gust: no comment

      First Freeze: November 15 in PDX, October 20 in Eugene, Oct. 28 in The Dalles.

      First Hilltop Snow (1000 feet): December 3

      First Valley Floor Snow (Portland AND Eugene will have same date methinks): some time between December 15 and January 15. This is THE hardest date to predict!

      First Complete East Gorge Snow: November 24 (complete means right down to the riverbanks)

      Coldest Temp: 18 in downtown Portland, 15 in Eugene and 8 in The Dalles.

      Ice: none in Eugene, two 24- to 36-hour events in Portland metro area (Troutdale westward), two 2-4 day events in The Dalles.

      Precip: about 20% above normal for Portland and Eugene, 40% more in The Dalles.

      February: slightly below average all three locations.

      First sunny 60+ day next spring: March 8 The Dalles, March 11 Eugene, and Mar. 17 Portland (yup, sooner in East Gorge than in Willamette Valley!)

  4. Justin (Brush Prairie) says:

    I’d go with downtown Portland all the way. Been recordingin some form or another since 1871 and is genrally a better spot for longterm data than PDX, I think.

  5. Rob "Wrath" S.E. Portland says:


  6. Garron near washington square says:

    Airports vs. cities. Apparently, Denver is in turmoil and protest over the readings taken by their “official” Denver airport readings, vs, the “actual” readings observed 12 miles away. They moved the observation to the new airport, and it has had profound effects on their temps, and precip. *ALSO* The use of automated measurements in terms of snow fall appear to be completely unuseable there. Kind of an eye opener in my mind since our airport seems to record differing anomalies, as we’ve all noted in the past, than the rest of the metro area at times. Makes you wonder if an asterisk should be added to ALL cities with “official” measurements made more than 5 to 10 miles from a city?

    • Gidrons says:

      I know a Portland snow level of 1500′ means snow for me at 900′, only 25 miles away by Scappoose

    • Garron near washington square says:

      *Micro climate* is our middle name. It can be so different a few miles away, hard to argue that a reading taken near a river and a gorge that’s not in a city that is literally separated by weather from the west side to the east, can be measured by a site that sits 8 miles to the east of the actual city.

    • Mark Nelsen says:

      So here’s the $$$ question…where WOULD you put the official Portland observations if you had a choice? In the last 120 years it’s been either downtown or at PDX.

      My argument is that there is no “perfect” place in a geographically diverse metro area. That’s why we show all the other stations (Hillsboro, Troutdale, Vancouver etc…) on our Metro maps of current weather.

    • Garron near washington square says:


      That’s my argument as well. Where should we claim the “official” reading be taken? It is an ongoing argument. Where is the “official” reading the most accurate, and for whom? There is so much speculation about weather readings being taken that, that has been the device for people on both sides to take stands about global warming. When you move the site, you can expect that there will be more critics.
      Thanks Mr. Nelsen for your input. I always have to compare weather stats, for both sites just to see what anomalies I can extract. There are just too many variables, IE heat island effects, movement of measuring locations, these days when it comes to making an informed decision , it makes it almost impossible to make a point without being contradicted. As if weather prediction wasn’t hard enough??? LOL

    • Sifton says:

      IMO the official reading should be in the dead center of any major city no?

    • …I’d say leave it at PDX for continuity, even though it may not be indicative of,..oh say 10 miles south, still, warm air eventually covers most of the metro area, as does cold and for other than day to day observations, is a good indicator of what airmass is doing what, and how many times it has before thru the years……IMHO..

    • W7ENK says:

      I’d love to see something like this: Take all the temps recorded from around the area, toss out the 2 or 3 highest and lowest extremes, average the rest, and there’s your official number. Highs, lows, wind speeds, precip totals, etc…

      Unfortunately, the real world doesn’t work like this.

    • Jesse-Orchards says:

      Government Island.

      Same basic geographic location as PDX, but removed from the IKEA/Cascade Station heat island.

    • RobWaltemate says:

      I think that we need to get away from one point on the surface and move to many points in an area when talking about climate, and maybe for enven for prediction. Maybe this is the next step in the evilution of weather.

  7. …now i remember why i bought those light airy clothes in Belize…..

  8. cgavic says:

    what kind of weather are we having??
    sun hi 60 wet
    mon hi 85 east wind hi hum
    today cloudy 71 hi humidy

    so much for a string of nice, sunny, cool days…

  9. cliff a gavic says:

    what has happened to our weather?

    monday here we had hi 60 wet chilly
    tues east wind hi 85 hi humidity
    today, cloudy, 71 hi humidity

    we must be getting some sub-tropical moisture influencing our weather.

    so much for a string of sunny, cool days….

  10. Front must be approaching me, seeing gusty west winds all of a sudden and hundreds of leaves are falling off my trees right now.

    Temp: 70% RH: 80%

  11. Tyler says:

    Mostly cloudy here with a few sunbreaks. Still muggy but a decent breeze today helps out!!!

  12. PaulB/Eugene says:

    Temp 73.8, Dpt 67.9….currently in Memphis, TN…no excuse me…Eugene

    • PaulB/Eugene says:

      Currently 78F, Dpt 45F in Eugene, excuse me…Memphis TN

    • Garron near washington square says:

      I love it! I had to deal with sooooooooo many uncomfortable customers at my store this morning! Thank heavens this will only last a few more hours before the relief FINALLY kicks in! This is why I am so happy to be in the NW! My friend in LA, so misses our weather up here. While he was BBQing for his son’s 3rd party in 110+ weather, we were suffering in low 80 degree weather.

  13. Rob "Wrath" S.E. Portland says:

    I see Alaska had some below zero readings this morning.

    Chalkyitsik -9

    Nice to see.

  14. Runrain says:

    The sun just broke out in the Salmon Creek area.

  15. Weak front dissipating across Southern Puget Sound right now. Dewpoints in low 50’s behind the front. Too bad it ruined ALL the sunshine. I have not had a sunbreak yet today and its 1:30pm. Just another day in this gloomy year that became cloudier than what was forecasted.

    Temp: 68.3 RH: 90%

  16. laurie(sylvan) says:

    I love it!

  17. Kyle says:

    74F aND Mostly sunny with a 63F dewpoint.

  18. WEATHERDAN says:

    How bizarre is this weather. 10 AM in Salem on September 28 and it’s already 67 degrees with a dew point of 65 degrees. This would be strange even in July but almost the first of October! We have had 6 nights with the minimum staying above 60 degrees this month so far. Everything points towards a very strange winter, and I guess we’re going to have a bizarre fall as well.

  19. september white air
    warm droplets drift aimlessly
    spider web jewels

  20. Kyle says:

    Glad to know that the late 90s was actually wet without much sunshine and it just wasn’t me and my parents being unused to it from Northern Cali.

  21. Tyler in Hazel Dell says:

    Sunbreaks here with a temp of 67.

  22. cgavic says:

    weird weather.
    We’re back to fog again….

    yet it’s very warm outside…62 degs this morn

    los angeles had a record hi of 113 degs yesterday?

    aclamation has been thrown out the window.

    • Jesse-Orchards says:

      So has acclimation.

    • Rob "Wrath" S.E. Portland says:

      Rather disrespectful to correct someone’s spelling or typos. More so the fact that you think you are in any position to do so. Very rude. Some folks do not spell as well as others. Some do not type as well as others. It doesn’t mean you or I should run to correct them personally insulting someone about it. You need to stop and think about things because that’s all you have done here. Be more mindful of this in the future.

  23. RobWaltemate says:

    So I went to Hawaii yesterday? haha. Had to go to Portland to pick up something. Left the coast at 8:30 in the rain (0.26″ all before 10:00) but ended up in the sun! It was nice. Wind was to my back (East wind) on the way back via I-5 13:00 and on the Washington Side to Naselle, but down by Astoria (Washington side of Columbia) it was out of the West by 15:00. The only bad thing… NO AC in tool truck! Grrrr.

    3 mile N of Long Beach yesterday at my house
    High temp 70.7 at about 14:00 DP 65.9
    and only a slight wind from the South.

  24. Ryan (Walnut Grove) says:

    Hmmm… perhaps a shift in the models? Can’t wait to see the 12Z.

  25. W7ENK says:

    What awesome weather to come back to! After spending 4 days in the desert playa with highs in the low 90s, lows in the upper 20s, humidity down into the single digits, and not a cloud to be seen the whole time… it’s 67 degrees and foggy right now… Sticky Icky!!! >_<

    And, twice now in one summer? Very strange…

    • Garron near washington square says:

      Yeah it’s been a bit muggy here the last couple. Glad you made it back, it would be hard to leave that nice weather!!!

  26. Looks like Portland Airport tied the all-time warmest September overnight low this morning of 64 degrees.

  27. O.C.Paul says:

    Here in Oregon City, temp 63. drizzle to light rain.
    Weird, didn’t see that coming.

  28. A fresh blanket of snow in Barrow this morning:

  29. Rob "Wrath" S.E. Portland says:

    Temp has gone UP to 64.1 due to increasing low clouds.

  30. Karl Bonner says:

    I’m fascinated as to what kind of high temps we would have gotten with more normal humidity levels yesterday (Monday). I’d expect them to be hotter but then again, drier air means a different airmass – and it would probably not be quite as warm as a humid subtropical one, at least as far as 850mb temps go. Still, I bet we could have flirted with 90 today….

    Get this humidity out of here! It was fun experiencing it for a day or two, but now I’m ready to move on. I’m not sure whether I would prefer a hot/dry start to October or a really chilly one. A cold snap with highs of 60 or slightly less, combined with overnight lows in the 35-40 range (low to mid 40s in heat islands) would really set off the fall foliage. Then a return to warm and dry for the second week of the month – say lows of 45 and highs of 75 (outside the heat island of course!) If it sets up just right, that pattern could give us something remarkably close to the Indian summers in the Midwest – a “heat” wave after the leaves have changed color profusely. The year 2008 was probably the closest scenario to this that I remember.

    • Karl Bonner says:

      Final note: I wonder how long the weather would have to stay cold (mid 50s to low 60s for highs, somewhere in the 30s for lows) to set the leaf colors in so that they peak in time for the Indian summer event. I’d think that it would be very tough to get temps like these to last more than about two days at the tail end of September or first few days of October; the same pattern responsible for the chilly days also brings rain and clouds that hold up the overnight lows. Every once in a while we get an early October event where chilly and dry coincide – but again, it might be tough to sustain long enough.

      Well I will try to enjoy this upcoming week to its fullest. I’m going to do lots of hiking and photography, and probably a little sun tanning.

      There’s a place called Catherine Creek on the north side of the Columbia, roughly across the river from Mosier. It has a lot of southern exposure and a mild downward-sloping hillside. I’d like to check it out this fall to see how hot it can get there, both in absolute terms and in terms of human comfort. The south facing slope may be too gradual, though I still suspect it would feel at least 2 or 3 degrees warmer there than other places, possibly 5 degrees or more. Combine with bright sunshine and a scrubby vegetative landscape, and I bet it would feel very similar to the French or Italian Riviera – or for that matter much of California!

    • RobWaltemate says:

      Now that I think about it didn’t the leaves start to turn in early Aug 2009? There is one tree I keep an eye on and now that I think about it, I don’t think it has started to drop any yet. It always seems to be the first. Maybe I just didn’t notice. It is at the corner of Sandridge and Sid Snyder down here and I drive by it all the time.

      Oh and the grass is loving this; not sure when I will get to cut it again, haha.

    • Garron near washington square says:

      I know that tree colors are on a schedule for fall color change and droppage, but I swear that a couple of mine didn’t even get foliage this year until late June. The maples that had leaves, got more leaves like in mid August, and the earlier leaves have already changed, while the later arriving ones may try to hang on until almost Christmas. Weird how even certain trees seem to have their own personalities. Happy hiking!!!! I’m jealous. : }

  31. Yevpolo1990 says:

    So much for thinking that my outside thermometer is broken…

  32. At midnight…65.8°…Td 63.7…RH 93%…

  33. Timmy_Supercell (Hillsboro) says:

    Icky sticky outside! Can somebody spell out “WINDSTORM” in two weeks? GFS is still showing an active pattern of intense low pressure systems. We are overdue for one. And these dew points are only adding to the possibility…

    • Timmy_Supercell (Hillsboro) says:

      Luckily I did not need to turn up my AC, I was close though. Iced water every 30 minutes did the trick 🙂

    • Ryan (Walnut Grove) says:

      If only one of those storms would actually go south of the Gulf of Alaska.

  34. Josh "The Snowman" From Everett, WA says:

    Yucky out there:

    At 10:44 PM

    67.8 deg F
    63.2 deg dewpoint

    84% humidity

    Yuck, yuckity, yuck yuck. Was much more comfortable in July.

    Just curious, any of you geeks have some analogs for other La Nina years that had late Sept. weather like this? Preferably, ones that led to colder/snowier winters?

  35. BrandonInNWSuburbia says:

    All I can say is Yuck! I can’t wait for some crisp, cool, DRY air to move in.

    • Rob "Wrath" S.E. Portland says:


      It’ll be here soon, but not soon enough, rather “sooner” than later? Ya.

  36. Paul D says:

    I thought the A/C in the house was running a bit too long for just being 80 outside. 80 + humidity = it all makes sense now! 🙂

  37. Justin (Brush Prairie) says:

    Mark, FWIW the highest NW OR/SW WA dewpoint events in recorded history were mostly set a long time ago. July 1941, June 1961, June 1978, May 1986, July 1998, and July 2006. This is really impressive for September, though, especially in places like Olympia.

    • Rob "Wrath" S.E. Portland says:

      Mark, thanks for the update. It will be refreshing to get rid of the Samoan Soup that has rudely invaded our region. Oh and I clearly remember seeing dewpoints of 75-79 back in 2006.

    • Mark Nelsen says:

      That’s good info Justin. I remember the July 1998 event and 2006 of course, but not the others.

    • RobWaltemate says:

      I remember that the winter of 98-99 was VERY wet! Like 99 inches down here wet.

  38. Tyler in Hazel Dell says:

    I really wouldn’t mind this weather as much…when it’s more typical, July etc. I’d much rather be dealing with record lows right now 🙂

  39. Tyler in Hazel Dell says:

    I had my AC on in my truck today, and even in the house…lame for September 27th.

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