July 26, 2009

Thunderstorms and the Upcoming Major Heat Wave

Last night there was some thunderstorms and rain from the central Sound northward associated with an upper level low/trough over the region (see upper level chart and radar image above and below). The action was greater to the north, particularly over southern British Columbia. Air rotates counterclockwise around lows and convection forming to the northeast rotated into BC and northern western Washington. But there wasn't enough rain to make a difference. As the trough/low moves out it sets the stage for the big action this week--a major, multi-day heat wave (my book has several sections on thermal troughs and their importance if you are interested). As I will describe below, we could have several days in the 90s and some locations in the south Sound could hit 100F.

Heat waves actually are the most dangerous weather phenomenon around the world...many more people die from them then hurricanes, tornadoes, and windstorms. And the elderly are the most vulnerable...particularly those without air conditioning (which includes most people in our region). So if you know some older folks in a hot apartment or house...it will be good to check on them. Long heat waves like this week allow time for buildings to heat up...which makes it all worse. But we have an advantage over most regions...our water stays cool and going to the shore of Puget Sound, the Strait or the Pacific brings cooler temps. And we don't have the high humidities like the eastern U.S. so sweating works well. And the dry air allows temperatures to cool at night. Another good reason to live in the NW!
Today (Sunday) will see temperatures getting into the upper 80s F for most of western Washington away from the water. During the week an upper level ridge will build over the region and high pressure will be strongest to the east. This will bring warm air aloft AND offshore (easterly) flow.....much more easterly flow than we have seen the past several weeks. This configuration brings downslope warming on the western slopes of the Cascades as air is compressed. With warm temperatures a thermal trough will build northward into western Washington...this is the pattern that gives us the highest temps. (see graphic for pressure prediction for Wednesday)

Looking at the latest computer models, it appears that we will warm progressively into mid-week and Wednesday or Thursday will be the warmest. High 80s today, lower 90s tomorrow, mid nineties on Tuesday, and upper 90s on Wednesday and Thursday--with some locations even higher each day (central and southern Sound on the east side). We could easily have five 90+ days in row--if we do so, we will tie the record for consecutive days above 90F in the Seattle record. If we beat 90F today, we could establish the record this week. (I am NOT hoping for this, I have to sleep at night too).

To get you "warmed up" for this event, I have placed below the computer forecasts for 5 PM on Wednesday and Thursday. The lightest colors are temps of 96-100F!

The surface is extraordinarily dry. I did not talk about the other issue...wildfires....but this is the kind of situation that can produce big fires west of the Cascades. People forget that the west can get huge fires...hopefully not this time. And there is one more threat in this purgatory of heat...high ozone values. Sustained warm temps in the 90s can produce very high ozone values...particularly on the lower slopes of the Cascades, which the nitrogen oxides of the city mix with the volatile organics emitted by vegetation (terpenes). Enumclaw and Pack Forest are often the worst spots.

The bottom line of all this is this is a very serious, and perhaps historic, heat wave.

Finally, let me note I will be speaking in Leavenworth on Friday evening if anyone is interested...see info on the side panel.


  1. I'm amused that I'll be returning home to Seattle from Orange County tomorrow to hotter weather then they have in Southern California.

    Time to plan some trips to the lake!

  2. Wow looking at the graphs, western washington will be warmer than eastern washington...weird.

  3. Dew points in the 60s yesterday, that is rare for western washington...

  4. typo - "we don't have the high humidities like the western US"? Shouldn't that be eastern US? Summer in the south or mid-atlantic involves humidities and temperatures both in the 90s.

  5. Mark, temperatures of 90+ degrees F and relative humidities of 90%+ only very rarely occur in the South or Mid-Atlantic. A temperature of 90 degrees F with a relative humidity of 90% would require a dewpoint of 87 degrees, which occurs only rarely in the east and south. You may see dewpoints in the upper 70s to occasionally lower 80s, but anything higher than that is rare, only occurs in extreme cases, and is not a normal part of summer there. Most of the highest dewpoints in the country will actually be found in the Midwest - particularly Iowa - because of evapotranspiration from all the agricultural crops (mostly corn).

    A comment on the blog entry itself... living in the east is still better than the Northwest this time of year because air conditioning exists in the East. It matters much less how hot it gets during the day and how much it cools at night, or how humid it is, if you have air conditioning.

  6. Weather,

    I'm from the South and Mid-Atlantic, just moved here a year ago after 15 years in DC and the previous 25+ years growing up and living in various areas of Florida, Southeastern Virginia and Coastal Carolinas. Temps and Humidities of 90+ are VERY common in those eares, especially between July and September. Getting soaking wet as soon as you step outside, feeling like you're drinking the air.

    While AC is very common there, I'll still take summer here temp/humidity wise. More regular rain would be useful though. Seattle gets about 10-12 inches less a year, and summers on the east coast are characterized by "popcorn" thunderstorms as fronts rapidly move through over very warm moist disturbed air. Most days in July/August have a quickly moving thunderstorm move through between 4 and 7pm, quickly dumping 1/2" or more, often with hail, in about 30 minutes.

  7. Except for a couple years in school at UW-Madison, I have lived most of my life in areas with marine influence. I currently live in Alki and think that it is one of the best places in weather like this--usually the N-NW winds kick in, and the Sound provides free air conditioning. Alki is typically 5-8 degrees F cooler than the city...except when the thermal troughs materialize. Then it can get hot even here. Well, this is the flip side from the Snowpocalypse.

  8. I remember when I lived in the upland South (for most of my life) that I counted the days for summer to end. I would come in from playing and be physically ill day after day, finally concluding I could do little outside till after 7 pm. Here it's painful renting, not having shade trees, poor insulation. We now have a couple of window AC units. In the South, we had central air after years of no AC. Lifesaver. But I remember spending some summers in Virginia Beach with family, and it would get up to about 100 degrees with high humidity. Wretched: and then the AC broke. Now, that was misery. If humidity doesn't get that high this week, we'll make it. I don't want to go through the VA Beach nightmare ever again.

  9. ...and yet for all my complaints, I so miss the violent thunderstorms we had in the southeast....

  10. Mark ---There was a typo (western should have been eastern)...fixed..

  11. @weather is my life: You are flat-out wrong about these temps and humidities in the East and South.

    "Mark, temperatures of 90+ degrees F and relative humidities of 90%+ only very rarely occur in the South or Mid-Atlantic."

    I grew up in North Carolina. And I lived there for many years without air conditioning. So I paid CLOSE attention to the weather, both temps AND humidities.

    In Durham, NC, there were at least three weeks' worth of days that were 90F+ and 90% or greater humidity. They almost always brought spectacular evening thunderstorms, which brought a few hours of relief, sometimes, to those of us without AC... but often greater agony for those with it, because the power would go out and they would actually get hot. LOL

    It is not at all uncommon for the summer overnight temps to stay in the 80s and for the humidity to stay above 80% as well. A "nice" night in Raleigh features a breeze and temps that cool into the 70s.

    Raleigh's weather this week is really typical; highs above 90 each day and lows around 72 each night. Thunderstorms are called for each afternoon by the current forecast.

    At the moment (2 am), Raleigh's temp is 78F, humidity is 79% and the dewpoint is 69F.

    Anyway, anyone who has lived in the Carolinas, Florida, Georgia, Mississippi, or Alabama is going to call BS on your "facts" here.

    Oh, and the majority of poor people across the south DON'T have air conditioning. It costs about a dollar an hour to run and that's $300 a month that a lot of folks just don't have. I didn't when I was living there.

    I LOVE living without A/C. You still have to go outside and running A/C in a car all the time is very expensive especially with higher gas prices. And going from A/C house outside to hot then A/C car, outside again to A/C office and back multiple times a day is a great way to get sick.

    Hey, but you LOVE horrible weather, right? Better not be using a fan this week!

  12. What's really scary is the possibility of blackouts due to constantly running ACs all over the Puget Sound. Especially for people with heart conditions. Scary stuff.

  13. Jewelz,

    Take Cliff's class. Then you'll see my facts are not wrong. Or just search online for a dewpoint calculator. There's really no need to learn the derivation of the equations, or even the equations themselves, just search for that. With a temperature of 90 degrees, it takes an awful lot of moisture to create a relative humidity of 90%. If the temperature is higher than 90, then you need even more than that.

    If you're interested, the relative humidity of the air is equal to the mixing ratio of the air - related to the dewpoint - divided by the saturation mixing ration of the air - related to the temperature. The mixing ratio of the air is equal to 0.622 * (partial pressure of the water vapor) / (air pressure - partial pressure of the water vapor). The saturation mixing ratio is equal to 6.122 * e ^ ((17.67 * air temperature)/(air temperature + 243.5)), where the air temperature is in degrees Celcius, and the saturation mixing ratio is in millibars. You can use that, but you probably don't care to, I'm guessing. You could just search for dewpoint or relative humidity calculator online. Then search for highest dewpoints recorded in the east. 87 is just very rare. It is a fact. Learn about it before you state that it is wrong.

    They might have relative humidities at 90% or higher at night, but they don't have 90 degree temperatures at the same time.

    And no, Jewelz, I don't like horrible weather. I like good weather. I like nice weather. Why would I ever call something that I like horrible?

    And going back and forth from A/C to not A/C does not get you sick.

  14. Hey Cliff, the Probcast got Sea-Tac's high right on today, 89. Do you realize that for Wednesday morning, the probcast is forecasting a low three degrees higher than the highest low temperature ever recorded in Seattle?? The record is 68, and the Probcast says 71, as low as 67 and as high as 75 for the low. The WRF-MM5 low temps Wednesday and Thursday morning look to be in the low to mid 70s as well. I'll be very curious what it says for the high for Wednesday - how close will it come to forecasting a record maximum temperature all-time for Seattle (which currently stands at 100)? Just the fact that it has a chance of as high as 101 on Tuesday is amazing.

  15. The question is why is this forecast not the same as Weather.com? I have no forecast on that site that shows 100+ highs in my area(98053).

  16. I could care less about what A/C costs in the south or their weather. I would rather talk about OUR heat wave. Geezus.

  17. I wonder if the Puget Sound Energy power plants have ramped up their production in anticipation of this heat wave.

  18. Weather is my Life - I grew up in DC and I certainly remember lots of days in our summers where it was 95 degrees and 95% humidity, and we didn't have AC either. Those days were just brutal.

    They were not all the time, but certainly, they did happen, and often enough that I would not call them rare.

    Oh, and Cliff, I love your blog!

  19. @Weather is my life: you can't have it both ways. You complain bitterly whenever we have nice weather here -- sunny skies with moderate temperatures. Now you're saying you don't like this weather? Being a contrarian is a pain sometimes, isn't it, getting caught up in the double- and triple-negatives.

    I know how to use a dewpoint calculator. I am not ignorant. Yes, it takes a LOT of moisture to make such high humidities in high temps. However, it does happen.

    Going in and out of A/C (~68 degrees, very low humidity) when the weather is in the 90s with high humidity makes many people develop sinus issues. It's not a matter of "catching a cold" -- that's a virus and it has nothing to do with weather -- and everything to do with torturing your mucus membranes.

    By the way, the east and south are considered humid subtropical climates. http://en.wikipedia.org/wiki/Humid_subtropical_climate#North_America

    I'm done talking to you about this subject. The weather in NC is not what you know best and it doesn't have much to do with the weather we're about to experience, though it will feel familiar to many of us who have escaped the hot and humid southland!!

  20. @Alex:
    "I wonder if the Puget Sound Energy power plants have ramped up their production in anticipation of this heat wave."

    I doubt it... there's no good way to STORE any extra energy they produced right now for later this week, when we will really need it for the folks who have A/C (and all those lovely cool workplaces, movie theaters, and stores! LOL)

    However, I'm sure they spent some time making sure that all the maintenance was done and that everything that they can bring online to deal with the spikes in demand is ready to go.

    Remember these strategies to help the utilities, your neighbors, and yourself during this weather:
    - do anything requiring electricity and water at night, if possible -- laundry, dishwashing, and so on
    - only run your A/C when you're home or turn it up to 80 when you're away
    - turn your A/C up a couple of degrees... even 75 will feel lovely compared to outside
    - use ceiling fans and regular fans even if you have A/C. A fan in the room you're in will make it feel 4-6 degrees cooler than the actual temperature
    - make sandwiches or other "cold" meals so you don't have to heat up your kitchen, or go out to eat
    - skip cutting the grass this week (and using any other gas-powered outdoor appliance) -- pollution will get really bad and there's a real risk of fire from any spark
    - don't let kids (or anyone else!) open or play in water from an open fire hydrant. Call 911 and report the open hydrant. Even a few open hydrants can dramatically reduce the water pressure available to fight fires, and they use phenomenal amounts of water, too. Put a sprinkler on your hose for the kids if you must, but consider going to an actual water park instead (Crossroads, anyone?!)
    - Check on your elderly or otherwise frail neighbors. Make sure they have fans, enough water, and so on. If they don't, consider calling local social services or the police non-emergency number to get them help. I bet the counties will open "cooling centers" this week -- community centers and other public spaces where people are welcome to come cool off.

    Hope these ideas help.

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  22. My lord, 84% humidity at 2:48AM. This must be a Puget Sound record.

  23. hi kyano, 95 degrees with 95% relative humidity means a dewpoint of 93 degrees. Did you live in the Persian Gulf region near Dubai, on the Persian Gulf in the United Arab Emirates, when they set the world record of the highest dewpoint of 93 degrees?

  24. Probcast shows 103 on Wednesday for SeaTac with a possible range of 98 to 107!!

  25. Probcast's forecast! Looks like records will be smashed. Wow, what an interesting year for weather this has been!

  26. weatherismylife - If you had read my comment, I said that it was in DC. But clearly you are a contrarian that just likes to tell other people that they are wrong. I am done too.

  27. lol kyano, I know you said it was in DC. That's the point - it has never happened before in DC and hasn't come close. I'm just trying to explain the facts - I'm a trained meteorologist and know what I'm talking about. Cliff could tell you the same thing.

  28. JewelyaZ - I'm allowed to dislike all sunny and hot weather, aren't I? There's nothing contrary about that. In the case of this week, I agree with everyone that it's not good weather. When it's sunny and 70 outside, I still don't like it. You obviously don't understand. Nice weather for me is cloudy, or if it has to be sunny, at least be under 50 or 60 degrees. I'm not contradicting anything. And unfortunately you can't use a subjective term and expect everyone to know what you're talking about or to agree with you.

  29. Thanks for the info about dew points, Weather. The 9:53AM reading at BLI shows a dew point of 66°F. That's pretty high for our area.

  30. It stayed warm all night. Another example of the extreme reach of the heat. I monitored the temps from Portland north driving back home to Olympia. It was 86 at 9 then dropped to 81 around Kalama, then 76 by Longview. Dropped to 74 at 10 by Castle Rock, then rose to 79 going up the south slope of the Toutle Hill, then 73 by Centralia and back up to 75 at 11pm by the time I arrived home.

  31. I think the confusion lies here:
    There are many, many days in summer where RH values are at or above 90% and temperatures are at or above 90°F in the southeast. However, these do not occur at the same time of day.

    In other words, as "Weather is my life" said, it's exceptionally rare to have temperatures at or above 90°F and RH values at or above 90% at the same time.

    In the morning, the low can be 80°F with a dewpoint in the upper 70s, giving RH values above 90%. But by the afternoon when the temperatures are above 90°F, the dewpoint is still in the upper 70s, yielding much lower RH values.

    This is why, in my opinion, we should not talk about RH when discussing how "humid" it feels... it just confuses the issue.

    Anyway, it's gonna be a hot stretch ahead of us. For Portland, I'm guessing we'll see the following Mon-Wed highs:
    100°F, 103°F, 104°F

    Combined with dewpoints in the mid 60s, this will make for some disgustingly hot weather, especially for people like me without AC.

  32. WIML, you obviously have quite a lot to offer to this discussion. When I hear you talk about the statistics and science of weather I feel I am being educated and respected and I am appreciative.

    When you actively take exception and contradict the dominant usage of subjective terms like good and bad in reference to weather it smacks of pettiness and you become less respected in this community. Everyone here certainly knows by now what your preferences are and I'm sure we can respect that while still applying terms as they are most commonly used. Yes, we understand that you prefer cooler, cloudier weather and consider temperate summer conditions not to be weather at all. You are not under attack by our language though you may feel so. It is simply common usage.

    I strongly encourage you to write your own blog that is specifically for people who share your preferences. I wouldn't ask you to leave this discussion, which is not my right anyway, any more than it is yours to "correct" MY perceptions. I am asking you to let go of conflict and truly contribute your very best which I AM seeing more of lately and I do appreciate it.

    I am truly sorry to have responded in a reactionary and negative manner in the past. I am here to learn.

    Yours Truly;



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