Marine air Starting to move in...

Marine air is starting to move along the coast..we should have a very weak marine push tonight...enough to cut the temps by 5-7F degrees tomorrow. The thermal trough is now moving over the mountains and an onshore pressure gradient has developed. Stratus is starting to push across the coast..and you can see this on an image I have never shown on this blog before...the fog product. By combining several infrared wavelengths observed by satellite we can see low clouds at night..take a look at the figure. See the whiter stuff on the coast..that's the low clouds. The latest surface chart below shows southwesterly and westerly flow pushing in around Hoquiam.
Low clouds may make it into the Strait and perhaps to Shelton and Olympia..but it should burn back rapidly in the morning. If today was a tad hot for you, tomorrow will be heaven.

If you want to see an extraordinary picture from the high resolution NASA MODIS satellite...look at this. You can clearly see massive amounts of smoke from the BC fires and the low clouds off the coast.

Finally, my kidding around with KING-5's hypesters should not be taken as a lack of respect for their weather personnel, which are really top rate. And lets face it, other stations partake in weather hype as well....although to be fair, none of them have ace Jim Forman, who is in a class by himself. And their segment on the heat wave tonight was quite reasonable. Sometime, perhaps after a few glasses of wine, I might blog about the TV weathercasters of our area, but the bottom line will be fairly unexciting..we have unusually good tv weather people in this market. But I better stop before I get into any more trouble.

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Killer Heat Wave or Killer Hype?

IRONY ALERT!!

Updated 2 PM, Wednesday. Guess who showed up at my office just now????...a reporter (Glenn Farley) and cameraman from KING-5 TV!!! They wanted to talk about the hot, dry summer and how unusual it was! When they closed my room's shades, turned on their blinding lights, and closed the door...well, I was a little concerned. I am afraid to see what will go on air tonight. Some sort of revenge tactic? Will they turn me into a scarester too? We'll see.


The media was up to its old tricks last night-- this time hyping the upcoming "dangerous" heat wave. All the TV stations do it, but none are better at it than KING-5. They are masters of the art. First the news anchors broach the topic, with tremulous voices asking the question--will a dangerous heat wave hit the region the next day? Then they turn to a smiling, yet serious, Jeff Renner who provides a knowing, sympathetic, nod of agreement. Last night, he had his work cut out for him, but finds the most extreme temperature maxima in the region to provide some reason for concern (last night he had to really stretch, quoting the temperature in Vancouver, WA.,which gets the Willamette Valley heat). And then they always turn to their on-scene scarester-reporter. And KING has the top weather scarester in the country...Jim Forman. I love this guy. I wish they sold tapes of his segments...I could watch it for hours. In the winter he hypes snow and in the summer heat. During the last heat wave he had a giant round thermometer stuck at 105F that he kept on flailing about. If nothing threatening is going on...no problem..he will describe the terrible events that will certainly happen to the unprepared. And he always shows people desperately buying emergency supplies in convenience stores and supermarkets. I mean...this guy has a winning formula.

Anyway, our models are indicating a substantial warm up tomorrow...and the central and south Sound could see a few 90s....particularly away from the water. The probcast forecast system (www.probcast.com), whose strength includes these types of days is predicting 92F for Sea Tac tomorrow. (Check the graphic for max temps tomorrow).

Easterly flow will develop tonight over the region, bringing further warming to the west side (and the over us is already quite warm). As you can see from the surface weather chart (pressure and temps shown), the famous thermal trough will move into western Washington (chart) with the heat....our temperatures will spike tomorrow and then decline a bit Thursday as some marine air moves in Thursday AM and the thermal trough jumps to the east side.

7 AM update...on wed..looks more like 89-90F at Sea Tac today..warmer, but not that warmer than yesterday

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Global Warming Misconceptions

There are several questions dealing with global warming that come up frequently...and it happened again this week when I gave a lecture at Google in Kirkland.

"How can you meteorologists possibly predict global warming fifty years from now when you have problems forecasting the weather three days ahead?"

(Some questioners use more earthy language to describe the current state of meteorological prediction skill, while others suggest that weather forecasters use dice for all the skill they have).

Well, we CAN predict what is going to happen fifty years from now and the forecasts are worth listening to. How can that be?

First, let me say that weather forecasts have gotten much more accurate during the past decade or so. And that is due to several reasons: far better computer forecast models (better understanding of physical processes, better resolution due to more powerful computers) and FAR better and much more observations that allow us to start our computer models with a better starting description of the current state of the atmosphere. We rarely get big storm forecasts wrong today and the day 4 forecasts has the skill of the day 2 forecast 25 years ago. Major progress. And these are basically the same computer models used to predict climate.

But forecast skill of even our new models degrades with time and by 1-2 weeks ago there is little forecast skill left. So knowing that, how can we forecast 50 years from now what will be happening with increasing greenhouse gases?


First, a fifty year climate forecast is completely different than a 2 day weather prediction. In a weather prediction we attempt to forecast the exact configuration of the atmosphere at specific times. Exactly what the temp will be at Olympia at noon, the strengths of all the highs and lows and their exact positions at 7PM Thursday, the wind conditions everywhere at exact times. Pretty challenging. And we know based on theoretical studies that our ability to do this degrades rapidly in time. But for climate predictions we don't do this. We forecast averages..like the average temp over 10 years or average precipitation for all the Marches for a decade. This is MUCH easier to do.

Second, the nature of a climate forecast is very different. For weather forecasts our predictions are dependent on the details of the initial state and small errors or differences grow during the forecast. For climate predictions averaged over decades, there is far less sensitivity to the initial state and far more dependence on the overall forcing by the sun's radiation and how the composition of the atmosphere changes its ability to absorb and transfer infrared radiation. For example, if the earth's atmosphere acts to hold in more radiation, than the planet will tend to warm. Technically, one is an initial value problem and other a boundary condition problem. We have run our climate models over the past hundred years and have been able to duplicate the climate variations over decadal time scales...providing confidence in climate forecasts.

The bottom line of all this is that useful climate predictions ARE possible even when weather prediction skill is lost in a few weeks. These climate prediction aren't and won't be perfect. But they provide great insights into what will happen over the next 50-100 years.

My next blog will deal with the other major argument used by those questioning the potential for human-induced global warming..the lack of warming over the past decade. And then I will talk about the hyping of global warming by some scientists and the media.

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Lightning, the "Crouch", and Joan Baez

I got a call yesterday from one of the organizers of the Joan Baez concert at the Woodland Park Zoo that was held tonight in Seattle. He was worried--the National Weather Service was forecasting showers and thunderstorms during the evening. Thousands of people would be out in the open...with the concert venue in a field surrounding by tall trees and the space filled with metal towers for lighting, sound, and other needs. (Sounds like the scene of some disaster movie!).

How could he keep these people safe? How could they tell whether lightning was approaching? The National Weather Service forecast was for showers and some lightning rolled in late in the afternoon. Their forecast was excellent and the concert started out on the damp side with lots of showers.

Here are some of the things I told him. If you are outdoors in lightning and can't get to safety you need to do two things. First, get away from any tall object--it will attract the lighting. Trees, towers, hills, you name it. It doesn't have to be metal. Just tall. Get at least 100 ft away if you can. Why? Well if lightning hits an object..lets say a tree, the current can reach the ground and spread out along the surface..and can kill up to 50-100 ft away if you are laying on the ground. Or the lightning can jump from a branch directly to you. So keep away from trees. (this was made very real to me while I was an undergrad at Cornell. There was a thunderstorm and a bunch of students gathered under its branches. Lightning hit the tree and most were stunned and several were very seriously, if not permanently, injured).

The second thing to do..the LIGHTNING CROUCH (see above figures). You don't want to lie on the ground..that could be deadly if lightning-induced currents are flowing on the surface. So what you do is to crouch down on your knees with your ankles touching. You can understand why you want to be low...less attractive to lightning, which likes high stuff. By keeping your ankles together, lightning currents riding up one foot will probably pass down the other..thus sparing your vital organs.
It is also recommended that you cover your ears to protect them from the loud sound of thunder. (I know this looks kind of ridiculous, but it works). And if you playing golf--PLEASE--get rid of those clubs and your fancy meta- cleated golf shoes.

I told the concert organizer that if I line of thunderstorms approached it would be best if people retreated to their cars. Cars are very safe...and NOT because they have rubber tires. It is because you are in a cage of metal and the lightning currents will pass around you (I would avoid touching the frame during the storm though).

And keep in mind that lightning can, and often does, strike the same place twice.

When in a thunderstorm you can tell how far the lightning bolt is by counting from the time of seeing the lightning to hearing the clap of thunder...for every 5 seconds you count, the lightning is 1 mile away. 20 second..4 miles distant. You see the lighting flash essentially immediately (since the speed of light is so fast), but sound travels much, much slower.

Well, enough weather safety tips... oil on the road with the first rain in my last blog and now lightning. I don't even want to discuss what happens during the first lightning storm after a dry period...just stay under your covers!

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The Dangers of the First Day of Rain

The first day of significant rain after a long dry period can be very dangerous on the roads. Why?
During the dry period oil, dust and other debris collect on roadways and the addition of water produces a slippery emulsion. After a few days of rain, it washes off. The other issue is that people are used to dry-road driving and driving habits (like taking that corner slower) are slow to change. There is in fact a literature on this first-day-after-a-long dry spell issue--check out: http://www.drivers.com/article/652/ as one example.

So be really careful driving today...I have already received a number of reports of significant local accidents.

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What season is this?

I was struck by the latest infrared satellite picture...a winter-like front is heading for us tomorrow morning (see image)...and look a the predicted 24-h rainfall ending 5 AM on Tuesday (image)! Wow..this is serious rainfall, particularly in the north Cascades. We are going to cooler and wetter than normal for a few days...but guess what...we get warm and dry for next weekend!

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Was the heat wave a sign of global warming?

Quite a few have emailed me asking whether last week's heat wave was a sign of global warming. Others have suggested that I have been strangely silent on this issue.

Anything, although I have commented on this subject in my blog and KUOW, let me give you my take on this--and I think the take of most meteorologists.

One heat wave, one storm, one event says nothing about global warming or its effects. That is why those who jumped on Hurricane Katrina as proof of global warming were really off-base.

First, this last hot event was completely localized...while we had record breaking heat, the upper plains and midwest (and parts of the east coast) had record breaking cold. The reason: a persistent ridge of high pressure over the western U.S. and a trough over the central/eastern U.S.-- NOT uniform warming. When I went back east for a meeting, people were complaining about the cold, and those of conservative bent were griping about the global-warming fanatics.

Second, one event does not provide much information on trends, and trends are what count in climate. The atmosphere has a certain amount of natural variability, and there will be records and extremes even if the large-scale situation remains the same. The atmosphere is rarely "normal" and the averages include extremes of both directions.

The media and some climate-action groups are continuously confusing the differences between weather and climate and some of their claims are unsupportable --like the frequently stated prediction that the NW will have more windstorms under global warming. There is NOTHING to support this conjecture. I have even heard some explain the unusual cold/snow wave last December on global warming! (the claim is that global warming will produce more weather variability). And another one is about heavy rain events--that our recent heavy rains/flooding are due to global warming. The truth is that heavy rain events are decreasing in Oregon and increasing over parts of NW Washington (I have a student working on this issue). Why would global warming produce such a dipole effect? (I can speculate on this but won't here).

Don't get me wrong...I am absolutely convinced that global warming is going to happen and will be significant here, but many of the claims about local effects are without support. And because we are downstream of the cool NE Pacific, the Pacific NW may see global warming's effects delayed and weakened.

The bottom line of global warming is that the effects will not be uniform, and that the differences will be profound. And there is much about local effects that we don't know. The whole topic has also gotten too political...with some believing that global warming is some left wing/Gore induced dementia, while others hyping its effects to induce a social/economic transformation or to enhance their political prospects.

I suspect mankind will not act fast enough to reduce fossil fuel use to stop large global warming effects and that we will learn to live with it. But that is another topic...

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Why Such High Humidities Last Week?

Several of you have asked why the humidities got so high last week. As I mentioned in the last blog, dew point is the preferred measure of how much moisture there is in the air and the dew points last week got into the mid to upper 60s--which are very high for us (the dew points today for example are in the lower 50s).

So lets play detective! One facility meteorologists have is the ability to compute trajectories of the air..the path that the air took over time--thus, we can determine where the air came from that was so sticky and humid.

I have done this...finding the air trajectories for air ending over Puget Sound at 500, 1000, and 1500 m at 5 PM on Tuesday the 28th...the evening before the warmest day and a time with high dew points (see figures). Where did the air come? From the desert southwest as some media types said? No! The humid air came from the north over southern B.C., including the forested slopes of the Cascades.

This makes complete sense if you think about it. Earlier than week, Sat through Tuesday it was quite wet up north...an upper low caused thunderstorms that rotated westward to our north. Don't believe me? Check out the radar image from the Sunday before (see below). So we had very warm air which was passing over moist forests and vegetated surfaces, picking up lots of moisture. But the fun doesn't stop there! The Strait of Georgia is warm! Well, at least a lot warmer than Puget Sound. Water temps there were in the 60s to near 70F...which mean it could provide much more water vapor to the air than the cold Pacific.

So I think we have our answer...warm air passed over moist forests and a warm water surface and picked up lots of water vapor. That made us uncomfortable and kept the temperatures up at night (remember water vapor acts like a blanket).

Now here is the interesting thing. The air really dried out on Wednesday as the temperature surged to record levels. Why? Well, the direction of the air shifted from the moist forests to the north to the dry continental surface to our east. Want proof? Below you will also see trajectories a day later...5 PM on Wednesday, July 29th. And this air was really sinking as it descending over the Sound...producing enhanced warming.

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The Other Side of the Heat Wave: Humidity

There was another side of the heat wave of the past week--the high humidity. It really felt like the torrid east coast the day before the big record.

Air with lots of water vapor makes us miserable in two ways: first, we can't evaporate water off our skin (sweat) as effectively...and thus feel warmer. Second, water vapor acts as an atmospheric blanket--keeping temperatures up at night.

Many of you have heard of relative humidity--with air have 100% relative humidity when completely saturated. But relative humidity varies with temperature and drops as the day warms. It is NOT an absolute measure of the amount of water vapor and thus meteorologists prefer to use another measure, dew point. (air with 100% RH at 45F has far less water than air with 100% RH at 85F)

Dew point is the temperature that air must be cooled to to become saturated (100% RH). The more water vapor in the air, the less you have to cool it down to get saturated (remember, warm air holds more water vapor than cold air). So dew point is actually a measure of the amount of water vapor in the air.

Still with me? In Seattle, the typical summer dew point is in the lower 50s. In DC it is closer to 70F (a very good reason to avoid living in DC and to appreciate our congressional/senatorial delegation that has to live there).

Take a look at the plot of dew point at Sea Tac for the last two weeks above. The dew point starts in the 50s and rises well into the 60s in the day leading up to the heat wave...that is why it felt so terrible. (some local stations had dew point rising near 70F) Then on the day of the heat, as the dry, easterly flow developed, the dew point dropped . During the past few days the dew point dropped in to the fifties again...and boy does it feel better. Today was spectacular and comfortable...with dew points dropping into the upper 40s in some locations.

And why are our dew points generally low and our summer air much drier than that of the East Coast? The Pacific Ocean. How can that be? Generally our air has traveled thousands of miles of the Pacific...but because the Pacific and the surface air is relatively cold...the air can't pick up much moisture. In contrast, those poor people of the East and Central U.S. have air coming off the Gulf of Mexico...which is well above 80F in the summer. If you want to read more about dew point, there is plenty more about it in my book.

So that's the unsung issue that made last week a terror...unusually high dew points.

PS: There was a question of why it was so humid. The air trajectory was not off the ocean (air would be too dry because the water is cold) and not from eastern WA (too dry because of the surface). Rather, it came from the north--passing over vegetated areas of southern BC....cliff

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The Warmest July Ever at Sea Tac

The numbers are in, July 2009 was the warmest since record-keeping began at Sea-Tac Airport (late 40s).


The air above remains very warm above us right now...at 850 mb--around 5000 ft-- it is 20C (68F)...which is much above normal. At low levels we have had weak onshore flow, bringing marine air and some clouds in the lower few thousand feet. A vertical profile at Sand Point is shown below. Notice the inversion at low levels, with temperatures increasing with height. The cool low-level air warms during the day and the inversion is slowly burned out in the morning hours...producing rapid warming. Temps remain warm in the mountains where they are above the marine layer.
In the lowlands away from the water temps will rise in the mid to upper 80s..with a few 90s. And very warm hiking weather in the Cascades. This hot period doesn't want to end.

There are some major changes suggested in the latest computer runs for the end of next week, when a strong upper low swings through....convection--thunderstorms--often come with such changes. We will see.

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The Cooling

4 PM Update...the Hoquiam-Seattle pressure difference is now 3.8 mb. A strong onshore push is thus guaranteed. Put up your wind chimes. It is coming. If anyone is planning on hitting the water...particularly in sail boats...please be prepared and careful. The winds will pick up later and get quite gusty.

We had a minor intrusion of cooler air at low levels last night into the interior, but this thin veneer is rapidly getting mixing out...so temperatures will surge now back into the 90s...sorry. The coast is much cooler (60s). There should be a modest onshore push of marine air tonight...watch the difference in pressure between Hoquiam and Seattle...when it gets above 3-3.5 mb you know it is coming. The thermal trough should jump into eastern Washington with the push and temps tomorrow should only get into the mid to upper 80s. Hard to believe that 80s seem cool.

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Update III (Updated 10:45 PM)

The 5 pm observations are in. Sea Tac got to 103F. Thunderstorms have developed and the clouds are spreading over the crests and foothills...beautiful anvils from space (see image). And low clouds have spread to the coast.

Temperature Readings

Several of you have been sharing temperature readings, which I and others really appreciate! But keep in mind the following:

(1) Bank thermometers are notoriously inaccurate. (I will refrain from generalizing this to the reliability of banks in general)

(2) Temperatures measured in cars driving over asphalt during the day are often too high and not representative of the true air temperatures. Air temperature should be measured in the shade over a vegetated surface. Roads can heat up to 120-140F and thus can inflate car temperature readings. So drive your car over grass or vegetated surfaces if you want a dependable reading.

That said, there have been a number of reports of western WA temps over 110F. Here is a report from Mark Albright, research scientist at the UW:

The highest temperatures in western Washington today (29 Jul 2009) seemed to be between Portland and Olympia. Check out this map for 2009073000 UTC:

http://www.atmos.washington.edu/marka/sfcplot.hot.gif

High temperatures reported today: Chehalis MS (CHHLS) reported 111F, Winlock (WINLK) 110F, and the Chehalis RAWS site reported 2 hours at 114 F (someone should check this thermometer for accuracy before we believe this one):

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UPDATE II: The Record is Broken!

It happened...Sea Tac is now 101 and STILL CLIMBING. Everett is an amazing 98 and Renton 102. And this is not over yet. We will not only break the record but smash it. Locations near the foothills are reaching 104- 106. This is an extraordinary event. Many stations will break their all-time record temperatures today and even more their daily values. Ballads will be written about the heat experienced today.

Convection is forming over the mountains. Today I noticed altocumulus castellanus...midlevel convection... on this side of the Cascades. The focus of the convection may shift our way.... In fact, looking at the radar and satellite imagery...it already has.

I went outside before...when I walked over asphalt or concrete my face felt on fire from the combination of high air temperature plus radiation emitting from the surface. Some students in my dept measured the surface ground temps with an infrared thermometer...they found 120-150F in some locations.

And did I mention that tomorrow will be almost as hot in the interior? Low clouds are pushing to the coast now...so go there if you want relief.

For those interested, I will be talking on the Weather Channel late this afternoon about the situation at 5:40 PM

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Update

I don't know if I have ever seen temperatures rise this fast around here before. We had very warm air aloft and a very shallow inversion above the surface. This inversion was rapidly mixed out by surface heating and the easterlies aloft...thus, the rapid temp rise. Some of the warmest temps are in the foothills (e.g., North Bend) due to the downslope flow off the Cascades. In fact, with offshore flow the foothills can be the warmest locations in the whole region. The north Sound is much warmer today (now 93 in Everett)

Probcast (www.probcast.com) is back up....the power outage on campus is over. I bet it was heat related (it was a transformer failure)

Sea-Tac actually went down last hour (93 to 90), as weak northwesterlies reached the airport. If the temps continued to rise at the rate they were going we would have been 120F today. So the pause is expected...don't worry, it will start up again next hour.

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One Record Down, One to Go?

Looking at the hourly data at Sea-Tac Airport, it appears that we have broken the record for highest minimum temperature in Seattle history. It was 69F and so far today the airport has only dropped to 71F, and it has subsequently rise...so that is probably it. This is a major record to break. At 9 AM Sea-Tac is 88F, 10F ahead of yesterday (due to the downslope flow). We are probably going to break the all-time record high--will be hard to stop it now.

Now, what about the high temperature record--of 100F. Yesterday probcast was giving the most probable maximum for the airport of 101F (by the way, so many of you have hit the site that it appears to be unavailable now--there is a major power failure on campus, probably heat related, and the building with the computer server is affected). If we do this, it will be close.

The sand point profiler and surface observations indicates that temps are warmer the lowest thousand feet or so, but slightly cooler air has moved in aloft (see figure, time in UTC, 2912 is 5 AM, heights on left in meters, red lines are temps in C). This air is associated with southeasterly flow that has developed aloft. This was forecast yesterday--high pressure building in east of the mountains has reversed the east-west pressure gradient, producing offshore and downslope flow. Downslope flow produces compressional warming and works against the cooling northerlies that often develop in the afternoon over the central Sound. But cooler air aloft obviously works against it. The models and probcast suggest the balance will be towards warming today. Below is the latest night's high resolution (4-km, WRF model) run for this afternoon at 5 PM, showing temperatures at 2 meters (surface temps). Note the zone of above 100F than includes Sea-Tac.
The Willamette Valley is much hotter--several locations will get to 105F. Their lack of proximity to water makes that area an oven in these situations and they are often 5-15F warmer than the Puget Sound region.



Anyway, more later...this is going to be close.

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