Thursday, July 30, 2009

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.

Wednesday, July 29, 2009

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:


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):

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

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.

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.

Tuesday, July 28, 2009

Heat Update

What is happening now is really amazing. The atmosphere above us has warmed substantially during the past 24-h. Seattle is 5F warmer than it was a day ago and the air aloft (measured by the Sand Point profiler) is about 6F warmer. The minimum temperatures this morning are considerable warmer this morning compared to yesterday morning. Clearly, today will be substantially warmer and SEA-TAC will get close to 100F today. Some warmer Puget Sound locations will get to the century mark. And remember, the Willamette Valley got to 100F yesterday...although they have done that many times (they don't have the cooling influence of the water that the Puget Sound region enjoys. My book has a section on the heat of the Willamette Valley and the major temp records around here)

We way well break another major record....the high low temperature record...which until now has been 69F. Will know in a few hours whether that record is gone.

Probcast is still going for over 100F tomorrow...and Thursday as well.

One unusual aspect of this heat wave...and something that has made it feel much worse....is the humidity. Dewpoints are very high for around here...generally in the 60sF and in some places close to 70F. Feels like an east coast summer. Dewpoint is a good measure of the amount of moisture in the air (much better than relative humidity which varies during the day as temperature changes). More moisture in the air makes us feel warmer by lessening our ability to evaporate water from our skin (sweat) and the moisture partially blocks the infrared radiation leaving the surface....thereby keeping the temperatures up.

Anyway, this is a very serious weather event, and the National Weather Service has upped their predictions to the century mark. People don't think about heat waves in the same vain as storms, but heat kills more people around the world. So drink lots of liquids and check on the elderly, who are particularly vulnerable. Another risk is for kids in sports camps, where heat prostration can strike even the young. I am going to bike to work as usual, but will go early and my route is in the trees.

Monday, July 27, 2009

Major Heat Wave and Possible Record



Today is running 7F ahead of yesterday, which got to 89F. It is clear that temps will get into the lower to mid 90s around the region today. Our most skillful tool for predicting temps...probcast..is now forecasting 102 for sea tac on Wed...this would be the all time record for any date in any year. Above is the probcast forecast for the max temps on Wednesday (you can see it yourself at www.probcast.com. The purple colors indicate where temps should be higher than 97F). Amazingly, this heat wave could last into the weekend (although the temps should modify a bit on Friday into Sunday, but still in the 80s). And remember, it will be hotter in Portland and the Willamette Valley, where temperatures well into the 100s will occur.

The heat wave is made worse by the high dewpoints today. Many locations are in the sixties, some in the upper 60s and near 70F. Dewpoint is a measure of the absolute amount of moisture in the air..we are usually in the lower 50s in the summer. High dewpoints keep nighttime temperatures up--which makes a heat wave much worse.

In short, we are about to enter an historic heat wave for our region. One day, your grandchildren will ask you... did you really experience the temperatures of July 29th, 2009? What was it like? How did you survive it?

Sunday, 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.

Friday, July 24, 2009

The Noctilucent Clouds Return and the Upcoming Heat Wave



Many saw the noctilucent clouds again last night and a few of you sent some pictures. Above are some pictures provided by Reid Wolcott (top) and Dennis Bell. The "tendrils" of white and blue-white structures of these extraordinarily high (roughly 50 miles up) clouds are other worldly.

The number of observations of these clouds seem to be increasing and some suggest that global warming is to blame. Global warming? Strangely enough, global warming warms the lower atmosphere (the troposphere), but cools the upper portion of atmosphere in which the noctilucent clouds reside. Very cold temperatures are needed to produce these ice clouds, since so little moisture is available at those levels. Interesting idea, but not proved at this point.

We are on track for an extraordinary heat wave next week...or so the models suggest.We will have very warm air over us. However, to get the real record-breakers, strong offshore and downslope flow is needed and it doesn't look that such easterly flow will develop until mid week. One unusual feature of the predicted heat wave is its duration. Normally, our really hot (above 90F) periods are brief...this could last for days. The warmest days look like Tuesday through Thursday. Some of the media jumped the gun going for the 90s over the weekend. More on this over the weekend...but be ready.

HOT TIP: Nothing does better getting the future temps right than the UW probcast system that uses post-processed ensemble predictions. It always beats other forecast guidance during such warm-up situations. Check it out at:

http://www.probcast.com/
Right now it is going 89F on Sunday. I bet it is on the mark for this!

Tuesday, July 21, 2009

Drought and Heat

This morning, Mark Albright of the UW shared these numbers with me:

2009 is the driest 20May-19 Jul period on record using the combined SeaTac/downtown observations:

2009 60 0.24
1925 60 0.42
1938 60 0.57
1922 60 0.61
1945 60 0.67
1911 60 0.72
2003 60 0.77
1965 60 0.79
1926 60 0.83
1927 60 0.87

This is really an extraordinary drought we are in. And the surface "fuels" are tinder-dry in eastern Washington and in the Cascades.

Tonight we will have a minor onshore push of marine air. The pressure difference between Seattle and the coast is now 2.7 mb and southwest winds are pushing through Shelton. It got to 87F today at Sea-Tac--tomorrow should be in the lower 80s.

I took a look at the long-range forecasts and was shocked. The temperature climbs through the weekend...into the lower 90s on Sunday and mid 90s at least on Monday and Tuesday. Too far out to be sure now....but be ready for real heat.

Monday, July 20, 2009

Eastern Washington Smoke


Today I flew to Cape Cod for a meeting on moving weather research to operations. I ALWAYS get a window seat. As we crossed the Cascades I was stunned on how murky it looked....there was clearly lots of smoke and it was pushed up against the eastern slopes of the Cascades.

Take a look at this satellite picture from this morning....there is a significant fire in southern BC and the smoke plume is heading south (see red arrow). Can you see the smoke entering eastern Washington?

You will also notice the extensive low clouds along the coast and the tendrils almost reaching the south Sound. Later on during the day the smoke plume was less distinct..the vertical mixing due to surface heating helps diffuse the smoke in the vertical.

There are going to be a lot more fires. In contrast, the people I talked to today here in New England were complaining about their cold, dreary summer.

Friday, July 17, 2009

When is the windiest time of the day?

This time of the year there are real differences in wind speed during various times of the day and in virtually all locations it is windiest during the late afternoon. Take a look at the above trace of weather observations at my department at the UW (you can click on it to see a bigger version). Note: times are in GMT/UTC... 00Z is 5 PM, 18Z is 10 AM, etc. Winds are light during the late evening and early morning, then pick up during the morning hours. You will also notice the wind shift...typically southwesterly in the morning and northwesterly during the higher wind period.

How about Hoquiam or Ellensburg over the past two weeks? See the attached graphics. You will see a strong daily (diurnal) variation in wind speed.
So why do winds vary during the day so much? A few reasons. The first is that winds generally increase with height in the atmosphere (since friction or drag is greatest near the rough surface). During the night when the surface cools, the atmosphere is more stable in the vertical (less mixing when cooler, dense air is low down). During the day, the surface warms and the air tends to mix in the vertical, as less dense, heated air rises. More mixing brings the winds down from aloft and thus the winds tend to be stronger.

But there is another reason...local, diurnal circulations like the sea breeze. At night land and water are similar in temperature around here, but during day, and particularly warm days, the land heats and pressure tends to fall over land compared to water. The result are sea breeze circulations that increase winds. On the coast near Hoquiam there is a classic sea breeze across the coast. Over Puget Sound there is the Sound breeze between the water-filled NW interior and central Puget Sound, which is mostly land. For Ellensburg, there is a huge "sea breeze" between the strongly heated eastern side of the state and the cooler west. If you want to learn more about these diurnal circulation, my book has a whole chapter on it.

Talking of weather, today (Saturday) is slightly cooler than Friday since there was more marine air moving in last night. Even more marine air will move into the western interior on Sunday. But temps will remain in the 70s and no precipitation is forecast. We have serious dry conditions, particularly east of the Cascade crest. The threat of major fires is quite real.

Wednesday, July 15, 2009

The highest clouds of the world over Seattle


Above is a picture taken after sunset at Seattle's Shilshole Bay Marina by Joseph Marsh on Tuesday evening. Just clouds? Not quite...these are very special clouds that are the highest clouds on earth...noctilucent clouds.

These clouds are most commonly seen on clear nights north of roughly 50N during the summer months. They are located in the mesosphere at heights of roughly 50 miles above the surface. (Remember...the layers of the atmosphere are troposphere, stratosphere, mesosphere). These are ice clouds that form on dust, probably produced by meteors. Such clouds often have a silvery or bluish color, and a ragged look.

Want to see the clouds in the department time lapse imagery? Check out the following and wait until the very end, after sunset:

http://www.atmos.washington.edu/images/webcam0/movies/20090714.mov

So on the next few clear nights take a look during twilight and see if you can spot them.

Monday, July 13, 2009

Amazing Amounts of Lightning




There were nearly 35,000 lightning strikes over the area over the 48h period ending this morning around 7:30 AM. Pretty amazing. The graphic above is from the national lightning network-- a series of sensors that can receive the electromagnetic pulses produced by lightning.

You will notice there is positive and negative lightning strikes indicated. Most cloud to ground strikes are negative, and only a small proportion are positive.

Friday, July 10, 2009

Thunderstorms

We have some potentially interesting weather coming up. But not tomorrow. Saturday will be beautiful...warm (into the lower 80s over much of the lowlands) and dry away from the mountains. Up in the Cascades there is a slight chance of some convective showers. But nothing serious.
And then there is Sunday. The air over us will be unstable, which means a little lift can release convection (i.e., thunderstorms). A measure that meteorologists look at to determine the potential for thunderstorms is CAPE--Convective Available Potential Energy. Sound impressive. Anyway, the values on Sunday will be high..particularly over the mountains (I have included a graphic of it that you can use to impress your friends). Normally we don't see CAPE of more than a few hundred here. But the CAPE tomorrow afternoon approaches 2000 over the northern Cascades, and over a thousand above all terrain. Something major is going to happen. In addition, an upper trough (which provides lift to release the instability) will move through on Sunday (see graphic). Between them, there is good chance of showers and thunderstorms over the mountains during the day and eastern Washington at night (see graphic of precipitation). Even a chance the lowlands could catch some of the action. Now a big worry is lightning caused fires...so we will have to watch this.

But wait! There's more! The trough will help incite an onshore push, which will bring cooler marine air into the region starting Sunday afternoon.

So enjoy a picnic tomorrow and enjoy the weather action on Sunday..particularly later in the day.

Also, If any of you are interested I will be giving a oublic talk in Leavenworth at 7 PM on July 31st and a book signing at 1 PM on August 1 (see more info to the right).

Wednesday, July 8, 2009

My Weather DVD


You have the book...now you can get the Northwest weather DVD! I am a strong supporter of Public TV and when they asked me to tape an introduction to Northwest Weather as a pledge gift, I was happy to do it. This hour-long presentation is a general introduction to Northwest weather and includes many of the graphics from the book. This was not easy for me...they even had me put on make-up. KCTS is asking for a donation of $50 to send it to you. Anyway, the funds go to a good cause, and if you are interested just click on the picture to the right or go to

https://secure.publicbroadcasting.net/kcts9/KCTSWeatherWisdom/form.pledgemain

Dry Sky Parties



One of the inside jokes of the meteorological profession is that summer in the Northwest begins on July 12. And usually that is about right. June often is cloudy and gloomy (but not this year!), and sometimes showers darken the skies around the fourth of July. But in the later portion of July the climatological probability of precipitation plummets to around 10% in the lowlands with many locations receiving less than an inch. Strangely, the lowlands of the Northwest are some of the driest locations in the entire U.S. in July and August. Drier even than the desert southwest, where "monsoonal" rainfall hits during the summer.
Take a look at the plot of the probability at Sea-Tac Airport of at least .01 inch of rainfall (.01 is the minimum required to call precip "measureable"). During July the probability drops from near 30% in the beginning of the month to LESS THAN 10% during the last few days. This is really extraordinary. The driest day of the year? July 29 gets the least on average.... .004 inches. For many meteorologists there is a tradition of having a "dry sky" party during that day or the closest weekend, with suitable libations that I won't discuss in this family-oriented blog. Want to plan a wedding? That is the weekend. Some wise people picked the first weekend of August for Sea Fair.
And you can see why July 12 is often suggested as the start of summer --this is just before the rapid drop off to dry conditions.
Talking about the forecast...a band of showers are now over NW Washington and the coast...and are headed for Puget Sound. But conditions should improve towards the weekend.

Sunday, July 5, 2009

The Onshore Push has occurred

As predicted, marine air has surged into western Washington. I can hear the leaves blowing outside my window right now..and the wind chimes are ringing. Just heaven! A weaker onshore surge than June 4th and one that started in the mid-afternoon--which is unusual...most wait until the evening....

Firework Pollution? and a Major Change



Many times I have noticed that particles in the atmosphere tend to increase rapidly on July 4th...with a reduction of air quality. I took a look this morning...and it was there again..above is the trace at Puyallup and Queen Ann Hill from the excellent web site of the Puget Sound Clean Air Agency (http://www.pscleanair.org/airq/aqi.aspx). As you might suspect, fireworks probably has something to do with this (the pale of smoke is often profound after all the official and unofficial fireworks). According to Mike Gilroy, the chief meteorologist for the agency, July 4 brings the worst air quality of the year.



Today is the last warm day west of the Cascades. A look outside or the latest high-resolution image shows an obvious change...more clouds--both at low levels and aloft (see image). I plotted the temperatures the last few days (see plot)...temps have been 10-15F above normal. Last night had very high minimum temps--in the 60s in several locations.

The ridge of high pressure over us is in the process of shifting east and the clouds are associated with an approaching offshore trough (see upper level maps for situation this morning and tomorrow). This trough will initiate an onshore push tonight and marine air will fill the western lowlands. So boaters should be prepared for the influx of marine flow from the SW tonight! Today will not be cool...the temperatures aloft are just as warm as yesterday and the clouds will thin...getting back into the 80s. But tomorrow will be very different...highs near 70F. Lots of clouds and a few scattered light showers...particularly on the western slopes of the Cascades. The trough should stay in place the entire week...so expect temps a little below normal.

Thursday, July 2, 2009

How Bad Has the Drought Been?

We have been in an extraordinary dry period--and this does not bode well for the summer. Here is some fascinating statistics given to me by Mark Albright (who used to be State Climatologist). For the period May 20 through the end of June, Sea-Tac this year was drier than ANY OTHER YEAR in the 116 yr record (see numbers below). On .18 inches of rain. I know...this is a somewhat artificial period...but the message is clear...we have been unusually dry.

Ten driest 20 May-30 Jun periods in Seattle:

2009 41 0.18
1934 41 0.28
1932 41 0.31
1925 41 0.36
1938 41 0.39
1924 41 0.50
1979 41 0.54
1911 41 0.55
1922 41 0.61
1918 41 0.63

What about June alone? This was the 7th driest June in 116 years.

10 lowest June precipitation amounts over the past 116 years from 1894 through 2009:

1922 30 0.03
1951 30 0.13
1908 30 0.15
1987 30 0.16
1925 30 0.16
1932 30 0.17
2009 30 0.18*
1934 30 0.23
1895 30 0.29
1940 30 0.34

The bottom line off all this is that we are going into the normal summer dry season with very low soil and surface "fuel" moisture values and the potential for big wildfires is greatly enhanced. The eastern slopes of the Cascades have also been dry and the climate prediction center is predicting increasingly severe conditions over eastern Washington (see graphic). This is really serious and people will have to be very careful with fire (and fireworks!).