Wednesday, September 18, 2019

The Weather Outlook for the Rest of the Fall and Winter

The question many of you are asking is:  what kind of winter do we expect?

The question you should also be asking:  do such forecasts have much skill?

Well, I can give you a forecast, based on the best tools we have.  But the forecast skill is not as good as one would hope...as it always true beyond two weeks.

For the next one and a half month, probably the most skillful tool is the extended range European Center ensemble mean forecast--which projects out 46 days.  This forecast now goes out through 1 November.

The EC forecast for precipitation anomaly (difference from normal) through 1 November is for wetter than normal over most of the Northwest, with a few exceptions--well offshore and over southern Vancouver Island.


Temperature anomaly?  Slightly warmer than normal offshore, which makes sense with the BLOB still there..and warmer along the coast.  But pretty normal over most inland areas.


This forecast seems very reasonable to me.   

For the longer term, it is useful to look at the El Nino/La Nina situation.  Remember that El Nino is associated with warmer than normal sea surface temperatures (SSTs) in the central and eastern tropical Pacific.  La Nina is when the water in that area is cooler than normal.   Neutral (or La Nada) situations are when the SSTs are within .5C of normal.

Here is a plot from the NOAA Climate Prediction Center (CPC) of the sea surface temperature anomalies (again difference from normal) for some well-defined areas in the tropical Pacific (a map of the areas is found below).  The Nino3.4 area is the one most commonly discussed.  Time increases to the right. 

You can see we have gone from an El Nino period to a neutral period---with the sea surface temperatures cooling off a lot over the summer.



A wide variety of statistical and full physics models are run to predict the temperatures in the Nino3.4 area. The results of these predictions made last month suggest that we will end up slightly warmer than normal-- in other words, a neutral state.

And the most recent probabilistic prediction of the NOAA CPC folks is that a neutral situation is most probable, with a bias towards the warm side.


OK, the best bet now is that we will be in a neutral situation in the tropical Pacific. 

So what does that mean for us this winter?

The bottom line is that there is no reason to expect an anomalous winter in our area.  Starting with a warm Pacific and the modest warming associated with increasing greenhouse gases, going for modestly warmer than normal temperatures here in the Northwest (normal being the conditions of the past 30 years), seems reasonable.

No reason not to buy an annual ski pass if that is what you like to do.  No reason to expect any kind of drought situation.    Good weather this fall for prescribed burns to clean up our forests (WA DNR take notice!).

Does such a forecast have a lot of skill?  Te El Nino/La Nina connection with our weather can explain  perhaps about a third of the year to year variability of our weather.   Not as much as we would like, but still useful.





Monday, September 16, 2019

Why have our low temperatures been so HIGH this summer?

Have you noticed something meteorologically very strange this summer?

The overnight low temperatures have been very warm for pretty much the entire summer.

I can demonstrate this in several ways.    Let's start with a plot of the temperatures at SeaTac Airport for the last 3 months, with the average highs (purple) and lows (cyan) shown.  Mama mia!  The observed minima were above normal of most days--often by 3-6 F.   Sometimes even more.


A plot of the difference between the observed and normal temperatures for the last 90 days shows the same thing (see below)--but with a few wrinkles.   The coastal zone is all warmer than normal, with some places 3-5F above normal.  But go inland and many areas have normal temperatures--some even below normal temperatures.  Why is that?

Scott Sistek on his KOMO-News blog ran some of the numbers, finding that this summer we had 79 days in a row at or above 55F...absolutely SMASHING the previous record of 52 days set in 2013. 

The high minimum temperatures have made my tomato plants very, very happy--but why have we been so warm in the morning?

I think I know the answer--- warmer than normal sea surface temperatures over the eastern Pacific.   Also known as the BLOB--or in this case BLOB junior.

Here is a plot of the sea surface temperature anomaly (the difference of sea surface temperatures from normal) for the past 90 days.  You see the warm area off our coast?   A large area of 2C above normal--some a bit more?   That is the key feature.  2C is about 3.6F above normal....just in the neighborhood of how much warmer than normal our minima have been.

Now physically this all makes a lot of sense.    On most days, he air over the western WA lowlands was over the Pacific Ocean a few hours earlier, with the temperature of the surface air determined by the temperatures of the ocean's surface.

But there is more--the amount of moisture that air can pick up from the ocean depends on sea surface temperature---since warm air is able to hold more water vapor.  In fact, the amount of moisture air can hold goes up exponentially with temperature--that means REALLY quickly.  This figure illustrates this fact (saturation mixing ratio is the maximum amount of water vapor a sample of air can hold at a certain temperature).  So having air above warm water means the air can pick up more water vapor from the water.
Why does this matter?  Because water vapor is a potent greenhouse gas that warms the surface of the earth by reducing the loss of heat to space (sort of like an atmospheric blanket).  And a measure of the amount of low-level moisture in the air--the surface dew point--HAS been higher than normal this summer in western Washington.

So how can we really clinch this relationship between warm sea surface temperatures in the eastern Pacific and our minimum temperature "heat wave"? 

There is a way: we can play God using our WRF weather prediction model.  I asked UW Research Scientist Dave Ovens to do an experiment.  Redo an extended (7.5-day) forecast but replace the atuall warm sea surface temperatures with normal (or climatological) values of sea surface temperature.

Here are the results for a 7.5 day run verifying 5 AM last Friday--specifically the differences in surface air temperature between the current sea surface temperatures and normal sea surface temperatures.  Warmer air temperatures over ocean, which extend into western Oregon and Washington.  The Cascades seems to be holding back the influence from the interior.  Bingo.



Dew point temperature (again a measure of water vapor content) differences.... same story.  Much more oven the ocean, but with higher values getting into the coastal zone (and a bit farther in eastern WA). Bingo2.

So I think we know the culprit for our warm minimum temperatures...it is the area of warm water over the eastern Pacific.   A.K.A. the BLOB.

What caused the BLOB?  A combination of persistent high pressure that reduced vertical mixing in the ocean and southerly winds.  Essentially, a highly anomalous atmospheric circulation over the North Pacific.   That also can be inferred by the SST anomaly map shown in the third figure, since the north Pacific seems to be a big outlier.

Global warming could be making a small contribution.  A map of the surface temperature change from 1930 to now (from the NASA GISS site) indicates a warming of .2-.5C (.35-.9F) over the period.   Some, but not all, of that temperature increase might well be associated with global warming.



Saturday, September 14, 2019

Two Strong Fronts will Bring Unusual Amounts of September Rainfall

If the model forecasts are correct, this is going to be one of the wettest Septembers in recent memory.  And it is clear: wildfire season is over.

The first act starts tonight as a strong front moves in this evening.  The coastal radar is being overhauled--so I can't show you an ominous radar view.  But the latest infrared satellite image is impressive--particularly for September.


The UW high resolution WRF model 3-h precipitation forecast for 2 AM this morning show the front moving in.  And with the front, winds are going to pick up.

And then as a low pressure area moves towards us on Sunday, the precipitation will blossom, filling much of the state with moderate rain (see 3-h rain ending 2 PM Sunday).  This would be a lot for November.  And extremely wet for east of the Cascades.  


And then ANOTHER unusually strong front moves in on Tuesday (see below)


Now...are you ready to be meteorologically shocked?  Here is the accumulated precipitation total through 5 PM Tuesday.  Amazing.  Big areas of 2-5 inches.  Lots of rain in eastern Washington.


This September is already wetter than normal.   After the next week, the region will be thoroughly soaked.   A good time to plant grass seed or put in some bushes or other plants in the garden.

Thursday, September 12, 2019

President Trump Damages U.S. Weather Prediction--But He Had Help

During the past week, there has been non-stop media coverage of Trump's  problematic foray into weather forecasting.

But what has not been covered is the damage done to NOAA and the future potential of U.S. weather prediction by this incident.  And the potential damage to the careers of some exceptional public servants caught in the undertow.  Or real evaluation of what Trump said about Dorian.

Although Trump, his chief of staff Mick Mulvaney, and his Commerce Secretary Wilbur Ross are prime villains in this story, some of the media, the political world, and even some in my community made the whole situation much worse than it had to be.   There are a lot of subtleties being missed in the public domain--so let me provide my take on it.

Trump works by doing outrageous things, getting lots of attention, provoking an excessive reaction from the other side, which he points to as proof he was right.  And on and on.  All kinds of folks start fighting each other, innocent individuals get hurt, and national interests are undermined.

Trump's Forecast

This unfortunate interlude began with Trump's tweet on Sept. 1st, in which he suggested that South Carolina, North Carolina, Georgia and Alabama would be hit much harder than expected by Dorian.   Now the forecast had changed before his tweet, with the storm moving northward towards the Carolinas.  So he was partially correct.  But what he said about Alabama was wrong-- with the new track Alabama had a sharply reduced threat.


Within 20 minutes of Trump's tweet, the Alabama NWS responded (they are in central time).
They make a strong blanket statement that Dorian would have no impacts on Alabama.  If they had said that there was a high probability that there would be no significant impacts, they would have been in an unassailable position.  But their wording left them open to criticism for two reasons.  

First, the most up to date forecasts on Sunday morning had a slight probability (5-10%) of tropical storm winds  reaching Alabama (see below)

Second, and even more important, as the storm passed there WERE modest impacts on Alabama, with winds gusting to around 25 mph.  Below is the proof, showing the maximum winds on September 5th.  The ovals indicate the areas of gusty winds reaching 25 mph over Alabama (click to enlarge).  And sinking air forced by the storm resulted in several daily temperature record being broken in Alabama.  So the impacts were minor (perhaps a few broken branches), but if one was talking literally, there were impacts of the storm.


And why did the Birmingham NWS forecaster provide a prediction for the entire state when his/her responsibilities were solely for the northern area around Bellingham?  Established NWS protocols were not followed.

You would think that there was not enough "meat on the bone" for this Alabama forecast business to have any traction, but that was not the case.   Many media sources went nuts, with all kinds of stories making fun of Trump.  And how he was undermining weather prediction, etc.  Just a bit too much (see below)


This was revved up even further, when Trump appeared to be unfamiliar with the occurrences of category five hurricanes during recent years (there have been a few):

“I knew it existed, and I’ve seen some Category 4s ― you don’t even see them that much ― but a Category 5 is something that I don’t know that I’ve ever even heard the term other than I know it’s there,” he told reporters.

It is clear that the President is uninformed about hurricanes--and he made a mistake on the Alabama threat.  But the media went into hyper mocking mode and tried to score some points on him...and this President doesn't like to be mocked and went into full defense mode. 

What makes the media reaction so overblown is that no one takes Trump's forecasts seriously, not even the most strident Republicans.  I confirmed this by asking a few enthusiastic Trump supporters.  They love the guy because he is bull in the national china shop--but for weather predictions, they trust the National Weather Service and the National Hurricane Center.

Sharpiegate

The next stage of this sad drama occurred on Wednesday, when President Trump talked about the hurricane and used an OLD National Hurricane Center uncertainty chart (see below).  I mean really old (the previous Thursday).   He was basically saying (correctly) that the previous track took the storm into Florida and the Gulf, but the latest predictions swung the storm north.  What he said was true.  But there was a line going into Alabama on the original map suggesting an extension into the Florida Panhandle and a bit of Alabama.  He never discussed it.


But that unmentioned line cause the media and some others to go wild, claiming he was deceiving the public, illegally altering official NOAA charts, and more.    This reaction was totally excessive and was meant to put Trump on the defensive.

But if someone knew anything about some uncertainty charts, that line was not unreasonable if it refereed to the path of the hurricane at the time the chart was released.   If the storm HAD followed the path shown, the storm might well have gone into Alabama.   In fact, the ensembles of many forecast at that forecast initialization time (Thursday morning, August 29th), DID have trajectories going into Alabama (see below), which Trump actually did mention.  He was right about that.


But now the media was going in full-tilt Trump mocking mode, particularly CNN.  A lot of it was simply unfair.   And their continuous attempts to embarrass him, particularly on the Alabama business, led to something far more serious.

According to the NY Times,  Trump told his Chief of Staff, Mike Mulvaney to have NOAA deal with the situation and particularly to "clarify" or publicly correct the forecasters' position.  Mulvaney then called Wilbur Ross, Commerce Secretary, who in turn telephoned Neil Jacobs, Acting Administrator of NOAA.   The NY Times sources then suggest that Ross told Jacobs to fix the situation, threaten to fire Jacobs and others if something wasn't done.  Ross denies giving such threats.

Neil Jacob's Dilemma

Dr. Neil Jacobs, who is now running NOAA, is a very good scientist and an expert on numerical weather prediction.  He is not political, but extraordinarily dedicated to improving U.S. weather prediction.  He is the change agent that NOAA has needed for a long time.  And I am not saying this in ignorance--I know him quite well and have worked with him for years, including at his previous position as lead weather scientist at Panasonic.  But he is a young man without extensive experience in DC and dealing with its shark-filled political waters.

Neil Jacobs

According to the NY Times, he pushed back on Ross' demands.  But he was under great pressure.  What should he do?  Neil knew that the Trump administrator was supportive of improving U.S. weather prediction (as are legislators on BOTH sides of the aisle).    So should he resign or publicly oppose the President, and jeopardize the potential to enhance weather prediction, which would save lives and property?  Or should he write an innocuous statement that was completely true and one that any real meteorologist would immediately know was meaningless, but would satisfy the weather-ignorant in the Trump administration?

You might disagree with the latter approach, but that is what Neal did--hoping to protect the long-term progress of US weather prediction.   Here is the statement that NOAA released on Friday


Let's examine it.    The first paragraph is completely correct--the National Hurricane Center guidance DID have a chance (admittedly a small one) of tropical storm force winds getting over Alabama.   And the Birmingham NWS forecasters said there would be NO IMPACTS and did not qualify the risks properly (impacts of what?, suggesting the chances were zero % rather than the predicted 5-10%).      Quite honestly, I have been at a number of professional meetings on this very topic, where forecasters are advised to use probabilities more and not to communicate risks as 0 or 100%.

This statement is like a dentist telling you that you did a great job on cleaning your teeth, but forgot to floss one tooth.

So Neil's approach was a clever way of not really criticizing the forecasters seriously but seeming to say something in the minds of the uninitiated.  I smiled when I read it.

OK, perhaps he should have called NWS Director Louis Uccellini and NOAA AOR Head Craig McClean and others to create a pact where they would all stand up to the Trump folks--but such an approach had risks with such an unsteady and unpredictable group in the White House.  What he did was not unreasonable and not unhonorable.  And he is getting severely criticized in some quarters for it....unfairly I believe.

The Knives Come Out

The NOAA statement caused a firestorm, both inside and outside of NOAA with folks suggesting it represented a profound attack on NOAA's independence, of unethical behavior from NOAA leadership, a degradation of NWS forecasters and worse.  Some individuals inside of NOAA, who should have understood the dynamics of the situation and what Neil was trying to do, took out the knives.


Just classic Trump---he stresses an agency or group until the good guys start turning on each other, producing the bedlam that is his hallmark.   And the impacts are profoundly bad for the American people.

On Tuesday, Neil talked to the professional group encompassing many National Weather Service forecasters (the National Weather Association).  Instead of discussing the key innovation he was working on to improve U.S. numerical weather prediction (the EPIC center), he spent his time giving an emotional talk about the importance of forecasters in the National Weather Service.  Everyone listened respectfully and at the end his received polite applause.  But the momentum to make U.S. weather prediction a world leader again has been greatly lessened.

It is time for my community to come together, stop attacking each other about how we deal with Trump, and get back to work making U.S. weather prediction the best in the world.   And I hope that political leadership in both parties will protect people like Neil Jacobs, whose only goal is to serve the American people in such a critical capability for the nation.  The battle between Trump and his opponents is loud and energetic, but NOAA should not be caught in the middle and end up collateral damage.

Tuesday, September 10, 2019

Super Heavy Rain in Everett Causes Flooding

On Monday night, an intense convective cell parked itself over Everett producing very heavy rain, sewer overflows, and flooding that closed some roads and Everett High School.

Steve Link's twitter feed showed some of the action:


How much rain?  During the 11h ending 11 PM Monday, there was about 3 inches (see below)..and much of that fell between 5 and 7:15 PM Monday.  Surrounding areas had a few tenths or less.


Let me show you as series of radar images between roughly 6 PM and 7:15 PM Monday.  Red colors are the really heavy stuff.

 At 5:56 PM, a strong cell was over Everett.


6:08 PM--still there.

6:20--it is pouring over Everett still

7:07 PM--starting to fade.

The visible image at 6:20 PM shows the convective cells:

The tops of these convective cells got to around 21,000 ft...nothing like the massive storms we had on Saturday night (see radar echo top below)--- thus, there was no lightning with them.   They just got locked up for a while over Everett, for reasons I can only speculate on.


Everett could use their version of Seattle RainWatch--a radar-based warming system we developed for Seattle. 

Monday, September 9, 2019

Why So Much Lightning over Western Washington on Saturday Night?

Saturday night was the "perfect storm" of western Washington lightning, producing the best display in 20 years.   There were thousands of lightning strikes between 6 PM and midnight, driven by unusually vigorous thunderstorms.

But why?

Before I answer that question, let me get you into the mood by watching an extraordinary video produced by the master of weather cams, Greg Johnson of Skunk Bay weather.   He has four cams looking northward from his home on the north side of the Kitsap Peninsula.  Stunning amount of lightning was captured by his cams...both cloud to cloud and cloud to ground. Be prepared to be moved....




To get strong thunderstorms, the key requirements are an unstable atmosphere--one that will convect if air parcels are lifted---and something that will push the air parcels upwards until they can rise on their own.   And for Saturday night's thunderstorms, we needed something else as well--winds aloft that would direct the thunderstorms away from their generation points in the Cascades and up Puget Sound.

Extraordinary Instability

A column of air is primed for instability when the temperature decreases rapidly with height, and
with plenty of moisture in the layer near the surface.     A measure of the potential for instability is something called CAPE:  Convective Available Potential Energy.  The values of CAPE forecast over western Washington for Saturday late afternoon and evening were amazing (see below), with CAPE at 5 PM getting to around 1500 J per kg over the Cascades and 700 over Puget Sound.  Around here, we get excited when we get values reaching 100-200.  So the values were very high, very unusual, and signified the potential for strong thunderstorms.


One reason that values were so high was the blob of warm water off our coast.  The  BLOB not only contributed to warmth at the surface but more water vapor--important fuel for instability.   The eastern Pacific sea surface temperature is roughly 5 F above normal and that implies substantially more moisture in the lower atmosphere.  At the same time, an upper level trough was bringing in cooler than normal air above the surface (see map for 500 hPa...roughly 18,000 ft).   So warm, humid air at low levels with cold air aloft.  That means a large change of temperature with height and lots of potential instability.


But as in the late night commercials, WAIT...there's even more!  The approaching upper level trough was associated with upward motion, which help trigger the convection (thunderstorms).   Initially, the focus of the storms were over the Cascades, because the mountains provide more lift and an elevated heat source.

But because the trough was negatively tilted--oriented northwest-southeast--the flow aloft had a southeasterly aspect to it (flow from southeast), which helped the thunderstorms born over the southern Cascades to move over the western lowlands.  This southeasterly flow was evident in the winds above SeaTac Airport as shown below (see blue oval indicates the relevant elevation and time). The heights are in pressure, with 700 about 10,000 ft.  Time is on the x-axis, with 08/03 being 8 PM and time increasing to the right.

So we had the trifecta for Puget Sound thunderstorms:  great instability, a sharp trough aloft given strong lift, and the perfect winds to drift the storms over the lowlands.

To have the combination of all three is quite rare around here. As noted in my earlier blogs, the large instability produced some of the tallest, strongest and most numerous thunderstorms we have seen here in a very long time.  Some tops got to 40,000 ft.

 The ultra-high resolution UW WRF model did an amazingly good job on the forecast.  Here is the simulated infrared 18-h forecast from the highest resolution domain.  It was going for big convective cells over western Washington. Impressive.






Saturday, September 7, 2019

Major Convective Event, with Heavy Rain, Lightning and Thunder, Moving Through Puget Sound

An unusual major lightning/thunder event is occurring over Puget Sound, delaying the UW Husky Game. 

And interestingly, the UW WRF model forecast the event earlier in the day.

The radar at 8:15 PM shows the action, with the red colors being very heavy precipitation within convection.


The view from Husky Stadium was amazing.   Good idea to get folks off the field and out of the stands.
Picture by Peter Benda


The WWLLN lightning network shows extraordinary amounts of lightning over the area.  Here is the lighting totals for the 30 minutes ending 8 PM.   Puget Sound is being pummeled by lightning!

What is really amazing is the large number of power outages associated with the lightning (see below).  Seattle's system is poorly protected from lightning because it is so rare.


The convection is associated with a very sharp upper trough that is making landfall, coupled with some unusually unstable air over western Washington. Here is the upper level (500 hPa) map for 8 PM Saturday...very sharp trough making landfall.



Forecasts were very good.  Here is the high resolution WRF forecast initialized 5 AM this morning showing the 3-h rainfall starting 8 PM.  Impressive.

Update Sunday Morning

Here is the incredible lighting strike map for the 24 h ending 1 AM.   Thousands of lighting strikes with hundreds over Seattle alone.  Amazing.


The tops of the thunderstorms were exceptional for around here, with some reaching 35,000 to 40,000 ft.    Here is an example of the radar echo top at 8:19 PM...the top was 36,000 ft.  Normally, we get excited when tops get to 20,000 ft in western Washington.


Thursday, September 5, 2019

The Eye of Hurricane Dorian Passes Right Over a NOAA Buoy with a Live Webcam

Something extraordinary has happened....a hurricane (Dorian) has passed right over a NOAA/National Weather Service buoy with a cam on board, providing a unique view of what it is like to be in a hurricane at sea.

The location of the buoy (41004) is shown below, with the current location (red dot) and predicted future track of the hurricane shown as well.


The pressure (green line) and wind plots (sustained and gusts) at the buoy are shown below.  You can see how the winds peaked in the eyewall of the hurricane, with gusts as high as 85 knots, and dropped to near zero in the middle of the eye where the pressure was a minimum.  Just amazing.


But now the amazing part....the pictures from the buoy!  Here is one, inside the eyewall at 1810 UTC (click to expand).  Huge waves, like a wall in front of the camera.


One hour earlier, you can see more...with big waves and a huge amount of spray

Looking back to 1610 UTC, when the buoy was in the center of the eye, the scene was bright, the waves were less and birds were flying around. They were trapped.


 If you want to check it out yourself, here is the link

The differences in wave height inside the eye and in the eye wall surprised me.   Here is the plot of significant wave height (average of top 1/3 of waves).  Increased to around 25 ft in the eyewall, follow by a drop to 11 feet in the eye.


 Next buoy to be hit is Frying Pan Shoals where the wave height is currently only 21 feet....and here is the image.  You don't want to be out there.