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Models need (and will get) improvement

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Two news stories about forecasting models caught my eye this week. The first dealt with a shortfall in the climate models and the second was good news about continuing improvements in our daily forecasting models.

I’ve written before about potential problems with initial data and assumptions in climate forecasting models – the ones used by climatologists to predict our global conditions decades in the future. Like it or not, they are not perfect.

NASA climate map

Credit: NASA, 2015. “NASA global data set combines historical measurements with data from climate simulations using the best available computer models to provide forecasts of how global temperature (shown here) and precipitation might change up to 2100 under different greenhouse gas emissions scenarios.”

Some researchers from Princeton University drove that point home with a recent paper in the journal Nature Communications. Jun Yin and Amilcare Porporato’s paper, “Diurnal cloud cycle biases in climate models” details how they carefully analyzed satellite data from 1986 to 2005 and compared the information they gleaned to what the models produce.  The two determined how the time of day that clouds form in reality versus the time of day averaged in the models can affect the amount of solar radiation the models predict.

In the climate models, the cloud cover peaks in the morning. In reality, the cloud cover peaks in the afternoon – the same time the radiation coming from the sun peaks. The amount of clouds and types of clouds between the earth’s surface and the sun make a difference in how much energy from the sun we receive. The climate models’ were over-estimating that amount and potentially forecasting hotter and drier conditions based on it.

The paper states, “Thus, on the one hand, consistent biases in DCC [diurnal cycle of clouds] between present and future climates give rise to similar TOA [top of the atmosphere] reference irradiance, so that the model tuning made for current climate conditions still remains largely effective for the global mean temperature projections. On the other hand, consistent biases have the potential to increase the uncertainty of climate projections.” In simpler terms, the researchers don’t think the temperature forecasts are completely wrong, but they have shown the margin of error may be much greater than most scientists have acknowledged up to this point.

The hope is for the results of the study to be used to improve the current models.

In another story, the National Oceanic and Atmospheric Administration (NOAA), released the news on Tuesday that they are in the third phase of a massive supercomputer system upgrade. This year’s improvements increase the processing speed to 8.4 petaflops and 60 percent more storage capacity. The added speed and storage will allow for more initial conditions data – extremely important information for forecasting – and higher resolution, which will help with accuracy with respect to geographical space and time.

The goal is to improve our forecasting capability, especially when it comes to warning of dangerous storms. The forecasting model specifically mentioned in the press release is the Global Forecasting System (GFS), which has a reputation among many forecasters of often being less than accurate more than two or three days out, even though it produces predictions for 10 days out. Improvements to the GFS are needed and quite welcome!

If you’re not a meteorologist or climatologist, you likely don’t know the frustration of making a forecast based on science and technology – much more than we had fifty years ago – and still knowing that there is a chance the models we rely on are missing critical input and getting it wrong. While most people may not consider a few degrees error in temperature a horrible thing, they’d probably agree when the temperature happens to be around 32 degrees, a few degrees in either direction can make a big difference in our weather reality.

Weather Blog

Obsessing over fractions of an inch

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It’s 11:00 on Wednesday morning, and I’m obsessing over every little change in the HRRR (High Resolution Rapid Refresh) model’s update. Will it be one inch or 2.5 inches of snow in eastern Wake County? Is that just half-an-inch in northwestern Wake? That’s different from what it said the last hour.

potential snowfall totals

A slide from the NWS Raleigh Office’s 10:30 AM, Wednesday, January 3, 2018 weather briefing

The HRRR is the model we put more stock in for short-term forecasting – of less than 24 hours – because it shows more detail than most of the rest. It’s usually pretty spot on because it updates so often. Each run has a better handle on where the storm will go, or at least, it should. So, we meteorologists watch it like hawks and bog ourselves down in fractions of an inch.

I literally just reminded myself that a half-inch more or less than two inches will still be a mess tomorrow morning on the roads. Yes, snow is much nicer than mix of ice and snow, but face it: we live in the south, and not everyone is a safe driver in the rain, much less on snow.

The major roads are brined thanks to the Department of Transportation. I could see the coating on my way into work early this morning on Highways 64, 96, and 98. The side streets will be another story. If you wake up tomorrow, and the news is reporting that emergency officials are asking you to stay off the roads, please heed that call if you can. I know some jobs are literally essential, but most of us can postpone our driving for better conditions.

If plows are needed, they require room to work to clear the roads. More cars for them to compete with for space means slower progress. Plus, driving before the roads are clear puts yourself and other drivers at risk. Remember what I noted above about not everyone being a safe driver? You might be the ultimate professional at driving on snow, but the guy in front of you could make a rookie mistake that leaves both of you in bad shape. Why risk it? Let the DOT and tomorrow’s sunshine do a little work first.

As for me and my obsession with how this forecast verifies… if we only get a trace of snow, I will be thankful – even if that means a busted forecast.

Weather Blog

La Nina fail?

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We are in the midst of a La Nina winter. I discussed in my blog two weeks ago how in a La Nina year, we should experience above-average temperatures and below-average precipitation. While we did have a few days of warmer-than-normal temperatures following that blog post, the cold returned with a vengeance, and it looks like it will stick around for a while.

On December 21, the Climate Prediction Center updated its outlook maps for January and the three-month period of January through March. According to those maps, North Carolina now has “equal chances” of having above-normal, normal, or below-normal temperatures and precipitation through January. I usually interpret that prediction as “your guess is as good as mine.”

CPC Jan Temps

The Climate Prediction Center’s Temperature Probability map for January 2018

Based on the long-range forecast models, it looks like we will have below-normal temperatures through at least the first full week of the month. While I don’t really trust the models almost two weeks in advance, I don’t see anything today that would make me think this cold pattern will break before January 8. So, at least the first week of January should be colder than normal.

If that first week ends up being wetter-than-normal as predicted in the CPC’s 8-14 Day Outlook, we could have some wintry precipitation. While that possibility should be expected in January, it does make me wonder where my milder winter went? Granted, climatological winter lasts through the end of February, but much of December was cold and the first part of January looks even colder. I’m feeling a little gypped and wondering if we are experiencing a La Nina fail.

But I digress.

The updated outlook for January through March still shows the likelihood for warmer-than-normal temperatures and below-normal precipitation. That map tells me that the forecasters at the CPC are still clinging to the idea that La Nina will win out over all the other factors that go into seasonal forecasting. I’m having a hard time buying it as I look at the local forecast today. Since I’m not a cold weather fan, I will cross my fingers that they are correct.

One thing to keep in mind is that these monthly outlooks are basically about average temperatures over a month or three-month period. If January verifies as a warmer-than-normal month, that would mean the last three weeks in January were likely well-above normal. Another point to remember is that a winter storm only takes a day or two to make a mess of central North Carolina. Just because the next three months could be warmer on average doesn’t mean we can’t have late season wintry weather. Ice storms happen pretty regularly for us in February and early March.

I’m always curious to see how these seasonal forecasts pan out. Every one that verifies true gives us more confidence. Each one that turns out to be a bust teaches us something. For now, all we can do is bundle up against the current cold streak and wait to see what the new year brings.

CPC JFM temp map

The Climate Prediction Center’s Temperature Probability map for January through March of 2018

Weather Blog

La Nina’s effects may finally take hold in NC

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It’s no secret that I’m not a fan of cold weather. Short, gray days alter my mood for the worse. Bitter cold makes my joints ache. Snow and ice cause transportation issues. I can’t help it. I’m a summer lover, which is why I live in the south. So, back in October, when the Climate Prediction Center issued a statement that La Nina was settling in for the winter, I did a quiet little happy dance.

La Nina tends to bring warmer and drier-than-average weather to the Southeast.

As you can imagine, the first half of December has been disappointing for me. I mean really! Near record-breaking cold, our first wintry mix of the season, and deceptively sunny, brisk days have had me crying foul. Some good La Nina is doing, right?

The reality is that La Nina is not the only factor in our weather. Our recent cold snap has been the product of a more active, wavy pattern over North America – one that brings arctic air from the northwest to the southeast. Its persistence has been good news to my friends who require chilly temperatures to get into the holiday spirit. I think they’ve enjoyed it quite a bit based on the photos of snow all over my Facebook feed last weekend.

Next week, the pattern will change and bring a more horizontal flow across the country. Our storms will be coming from the southern part of the United States, and our temperatures will warm to above normal levels. The cold air will stay to our north, where Snow Miser says it should be. (If you don’t get the reference, please watch “The Year Without a Santa Claus,” or look him up on Youtube.)

cpc map

The Climate Prediction Center’s temperature probability map for December 19-23, shows above-average chances for above-normal.

The Climate Prediction Center forecasted November, December, and January to have better-than-average chances at being warmer than normal back in October, when they noted La Nina’s cooler waters taking hold in the equatorial Pacific Ocean. North Carolina has not really seen that forecast verify so far, but the Global Forecasting System (GFS) long-range model shows a warm-up starting early next week. It’s possible that La Nina’s moderating effects on the South’s weather may finally be coming into play.

Does that mean a white Christmas is highly unlikely for the Triangle? Maybe. Maybe not. It may be a wet Christmas or sleet-filled Christmas if the latest run of the GFS verifies. While rain or sleet will make gift delivery a soggy – or even treacherous – ordeal, our area could use the precipitation. As of today, the U.S. Drought Monitor shows much of North Carolina under abnormally dry conditions with the central portion of the state experiencing moderate drought.

Don’t be too upset or excited about the Christmas forecast. If you’ve read my previous blog posts, you know any model predictions longer than five days away are not as trustworthy as we’d like them to be. I expect the forecast to change several times between now and December 24.

drought map

U.S. Drought Monitor map issued December 14, 2017

Weather Blog

Impending wintry mix on big event weekend

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Those people who say they need cold weather to get into the Christmas spirit ought to be happy about this weekend’s forecast… unless of course, they are planning on attending the Wake Forest Christmas Parade or the Wake Forest High School football playoff in Winston-Salem. In that case, they may be a little stressed over the fact that it’s beginning to feel a lot like Christmas.

A few days ago, the forecast looked like we would see mostly rain with some flakes mixed in at times. This morning, the forecast is leaning more toward rain mixing with and possibly changing to snow, and in some places, sleet could fall. On Saturday, as the temperature warms with what little daytime heating we’ll get, the precipitation could change back to rain before exiting the region. The models are agreeing on the fact that there will be precipitation, but what kind, how much, and when it will end is still a little up in the air (forgive the pun).

Typically, this is the type of storm I write about in February or March. You know – the ones that have meteorologists obsessed with the freezing line at the surface, just above the surface, and up in the clouds. Where those freezing lines are mean everything in a situation like this weekend’s. If the air is at freezing or below in all the levels of the atmosphere, we see snow. If the air is warmer at the surface, we get cold rain with maybe a few flakes or ice pellets mixed in. If the air is colder at the surface, but above freezing up higher, we’ll see more ice pellets or freezing rain.

Each model run over the last 24 hours has moved the freezing line at the surface in one direction or the other.  Wake County is a big county! With 857 square miles, it often happens with these kinds of storms that one part of the county gets snow dumped on it, and the opposite side sees nothing but rain. At this point, we aren’t expecting any area to get more than an inch of snow on grassy areas around here because the snow will be wet, and the ground is still warm.

Other than a few cold early mornings in recent weeks, the temperature has not spent much time below freezing. For that reason, the roads around here should be in relatively good condition Saturday morning even if we have a change from rain to snow early Friday night. If you happen to be driving to Winston-Salem for the football game at noon, the drive between here and there on the way to the game could take you through rain, sleet, and snow. Just take it easy on bridges and overpasses because they are more exposed to cold air above and below them, which means they could be a little slippery.

The western Triad has a slightly better chance of seeing snow versus rain Friday night and Saturday morning. Because the system will be moving from west to east, whatever precipitation does fall will end in Winston-Salem before it ends in the Triangle. As of this writing on Thursday morning, one model has the snow ending there early in the morning on Saturday, but another shows snow or rain showers could linger into the afternoon.

In any case and whether you are staying in town or traveling for the game, leave yourself time and stopping space while driving, wear warm layers, and make the most of the first winter storm of the season.

Saturday map

The National Weather Service forecast map shows one possibility of where the precipitation may be and what type could be falling at 7:00 AM Saturday.

Weather Blog

Could Mount Agung’s latest eruption cool the planet?

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Nearly 60,000 travelers have been stranded after yesterday’s eruption of Mount Agung in Bali. The volcano has been threatening a major eruption since earlier this year. In September, residents within a six-kilometer radius of the crater were told to evacuate for their own safety. Some did and have not returned, while others returned daily to feed and care for their livestock.

Yesterday’s eruption was the second in a week. According to reports, it spewed “ash 13,000 feet (4,000 meters [or nearly 2.5 miles]) into the atmosphere, and created plumes as high as 3.7 miles (6,000 meters).” The alert for the area has been raised, and people within 10 kilometers of the crater have been told to evacuate due to fears of a larger eruption to come.

Mount Agung map

Google Map showing Mount Agung’s location in Bali, Indonesia.

Bali is a small island in Indonesia, north of Western Australia. It’s proximity to the equator and mild weather make it a popular tourist destination for holiday travelers. It also gives Mount Agung the potential to affect weather on a global scale after a massive eruption.

If yesterday’s eruption is the worst of this round, then the weather in the region will be affected only in the near term. Ash contains sulfur dioxide, which when combined with water forms sulfuric acid aerosols. Those aerosols can “reflect incoming sunlight and influence cloud formation.” Australia’s Bureau of Meteorology predicts the weather could return to normal within a few weeks if the current wind direction continues.

If a larger eruption occurs – large enough to send ash into the stratosphere (18,000 meters) – the entire planet could be cooled for a year or more. While that sounds impressive, we’re really only talking about an estimated one degree Fahrenheit or less (0.55 degree Celsius or less).  Considering the upward global temperature trend in recent years, that much of a temperature drop would only take us back to 2014’s average temperature according to a report published by Carbon Brief back in October.

There have been major volcanic eruptions in the past that affected the earth’s temperature on a grand scale. Mount Tambora’s eruption in 1815 – just a few small islands east of Bali – may have caused the “year without a summer” as it is referred to in historical records in North America and Europe in 1816.

On their website longrangeweather.com, Climatologist Cliff Harris and Meteorologist Randy Mann have graphed global temperature swings over the past 4,500 years and correlated times of cooling to low solar activity and high volcanic activity. Alternately, periods of higher warming tend to be associated with peaks in solar activity and fewer eruptions. They also point out that El Nino and La Nina also play a role in global temperatures on smaller time scales.

Currently, we are seeing La Nina conditions in the Pacific, which is often associated with cooler-than-average global temperatures. If we were to add a major volcanic eruption to the mix, we could easily see that drop scientists are hypothesizing of a degree or more in the next year. It definitely bears watching, even from the other side of the world.

Weather Blog

How well did last spring’s Atlantic hurricane season’s forecasts perform?

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Hurricane season starts on June 1 and runs through November. Despite our man-made timeline for storms, which is based on typical start and end dates over the years, mother nature occasionally starts the year early as she did this year with Tropical Storm Arlene which developed on April 19.

Every spring, Colorado State University and North Carolina State University use statistics, global models, and other information to create their own seasonal forecasts for the upcoming hurricane season. The predictions garner a good deal of attention for a few days, and then are typically forgotten by the general public.

What they predicted:

Colorado State’s initial forecast was issued on April 6, 2017. For the purpose of this blog, I am only looking at the initial forecasts of each school. Revisions are usually transmitted in August, after the season has begun and the forecasters have a chance to see how the conditions may differ from what the models predicted in April.

CSU predicted slightly below average activity (citing 12 to be the median number of named storms from 1981-2010) with 11 named storms, four becoming hurricanes, and two major hurricanes (category 3 or higher on the Saffir-Simpson scale).  One key factor they considered was their expectation for the development of El Nino with its warmer-than-normal sea surface temperatures in the Pacific. Yes, water temperatures in the Pacific affect the number of storms we have in the Atlantic. In weather, everything is connected.

NCSU’s Dr. Lian Xie – one of my professors when I earned my degree – saw things slightly differently and predicted an above-average year. He and his cohorts predicted 11 to 15 named storms (citing 11 to be the average number of named storms in the Atlantic from 1950-2014). They thought four to six of those may become hurricanes, and one to three of those could become major hurricanes.

2017 map

The National Hurricane Center’s 2017 Preliminary Hurricane Season Summary map

How they did:

The reality of the season was even greater than either group expected. The summary on the National Hurricane Center’s website lists 16 named storms, 10 of which became hurricanes, and six of those became major hurricanes. While the season isn’t technically over, it looks like Tropical Storm Philippe was our last named storm of the season. You might not have even noticed him. He spent his time far out in the Atlantic on October 28 and 29.

Why it matters:

Whether meteorologists are forecasting for a season or just the next three days, looking at predictions versus reality after the period ends helps us learn from our mistakes and confirm what we got right. This summer, El Nino never really formed as the CSU team thought it would. In fact, in August, the sea surface temperatures were slightly cooler than average in the equatorial Pacific. That fact might have been a contributing factor to the final tally for the Atlantic basin.

Weather Blog

Don’t be distracted by the shine.

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We seem to live in a world of extremes these days. If you don’t absolutely love or absolutely hate something, the suggestion is that you just haven’t made up your mind. While there is a “like” button on Facebook, just being lukewarm to an idea is portrayed the same way as being totally against it in many news outlets and blogs. So, instead of focusing on the merits of both sides of the coin, we’re told we must pick heads or tails and there can be no in-between.

I want to remind the world it takes two sides to make a complete coin. So, let’s focus for a minute on something more substantive than the shiny sides by considering what the coin represents – a topic with important implications for everyone.

What do anthropogenic climate change “skeptics” and “believers” have in common? While most media outlets would have you think the answer is “nothing,” it’s far from true.

No matter which side of the debate you lean toward – human-caused warming versus natural variation – the ultimate goal of both sides should be mitigation of present and future risk. I’ve written about this topic before, but with recent articles about the U.S. government’s Climate Science Special Report, the likelihood of more hurricane Harvey-type storms, and how important changes in non-extreme rainy and dry spells are to the climate, I feel safe revisiting this subject.

Harvey

Image credit: NASA. A satellite image shows Hurricane Harvey as a Category 4 storm on August 25, 2017.

Case in point: when the Climate Science Special Report was released, it was taken by many at face value and reported with a tone of urgency and alarm by most news channels. However, other scientists such as Steve Koonin, who wrote a post about it for the Wall Street Journal, and Judith Curry, a climate scientist often called a “lukewarmer” because she questions how much faith we should put in climate models she knows intimately, looked at it with a more discerning eye. They questioned the timeline used in the report with regard to sea level rise. The report looked at the late 20th century through the early 21st, but apparently ignored higher sea levels that existed in the first part of the 20th century. That framing of the study has caused concern and become yet another topic of debate.

What both sides agree on, though, is that with rising sea level of any amount, coastal areas need to look closely at land-use policy and engineering to best protect their populations and natural resources.

Houston is a prime example, especially since an article on The Atlantic’s website published this week claims that with a warming climate, storms like Harvey will be much more likely to happen than they once did. While Harvey had a devastating effect on Houston, I can’t help but question some of the logic in that article, which was based on a rushed-to-print study by a well-respected scientist. I recall the dire warnings during the historic hurricane season of 2005 – how that season would set the tone for every year thereafter because it heralded the worst-case scenario for a warming climate. It took 12 years for us to see another season of landfalling, monster storms, and even this year wasn’t as bad as 2005. Not that I’m complaining.

Houston’s situation is more complicated than many coastal cities because Houston is sinking. Poor judgement in land-use for a quickly growing population over decades in the form of groundwater withdrawal has caused subsidence, especially in northwestern Harris County. Houston’s exposure to flood risk has been exacerbated by its sinking. A report published in 2010 cites a difference in ground elevation for that area of 2.5 meters between the 1930s and the 1970s. That change is huge! This fact isn’t news to Houston residents, but it probably is to most people outside of that region.

By the way, the report on Harvey’s effect on Houston was rushed so that it could be used by planners and engineers in the rebuilding process for the purpose of mitigating risk. Can you blame them?

I have always been one to weigh both sides of an argument. I learned the importance of being able to argue any point in debate class in tenth grade. If you don’t understand all aspects, you are making decisions based on incomplete information. So, please, don’t just choose heads or tails because one is shinier than the other. Consider the whole coin and understand that there’s value to it as a whole.

Weather Blog

Today’s high temperature could beat a record

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Like all scientists, meteorologist love data. We keep records for as many things and as many places as possible. We have daily maximum and minimum temperature and rainfall records going back over a century.

dreary fall day

The view from the author’s office window on a dreary, colder-than-normal November 8.

When you collect that much information, you’re able to compare dates year-over-year and extract other useful information, too. For example, two of my favorite records to consider are the lowest maximum temperature and the highest minimum temperature. They give an idea of whether a day has really been “this cold” or a night really has been “this warm” on a particular date in the past.

When we have a day like today – cold, dreary, damp, and winter-like in early November, I always look at the lowest maximum temperature records to see how unusual the weather really is. Today’s weather could actually be noteworthy, especially since we’re not expecting the temperature to move much at all day.

The official climate records for the greater Triangle are kept at Raleigh-Durham International Airport, so even though we are not necessarily at that location, that’s where we have to look. On this day in 1971, the high temperature was 46 degrees – the record for the lowest maximum temperature for the day. The runners-up are 48 degrees in 1933 and 50 degrees in more than one year. So, if we stay cooler than 46 degrees today, we will break that record for the coolest high temperature on this date.

In case you are wondering, our normal (30-year average) high temperature for today is 66 degrees, and our normal low is 43 degrees. Yes, this is definitely an unusually chilly day.

Weather Blog

Late October storms can be devastating

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This weekend, Minnesota had the earliest snowfall of the season since 2009. It caused more than 300 auto accidents and spinouts across the state. As the low-pressure system that caused that snowfall moved eastward, the trailing cold front joined up with the remnants of Tropical Storm Philippe causing that center of low pressure to move northward up the east coast.

sat image

Experimental product from the new GOES-16 satellite system and the National Weather Service showing the massive storm over New England the morning of October 30, 2017

By this morning, the resulting massive storm had left over one million customers without power from the northern Mid-Atlantic states into New England. Heavy rains and high winds caused flooding, downed trees, and additional accidents.

All of this happened on the weekend we observed the five-year anniversary of Superstorm Sandy. Sandy was a hurricane that hit the northeast coast directly, became extra-tropical, and was devastating on a larger level, being credited for 233 deaths and $75 billion in damages.

Tropical storms and hurricanes that make landfall are disastrous on their own, but when they collide and/or combine with other storm systems – such as a strong cold front – they become even more powerful. The moisture content of the tropical storms adds to the potential for extreme precipitation events, which could take the form of torrential, flooding downpours or heavy snow depending on the temperature. This weekend, residents of New England avoided the addition of the snowfall that accompanied Sandy. While those affected would probably not call themselves “lucky,” it clearly could have been worse.

I doubt we’ll see a fatality count recorded from this weekend’s system the way that we did with Superstorm Sandy, but I read there were four in Minnesota and I personally know of one here in North Carolina that can be blamed on the weather. I would not be surprised if there were more that haven’t been tallied nationally, yet. It goes without saying that those five are five too many.