Category Archives: Weather
Super-Typhoon Haiyan produced some of the strongest winds ever recorded within a tropical cyclone as it moved across the northeastern Philippines early Friday morning, Philippines Time (yesterday evening, U.S. Mountain Standard Time). With sustained winds estimated at least as high as 190 mph (165 kts, 306 kph), and gusts over 220 mph (191 kts, 354 kph) at landfall, Haiyan had winds similar in strength to Typhoon Tip from 1979. Very impressive! Depending on a reanalysis of the storm winds once more data can be made available, Haiyan will probably rank as one of the top three strongest tropical cyclones ever measured. Here’s a visible image of the storm from a geostationary weather satellite as it made landfall (Thanks to the U.S. Naval Research Laboratory in Monterey, CA for the image):
The following animation of the landfalling typhoon shows it having all the characteristics, as seen from a geostationary weather satellite, of a very strong tropical cyclone. It has a small, well-defined, very warm eye; the eye is embedded in a circular, symmetric, and uniform area of dense cloudiness with very cold cloud-top temperatures; and higher clouds emanate from the storm almost equally in all directions. This is a 7-hour loop showing the storm as it moves into the northern Philippines (Thanks to NOAA for this set of images):
Some days, especially in summer, the clouds of central Colorado present a spectacular skyscape constantly changing and shifting from puffy cotton balls to ominous thunderclouds to occasional bright blue skies of the American West. One such day was last Sunday and the following time-lapse video captured the scene:
A brief aside, if you like Madeleine Peyroux‘s music, you can buy her “Careless Love” album at:
Why the clouds?
The Rocky Mountains, as with all imposing mountain chains, affect weather and climate in a number of significant ways. Summertime heating of the mountain slopes causes one of the more majestic effects, the regular, almost daily, development of thundershowers over the higher terrain.
The Rockies in central Colorado reach elevations just above 14,000 ft (4267 m), about one-third of the way up into the troposphere (the layer in the earth’s atmosphere closest to the ground where most of our weather and clouds form). When the sun warms a high-elevation mountainside during the day in summer, that heat is quickly transferred to the atmosphere. Putting a heat source at 14,000 ft up in the troposphere, a level where the atmosphere is usually chilly, causes convection, the rising of air due to heating. Even on relatively dry days with only a meager amount of moisture in the troposphere, the convection caused by the elevated heat source of the mountains is so strong clouds can still form. If there is enough moisture, those clouds will become showers and thundershowers.
Ah, summer! (Well, in the Northern Hemisphere, that is.) Aside from ice cream, beaches, flowers, vacations, and sunburns, summer also means impressive thunderclouds (cumulonimbus clouds). Over the mountains of central Colorado, we usually don’t get the massive “supercell” thunderstorms that occur over the Great Plains of North America, but picturesque convective clouds still form almost daily. Here are just a few examples from the last couple of weeks:
Yesterday was an active weather day along Colorado’s Front Range. A relatively cool springtime weather system from the Pacific, which had moved through the Pacific Northwest on Memorial Day Monday (even affecting San Francisco with a bit of light rain), made it to the central Rockies yesterday morning. Bands of thundershowers formed ahead of the system and moved out of the mountains into the Denver area during the late morning. From a park in Littleton, I took a few photos of one of the approaching lines of storms. The silhouetted darkness of the distant foothills and the angry look of the sky contrasted vividly with the green spring grass in the foreground. I used Aperture to modify some of the images to discover how different enhancements changed the photographic mood of the morning. The results follow…
And, just what did this menacing line of storms look like from above? Fluffy white, and relatively disorganized, as this image from NASA’s Aqua satellite shows (taken a couple hours after the ground-based images; Denver is near the center of the image):
Often in May, with the air still retaining some winter chill, and the land warming rapidly from near-summer sunshine, convective showers of snow and hail form over the Rockies and adorn the sky-scape. This happened over the weekend and I caught this image showing a beautifully picturesque shower as it was passing by to the east. The fibrous texture of the cloud’s top results from ice crystals formed as the shower cell bubbles skyward due to the heating below. Grayish snow and soft-hail can be seen falling out of the cloud obscuring the land surface underneath it. Surface temperatures were in the low 50s°F (12°C) in the sunshine, dropping to about 40°F (4°C) when one of these showers passed overhead. The snow and soft hail would whiten the ground, briefly providing a wintertime look to the May landscape and angering the nesting robins chilled by the sudden squall.
Ever since I learned about the Cloud Appreciation Society (CAS) a few years ago, I became an instant fan and, as quickly as international post would allow, I became a life-long member. Not only does the society have a wonderful collection of cloud pictures and videos from its 32,000+ members (not to mention cloud music, art, and poetry), but they (we) also encourage learning about clouds through a mix of solid science and a bit of whimsy. After all, learning while laughing definitely speeds learning, no matter what the subject—especially, if it is about something as ephemeral as clouds.
Given my enthusiasm for the Society, it’s no big surprise that I have managed to convince a few wise members of my friends and family clan to appreciate clouds with me and join the CAS. There is at least one very important member of the family, though, who I missed. And, she made it quite obvious to me today that she, too, has as strong an appreciation for clouds as anyone else. Meet Olive, the cloud-spotter feline of the household:
Just what has attracted her attention, you ask? It is a picture of one of several thunderstorms which moved over the Boulder, Denver, and Colorado Springs metro areas today. I took the thunderstorm picture earlier in the day thinking it would be a nice contrast to the winter weather pictures I took last week during our late-season snowfall (Last week was winter, this week is spring; extrapolation predicts summer soon). While cropping the image on the computer, Olive the cloud-spotter feline spotted it. She was mesmerized, quite unusual for her capricious personality. In fact, she was mesmerized to the point where she remained still long enough for this, and a few other, cute cat pictures. To keep her purring, I promised to remit her lifetime membership fee for the Cloud Appreciation Society as soon as possible. They already have a dog who is a member, but I think Olive would be the first cat.
To complete the story, here’s the thunderstorm image that so intrigued Olive:
With this storm and the showers that followed it, we received about 0.5 inch (12 mm) of rain today. Any rain (or snow, for that matter) this spring is a big help for us because we are still trying to get out of long-term drought.
With the early May sun providing about 5 times the energy as the mid-winter sun (in the Northern Hemisphere at 40ºN latitude assuming a clear sky), it doesn’t take long to melt the 6-15 inches (15-38 cm) of snow that fell along the Colorado Front Range yesterday. Before it all melted, I took this beautifully white picture looking west from the southern Denver suburbs towards the mountains. The higher peaks along the Continental Divide which would typically be visible behind the mountains shown are obscured by the cumulus clouds in the picture.
Central Colorado had a very snowy April—for instance, Boulder, CO set a record for April snowfall measuring more than four feet (122 cm) of snow during the month…and most of that fell during a two-week span in the middle of the month. May has continued the pattern with an all-day snowfall today along the Front Range of the central Rockies. What does a mid-spring snow day look like? Much like a mid-winter snow day except for the perturbed robin and the confused buds…
This has been a snowy March along the Front Range of Colorado and the most recent storm which blew in Friday night and lasted through much of yesterday (Saturday) was unusual in a number of ways. First, it was quite a cold storm for late March. For instance, yesterday’s clouds, snow, and strong north winds held Denver’s high temperature to only 23°F (-10°C), a whopping 34°F (19°C) below normal. The storm also broke several records for single-day snowfall for March 23, almost 11 inches (28 cm) in Boulder, more than a foot and a half (46 cm) east of Denver over the wheat fields that spread to Kansas.
One other weirdly interesting aspect of this storm is that it is following a track just about due eastward from the snow field it left in Colorado yesterday to the areas it will affect tomorrow as it moves off the east coast of the U.S. in the afternoon. In fact, it seems to be using I-70, one of the essential east-west routes of the Interstate Highway system, as its guide. Just look at this map of I-70’s route overlaid with the area of snow already deposited by the storm and forecasted to fall in the next 24 hours:
There’s not a bad correlation at all between the path of I-70 and the path of the storm’s snowfall.
It is not uncommon for a storm to move more-or-less due eastward across the U.S., following the winds in the upper atmosphere which usually blow from west to east at mid-latitudes. However, it is unusual in late March for a storm to take this track and and leave such a continuous layer of snow this far south across the central U.S. The biggest downside from the storm is probably the chaos it has had and will have on I-70 traffic, the biggest upside: the farmers in the grain belt will be happy. Now, I’m looking forward to spring!
Hurricane Sandy came ashore on the evening of Monday, 29 October, just south of Atlantic City, NJ. It was definitely a unique, “storm of the age” kind of event as it transitioned from a tropical system while it was offshore to a non-tropical (or “extratropical,” as meteorologists like to say) super storm as it crossed the coast and moved inland. The combination of tropical energy (in the form of moisture and heat) and winter storm energy (in the form of jet stream winds and a sharp temperature gradient between very cold air to its west and warm, tropical air to its east) led to the lowest sea level (barometric) pressure ever recorded off the northeastern U.S. Just before landfall, a hurricane hunter aircraft measured a sea level pressure of 940 mb (27.76″) in the center of Sandy and when it came ashore a weather observing site near Atlantic City measured a pressure just above 945 mb (27.91″). Both values broke the previous record of 946 mb (27.94″) measured at the Bellport Coast Guard Station on Long Island during the Great New England Hurricane of September 1938. The surface map showing contours of sea level pressure looked like this just as Sandy was crossing the coast and transitioning to an extratropical super storm on the evening of Monday, 29 October:
Even more remarkable than the storm itself was the accuracy of the weather model forecasts of the storm as much as 8 1/2 days in advance. The forecasts showed how much progress has been made in weather forecasting as computers have become more and more powerful. The model from the European Center for Medium Range Weather Forecasts (ECMWF) gave a surprisingly accurate depiction for the location and intensity of Sandy at landfall from both its morning and evening runs on Sunday, October 21. That’s 8 days before the storm hit New Jersey and a couple days before it had even become very well organized in the Caribbean. Truly incredible! Here is what the model predicted on Sunday evening, 21 October:
Unfortunately, most of the stories about this excellent forecast have focused on how much better the European model forecast was with Sandy compared to the output from the primary American global weather forecast model, the Global Forecast System (or GFS), at the same time. For instance, see these stories:
The forecast from the GFS model was noticeably poorer as evidenced by this map showing its output from the same time as the ECMWF model run on October 21:
While the GFS did develop the storm, it clearly was taking it out to sea into the central Atlantic and entirely missed the intensity of the cold air diving into the eastern United States and its interaction with the storm. The GFS needed a few more days before it finally started bringing the storm closer to the coast and had it deepen when encountering the cold trough in the eastern U.S. It definitely was the poorer model for this storm.
On average, the ECMWF model beats the GFS, as it has for decades, because the Europeans have focused their energies and resources on improving one thing: medium-range weather forecasting. They have a a higher resolution model with a better scheme for ingesting initial observations and satellite data which runs on a more powerful computer system than what the U.S. has. The U.S. agency containing the National Weather Service and responsible for developing weather models, NOAA, has limited resources and must allocate them across a broad spectrum of needs to protect life and property in the U.S.—the needs range from short-term forecasting of severe weather events, such as tornadoes, to the long-term issues such as summertime drought or wintertime cold. And, while the ECMWF model is better on average than the GFS, it is far from perfect. Just a month before Sandy, the ECMWF model was consistently trying to bring another storm, hurricane Nadine, into southern Europe as a destructive extratropical storm. The GFS, on the other hand, generally kept Nadine out at sea with a looping track south and southwest of the Azores. The GFS was the much better model in this case as the storm got nowhere near southern Europe and threatened the Azores twice.
Back to Sandy, for a moment—I would hate for us to get mired in a controversy about ECMWF vs. GFS and miss the incredible skill shown by the ECMWF model more than eight days in advance. Billions of dollars will be saved or losses prevented if such forecast skill becomes commonplace. This forecast gives us an example of what is possible as we continue to advance the science of meteorological modeling. Now if we can just find the money to continue funding the research in this all-important area…