October 6, 2008
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Space Cadets! Eschew sunshine. EmBRACe the night. Watch the International Space Station make a fine appearance Tuesday evening. Look for a steady, Jupiter-bright object rising above the northwest horizon at exactly 8 p.m. It will climb high overhead by 8:03 p.m., soaring over Central Virginia. See it glide past bright Altair, southernmost star of the Summer Triangle, then vanish into Earth's shadow, in the south, at 8:04 p.m.
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Weather enthusiasts! The National Weather Service office at Sterling, Va., which handles Baltimore's forecasts, will hold an Open House on Oct. 18 (9 a.m.) and Oct. 19 (noon). Watch weather balloon launches, hear talks on severe weather, storms and weather careers. Tour their new offices, learn how to become a NWS weather spotter. For details, visit www.erh.noaa.gov/er/lwx/openhouse
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September ended this week warm and wet. BWI was 2 degrees above the long-term average, despite a cool second half. We had four days in the 90s, two in the 60s. Hanna and last weekend's Atlantic storm pushed BWI rain totals 3.24 inches above the norm, to 7.22 inches. The cooling season is almost over, with cooling degree days - a measure of energy demand - running 4.5 percent above the 30-year average.
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October can be Maryland's prettiest month. But anything can happen. Record highs linger in the 90s. In 1941, we hit 97 degrees Oct. 5. Lows can reach the 20s, with a 25-degree record Oct. 24, 1969. It can be sweltering, or it can snow. The earliest trace fell Oct. 9, 1903, and most recently Oct. 22, 2003. The deepest measurable snowfall was 2.5 inches Oct. 30, 1925. The oldest daily record is a 2.22-inch rainfall on Oct. 25, 1872.
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On this date in 1881, Baltimore began a week that just wouldn't cool off. For the next seven days, through Oct. 3, the overnight LOW temperature in the city never slipped below 72 degrees. (Average lows are in the 50s.) All seven of those daily "high minimums" from 1881 still stand as records, though one was tied in 1954. The four from Sept. 27-30 are among 10 record-high minimums for September that have stood since the 19th century.
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Mike Shriver in Linthicum wonders what became of a 2002 project called Enlighten Maryland. Participants had maps of the constellation Orion and circled the stars they could see on a clear February night. A total of 1,100 reports were processed into a map of Maryland light pollution. That map proved disappointing. But there's a good, zoomable dark-sky map for North America at baltimoresun.com/pollution
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Sally (last name and hometown withheld for obvious reasons) writes: "My family will be on the Nile in Egypt Feb. 14-28, 2009. Any chance we may experience a full moon?" A full moon over the Pyramids? Alas, you'll miss the full moon on the 9th. But a very slender crescent moon will appear after sunset on the 27th, low in the west, alongside the bright planet Venus, evoking a symbol of the old Ottoman Empire.
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John Stratton writes from Catonsville: "Has a hurricane ever split into two separate storms?" Jeepers, John, haven't we got enough to worry about in this brutal hurricane season without dreaming up new nightmares? These storms sure can spin off violent squalls, tornadoes and drenching rain bands. And Ike was pulled apart after landfall and absorbed by surrounding weather systems. But hatch a clone? Can't happen.
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Attention, Space Cadets! Last night marked the return of the International Space Station to our evening skies. I'll post several good weekend viewing opportunities on my Maryland Weather blog. Tonight, look for the ISS at 7:59 p.m., rising near brilliant Jupiter in the southern sky, then passing just below the Summer Triangle in the southeast at 8:01 p.m. It disappears into the Earth's shadow, in the east, at 8:03.
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The full harvest moon rises tomorrow night in the east about 7:12 p.m. But if forecasters got it right, we may be socked in by remnants of Hurricane Ike. So try looking tonight instead. Luna rises over Baltimore at 6:48 p.m., indistinguishable from the real thing. The harvest moon's light allowed farmers to reap into the night. It's defined as the full moon closest to the fall equinox, which is Sept. 22 this year.
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Luke Engles lives in Salisbury. He's in third grade. "I am learning about my home state in home school," he writes. "We need to know what the average temperature highs and lows are for each month ... and we couldn't find it online. ... I was hoping you could help." The National Weather Service forecast office in Sterling, Va., keeps that information for Baltimore. You can find it at erh.noaa.gov/lwx/climate/bwi/NME.htm. Good luck!
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Dennis Ferguson writes from Easton to ask: "Do hurricanes pull their moisture from the Atlantic? ... If so, where does the salt in the water end up? Does the rain's composition become saltier during hurricane season?" Nope. Hurricanes do draw their energy from evaporation of ocean water. But evaporation leaves the salt behind. Hurricane rain is fresh water, but these storms can blow salt spray far inland, turning leaves brown.
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Space Cadets! Venus, Mercury and Mars gather this week in a tight cluster, low in the western sky after sunset. But Mercury and Mars are quite faint. And, they're all still deep in the sun's glare. You'll spot Venus first. She's quite bright, but demands a clear view. Mars and Mercury are close by to her left. Binoculars may help. Venus will become more obvious as the month passes, in the western twilight.
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Chuck Grene in Westminster read a Smithsonian article about Cherry Springs State Park, in north-central Pennsylvania, which claims some of the darkest skies in the northeast - great for stargazing. Unwilling to drive so far, he asks, "Is there some stargazing spot in Maryland that is just as good?" None that minimizes light pollution so well. Find your dark skies at observingsites.com.
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Joe Borchetti in Pasadena has watched this summer as tropical waves roll off the African coast and become tropical storms: "What causes these disturbances and why ... at this time of year?" Blame summer heat in the Sahara and cooler air over the Atlantic. The contrast forms low-pressure troughs, carried west by trade winds. Thunderstorms boil, and winds circle the low. A new tropical storm is born.
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September arrives tonight, the longest month of the year (count the letters). It's also Baltimore's wettest (3.98" on average), probably thanks to a century of passing tropical systems. Average high temperatures at BWI slip from 82 degrees to 73. Average lows dip from 61 to 51. Records range from a high of 101 degrees on Sept. 7, 1881, to a low of 35 degrees, on Sept. 25, 1963. We'll lose 74 minutes of daylight.
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Tomorrow marks the last day of the three-month meteorological summer. Despite a cool August, the season ends 1.2 degrees warmer than the long-term average at BWI. August dried up rain surpluses from June and July. We had 23 days in the 90s from June through August. The high was 96 degrees on June 10. The low was 52, on June 18. The low of 59 on July 25 tied a record set in 1976. Autumn should be warm.
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The National Weather Service forecast office serving Baltimore is moving again - to State College, Pa. The old quarters in Sterling, Va., next to Dulles Airport, must make way for runway expansion. But it's only temporary this time. Forecasters will spend the week of Sept. 22 issuing their forecasts, watches and warnings from State College, then move back to new quarters, a half-mile from the old Sterling digs.
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It's chilly by the pool in Dundalk. "Is it my imagination or has it been unseasonably low this August?" asks Lauren Zielski Paneto. "We loved swimming in July. ... But this whole month of August ... our pool sits useless 'cause the water is too cold!!'" My, you're a delicate thing. It's been cool - about a degree below the long-term August average, with 13 days so far below the norm. Radiational cooling on clear, dry nights might also be draining your pool's heat. So swim faster.
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Charles Grene in Westminster asks: "In the Central and Mountain time zones, with all their mountains, hills, forests and deserts, how are the sunset and sunrise times arrived at?" Same as for urban canyons: math. Local conditions vary so widely that published tables for any location must assume ideal conditions: a clear, flat horizon at the same altitude as the observer. Rise and set times are pegged to the moment when the top of the sun's disk would first appear and the last bit would disappear.
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Stuart Godwin Jr. wrote from Chestertown a while back to ask: "What is the relationship between Dew Point and Relative Humidity? Is one dependent on the other?" You bet. Warmer air can hold more water vapor. The RH is a percentage, telling us how close to saturation (100 percent) the air is at ground level. As air cools, it can hold less moisture, and RH rises. At the dew-point temperature, it's saturated (100 percent), and the vapor condenses as rain or fog.
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The full August moon was once known as the Fruit Moon, denoting its appearance while fruit is ripening on the trees. Last night's full moon was partially eclipsed during the afternoon, our time. At its peak, the Earth's shadow darkened about four-fifths of the moon's face as people from western China to western Europe watched. We in the New World were on the wrong side of the planet for this one. The next total lunar eclipse visible here will occur (numerologists take note) on 12/21/2010.
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Marj Ashcroft's mom lives in Towson, with a fine view of the night sky. "Looking southeast on clear nights about 9:15, she sees a bright object in the sky. ... I thought it might be a police helicopter. ... But through binoculars, they say it appears white, round and flat like a paper plate. They are very curious about what it is." Nothing so dull as a chopper. It's Jupiter, just past its brightest appearance of the year, drifting slowly each night from southeast to southwest.
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Bill Bonneau writes from Sparks: "What events occurred in August 1955 to cause such a huge rainfall accumulation (18.35 inches) ? ... I have never heard anything about the 'Monsoon of 1955.'" It was Baltimore's wettest month by far, dumping nearly half the city's average annual precipitation. Blame Connie, a minimal hurricane that came up the bay and dropped almost 10 inches here in 72 hours. Three days later, remains of Diane unloaded 2.3 inches more. By Aug. 31, other storms had added almost 5 more inches.
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Space Cadets! It's time for the annual Perseid meteor shower, which peaks early Tuesday morning as the Earth crosses Comet Swift-Tuttle's dust trail. Bits of rock will put on a light show as they streak through the atmosphere at 37 miles per second. Flee city lights. Go after 11 p.m., but it's better between 2 a.m. and dawn. That's after moonset, when our side of the planet will be headed straight into the comet's trail. Bring a blanket or a lounge chair and just look up.
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Jeannie Clancy reports swarms of "biting black flies chased us off the beach" in Ocean City on July 31. Next afternoon, "millions of grasshoppers appeared in the ocean and on the beach." What's going on? she asks. UM entomologist Mike Raupp accuses bloodsucking stable flies. They breed in horse dung and rotting vegetation, both plentiful on the Delmarva coast. He says migrating "differential" grasshoppers can reach "astonishing numbers" in roadsides and meadows. Maybe they were blown to sea and washed ashore. I say: Eight plagues to go.
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Ray Digiondomenico in Catonsville was watching the sunset. "The sky was still blue, with some wispy, pink-orange clouds near the horizon," he said. Within those clouds, he spotted "a bright object, the same color as the clouds, which seemed to be streaking toward the sun. ... What do you think it is, and why do I see it at sunset?" My best guess? Probably the contrail of a westbound airliner, foreshortened by your perspective. It reflected bright light from the setting sun, just like the clouds.
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Space Cadets! If you missed Tuesday's flyover by the International Space Station, you'll get another shot tonight as the enormous contraption passes overhead again on nearly the same trajectory. A very bright ISS and its crew of three will rise in the northwest at 8:48 p.m. as they pass over Lake Michigan. They'll climb very high overhead (243 miles above Baltimore), passing the bright star Arcturus at 8:51 p.m. Then they'll head southeast off the Carolina capes, skirting brilliant Jupiter and disappearing at 8:53 p.m.
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Space Cadets! Clip and save! If skies are clear Tuesday evening we'll have a great view of the International Space Station as it performs a vanishing act high over Maryland. Watch for a very bright starlike object rising in the northwest at 9:31 p.m., passing just south of the Big Dipper. The ISS will fly almost directly over head at 9:34 p.m., zipping southeast toward the Atlantic coast. It will disappear suddenly, at 9:35, as it flies into the Earth's shadow.
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John Polyniak in Lake Shore says the downtown temperature he gets from the phone company's weather line is so much higher than BWI's that "it seems irrelevant. ... Is the thermometer laying on the tar atop the Maryland Science Center?" It's actually on a phone company building downtown. It's a hot spot, but downtown summer temperatures are always higher than BWI's because of urban "heat island" effects - solar energy reradiated by concrete and asphalt. The Sun'sstation at Calvert and Centre streets is a cooler choice: baltimoresun.com/sunstation.
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August is here. This month often brings our first big break in the summer heat, with a cold front sometime after midmonth. It happened last year on the 18th. Average daily highs at BWI slip from 87 to 82 degrees by month's end. Lows sink from 66 to 61. The record high is 105 degrees, on three dates in 1918 and 1983. The coldest night (45 degrees) was Aug. 30, 1986. The oldest daily record still standing is the 72-degree high minimum for Aug. 13, set in 1872.
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We can't see it from here, but there is a total eclipse of the sun early tomorrow morning. The path will sweep from Canada's arctic territory of Nunavut, across northern Greenland and Siberia, into Mongolia and China. The eclipse begins at 5:21 a.m. EDT and ends at 7:21 a.m. NASA TV will cover it live from China ( www.nasa.gov/eclipse), beginning at 6 a.m. EDT. The total eclipse there occurs at 7:08 a.m. EDT. Biggest audience under the moon's shadow? Xian, China, population 3.9 million.
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Joe Bollinger in Glen Burnie listens to his NOAA Weather Radio. He keeps hearing the term "dominant period" and wonders what it means. "What factors cause the time to vary, and why report it at all?" he asks. Sailors and boaters need to know. The term refers to the time, in seconds, between peaks of the highest energy waves on a body of water. Higher waves and shorter dominant periods can mean rougher waters. Longer periods provide smoother sailing, and lower demand for Dramamine.
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Donald Gansauer writes from Canton: "Your column often reports on the transits of the International Space Station ... I made sure to look for it. Was it reflected sunlight that I saw, or is there an actual light bulb on the station that gleams on the Earth?" Like Motel 6? "We'll leave the light on for ya..." Nah. It's all just sunlight, reflected off the station's solar panels and other shiny surfaces. That's why the ISS often "disappears" suddenly when it moves into Earth's shadow.
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Attention, space cadets! If skies stay clear enough, Marylanders can step outside this evening and watch the $100 billion-plus International Space Station as it flies up the East Coast. Look for a very bright, star-like object rising above the southwestern horizon at 9:48 p.m. The ISS will climb about halfway up the southeastern sky by 9:51. It will be nearly as bright as Jupiter, visible just below it. Zipping away at 17,500 mph, the station will fade to black, low in the northeast, at 9:53.
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Thomas Sjolander from Abingdon was riding a personal watercraft off Ocean City a few weeks back and was surprised by the water temperature. "It was frigid," he said. Last week it was better, 71 degrees. But then it dropped, suddenly, back into the 60s. "My guess is the wind blew the warm layer off and colder water rose up," he said. Close. Strong winds can churn the water and mix in cold layers from below. More recently, the churning has come from strong swells driven by Tropical Storm Bertha.
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Louis Rosenstock in Baltimore reminds me that humidity determines comfort in a Chesapeake summer. He and others plead for humidity forecasts, not just data on yesterday's mugginess. Many older people step into suffocating humidity and turn back, Rosenstock says. "They can't handle a certain level of oppressive heat." The problem is cramming more data into this space. Try a NOAA Weather Radio. Dew point's over 70? Stay indoors. Or go online. The NWS has a nifty interactive forecast at www.weather.gov/forecasts/wfo/sectors/lwx.php
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Bob Walsh, in Baltimore, wonders about the summer solstice. Usually it is June 21, but it was June 20 this year, for the first time since 1896. It can occur on June 22, but not again until 2203. "What causes the date/time to change?" Bob asks. Our 365/366-day calendar year doesn't perfectly match the "tropical year" - the time it takes Earth to return to the same spot in its journey around the sun. Mostly, that orbit varies because of gravitational tugs from Jupiter and other planets.
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This gig's easier with Donald Gansauer's questions from Canton: "Television weathermen say that we have the potential for thunderstorms because of an 'unstable' atmosphere. What makes the atmosphere unstable?" It's sharp temperature contrasts with altitude. Sunshine heats air at the surface, causing it to rise through colder air aloft. The rising warm air expands and cools. If the surrounding air aloft is no cooler, the updraft stops. Stable air. If it's still colder, the updraft continues, forming tall, cumulous clouds and thunderstorms. That's unstable.
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Lynn Alan Snodderly works late and gets home to Dundalk around 1 a.m. For reasons known only to him, that feels like a good time to clean his windshield. "Cleaning is easy," he says, "but I have a very hard time drying the windshield. Why? Is it humidity ... in the early mornings?" Bingo! As the air cools overnight, it's less able to hold moisture. The relative humidity climbs, and evaporation slows. You wipe the glass, but residual water refuses to vanish. Leave it till morning.
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Stuart Godwin Jr. in Chestertown noticed that the June 30 relative humidity, reported here on July 1, soared from 51 percent at 1 p.m. to 76 percent at 3 p.m. before falling back. "Did [the] relative humidity actually fluctuate that much?" he asks. It did. BWI reported "light rain" about 3 p.m. The shower added moisture and cooled the air by 9 degrees. Cooler air can't hold as much water, so the RH - moisture relative to the air's capacity to hold it - spiked.
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If clouds clear in time, there's a terrific show in the western sky after sunset tonight. It is a close lineup (upper left to lower right) of planets Saturn and Mars, the bright star Regulus and a delicate crescent moon. Just step outside after the sky darkens and look west. Binoculars will help. It is busier up there than it looks. NASA's Cassini spacecraft is circling Saturn. Mars has three active orbiters and three surface robots. Craft from Japan and China are orbiting the moon.
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Does the sun seem somehow smaller today? At 4 a.m. EDT, the Earth reached "aphelion," its greatest distance from the sun for this year. At that hour, we were about 94,513,039 miles from the sun. That's 3.4 percent farther out than at "perihelion" - the nearest point - on Jan. 3. So why is it so darn hot? It's because the Northern Hemisphere is tilted toward the sun at this time of year. That brings us more direct, more intense sunshine. Add longer days, and we're sizzlin'.
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Joe Howlett in Abingdon says he's 74, but "I'm paying attention." He noticed Saturday when I said here there are no such words as "mostly" or "sunny" in the official meteorological glossary, while 8 inches away, Norm Lewis used those very words. Vito in Jarrettsville saw a "blatant contradiction ... Are you and Norm not on speaking terms?" Dunno. We've never met. (Hi, Norm!) Forecasters don't have to stick to the glossary. Optimists like Norm can say "mostly sunny." Pessimists (or purists) prefer "partly cloudy."
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Donald Gansauer of Canton noticed the record-high number of tornadoes in the U.S. so far this year and wonders: "Is there any correlation between that number and the potential number of Atlantic hurricanes?" No. In 2004, there were a record 1,717 tornadoes reported, but only 15 named Atlantic storms. But it can work the other way. That is, tropical storms can spawn tornadoes and inflate the tally. Three hurricanes in 2004 - Frances, Ivan and Jeanne - added 237 tornado reports to that year's record tornado count.
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Alan Lazerow of Frederick and his co-workers have been wondering: "What is cloudier: 'cloudy' or 'mostly cloudy'? ... 'Partly sunny' or 'partly cloudy'?" Pay attention, class: There are no such words as "mostly" or "sunny" in the American Meteorological Society's Glossary. It says "cloudy" means at least 70 percent cloud cover, while "partly cloudy" means 30 percent to 60 percent cloud cover. "Clear" means a maximum cloud cover of 20 percent. Anything else is a personality test. Is your TV meteorologist's sky half-full? Or half-empty?
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June 20 might have been the longest day of this year, but today will seem longer. Sunset this evening is the latest of the year, at 8:37 p.m. in Baltimore. Since we're more likely to witness sunsets than sunrises, the date with the latest sunset always seems longer than Midsummer's Day, the 20th this year, which had the most minutes of sunlight. The hottest days are still ahead, but from here on, the daylight wanes as sunrises grow later and sunsets get earlier.
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Jeff Ehmsen moved to Baltimore from Southern California. "We pretty much never get thunderstorms there," he says. Since landing in Mobtown he's "come to appreciate them as part of the seasonal cycles, but wondered what explains them." I love T-storms, too. Their beauty and drama is fueled by our heat and humidity. Moist air buoyed by solar heating or clashing fronts rises through colder air. The updrafts generate electric fields, lightning and thunder. Cooling aloft condenses water vapor, which falls as rain and hail.
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John Guthmann, in Cockeysville, noticed that the summer solstice this year fell on June 20. "This is the first time I have seen the summer solstice fall on the 20th of June," he says. No wonder. It's a rarity. The last time was in 1896. But you may catch the next one, in 2012. This one barely made it – 11:59 p.m. on June 20 (Universal Time). Most fall on the 21st, but the 22nd, too, is possible. Don't wait up. The next is in 2203.
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Roy Tarbutton, a self-described global warming "skeptic" in Pasadena, noticed that two of the three unbroken May high-temperature records noted in a recent Sun heat story were set in the 1920s and 1930s. If the planet really is heating up, he asks, "why are so many temperature records so old?" Because it's hard to break records. But with global warming, it's averages, not record highs, that matter. Baltimore's average annual temperature has warmed almost 2 degrees since 1895, most of that since 1970.
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Carroll Rinehart, out in Bel Air, remembers that May rainfall had threatened to top the all-time record for the month in Baltimore, and asks: "Did the last couple of days put us over the top?" Happily (or sadly for us weather geeks), no. The last day of May brought a final quarter-inch of rain. That pushed the month's total to 7.77 inches, cementing its standing as the second-wettest May on record here. But it was still an inch short of the 1989 record of 8.71 inches.
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Back in his Army days, Barry Neistadt of Baltimore learned an acronym for the time before sunrise, and after sunset, when there was just enough light to see. But he's forgotten it, and figured I'd remember. Hah! I looked it up. He's probably thinking of BMNT (begin morning nautical twilight) and EENT (end evening nautical twilight). Both are times to "stand to" with heightened security. The practice dates from the French and Indian War, when both sides exploited the low light to launch attacks.
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This morning marks the year's earliest sunrise. Sleepers wish it were later, but Old Sol popped above the eastern horizon at 5:39 a.m. EDT as seen from Baltimore (5:36 at Ocean City, 5:40 in Oakland). The summer solstice is early this year, at 7:59 p.m. on the 19th, and the latest sunset falls on the 27th, at 8:39 p.m. The sequence reverses in December, beginning with the earliest sunset on Dec. 7, the winter solstice on Dec. 21, and the latest sunrise Jan. 5.
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If you're reading this today, your paper arrived and your luck isn't all bad. But it is Friday the 13th, the only one on the calendar this year. Guy Ottewell's Astronomical Calendar says that happens 42 to 44 times each century. Next year, there will be three Fridays the 13th. That happens 14 or 15 times per century. While many here regard both Friday and 13 as unlucky, in South America Tuesday is the unlucky day. And for Italians, the luckless number is 17. Go figure.
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May rains helped end the latest drought and got Greg Koppenhoefer of Ellicott City thinking about the past: "This area suffered a 14-year drought (1958-1971) which ended dramatically in June of '72. Comment?" We did have quite a stretch of dry weather between 1962 and 1970 - nine years. Only 1966 topped the 42-inch annual average. And 1965 was the third-driest year on record for Baltimore, with just 28.22 inches. The streak ended with 53 inches in 1971, well before Tropical Storm Agnes in June 1972.
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Space Cadets! If you missed Thursday's flyover by the International Space Station, you can get make-up credit tonight. The station's course is the same, flying from high over New Orleans to Baltimore and Nova Scotia. Look southwest at 8:39 p.m. Have the kids watch for a bright "star" climbing quickly toward the zenith. It will pass between Saturn and Mars before reaching its highest altitude at 8:42 p.m. Then see it cruise off toward the Big Dipper, disappearing in the northeast at 8:45 p.m.
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Donald Gansauer, in Canton, remembers that the 1991 eruption of Mount Pinatubo in the Philippines caused global cooling for several years. "Do climatologists believe the current eruptions of the Chaiten volcano in Chile and Mount Etna in Italy will have a similar effect?" Not Mount Etna. Chaiten's blast, while smaller than Pinatubo's, has sent dust to 55,000 feet, high enough to persist and cut sunlight. But the southern oceans steady temperatures below the equator. Dust needs to spread north to cool the planet. Scientists are watching.
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Space Cadets! With luck, skies will clear enough tonight to reveal the International Space Station as it cruises high over Baltimore. Grab the kids and watch for a bright, steady, starlike object rising briskly above the southwestern horizon at 9:30 p.m. It will climb just to the right of closely paired Saturn and Regulus and be high overhead by 9:33 p.m. Station and crew will then zip through the Big Dipper and skip off toward the northeast, vanishing there at 9:35 p.m.
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It was pouring when Charles Grene got home to Westminster on Sunday. He dialed the weather phone; the relative humidity was 79 percent. The Weather Channel said it was 81 percent. He's puzzled: "I thought that when it is raining the relative humidity was 100 percent." It is, Grasshopper, at least up where the water vapor is condensing. But the air is often drier at the surface, around our instruments. Raindrops can evaporate as they fall, producing veil-like clouds called "virga."
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Hell must have frozen over. After 20 months of nagging from me, our IT folks have finally done it. The Sun'snot-so-new-anymore Davis Vantage PRO 2 weather station at Calvert and Centre streets is feeding nearly real-time data to a Weather Underground Web site. You can check the downtown Baltimore temperature, humidity, wind, rain and barometric pressure - posted every 10 minutes around the clock - with the click of a mouse. The link is right below the five-day forecast at baltimoresun.com/news/weather/. Cool!
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If the clouds part enough this evening to reveal some stars, Marylanders can watch as the moon drifts past Mars in the western sky. Go out about 10 p.m., and you'll see the near-first-quarter moon almost halfway up the sky. The steady, faintly reddish "star" to its lower right is Mars, where NASA's Phoenix spacecraft will land May 25 in a search for water ice in the Martian arctic. To Mars' right are the twin bright stars of Gemini-Pollux and Castor.
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Bob Carterof Harrisonville asks: "How much has Earth's atmosphere declined, and in which amounts, to cause climate change? Keep it simple!" Cliff Notes version: Carbon dioxide levels in the atmosphere have increased 34 percent since 1800, from 280 parts per million to 377 ppm. Methaneconcentrations are up 145 percent. Our emissions of these "greenhouse gases" have jumped 70 percent since 1970. Scientists agree these higher concentrations are "very likely" responsible for most observed climate warming.
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Mitchell Thompson of Easton needs help with a new digital barometer. "Readings have ranged from 998 to 1016 MBR," he says. "I am accustomed to readings such as 29.1 to 30.8." Welcome to the metric system. Your old readings were in "inches of mercury." Your new instrument displays millibars. One millibar equals 100 newtons per square meter. Huh? Standard pressure at sea level is 1,013 mb. Hurricane Katrina's pressure sank to 902 mb. For a conversion table: pcwp.com/mb_conversion.html.
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Ken Legace of Stewartstown, Pa., writes: "I thought lightning happened when positive-charged clouds and negative-charged earth connected electrically with a huge ZAP. Then what causes cloud-to-cloud lightning?" While the tops of thunderclouds become positively charged, the bottoms go negative, which induces a positive charge in the ground. Wherever the difference reaches 15 million volts per mile, it discharges. Bolts fly twice as often within clouds as between clouds and ground.
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Jeffrey Brauner of Baltimore spotted an odd-looking tornado on TV news recently. It was no funnel, he said, "just a big, dark blob of clouds sagging down going the same speed as the clouds in the sky. Is this type of tornado more or less dangerous than the funnel type?" Tornadoes take many forms (wedge, funnel, cone, tube, rope) and colors. Some start as funnels, broaden, then die as ropes. There is no correlation between shape and strength. They're all bad news.
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May at last. Maybe we can finally shake April's drizzle and chill. This month ends our risk of frost. Baltimore's latest trace of snow fell May 11, 1951. Average daytime high temperatures at BWI Marshall Airport climb from 69 to 79 by month's end. The average lows rise from 47 to 57. Record highs reach 98, while all-time lows linger in the 30s until the 30th. One of Baltimore's oldest record lows is 34, on the books since May 1, 1876.
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Space Cadets! It's been ages since the last good flyover by the International Space Station. Blame orbital mechanics and crummy weather. Tomorrow's forecast is iffy, too. But Baltimore's early risers may have a view of the star-like ISS as it rises in the southwest at 5:26 a.m. It will pass bright Jupiter in the south, climbing halfway up the southeastern sky by 5:29 a.m. Then watch it fly just above a rising crescent moon before vanishing in the east at 5:31 a.m.
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One hundred ten years ago tomorrow, Baltimore saw the latest measurable snowfall on record here. The coastal storm on April 28, 1898, left a tenth of an inch behind, with temperatures dipping to 34. Rain turned to snow and sleet before dawn and continued into the afternoon. On the Eastern Shore, the gale dropped up to 2 inches of snow, damaging strawberry plants as they flowered. Peaches and peas also suffered. A world away, an American naval squadron battled the Spanish in the Philippines.
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Where's Venus? Our brilliant sister planet, so familiar to morning and evening commuters, has been increasingly hard to find since winter, sinking low in the east before dawn. But it will pass behind the sun in early June and reappear in the west after sunset. As the Morning Star, Venus was "Eosphoros" to the Greeks. As the Evening Star, it was "Hesperos." Venus joins bright Jupiter Nov. 30 as a strikingly close pair in the evening sky.
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Where's Venus? Our brilliant sister planet, so familiar to morning and evening commuters, has been increasingly hard to find since winter, sinking low in the east before dawn. But it will pass behind the sun in early June and reappear in the west after sunset. As the Morning Star, Venus was "Eosphoros" to the Greeks. As the Evening Star, it was "Hesperos." Venus joins bright Jupiter Nov. 30 as a strikingly close pair in the evening sky.
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Paul Manacher of Baltimore says our local forecasters are "usually accurate." But he asks why they "invariably underestimate summer high temperatures." The NWS warning coordination meteorologist for our area, Chris Strong, says his forecasters' predictions last summer averaged a quarter-degree too high for BWI. But they underestimated downtown highs by 3 degrees. Strong says they are not allowing for enough "heat island" effect -- heat absorbed, reflected or re-emitted by buildings and pavement.
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John Stratton of Catonsville knows the old saying, "April showers bring May flowers." But he asks: "Isn't April historically one of the driest months of the year in ... Baltimore?"