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Kevin Myatt grew up in Arkansas to the tune of tornado sirens and the rhythm of hailstones. Chasing twisters like he did in 1999 and getting within a quarter-mile of one was exciting, but he finally tired of 5-month-long summers and 2-inch snowstorms and moved to the cooler climes of Southwest Virginia's mountains in 1999. Kevin thought he was going to be a meteorologist growing up but he credits divine intervention with continually detouring him to a newspaper career instead, landing him in an managing editor job of a small Arkansas paper before coming to The Roanoke Times as a copy editor in 1999. But his love of weather continues to this day, and at the beginning of 2003 he began this weather column in addition to the hiking page he has updated occasionally on Roanoke.com since early 2000. He now works the copy desk for The Roanoke Times and is its principal weather geek, offering weather reporting training classes to reporters and advising the newsroom on upcoming weather stories. He updates this column most Tuesdays and Fridays -- and other times as conditions warrant. Email your weather or comments questions to kevin.myatt@roanoke.com For more on Kevin |
WEATHER JOURNALNovember 28, 2003
This week has turned out perhaps a bit chillier than I spoke of earlier this week. Part of it is that it just seemscolder because it's been so warm, but you've probably actually had to bundle up some to enjoy outdoor activities, unlike what I said on Tuesday. We have been a few degrees below normal of late.
Now, with the passage of the cold front today and a deepening low pressure over New England, we may cap the Thanksgiving weekend with a few snowflakes.
Don't panic, we're not talking snow shovels and tire chains, but don't be surprised to see some white particles of ice fluttering in the abundantly nippy breeze tonight and Saturday. Some of the upslope areas in West Virginia will probably see enough snow to turn the ground white, maybe a few inches in some areas.
This low pressure area will bring a substantial snowstorm to southeast Canada and some of the northeastern United States. One thing I am noting is a tendency for low pressure areas to move west of us and explode near the St. Lawrence Seaway. This is about the third one in the past two months to do so. This is not a favorable storm track for snow-bearing systems, and should it lock in like this later in the season, we'd be caught on the south side of a lot of storms and get rain or ice.
But it's early, and it does look like we are in the initial stages of a gradual, but significant, weather pattern change.
Don't let the sunny warmth of most of November fool you. Winter is lurking. SNOW? The week's second cold front and a vigorous low pressure area winding up along it will give us another shot of rain on Thanksgiving Day -- and then some blustery cold and a few snowflakes for the weekend. Some of the favored upslope areas of West Virginia may even get a few inches by Saturday morning. Here in Roanoke, do not be surprised at all to see flurries in the air Friday night and Saturday morning on brisk northwest winds. The cold air that we talked about making some inroads is indeed doing so, maybe a little stronger and faster than first thought. The first step in a large-scale pattern change that will bring visions of Christmas snowmen dancing in your children's heads? We'll see. But, as the National Weather Service forecasters in Blacksburg note in their discussion on Wednesday, it might be enough this weekend to get Christmas shoppers in the holiday spirit. Nov. 24, 2003 A LATE TRICK OR TREAT? It just feels weird for it to be as warm as it has been approaching Thanksgiving. We'll get a tad of a chill back in the air before Thursday, but most of this month has felt more like Memorial Day. November is averaging about 7 degrees above normal. That's about as toasty as a month gets, relative to normal. I've heard folks wondering aloud whether that's a sure sign that we'll have a mild winter. I don't have the data at hand to back it up, but it's been my experience that the winter often seems to turn out opposite of whatever it's doing in late fall. I've seen plenty of cold Novembers get everybody thinking the next ice age is about to come crashing down only to fizzle into short-sleeve weather come the first week of January. Last year was different, though. It got cold early and pretty well stayed that way. By this time a year ago, the basic weather pattern that would last through winter -- and indeed, through spring and part of summer too -- was setting up. The big high was parking itself in the West and the jet stream was diving over the top of it from Canada all the way to the Gulf Coast, then bending back northeast along the Eastern Seaboard. The pattern wiggled a little, there were a few warm days last November in between the cold blasts, but nothing like this month's almost constant May-like climate. November 2002 averaged a degree below normal. At Thanksgiving last year, we were having plenty of cold nights and enough rainy storm systems moving through to curtail the now long-forgotten drought. Many Appalachian ski resorts got off to their earliest start of the season ever in late 2002 because of all the cold weather hanging around, enabling them to get the snow guns going. By the first week of December, we had our first snow of the season. I think it's safe to say that we won't have a repeat of that this year. It does appear, though, there is a subtle shift in the weather pattern this week, and some meteorologists out in cyber-land are saying that it hints at what could be the beginning of something larger down the road.
The trough, or southward dip in the jet stream, that has been along the West Coast appears to be shifting more to the middle of the country. Some Arctic air spilled into the Plains states this past weekend, even as far south as Oklahoma and Texas, where freeze warnings were posted. Minnesota had some snowy, windy weather over the weekend, but they just sneeze at 6 to 12 inches up there.
The shift will not be enough to turn us to wintry conditions anytime soon, but it could be a first step toward a significantly colder, wetter, maybe whiter pattern. A couple of cold fronts this week will drive our temperatures more down toward average, but other than some showers with each front, it will be another fine week to enjoy the outdoors without bundling up. Some weather experts are noting that the sea surface temperatures that preceded our warm November have changed dramatically. Some places in the Atlantic and Pacific that had cool pockets of water are now warm, and vice versa. The connection between sea surface temperatures and the air masses above them are convoluted and controversial, but such a change does imply a coming pattern change. Still, it often takes weeks for pattern changes to fully implement themselves. So I'm still doubting that we get any significant winter precipitation before Christmas. Turn off the Bing Crosby. November 20, 2003 MOUNTAINS MATTER It might sound more like something your dentist would talk about, but orographic effects are a big part of the weather we have in Southwest Virginia. Orographic effects are weather phenomena caused or aided by the Earth's topography, such as mountains. While large-scale weather systems such as the jet stream, fronts and massive high and low pressure systems are the prime drivers in our weather, valleys and bodies of water play a significant role in determining the details of our local weather. One effect of our region's topography is a greater inclination for flash flooding. The 3 to 8 inches of rain that fell in some areas Tuesday and Wednesday would have been a flooding rain most anywhere, but the steep ridges and tight drainage valleys channel it rapidly. In a flatter area, it might have puddled up and spread out and not drained as quickly. But this is more a secondary effect, geography affecting the results of weather rather than being a cause of it. A common orographic issue in a mountain region is upslope precipitation. As moist winds blow against the mountains, the air rises, cools and condenses, squeezing out the moisture. South, east or southeast winds in our region, ahead of storm systems approaching from the west, often transport Gulf of Mexico and/or Atlantic moisture in abundance. When these winds hit the Blue Ridge, they are lifted and the moisture is wrung out of them. Upslope-enhanced rains were a contributing factor in our downpours this week, especially along the Blue Ridge south of Roanoke. A similar effect occurs on the west-facing slopes when cold winds from the northwest are lifted up the mountains, squeezing out snow showers and even heavier snow squalls. West Virginia ski resorts reap a lot of snowy benefits off this effect; Snowshoe averages well over 100 inches of snow a year, while Virginia locales just a few miles to the east get only a quarter of that. Topography becomes a crucial forecasting factor in winter weather situations. Temperature usually drop with elevation, and a difference of a few thousand or even several hundred feet can make all the difference between a 35-degree rain and 32-degree snow. Residents of Bent Mountain who commute to work into the Roanoke Valley are highly familiar with this scenario. In other weather situations, though, it is valley areas that trap cold air, and this can lead to pockets of freezing rain while surrounding ridges are in the 40s. In summertime, the difference in temperature between ridges and valleys can create enough instability for thunderstorms to form. At any time of year, fog condensing in cool valleys or winds ripping along ridgelines or through narrow mountain gaps can create weather on a minute local scale. This becomes a particular danger on highways, where bright sunshine can give way to blinding fog or calm conditions can turn into a truck-tumbling tempest just a few mileposts later. So while meteorologists everywhere must be knowledgeable about the same kinds of phenomena and large weather patterns, they also must adapt to the local quirks of geography in the specific area for which they are assigned. You can have all the L's and H's and blue-pointed lines right on the weather map and still miss the forecast. The meterorologists at the National Weather Service office in Blacksburg have a solid grasp on the local orographic quirks of Southwest Virginia, and I've learned a lot in four years from their discussions of our weather events. FARMER'S ALMANAC UPDATE For the first 19 days of November, the Old Farmer's Almanac is carrying a 5-14 record: it's gotten five days correct, using a very lenient definition of what's correct, and it's flat-out missed 14 days. For the latest period, Nov. 16-19, the almanac called for "Sunny, cooler." In fact, this was a period of warming weather, and two days feature rain instead of sun. So all four days were misses. For the period Nov. 20-26, the call for our region is "Rain, then sunny, cold." We got our rain over before the period started, and it looks like this will be a warming period, as well, so it doesn't look good for the almanac forecast. Its November forecast of temperatures 1 degree below average is sunk. We're averaging about 6 degrees above normal and there's nothing short of a sudden ice age that could balance that in the 10 days left. It also predicted .5 inch below normal in precipitation, and this week's rain took us over the month's normal. Nov. 19, 2003 WIND-DRIVEN RAIN Expect a breezy, rainy day in our area today, as a surface low passes nearly right on top of us, supported by a trailing upper level low. Some flooding has been reported in some parts of Southwest Virginia, and more may occur, especially on small streams. It appears the bulk of any severe thunderstorm threat will occur to the southeast of us, in the Carolinas and eastern Virginia. That's where the most turbulence will be, in the "warm sector" of the system, between the cool front slicing from the west and a warm front pushing northward ahead of the low. A tornado watch is already in effect for some of those areas. Once the sheets of rain clear out by tomorrow, the rest of the week and weekend look to be mostly dry and mild for this time of year. Nov. 18, 2003 TON OF RAIN Any threat of severe thunderstorms seems to have dampened. We won't get much sun today to destabilize the weather, the better atmospheric dynamics for big storms will be farther south, and the bulk of the rain will likely push through during the morning on Wednesday, during the coolest part of our daily heat cycle. Nov. 17,
2003 Stormy weather OK, sing along: "It's beginning to look a lot like ... uh ... April?" Here comes a strong Pacific cool front (note I didn't say cold front) pulling up wads of Gulf of Mexico moisture in front of it, triggering heavy rain and thunderstorms from Texas to the Tidewater. More the kind of fare we usually have when trees are budding rather than when they are bare. Tuesday night looks like a gullywasher for us. Most of us will probably be measuring rainfall by the inch come Tuesday night, as this bulldozer of a cool front shoves gooey air thicker than Louisiana gumbo our way. The question that hangs in the balance is how much sunshine will we get during Tuesday that can heat things up for possible severe thunderstorms. Will there be too much moisture and cloudiness to let the sun shine in, or will it pop out and shoot us to near 70? The warmer it gets, the more unstable the atmosphere will be when the front arrives, and the bigger the threat will be of big hail and big wind thunderstorms. If it stays cooler and cloudy, you'll still probably hear it thunder and maybe see the trees bend a bit, but probably nothing around here will lose its roof. Pay attention to what happens in the lower Midwest and Deep South overnight Monday into early Tuesday. If the dots connect right, the potential is there for a widespread severe weather outbreak, with some tornadoes. More like April than November The front is of Pacific origin, not Arctic, so that's why I say "cool front" and not "cold front." It's more Seattle than Siberia. It's a "strong" front mostly because it's being driven along by some hefty jet stream winds aloft, not because of its frigid weather. Late week temperatures will be 50s and 60s in the day, 30s at night, nothing drastic. Behind the front -- you guessed it -- more wind. Maybe not last week's tree-toppling tempest, but things will be plenty breezy come Wednesday. In an active weather pattern like this, wind is a given. Meanwhile, the truly Arctic air is banking up in Siberia. When, if ever, does it break loose and come pouring across the Arctic Circle and the Canadian plains toward America? The current pattern doesn't favor it happening anytime before the turkeys are on the tables. Hail to L.A Did you see the photos last week of the hail piled up like snowdrifts in Los Angeles? Either look at last Friday's front page or scroll to the same day on Weather Journal on roanoke.com It's a rare event, to be sure, but not unprecedented. It's a bit more common to see hail thick enough to accumulate occurs in the Plains states like Oklahoma, Kansas and Nebraska, where they occasionally have to call out the snowplows to clear the hail. Why didn't the hail melt faster in a warm place like L.A.? Hail is very dense ice, compared to snow, which is a clustering of fragile crystals with lots of air between them. Hail freezes high in the clouds as it's lifted by updrafts. Those repeated updrafts into the highest part of thunderstorm clouds, sometimes 10 to 12 miles high, build multiple thick layers on the hail until it gets heavy enough to fall to the ground. Each dense layer of ice also makes it harder to melt, both on the way to the ground or once its on the ground. Even if there are some hail-bearing thunderstorms near us today, I certainly don't see a need to go out and buy any hail-shovels. Nov. 14, 2003 WE'LL HAVE A LATE, WEIRD WINTER -- PROBABLY Tip for defense attorneys: If you can arrange a jury entirely composed of meteorologists, I can assure you in advance that it will be hung. Twelve of them could never agree on anything at anytime. A few samples of general opinions: >Joe Bastardi of Accuweather.com favors a cold early winter and a milder late winter, with somewhat above average snowfall for us. >David Tolleris, a private meteorologist in Richmond who runs long-range forecast Web site WxRisk.com, says the early winter will be mild and then get colder and stormier in January and February, with above average snowfall likely for us. >Gary Grey of Baltimore expresses confidence on his Web site, Millenniumweather.com, that the winter will be warmer than normal and have 20 percent less snow in our area. >The federal government's Climate Prediction Center has thrown its hands up, saying there is an equal chance of normal, above or below normal temperature and precipitation. Kind of a gutless prediction for our tax money, if you ask me, but perhaps that's a smart move after a run of bad winter forecast years. >Joe D'Aleo - Intellicast.com's "Dr. Dewpoint" and arguably the forecasting champion of last winter - has yet to issue a definitive winter forecast, but seems to be implying a cold winter with notes about increased Northern Hemisphere snow cover and low solar intensity. So now, it's time for this weather geek to take his guess. I'll summarize in four key phrases, with a brief general explanation. Variable Without truly overpowering climatic factors, I just don't see anything locking into place for very long. We've gone from almost hot to chilly to warm to blustery cold in just the past week. This could be a winter when we wear shorts one day and build snowmen the next. No accumulating snow before Christmas It's become fairly obvious that the "default" weather pattern, if you will, for mid- and late fall favors a low pressure trough in the West and a high pressure ridge in the East (PNA-negative, if you remember Tuesday's discussion). It breaks down for a few days now and then, but then springs back into place on a strong jet stream out of the Pacific. I think this will keep us from going into a deep freeze through the Christmas season, and also discourage a storm track favorable for snow here in the Roanoke Valley. A late-arriving winter Sooner or later in such a highly variable pattern, the North Atlantic Oscillation will surely go negative as high pressure builds aloft over Greenland. Since there's little sign of it happening in the next few weeks, it will probably happen later. This will realign the whole weather pattern for a period of time, flooding us with Arctic air and crinkling the jet stream to a south-dipping storm path. Canadian snowpack, paltry just a few weeks ago, is impressive now, and this will serve to hold in the cold blast for more than a few days. One big snowstorm With so much variability, the atmosphere will be cocked and loaded with energy. I'm also intrigued by the possible reappearance of El Nino later in the winter, which could be just enough to energize a Southern storm track without overpowering us with balmy, winter-killing subtropical air. Plus, since it's been eight years since our last foot-plus snowfall in Roanoke, we're just due for one.
My call is that the winter will average about normal in temperature -- the mean between dramatic shifts -- and snowfall will rally late to average slightly above normal, say about 30 inches total (24 is normal), with one big storm and a few small- to medium-sized ones, mostly between Jan. 20 and March 1.
But I could be wrong. Consult your nearest woolly worm.
Nov. 13, 2003 WINTER FORECAST TOMORROW Appearing both online and in print tomorrow will be my official weather geek forecast for the Roanoke Valley winter, along with a few other national meteorologists' ideas about the winter to come in the Eastern United States I'll give you a sneak preview with one piece of it: No accumulating snow before Christmas. Last year, if you recall, we had quite a big storm the first week of December, with 4-10 inches of snow across the area, topped by sleet and ice. I don't think the fast-moving Pacific jet and the repeating pattern of low in the West, high in the East, are going to allow that to develop so soon. Cold air isn't going to be allowed to settle in for a long period of time and the storm track will mostly be north of us. But that could change later. Tune in tomorrow. WEAR HEAVY SHOES I was awakened this morning by the rattle of wind against my window. Gusts have already topped 40 mph here in Roanoke and could top 50 mph at many locations through the day and even into the evening. A high wind warning is in effect. It's that tight isobar packing I wrote about yesterday, which you can scroll down to see for yourself if you want an explanation of the winds. The speedy west winds may carry enough snow to just turn the ground white on some west-facing slopes in West Virginia. Here on the downslope side, expect blue skies with a few puffy white clouds racing by. FARMERS ALMANAC UPDATE After opening the season 0-4 with predictions of "chilly, showers" during four days of sunny, unseasonably warm weather to begin the month, the Old Farmers Almanac has recovered slightly with a 4-4 period over the last 8 days to stand 4-8 on its day-by-day win-loss record through Wednesday. For the period Nov. 5-15, the forecast calls for "Warm, sunny, then showers." Nov. 5 qualified as a truly warm, sunny day, with a high of 82 and a low of 62, some 22 degrees above normal. Nov. 7 also had some sun and was slightly above normal, Nov. 11 had some sun and was above normal, and Nov. 12 had showers late enough in the period to qualify as a hit in the "then showers" part. On the miss side, the showers on Nov. 6 were just too early in the period to count and temperatures were below normal Nov. 8-10. The windy, chilly weather expected today through Saturday threatens to add three more losses. And the Nov. 16-19 forecast of "Sunny, cooler" appears to be during a period when temperatures will in fact be warming and there could be some rainy, even stormy, weather as well. The Old Farmers' temperature forecast for the month of November as a whole is 1 degree below average. Considering we're running about 8 degrees above average through today, it would take a massive, near-record Arctic outbreak to offset our early warmth for that to be anywhere near right. That kind of cold weather thrust doesn't look to be in the cards. Nov. 12, 2003 So much for the tranquil weather this week. Nov. 10, 2003 WINTER PLAYERS Whether it is readers who e-mail, or people I bump into at church, in town or in the office break room, there is one question I get asked most: "What kind of winter do you think it will be?" While they vary somewhat in degree, summers are always hot, springs always gradually warm and autumns always gradually cool. But winters run the gamut. Roanoke has had anywhere between a trace and 73 inches of annual snowfall, the difference between Mississippi and Michigan. It can be in the low 80s or 10 degrees below zero in late January. All the winter's snow can occur in a couple of weeks, or be scattered from the first week of December to the last week of March, like last year. I will eventually get around to answering the question. But first, a look at some of the main players on the winter stage: El Nino/La Nina Most people who aren't even into weather have heard of these phenomena. Their level of influence on worldwide weather is subject to great debate among meteorologists and climatologists, and frankly, El Nino is overplayed in the media. El Nino refers to a warming cycle of sea surface temperatures from the coast of Peru westward into the middle Pacific, while La Nina refers to a cooling cycle of the same. In general, for our winter, it seems El Nino has been linked to wet winters and La Nina to dry ones. In recent years, both have tended to be warm, but there are also some cold, snowy El Nino years in decades past. Over the past two years, there hasn't been a strong trend either way in the Pacific. A very weak El Nino piddled out last winter. Currently, the trend is neutral with some indication of a weak El Nino developing by late winter -- but nothing certain or outstanding. Pacific-North American jet stream pattern This has to do with the ridges and troughs in the jet stream. If the high pressure ridge is in the West and the low pressure trough is in the East, it is a "PNA-positive" pattern, and results in cold air being circulated upon us from Canada, with an added likelihood of storms forming in the Eastern trough, siphoning Gulf moisture into Canadian air. In short, a snowy/icy pattern. Flip that for "PNA-negative," where the cold air and storminess dive into the Western trough while warm air rises north with the Eastern ridge. During the past year, we've had a persistently recurring "PNA-positive" pattern that ended our drought and caused our cold, snow-a-week winter. Of late, though, the "PNA-negative" pattern has showed up more often. North Atlantic Oscillation Football coaches are not the only ones concerned about "blocking" in the cool weather months. Meteorologists watch the northern Atlantic to see if high pressure develops aloft near Greenland. If it does, it throws a big kink in the jet stream that causes it to dip deeply over the Eastern U.S. and then rise northward steeply in the western Atlantic up over the high. This is the "negative-NAO" pattern and it is almost always present when major East Coast winter storms develop. When there is no blocking, a "positive-NAO" pattern often forms with a low near Greenland and a high near Bermuda. This can spell tranquil or even warm winter periods. So what will the winter be like? Unless fresh weather news pre-empts my plan, I'll give you a sampling of what some sources are saying and give you my best guess in Thursday's Weather Journal. November 6, 2003 DE-AMPLIFYING PATTERN "Indian Summer," as it is called in a perhaps not very politically correct way, has broken. If you didn't get out and enjoy this past week of temperatures in the 80s, it could be May before you see a week this warm again. Roanoke set a record high on Wednesday when it hit 82 degrees, a degree above the 81 set in 1975. Several records were tied or set this week at Blacksburg. Normal highs for this time of year run in the low 60s. But then, on Thursday, came the rain, as a cold front began moving through the area. Behind the front is colder weather we'll get this weekend. Temperatures will be more typical for early November and maybe even a tad colder than normal. Lows should be back around the freezing mark with highs in the 50s by Sunday. We're not seeing a wholesale shift in the weather pattern, the kind that would turn our recent spate of warmth into a prolonged and harsh blast of Arctic cold, but we are seeing a relaxing of the pattern that we have experienced recently. As the jet stream weaves from west to east across our continent, it develops rises and dips called "ridges" and "troughs" that correspond to areas of high and low pressure aloft. Sometimes, these ridges and troughs are heavily pronounced, or "amplified," where they rise north and dig south steeply. At other times, they are not pronounced at all. Or, the jet stream flattens into a straight-as-an-arrow west-to-east mode, which is called a "zonal flow." In the past week, as we speculated beforehand, an amplified pattern set up with a deep trough in the West and a huge ridge in the East. This allowed cold, stormy, wet and snowy weather to dive into the West, bringing the season's first big snowstorms to the Rockies and finally squelching California's wildfires. Meanwhile, the jet stream rose far north over a steep ridge in the East, allowing unseasonably warm air to bubble up as far as southeastern Canada. Now, the pattern is relaxing. The rises and the dips are not going to be as pronounced over the next week. While fronts will move across and stir up a little rain, and the temperatures will waver up and down some, expect no dramatic warmups or cooldowns and nothing exceptional about our weather. Just kinda typical. Meteorologists will be anxiously eyeing data to try and foresee the next pattern amplification. A winter-like cold outbreak late month or early in December? Some signals point that way, but it's not a consensus. More on that later. FARMER'S ALMANAC UPDATE From time to time, I'll be updating you on the current accuracy level of the Old Farmer's Almanac in its forecasts for the current season. Its accuracy rating is widely disputed, so we'll just put it to the test this season and see how it does. We'll count it day by day as a "win" or a "loss," and keep a record like a sports team. The 2004 version of the revered guide, which forecasts weather November through October, is off to a bad start. For Nov. 1-4, the Old Farmer's Almanac called for "Chilly, showers" in the Mid-Atlantic region that includes Roanoke. Our weather during that time was diametrically opposed, with record warmth and no rain. For Nov. 5-15, it calls for "warm, sunny, then showers." There was sun and warmth on Wednesday, Nov. 5, so I'll mark that down as a "win." But showers also arrived Wednesday and Thursday, not later in the period as implied here. It doesn't look good for an ongoing forecast of "warm" over the next 10 days, either, though some days within that period may qualify. Current Almanac day-by-day won-loss record through Nov. 6: 1-5. November 4, 2003 A LITTLE WETTER? A slight backtrack from yesterday -- we may get a front through here as early as Thursday night as the warm high appears to be eroding substantially, at least for a short while. A front combined with the moisture that will build from the Gulf could spell more significant rain than first thought ... but the weekend's looking better and better! Though it's debatable in weather geekdom, there are some signs brewing that there could be a dramatic reversal of our weather fortunes toward the end of the month, maybe with a much colder weather regime. More on that as time goes along. The speculation is a bit early now. Snow cover is building rapidly in Canada, not to mention over the north-central U.S. Check it out. Nov. 3, 2003 SUBTLE WEATHER CHANGES As this week goes along, we're going to see an increase of moisture in our atmosphere. This is because the big high that has been giving us this warm period will both weaken and slip a little east. This will allow for a south wind to start bring Gulf moisture back on us. So it'll stay unseasonably warm, but get a bit more cloudy and humid. Still, though, there are just not going to be any major weather systems get through the high, at least until the weekend, so expect some showery weather at best by mid-week as opposed to all-day downpours. AIR HEATS FASTER THAN WATER Air heats quicker than water. Air loses heat faster than water. It's a principle that has broad ramifications for climate patterns around the world, and it's been in evidence over the weekend in our temperatures as a dry weather regime has established itself. Blacksburg set a record high on Friday at 77, after a chilly morning low of 37. That's a 40-degree temperature shift. Usually, without a major cold front having passed, a day's high and low are separated by about 25 degrees or so. By Saturday morning, it was back down to 40 at Blacksburg, then back up to 76 on Saturday afternoon. Roanoke rode a similar seesaw, going from 40 to 79 to 49 to 81 in the same time span. With less water vapor in the atmosphere under the dome of high pressure that has developed, the air absorbed the heat quickly from brilliant daytime sunshine, then lost it quickly at night under starry skies. This principle is of why some desert and high mountain areas, like those in the West, can have enormous temperature differences between day and night, sometimes or the order of 50 or 60 degrees. Meanwhile, perenially moist climates like the beaches of Hawaii may not vary 30 degrees over the course of an entire year. We don't vary as much in the humid summer months, when daily ranges can be 20 degrees or less. A foggy, drizzly day sometimes means the mercury doesn't budge up or down appreciably for hours. This principle becomes critically important in winter weather scenarios. Ever noticed how sometimes it can hold at 34 degrees and just rain, while other times it can be in the 40s but the temperatures will fall as it begins raining and it can turn to snow and ice? Often, the reason this can be is that if the humidity is high and the air is full of moisture, the temperature will not fall much. But if the humidity is lower when precipitation starts falling, the temperature will drop until the air becomes saturated. This is called "evaporative cooling." On a broader scale, the oceans' ability to hold in heat long after the air above it has chilled, or to not heat as rapidly as land masses, plays an enormous role in the formation of large storms, the steering of air currents and even climate patterns spanning decades -- much too large a topic to discuss today.
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