Rob McClure
Weather
May 14 thunderstorms
05/15/13 5:11 PM | Weather
The local National Weather Service – Sullivan website is quite good about posting retrospectives on events of meteorological note, so it’s often a good place to look for analysis if something’s occurred that you find particularly noteworthy or unusual. But the site also often presents interesting debriefings on events that might otherwise have seemed mundane. The thunderstorms that formed west of Madison and moved over the area on Tuesday evening (May 14th) didn’t seem particularly unusual to most of us — they were in a declining state as they moved in, so by-in-large, they weren’t even terribly strong. But dying thunderstorms can produce an unusual phenomenon called “heat bursts,” and the NWS-Sullivan article about this in regard to the May 14th storms is typically fascinating and instructive. rm
read article »The Cruelest Month
04/29/13 8:38 AM | Weather
After a brief flirtation with spring, including the first 70 degree temperature on 4/28 since back on October 25, we’ll see a cool-off of several days duration starting Wednesday, 5/1. Typical for the season, a “cut-off” low — a closed, mid-level circulation of cold air, detached from the bulk of the hemisphere’s cold air further north — will develop over the eastern Midwest Thursday and Friday, wobbling around nearly in place on most forecast maps through the weekend, bringing cool and intermitantly showery weather. But before then, we’ll have a foretaste of summer. As warmer weather starts to bring more convective activity into the area, you might find a couple of online resources quite useful. The first is the Milwaukee-Sullivan radar image, as processed by Weather Underground. It’s especially useful since it includes tracking information (bearing, speed) that allow you to assess when a thunderstorm will arrive in your area. It also gives information on the strength of individual cells, including estimated cloud-top height and whether a mesocyclone (rotating updraft) or hail is present. The Storm Prediction Center site is also very useful during severe weather. Of particular interest in looking forward to possible threats are the Convective Outlook pages, often refered to as SWODY 1, SWODY 2, etc. (“Severe Weather Outlook DaY 1, 2, 3″), which provide the go-to analysis for severe weather prospects on upcoming days. As ever, the Visible/IR image of the Upper Midwest and the 12-hour Water Vapor image of the US will be of use getting a wider perspective on what’s happening.
read article »Warmer — but when?
04/22/13 8:43 AM | Weather
Have a look at this page — the 3-month outlook from the Climate Prediction Center. You can click into maps for a rough-sketch prediction of both temperature and precipitation anomalies for any 3-month period stretching forward over the coming year and a quarter. This tells you the probability of it being either warmer or colder, wetter or drier, than usual — not a terribly strong or reliable indicator necessarily – but of use to the idly curious, and especially to farmers and orchardists who need to bank on general weather trends relatively far in the future. The “Prognostic Discussion” link provides the latest meteorological thinking over the coming 90 days, and tells you what longer term factors (atmospheric phenomena like the Madden Julian Oscillation or El Nino/La Nina (“Enso”) cycles, and geophysical factors like sea-surface temperatures and soil-moisture) figure into the prediction. rm
read article »Warmed by a dying storm
04/15/13 8:33 AM | Weather
An occluding cyclone (a low-pressure cell that is filling-in and dissipating) is quite prominent over Minnesota on the IR/visual image of the upper Midwest Monday morning, April 15th. (This image is live, and will look different if you’re viewing at a different time). The northbound portion of the circulation has brought a temporary respite in Madison from the endless winter we’ve been experiencing. But, light snow is likely to be back in the forecast by Friday the 19th. A listener called in last week to ask about an article she had seen in the Wisconsin State Journal about “atmospheric rivers.” This term was coined in the 1990s to describe the predominant mode of moisture transport away from the tropics toward the poles, which tends to occur in long, narrow plumes. A caller several months ago asked about the structural causes of these plumes and I still need to make good on answering him. The causal mechanisms are still under study, but what is known so far is quite interesting. I’ll talk about them on air soon since the local “AR” here in the upper MIdwest is the low-level jet which transports moisture from the Gulf of Mexico; it’s most active in the upcoming warmer seasons. In fact, some of the nearly 3 inches of rain that came down in Madison between April 7th and 14th was delivered by the LLJ. rm
read article »A More Nuanced View from the Weather Service
04/8/13 8:36 AM | Weather
The National Weather Service is the go-to resource for most weather information, but the public forecasts tend to be a bit constrained by the need to communicate simply and briefly. For those of you looking for a more in-depth and nuanced perspective on upcoming weather, the Forecast Discussion section of the local NWS websites can be quite instructive. It can also be quite instructional for learning meteorological terms — most of the obscure ones are hyperlinked to definitions so you can understand what the forecaster is talking about. You might have a look at both the LaCrosse Forecast Discussion and the Sullivan (Milwaukee) version. The former is sometimes more useful here in Madison since LaCrosse is “meteorologically upstream” of us. rm
read article »April Fool’s…
04/1/13 8:21 AM | Weather
It’s still absurdly cold for the season. March ended -7.4 degrees F. below normal, with only three of the 31 days modestly above normal in average temperature. Here is an animated graphic from the Climate Prediction Center showing a North polar view of the earth, with warm and cold air (red and blue) battling for contention in the arctic. This is technically a map of mid-level atmospheric height anomalies, showing ridging (warm at surface) and troughing (cold at surface) over the past month. “500-hPa” refers to the mid level of the atmosphere, roughly halfway from the ground to the tropopause. Notice how strongly and repeatedly warm air intrudes across the arctic, pushing the cold, blue regions down into the temperate latitudes and squarely into our region of North America. This is a classic “negative phase” of the Arctic Oscillation or Annular Mode. rm
read article »test graphic, 2.0
03/18/13 10:37 AM | Weather
Sunday, March 24, 2013. We’re still in the process of getting this page organized — thanks for bearing with us. One constant is likely to be the graphics that I regularly refer to in the Monday morning (10 AM) and Wednesday evening (6:30 PM) weather reports. At right is an infra-red / visual image of the upper Midwest. Click to see the animation. It is a live link, updating roughly every 15 minutes, and switches between IR and visual at sunrise and sunset. Once you’ve clicked into it you can set the length of the loop in the upper left and control the replay speed and level of zoom in the menu bar at the top. Here is a link to GOES-12 water vapor imagery. It is updated once a day, and captures goings-on in the upper part of the troposphere (“jet-stream level”) during the overnight period, between about 6 PM and 4 AM. This is the one I often describe on the Monday morning forecast. Once you’ve clicked-in, you might want to set the animation-speed slider further to the right to speed it up — this will render a very fluid image that’s useful for getting a sense of what’s going on in the upper atmosphere over continent. I’ve not tested it yet to see if it updates, but you can check the date and time at the bottom of the image (time is in “UTC,” essentially Greenwich Mean Time, so subtract 6 hours for CST or CDT). Future posts will explain how to interpret what you see on WV imagery. One last link that might be relevant to the 3/25 forecast: 7 day satellite retrospective from the SSEC. If you’re interested in additional graphics, you might want to check out the UW’s SSEC Data and Imagery page.
