Day 334: Cross Section Through a Cold Front
It is often useful for meteorologists to examine that the vertical structure of atmospheric phenomena. One tool that meteorologists use to do this is called a vertical cross section. The image above, and annotated below, depict a vertical cross section from Omaha, Nebraska to Charleston, South Carolina constructed from today’s 18 UTC (12 PM CST) Rapid Update Cycle (RUC) Model.
This cross section depicts the saturated equivalent potential temperature (Kelvin; red lines), geostrophic absolute momentum surfaces (Mg; black dashed lines), and relative humidity (%; green color-fill). A cross section with these variables plotted is typically used to look for regions of Conditional Symmetric Instability, or CSI*. CSI, sometimes referred to as slantwise instability because the instability is released both in the vertical and horizontal, giving it a “slant” appearance on a vertical cross section, is often a good indicator of the potential for banded precipitation. With respect to snow, this banded precipitation can lead to narrow bands of higher snowfall amounts, with little snow between these bands.
I’m not going to discuss CSI tonight. Instead I wanted to draw attention to the packing of the isotherms (lines of saturated equivalent potential temperature). When the isotherms pack like this it is indicative of a front. The easternmost (right) packing of the isotherms (the one that stretches from the upper-left to the bottom-right) is the Polar Front. It marks the boundary between the warm air to the south/east of the front and the cold air to the north/west of the front. The Polar Front is associated with the Polar Jet Stream, so it can be inferred that above the Polar Front, stronger winds must be present.
Interestingly, the isotherms indicated that a second, shallower front also exists. This secondary cold front often marks the boundary between cold air and really cold air. Sometimes this is referred to as an Arctic Front, although, based on observed temperatures across the eastern United States, I’m hard-pressed to call this a true “Arctic Front”
Day 333: Tornado In Yazoo City, MS (again)
As mentioned last night, a severe weather episode was forecast for parts of the southeastern United States this evening. The image above depicts a thunderstorm as it moves through Yazoo City, Mississippi this evening. The velocity signature indicates a weak-to-moderate circulation as it exits the northeast side of town. Based on early (unconfirmed) reports, it appears that this was a tornado, and there is some structural damage. For those who don’t remember, Yazoo City was hit be a violent, EF-4, tornado earlier this year.
Day 332: Gulf Coast Severe Weather (Forecast)
In contrast to last night’s blog post depicting tranquil weather across much of the eastern United States, tonight is a bit different. The Storm Prediction Center (SPC) is forecasting a slight risk of severe thunderstorms across the northern Gulf Coast tomorrow. There is a threat of significant severe thunderstorms as well, so if you live in along the northern Gulf of Mexico, please review your severe weather preparedness plans.
Day 331: Football Weather
In the wake of the powerful cyclone that traversed the eastern United States this week, high pressure has dominated the weather across the eastern United States. This has resulted in clear skies, calm winds, and great football weather.
In other news, Woooo Pig Souieeee! Go Razorbacks! Great win against LSU!
Day 330: Coldest Morning (so far) this Autumn
This morning was the coldest morning in Oklahoma so far this winter autumn. Above are the low temperatures recorded by the Oklahoma Mesonet.
Day 329: Thanksgiving Day Ice
Eastern Oklahoma and western Arkansas had their first taste of wintry weather today with light freezing rain and sleet mixing in with the rain. The image above comes from the Oklahoma Mesonet and depicts what happens when freezing rain falls on non-heated meteorological instruments. The second row (blue) depicts the wind measurements at an altitude of 10 meters above ground level. Notice how the measurements just stop? This is because the instruments froze because of freezing rain!
Day 328: Find the Cold Front
Well, the long awaited cold front is pushing through Oklahoma this evening. Can you find it?
Happy Thanksgiving (Eve)!
About Patrick
Patrick Marsh is a Ph.D. candidate at the University of Oklahoma's School of Meteorology. He earned a Bachelors of Science in Mathematics and Physics (cum laude) from the University of Arkansas in 2005 and a Masters of Science in Meteorology from the University of Oklahoma in 2007. In addition to working on his doctorate, Patrick serves as the National Severe Storms Laboratory Liaison to the Hazardous Weather Testbed where his research interests lie in working with operational forecasters, data mining, data visualization, and all things high-impact weather. For more about Patrick's work, check out his complete CV!
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