Day 345: Blizzard!
As mentioned in last night’s post, a major winter storm was forecast to target the northern United States today, and it didn’t disappoint. My original thought for a blog post tonight was to do an anatomy of a blizzard, but one of my former students, Jonathan Whitehead, (who is available for hire!) put together an image (above) that sufficiently describes the anatomy of this cyclone. Although, I personally do not like the term “TROWAL” since this feature is merely an extension of the warm conveyor belt, it is widely used in the National Weather Service and I can’t really complain. So, my image tonight is simply a radar mosaic from this evening. This cyclone has everything ranging from severe thunderstorms (South), to heavy rain (Ohio Valley), to snow and blizzard (North).
Day 344: Developing Major Winter Storm
Tonight’s National Weather Service National Watch Warning graphic depicts a wide swath of winter weather products across the northern United States. Everything ranging from Winter Weather Advisories to Winter Weather Warnings to Blizzard Watches to Blizzard Warnings are in effect. Tomorrow will be a doozy of a travel day across the north. If you can avoid going out, please do. If you do have to venture out, please take all necessary precautions, including taking an emergency survival kit.
Day 343: Great Lakes Snow
A compact, mid-level short-wave trough is currently moving through the midwest, bringing with it (mainly) light to moderate snow across portions of the Great Lakes. This short-wave trough is just the tip of the iceberg, however, as a much stronger cyclone is forecast to traverse the region this weekend. This cyclone promises to bring snow, wind, and cold to much of the east. Granted, the southeast and Florida might not see snow, but they will see rain, and the cold will certainly follow closely behind.
Day 342: Even Colder Air Upcoming For the Eastern US
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- It is really cold in the east.
- It is fairly warm in the west.
- Citrus growers in the southeast, including Florida, will need to worry about additional freezes.
- Parts of north-central Florida will reach the teens (Fahrenheit).
- It will be colder in Tampa, Florida and Orlando, Florida than in parts of Colorado, Wyoming, and Montana!
Day 341: It’s Raining; Now, It’s Snowing???
I took a look at the Oklahoma Mesonet this evening to see what the temperature was across Oklahoma and noticed an elongated area of colder temperatures in central Oklahoma. This was particularly interesting because in this same area, temperatures were in the 50Fs this afternoon!
Sure enough, examination of the 3-hour temperature trends indicate that the aforementioned elongated band of colder temperatures coincides with the greatest 3-hour temperature decreases. So why the narrow band of colder temperatures? The answer lies in the “wet-bulb effect”, otherwise known to meteorologists as the bane of winter weather forecasting.
As anyone who lives in central Oklahoma can attest to, it has been very dry across the southern plains over the last few days. (Anyone else notice an increase in the number of times one is shocked by a static electricity discharge?) However, in the mid-levels of the atmosphere today, a strong short-wave trough, closed low, has produced enough lift to produce clouds and precipitation. As this short-wave trough moved southeast into the state today, the associated precipitation did as well.
Now is where it gets a bit complicated. Even though it was quite warm this afternoon, it was also very dry at the surface. Thus, when the precipitation fell into the dry air, it evaporated before reaching the ground. This kind of precipitation is called “virga”. So, what does this have to do with cooling at the surface?
Evaporation is a cooling process. In order for water to evaporate, it must absorb (or remove) heat from the surrounding environment. This is why you sweat when you are hot. The water on your skin absorbs your body heat when it evaporates and cools you down. In the atmosphere, the same thing happens. When precipitation evaporates before reaching the ground, it cools the air temperature.
Taking a look at radar from about the same time this evening, you can see a band a heavier precipitation falling just south of the coldest air. If I told you that this heavy precipitation band was moving southward, it would make perfect since that the coldest air temperatures would be found where the heaviest precipitation (and hence greatest evaporation) had taken place.
So, how does this tie into the blog title? Well, when a very cold airmass moves into a region, it tends to be very dry. As the airmass begins to modify (warm), it often remains dry, especially in winter. When precipitation begins to move into a region with very dry air, even though the temperature might be in the upper 40sF or 50sF, the temperature can wet-bulb into the low 30sF very quickly. This means that precipitation that starts out as rain can very easily transition to snow or freezing rain as the wet-bulb effect cools the temperature.
This happened today in central Oklahoma. Temperatures were in the low 50sF this afternoon, but as the precipitation began to fall and evaporate, the wet-bulb effect rapidly cooled the temperature into the low 30s and the light rain transitioned to light snow.
Oftentimes in environments where the atmospheric temperature profile is flirting with being conducive for snow, but only rain is reaching the ground, when the precipitation intensity picks up, the rain transitions to snow, and then when the precipitation intensity begins to lessen, the snow changes back to rain. This is due to a couple of things. For starters, if the atmosphere is not already at the wet-bulb temperature, the heavy precipitation might allow the observed temperature reach the wet-bulb temperature. Also, the heavier precipitation acts to “drag” some of the colder air aloft down to the ground with it. This process is called “precipitation drag”. It is this downward transport of colder air that prevents snowflakes from melting, allowing them to reach the ground. This also happened today. As the heaviest precipitation fell across central Oklahoma, the rain transitioned to snow, but as the heaviest band passed and the precipitation became lighter, it transitioned back to rain.
Lastly, notice the yellow area in the precipitation across central Oklahoma? This is known as the “bright band“. It is indicative of where snow is melting and transitioning to rain. It just so happens this transition was occurring near the ground, so the “yellow band” only appeared very near the radar. Since the radar is located in central Oklahoma, this is where we found the yellow band.
Day 340: Bad News for Citrus Lovers
A quick look at the National Weather Service’s National Watch, Warning graphic shows Hard Freeze Warnings for southern Louisiana and the northern Florida peninsula. Across extreme southern Louisiana and central to southern Florida, a Freeze Warning is in effect. (In fact, a wind chill advisory is in effect for Miami, Florida!) This likely freeze does not bode well for the Florida citrus crop, which, unfortunately, was decimated last year. Whatever crops might survive this freeze will be tested again next weekend, when an even colder airmass is forecast to plunge into the southeast.
Day 339: (Yet Another) Lake-Effect Snow Event
Last week, a very impressive Lake Effect Snow event took place across areas to the northeast of Lake “Eerie” and Lake Ontario. It appears that another Lake-Effect Snow event will take place again this week. However, this event will take place in areas to the southeast of the Lake “Eerie” and Lake Ontario. Based on the precipitation amounts forecast by the Hydrometeorological Prediction Center (HPC), over 2 inches of liquid equivalent will be possible over the next five days. This would most likely end up being over 2 feet of snow for portions of northeast Ohio, northwest Pennsylvania, and upstate New York!
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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