From the Lee Side

Thunder-Snow

Posted by: Lee Grenci, 2:45 AM GMT on February 26, 2013

As I was composing a blog on thunder-freezing rain in southwest Missouri on Thursday morning, February 21, 2013, I received a call from my fearless leader, Jeff Masters, who asked me to talk to National Public Radio about reports of thunder-snow coming out of the Middle West in concert. The thunder-snow and thunder-freezing rain were produced by the developing storm system over the southern Plains (check out the 12Z surface analysis below). At the time, I had already collected the METARS at Springfield, Missouri, from 13Z to 15Z on February 21 (check them out; I annotated important data for your convenience).

On the list of METARS, note the present weather (in red), which was freezing rain during this period. But there were also reports of lightning all around the Springfield airport (in blue). So thunder-freezing rain was ongoing at surface air temperatures of minus 1.7 degrees Celsius = 29 degrees Fahrenheit.

The 12Z surface analysis on February 21, 2013. At the time, a developing surface low-pressure system over the Texas Panhandle drew relatively warm, moist air from the Gulf of Mexico over a layer of cold air north of the low's warm front. Courtesy of HPC.

Many people naturally associate thunder and lightning with the warm season, so freezing rain, sleet, or snow reaching the ground during a thunderstorm in winter seems like an enigma, leading, not surprisingly, to lots of inquiries.

Let's face it, thunder-snow draws the most attention. Check out (below; larger image) the METARS from 12Z to 14Z at Topeka, Kansas, on February 21. I annotated the observation with heavy thunder-snow.

The METARs at Topeka, KS, from 12Z to 14Z on February 21, 2013. Larger image. Courtesy of UCAR.

I'm not shy, so I jumped at the opportunity to discuss weather on National Public Radio (here it is). When I was teaching at Penn State, I conducted many similar interviews with the media, so I knew going into the interview that I had to be succinct and not too "professorial" in order to convey something meaningful and understandable to the listening public. My goals in this blog will be a loftier and more comprehensive explanation as I cover the topic of elevated thunderstorms that produce wintry precipitation (sleet, freezing rain, or snow).

While talking to NPR, I didn't get too deep into the science, but I also didn't take any dramatic shortcuts in science like the national news did Thursday evening. One anchor succinctly pontificated that thunder-snow is caused by "the clash of warm and cold air" and that thunder-snow is "rare." In my opinion, the "clash" between air masses is a catch-all, generic argument frequently used by the media as a watered-down explanation for all kinds of weather, but I'll bet it really leaves some viewers wanting more.

The anchor followed up his "clash metaphor" by describing thunder-snow as "rare." Using "rare" in the same context as the "clash of warm and cold air" seems contradictory to me because the juxtaposition of warm and cold air masses is the hallmark of winter. I mean, it happens all the time during the cold season. So, using the news anchor's "logic," if cold and warm air clash frequently, shouldn't thunder-snow be just as frequent?

Again, I didn't jump right into an in-depth scientific discussion during my NPR interview. I began by stating that, in my view, thunder-snow is not really a rare event. I admit that I was being a bit coy by taking such an opposing view, but there's always a method to my madness.

The 14Z mosaic of composite reflectivity on February 21, 2013. Larger image. Courtesy of Penn State.

Here's the scoop. Almost all of the precipitation that falls over the middle latitudes (roughly 30 degrees to 60 degrees latitude) begins as snow at cold, high altitudes. Thus, on a hot, humid July day after surface temperatures surge into the 90s (Fahrenheit), for example, and thunderstorms subsequently erupt, there's thunder-snow four miles up in the atmosphere. From this standpoint, thunder-snow is not rare at all. Of course, I realize that the context of thunder-snow as a "rare" event was meant to apply to winter. Even so, strong low-pressure systems that emerge from the southern Rockies and establish a surface low over the southern Plains (like the one over Texas early Thursday), draw relatively warm, moist air from the Gulf of Mexico over a layer of cold air north of the low's warm front (revisit the 12Z surface analysis on February 21). This lifting of air can result in wintry precipitation from elevated thunderstorms, assuming the middle part of the troposphere is sufficiently unstable. For confirmation, check out the lightning display at 14Z on February 21 and the 14Z mosaic of composite reflectivity (see above; larger image).

On NPR, I stated, as succinctly as I could, that the thunder-snow four miles overhead during summer is often observed at the ground as rain with lightning and thunder (snowflakes melt into raindrops at, say, 10,000 feet above the ground). During winter, snow sometimes reaches down to the earth's surface where observers also see flashes of lightning and then hear thunder. Of course, it's not quite as simple as snow not melting into raindrops during winter, so I saved the real science for this blog.

The low I pointed out on the 12Z surface analysis over Texas produced warm advection north of the low's warm front. The 14Z Rapid-Refresh model analysis of 850-mb heights (dark contours), 850-mb isotherms (dashed red contours), and 850-mb temperature advection (color filled in degrees Celsius per hour) shows warm advection (red and pink color filled areas) surging northward into western Missouri. You can see the impact of the warm advection over the layer of cold air next to the ground on the 14Z Rapid-Refresh model skew-T at Springfield (below; larger image).

The 14Z Rapid-Refresh skew-T at Springfield, Missouri, on February 21, 2013. The line designating 0 degrees Celsius is highlighted in yellow. Courtesy of Penn State.

The lower troposphere was very stable...note the strong temperature inversion from roughly 925 mb to 800 mb on the Rapid-Refresh skew-T above. In effect, the relatively warm, moist air feeding the updrafts of thunderstorms began at 800 mb, not the ground, qualifying any developing thunderstorms as elevated convection (as opposed to surface-based convection).

The convective available potential energy (CAPE), which is a measure of the potential strengths of updrafts, is surface-based, and really should not be applied to elevated thunderstorms (in most cases of elevated convection during winter, surface-based CAPE is zero; it might fool you into believing that winter thunderstorms aren't possible). But, of course, they are. Instead of CAPE, weather forecasters use MUCAPE in situations where elevated thunderstorms are slated to occur. MUCAPE stands for Most Unstable CAPE, which essentially identifies the most unstable parcel of air near the top of the low-level stable layer. In other words, MUCAPE refers to the air parcel aloft that feeds into the updraft of an elevated thunderstorms and whose upward acceleration in the updraft is greatest. Keep in mind that the upward acceleration of an air parcel is governed by the difference between the parcel's temperature and the temperature of its environment. In a nutshell, the warmer the air parcel is compared to its environment, the greater its upward acceleration (the good old hot-air balloon analogy).

Here's the 14Z Rapid-Refresh model analysis of MUCAPE (the thick and thin red contours, expressed in Joules per kilogram) and the altitude of the most unstable air parcel (color-filled, dashed black contours, in meters). In southwest Missouri (near Springfield, for example), the altitude of the most unstable air parcel was a bit lower than 3000 meters (a bit greater than 700 mb). I realize this is a very rough estimate, but, for ease of presentation, let's assume the most unstable parcel lay near 740 mb. With this very rough estimate in mind, I went back to the 14Z Rapid-Refresh skew-T and I marked the path of the most unstable air parcel rising along the local moist adiabat from roughly 740 mb (see annotated skew-T below). The saturated parcel, whose path is indicated by the blue curve, lies to the right of the environmental temperature sounding (in red). In other words, the parcel was warmer than its environment and, thus, positively buoyant, rising to relatively high altitudes and setting the stage for deep convective clouds.

The MUCAPE (most unstable convective available potential energy) associated with this parcel was simply the area bounded by the blue curve and the red curve (according to the 14Z Rapid-refresh analysis, about 250 Joules per kilogram). That's relatively low by most CAPE standards, but sufficiently strong for updrafts to create pockets of positive and negative electrical charges in the convective cloud and to pave the way for lightning. In order to achieve an adequate separation of electrical charge for lightning to occur, the convective cloud must have an updraft that extends to altitudes where temperatures are well below minus 20 degrees Celsius. Moreover, the convective cloud must have a base warm enough for liquid drops (supercooled or otherwise) to exist.

The 14Z Rapid Refresh skew-T at Springfield, Missouri, on February 21, 2013. Courtesy of Penn State.

Farther to the northwest, Topeka, Kansas, was deeper in cold air, and, even though there was weak warm advection at 850 mb, temperatures in the lower troposphere stayed below 0 degrees Celsius, the melting point of ice, so, unlike Springfield, Missouri, there wasn't any melting layer and snowflakes made it to the ground while lightning flashed and thunder rumbled across the landscape. In case you're interested, here's the 13Z Rapid-Refresh skew-T at Topeka, KS on February 21 (around the time when heavy thunder-snow was reported).

I'm sure you're getting the picture for why I didn't go into as much scientific detail during my NPR interview. Hopefully, you've learned the meteorology of thunder-snow during winter. Thunderstorms are elevated, and temperatures throughout the troposphere are lower than the melting point of ice.

Lee

P.S. I will continue to call 0 degrees Celsius = 32 degrees Fahrenheit the melting point of ice and not "freezing" or the "freezing mark." I know I'm fighting a losing battle, but at least I'll go down fighting. :-)

The Cranky Old Man :-)

Categories: Synoptic and Mesoscale Meteorology Thermodynamics

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1. Astrometeor 2:52 AM GMT on February 26, 2013
I have personally never witnessed thunder snow, but my best memory of it from the TV is Jim Cantore reporting from Chicago I believe, and thunder clapping behind him. His reaction was classic. Thanks for the blog Lee, I really enjoyed it. P.S. It is the freezing point Lee (yes you are losing, lol) Member Since: July 2, 2012 Posts: 42 Comments: 1760

2. Lee Grenci, Retired Senior Lecturer and Forecaster 11:55 AM GMT on February 26, 2013
Quoting Astrometeor: I have personally never witnessed thunder snow, but my best memory of it from the TV is Jim Cantore reporting from Chicago I believe, and thunder clapping behind him. His reaction was classic. Thanks for the blog Lee, I really enjoyed it. P.S. It is the freezing point Lee (yes you are losing, lol) I'm glad you enjoyed it. Thanks! Yes, I'm losing the battle, I admit (story of my life :-), but 32 degrees Fahrenheit is not the freezing point of water, as my water-drop experiment proves (see photograph below). I greased the bottom of am empty tuna can, put several small drops of tap water on the can, put it in my freezer at 14 degrees Fahrenheit for about 20-30 minutes. Several drops refused to freeze (lack of freezing nuclei). Larger image. Hopefully this convinces you, but, if you're still wavering, here's the AMS (American Meteorological Society) glossary definition of freezing point...please pay close attention to the last two sentences. Only pure water freezes at 32 degrees, and, in nature, pure water really doesn't exist. Even my reverse-osmosis water we have in our kitchen contains some impurities, not many, I admit, but it's not pure either. I hope this helps, but I admit I'm losing the battle...it's so ingrained in our culture that even some folks here call 32 degrees Fahrenheit freezing. If 32 degrees Fahrenheit really was the freezing point, how can we explain the fact that tiny water drops in clouds can resist freezing down to temperatures as low as minus 40 degrees Fahrenheit? Please forgive my passion. It's been a long-time pet peeve of mine. I guess I'm just an old, complicated Italian guy. :-) Thanks again for reading and commenting. Much appreciated. Member Since: October 24, 2012 Posts: 53 Comments: 445

3. Lee Grenci, Retired Senior Lecturer and Forecaster 12:15 PM GMT on February 26, 2013
Quoting Astrometeor: I have personally never witnessed thunder snow, but my best memory of it from the TV is Jim Cantore reporting from Chicago I believe, and thunder clapping behind him. His reaction was classic. Thanks for the blog Lee, I really enjoyed it. P.S. It is the freezing point Lee (yes you are losing, lol) P.S. I forgot to tell you that I got into a lot of thunder-snow in the early 1980s when I would chase lake-effect snow bands in late fall / early winter downwind of Lake Ontario. Very surreal stuff. Member Since: October 24, 2012 Posts: 53 Comments: 445

4. georgevandenberghe 2:07 PM GMT on February 26, 2013
Quoting 24hourprof: I'm glad you enjoyed it. Thanks! Yes, I'm losing the battle, I admit (story of my life :-), but 32 degrees Fahrenheit is not the freezing point of water, as my water-drop experiment proves (see photograph below). I greased the bottom of am empty tuna can, put several small drops of tap water on the can, put it in my freezer at 14 degrees Fahrenheit for about 20-30 minutes. Several drops refused to freeze (lack of freezing nuclei). Larger image. Hopefully this convinces you, but, if you're still wavering, here's the AMS (American Meteorological Society) glossary definition of freezing point...please pay close attention to the last two sentences. Only pure water freezes at 32 degrees, and, in nature, pure water really doesn't exist. Even my reverse-osmosis water we have in our kitchen contains some impurities, not many, I admit, but it's not pure either. I hope this helps, but I admit I'm losing the battle...it's so ingrained in our culture that even some folks here call 32 degrees Fahrenheit freezing. If 32 degrees Fahrenheit really was the freezing point, how can we explain the fact that tiny water drops in clouds can resist freezing down to temperatures as low as minus 40 degrees Fahrenheit? Please forgive my passion. It's been a long-time pet peeve of mine. I guess I'm just an old, complicated Italian guy. :-) Thanks again for reading and commenting. Much appreciated. It is true that only pure water (with a freezing nucleus present ) freezes at 32F. However the melting point depression from dissolved materials in most bodies of water found in nature is small. For example sea water melts at about 28F and that's very salty (yes only about 15% saturated but still very salty) The rule of thumb that below 32F one starts seeing outdoor ice does work. Most tissues of really tender plants freeze at between 30F and 31F. I think you are right, most people underestimate how much even tender plants sometimes supercool and escape freezing on calm clear nights when the period below 31F is short. Some species that are hardy utilize supercooling to avoid freezing to as much as -20C. (Most species hardy at colder temperatures tolerate freezing in their tissues) The larger term in freezing point depression is supercooling as demonstrated with your droplets. That can lead to large depressions especially in clean water. If you take the bottled water sold in plastic bottles in stores and cool it to -5C to -7C or so it will likely stay liquid for awhile. If you shock it or drop the bottle some of the contents will freeze immediately. That makes a neat elementary school demonstration of supercooling. As another tangential research project in horticulture, I think supercooling of tender species (and ways to enhance and exploit it) warrants further investigation. One species this could really be helpful with is irish potatoes which are frost tender but grow best in really cool weather. But I'll start reinforcing the crusade to replace "freezing point" with "melting point" in discussions of ice and water. Determining when to forecast snow and when to forecast freezing drizzle with shallow moist layers, is a tough forecast problem. Member Since: February 1, 2012 Posts: 3 Comments: 297

5. Lee Grenci, Retired Senior Lecturer and Forecaster 2:24 PM GMT on February 26, 2013
Quoting georgevandenberghe: It is true that only pure water (with a freezing nucleus present ) freezes at 32F. However the melting point depression from dissolved materials in most bodies of water found in nature is small. For example sea water melts at about 28F and that's very salty (yes only about 15% saturated but still very salty) The rule of thumb that below 32F one starts seeing outdoor ice does work. Most tissues of really tender plants freeze at between 30F and 31F. I think you are right, most people underestimate how much even tender plants sometimes supercool and escape freezing on calm clear nights when the period below 31F is short. Some species that are hardy utilize supercooling to avoid freezing to as much as -20C. (Most species hardy at colder temperatures tolerate freezing in their tissues) The larger term in freezing point depression is supercooling as demonstrated with your droplets. That can lead to large depressions especially in clean water. If you take the bottled water sold in plastic bottles in stores and cool it to -5C to -7C or so it will likely stay liquid for awhile. If you shock it or drop the bottle some of the contents will freeze immediately. That makes a neat elementary school demonstration of supercooling. As another tangential research project in horticulture, I think supercooling of tender species (and ways to enhance and exploit it) warrants further investigation. One species this could really be helpful with is irish potatoes which are frost tender but grow best in really cool weather. But I'll start reinforcing the crusade to replace "freezing point" with "melting point" in discussions of ice and water. Determining when to forecast snow and when to forecast freezing drizzle with shallow moist layers, is a tough forecast problem. Fantastic post, George!!!! And yes, I'm probably going overboard (you were polite, so this is my word). I just can't explain why it bothers me. Maybe, at 65, I'm just getting cranky in my old age. :-) I think my biggest objection hinges on subcooled cloud drops (I prefer "subcooled" to "supercooled") being able to resist freezing down to temperatures as low as minus 40 degrees Fahrenheit = minus 40 degrees Celsius. In this matter, I don't think I'm going overboard. I hope you agree. After all, precipitation over the middle latitudes depends on the growth of ice crystals via the depositing of dramatically subcooled cloud droplets onto the growing ice crystals. Thanks again, George. I always appreciate your input. Member Since: October 24, 2012 Posts: 53 Comments: 445

7. JNCali 5:42 PM GMT on February 26, 2013
Hello Lee.. another welcome dissertation, thank you! "..P.S. I will continue to call 0 degrees Celsius = 32 degrees Fahrenheit the melting point of ice and not "freezing" or the "freezing mark." I know I'm fighting a losing battle, but at least I'll go down fighting. :-).." You really are a 'cup is half full' kind of guy! and I guess if you have to choose your battles this is as good as any... I had the delightfully frightful experience of skiing during a thunder snow event in CA.. the snow was great but being on a steel chairlift with that huge steel cable being the most elevated structure on the mountain was a bit unnerving... and being 6500 feet up in the cloud the sound was quite loud.. though not near as loud as the summer thunderstorms I'd experience at 12K feet backpacking in the Sierra Nevada's. Those where indescribable, it was like bombs exploding while we cowered in our orange tube tents hoping the wind and hail wouldn't destroy that thin little sheet of plastic...Good times....good times.. Member Since: September 9, 2010 Posts: 5 Comments: 1032

8. Lee Grenci, Retired Senior Lecturer and Forecaster 5:54 PM GMT on February 26, 2013
Quoting bappit: Wikipedia is with you Lee, but common usage is not. The all-knowing wiki cites a 1949 article about determining freezing point, but makes the following statement. "The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends (usually slightly) on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point." Excellent! Many thanks for this great contribution. I need all the encouragement I can get! :-) Member Since: October 24, 2012 Posts: 53 Comments: 445

9. Lee Grenci, Retired Senior Lecturer and Forecaster 5:56 PM GMT on February 26, 2013
Quoting JNCali: Hello Lee.. another welcome dissertation, thank you! "..P.S. I will continue to call 0 degrees Celsius = 32 degrees Fahrenheit the melting point of ice and not "freezing" or the "freezing mark." I know I'm fighting a losing battle, but at least I'll go down fighting. :-).." You really are a 'cup is half full' kind of guy! and I guess if you have to choose your battles this is as good as any... I had the delightfully frightful experience of skiing during a thunder snow event in CA.. the snow was great but being on a steel chairlift with that huge steel cable being the most elevated structure on the mountain was a bit unnerving... and being 6500 feet up in the cloud the sound was quite loud.. though not near as loud as the summer thunderstorms I'd experience at 12K feet backpacking in the Sierra Nevada's. Those where indescribable, it was like bombs exploding while we cowered in our orange tube tents hoping the wind and hail wouldn't destroy that thin little sheet of plastic...Good times....good times.. Oh, great story. I can't imagine what it was like. Thanks so much for sharing. Best, Lee Member Since: October 24, 2012 Posts: 53 Comments: 445

10. cicadaknot 6:09 PM GMT on February 26, 2013
Lee your timing is perfect. Just yesterday I was caught up in a discussion about the possibility of thundersnow with this current system moving through the midwest. Nearly all of the skew t's i came across looked identical to those in your post. From what I gather, a prerequisite is certainly strong WAA as this leads to a larger positive energy area above the warm layer. Member Since: July 17, 2004 Posts: 0 Comments: 66

11. Lee Grenci, Retired Senior Lecturer and Forecaster 7:03 PM GMT on February 26, 2013
Quoting cicadaknot: Lee your timing is perfect. Just yesterday I was caught up in a discussion about the possibility of thundersnow with this current system moving through the midwest. Nearly all of the skew t's i came across looked identical to those in your post. From what I gather, a prerequisite is certainly strong WAA as this leads to a larger positive energy area above the warm layer. Exactly correct!!!! Great meteorology! And thanks! Lee Member Since: October 24, 2012 Posts: 53 Comments: 445

12. Bogon 10:58 PM GMT on February 26, 2013
@JNCali (#7) You should be safe sitting on a chair lift, unless lightning strikes very close to where you are sitting. You are at risk when you climb on the chair and when you step off. At those moments your body might complete a circuit between the cable and the ground. Member Since: June 26, 2008 Posts: 73 Comments: 2790

13. TropicalAnalystwx13 3:08 AM GMT on February 27, 2013
Lee, check out the reflectivity values on these bands in upstate New York. Above 60 dBZ: Though to be fair, I think it's mixing with some rain and not all frozen. Member Since: July 6, 2010 Posts: 92 Comments: 25963

14. Astrometeor 3:16 AM GMT on February 27, 2013
Wow, after that "short" explanation of why 32 isn't the freezing point Lee, you might have just switched me over to your side. Member Since: July 2, 2012 Posts: 42 Comments: 1760

15. Lee Grenci, Retired Senior Lecturer and Forecaster 11:50 AM GMT on February 27, 2013
Quoting TropicalAnalystwx13: Lee, check out the reflectivity values on these bands in upstate New York. Above 60 dBZ: Though to be fair, I think it's mixing with some rain and not all frozen. Good contribution. Thanks. Man, there's a lot of that going around on radar these days. Check out the radar from State College yesterday afternoon. Very similar to yours. Large, wet snowflakes (partially melted) or wet sleet. Many thanks for joining the discussion. Lee Member Since: October 24, 2012 Posts: 53 Comments: 445

16. Lee Grenci, Retired Senior Lecturer and Forecaster 11:54 AM GMT on February 27, 2013
Quoting Astrometeor: Wow, after that "short" explanation of why 32 isn't the freezing point Lee, you might have just switched me over to your side. Hurray!!!!!!! You made my day. Yesterday was a bad one...we got a new roof, and, unbeknownst to me, it leaked. Brand new roof. Lots of damage and mold. I'm just sick about it. Member Since: October 24, 2012 Posts: 53 Comments: 445

17. georgevandenberghe 2:50 PM GMT on February 27, 2013
I posted it somewhere on WU but forgot so I'll repeat it. I've experienced thundersnow several times and expect it in very intense snow storms. Two events though stand out. The first (and the first time I saw thundersnow) was in February 1973. We were in the upper 40s and a moderate cold front came through. Flurries were expected and forecast but we got strong snow squalls with lightning (at least one REALLY close flash) along the front. We got a half inch coating in about 15 minutes. DCA missed these so the winter of 1972-73 verified with 1/10 inch of snow total for the year, the only year to that time with less than 2" winter total. ^^. THis was notable because it was not like the other thundersnows I've seen. It was with a line of convection along a (actually not real strong) front. The second time was more dramatic. During the Feb 11, 1983 snowstorm in Princeton NJ I experienced about a half hour period of frequent close cloud to ground lightning more intense than in most summer thunderstorms. I was going to try out the cross country skis I'd just rented but was afraid to go out with that much lightning. The thunder was very loud and within a second of the flashes so the lightning was very close. During this period snow was accumulating around 2-3" per hour. The other oddity with this storm is that even with a subfreezing sounding all the way up I observed a few ice pellets and this was confirmed by colleagues elsewhere. Storm total was 20" with this storm. ^^Since then we've had another, the winter of 1997-98. My twins were born that winter and I'm grateful for not having to deal with either snow or arctic outbreaks that winter when I was just crushed by having three kids under two at home.) Concerning roofs, I also just repaired a leak. 90% of my roof is easily visible from the attic and thus checkable. 10% is hidden by a modular attic bedroom I had built three years ago and insulated between roof and ceiling. Guess where the leak happened! Member Since: February 1, 2012 Posts: 3 Comments: 297

18. Lee Grenci, Retired Senior Lecturer and Forecaster 4:14 PM GMT on February 27, 2013
Quoting georgevandenberghe: I posted it somewhere on WU but forgot so I'll repeat it. I've experienced thundersnow several times and expect it in very intense snow storms. Two events though stand out. The first (and the first time I saw thundersnow) was in February 1973. We were in the upper 40s and a moderate cold front came through. Flurries were expected and forecast but we got strong snow squalls with lightning (at least one REALLY close flash) along the front. We got a half inch coating in about 15 minutes. DCA missed these so the winter of 1972-73 verified with 1/10 inch of snow total for the year, the only year to that time with less than 2" winter total. ^^. THis was notable because it was not like the other thundersnows I've seen. It was with a line of convection along a (actually not real strong) front. The second time was more dramatic. During the Feb 11, 1983 snowstorm in Princeton NJ I experienced about a half hour period of frequent close cloud to ground lightning more intense than in most summer thunderstorms. I was going to try out the cross country skis I'd just rented but was afraid to go out with that much lightning. The thunder was very loud and within a second of the flashes so the lightning was very close. During this period snow was accumulating around 2-3" per hour. The other oddity with this storm is that even with a subfreezing sounding all the way up I observed a few ice pellets and this was confirmed by colleagues elsewhere. Storm total was 20" with this storm. ^^Since then we've had another, the winter of 1997-98. My twins were born that winter and I'm grateful for not having to deal with either snow or arctic outbreaks that winter when I was just crushed by having three kids under two at home.) Concerning roofs, I also just repaired a leak. 90% of my roof is easily visible from the attic and thus checkable. 10% is hidden by a modular attic bedroom I had built three years ago and insulated between roof and ceiling. Guess where the leak happened! Roof leaks are a bummer. I haven't slept much lately. Member Since: October 24, 2012 Posts: 53 Comments: 445

19. DocNDswamp 6:37 PM GMT on February 27, 2013
Quoting 24hourprof: Roof leaks are a bummer. I haven't slept much lately. Ditto and condolences to you Lee, especially frustrating after new roof install. H Gustav shredded mine, but chose to weave in new shingles where damaged worst, repair rest w roof caulk... been repeatedly repairing new leaks that pop up since (combination rusting nail heads driven within cracks between old 3/4" / 1X6 center-match - another awaits my attention now!). I'm in constant fear / anxiety of every hvy tstm coming... Er, rather frequent in SE Louisiana - I've tallied 100" rain past 14 months, many were 4-6" downpours. (Reference Louisiana on AHPS Precipitation Analysis page). Best wishes on the fix. (And thanks for the thundersnow analysis! - Sorry I responded off-topic, but feel your pain). Member Since: September 21, 2005 Posts: 92 Comments: 4650

20. Lee Grenci, Retired Senior Lecturer and Forecaster 7:25 PM GMT on February 27, 2013
Quoting DocNDswamp: Ditto and condolences to you Lee, especially frustrating after new roof install. H Gustav shredded mine, but chose to weave in new shingles where damaged worst, repair rest w roof caulk... been repeatedly repairing new leaks that pop up since (combination rusting nail heads driven within cracks between old 3/4" / 1X6 center-match - another awaits my attention now!). I'm in constant fear / anxiety of every hvy tstm coming... Er, rather frequent in SE Louisiana - I've tallied 100" rain past 14 months, many were 4-6" downpours. (Reference Louisiana on AHPS Precipitation Analysis page). Best wishes on the fix. (And thanks for the thundersnow analysis! - Sorry I responded off-topic, but feel your pain). Thanks for your condolences. It's a huge mess up there, and I get upset when I think about having to pay off the loan for a new roof that leaks. Story of my life, I'm afraid. Member Since: October 24, 2012 Posts: 53 Comments: 445

21. Lee Grenci, Retired Senior Lecturer and Forecaster 7:52 PM GMT on February 27, 2013
Quoting bappit: Wikipedia is with you Lee, but common usage is not. The all-knowing wiki cites a 1949 article about determining freezing point, but makes the following statement. "The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends (usually slightly) on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point." P.S. Stay tuned for blogs about my other pet peeves: 1) Warm (cold) air holds more (less) water vapor. This is one of the media's favorite go-to explanations, but it's really not scientifically sound (and I'm even being polite). I think it's on par, maybe even worse than, "the sky is blue because air molecules scatter blue light," which, as one of my early blogs pointed out, is just plain nonsense. Warm (cold) air holding more (less) water vapor is just as bad, but you see it everywhere. I don't know why it's caught on so much. 2) Rising air causes low pressure. I hear it or read it much too frequently, and it's probably the most ill-informed statement a weather forecaster could possibly make (someone who should know better). I have other pet peeves, of course. Slowly but surely, I'll address them all in WU blogs. Sort of a cleansing of my soul. :-) But a meteorologist calling 32 degrees Fahrenheit the "freezing point" or "freezing" when he or she also acknowledges that precipitation over the middle latitudes starts out as snow at high altitudes, where snow crystals grow at the expense of surrounding tiny water droplets that can exist in liquid form down to temperatures as low as minus 40 degrees Fahrenheit, is, in my view, the ultimate paradox. So please stay tuned for more Lee pet peeves, and many thanks for that wiki reference. Member Since: October 24, 2012 Posts: 53 Comments: 445

22. georgevandenberghe 10:57 PM GMT on February 27, 2013
I have a bunch of pet peeves too. I think the phrase "all time record" is way overused. It only applies to the last hundred or few hundred years of record, not the previous few million years where the continents had their present shapes. Further back than that I think you could say the location had been uuhhh... moved. Most weather bugs, especially younger ones use the word "unprecedented" too much. This is insidious because it also implies that rare events will never happen again. The general public (not meteorologists) often refer to the combination of temperature and relative humidity both in the 90s. This never happens in the U.S or most of the rest of the world except for a very short time in urban areas immediately after a light rain shower. Exaggerations like "it didn't go below 90F all month" persist and propagate but have never actually occurred in North or south America. (I don't think it's happened anywhere actually) Member Since: February 1, 2012 Posts: 3 Comments: 297

23. Lee Grenci, Retired Senior Lecturer and Forecaster 12:13 AM GMT on February 28, 2013
Quoting georgevandenberghe: I have a bunch of pet peeves too. I think the phrase "all time record" is way overused. It only applies to the last hundred or few hundred years of record, not the previous few million years where the continents had their present shapes. Further back than that I think you could say the location had been uuhhh... moved. Most weather bugs, especially younger ones use the word "unprecedented" too much. This is insidious because it also implies that rare events will never happen again. The general public (not meteorologists) often refer to the combination of temperature and relative humidity both in the 90s. This never happens in the U.S or most of the rest of the world except for a very short time in urban areas immediately after a light rain shower. Exaggerations like "it didn't go below 90F all month" persist and propagate but have never actually occurred in North or south America. (I don't think it's happened anywhere actually) George, You can tell we're old timers. LOL!!! Heck, I'm still bothered by the NWS removing the temperature requirement from the definition of a blizzard years and years ago. I just get the feeling, fairly or unfairly, that the weather is hyped more these days. I think it's also a function of my age. I admit that I've become more of a stickler in my 60s. Still, I have high hopes for the younger generation, even though they sometimes do things I'll never understand (like texting and driving...I worry a lot when I'm cycling). Member Since: October 24, 2012 Posts: 53 Comments: 445

24. vis0 2:31 AM GMT on February 28, 2013
Excellent writing Mr. Grenci where instead of filtering out people, you filter more in (seems oxymoron-ic) BUT, by first getting the attention of the layman. Then as you explain "weather" it allows the least whom know to join those to whom deep "weather/science" knowledge is their profession, its as if flattening a pyramid upward. i.e. pyramids base, the most people whom knows less of science(s) and at the top those few whom know/luv to learn of weather/science(s) and in your style (Dr Masters too) you elevate those at the bottom slowly upwards so in the end all are at the higher thinking level. Luv the 14Z Rapid-Refresh model skew-T(img). Going to use it to explain in picture form (at private site were i explain to other countries) how the ml-d (a device i state influences nature its "ml-d diary" is on my "vis0" wunderground blog) One of its features is how it continuously raises cooler air upward, thus creating a stacking of cooler air higher than just nature usually creates. This upward stacking of ever so slightly cooler air leads to its ability to influence weather,peace Member Since: December 15, 2006 Posts: 150 Comments: 107

25. vis0 2:41 AM GMT on February 28, 2013
BTW i in college called 0 Celsius the "goulash point", everything is going on at that point. (read the blog as to this comment) Member Since: December 15, 2006 Posts: 150 Comments: 107

26. Astrometeor 2:56 AM GMT on February 28, 2013
I remember from 2010, when my town Nashville had its flood of May 1-2, we received 14 inches of rain and a few tornadoes. The media all around town called it unprecedented. 1 in 5000 years. However, when a reporter actually went and looked the data up, it turns out this flood happens every 1 in 40, the dams though are supposed to keep the water back. Just this time, the Core failed on their part. Even more interesting was the fact that out of the floods recorded in Nashville's 230-year existence, this flood ranked #3. Now 40 years will pass, or maybe it will hit us just around the corner, but it will catch everyone by surprise. Quoting georgevandenberghe: Most weather bugs, especially younger ones use the word "unprecedented" too much. This is insidious because it also implies that rare events will never happen again. Member Since: July 2, 2012 Posts: 42 Comments: 1760

27. Lee Grenci, Retired Senior Lecturer and Forecaster 11:44 AM GMT on February 28, 2013
Quoting vis0: Excellent writing Mr. Grenci where instead of filtering out people, you filter more in (seems oxymoron-ic) BUT, by first getting the attention of the layman. Then as you explain "weather" it allows the least whom know to join those to whom deep "weather/science" knowledge is their profession, its as if flattening a pyramid upward. i.e. pyramids base, the most people whom knows less of science(s) and at the top those few whom know/luv to learn of weather/science(s) and in your style (Dr Masters too) you elevate those at the bottom slowly upwards so in the end all are at the higher thinking level. Luv the 14Z Rapid-Refresh model skew-T(img). Going to use it to explain in picture form (at private site were i explain to other countries) how the ml-d (a device i state influences nature its "ml-d diary" is on my "vis0" wunderground blog) One of its features is how it continuously raises cooler air upward, thus creating a stacking of cooler air higher than just nature usually creates. This upward stacking of ever so slightly cooler air leads to its ability to influence weather,peace Many thanks for your kind words. Member Since: October 24, 2012 Posts: 53 Comments: 445

28. Lee Grenci, Retired Senior Lecturer and Forecaster 12:01 PM GMT on February 28, 2013
Quoting Astrometeor: I remember from 2010, when my town Nashville had its flood of May 1-2, we received 14 inches of rain and a few tornadoes. The media all around town called it unprecedented. 1 in 5000 years. However, when a reporter actually went and looked the data up, it turns out this flood happens every 1 in 40, the dams though are supposed to keep the water back. Just this time, the Core failed on their part. Even more interesting was the fact that out of the floods recorded in Nashville's 230-year existence, this flood ranked #3. Now 40 years will pass, or maybe it will hit us just around the corner, but it will catch everyone by surprise. I remember that terrible flood. Member Since: October 24, 2012 Posts: 53 Comments: 445

29. WunderAlertBot (Admin) 4:54 PM GMT on March 02, 2013
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Retired senior lecturer in the Department of Meteorology at Penn State, where he was lead faculty for PSU's online certificate in forecasting.

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