Lecture 23Outline of Last Lecture I. Weather of the dayII. A little more about Tornadosa. Enhanced F Scale for Tornado Damageb. Tornado FrequencyIII. Hail and LighteningIV. Origins of hailV. Ways that ice interacts with supercooled liquid waterVI. Haila. How big?VII. Supercell structureVIII. Hail SwathsOutline of Current Lecture II. Weather of the dayIII. Hail, some radar informationIV. Where does hail occur?V. LightningVI. Where lightning occursa. United StatesVII. More Lightning Current LectureRemindersHomework due todayTest 2 is next FridayWeather of the dayWe can see isotherms and isobars. We can see that there is strong high pressure dropping to the south through North Dakota, Nebraska, and so on. Right now the frontal zone, at midnight last night, is moving across us. It brought us snow last night. It was always a possibility that we saw from last week, but we didn’t predict it to be last night. Atm Ocn 100 1nd Edition1000-500 mb thickness is a good map of telling the temperature. The cold tongue pushing south is an indication of cold air from the artic going south. We can look at thickness to find the rain snow line. When the cold air moves over the warm lake instabilities develop and there can be showers from this. Lake effects don’t always bring snow, but we may see it in the next day or two. This will be one of the first blasts into the Gulf of Mexico. Very typical weather, we usually see this cold right around Halloween. By Sunday may be a little warmer. There will be some warmer air towards us. We can see the magenta coloring right on top of us, but we are recovering quickly. It will get warm again at 850mb by Monday night. This morning there were stratocumulus clouds. Now a lot of clouds are forming outside. The warm ground will keep the air warmer then it would normally be with the same temperatures in the winter. This will produce an instability that causes overturn. We may have snow later today from this instability. At night ground cools so instability stops. So there shouldn’t be snow later tonight. But there is potential for getting super cold tonight maybe even into the 20’s. Back to lectureHail, some radar informationHow we observe hail with radar…Radar measures reflectivity, measures power returned…Radar receives and transmits information. It listens and receives the echo from a pulse that it emitted. It is a continuous pulsing and a very high frequency and then there is a return.From a frequency shift you can see Doppler. The radar beam reflection is due to scattering of targets and some of it reflects back which is detected. The sizeof the particle matters for a radar. If you use longer wavelength radar a different reflectivity comes back than short wave radar. There is a strong dependence between wavelength and droplet size. Droplet size is not uniform, could be bigger on horizontal axis compared to vertical axis. On the polarized beam out we focus on detecting the horizontal axis that affects reflectivity.Hail particles tend to be more spherical than rain droplets. The larger ones are oblique. The larger the rain droplet gets the more oval shape it becomes orientated with the big axis horizontal. The smaller the rain droplet the more spherical it would be. If you compare horizontal to the vertical you can get a measure of how big the rain droplets are. And then that can tell you as well how fast they are falling. The weather service converted to the polarized radar only a few years ago. This is about 20 years old. Doppler radar is nearly 40 years old. We are looking at 3 pictures of the same cloud derived from polarized radar.The top one is reflectivity factor. It is a cloud with hail in it, large reflectivity means large hail.If ice is undergoing wet growth, which is collecting water, super cool liquid water, as it falls, it is collected on falling ice particle and doesn’t freeze. If it freezes immediately than that is dry growth because the particle never gets wet. If there is a ton of liquid water, heat cannot be transferred fast enough, so the particle will warm to 0 degrees Celsius where rain cannot freeze. Then the particle will keep warming and then stay there. Even if the temperature of the air is -20. A reflectivity factor of 60 or 70 shows hail, which is pictured in the first cloud on this picture. We can see the differential reflectivity between horizontal and vertical polarized beams.At the bottom part of the cloud we see the greatest difference in differential reflectivity because rain is happening down there. The 3rd picture is labeling the different things in the cloud like hail. The orange is light rain. We see big differential reflectivity and it shows the type of precipitation that is occurring. New radar science, differential reflectivity, it is a new thing for weather service offices. Now forecasts of hail or precipitation will improve a lot from these radars because they can detect the sizes. Where does hail occur?3 inch hail or bigger is considered a severe storm Hail occurs really between Texas and Oklahoma.Supercells are big hail producers. This is why you get supercells too.When you get large storms, large supercells, it occurs a lot in Northern Texas. This is very similar to tornado bowl.LightningLightning is the number one killer compared to any other weather. But it is not considered severe for a storm to have lightning.Where lightning occursFrequency being the reds or up to the blacks are the most frequent. Lightning is only over land. Why?What is going on here is the thunderstorms over land are stronger than over water. They are stronger thunderstorms and they have more ice. What is different over land? Land is much warmer than the ocean. Land creates heat masses that can contain contribute a lot to a thunderstorm. During the warmest part of the day the land is warmer than the ocean ever gets. The land produces the warmest and coldest temperatures. The largest features will appear over land where the air gets the most warm.When you go over ocean in the afternoon it is not warmer than it is at night.And we see them concentrated in the areas where the inner tropical convergence zone is. In Florida, sea breeze fronts.Over water we get weaker thunderstorms that really have to work hard to get up the equilibrium. Over land updrafts stronger and more violent thunderstorms.United StatesLightning is concentrated over Florida. This is a result of the sea breeze front over Florida. Everyday there is a line of