So the fall severe weather season for the United States is about to begin. With hurricane season being a dud for me (which is a good thing) I am really looking forward to the brief few weeks in which I will get to have a few quality chases before the jet stream dives to its winter resting spot to the south with the birds. As the jet makes its transit to the south from hanging out in Canada (with @Melding
I presume) for the summer it becomes highly amplified with big kinks and waves in it. It is during this change of seasons that we get the bulk of our severe weather in the continental US. The most active of these two times of course being the mid spring to early summer but every year for a few weeks in the late fall we get a second tornado season.
In honor of this time of year I have decided to create a thread to post some forecasts of mine in advance of each system I may chase and also wanted to start up a conversation on here about meteorology and the weather currently effecting each of you on her (whether or not it is severe or boring).
How many of you were effected by the nor'easter that gave New England, "snowtober?" Anyone on here about to be effected with the first round of severe weather the plains is about to have?
...or maybe you have a story from your past of a close encounter you had with some form of extreme weather like a hurricane or a tornado?
Well here goes my first forecast for a system I may chase this coming Monday.
Day 5 (11/7/11) outlook.
The fall severe weather season for the central plains is due to kick off early next week with a high amplitude trough digging into the Texas panhandle and then moving across Oklahoma. As of now it looks like there is a slight chance that we can get some diurnal supercells in an area that stretches from Wichita, KS down to Abilene, TX and covers most of Oklahoma (excluding the panhandle) on Monday. These storms will have the chance to produce some large hail and strong straight line winds. In addition to those threats there is the possibility that a few tornadoes may occur with isolated storms during the late evening and over night as the diurnal low level jet (LLJ) looks to kick up at a brisk 50knts.
Really I am not a big fan of chasing these kind of events as they typically are low CAPE (<-see bellow) and high shear events. Earlier in the day around 0z the surface winds will be a little too weak for my liking but any storm that forms along the warm front and will be able to ride along it during the day will have a chance at a photogenic tornado. The dryline is also not very sharp in Oklahoma but the moisture gradient is steep enough to initiate a storm along the dryline to the south of the Red River. If I were to chase this event based solely off what the GFS is showing I would likely chase the southern end of the event and hope for early storms to fire along the dryline and ride along the red river as the hodographs look great there. The CIN (capping inversion) also looks to be pretty strong for this even which is not good. The area that it is at its weakest is on the southern half down below the Red River. My last major concern with this system is the type of shear that will be in place. There will be plenty of speed shear (which helps a storm tilt) but the directional shear (helps a storm's updraft rotate) seems to be lacking until you are well away from the dryline. This means that storms may not be able to mature as they will get toppled over before moving far enough off the dryline to get into a better shear environment.
The good news is that the LCL heights (the level at which the base of a storm forms) is going to be pretty low which will allow the storms to become surface based. If a storm is elevated and is not surface based your chances of a tornado drop almost completely to nil but your chances for large hail can stay unaffected and in some cases even enhanced.
This is a very strange time of the year to chase and forecast. Unlike in late May (my busiest time of the year) you really don't need a lot of CAPE to get a good storm going. At the same time you also don't need your storms to be as tall and they won't be able to reach the massive heights that you see in the warmer months since the atmosphere is not as tall in the late fall and winter as it is in the late spring and summer.
Right now if I had to chose a target (and this is just glancing at the GFS for only one run (12z run on 11/3/11)) I would start my day out heading down I-44 from Tulsa, OK to Wichita Falls, TX.
Okay so for those of you that took the time to read that above, BRAVO! For those of you that read it and actually understood what I said you get double kudos.
Now for a little lesson in forecasting terminology. (not all references to directions, i.e. west, east, south, etc are for typical North American weather systems commonly found east of the Rockies.)CAPE = Convective Available Potential Energy.
It is measured in j/kg and is a measurement of the energy that a parcel of air has potentially available to it to rise in the atmosphere. There are two forms of energy in the universe, kinetic and potential. Kinetic is energy that being released where potential energy is the amount of stored energy that has yet to be released so CAPE is basically telling us the amount of energy that is presently bottled up in a parcel of air that has yet to ascend.CIN (or CINH) = Convective INhibition.
This is basically anti-CAPE. It is measured in -j/kg. It is a measurement of how strong the lid (also called the cap or capping inversion) is over an area. It is telling us the amount of energy in place to prevent a parcel of air from rising. Think of a pressure cooker as our atmosphere. Inside the cooker you have warm air (steam) that wants to rise rapidly and escape but it is blocked the lid that is in place on top of the cooker. The stronger the lid the greater the stored energy will be needed to break it. CIN is a measurement of how strong that lid is. In the case of that analogy I used the energy comes in the form of steam pressure.(NOTE: When forecasting for the CAPE and CIN it is important to note the depth of both features in the atmosphere. This is down with a skew-t plot. To explain how to use one of those could have its own thread and so I will simply give you this link: http://www.atmos.millersville.edu/~lead/SkewT_Home.html There are also different kinds of CAPE and CIN products but that is for mentioning another day.)Dryline = a boundary between a warm/hot and dry air mass and a warm/hot and moist airmass.
The sharper the gradient of the dryline the better. By this I mean the rate at which you go from saturated air to dry air. A good way to experience this is to be driving across the plains to the west. As you drive through the dryline you will see that suddenly most of your cumuloform clouds will dissapear and in the matter of a few miles the humidity will go from very high to non-existent. We can see the placement of the dryline by looking at the surface observations and reading what the dew point is in a give place. Bellow is an example.
In the image above the brown bumpy line is the dryline. Your numbers in the green are the dewpoint and your numbers in the red are your temps. Storms will form along this boundary, especially where ever it bulges to the east. It is harder for storms to form on a totally stationary dryline with out a section bulging east and is even harder for storms to fire on a retrograding dryline that is retreating to the west. If the dryline moves too fast to the east it can over take storms and rob them of their needed moisture. The forcing of warm moist air up over the advancing dry air is one of the primary forms of forcing that helps a parcel of air over come the lid/cap/CIN in place over an area and form a storm.GFS = Global Forecasting System.
It is one of the ensembles of computer models used to generate the forecast graphics that meteorologists use to determine their forecasts. It is the newest of the models and is a somewhat lesser resolution but is able to see much farther out into time (up to 384 hours into the future). The three big models are the GFS, ECMWF, and the NAM/WRF. In the particular forecast I gave above I just looked at one run and did not compare it to the other major models. If I had been doing a more extensive forecast and was looking at it much more seriously to consider where I were to target I would have looked to at least the past day or two of runs of EACH of the models and compared them to one another for consistent traits between each run. For example, the Euro (ECMWF) has the position of the trough much father north and a bit west than what the GFS is showing (but I don't agree with that).LLJ = Low Level Jet.
This is a region specific definition for the purposes of the above forecast. The low-level jet is a common experience for forecasters in the Great Plains and Eastern US. As the name implies, it is a fast moving ribbon of air in the low levels of the atmosphere. It can rapidly transport Gulf moisture and warmer temperatures to the North at speeds ranging from 25 to over 70 knots. There are two primary classifications of low-level jets. They are the nocturnal low level jet and the mid-latitude cyclone induced low level jet. My focus in the above forecast was on the nocturnal low level jet which begins to form near sundown and is a conveyor belt of air in the low levels of the atmosphere that races north at night ahead of a low pressure system's (trough) dryline (or cold front if there is no dryline present). It is what helps push the warm front north after dark and even retrograde a cold front or dryline back to the west.LCL = Lifted Condensation Level.
Basically this is the level at which water condenses in a parcel of air as it rises and forms clouds and the base of your storm. The lower to the ground the better for tornadoes. There is a lot more too it than just that simple definition but it is a bit too advanced to just dive into right now. You find the LCL height by looking at a Skew-T plot. To learn more about those just look at the link above. The LCL height is measured in feet or kilo-feet (meters or kilometers). This is different than most other products that refer to "levels" in the atmosphere in meteorlogical contexts. Most of the time we measure the altitude in pressure (most commonly millibars) as apposed to feet or meters since the atmosphere changes height with the seasons, furthermore the farther north you go in latitude on the earth the shorter the atmosphere is.Hodograph = A graph that shows the speed and direction a weather balloon travels as it rises in the atmosphere.
When a sounding balloon is launched the censors aboard it collect information on speed, altitude, temperature, altitude by pressure and feet/meters, and dew point. It radios this information back to the meteorologists that released it and that info is used to produce two diagrams, the skew-t plot and the hodograph. The skew-t (full name is Skew-T Log-P diagram) is a thermodynamic diagram of our atmosphere. The hodograph is a physical diagram that shows what the speed and direction the air is moving in the atmosphere with height. Together these two products are called a sounding. The hodograph is used to help us determine what quality the shear is in relation to forecasted storm motion and what type of storm mode based of the shear we can come to expect in the day.Trough = Area of low pressure.
The trough I was referring to was a trough in the jet stream which is at the 500mb level. When measuring by mb level it is important to know the smaller the mb level the higher you are. For example you are likely sitting at around 1024mb while airplanes leaving those contrails over your house are at the 500mb level or lower. Don't worry how high that is in feet or meters. Just know you can't jump that high and commercial jet liners fly around at that altitude. As the jet stream snakes around the earth it takes on a wave like shapes. These waves make up the areas of high and low pressure that influence our daily weather. The top of a wave, the crest, is called a ridge. A ridge is an area of high pressure. The lowest point in a wave, at the base of the wave or the low point between two waves is known as the trough. This area is low pressure. A high amplitude trough is once that digs WAY far south and will posses a large Peak-to-peak amplitude. This form of amplitude is the change between peak (highest amplitude value) and trough (lowest amplitude value, which can be negative). High amplitude troughs have large amounts of upper level energy they bring with them and this translates to vigorous storm systems. That said, just because you have a large amount of upper level support in the form of a lot of CAPE at higher mb levels it does not mean you can get storms to form. Simply that is just the energy that helps a storm stay alive and become more vigorous. You still need to over come the cap and have enough low level energy to lift your parcel of air in the first place.Supercell = A supercell is a thunderstorm with a rotating updraft.
These are the strongest and most deadly form of storms. Only these kinds of storms are capable of producing hail larger than golf balls and your most violent of tornadoes.Z or UTC time = Zulu or Universal Time Code.
This is the time it is in London, UK and other locations along the prime meridian. All meteorological products, forecasts, time stamps, chronological references, and information produced in and for areas and countries that are covered by The Convention of the World Meteorological Organization Treaty (signed 11 October 1947 and established upon ratification in 1950) are expressed in UTC time in a forecast, nowcast, or pastcast setting.
If there is any other part of the forecast that was confusing to you, or if you want me to elaborate deeper on it or do a forecast for you your area let me know. Please keep forecast requests to the CONUS (continental United States).
Anything fancy in the works for the San Antonio area or will it just be "Dang it's cold?"
You did! Well if you are well into the metro you likely will stay just above freezing thanks to the heat island effect of a larger city. Also the greater the cloud cover the warmer it will be for you. That said with the ridge that is in place over you I doubt you will see a cloud in the sky tonight. I would recommend a coat tonight.
Looking into the future things will start to heat back up tomorrow as the ridge begins to be pushed to the east in advance of the trough that I mentioned in my forecast above. On the backside of the ridge and the front side of the trough you will find your winds starting to come out of the south and with it will come sorely needed moisture and warmer temps. This will help with a bit of drought relief that you will get early next week. Luckily for you, the chances for severe weather is slim as you will be to far south from the nose of the jet and the surface low that will produce storms I may chase on Monday.
As things stand now, expect the bulk of your rain to start late Sunday and over Monday and possibly into Tuesday. If the system speeds up or slows down, those times will change. This will not be enough rain to put a significant dent in the drought. You may get some thunder though!
Once that trough passes by, expect cold temps again behind the front.
much like i was waiting for the fucking buses this morning
a cold front is the perfect thing for the opening weekend of deer season, but rain is not, and if it heats up it needs to get really cold again for them to get to running
it was 80 degrees the day before it snowed the first time
it's pretty warm today
I have an idea, how are you on Jell-O?
@Dead Legend, you can mount a trophy on your wall with photography of the tornado.... I really don't recommend trying to eat one though since it will more than likely just eat you instead.
Anytime our weather gets all dramatic it's always snow up here. Boo.
i could...melt them into jello?
I meant more what is your opinion.
The latter. I prefer to not have snow, or ice or any sort of water on the road because everyone forgets how to drive down here.
I couldn't live somewhere with boring weather. Places like Seattle, Montreal, even San Diego would be far too boring for me.
@yukira, no more snow for me, thanks. i'd rather go visit the snow than have it come visit me!
also, i really dig weather, so good work, chimera
edit: though that idea is pretty genius for being on the fly
Could be worse, you could live in Dallas. I hate having to pass through DFW when chasing. People there can barely drive in a drizzle let alone during a thunderstorm and to make it worse, Texas obsesses over how high and narrow they can make their interstate intersections be which makes cleaning up accidents stupid impossible to do in a timely manor.
That'll be nice. I'm starting to get fucked up with how early shit is. That'll get me some rest.
Though then seasonal affective disorder kicks in when it starts being dark all the god damn time.
Hear, here! I concur. I try to avoid that state like the plague when not chasing.
Also, thanks for the complement! If you want I can go deeper into the science behind severe weather in this thread.
I've been as far south as El Paso when chasing. I almost went to Brownsville this year for Alex but he turned to the left. I almost came to Austin to cover the fire weather but I needed a vacation after this insane spring. Last time I was in Austin was in 2010 for Thanksgiving. I was actually in SA but drove there so I had to go through Austin.
When I was a kid I used to go to the John Newcombe Tennis Ranch in New Braunfels each summer to work on my skills with a racket.
The good news is that with the solar cycle we are moving into, you will have plenty of chances to see the aurora in the coming years during the winter! I have only seen it twice but plan on taking a photography expedition to northern Greenland in a few years to capture the Aurora.
Space and solar weather is just as fascinating to me as meteorology.
between cities not so bad as far as driving, and if you know backroads that can be well worth it, but goddamn it's like every fucking person responsible for roads in this state had their head up their ass
and yeah, that would be cool. i'm still trying to understand the OP but one of my buddies is trying to get a degree in meteorology so he kind of infected me with this enjoyment
Nope, not far north enough for that. Also, the city lights would drown it out even if they were visible at this latitude.
The true upside to living here comes at the summer solstice, at which time thanks to daylight saving the sun goes down at 10 PM. There's nothing like sitting on a patio with a beer and a hot dog and the sun is setting and it's 9.
I'm always very ready to get back to Dallas after driving around Austin for a while.
Today was the first day I could call cold. It's 57 degrees and I wish I had remembered my jacket this morning.
I have a fear that this winter will be like 2010's and 2009's, which were apocalypticly icy and horrible. If this keeps up with the horrible record-setting summers, I'm freaking getting out of here.
If you're ever back in the area, @Sier and I do have fun going to dinner with various forumers passing through.
You would be surprised. The one thing with this cycle we are entering is we can expect to see a larger amount of CMEs and flares effecting us. In fact a pretty decent geomagnetic storm caused the auroral oval to migrate so far south a few weeks ago that I could see the aurora clearly here in Tulsa!
A fellow storm chaser and friend of mine shot this photo from even father south of where I live.....
It was taken on the 24th of October and was the first time in 13 years the Aurora made it this far south. We could see it here for 10 min. For areas in your latitude it will become a somewhat semi common sight during the coming solar cycle which is forecasted to be one of the most active ever on record. With any luck sunspot AR1339, which is coming around right now to face us, will give us another great show.
Alright! Well just ask away with any questions you have and I will try to answer them. You can also ask me about specific severe weather events in the past and why they happened. For example you could ask about the Joplin tornado or the super outbreak of 74.
Still got the whole light pollution problem up here though. Even on a clear night it's hard to see the stars in Montreal.
Also there aren't a whole lot of clear nights. We're located in a geographical "bowl" (surrounded by the Adirondacks, the Appalachians, the Laurentides and the Canadian Shield), on an island in the middle of a river barely over sea level. Meaning there's a lot of cloud cover and a lot of precipitation. It's about as damp as it gets at this latitude up here (that makes our summers very uncomfortable and our winters very snowy).
We actually are on tract to have another harsh and cold winter. In Texas expect it to stay very dry and have little drought relief. In my neck of the woods we are preparing for another harsh winter but one that will be just slightly warmer which means instead of the blizzards we had last year, we will likely get some gnarly ice storms.
Just watch Spaceweather.com or sign up for their text alerts and they will tell you in advance of when the aurora will become excited and move south. That way you will have time to scuttle through your tunnels and then drive or take a train out of town to see the colors.
What was really neat about this last storm was not only was the aurora way south, it was also the rarest kind of aurora..... a pure red aurora (comprised largely of oxygen ions at a much higher altitude than normal IIRC).
so far the last two years have proven me right!