A good question about the latest forecasting..Mets Welcome
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Weatherfreak000
I'm really getting a very scary feeling for the scenario with the models now beginning the shift to the West. This IS the first time the models have shifted back to the West for days. Will this become a new trend for the storm? Remember guys even if it opens up completely unto a wave, regeneration over the Gulf Waters is definitely possible.
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Weatherfreak000
CajunMama wrote:Weatherfreak, you are winning me over with your analysis. I'm a very amateur amateur, read alot, don't ask many questions but i understand what you are talking about. You may be onto something.
Thanks, i'm really surprised to not see alot of discussion about this. I mean, landfall is coming soon based on the NHC, something like two days. And the cold front doesn't look like it's penetrating south at all.
Seems like one of those possible hit and miss scenarios for the models...
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Stratosphere747
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I have been wondering the same thing, and here is a good water vapor loop of the US. Is it me, or does the trough appear to not be pushing as far south as maybe it was forecast to? It almost looks like it is lifting NE slightly.
http://www.rap.ucar.edu/weather/satelli ... duration=7
http://www.rap.ucar.edu/weather/satelli ... duration=7
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timNms
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link to models site and a question or two
http://weather.net-waves.com/modelplot.htm Here you can see model plots for storms/invests. it's the same site someone posted showing Ernesto's model tracks, but on this page you can click on other storms.
Now, I'm beginning to wonder about the WNW movement also. Just about time we think we can relax and not have to worry bout Ernesto, he pulls this WNW movement. Let's just hope it's a "wobble" and nothing permanent...but then again, we must remember Elena from the mid-80s...she did some strange things in the gulf...gave MS a scare, turned to go to FL and decided that wasn't where she wanted to go and ended up visiting Pascagoula, MS. ....ON LABOR DAY!
Now, I'm beginning to wonder about the WNW movement also. Just about time we think we can relax and not have to worry bout Ernesto, he pulls this WNW movement. Let's just hope it's a "wobble" and nothing permanent...but then again, we must remember Elena from the mid-80s...she did some strange things in the gulf...gave MS a scare, turned to go to FL and decided that wasn't where she wanted to go and ended up visiting Pascagoula, MS. ....ON LABOR DAY!
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CYCLONE MIKE
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MississippiHurricane
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AL Chili Pepper
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CYCLONE MIKE wrote:FWIW our local weather guy just explained that the trough will slide east and therefore will push the high centered over GA east and Ernesto will ridge the back edge of the high north. Does not matter if the front drops more south or not.
You can see that high moving east on the water vapor. FL is as far west as the thing goes.......I think.
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Ah crap. I just had a big long 4-paragraph answer ready, but Firefox crashed on me. 
I will say that you cannot see fronts on water vapor imagery. WV displays moisture content in the mid- and upper-levels, where there tends to be little in the way of frontal zones (there are fronts aloft, but we won't talk about that). Most fronts that you'll be talkign about (cold fronts, warm front, etc) do not extend into the mid-levels, though processes that drive low-level features such as fronts are impacted by upper-level processes (and vice versa -- they feedback to each other). Let me try to retype my last post to explain a bit.
The point of this short one is that you are not seeing a front on water vapor, since water vapor won't show you fronts. What you are seeing will be explained in a later post.
I will say that you cannot see fronts on water vapor imagery. WV displays moisture content in the mid- and upper-levels, where there tends to be little in the way of frontal zones (there are fronts aloft, but we won't talk about that). Most fronts that you'll be talkign about (cold fronts, warm front, etc) do not extend into the mid-levels, though processes that drive low-level features such as fronts are impacted by upper-level processes (and vice versa -- they feedback to each other). Let me try to retype my last post to explain a bit.
The point of this short one is that you are not seeing a front on water vapor, since water vapor won't show you fronts. What you are seeing will be explained in a later post.
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OK, so here's goes "Take 2". Dang Firefox!
Let's take a look at a water vapor loop -- a good one is available HERE. So, we can see all sorts of neat features on this graphic, including: an upper-level low in the western and southwestern Gulf of Mexico, a relatively compact upper-level low spinning near the Florida straights, a deep high in the southeastern US, a positively-tilted trough in the central US, a building ridge in the northwestern US / southwestern Canada, and a digging trough off the northwestern US / western Canada coast. Southwesterly flow downstream of the digging trough off the northwestern US coast is providing relatively strong warm-air advection across western Canada and northwestern US, which is helping to pump the ridge northward. This trough-ridge couplet is amplifying and slowly shifting eastward in time. But hey, that's a long ways from Ernesto (though it will still affect the steering flow that Ernesto will deal with), so let's move east.
Our attention turns to the upper-level trough in the central United States. What you were probably referring to as the cold front isn't actually the cold front per se. Let's look at the NAM 00z 500mb vorticity initialization, available HERE. We see a vort max stretching from the western Great Lakes to the central plains, with a more compact vort max along the OK/TX border. The dry air you see on water vapor can be attributed to several things, two of which are differential negative vorticity advection (DNVA) and cold-air advection (which is related to the front, but is not the front itself). Don't worry about DNVA, just know that it contributes to subsidence. A map of the 500mb temperatures and height field, HERE, shows that there is also a moderate amount of cold-air advection occurring at 500mb. DNVA and cold-air advection are processes that result in subsidence, which acts to 'dry' the atmosphere. Ahead of the trough axis, there is broad southwesterly flow, which is driving warm-air advection. So, ahead of the trough, we have warm-air advection and DPVA (differential positive vorticity advection) -- both processes that lead to large-scale ascent. This is getting slightly long-winded, so I'll draw this part to a close. Just remember -- use a surface map (start at http://www.rap.ucar.edu/weather/surface/ ) if you want to see surface fronts -- don't use water vapor imagery!
OK, so back to the water vapor loop. You can see the ridge in the western US/Canada building northward, and the central US trough slowly moving eastward. As the flow in the west amplifies and the central US trough shifts eastward, the trough will cut-off into an upper-level low. As is common with ULLs, vorticity advection aloft will not be very significant (since the flow is pretty much circular, there isn't much vorticity advection, so heights aloft don't change much -- the ULL doesn't move quickly). In step with this, the NAM and GFS suggest this low will meander into the eastern US by mid-week. Meanwhile, the cold front trailing southwestward from a low near Cincinatti will also make it into the northern Gulf coast (per GFS and HPC). Cold-air advection behind this cold front will result in lowering heights aloft (actually, differential cold-air advection lowers the heights; CAA itself results in subsidence). While the NAM is more circular with the upper-level low in the eastern US, the GFS is a little more elongated, showing a NNE-SSW-align vort max near the MS River Valley by Wednesday. As this moves eastward, heights aloft with fall, effectively pushing the ridge eastward, into the Atlantic. Southwesterly flow ahead of this feature will provide the necessary "streering currents" for Ernesto to curve northward and north-northeastward (or northeastward) by Wednesday afternoon.
Of course, all bets are off if the LLC becomes detached from the MLC (or Ernesto weakens into a wave). I won't go into that situation, however.
This is shorter than my origin write-up, but there's nothing I can do about it (well, I could expand more, but I'll save you the boredom of reading it LOL). I hope that answers some questions.
Let's take a look at a water vapor loop -- a good one is available HERE. So, we can see all sorts of neat features on this graphic, including: an upper-level low in the western and southwestern Gulf of Mexico, a relatively compact upper-level low spinning near the Florida straights, a deep high in the southeastern US, a positively-tilted trough in the central US, a building ridge in the northwestern US / southwestern Canada, and a digging trough off the northwestern US / western Canada coast. Southwesterly flow downstream of the digging trough off the northwestern US coast is providing relatively strong warm-air advection across western Canada and northwestern US, which is helping to pump the ridge northward. This trough-ridge couplet is amplifying and slowly shifting eastward in time. But hey, that's a long ways from Ernesto (though it will still affect the steering flow that Ernesto will deal with), so let's move east.
Our attention turns to the upper-level trough in the central United States. What you were probably referring to as the cold front isn't actually the cold front per se. Let's look at the NAM 00z 500mb vorticity initialization, available HERE. We see a vort max stretching from the western Great Lakes to the central plains, with a more compact vort max along the OK/TX border. The dry air you see on water vapor can be attributed to several things, two of which are differential negative vorticity advection (DNVA) and cold-air advection (which is related to the front, but is not the front itself). Don't worry about DNVA, just know that it contributes to subsidence. A map of the 500mb temperatures and height field, HERE, shows that there is also a moderate amount of cold-air advection occurring at 500mb. DNVA and cold-air advection are processes that result in subsidence, which acts to 'dry' the atmosphere. Ahead of the trough axis, there is broad southwesterly flow, which is driving warm-air advection. So, ahead of the trough, we have warm-air advection and DPVA (differential positive vorticity advection) -- both processes that lead to large-scale ascent. This is getting slightly long-winded, so I'll draw this part to a close. Just remember -- use a surface map (start at http://www.rap.ucar.edu/weather/surface/ ) if you want to see surface fronts -- don't use water vapor imagery!
OK, so back to the water vapor loop. You can see the ridge in the western US/Canada building northward, and the central US trough slowly moving eastward. As the flow in the west amplifies and the central US trough shifts eastward, the trough will cut-off into an upper-level low. As is common with ULLs, vorticity advection aloft will not be very significant (since the flow is pretty much circular, there isn't much vorticity advection, so heights aloft don't change much -- the ULL doesn't move quickly). In step with this, the NAM and GFS suggest this low will meander into the eastern US by mid-week. Meanwhile, the cold front trailing southwestward from a low near Cincinatti will also make it into the northern Gulf coast (per GFS and HPC). Cold-air advection behind this cold front will result in lowering heights aloft (actually, differential cold-air advection lowers the heights; CAA itself results in subsidence). While the NAM is more circular with the upper-level low in the eastern US, the GFS is a little more elongated, showing a NNE-SSW-align vort max near the MS River Valley by Wednesday. As this moves eastward, heights aloft with fall, effectively pushing the ridge eastward, into the Atlantic. Southwesterly flow ahead of this feature will provide the necessary "streering currents" for Ernesto to curve northward and north-northeastward (or northeastward) by Wednesday afternoon.
Of course, all bets are off if the LLC becomes detached from the MLC (or Ernesto weakens into a wave). I won't go into that situation, however.
This is shorter than my origin write-up, but there's nothing I can do about it (well, I could expand more, but I'll save you the boredom of reading it LOL). I hope that answers some questions.
Last edited by WxGuy1 on Tue Aug 29, 2006 3:24 pm, edited 1 time in total.
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southerngale
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