The 2007 tornado season was a fantastic one for chasers who went early. Synoptically evident event after event. Although the mesoscale often went awry (you can't predict that stuff from way out), most chasers from March-early May were treated with many good events. But then came the "Death Ridge". There were still events in late May, and June, but they were not as numerous, and often came down to the mesoscale. Of course though, my general rule of thumb is that more things will go wrong with the mesoscale, in a given length of time, than will go right. Although two events pop out in my mind, when nearly everything went right (March 28 and April 21), there were numerous other events which everything went wrong. Nevertheless, the synoptic events are listed below:
Feb. 23-24 (Early season tornadoes in TX, Lower Miss. R. Valley tornadoes)
Feb. 28 - Mar. 1 (Early season EF4 in KS, SE Enterprise, AL Tornado outbreak)
March 28 (High Plains tornado outbreak)
April 13-14 (Mainly bust, few tornadoes in TX and Atl Coastal Plain)
April 21 (TX Panhandle tornado outbreak)
April 23-24 (Plains tornadoes, mainly bust, but Eagle Pass, TX tornado included)
May 4-5 (Greensburg tornadoes, tornado outbreak)
June 6-7 (Mainly bust, few tornadoes in WI)
Chasers also caught tornadoes on March 21, May 22-23, and then June 23 in Canada. But otherwise, that was it. However, March 28, April 21, April 23-24, and May 4-5 were epic days for chasers, with many bagging multiple tornadoes, some wedges (exception of last one with Apr 23-24). For many it was a nice reprieve of the relatively boring years of 2005-2006, although certainly not legendary like 2004, 1991, 1993, 1995, 1999 et al (that I would like to correct from my previous post).
For myself, it was a new beginning. This year was the first which I had even attempted long-range severe wx forecasts. They were quite experimental, and I really did not know what to expect. And I did fairly well. Not bragging, but for my first year at attempting this, I felt like I had grabbed onto something that was right.
My high points:
-Seeing the Feb. 23 event several weeks in advance, though I was a little early with the timing
-Seeing that April would be an active month (that was true b/c the pattern was active, even though due to mesoscale factors, the tornado count was around average)
-Correctly forecasting the early June event and the subsequent arrival of the Death Ridge
My low points:
-Seeing the March 28 outbreak from several weeks out, then rescinding my prediction, only to have it happen
-Thinking early April was going to be extremely active (turns out there was a break from April 3-12)
-Not updating the blog as much as I should've
I guess my overall grade for this year's predictions would be a B+. Long-range, that is. Could've been better w/ more updates, and maybe it was luck that helped me, so an A will never be a grade until I've done this for at least 2 or 3 years.
As it is July already, my focus will now shift toward the tropics. With the tropics, I have yet to do a significant amount of research, but I will try my best.
(P.S. Since this only includes Feb thru Jun, my horrible January forecasts do not count. This is not to vindicate myself; rather, there was not enough tornadic activity in January to justify it as part of the 2007 'tornado season'.)
Wednesday, July 4, 2007
Friday, May 18, 2007
The second half of "tornado season" - what will it bring?
Since the outbreak of May 4-6, it has been very quiet. The major polar vortex centers have shifted toward the Atlantic and Europe, leaving positive anomalies over the U.S. and a lackluster Pacific jet. This will likely change. I have been harping on renewed activity late this month, but that is most likely not happening on a grand scale. However a disturbance from the Pacific will dive into the CONUS and provide severe chances for the northern Plains for the next few days, with marginal moisture being the major limiting factor for an otherwise nice shortwave trough.
The bigger event should come in June. As the polar vortex centers shift back into the Pacific as Indian Ocean convection is renewed, the Pacific jet should be reasserted. The subtropical jet is still in full force and there has yet to be a full fledged subtropical block, meaning the jet will have a chance to extend into the eastern Pacific and amplify a trough. Obviously, this threat should be further north, most likely encompassing the Central and/or Northern Plains. And once again, just based on the trends this year, the Midwest should not get the brunt of severe. This idea is supported by the GFS ensembles, though the European model continues to show brutal ridging reasserting itself in early June.
As the month continues, the high should strengthen and I'd expect "summer" to truly set in around mid-June. Early June activity, IMO, will be the last gasp of Tornado Season 2007, which will go down in infamy as the biggest season in the Plains in 8 years, and comparable to the infamous seasons of 1995, 1993, and 1977. The reason for this is based on trends and the fact that the Pacific jet and Alaska vortex becomes a weaker factor closer to summer, compared to the building subtropical high.
The bigger event should come in June. As the polar vortex centers shift back into the Pacific as Indian Ocean convection is renewed, the Pacific jet should be reasserted. The subtropical jet is still in full force and there has yet to be a full fledged subtropical block, meaning the jet will have a chance to extend into the eastern Pacific and amplify a trough. Obviously, this threat should be further north, most likely encompassing the Central and/or Northern Plains. And once again, just based on the trends this year, the Midwest should not get the brunt of severe. This idea is supported by the GFS ensembles, though the European model continues to show brutal ridging reasserting itself in early June.
As the month continues, the high should strengthen and I'd expect "summer" to truly set in around mid-June. Early June activity, IMO, will be the last gasp of Tornado Season 2007, which will go down in infamy as the biggest season in the Plains in 8 years, and comparable to the infamous seasons of 1995, 1993, and 1977. The reason for this is based on trends and the fact that the Pacific jet and Alaska vortex becomes a weaker factor closer to summer, compared to the building subtropical high.
Friday, April 27, 2007
BIG UPDATE
I haven't had enough time to update this blog. But here are the major severe wx events of April:
April 3 - big severe wx outbreak with a couple of tornadoes.
April 10-11 - small event with two very impressive supercells, one over OK, one over AL.
April 13-14 - really had potential with a high risk over TX on the 13th that did not verify.
April 20-21 - tornadoes over the Plains, specifically, NE and the TX Panhandle.
April 23-24 - started out with several discrete and powerful, but widely isolated, Plains supercells. Ended with a high risk bust just to the east over I-35.
Granted, I didn't post a lot on the last two events. But as one can see, it was an active month for severe wx, although not even close to last year.
The limiting factor for this year so far has been the stagnant pattern over Western Europe and the Atlantic, which has been crunching up a fast Pacific jet. The jet is a result of Indian Ocean convection and the associated IO subtropical jet/Siberia polar jet "phasation" (is that even a word, lol?). At any rate, the flow is not as progressive when it punches into the CONUS, so basically a big bowling ball closed low results as the jet energy is forced to crunch up. These big bowling balls tend to not be prolific tornado producers. Case in point: April 24.
WHY DID APRIL 24 BUST?
For those who don't know, April 24, 2007 was predicted to be potentially one of the biggest outbreaks in the Plains in recent years. A big 500mb low was progged to hit a very moist and unstable airmass (the GFS, for instance, had predicted -10 LI's in central OK about a week out, although it did not verify). Many of the ingredients were there. Dr. Greg Forbes of TWC, Larry Cosgrove, among other very good mets were predicting an outbreak on the scale of the intensity of May 3, 1999. An almost unprecedented Day 3 Moderate risk was hoisted by the Storm Prediction Center.
In the end though, it all went bust, as convection formed too early. But why?
IMO, the reason it busted is mainly because the bowling ball closed low which had already stacked by the time. It is fairly common knowledge that a stacked low tends to be less condusive for severe wx. In this case, the dry line pushed very far east as CAA behind it intensified and the low matured and began to stack. Convergence along the dry line intensified, and coupled with strong upper air support, a line formed early and hard.
I think, that perhaps with less instability in the morning, or with some type of earlier convection to stabilize, this could've still ended up being a notable event. Strong instability fostered big anvils, which stablized things, and the convection developed into a line quickly, preventing moist inflow to areas later.
Still though, one tornadic supercell did form along the dryline later that day, a testament to how much potential this setup really had. A high risk was hoisted for central TX later that afternoon, but it mainly busted with few reports in the area. The lack of juxtaposition between the instability axis, the location of initiation, and the low level shear axis probably prevented from supercells which formed there in the afternoon, from being tornadic.
Ironically, the one strong, classic supercell that formed, formed in northern MX and entered deep south TX near Eagle Pass, TX, killing 10 people, 3 in MX, 7 in TX. It had perhaps one of the most impressive radar signatures I've ever seen, along with a monster supercell in rural northwestern KS the night before.
April 3 - big severe wx outbreak with a couple of tornadoes.
April 10-11 - small event with two very impressive supercells, one over OK, one over AL.
April 13-14 - really had potential with a high risk over TX on the 13th that did not verify.
April 20-21 - tornadoes over the Plains, specifically, NE and the TX Panhandle.
April 23-24 - started out with several discrete and powerful, but widely isolated, Plains supercells. Ended with a high risk bust just to the east over I-35.
Granted, I didn't post a lot on the last two events. But as one can see, it was an active month for severe wx, although not even close to last year.
The limiting factor for this year so far has been the stagnant pattern over Western Europe and the Atlantic, which has been crunching up a fast Pacific jet. The jet is a result of Indian Ocean convection and the associated IO subtropical jet/Siberia polar jet "phasation" (is that even a word, lol?). At any rate, the flow is not as progressive when it punches into the CONUS, so basically a big bowling ball closed low results as the jet energy is forced to crunch up. These big bowling balls tend to not be prolific tornado producers. Case in point: April 24.
WHY DID APRIL 24 BUST?
For those who don't know, April 24, 2007 was predicted to be potentially one of the biggest outbreaks in the Plains in recent years. A big 500mb low was progged to hit a very moist and unstable airmass (the GFS, for instance, had predicted -10 LI's in central OK about a week out, although it did not verify). Many of the ingredients were there. Dr. Greg Forbes of TWC, Larry Cosgrove, among other very good mets were predicting an outbreak on the scale of the intensity of May 3, 1999. An almost unprecedented Day 3 Moderate risk was hoisted by the Storm Prediction Center.
In the end though, it all went bust, as convection formed too early. But why?
IMO, the reason it busted is mainly because the bowling ball closed low which had already stacked by the time. It is fairly common knowledge that a stacked low tends to be less condusive for severe wx. In this case, the dry line pushed very far east as CAA behind it intensified and the low matured and began to stack. Convergence along the dry line intensified, and coupled with strong upper air support, a line formed early and hard.
I think, that perhaps with less instability in the morning, or with some type of earlier convection to stabilize, this could've still ended up being a notable event. Strong instability fostered big anvils, which stablized things, and the convection developed into a line quickly, preventing moist inflow to areas later.
Still though, one tornadic supercell did form along the dryline later that day, a testament to how much potential this setup really had. A high risk was hoisted for central TX later that afternoon, but it mainly busted with few reports in the area. The lack of juxtaposition between the instability axis, the location of initiation, and the low level shear axis probably prevented from supercells which formed there in the afternoon, from being tornadic.
Ironically, the one strong, classic supercell that formed, formed in northern MX and entered deep south TX near Eagle Pass, TX, killing 10 people, 3 in MX, 7 in TX. It had perhaps one of the most impressive radar signatures I've ever seen, along with a monster supercell in rural northwestern KS the night before.
Saturday, April 7, 2007
Long-awaited update: 3 significant events including possibly a massive outbreak to come April 10-17
Sorry I have not updated this; been busy.
Regarding the last event in the previous blog, March 28 there was a big outbreak across the Plains. The second system failed to amplify significantly but spawned a big severe wx outbreak with minimal tornado activity on April 3.
If I had time to post, I would've said that there looked to be potential. Now it looks even more likely. Strong 150 kt Pacific Jet (PJ) is coming in. Reloading with record low temperatures across the east and snow all the way down to TX (in April!). Indeed, powerful polar vortex (PV) is right now parked over the Eastern 2/3 of the country. As the PJ moves in, it will kick the PV out, reasserting it near the North Pole. Pacific air will flood the country as several disturbances within the flow amplify over the Intermountain West.
The first threat looks to be from the 10th to the 11th. This one will be a phase of a piece of the PV and an impulse riding along the Pacific Jet. Right now, a lead disturbance that goes through in the morning is the question mark. Will it be weak enough to not cause too much an effect for the bigger stuff in the afternoon? Nevertheless, given my analysis of previous events, the fact that moisture might be limited will not allow this to be a historic outbreak, IMO.
Next threat: 13th thru 15th. This one could be the biggest depending on the third system (see belwo). Another disturbance will come in via the Pacific Jet Highway. This time there could be more moisture to work with. Details are sketchy right now, since it's a week away, but dynamics look incredible (just as they will for the first system), but there will be more moisture to work with - latest GFS paints 65° to 70°F dewpoints all the way north to Memphis, TN. Caveat may be if the first system doesn't move out quickly enough.
Final threat before I think things calm down again: 15th thru 18th. This one is a question mark. The full force of the PJ rolls in this time, so this certainly has the most potential with regards to dynamics. But the instability is the question mark. It looks like this might be the signal of another pattern change as the Pacific becomes extremely convoluted after this and the NAO tanks. In other words, another cold pattern for the east. (BTW, do want to remind everyone that the idea of the "reloading pattern" with the PV over Hudson Bay -- only works consistently for early season and cold season outbreaks. Not going to go further into that though). If the NAO tanks early, this system will not have moisture to work with as the second system gets caught up and trapped behind the building ridge/block. If the NAO does not tank early, or more specifically, the second system moves out of the way, this might be the biggest of the three events as it will have the full mass of the PJ helping it to amplify into a low-amplitude high-wavelength trough -- most ideal for big outbreaks. Won't get into too much detail here as well.
Most of the major global models that go to the 240 hr range - specifically the GFS, CMC, and EURO, show the progression of these three systems. So confidence is much higher than last time where I had the right idea initially but bombed it due to relying too much on the poor model performance.
Regarding the last event in the previous blog, March 28 there was a big outbreak across the Plains. The second system failed to amplify significantly but spawned a big severe wx outbreak with minimal tornado activity on April 3.
If I had time to post, I would've said that there looked to be potential. Now it looks even more likely. Strong 150 kt Pacific Jet (PJ) is coming in. Reloading with record low temperatures across the east and snow all the way down to TX (in April!). Indeed, powerful polar vortex (PV) is right now parked over the Eastern 2/3 of the country. As the PJ moves in, it will kick the PV out, reasserting it near the North Pole. Pacific air will flood the country as several disturbances within the flow amplify over the Intermountain West.
The first threat looks to be from the 10th to the 11th. This one will be a phase of a piece of the PV and an impulse riding along the Pacific Jet. Right now, a lead disturbance that goes through in the morning is the question mark. Will it be weak enough to not cause too much an effect for the bigger stuff in the afternoon? Nevertheless, given my analysis of previous events, the fact that moisture might be limited will not allow this to be a historic outbreak, IMO.
Next threat: 13th thru 15th. This one could be the biggest depending on the third system (see belwo). Another disturbance will come in via the Pacific Jet Highway. This time there could be more moisture to work with. Details are sketchy right now, since it's a week away, but dynamics look incredible (just as they will for the first system), but there will be more moisture to work with - latest GFS paints 65° to 70°F dewpoints all the way north to Memphis, TN. Caveat may be if the first system doesn't move out quickly enough.
Final threat before I think things calm down again: 15th thru 18th. This one is a question mark. The full force of the PJ rolls in this time, so this certainly has the most potential with regards to dynamics. But the instability is the question mark. It looks like this might be the signal of another pattern change as the Pacific becomes extremely convoluted after this and the NAO tanks. In other words, another cold pattern for the east. (BTW, do want to remind everyone that the idea of the "reloading pattern" with the PV over Hudson Bay -- only works consistently for early season and cold season outbreaks. Not going to go further into that though). If the NAO tanks early, this system will not have moisture to work with as the second system gets caught up and trapped behind the building ridge/block. If the NAO does not tank early, or more specifically, the second system moves out of the way, this might be the biggest of the three events as it will have the full mass of the PJ helping it to amplify into a low-amplitude high-wavelength trough -- most ideal for big outbreaks. Won't get into too much detail here as well.
Most of the major global models that go to the 240 hr range - specifically the GFS, CMC, and EURO, show the progression of these three systems. So confidence is much higher than last time where I had the right idea initially but bombed it due to relying too much on the poor model performance.
Thursday, March 22, 2007
Update; multiple threats at end of month and perhaps early April
The severe threat for this week does not seem significant to me, cutoff lows usually do not do much in the way of severe. I do not think there is any major event regarding the cutoff.
A lot of things look up for major events (perhaps four), coming up in the next two-three weeks. First of all is the one that I sorta called off twice. Way back about 1-2 weeks ago, I had predicted an event around this time period (did not write it on the blog). Then I "cancelled" the event after models had consistently predicted no such event would happen for several days. Shortly after that, the models caught on (goes to show that it's perhaps better to go with observations and extrapolation than pure models in the long range). But I had doubts on whether it would cut off, and believing that it would, in my last post I had written that it might.
That idea looks to be wrong. A strong Pacific jet will prevent that from happening this time. The 500mb hemispheric pattern looks pretty ideal, in fact. In many outbreaks, there was a cutoff or a closed low over the SW that gave way to a strong jet stream which drove a larger, more mobile longwave trough that ended up being a big event. The reloading period had already been done a few days ago. Right now, the key continues to be the ridging over the CONUS.
Revision: the posts I had...
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1831884
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1832127
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1833459
There are two disturbances that the renouned polar vortex over Alaska (key forsynoptic severe outbreaks) are going to spit out. One initially will amplify pretty far west according to models. The problem with this one is because it amplifys over the EPAC instead of the Intermountain West, it will likely become very high amplitude once it approaches the Plains, and thus, shear vectors will be unidirectional. Another potential problem is regarding moisture return, since models do predict a closed low over the Bermuda area which could lead to a high pressure cell too far north to tap into a Caribbean moisture source. Although I believe the models are underdoing the moisture return, most of the biggest outbreaks do not have that feature and instead have a semizonal, maybe slightly purturbed, flow.
The second disturbance is the question mark. If this trough materializes, it has a lot of potential. This one should have a source region closer to Alaska as the polar vortex splits, and one piece flies into Siberia. The question mark for this is indeed how the first trough moves away, and how strong a ridge is left behind over the southern CONUS. Will it amplify? If the first trough does not move away quickly enough, will there be enough return flow and instability? All those questions should be resolved within the coming days. FWIW, the Euro has been questioning the validity of the possibility of this, being incredibly pessimistic. So obviously, I'd trust the better model for now. Analysis, extrapolation, and pattern recognition suggests that in a case like this, the more widespread severe wx the first produces, the less the second produces. So really, I don't know which is bigger, except that I'd expect a least one significant severe wx outbreak with these two threats.
As the other piece of the PV moves into Siberia, the pattern will reload. A ridge will redevelop over the Aleutians, but it will be short-lived as the reformed polar vortex over Siberia reinvigorates the Pacific jet, which will most likely undercut the Aleutians ridge yet again. This new piece could lead to another big event in early April.
Stay tuned.
A lot of things look up for major events (perhaps four), coming up in the next two-three weeks. First of all is the one that I sorta called off twice. Way back about 1-2 weeks ago, I had predicted an event around this time period (did not write it on the blog). Then I "cancelled" the event after models had consistently predicted no such event would happen for several days. Shortly after that, the models caught on (goes to show that it's perhaps better to go with observations and extrapolation than pure models in the long range). But I had doubts on whether it would cut off, and believing that it would, in my last post I had written that it might.
That idea looks to be wrong. A strong Pacific jet will prevent that from happening this time. The 500mb hemispheric pattern looks pretty ideal, in fact. In many outbreaks, there was a cutoff or a closed low over the SW that gave way to a strong jet stream which drove a larger, more mobile longwave trough that ended up being a big event. The reloading period had already been done a few days ago. Right now, the key continues to be the ridging over the CONUS.
Revision: the posts I had...
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1831884
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1832127
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1833459
There are two disturbances that the renouned polar vortex over Alaska (key forsynoptic severe outbreaks) are going to spit out. One initially will amplify pretty far west according to models. The problem with this one is because it amplifys over the EPAC instead of the Intermountain West, it will likely become very high amplitude once it approaches the Plains, and thus, shear vectors will be unidirectional. Another potential problem is regarding moisture return, since models do predict a closed low over the Bermuda area which could lead to a high pressure cell too far north to tap into a Caribbean moisture source. Although I believe the models are underdoing the moisture return, most of the biggest outbreaks do not have that feature and instead have a semizonal, maybe slightly purturbed, flow.
The second disturbance is the question mark. If this trough materializes, it has a lot of potential. This one should have a source region closer to Alaska as the polar vortex splits, and one piece flies into Siberia. The question mark for this is indeed how the first trough moves away, and how strong a ridge is left behind over the southern CONUS. Will it amplify? If the first trough does not move away quickly enough, will there be enough return flow and instability? All those questions should be resolved within the coming days. FWIW, the Euro has been questioning the validity of the possibility of this, being incredibly pessimistic. So obviously, I'd trust the better model for now. Analysis, extrapolation, and pattern recognition suggests that in a case like this, the more widespread severe wx the first produces, the less the second produces. So really, I don't know which is bigger, except that I'd expect a least one significant severe wx outbreak with these two threats.
As the other piece of the PV moves into Siberia, the pattern will reload. A ridge will redevelop over the Aleutians, but it will be short-lived as the reformed polar vortex over Siberia reinvigorates the Pacific jet, which will most likely undercut the Aleutians ridge yet again. This new piece could lead to another big event in early April.
Stay tuned.
Sunday, March 18, 2007
Major update - Multiple threats coming at the turn of the month possible
OK yeah I wrote two days ago that I did not expect any major outbreaks in March. I will change that because the timing of the "big tamale" may be earlier than expected.
Note that the latest European has a significant system around the 240 hr range, and so did the 18Z GFS. I am divided on the threat will not materialize like what is depicted on those runs, because the fundamental pattern really is sorta tricky. Sure, we just had the reloading with the sleet storm over the NE, and that piece will reinforce the Hudson Bay PV, but the big problem is the flat ridge over the CONUS. When does this go away is the question? We've had the Aleutian blocking high now eroded. As the next system dives down into the CONUS, the energy over the EPAC will split, sending the next system into Mexico where it will cut off (still a severe threat around the 21st but not too big given that cutoffs usually don't produce a lot of severe). The other piece will deflect northward and form a very strong and deep polar vortex (PV) over Alaska. This is where it gets interesting.
As this happens, a massive block develops over Scandanavia (yes, another block, as I said blocks don't go away easily). Some ensemble members are progging closed 576 contours at 500mb over northern Scandanavia (keep in mind, this is March and that's near the Arctic circle!). So this pattern becomes pretty stagnant, with the PV on the Alaska and Russia side, and the block in northern Europe, and flat zonal flow pretty much everywhere except invof the block. So now the question is, how powerful does this block become? If it becomes so strong that there's cross polar flow, the PV over Alaska becomes essentially trapped. OTOH, if the block slowly breaks down, this will allow the PV energy to branch off. The timing of the PV branching off is indeed the timing of what I think could be an extremely active period. This, according to the GFS Ensemble mean, should occur ~228 hr.
However, as the PV branches off and leaves a small portion over the GOA to amplify into the next longwave over the western CONUS, what happens to the flat zonal ridge over the CONUS? This is why I am divided on the initial threat. If that ridge is too powerful, the low cuts off again. BUT, many of the biggest outbreaks occur after a cutoff over the SW is ejected out. The reason is that following pieces of energy start out more progressive and less amplified in the EPAC and thus don't have as much tendency to cut off after amplifying over the West (in fact, just take a look at Palm Sunday 1965 for an example of this, the pattern was very much in support of cutoffs, the the shortwave that spawned the outbreak just barely missed being cut off over the SW, even though the part that it split from did indeed cut off).
The next few disturbances after that are uncertain, but let me just say this: ANY disturbance which manages to stay progressive (the chances will be enhanced if we have semizonal Pacific jet with small kinks in it) will have the potential to be significant severe producers. This is going well after 240 hr, and will most likely feature big events from March 29-April 10. The caveat for multiple threats is if the first disturbance manages to really amplify and form into a new PV, which will shut down the pipeline.
Note that an alternative option would be for the big event to occur at ~240 hr, but although the mainstream models seem to show it, it seems like the less likely option right now.
All of this is subject to much change, of course, as this pattern's pretty dynamic and unpredictable.
Note that the latest European has a significant system around the 240 hr range, and so did the 18Z GFS. I am divided on the threat will not materialize like what is depicted on those runs, because the fundamental pattern really is sorta tricky. Sure, we just had the reloading with the sleet storm over the NE, and that piece will reinforce the Hudson Bay PV, but the big problem is the flat ridge over the CONUS. When does this go away is the question? We've had the Aleutian blocking high now eroded. As the next system dives down into the CONUS, the energy over the EPAC will split, sending the next system into Mexico where it will cut off (still a severe threat around the 21st but not too big given that cutoffs usually don't produce a lot of severe). The other piece will deflect northward and form a very strong and deep polar vortex (PV) over Alaska. This is where it gets interesting.
As this happens, a massive block develops over Scandanavia (yes, another block, as I said blocks don't go away easily). Some ensemble members are progging closed 576 contours at 500mb over northern Scandanavia (keep in mind, this is March and that's near the Arctic circle!). So this pattern becomes pretty stagnant, with the PV on the Alaska and Russia side, and the block in northern Europe, and flat zonal flow pretty much everywhere except invof the block. So now the question is, how powerful does this block become? If it becomes so strong that there's cross polar flow, the PV over Alaska becomes essentially trapped. OTOH, if the block slowly breaks down, this will allow the PV energy to branch off. The timing of the PV branching off is indeed the timing of what I think could be an extremely active period. This, according to the GFS Ensemble mean, should occur ~228 hr.
However, as the PV branches off and leaves a small portion over the GOA to amplify into the next longwave over the western CONUS, what happens to the flat zonal ridge over the CONUS? This is why I am divided on the initial threat. If that ridge is too powerful, the low cuts off again. BUT, many of the biggest outbreaks occur after a cutoff over the SW is ejected out. The reason is that following pieces of energy start out more progressive and less amplified in the EPAC and thus don't have as much tendency to cut off after amplifying over the West (in fact, just take a look at Palm Sunday 1965 for an example of this, the pattern was very much in support of cutoffs, the the shortwave that spawned the outbreak just barely missed being cut off over the SW, even though the part that it split from did indeed cut off).
The next few disturbances after that are uncertain, but let me just say this: ANY disturbance which manages to stay progressive (the chances will be enhanced if we have semizonal Pacific jet with small kinks in it) will have the potential to be significant severe producers. This is going well after 240 hr, and will most likely feature big events from March 29-April 10. The caveat for multiple threats is if the first disturbance manages to really amplify and form into a new PV, which will shut down the pipeline.
Note that an alternative option would be for the big event to occur at ~240 hr, but although the mainstream models seem to show it, it seems like the less likely option right now.
All of this is subject to much change, of course, as this pattern's pretty dynamic and unpredictable.
Friday, March 16, 2007
ok yeah I do apologize for not updating this
There was a big tornado outbreak on Mar. 1. Moisture was good and the dynamics were more than sufficient with the only thing preventing a bigger tornado outbreak was the convection to the south which resulted in a more concentrated tornado outbreak rather than a larger more spread out one, and also, the separation of the better low-level kinematic fields from the better instability in the north.
The pattern since then has been docile. Large flat zonal ridge over the U.S. Because of that, I do not believe there will be any MAJOR severe wx outbreaks for the rest of March. REVISION 11:49 AM PDT Mar 16... the 12Z GFS is particularly ominous for an outbreak in about a week. This one is a tough one to forecast since there could be a potential for the disturbance to cut off at a very early stage of the game, which will cut down the severe chances. Right now am leaning on a minor severe wx event, and go more bullish as time goes by if it warrants. The overall synoptic scale looks pretty good actually with an ejection of a trough over the NE giving way to the Pacific jet. So of course it deserves watch...I may have overlooked it yesterday night when I posted this entry.
I think the next big severe wx event(s) will come when we get the next major "reloading period", the time when we get some time of sufficiently long lasting cold intrusion. The current pattern is downright terrible for any type of severe wx, if this was in May or June, and could in fact be one of those severe season enders since cool snaps are pretty difficult to get in June. So definitely, better now than later. Research from some renouned long-range experts do suggest that the NAO would switch to negative sometime in April. The long range progs also suggest that the Pacific jet should be somewhat above normal in terms of strength. In this case, the PJ is NOT GOOD if it keeps things zonal. We're gonna need some type of minor amplification, outside of the major amplification, the block over the Aleutians that's causing the backup and resultant stale pattern.
I still think a big outbreak is very possible during April, especially early April (in fact, with the polar vortex over the Pole and dropping energies down, along with a fairly zonal Pacific, prelim indications are this could be significant -- if it materializes). Looking at the really long range, right now it seems the Aleutian block could remain for reappear frequently given the tropical influences (the Nina). Since wavelengths do shorten in the summer, what effects that could have is still uncertain to me right now.
The pattern since then has been docile. Large flat zonal ridge over the U.S. Because of that, I do not believe there will be any MAJOR severe wx outbreaks for the rest of March. REVISION 11:49 AM PDT Mar 16... the 12Z GFS is particularly ominous for an outbreak in about a week. This one is a tough one to forecast since there could be a potential for the disturbance to cut off at a very early stage of the game, which will cut down the severe chances. Right now am leaning on a minor severe wx event, and go more bullish as time goes by if it warrants. The overall synoptic scale looks pretty good actually with an ejection of a trough over the NE giving way to the Pacific jet. So of course it deserves watch...I may have overlooked it yesterday night when I posted this entry.
I think the next big severe wx event(s) will come when we get the next major "reloading period", the time when we get some time of sufficiently long lasting cold intrusion. The current pattern is downright terrible for any type of severe wx, if this was in May or June, and could in fact be one of those severe season enders since cool snaps are pretty difficult to get in June. So definitely, better now than later. Research from some renouned long-range experts do suggest that the NAO would switch to negative sometime in April. The long range progs also suggest that the Pacific jet should be somewhat above normal in terms of strength. In this case, the PJ is NOT GOOD if it keeps things zonal. We're gonna need some type of minor amplification, outside of the major amplification, the block over the Aleutians that's causing the backup and resultant stale pattern.
I still think a big outbreak is very possible during April, especially early April (in fact, with the polar vortex over the Pole and dropping energies down, along with a fairly zonal Pacific, prelim indications are this could be significant -- if it materializes). Looking at the really long range, right now it seems the Aleutian block could remain for reappear frequently given the tropical influences (the Nina). Since wavelengths do shorten in the summer, what effects that could have is still uncertain to me right now.
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