weatherwiz Posted September 5, 2012 Share Posted September 5, 2012 Summer may be over as we are now into September and meteorological fall began 5 days ago, however, this does not mean convective season is over! While large scale severe weather outbreaks or major severe weather events are unlikely this time of year we can still get our share of strong to severe storms and this time of year we usually do so thanks in part to the low-topped squall line! When dealing with the threat for convection and especially strong to severe convection we typically like to look at instability values and would like to see large amounts of instability. Across our portion of the country this time of year it's much more difficult to achieve large amounts of instability, however, the lack of instability can be compensated by cold fronts which are stronger (allowing for more uplift and forcing) and by stronger dynamics aloft. The stronger forcing and stronger dynamics work to develop and sustain convective development. As we move towards Saturday it appears we may see the potential for a low topped squall line! As we approach the weekend a vigorous trough will be approaching New England accompanied by perhaps several strong pieces of shortwave energy and pushing a fairly strong cold front eastward. Out ahead of this system we will see a strong southerly and southwesterly flow pumping in ample moisture and also allowing for much warmer air to work back into the region. In fact, Thursday/Friday will feel more like summer as temperatures soar through the 80's with dewpoints well into the 60's! By Saturday substantial cloud cover should hold temp's back into the mid to upper 70's, however, a few locations could sneak to 80F or a few ticks higher if any areas manage to see a few peaks of sun. The combination of increasing dewpoints/low-level moisture and rich theta-e air will yield to a fairly unstable airmass across the region out ahead of the approaching cold front. Limited solar heating and weak mid-level lapse rates will prevent the airmass from becoming much more unstable. As of now computer forecast models are showing some pretty potent dynamics associated with the approaching trough. Some models show a 45-55 knot mid-level jet working into the region along with the region being placed in the right entrance region of an 85-95 kt upper-level jet. Some computer models also develop a very weak 925/850mb low which would indicate the potential for a small area of an enhanced low-level jet, possibly in excess of 25-30 knots. Looks like forcing along the front will be rather strong and with the potential for strong dynamics along and out ahead of the front and the potential for at least weak instability across the region we could be looking at the potential for a low-topped squall line with the main hazard being strong winds, potentially causing isolated pockets of damage and of course torrential rainfall given rich low-level moisture in place. Should be fun monitoring this over the next several days! Link to comment Share on other sites More sharing options...
CoastalWx Posted September 5, 2012 Share Posted September 5, 2012 Why would it be low topped? Link to comment Share on other sites More sharing options...
weatherwiz Posted September 5, 2012 Author Share Posted September 5, 2012 Why would it be low topped? I would think it would probably depend on how unstable the atmosphere can become. If we're only able to manage 1000-1500 Cape I think it would be rather difficult to get cloud tops really high, especially given the strength of the shear and the weak lapse rates. If we we're able to manage perhaps 2000 Cape (or greater) then convection certainly wouldn't be low topped at all and we would certainly see a higher severe threat! Going to be hard though to muster up enough sun given the thermo look on the GFS skew-t profiles but we'll see. Link to comment Share on other sites More sharing options...
Damage In Tolland Posted September 5, 2012 Share Posted September 5, 2012 Here's thread # 1 of at least 5 this autumn of a low topped squall line..which never materialize Link to comment Share on other sites More sharing options...
radarman Posted September 5, 2012 Share Posted September 5, 2012 Summer may be over as we are now into September and meteorological fall began 5 days ago, however, this does not mean convective season is over! While large scale severe weather outbreaks or major severe weather events are unlikely this time of year we can still get our share of strong to severe storms and this time of year we usually do so thanks in part to the low-topped squall line! When dealing with the threat for convection and especially strong to severe convection we typically like to look at instability values and would like to see large amounts of instability. Across our portion of the country this time of year it's much more difficult to achieve large amounts of instability, however, the lack of instability can be compensated by cold fronts which are stronger (allowing for more uplift and forcing) and by stronger dynamics aloft. The stronger forcing and stronger dynamics work to develop and sustain convective development. As we move towards Saturday it appears we may see the potential for a low topped squall line! As we approach the weekend a vigorous trough will be approaching New England accompanied by perhaps several strong pieces of shortwave energy and pushing a fairly strong cold front eastward. Out ahead of this system we will see a strong southerly and southwesterly flow pumping in ample moisture and also allowing for much warmer air to work back into the region. In fact, Thursday/Friday will feel more like summer as temperatures soar through the 80's with dewpoints well into the 60's! By Saturday substantial cloud cover should hold temp's back into the mid to upper 70's, however, a few locations could sneak to 80F or a few ticks higher if any areas manage to see a few peaks of sun. The combination of increasing dewpoints/low-level moisture and rich theta-e air will yield to a fairly unstable airmass across the region out ahead of the approaching cold front. Limited solar heating and weak mid-level lapse rates will prevent the airmass from becoming much more unstable. As of now computer forecast models are showing some pretty potent dynamics associated with the approaching trough. Some models show a 45-55 knot mid-level jet working into the region along with the region being placed in the right entrance region of an 85-95 kt upper-level jet. Some computer models also develop a very weak 925/850mb low which would indicate the potential for a small area of an enhanced low-level jet, possibly in excess of 25-30 knots. Looks like forcing along the front will be rather strong and with the potential for strong dynamics along and out ahead of the front and the potential for at least weak instability across the region we could be looking at the potential for a low-topped squall line with the main hazard being strong winds, potentially causing isolated pockets of damage and of course torrential rainfall given rich low-level moisture in place. Should be fun monitoring this over the next several days! Good stuff Wiz. The setup reminds me of Aug. 10th a bit. We won't need too much instability to get impressive storms; 2K j/kg might yield moderate risk in fact. I'd favor initially discrete cells, possibly training with eventual interactions forming linear segments, but not necessarily a west-east propagating bow. Link to comment Share on other sites More sharing options...
Damage In Tolland Posted September 5, 2012 Share Posted September 5, 2012 Good stuff Wiz. The setup reminds me of Aug. 10th a bit. We won't need too much instability to get impressive storms; 2K j/kg might yield moderate risk in fact. I'd favor initially discrete cells, possibly training with eventual interactions forming linear segments, but not necessarily a west-east propagating bow. Moderate risk? in Sept? In Sne? Link to comment Share on other sites More sharing options...
NorEaster27 Posted September 5, 2012 Share Posted September 5, 2012 I would think SEP has a larger number of severe events compared to AUG in SNE, no? Link to comment Share on other sites More sharing options...
radarman Posted September 5, 2012 Share Posted September 5, 2012 Moderate risk? in Sept? In Sne? You're right, they'd probably not go for it. But if that much instability were to verify (not saying it will by any means), we'd probably have one of our better events of the summer. Link to comment Share on other sites More sharing options...
weatherwiz Posted September 5, 2012 Author Share Posted September 5, 2012 Good stuff Wiz. The setup reminds me of Aug. 10th a bit. We won't need too much instability to get impressive storms; 2K j/kg might yield moderate risk in fact. I'd favor initially discrete cells, possibly training with eventual interactions forming linear segments, but not necessarily a west-east propagating bow. Looks like we may be dealing with dews in the low 70's which is certainly much higher than what we typically see in these setups, usually we see mid or even upper 60's. If we can get any breaks of sun and get temps into the 80's that could certainly create pockets of 2000+ Cape which could make for some fun given the strength of the shear. Also have to watch for that weak wave developing which not only may enhance shear but enhance directional shear as well, especially in the low levels. Link to comment Share on other sites More sharing options...
Damage In Tolland Posted September 5, 2012 Share Posted September 5, 2012 Euro says this is an absolute PHAIL Link to comment Share on other sites More sharing options...
weatherwiz Posted September 5, 2012 Author Share Posted September 5, 2012 Euro says this is an absolute PHAIL I just looked at the SPC D4-8 outlook and they have mention of severe here on Saturday. What do you have to say to that? Link to comment Share on other sites More sharing options...
Damage In Tolland Posted September 5, 2012 Share Posted September 5, 2012 I just looked at the SPC D4-8 outlook and they have mention of severe here on Saturday. What do you have to say to that? That the Euro doesn't agree and that's all GFS based Link to comment Share on other sites More sharing options...
CoastalWx Posted September 5, 2012 Share Posted September 5, 2012 That the Euro doesn't agree and that's all GFS based Well the euro would argue for some severe too in Ern NY state I think. It depends where and how the low develops. Certainly not a lock. Link to comment Share on other sites More sharing options...
CoastalWx Posted September 5, 2012 Share Posted September 5, 2012 Maybe some sct stuff on Friday aftn. Link to comment Share on other sites More sharing options...
free_man Posted September 6, 2012 Share Posted September 6, 2012 mostly light storms, isolated flash of lightning and scattered downpours. Link to comment Share on other sites More sharing options...
earthlight Posted September 6, 2012 Share Posted September 6, 2012 The SREF has an impressive area of 0-6km bulk shear over 50 kts through parts of the Interior Northeast at 00z Sunday Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 NAM bufkit soundings don't look too bad as well; have almost 1500 Cape along with the strong bulk shear as John posted above. Helicity quite high as well, especially 0-1km. Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 6, 2012 Share Posted September 6, 2012 Decent low level shear, both directionally and speed. This setup certainly looks to provide great speed shear from 0-6km with the really fast 500mb winds, but not much directional shear above 850mb. Perhaps a damaging wind squall line with some embedded low level mesocyclones? Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 Decent low level shear, both directionally and speed. This setup certainly looks to provide great speed shear from 0-6km with the really fast 500mb winds, but not much directional shear above 850mb. Perhaps a damaging wind squall line with some embedded low level mesocyclones? Completely agreed. LCL's will be quite low so that could help with the potential for an isolated brief spin-up. The NAM and GFS have one helluva llvl jet...NAM probably overdone a bit but even the GFS has 30-35 knots! Link to comment Share on other sites More sharing options...
andyhb Posted September 6, 2012 Share Posted September 6, 2012 Rather nice amount of potential here, NAM/GFS both indicate a fair amount of directional shear in the lowest 3 km, with the NAM even indicating a sub 996 mb low helping to increase low level wind response, with both models indicating a nice influx of relatively high theta-e air from the southeast, enhancing low level cyclogenesis/deepening along with associated height falls (along with the solid upper/mid level height falls with the potent incoming trough). I think the NAM may be a bit overdone with the intensity of the sfc low, but given the rather strong upper dynamics, that could set the stage for an event of some sort (although tornado potential is quite reliant on the storm mode, which seems to currently trend towards a more linear based scenario). Spin ups along a possibly damaging squall line (if it can develop, that is), as mentioned, seem quite possible given rather strong low level helicity. As per usual, typical NE severe caveats apply, whether the lapse rates and/or instability (although the GFS/NAM suggest anywhere from 750-2000 J/kg of CAPE around peak heating, which would certainly be enough to support some activity) will be adequate for organized severe is probably the biggest (like it usually is). Also, as mentioned, the directional turning/veering with height isn't that great above H85 (owing to the trough's rather meridional orientation), which I'd like to see a bit more of. Will check the Euro momentarily. Link to comment Share on other sites More sharing options...
andyhb Posted September 6, 2012 Share Posted September 6, 2012 Is that a 987 mb low on the Euro at 72 hrs? Whoa... Hello there low level shear... Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 Is that a 987 mb low on the Euro at 72 hrs? Whoa... Hello there low level shear... Holy crap Link to comment Share on other sites More sharing options...
andyhb Posted September 6, 2012 Share Posted September 6, 2012 Euro says this is an absolute PHAIL Well from a general synoptics standpoint, it certainly doesn't now! Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 Not bad forecasted capes either Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 I wonder if we see a slight on the D3 for much of NY into extreme western SNE extending southward into portions of PA/NJ? Link to comment Share on other sites More sharing options...
andyhb Posted September 6, 2012 Share Posted September 6, 2012 I wonder if we see a slight on the D3 for much of NY into extreme western SNE extending southward into portions of PA/NJ? I could see this rather easily. Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 I could see this rather easily. I don't recall seeing too many setups like this in the past where we've seen some fairly hefty (for the time of year) Cape values to go along with very impressive shear. That euro setup is pretty intense as well. Link to comment Share on other sites More sharing options...
andyhb Posted September 6, 2012 Share Posted September 6, 2012 I'd change the title to "Severe Potential" based on tonight's model runs. Ukie: CMC is faster, but still fairly impressive: Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 What's also somewhat impressive is we have a very moist and rich theta-e airmass below 850mb while above that there is some dry air aloft which is great for helping to get some breaks of sun. Tonight's runs are certainly rather intriguing! Link to comment Share on other sites More sharing options...
weatherwiz Posted September 6, 2012 Author Share Posted September 6, 2012 Well the new day 3 has a SEE TEXT and mentions lack of instability. Link to comment Share on other sites More sharing options...
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