weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 well with low-level helicity less than 200...I don't typically think tornadoes. 0-1 km helicity is 171 on the NAMM at 00z in HFD. 0-1km shear is 30-35 kt...that's pretty significant.. Do you think the helicity will stronger than what is modeled by the GFS and the NAM if the synoptic depiction remains the same? From what I've seen in the past and from reading things on SNE severe, for SNE once you get above 150 0-1km helicity that is pretty damn decent. Link to comment Share on other sites More sharing options...
OSUmetstud Posted May 30, 2011 Share Posted May 30, 2011 Quite possibly... it's impossible for the models to try to resolve mesoscale features that will modulate the boundary layer flow. I've found more often than not you see the winds backed a bit more than modeled (resulting in much higher helicity) with this kind of setup. You'll see the models print out what seems relatively modest shear and then you'll see the SPC analysis with much higher shear owing to a much more backed sfc wind than the coarse resolution models printed out. Seeing 2000 j/kg of CAPE with 0-1km helicity >150 on the GFS in CT is very impressive. From what I've seen in the past and from reading things on SNE severe, for SNE once you get above 150 0-1km helicity that is pretty damn decent. fair enough..when Ryan is thinking tornadic potential and I'm not...maybe I should reconsider. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 fair enough..when Ryan is thinking tornadic potential and I'm not...maybe I should reconsider. Obviously if you want the potential for stronger tornadoes you want higher amounts of helicity but 150-200 is plenty good for weaker tornadoes (EF0 and EF1 types)...perhaps EF2 possible is instability is great. Around here though when we get thsse higher helicity values usually we are drawing in an incredible amount of marine contaminated air due to the backed flow...especially if the low-level flow is backed SE. This is why you want to see SSW to SW winds at the sfc turning to the NW as you go aloft (hence why NW flow events tend to be the kings here if the setup is right). Link to comment Share on other sites More sharing options...
nzucker Posted May 30, 2011 Share Posted May 30, 2011 Obviously if you want the potential for stronger tornadoes you want higher amounts of helicity but 150-200 is plenty good for weaker tornadoes (EF0 and EF1 types)...perhaps EF2 possible is instability is great. Around here though when we get thsse higher helicity values usually we are drawing in an incredible amount of marine contaminated air due to the backed flow...especially if the low-level flow is backed SE. This is why you want to see SSW to SW winds at the sfc turning to the NW as you go aloft (hence why NW flow events tend to be the kings here if the setup is right). I think I'm fine with weaker tornadoes...don't need another Joplin in our region. I've never seen a twister and wouldn't mind witnessing an EF0 rope in the distance, but I'll pass on the destructive ones. I also get worried about the vegetable garden when we have severe weather since hail can really do a number on the plants, especially when they're younger like right now. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 I forgot to mention this earlier but I was just reading BOX AFD and they mentioned there could be alot of dry air working in through the mid-levels on Wednesday...this could kill things too, saw this on a few of the soundings. Link to comment Share on other sites More sharing options...
Guvna Posted May 30, 2011 Share Posted May 30, 2011 I forgot to mention this earlier but I was just reading BOX AFD and they mentioned there could be alot of dry air working in through the mid-levels on Wednesday...this could kill things too, saw this on a few of the soundings. This is SNE......does that surprise you? If we were to get any sig severe...it seems this would be the year. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 This is SNE......does that surprise you? If we were to get any sig severe...it seems this would be the year. Something is probably going to prevent this from being a major outbreak Link to comment Share on other sites More sharing options...
Chrisrotary12 Posted May 30, 2011 Share Posted May 30, 2011 Something is probably going to prevent this from being a major outbreak Well I live inside 495, I have no hope. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 The 0z NAM keeps the strongest instability to the west of SNE. Link to comment Share on other sites More sharing options...
OSUmetstud Posted May 30, 2011 Share Posted May 30, 2011 I forgot to mention this earlier but I was just reading BOX AFD and they mentioned there could be alot of dry air working in through the mid-levels on Wednesday...this could kill things too, saw this on a few of the soundings. well mid-level dry air and an EML go hand in hand....can't have one without the other. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 well mid-level dry air and an EML go hand in hand....can't have one without the other. Yeah that's true. This is what the 18z NAM showed working in...this is some location in northern CT. Might be associated with the EML that was working in but looking at the temperatures associated with it perhaps the full fledged strength of the EML will be weakening...the ML lapse rates really aren't as steep as they usually are with a more "true EML". Link to comment Share on other sites More sharing options...
radarman Posted May 30, 2011 Share Posted May 30, 2011 I'm sure someone's mentioned it in this thread already, but for whatever reason the May 31st/June 1st timeframe has been unusually productive around here in terms of severe wx. The strongest winds I've ever experienced here were May 31st 2008, which I'd estimate at 75+. So we have that going for us... which is nice. Will or someone mentioned the fine line between cheering for some CINH, but not too much. If anyone is chasing, they might be better off if only one or two storms go.... Also the 00z NAM is now hinting at some morning precip for Western MA... Might be the kiss of death. Generally it winds up being a nowcast thing, see how early you can clear out and destablize again. South and East show no real contamination. Cursury glance 00z looks a tiny bit faster, and a hair further south at H5 than 12z. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 I'm sure someone's mentioned it in this thread already, but for whatever reason the May 31st/June 1st timeframe has been unusually productive around here in terms of severe wx. The strongest winds I've ever experienced here were May 31st 2008, which I'd estimate at 75+. So we have that going for us... which is nice. Will or someone mentioned the fine line between cheering for some CINH, but not too much. If anyone is chasing, they might be better off if only one or two storms go.... Also the 00z NAM is now hinting at some morning precip for Western MA... Might be the kiss of death. Generally it winds up being a nowcast thing, see how early you can clear out and destablize again. South and East show no real contamination. Cursury glance 00z looks a tiny bit faster, and a hair further south at H5 than 12z. Yeah it shows some sort of vort max going through in the AM causing morning precip crap and we really don't begin destabilizing to much later in the morning/afternoon and our instability potential gets limited. We'll see how this works out...probably won't know until Wednesday morning itself. Link to comment Share on other sites More sharing options...
CT Rain Posted May 30, 2011 Share Posted May 30, 2011 FWIW I'm even more confident tomorrow pm winds up convection free given the s/w ridging that will take place behind this MCV through most of tomorrow. That when coupled with the SE ridge flexing its muscle and heights kicking up a bit during the day I think the threat for convection in the PM is pretty low. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 FWIW I'm even more confident tomorrow pm winds up convection free given the s/w ridging that will take place behind this MCV through most of tomorrow. That when coupled with the SE ridge flexing its muscle and heights kicking up a bit during the day I think the threat for convection in the PM is pretty low. I just want to flash forward to Wednesday. Link to comment Share on other sites More sharing options...
CT Rain Posted May 30, 2011 Share Posted May 30, 2011 I'm excited for a vortex95 post lol Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 I'm excited for a vortex95 post lol If it's finished by Wednesday Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 Some of the hodos are actually even more impressive on the 0z NAM. Link to comment Share on other sites More sharing options...
radarman Posted May 30, 2011 Share Posted May 30, 2011 Yeah it shows some sort of vort max going through in the AM causing morning precip crap and we really don't begin destabilizing to much later in the morning/afternoon and our instability potential gets limited. We'll see how this works out...probably won't know until Wednesday morning itself. The early morning garbage convection might be limited to Berkshire and Litchfield counties, which would be ideal for us in the valley. Might even lay kick out a boundary for us. I think you have a better chance of staying contamination free than I do, but on the whole I'd sign for something like the NAM. Trended the right way, albeit slightly. Also looks a little more consolidated. Link to comment Share on other sites More sharing options...
ORH_wxman Posted May 30, 2011 Share Posted May 30, 2011 I'm sure someone's mentioned it in this thread already, but for whatever reason the May 31st/June 1st timeframe has been unusually productive around here in terms of severe wx. The strongest winds I've ever experienced here were May 31st 2008, which I'd estimate at 75+. So we have that going for us... which is nice. Will or someone mentioned the fine line between cheering for some CINH, but not too much. If anyone is chasing, they might be better off if only one or two storms go.... Also the 00z NAM is now hinting at some morning precip for Western MA... Might be the kiss of death. Generally it winds up being a nowcast thing, see how early you can clear out and destablize again. South and East show no real contamination. Cursury glance 00z looks a tiny bit faster, and a hair further south at H5 than 12z. May 31, 1998 had the 100mph macroburst here. Still the best severe event I've ever experienced up here. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 The ML lapse rates aren't as impressive though on the NAM as past runs, only just above 6 C/KM...that's still pretty decent but they aren't the 6.5-7 C/KM we were seeing before. This could make morning crap hurt even worse. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 Wow...some of these hodographs are REALLY impressive. Link to comment Share on other sites More sharing options...
ORH_wxman Posted May 30, 2011 Share Posted May 30, 2011 The ML lapse rates aren't as impressive though on the NAM as past runs, only just above 6 C/KM...that's still pretty decent but they aren't the 6.5-7 C/KM we were seeing before. This could make morning crap hurt even worse. This is one of the things I was concerned about as we got closer. The models will often be over zealous in getting an EML in here, but it often will get washed out in W NY, OH or eastern Lakes. Link to comment Share on other sites More sharing options...
radarman Posted May 30, 2011 Share Posted May 30, 2011 May 31, 1998 had the 100mph macroburst here. Still the best severe event I've ever experienced up here. That's just incredible. Was that an airport anemometer measurement? Also, it's interesting that all the documentation I can find on the May 31st '98 Derecho say it ended in New York- Did the squall line weaken and discrete cells form out ahead or something? Just wondering how ORH can hit 100+, but get no mention in the Derecho pages. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 This is one of the things I was concerned about as we got closer. The models will often be over zealous in getting an EML in here, but it often will get washed out in W NY, OH or eastern Lakes. That's exactly what looks like is happening, the temperatures associated with it cool a bit but the air is still pretty damn dry. Link to comment Share on other sites More sharing options...
vortex95 Posted May 30, 2011 Share Posted May 30, 2011 The EML is so important..it's probably at least a little bit coincidental...but in recent years, every time we have a decent EML present we get a good a severe weather event. It's slightly concerning to see the models worsening the lapse rates between 00 and 18z Wednesday...but the setup is still good. We have a great thermodynamic environment and seemingly just the right amount of shear. Absolutely correct...EML is the key. It does two things...one, it allows CAPE to get higher than if it did not exist due to the cap, and two, since you have a cap, this keeps convection isolated so supercells are more likely. From a NAM re-run of 6/9/53, it showed CAPE exceeding 4000 in SNE around 18z. The other thing about this kind of set up is the W to NW flow minimizes the marine influence. The more northerly the flow, the better, so even south coastal areas can get hit very hard (re: 7/10/89...I tried to vain to catch the Waterbury/HVN monster HP supercell that day coming from MA but it was moving just too fast!). Looking at the 00z NAM, timing of it all looks good, but CAPEs are not as high as I would like to see them. However, the low level winds fields/shear are excellent. 40 kts at 700mb, 35kts at 850mb, and 30-40 kts at 925mb 02/00z. 0-1 km helicities are 200. The turning/speeds of the winds at the low levels are most important for tornadic storms. We're talking just the lowest km or two here. Looks like 60-70 deg of turning between the sfc and 500mb wind directions, but the best turning is below 850mb. When push comes to shove for sig svr, shear is paramount. You don't need a lot of CAPE for tornadoes, as long as the shear is there. CAPE is only half the picture for updraft strength. A rotating updraft (meso) effectively doubles the updraft acceleration potential due to dynamically induced vertical pressure perturbations, greatly increasing the probability of svr wx. Now for violent tornadoes, you usually need a high CAPE/ high shear environment. Note I say *usually* b/c there are always exceptions on both ends of the spectrum (RDU 11/28/88 at one end and Plainfield IL 8/28/90 on the other). Link to comment Share on other sites More sharing options...
ORH_wxman Posted May 30, 2011 Share Posted May 30, 2011 That's just incredible. Was that an airport anemometer measurement? Also, it's interesting that all the documentation I can find on the May 31st '98 Derecho say it ended in New York- Did the squall line weaken and discrete cells form out ahead or something? Just wondering how ORH can hit 100+, but get no mention in the Derecho pages. I don't think it was the same thing that hit NY and the Great Lakes. The ORH macroburst was a line of storms if I recall correctly that was maybe 30-40 miles N to S...covered most of the county, but the most intense part was in the middle. It was much smaller in coverage than the derecho. I found this on google from an old skywarn letter: Severe Storms Struck Southern New England - Summer of 1998 Due to space considerations, we cannot go into great detail about these storms, but in the summer of 1998, three storms stand out from the rest. On May 31, 1998 a very intense macroburst stretched across Worcester County from North Brookfield through Spencer, Leicester, Worcester, Shrewsbury, and Grafton. A wind gust to 104 mph was clocked at Holy Cross College in Worcester (elev. 750 ft.) and a peak gust to 94 mph was recorded by the ASOS at Worcester Airport. A tornado warning was issued for this storm, which helped heighten the awareness as to the intensity of the storm. A tornado was confirmed on that day in Antrim, NH, which is in Hillsborough County. It was determined to be a F2 tornado (on a damage scale of 0 to 5) that was 85 yards wide and 0.5 miles in path length. A Severe Thunderstorm Warning was upgraded to a Tornado Warning for this storm before any reports of a tornado were received. One family in Antrim said they saw the Tornado Warning on the red scrolling screen on The Weather Channel...saw that it said Antrim...and then the tornado struck a couple of minutes later, when they were in their basement! The third big event was on June 30, 1998 when baseball size hail (2.75 inches in diameter) was observed in Richmond, RI !!! This storm went on to produce a 75-85 mph microburst in Fairhaven, MA. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 Looks like the ML lapse rates actually decrease throughout the day a bit...that would cut back on the instability numbers as well. Link to comment Share on other sites More sharing options...
weatherwiz Posted May 30, 2011 Share Posted May 30, 2011 This is very nice Link to comment Share on other sites More sharing options...
radarman Posted May 30, 2011 Share Posted May 30, 2011 May 31st 1987 also produced 90+mph gusts at ORH. Seems like June 1st not so much. Oh well. Link to comment Share on other sites More sharing options...
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