earthlight Posted September 16, 2012 Share Posted September 16, 2012 Yeah I would think this would be a case of widespread gusts of 30-40 outside of the squalls and then some severe gusts in the squalls themselves, just because of how strong the winds appear to be just off the surface. An isolated tor can't be ruled out. Yeah I agree. Instability is so limited on models so it's hard to get too excited about it despite the big time dynamics and talk of widespread wind damage from spc. I think a low topped line of convection could push through most of the Northern MA, though, and despite the poor timing there should still be a decent amount of strong winds mixing down to the surface. Link to comment Share on other sites More sharing options...
Quincy Posted September 16, 2012 Share Posted September 16, 2012 The wind threat looks more potent than last Saturday. New SREF came in with helicity values now over 500! for parts of NYS. Not to mention ML/LL winds are now looking stronger too. Link to comment Share on other sites More sharing options...
Weathergun Posted September 16, 2012 Share Posted September 16, 2012 12z GFS still has winds 50-55kts not far above the surface, 8pm Tues. over LGA . It won't take deep convection, to bring some of those winds down: Link to comment Share on other sites More sharing options...
bluewave Posted September 16, 2012 Share Posted September 16, 2012 I think that this may be the first time that I can remember the models showing LLJ wind speeds of 50-60 KT around 950-900 mb during a warm season convective event. The models are also showing some very high helicity values across the region. We may see WAA convection during the day Tuesday well out ahead of the main line. Any discrete convection will have to be monitored for rotation and possible isolated tornadoes. The models suggest that the there will be a forced squall line passage Tuesday evening or at night. With SST's of over 70 degrees, most of the 50-60 KT LLJ could mix down if the line holds together. There could be an embedded isolated tornado threat along the strongest part of the line. The model runs should be interesting of the next few days to help refine this high wind threat across the region. 4 km NAM afternoon WAA convection powerful LLJ with main line Link to comment Share on other sites More sharing options...
Superstorm93 Posted September 16, 2012 Share Posted September 16, 2012 Impressive feed from the EPAC as our storm takes shape... Link to comment Share on other sites More sharing options...
NorEaster27 Posted September 16, 2012 Share Posted September 16, 2012 The interaction of the LLJ and warm SSTs will need to be monitored, if we can mix the inversion out, a short fused HWW on the coast isnt impossible Link to comment Share on other sites More sharing options...
Hailstorm Posted September 16, 2012 Share Posted September 16, 2012 @bluewave: Thanks for those images. Did the overall trend of the 12z model suite today put us more into the warm sector with higher instability with the 250-300 mb jet punching through it with very high Gulf and Atlantic moisture? I don't have access to the models since I'm on mobile. Link to comment Share on other sites More sharing options...
forkyfork Posted September 16, 2012 Share Posted September 16, 2012 the euro shifts the best rains further east into our region and sped up fropa timing Link to comment Share on other sites More sharing options...
andyhb Posted September 16, 2012 Share Posted September 16, 2012 Impressive feed from the EPAC as our storm takes shape... That's always a good sign. Link to comment Share on other sites More sharing options...
Quincy Posted September 16, 2012 Share Posted September 16, 2012 the euro shifts the best rains further east into our region and sped up fropa timing bulk of FROPA moisture looks to come through 3z-6z per 6hrly ECMWF. Link to comment Share on other sites More sharing options...
WeatherFox Posted September 16, 2012 Share Posted September 16, 2012 0900 today SREF ensemble mean shows about 1" of rainfall for NYC with 2" numbers in central PA and NY. Link to comment Share on other sites More sharing options...
earthlight Posted September 16, 2012 Share Posted September 16, 2012 The SPC SREF has some pretty impressive parameters just glancing through the wind fields and low level shear...the 0-1km helicity is pretty impressive right ahead of the front. But the surface instability is very meager...the best instability is south of our area (and coincidentally away from the best kinematics). The "best case" scenario for severe weather/wind enthusiasts will probably be a low-topped squall line along the periphery of the 60kts of 0-6km bulk shear and juxtaposed with some weak instability at the surface. The image below is valid for 60 hours...timed with the best lift as the front comes through. Timing (as in time of day) is poor for severe wx...but you never know with these numbers. Link to comment Share on other sites More sharing options...
CT Rain Posted September 16, 2012 Share Posted September 16, 2012 I'm sort of meh on any squall line/NCFR potential. The best dynamics begin to lift out as fropa occurs and the timing is overnight. I think the more interesting possibility is more low topped supercells and a conditional tornado threat if we can generate some surface based instability. Also some damaging synoptic gusts possible if LLJ overperforms and we are able to mix down with steep low level lapse rates. Link to comment Share on other sites More sharing options...
earthlight Posted September 16, 2012 Share Posted September 16, 2012 I'm sort of meh on any squall line/NCFR potential. The best dynamics begin to lift out as fropa occurs and the timing is overnight. I think the more interesting possibility is more low topped supercells and a conditional tornado threat if we can generate some surface based instability. Also some damaging synoptic gusts possible if LLJ overperforms and we are able to mix down with steep low level lapse rates. Certainly a possibility. It's worth noting that we're once again dealing with a situation where the shortwave in association with the 500mb trough and best height falls is well off to the north and west...falling into some of the questions you presented above in respect to the development of a squall line or low topped type deal. The low topped supercell idea is interesting .. the SPC SREF has increased the surface instability a little bit but it still remains pretty meager (500 j/kg)...We'll see if that will suffice. The 50-60kt LLJ at 900-950mb is impressive. Link to comment Share on other sites More sharing options...
andyhb Posted September 16, 2012 Share Posted September 16, 2012 500-750 j/kg would likely be sufficient for some low topped action if the low level wind fields progged by guidance verify, IMO. Link to comment Share on other sites More sharing options...
CT Rain Posted September 16, 2012 Share Posted September 16, 2012 Certainly a possibility. It's worth noting that we're once again dealing with a situation where the shortwave in association with the 500mb trough and best height falls is well off to the north and west...falling into some of the questions you presented above in respect to the development of a squall line or low topped type deal. The low topped supercell idea is interesting .. the SPC SREF has increased the surface instability a little bit but it still remains pretty meager (500 j/kg)...We'll see if that will suffice. The 50-60kt LLJ at 900-950mb is impressive. Yeah the synoptic forcing does begin to decrease a bit but still sizable given the strengthening jet streak to our NW with us in the right entrance region. I noticed on the SREF plumes that dew points were struggling out of the mid 60s even for places like ISP. That won't cut it. The op NAM does get some 70+ td air in here. If we're looking at 74/66 stick a fork in any decent convection. 74/73 is a different story. 500-750 j/kg would likely be sufficient for some low topped action if the low level wind fields progged by guidance verify, IMO. Yeah if we can muster >500 j/kg of surface based CAPE then we certainly could see some low topped stuff. 0-1km shear is more impressive than last Saturday and LCLs are about as low. The issue IMO is the amount of moisture advection in the boundary layer. Link to comment Share on other sites More sharing options...
rcad1 Posted September 16, 2012 Share Posted September 16, 2012 Even without any severe weather were still looking at atleast a low end wind event right? I see upton says they will likely have to issue a wind adv atleast that's what the am disco said..... Link to comment Share on other sites More sharing options...
CT Rain Posted September 16, 2012 Share Posted September 16, 2012 Even without any severe weather were still looking at atleast a low end wind event right? I see upton says they will likely have to issue a wind adv atleast that's what the am disco said..... Possibly. LLJ magnitude will need to verify as modeled and not shift away from the tri-state or weaken much. In addition the boundary layer will need to remain mixed in order to transport some of that momentum down to the surface. Not a slam dunk. Link to comment Share on other sites More sharing options...
rcad1 Posted September 16, 2012 Share Posted September 16, 2012 I see moumt holly is saying they will prob have wind damage without gettimg any severe weather.. And the latest upton disco they say if the lattest models are right they will have to increase there forcasted wind speeds witch are 25-30 with gust to 40 but like you said thats if the models are right and dont change..... Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 16, 2012 Share Posted September 16, 2012 The trough is definitely a bit NW of my liking, similar to last Saturday. However, the trough is more amplified than the past one was, so I think we will be closer to the latitude of the best lift this time around than we were last Saturday. It's still a potential problem, though. Our SB CAPE for last Saturday's event was really high...it was >2000 J/KG in the NYC/LI areas. Our low-level lapse rates were also not too bad. I'm not sure we'll be able to generate those impressive surface parameters that we had last Saturday. However, the low-level wind fields are even more impressive...perhaps significantly so. But if the lapse rates near the surface are not that high, and the SB CAPE stays too low, then any updraft might get sheared apart. Link to comment Share on other sites More sharing options...
earthlight Posted September 16, 2012 Share Posted September 16, 2012 You can see the impressive low level jet on the 18z NAM as well as the surge of 70+ dew points directly ahead of the front. Also a cool 10m wind shift visible with strong southeast winds into the harbor ahead of it. Link to comment Share on other sites More sharing options...
SBUWX23 Posted September 17, 2012 Share Posted September 17, 2012 I dont see any inversion in this event during the time of max LLJ. Why would warm SST's bring an inversion like we see with similar systems in the winter/fall/spring? That needs to be monitored, because the way things look on soundings I have seen, the mixing will occur when the strongest winds are just above the deck. In fact, its dry adiabatic to the height of the max LLJ at 925 mb. Link to comment Share on other sites More sharing options...
CT Rain Posted September 17, 2012 Share Posted September 17, 2012 I dont see any inversion in this event during the time of max LLJ. Why would warm SST's bring an inversion like we see with similar systems in the winter/fall/spring? That needs to be monitored, because the way things look on soundings I have seen, the mixing will occur when the strongest winds are just above the deck. In fact, its dry adiabatic to the height of the max LLJ at 925 mb. Yeah that's just the thing. There's a short window around here climatologically when we can develop surface based instability/maintain steep low level lapse rates during strong southerly LLJs. Link to comment Share on other sites More sharing options...
earthlight Posted September 17, 2012 Share Posted September 17, 2012 Link to comment Share on other sites More sharing options...
uofmiami Posted September 17, 2012 Share Posted September 17, 2012 High Wind Watch perhaps if the NAM is right at all based on that map. Link to comment Share on other sites More sharing options...
earthlight Posted September 17, 2012 Share Posted September 17, 2012 ...NY/WRN NEW ENGLAND TO NERN GULF COAST... NARROW LINE OF CONVECTION SHOULD DEVELOP EARLY IN PERIOD AND CROSS MID-ATLC AND CENTRAL PIEDMONT REGIONS...WITH DAMAGING WIND BEING PRIMARY THREAT. A FEW TORNADOES ALSO ARE POSSIBLE. AT START OF PERIOD...MORE THAN ONE BAND OR CLUSTER OF TSTMS MAY BE ONGOING...MOST LIKELY OVER SRN APPALACHIANS REGION AND OVER ERN OH/WRN PA AREA. AS EACH MOVES INTO PROGRESSIVELY HIGHER-THETAE AIR MASS...SVR POTENTIAL WILL INCREASE...WHILE EVOLUTION OF MORE UNIFIED SQUALL LINE IS EXPECTED. FLOW ALOFT WILL BE MOSTLY PARALLEL TO CONVECTIVE FORCING...INDICATING RAPID DEVELOPMENT OF LINEAR MODE THAT WOULD BE MAINTAINED THROUGH PERIOD. OVER MID-ATLC REGION...SFC LOW SHOULD LIFT NEWD FAST ENOUGH TO OUTPACE NWD EXTENT OF FAVORABLE DESTABILIZATION. BEFORE THAT HAPPENS...HOWEVER...RELATED ISALLOBARIC FORCING AND BACKING OF LOW-LEVEL FLOW TO ITS E SHOULD AFFECT NRN FRINGE OF AT LEAST MRGLLY UNSTABLE AIR DURING DAY...BENEATH 50-65 KT LLJ. THIS WOULD ENLARGE LOW-LEVEL HODOGRAPHS FAVORABLY FOR SUPERCELL/TORNADO POTENTIAL WITH ANY DISCRETE/SUSTAINED CELLS THAT CAN FORM AHEAD OF MAIN LINE...AND QLCS TORNADO THREAT WHERE SQUALL LINE ENCOUNTERS UNSTABLE AND SFC-BASED EFFECTIVE INFLOW PARCELS. BUOYANCY WILL DIMINISH WITH NWD EXTENT AMIDST WEAK MIDLEVEL LAPSE RATES. FCST SOUNDINGS SUGGEST MLCAPE RANGING FROM AROUND 1000 J/KG OVER ATLC COASTAL DELMARVA TO LESS THAN 100 J/KG OVER ERN NY. STILL...NEAR-NEUTRAL TO VERY SLIGHTLY UNSTABLE THERMODYNAMIC PROFILES MAY BE SUFFICIENT TO SUPPORT CONDITIONAL WIND POTENTIAL OVER PARTS OF ERN NY AND WRN NEW ENGLAND...GIVEN STRENGTH OF AMBIENT/DEEP-LAYER FLOW. HODOGRAPHS SHOULD DIMINISH IN SIZE WITH SWWD EXTENT AS LLJ GETS WEAKER AND SFC WINDS ARE RELATIVELY VEERED. HOWEVER...GREATER BUOYANCY IS EXPECTED OVER VA/CAROLINAS...GIVEN RICHER LOW-LEVEL MOISTURE AND MORE TIME FOR CLOUD-MUTED SFC DIABATIC HEATING IN ADVANCE OF MAIN TSTM BAND. MEANWHILE...SERN RIM OF FAVORABLE DEEP-LAYER FLOW/SHEAR WILL OVERSPREAD WRN FRINGES OF WARM SECTOR...CONTRIBUTING TO SVR POTENTIAL. HOWEVER...WITH SWWD EXTENT...THREAT WILL BECOME MORE TRANSIENT AND CONDITIONAL...AS STRONGEST DEEP-LAYER ASCENT AND ISALLOBARIC FORCING PULL AWAY FROM THOSE PORTIONS MS/AL/FL PANHANDLE ALONG/AHEAD OF FRONT. Link to comment Share on other sites More sharing options...
Hailstorm Posted September 17, 2012 Share Posted September 17, 2012 Meh, I thought the SPC would have added a hatch to most of the 30% risk area in this new outlook. Link to comment Share on other sites More sharing options...
Jefflaw77 Posted September 17, 2012 Share Posted September 17, 2012 This morning's water vapor loop looks rather impressive.. With a storm system in the lower tier of the states w/ a vigoreous shortwave diving south, It looks like something big may come together... Like in yester years.... Link to comment Share on other sites More sharing options...
NorEaster27 Posted September 17, 2012 Share Posted September 17, 2012 NAM still brings dews into the lower 70s which seems too agressive....if we dont get dews into the 70s its going to be harder to get the good winds to mix down. Currently 70 dews are confined to the gulf coast, we are going to need some serious WAA to get those this far north. Link to comment Share on other sites More sharing options...
Stebo Posted September 17, 2012 Share Posted September 17, 2012 NAM still brings dews into the lower 70s which seems too agressive....if we dont get dews into the 70s its going to be harder to get the good winds to mix down. Currently 70 dews are confined to the gulf coast, we are going to need some serious WAA to get those this far north. The moisture advection will occur with the strong LLJ progged with this system, you should have no problem getting to 70 degree dew points. Plus you have mid to upper 60 degree dews all the way to Southern IL. Link to comment Share on other sites More sharing options...
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