earthlight Posted September 18, 2012 Share Posted September 18, 2012 For the general probability forecast from the SPC, I agree with you. But I do think the tornado threat is increasing as well for S NJ and into the NYC Metro/western LI areas in the post 18z period through maybe 21 or 22z? It will be interesting to watch unfold. Obviously the rain/convection earlier in the day will be a major player as well. To back up your point, here is the 4km NAM showing 1200 or so j/kg of surface based cape over NYC and points south tomorrow afternoon. ...and check out the 900 hPa winds just a few hours later. http://www.weatherbellmodels.com/weather/hires/2012091800/nyc/hires_uv900_slp_nyc_23.png Link to comment Share on other sites More sharing options...
Superstorm93 Posted September 18, 2012 Share Posted September 18, 2012 3/13/10 is probably one of my favorite spring storms over the past six years. Just insane how long the wind stayed over 40mph (to kind of give a howling or roar effect) Link to comment Share on other sites More sharing options...
SBUWX23 Posted September 18, 2012 Share Posted September 18, 2012 It doesnt matter what happens in the afternoon. The higher instability could ADVECT northward even if it pours all day long in this set up. Link to comment Share on other sites More sharing options...
tmagan Posted September 18, 2012 Share Posted September 18, 2012 KLGA RAP forecast sounding for 20Z Tuesday. Link to comment Share on other sites More sharing options...
earthlight Posted September 18, 2012 Share Posted September 18, 2012 It doesnt matter what happens in the afternoon. The higher instability could ADVECT northward even if it pours all day long in this set up. Not sure I totally get what you're saying, but generally it's not a good idea to expect surface based instability to "advect" into pouring rain. The NAM shows some better surface based instability farther north because it shows some clearing of the high and mid level cloud deck in the warm sector with southerly winds. Which is certainly a possibility. Such an occurance could help develop a localized tornado threat from South-Central NJ on northward to Northern NJ and the NYC area. Link to comment Share on other sites More sharing options...
SBUWX23 Posted September 18, 2012 Share Posted September 18, 2012 The LLJ could innfluence the advection of higher lapse rate and thus more instability with low level moisture etc to the area. I just think the notion well its cloudy and raining, welp no instability, is not accurate. Its not only a factor of heating. Obviously the NAM is not seeing it just being heating if theres still 750 to 1000 J/kg of SBCAPE over Long island at 11pm at night. Actually, it increase SBCAPE AFTER DARK. Not sure I totally get what you're saying, but generally it's not a good idea to expect surface based instability to "advect" into pouring rain. The NAM shows some better surface based instability farther north because it shows some clearing of the high and mid level cloud deck in the warm sector with southerly winds. Which is certainly a possibility. Such an occurance could help develop a localized tornado threat from South-Central NJ on northward to Northern NJ and the NYC area. Link to comment Share on other sites More sharing options...
earthlight Posted September 18, 2012 Share Posted September 18, 2012 The LLJ could innfluence the advection of higher lapse rate and thus more instability with low level moisture etc to the area. I just think the notion well its cloudy and raining, welp no instability, is not accurate. Its not only a factor of heating. Obviously the NAM is not seeing it just being heating if theres still 750 to 1000 J/kg of SBCAPE over Long island at 11pm at night. Actually, it increase SBCAPE AFTER DARK. Yeah I agree essentially. But the mid-day convection/rain can be important for a multitude of reasons regardless of the surface based instability. On the contrary to your point, I usually find that the NAM can often overdo the surface based instability development in this type of situation where the low level jet starts to crank in the warm sector and you're working through the lapse rates. I think the 1000+ j/kg amounts on the higher resolution NAM/WRF may be a product of the destbilization through moisture advection as well as some heating. I'll be interested to see if the NAM is too high with the parameters tonight. Regardless of all of this, if these values come to fruition (750+j/kg of surface based instability)...you have to wonder if a localized tornado threat could eventually develop over Southern NJ and move north towards Central NJ and NYC. Just perusing through the NAM soundings and boundary layer to mid level data, there seems to be a signal for some enhanced low level convergence and shear that could help develop either discrete supercells capable of spinups or embedded ones which could offer the same potential. On top of all of this, the higher resolution data has near-70kt 900 hPa winds over Western LI at 23z. Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 18, 2012 Share Posted September 18, 2012 Yeah, the NAM might be overdoing the SB CAPE a tad as it has in these setups in the past...it has "advected" too much CAPE in these types of setups in the past. But the LLJ here is just so strong that previous model convention might have to be thrown out the window. On the 8th, there was actually a bit more SB CAPE than what was originally forecast, perhaps because the LLJ then was also pretty strong. I do think that clearing can be the difference between 750-1000 J/KG of SB CAPE and 1000-1500 J/KG of SB CAPE, and that might make a difference. I'm also not sure if at this point there is going to be a "gap" in the tornado threat in between the Delmarva/DC areas and Southern NJ, or if it will be a general narrow circle from the Delmarva areas near DC up through NJ and NYC/western LI. I'd almost kind of rather have two "separate" tornado areas as opposed to hoping that the individual cells from the Delmarva make it all the way up here. Though I guess regardless, there can be separate areas of convective initiation within a tornado threat area without there being a gap per-se. I'm probably just rambling a bit now. Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 18, 2012 Share Posted September 18, 2012 Regardless of all of this, if these values come to fruition (750+j/kg of surface based instability)...you have to wonder if a localized tornado threat could eventually develop over Southern NJ and move north towards Central NJ and NYC. Just perusing through the NAM soundings and boundary layer to mid level data, there seems to be a signal for some enhanced low level convergence and shear that could help develop either discrete supercells capable of spinups or embedded ones which could offer the same potential. On top of all of this, the higher resolution data has near-70kt 900 hPa winds over Western LI at 23z. This might also help with the lift...locally enhanced low-level vorticity...I guess that probably ties into the enhanced low-level convergence. Link to comment Share on other sites More sharing options...
WE GOT HIM Posted September 18, 2012 Share Posted September 18, 2012 Dew point is exploding upward (up almost 13 degrees in 6 hours) Link to comment Share on other sites More sharing options...
Hailstorm Posted September 18, 2012 Share Posted September 18, 2012 The new SPC Day 1 outlook has a large 10% tornado risk area. I wouldn't be surprised if later outlooks would upgrade us to a moderate risk solely based on a small 5% increase in tornado probabilities instead of damaging wind probabilities. Link to comment Share on other sites More sharing options...
rcad1 Posted September 18, 2012 Share Posted September 18, 2012 Upton changed the high wimd watch to a an adv that sucks thoight they woild go with a warning.. Link to comment Share on other sites More sharing options...
NaoPos Posted September 18, 2012 Share Posted September 18, 2012 Wonder what type of clearing, if any, we can see with this highlighted area? Something to keep an eye on as daylight breaks.. Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 18, 2012 Share Posted September 18, 2012 Here are my thoughts: http://www.nymetroweather.com/2012/09/18/severe-weather-threat-with-tornadoes-possible-today/ Link to comment Share on other sites More sharing options...
Hailstorm Posted September 18, 2012 Share Posted September 18, 2012 Upton changed the high wimd watch to a an adv that sucks thoight they woild go with a warning.. I think it has to do more with the fact that a different NWS meteorologist updated our forecast grids and AFD this morning versus the one who did it yesterday afternoon. The AFD for this morning is way less bullish for some reason despite the overnight models being more bullish for our area. Link to comment Share on other sites More sharing options...
NaoPos Posted September 18, 2012 Share Posted September 18, 2012 Better watch them storms down in south jersey.. It's almost déjà vu from the last event. Link to comment Share on other sites More sharing options...
jdt Posted September 18, 2012 Share Posted September 18, 2012 In the office near Round Valley Reservior, Hunterdon County. Early rain has cleared reveling a very low fast turbulent sky. A lot of wind energy sitting right above the surface. The sky just has that look that a few tornados will occur a little later. Link to comment Share on other sites More sharing options...
NorEaster27 Posted September 18, 2012 Share Posted September 18, 2012 winds already starting to rip on the coast, JFK almost gusting to 30 now. Link to comment Share on other sites More sharing options...
Stormlover74 Posted September 18, 2012 Share Posted September 18, 2012 Line of heavy rain/storms are headed right for the area from the south Link to comment Share on other sites More sharing options...
Weathergun Posted September 18, 2012 Share Posted September 18, 2012 Line of heavy rain/storms are headed right for the area from the south Needs to be watched. SBCAPE increases to in near 500 J/kg to along NJ and LI shore. Link to comment Share on other sites More sharing options...
tmagan Posted September 18, 2012 Share Posted September 18, 2012 Would be a good day for 18Z soundings. Link to comment Share on other sites More sharing options...
tmagan Posted September 18, 2012 Share Posted September 18, 2012 12Z Soundings KOKX KIAD Link to comment Share on other sites More sharing options...
NorEaster27 Posted September 18, 2012 Share Posted September 18, 2012 storms developing along jersey shore, however dews are not what they were 2 saturdays ago Link to comment Share on other sites More sharing options...
SmokeEater Posted September 18, 2012 Share Posted September 18, 2012 storms developing along jersey shore, however dews are not what they were 2 saturdays ago It's 73/73 down here in South Jersey, and most places up around NYC are in the high 60's, not exactly low DP's. Link to comment Share on other sites More sharing options...
Weathergun Posted September 18, 2012 Share Posted September 18, 2012 The 12z OKX sounding, has 6.4 C/km sfc-3km lapse rate. That's pretty high for 8am. Link to comment Share on other sites More sharing options...
NorEaster27 Posted September 18, 2012 Share Posted September 18, 2012 It's 73/73 down here in South Jersey, and most places up around NYC are in the high 60's, not exactly low DP's. yes but during the last event dews were in the mid 70s, it makes a pretty big difference. Link to comment Share on other sites More sharing options...
NorEaster27 Posted September 18, 2012 Share Posted September 18, 2012 JFK already gusting to near 40 mph Link to comment Share on other sites More sharing options...
bluewave Posted September 18, 2012 Share Posted September 18, 2012 JFK already gusting to near 40 mph Pretty decent LLJ developing already this morning from the JFK TDWR. Link to comment Share on other sites More sharing options...
MJO812 Posted September 18, 2012 Share Posted September 18, 2012 JFK already gusting to near 40 mph Yep, getting pretty windy here also. Going to be an interesting day. Link to comment Share on other sites More sharing options...
IsentropicLift Posted September 18, 2012 Share Posted September 18, 2012 Very impressed so far this morning with the intensity of the convection over NE NJ. It may not look like much on radar but it's effectively mixing the stronger winds down to the surface. I keep oscillating back and forth between a heavy, blinding, wind swept rain and a light drizzle with little or no wind. Link to comment Share on other sites More sharing options...
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