bluewave Posted September 27, 2012 Share Posted September 27, 2012 While the instability forecast for Friday morning is going to be on the weak side, we have seen these morning warm frontal passages perform above what we might expect. We will see a strong LLJ and a low closing off to our west. It also looks like the NAM is trying to create a coupled upper jet region near us with the split flow. At the very least, we may just have some heavy thunderstorms to track in the morning into the early afternoon. Link to comment Share on other sites More sharing options...
earthlight Posted September 27, 2012 Share Posted September 27, 2012 Nice thread bwave and I agree with your ideas. If the near term guidance is correct there could be an isolated severe weather threat along the warm front and in the (very) small warm sector to the south and east of the surface low tomorrow. The SPC SREF mean is indicative of good low level shear with 0-1km helicity over 250-300 m2/s2 in Northern NJ, Northeast PA, and Southeast New York. These parameters are also positioned favorably on the nose of the low level jet and increasing surface based instability...with the SREF mean SBCAPE over 1000 j/kg in Central NJ (closer to 750j/kg near Northern NJ and 500 j/kg or less north of there). We'll once again be dealing with poor lapse rates but dynamically this system is actually fairly strong over a small area...with a juxtaposition of favorable low level shear and some surface instability coincidentally in the NYC Area as well as Central/Northern NJ..and to a lesser extent Southeast NY and Western New England (with much more meager surface based instability there despite favorable dynamics). It will be interesting to see if we can get any strong storms developing along the warm front tomorrow or southeast of the surface low in this environment..I would imagine the updrafts would be somewhat weak but could produce some low level spinups. Link to comment Share on other sites More sharing options...
bluewave Posted September 27, 2012 Author Share Posted September 27, 2012 ^^^^ Very nice post, Earthlight. We have even seen some isolated low level spin ups in the past with high helicity values and mostly elevated instability along morning to early afternoon warm fronts. It's usually a wait and see situation with what the radar actually looks like tomorrow morning into the early afternoon. The 4km NAM was also hinting at some possible training of cells and heavy rain potential. Link to comment Share on other sites More sharing options...
earthlight Posted September 27, 2012 Share Posted September 27, 2012 ^^^^ Very nice post, Earthlight. We have even seen some isolated low level spin ups in the past with high helicity values and mostly elevated instability along morning to early afternoon warm fronts. It's usually a wait and see situation with what the radar actually looks like tomorrow morning into the early afternoon. The 4km NAM was also hinting at some possible training of cells and heavy rain potential. Definitely. The one caution flag I would throw up is that the NAM and SREF have been just a little too robust with surface based instability in these types of events the last few occurrences. But even with slightly undercut instability parameters, the synoptic scale set up still argues for potential isolated strong storms and a weak tornado or two from the NJ Shore to Long Island/NYC and maybe Northern NJ. Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 27, 2012 Share Posted September 27, 2012 You don't really need the steep lapse rates for isolated low level spin ups in this area...if the SB CAPE can get up to what is modeled, the updrafts should be robust enough to not get sheared off by the low level shear and helicity. Link to comment Share on other sites More sharing options...
BxEngine Posted September 27, 2012 Share Posted September 27, 2012 Just hit this system driving through eastern Ohio....honestly some of the heaviest rains Ive ever seen. Curious to see if that translates to our area at all. Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 27, 2012 Share Posted September 27, 2012 It might be hard to actually advect the good SB CAPE values into the high helicity values. There is going to be a VERY SMALL area, if any, where the two are actually juxtaposed. As we saw a couple of weeks ago, 500-750 J/KG of SB CAPE is usually not enough. We had really high SB CAPE values for the September 8th tornado event, however. Link to comment Share on other sites More sharing options...
Dsnowx53 Posted September 27, 2012 Share Posted September 27, 2012 NAM JFK sounding for 15z. Nice very low-level lapse rates which should help updrafts stay somewhat robust...nearly 1000 J/KG of SB CAPE, which is borderline but okay...and aiding from the lapse rates might help a tad more. Nearly 150 m^2/s^2 of 0-1km helicity, which is also good. Considering how putrid the lapse rates are past like 900mb, the 0-3km helicity doesn't really matter since updrafts are not getting up that high. As John said, though, the NAM has often overdone the SB CAPE in these setups, which would instantly put a dent on things. If the SB CAPE is not what is modeled, we're really going to need to get those steeper lapse rates/"mixed" layer up to the full 1km to fully utilize the helicity in place. Link to comment Share on other sites More sharing options...
earthlight Posted September 28, 2012 Share Posted September 28, 2012 As hinted at earlier, the SPC SREF decreased surface based instability by 300 or more j/kg across the board for Friday afternoon. It could be argued that the best juxtaposition of low level shear and instability occurs around 12-15z. The 0-1km helicity parameters are extremely robust from 12 to 15z over much of New Jersey and Southeast New York...but the instability doesn't really spike until after that point. A noticeable disconnect between the two..likely owing to both the time of day and the timing of the LLJ. This...combined with the lacking deep layer shear profiles should really mitigate the threat for severe weather Friday. Still..I think there is an outside chance of a spinup or some strong wind gusts. Link to comment Share on other sites More sharing options...
earthlight Posted September 28, 2012 Share Posted September 28, 2012 SPC WRF has a strong storm in Northeast NJ/Just west of NYC at 15z near the front..with isolated activity prior to that. Other storms develop in the warm sector in Eastern New Jersey at 18z as well. Link to comment Share on other sites More sharing options...
Sundog Posted September 28, 2012 Share Posted September 28, 2012 I got a ton of rain from a very slow moving cell around 4 AMish. Link to comment Share on other sites More sharing options...
uncle W Posted September 28, 2012 Share Posted September 28, 2012 the radar this morning looks like yesterdays predicted precip map...Not bad at all... Link to comment Share on other sites More sharing options...
Weathergun Posted September 28, 2012 Share Posted September 28, 2012 I got a ton of rain from a very slow moving cell around 4 AMish. I got that too. Looks more heavy showers are forming over NYC. Link to comment Share on other sites More sharing options...
ag3 Posted September 28, 2012 Share Posted September 28, 2012 LGA reported about .40" in that 1 hour heavy shower earlier. Looks like another heavy rain shower popped up right over NYC. Link to comment Share on other sites More sharing options...
bluewave Posted September 28, 2012 Author Share Posted September 28, 2012 It looks like Hudson CO may have picked up a quick .5-.9 of an inch in the last hour or so. Link to comment Share on other sites More sharing options...
Brian5671 Posted September 28, 2012 Share Posted September 28, 2012 Radar lighting up around NYC! Link to comment Share on other sites More sharing options...
Cfa Posted September 28, 2012 Share Posted September 28, 2012 Pouring in SE Queens, I got caught in it seconds before I made it inside. Link to comment Share on other sites More sharing options...
bluewave Posted September 28, 2012 Author Share Posted September 28, 2012 Statement as of 8:46 AM EDT on September 28, 2012 The National Weather Service in Upton NY has issued an * Urban Flood Advisory for... Kings (Brooklyn) County in southeast New York... Bronx County in southeast New York... New York (Manhattan) County in southeast New York... northern Nassau County in southeast New York... Queens County in southeast New York... * until 945 am EDT... * at 843 am EDT... an area of heavy showers and embedded thunderstorms developing over the region is producing rainfall rates of around 1 to 1 1/2 inches per hour. This activity is expected to gradually slides northeast of the region through 10 am. Excessive runoff from this storm will cause minor flooding of urban areas... highways... streets and underpasses as well as other drainage areas and low lying spots. Precautionary/preparedness actions... Do not drive your vehicle into areas where the water covers the roadway. Most flooding deaths occur in automobiles. Turn around and find another Route. Be prepared to take action if the flooding threat increases... or a warning is issued. Link to comment Share on other sites More sharing options...
billgwx Posted September 28, 2012 Share Posted September 28, 2012 SPC Day 1 Outlook has us in 2% TOR risk, and that cell over the Bronx has some low level rotation per EWR/JFK TDWR's and an "appendage" shall we say? Link to comment Share on other sites More sharing options...
ag3 Posted September 28, 2012 Share Posted September 28, 2012 .88" in Central Park in the past hour. Link to comment Share on other sites More sharing options...
Analog96 Posted September 28, 2012 Share Posted September 28, 2012 .88" in Central Park in the past hour. And .02 here in the past hour, lol. Link to comment Share on other sites More sharing options...
Snowlover11 Posted September 28, 2012 Share Posted September 28, 2012 Been pouring all morning. Link to comment Share on other sites More sharing options...
ag3 Posted September 28, 2012 Share Posted September 28, 2012 NYC rain special so far through 10:00a.m.: NYC: 1.44" LGA: .66" EWR: .33" JFK: .28" BDR: .10" Link to comment Share on other sites More sharing options...
Quincy Posted September 28, 2012 Share Posted September 28, 2012 Helicity is good (southern CT) and convection is forming a bit along and ahead of the cold front. SPC has gone with a 2% tornado probability around the area. Link to comment Share on other sites More sharing options...
Sundog Posted September 28, 2012 Share Posted September 28, 2012 NYC rain special so far through 10:00a.m.: NYC: 1.44" LGA: .66" EWR: .33" JFK: .28" BDR: .10" I think LGA just missed out on the heaviest of the overnight stuff. That's what it looked like on radar when i checked it last night. Link to comment Share on other sites More sharing options...
ag3 Posted September 28, 2012 Share Posted September 28, 2012 I think LGA just missed out on the heaviest of the overnight stuff. That's what it looked like on radar when i checked it last night. LGA reported .37" for that overnight stuff. Most out of any local station. They JUST missed out on the very heavy band around 8:00am today where NYC got .88" in 1 hour. At home in Astoria, I caught that band and easily also had .75" during that hour. Link to comment Share on other sites More sharing options...
ag3 Posted September 28, 2012 Share Posted September 28, 2012 That little cell just west of LGA is showing a litte rotation on TJFK radar. Link to comment Share on other sites More sharing options...
earthlight Posted September 28, 2012 Share Posted September 28, 2012 That little cell just west of LGA is showing a litte rotation on TJFK radar. SPC WRF was off by maybe a few miles and a few minutes (this image was valid for 11am). Crazy.. http://www.emc.ncep....d_1000m_f15.gif Link to comment Share on other sites More sharing options...
CT Rain Posted September 28, 2012 Share Posted September 28, 2012 That little cell just west of LGA is showing a litte rotation on TJFK radar. Indeed it is Link to comment Share on other sites More sharing options...
CT Rain Posted September 28, 2012 Share Posted September 28, 2012 Warm front sneaking north. Dews have jumped at FRG. Link to comment Share on other sites More sharing options...
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