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Sept 11-12 Wednesday, Thursday Storm Threat


free_man

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Its a Catch-22 for tomorrow: If the skies don't clear out then the CAPE forecasts will bust; on the other hand if the warm front lifts fast to the north or northeast and we clear the CAP will rule. Best scenario for severe weather tomorrow is clearing but warm front slows across NNY/NNE so both best shear and CAPE are manifested.

Wild card for severe tomorrow is shear params are correct and even 1/3rd to 1/2 CAPE is materialized even w/ cloud cover. My personal experience is that even w/ only minor insolation/warming at least some isoalted to scattered severe is still possible.

It's a complex setup and the high res short-term models are all over the place with it. All we can do for now is keep a close eye on radar and surface obs to track that front.
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I actually think... given upstream soundings... CAPE forecasts are probably underdone in some areas. 00z GRB sounding has MUCAPE >4000 j/kg. 

 

Agreed re: kinematics but EML presence argues for high end severe where convection can occur. That's a bit trickier to figure out. 

Valid point Ryan BUT lower sun angle this time of year tends to mitigate and actually aid CAP in lidding things. My personal experience with Fall/early spring convectiion outbreaks tends to lead me to rely more on shear values rather than CAPE. All I was trying to say was that even if the CAPE is overdone, even just 1/2 to 1/3rd of what is forecast combined w /tomorrow's  forecast shear params could lead to some decent severe. Even w/out any insolation. Personally I think some are looking at the forecast CAPE and are wetting themselves; these folks need to know what the P in CAPE stands for.

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For Thursday, the better forcing might not really arrive here until late evening.  The NAM develops a pretty strong LLJ though late in the day but it also has some pretty meh lapse rates but does have some nice elevated cape.  If anything, perhaps we can maintain a strongly forced convective line but not low topped so some decent lightning and maybe a threat for hail.  hodographs do lengthen though around 0z thanks to the LLJ.  

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WOW...the 21z SPC SREF has some hefty 24-HR svr probs Wed/Thurs across NNE...would be close to mod risk issuance.

That's why I prefer to look at the 12hr probs. Note that those 40% probabilities are spread over two days. The 12hr probs line up with marginal SLGT risk for one given day.
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Still, pretty impressive for mid-September and I think there's a good shot at some significant severe somewhere north of I-90 over the next few days.

 

Yeah someone is going to get hit good.

 

now it's just all about ironing out details and such.  We know what we are looking at from a synoptic/kinematic/thermodynamic standpoint but it's just getting everything to evolve together.

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Might this be the main event for Tuesday? :/

 

Very well may be.  It really will be difficult tomorrow to break through the Cap, especially with rising heights.  I guess just have to watch to see if Lake Breeze can fire anything or if any action forms in Canada and OFB trigger something in NYS.  

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Very well may be.  It really will be difficult tomorrow to break through the Cap, especially with rising heights.  I guess just have to watch to see if Lake Breeze can fire anything or if any action forms in Canada and OFB trigger something in NYSS

Sum of the parts may be sig for Tuesday.

Minor additives triggers, CAPE, etc. combining in time and place coincidentally COULD make for decent severe.

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Sum of the parts may be sig for Tuesday.

Minor additives triggers, CAPE, etc. combining in time and place coincidentally COULD make for decent severe.

 

Wednesday looks to be the more fun day up that way, will actually have a trigger and good cape/shear combo.  Storm mode may end up becoming linear quickly but initially storms should be discrete so there should be a tornado threat for the first few hours of the event then a quick transition to straight line winds, though you do have to watch for spinups embedded in the lines.

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Very well may be.  It really will be difficult tomorrow to break through the Cap, especially with rising heights.  I guess just have to watch to see if Lake Breeze can fire anything or if any action forms in Canada and OFB trigger something in NYS.  

I'm looking at that MCS and trying to judge its trajectory along the ridge... I must say... Its a little more south than I expected

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Wednesday looks to be the more fun day up that way, will actually have a trigger and good cape/shear combo.  Storm mode may end up becoming linear quickly but initially storms should be discrete so there should be a tornado threat for the first few hours of the event then a quick transition to straight line winds, though you do have to watch for spinups embedded in the lines.

Agree on discrete/lines and tornadoes...tornado threat may actually be more where lines have breaks.

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SPC for Thursday

 

 

..NERN STATES...
AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE EWD ACROSS THE GREAT LAKES
REGION ON THURSDAY AS A COLD FRONT ADVANCES SEWD INTO WRN NY AND WRN
PA. WIDESPREAD THUNDERSTORM ACTIVITY MAY BE ONGOING ALONG THE
BOUNDARY THURSDAY MORNING. SFC DEWPOINTS AHEAD OF THE FRONTAL
CONVECTION SHOULD BE IN THE MID TO UPPER 60S F ALLOWING FOR MODERATE
DESTABILIZATION ACROSS A BROAD CORRIDOR IN THE NERN STATES THURSDAY
AFTERNOON. AS INSTABILITY INCREASES THURSDAY...A LINE OF STORMS MAY
BECOME ORGANIZED AND MOVE EWD ACROSS THE SLIGHT RISK AREA.

FORECAST SOUNDINGS AT 21Z THURSDAY JUST AHEAD OF THE FRONT FORM NRN
NEW ENGLAND SWWD ACROSS NY SHOW MLCAPE IN THE 2000 TO 2500 J/KG
RANGE WITH 35 TO 40 KT OF 0-6 KM SHEAR. THIS ENVIRONMENT SHOULD
SUPPORT SUPERCELLS AND ISOLATED LARGE HAIL. THE GREATEST THREAT FOR
SUPERCELLS SHOULD EXIST WITH DISCRETE CELLS THAT FORM AHEAD OF THE
APPROACHING LINE. STEEP LOW-LEVEL LAPSE RATES WILL ALSO BE FAVORABLE
FOR WIND DAMAGE ESPECIALLY IF A LINEAR MCS CAN ORGANIZE THURSDAY
AFTERNOON.

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