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2013 Mid-Atlantic Severe General Discussion


Kmlwx

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the derecho talk is pretty funny

 

   
*** ALERT ** 1ST POSSIBLE DERECHO EVENT OF THE SEASON FOR OHIO VALLEY and MIDDLE ATLANTIC Wed afternoon ...evening ...into early Thursday morning

Here is the 18z WRF /NAM ... at 72 hrs ( top 3 maps) and six hours later at 84 hrs . The LEFT maps are UPPER AIR ( 500mb) .. and shows a Powerful piece of energy in the Jet stream over Chicago ( CIRCLE IN YELLOW) ... 6 hours later that feature is over IND/ OH., The huge cluster of storms over southern WI and raced ESE .. classic DERECHO track-- into southeast MI and Northeast OH.

IF .... IF .. this is correct the DERECHO would hit western and / or central PA western / central MD and DEL... It Might skim Northern VA early Thursday morning

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So long as we have cloud cover, I don't see anything happening today.

 

Thats what I thought.... but apparently LWX sees different

 

GIVEN CLOUDS/SHOWERS TO START THE DAY...AMOUNT OF INSTABILITY IS

SOMEWHAT UNCERTAIN. MODELS FAVOR CLOSE TO 500 J/KG...BUT SOUTH OF

THE WARM FRONT IF THERE ANY BREAKS THIS COULD EASILY BOOST VALUES

AOA 1000 J/KG. EVEN IF INSTABILITY REMAINS

WEAK/MARGINAL...AFOREMENTIONED SOUTHERLY LOW LEVEL JET WILL

ENHANCE SHEAR AND THIS MAY COMPENSATE FOR A LIMITATION IN

INSTABILITY. THUS...SOME STORMS MAY BECOME SEVERE PRODUCING

DAMAGING WIND GUSTS. AND GIVEN FORECAST SHEAR/HODOGRAPH

CONSIDERATIONS CAN NOT RULE OUT THE RISK FOR ISOLATED TORNADOES

ESPECIALLY IN AREAS THAT WIND UP HAVING HIGHER INSTABILITY.

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Scattered clearing starting in WV and SW VA.

We know how these things work - the clearing will just never make it to the bulk of us. There will be like one good storm later on in an isolated spot and the rest of us will fail and just get flooding.

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Sheesh that didn't take long for people to start running with the D-word. In all seriousness, I like the *potential* for some sort of long tracking MCS across the Midwest, possibly into the mid-atl late Wed. That is an impressive looking temp boundary with dews probably around 70 on the southern reaches there. I do not see an EML which was mentioned in a prev post, and I dont see 105/75 in DC (hottest ever June day) so yeah..but models are picking up a meaningful short wave that would spark and help sustain a system. If I'm not mistaken, last year's June 29th event had a very subtle trigger, and no shortwave providing/sustaining the lift..It was all driven by a cold pool from there, and that's all it needed. 

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It's a pretty good mid lvl trough passage historically. Most of our svr events are kind of meh. Hard to be too down on it with the right expectations. If it wasn't going to try to rain all day might be more fun..

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woah....take it easy. I was nearly run off the board last year for suggesting our weather was boring. Remain calm and hope for a derecho, some F 0's and torrential downpours this week.

I've given up on seeing exciting weather in the MA...guess I'll have to move to the Midwest.

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It's a pretty good mid lvl trough passage historically. Most of our svr events are kind of meh. Hard to be too down on it with the right expectations. If it wasn't going to try to rain all day might be more fun..

 

 

There are breaks to the south, it's definitely not write-off time at 10am.

 

Yep. The morning thoughts on 4/19 were also pretty negative and wrong and then LWX ended up confirming a couple of TORs in the area:

http://www.spc.noaa.gov/exper/archive/event.php?date=20130419

 

Overall, it is setups like these that usually bring the northern Mid Atlantic their tornado threat (probabilistically-speaking of course): deep moisture, low LCL, decent directional/speed shear with enough CAPE (storm-relatively balanced of course).  

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Remember guys, supercells generate their own omega to some extent.  You don't need 2000 j/kg of CAPE.  If you can get a little instability going at surface to touch things off (i.e. a little sun OR theta convection) you can get supercells.

Given the clearing to the southwest and the fact that guidance has sufficient instability verbatim, it is far to early to be writing this one off.

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Updated LWX AFD as of 11 AM (just posting svr wthr risk part)... seems like the modified sounding showed a bit more instability:

 

 

 

DESPITE LIMITED DAYTIME DESTABILIZATION WITH GENERALLY MINIMAL
BREAKS IN THE CLOUD COVER...12Z IAD MODIFIED SOUNDING SHOWS SBCAPE
AROUND 1000 J/KG AS DEWPOINTS INCREASE TO THE LOW 70S SOUTH OF THE
BOUNDARY. GIVEN LOCATION OF THE WARM FRONT AND LATEST VIS SAT
SHOWING SOME CLEARING NEAR THE VA-NC BORDER...SOME BREAKS IN THE
CLOUD COVER MAY DEVELOP THIS AFTN ESPECIALLY OVER PORTIONS OF
CENTRAL VA AND SRN MD...WHICH WOULD ALLOW FOR POCKETS OF HIGHER
INSTABILITY WITH SBCAPE GREATER THAN 1500 J/KG. EVEN IF
INSTABILITY REMAINS WEAK...AFOREMENTIONED SOUTHERLY LLVL JET WILL
ENHANCE SHEAR AND THIS MAY COMPENSATE FOR A LIMITATION IN
INSTABILITY. THUS...SOME STORMS MAY BECOME SEVERE PRODUCING
DAMAGING WIND GUSTS. AND GIVEN FORECAST SHEAR/HODOGRAPH
CONSIDERATIONS CAN NOT RULE OUT THE RISK FOR ISOLATED TORNADOES
ESPECIALLY IN AREAS THAT WIND UP HAVING HIGHER INSTABILITY AND SFC
WINDS CAN REMAIN BACKED MORE OUT OF THE SE.
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If we are to accept them as correct, 12z NAM showing some nice curved hodo's from 18z on till around 03z at KIAD... 03z has a "loop de loop" hodo... SBCAPE is around 1100 J/KG with really low (and I mean REALLY LOW) LCL heights - as in below 185m at 18z and 21z

 

About the same at DCA... 0-1 km shear is nice, SRH at both levels 200+... 0-6 km shear is decent around 30-35 kts

 

FWIW, 00z GFS also looked decent for the area as well looking at soundings

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