JULY 2012 Severe Weather /Convection Discussion

[NYCSuburbs]

i agree with john, isotherm and bluewave. thursday if the imgredients all come together as far as the location of the surface low, cold/warm front we could be in for some intense severe weather from PA, to the coast into new england. im not sure of the comparison, but last year we had a similar setup where we were in the bullseye for a big severe outbreak and new england got it including that live streamed feed of the springfield,ma tornado. my only concern is that this surface low does track too far to the north and we miss alot if not all the parameters to create and sustain severe weather for our area including coastal areas. the ingredients are there now we just gotta see where they can maximize there potential. hoping this doesnt go north, because this outbreak could finally make some people who have missed out this year have a smie like me lol

I'm not too sure about Thursday, the set up doesn't look too bad but the timing is especially my biggest concern as the cold front doesn't move through until Friday with the main rain axis setting up further west/north on Thursday. That doesn't rule out storms for Thursday, especially in the morning, but if we do see storms in the late afternoon to early overnight time frame, I'd think we end up close to the southern end of such activity, with more widespread storms further south possible on Friday depending on the exact timing of the cold front.

[earthlight]

Thursday is an interesting situation, the first thing that caught my eye was the strong LLJ (especially for July) and the potential for backed sfc winds, which would create a lot of LL turning considering the southwesterly LLJ at 35-50 kts. Synoptically, definitely some potential here, the position/strength of the sfc low/warm front (and subtle adjustments to it) is obviously going to make a big difference with the possible magnitude of this event.

Earthlight raised a good point with the first point on this page, although I'd actually expect some stronger instability than the GFS depicts given the intensity of the LLJ streaming northward throughout the day.

The NAM has an entirely different look, though. Will await the 00z Euro to comment further.

The NAM really brings some of the potential timing issues to the forefront. There appears to be enough forcing for an MCS which moves through much of the Northern Mid Atlantic and New England between 10 and 15z on Thursday. There is still some additional convection later on Thursday afternoon both along the cold frontal boundary near the Ohio Valley and continuing northeastward to near a 1002mb sfc low over Southeast New York. But the mid level heights seem to be indicative of capping south of there.

More convection forms Friday with the cold front over the area.

But glancing at the 03z SREF, the probabilities remain fairly impressive on the mean solution. Effective shear remains around 40 kts at 18z Thursday with 2000 joules of surface based cape into the area around that time give or take a few hours. That being said, note the trend for the low level shear to get more disjointed from the best instability near/south of the WF. Valid 21z Thursday, the SREF has trended farther northeast/faster with the best area of 0-3km helicity each run.

http://www.spc.noaa.gov/exper/sref/sref_matrix_hover.php?fhr=f066&startdate=2012072403&field=SREF_3KMHEL_SSB_MEDIAN_MXMN__

[bluewave]

Thursday looks like mainly elevated morning convection with the warm front followed by surface

based storms with the low pressure moving across from the west later. As we have seen many times

in the past, the track of the morning convection may telegraph where storms fire later in the

day. It will be interesting to see what the models come up with in later runs. It still looks a little

early to pin down which portions of the Northeast will see the main focus of the storms. If the

warm front pushes too far north, then would would be more of I-80 N to Southern New England jackpot.

[psv88]

Partial bust yesterday. NAM and euro hinted that the convection wouldn't make it to the coast...but spc/new/Upton called for heavy rain for our area. I received about .03 last night.

Driving from BK to Nassau saw some decent cloud to cloud lightning which is a much better show than ctg. Rain really was much lighter in Nassau than queens even. Just a light shower. I call it a pretty big bust

[TheTrials]

Partial bust yesterday. NAM and euro hinted that the convection wouldn't make it to the coast...but spc/new/Upton called for heavy rain for our area. I received about .03 last night.

Driving from BK to Nassau saw some decent cloud to cloud lightning which is a much better show than ctg. Rain really was much lighter in Nassau than queens even. Just a light shower. I call it a pretty big bust

Well, the NAM also showed the morning stuff wouldn't make it to me, and it did, so I wouldn't be giving the NAM too much credit, and it was woeful last week on the Friday rains, and has under estimated several time overnight early morning convection that has surprised many a folk. True story.

[earthlight]

Thursday looks like mainly elevated morning convection with the warm front followed by surface

based storms with the low pressure moving across from the west later. As we have seen many times

in the past, the track of the morning convection may telegraph where storms fire later in the

day. It will be interesting to see what the models come up with in later runs. It still looks a little

early to pin down which portions of the Northeast will see the main focus of the storms. If the

warm front pushes too far north, then would would be more of I-80 N to Southern New England jackpot.

I would think the warm front could offer at least some potential for severe storms ...there's usually at least some stuff along the nose of the llj.

But I think there could be additional severe potential near the surface low even if the warm front is a little north of the area. The enhanced low level shear could really make things interesting if the low tracks like some of the models are indicating it will.

[NorEaster27]

I would think the warm front could offer at least some potential for severe storms ...there's usually at least some stuff along the nose of the llj.

But I think there could be additional severe potential near the surface low even if the warm front is a little north of the area. The enhanced low level shear could really make things interesting if the low tracks like some of the models are indicating it will.

if we do get an MCS, look for it to be a tad south of where the models have it now. This would fit the trend we have been seeing this whole summer.

[Cfa]

Does the "Derecho" have any chance of making it here? This one looks a little bit further north than the last one (I think).

[NorEaster27]

Does the "Derecho" have any chance of making it here? This one looks a little bit further north than the last one (I think).

no one is talking derecho, forecasting an MCS is hard 6 hours out let alone 2 days.

[earthlight]

SPC AC 240714

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0214 AM CDT TUE JUL 24 2012

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE OH VALLEY INTO THE

NERN U.S....

...OH VALLEY INTO THE NERN U.S...

LATEST MODEL GUIDANCE IS IN GOOD AGREEMENT REGARDING THE EVOLUTION

OF UPPER TROUGH AS IT DIGS INTO THE GREAT LAKES THURSDAY. WITH

HEIGHT FALLS EXPECTED TO OVERSPREAD THE REGION A BROADENING CORRIDOR

OF STRONGER FLOW ALOFT WILL SHIFT SOUTH ACROSS THE OH VALLEY IN

CONJUNCTION WITH ADVANCING FRONTAL ZONE. WITH SUBSTANTIAL

CONVECTION EXPECTED ACROSS THE UPPER MS VALLEY/NRN GREAT LAKES

REGION DAY2 THE SFC BOUNDARY SHOULD EASILY SAG TO A POSITION ALONG

THE ON/NY BORDER...SWWD INTO CNTRL IL BY 18Z. EARLY IN THE PERIOD

BOTH THE NAM/GFS SUGGEST STRONG LOW LEVEL WARM ADVECTION WILL BE

FOCUSED ACROSS NY AHEAD OF SFC LOW. ELEVATED CONVECTION IS EXPECTED

ALONG NOSE OF VEERED LLJ AND TSTMS ARE EXPECTED TO SPREAD INTO NEW

ENGLAND BY MID DAY AS WARM SECTOR ADVANCES NEWD. WHILE THIS EARLY

ACTIVITY MAY PRODUCE SOME HAIL THE GREATER SEVERE THREAT IS EXPECTED

ALONG COLD FRONT AFTER RAPID BOUNDARY LAYER HEATING REMOVES

INHIBITION. A CONSIDERABLE AMOUNT OF TSTM ACTIVITY MAY EVOLVE ALONG

THE FRONTAL ZONE WITHIN A FAVORABLY SHEARED ENVIRONMENT THAT SHOULD

PROVE SUPPORTIVE OF ORGANIZED MULTI-CELL CLUSTERS AND PERHAPS EVEN

AN ISOLATED SUPERCELL. IF SFC TEMPERATURES SOAR INTO THE MID-UPPER

90S ACROSS THE OH VALLEY AS NAM SOUNDINGS SUGGEST THEN RELATIVELY

HIGH BASED STORMS FOR THIS REGION COULD PROVE PRODUCTIVE IN

GENERATING DAMAGING WINDS WITHIN BROAD WLY FLOW REGIME.

..DARROW.. 07/24/2012

[earthlight]

Does the "Derecho" have any chance of making it here? This one looks a little bit further north than the last one (I think).

Nobody is forecasting a Derecho.

[Cfa]

no one is talking derecho, forecasting an MCS is hard 6 hours out let alone 2 days.

There's one in progress right now.

[bluewave]

I would think the warm front could offer at least some potential for severe storms ...there's usually at least some stuff along the nose of the llj.

But I think there could be additional severe potential near the surface low even if the warm front is a little north of the area. The enhanced low level shear could really make things interesting if the low tracks like some of the models are indicating it will.

Yeah, sometimes with these morning warm fronts we have seen severe reports even

with mostly elevated convection. It will be interesting to see how close to us the AM

and PM storms get. Still plenty of time for the models to work out the details.

[IsentropicLift]

There's one in progress right now.

That is a nasty line out in western Ohio at the moment, but not a derecho

[Dsnowx53]

Warm fronts have proven to be a better lifting mechanism for rotating updrafts than cold fronts. Obviously being near the triple point of the surface low and the fronts is best for tornado action, which is why I ultimately think the tornado threat will be north of us, but we still will have sufficient shear and good lift with the very potent surface low. We might actually be able to obtain a bit of low level veering with S and SSE winds in advance of the surface low and a strong westerly flow aloft.

If there can be just enough instability just north of the warm front, I'd expect severe storms and perhaps supercells to initiate there and then track SE (towards us?) towards the area of better instability.

[Stormlover74]

It did produce 60 mph winds in chicago and started in Wisconsin early this morning

That is a nasty line out in western Ohio at the moment, but not a derecho

[IsentropicLift]

The 12z NAM keeps the best action over New England with an MCS sliding through to our north and east, but hints at some scattered activity down our way. So hard to pinpoint.

[IsentropicLift]

It did produce 60 mph winds in chicago and started in Wisconsin early this morning

Look at the number of severe weather reports from 6/29. 1195 reports of wind damage along with 37reports of 65k + That is a derecho

[psv88]

Early morning tornados while people are asleep. Sounds like candy for most on this board. Scares the **** out of me.

That being said I think this will perform.

[earthlight]

It did produce 60 mph winds in chicago and started in Wisconsin early this morning

That still does not make it a derecho. There is a specific criteria that needs to be met for it to be classified as a derecho.

[psv88]

That still does not make it a derecho. There is a specific criteria that needs to be met for it to be classified as a derecho.

Yea it needs to be a certain length. I thinks its like 250 miles long something like that. Was reading about it this weekend. Winds also need to reach severe criteria. 57 I think

[forkyfork]

Yea it needs to be a certain length. I thinks its like 250 miles long something like that. Was reading about it this weekend. Winds also need to reach severe criteria. 57 I think

svr criteria winds along most of its length and a path length of at least 240 miles

http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm#definition

[bluewave]

svr criteria winds along most of its length and a path length of at least 240 miles

http://www.spc.noaa.....htm#definition

Great Video..

http://www.spc.noaa.gov/misc/AbtDerechos/loopimages/Blowdown_from_house_EDIT.mp4

[IsentropicLift]

Early morning tornados while people are asleep. Sounds like candy for most on this board. Scares the **** out of me.

That being said I think this will perform.

I would be very content to get a line of storms like the one ongoing in western Ohio, but you can skip the tornados. Having witnessed that derecho first hand in an RV I hope I never see that again. You couldn't go more than a few hundred feet without seeing a tree down, a tree into a car, a house, you name it. Widespread tree damage. One house had three trees down in the front yard alone. And this was all in Atlantic county after the line redeveloped east of Baltimore.

[Stormlover74]

70-80 mph wind gusts with that line

I would be very content to get a line of storms like the one ongoing in western Ohio, but you can skip the tornados. Having witnessed that derecho first hand in an RV I hope I never see that again. You couldn't go more than a few hundred feet without seeing a tree down, a tree into a car, a house, you name it. Widespread tree damage. One house had three trees down in the front yard alone. And this was all in Atlantic county after the line redeveloped east of Baltimore.

[IsentropicLift]

70-80 mph wind gusts with that line

I believe it, but it has a long way to go. I wonder how much the activity ongoing ahead of it will stabalize the atmosphere as time goes on.

[PB GFI]

being classified as a Derecho @ some outlets .

Live: Derecho Hitting Dayton; Cincinnati Next

By Meghan Evans, Meteorologist

Jul 24, 2012; 7:50 AM ET

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Severe storms, called a derecho by meteorologists, moved through Chicago this morning. The derecho is now spreading across Ohio.

A derecho is defined as a widespread and long-lived wind storm that accompanies rapidly moving showers or thunderstorms. The derecho tore through the Chicago area, stirring winds of 60-70 mph, during the morning commute. Thousands of customers are without power across northern Illinois,

[Analog96]

why are we in a slight risk today?

[Isotherm]

Some maps from the 12z NAM valid Thurs afternoon. Near 3000 CAPE values juxtaposed with 30-40 kts of bulk shear by afternoon. Best helicity values further north and east -- makes sense, closer to the track of the sfc low.

However, given the values progged right now, I think the PA/NJ/NYC area should light up like a Christmas tree thur aft/eve with plenty of organized clusters of multicellular storms. I could see a few supercells popping up in NY State where low level wind shear is more impressive.

My idea right now -- red shade: isolated supercells with highest risk of tornado, orange shade: primarily wind damage risk from multicellular storms associated with the front late aft/eve, green shade: hvy rain

[andyhb]

WRT Isotherm's post, that is an interesting trend, the instability has expanded further north and east compared to previous runs, and is now overlapping a few of the areas of the highest LL shear. I'm interested in seeing whether this trend continues.

If we can get discrete convection to form along the northern axis of instability...oh boy...although I'm not sure that areas around NYC get the brunt of that given the trend northeast. Looks more of a CT/western MA/eastern NY deal (i.e. where Isotherm highlighted in the red area).