SE PA/Mt. Holly severe threats..

[stormspotterlive]

Well Thought I would start an early thread on the thunderstorm potential for friday as it seams to be better then the threat we just had. The spc already has us in a slight risk and has 30% probs up just south southwest already.

What has yet to be worked out on the models is the timing some are slower some are faster so for now I would blend in between until we see some agreement. what has gotten interesting is the 12z Nam which just came in it is putting out a very vigorous line.

It then weakens as it gets closer to us much like the yesterday however we got plenty of time to work things out and this is only 1 solution.

So now we watch how dynamics and instability pan out on future model runs to see just where a possible moderate risk may be placed. even with the 30% already out on the spc they are still a bit uncertain about a possible tornado threat along the east coast. I would think if there was to be any tornado threat it would be closest to the jet which we can work out later on.

[Thunder Road]

omg

is it getting hot in here or is it just me?

i'm going to need a cold shower soon if i keep dwelling on it

The 12z is very similar. There's a secondary SLP over Balt-Wash which is what backs the surface flow so much. Associated convergence with a weak thermal gradient would probably be enough to get storms firing off the Apps and then potentially turning supercellular as they cross DC.

Here's a hodo from northeastern MD:

Winds get linear from 700 mb up, so it's not perfect, but it's still pretty hawt looking for this region anyway. Note that despite being in the warm sector, LCLs are quite low since it's not all that warm (maybe 70 F at the surface) and CAPE is also only marginally impressive, but with a wind profile like that I think things could happen.

[NaoPos]

i heard you were making the thread for svr weather for the day 3 slgt risk

I was gonna start a day 7 outlook!

I've been watching it since last sat when the euro was showing that potent trough dropping east.

Right now, my biggest concern would be how far north the warm front gets and a cap in place. While the nam does spit out some solid EHi and shear, we're lacking instability. We're gonna need that warm front to come through north of us and get into some clearing. If the warm front does clear us, and we don't get under the sun, we'll stay capped. Either way, it's better than 90 degrees and 70 DP's and no storms.

Could be a mini chase day.

[NaoPos]

Joe, I changed the title thread

From my one to keep all severe chances in 1 thread, kind of how other threads are doing it. I'll update the dates accordingly. No need to clutter up for each chance. (hopefully a lot this year). Maybe Adam can move this in there if you and him agree.

[Voyager]

I didn't even know this was a possibility.

[NaoPos]

Here's the 12z NAM for 21z n the 1st. Notice the cap in place.

Sent from my iPad HD

[am19psu]

Merged.

[stormspotterlive]

Joe, I changed the title thread

From my one to keep all severe chances in 1 thread, kind of how other threads are doing it. I'll update the dates accordingly. No need to clutter up for each chance. (hopefully a lot this year). Maybe Adam can move this in there if you and him agree.

Perfect going to be a long season at this rate. if all is right this could be our best tornado threat in a longtime. fingers crossed we can get the warm front to lift north. Places just south of it would have a greater risk of super cells with tornadoes. Kind of like western new England yesterday.

[tombo82685]

just looking at some of the models, timing could be an issue with this also. Some of the models like the euro and gfs bring this in around 3-6z, which would be in the 9-12pm time frame

[Boch23]

^{We should focus on getting an actual line of storms to move through delco on east before we start talking about a line of severe storms moving through delco on east.}

[LMolineuxLM1]

^{We should focus on getting an actual line of storms to move through delco on east before we start talking about a line of severe storms moving through delco on east.}

So true. Couldn't have said it better myself. Lol.

[fsu_wxgirl]

Looks like hubby and I could have an interesting drive down to VA Beach Friday night. 12Z GFS has similar timing to the 00Z ECM showing showers moving into the Mid-Atlantic and Central PA by 00Z. By 06Z the front is passing through Eastern PA and right over where we'll be driving south. I always love impromptu storm chasing!!

[stormspotterlive]

Anyone one have text data or know what the dynamics are on the 12z euro it looks like a strong to potentially severe line moves through Friday night on the 12z run despite loss of day time heating I would assume shear and other dynamics are rather impressive but do not have access to that.

[bluehens]

It's just too funny watching these lines break up Everytime they come near us. Someone should do a case study on how we get fu**ed Everytime. Lee?

Timing just seems to be killing us a lot lately. All too often the storms/fronts don't get down our way until right around dusk or after so then we're losing the instability. I can't remember the last time we had something move through mid-day or early afternoon.

[yoda]

LWX came out strongly in their AFD this afternoon

[tombo82685]

Anyone one have text data or know what the dynamics are on the 12z euro it looks like a strong to potentially severe line moves through Friday night on the 12z run despite loss of day time heating I would assume shear and other dynamics are rather impressive but do not have access to that.

i don't have txt soundings and what not, but its putting down 1-1.5 inches of rain from m/d line north, and .5-1 south of m/d line.

[tombo82685]

I was gonna start a day 7 outlook!

I've been watching it since last sat when the euro was showing that potent trough dropping east.

Right now, my biggest concern would be how far north the warm front gets and a cap in place. While the nam does spit out some solid EHi and shear, we're lacking instability. We're gonna need that warm front to come through north of us and get into some clearing. If the warm front does clear us, and we don't get under the sun, we'll stay capped. Either way, it's better than 90 degrees and 70 DP's and no storms.

Could be a mini chase day.

solely going off the 12z nam it gets the warm front to about baltimore.

[stormspotterlive]

18z NAM just in has a large line of strong to severe storms for us with very heavy rain fall Friday. It looks as if the warm front this run gets very close to Philly. Looks quite a bit more like the 12z euro now.

[NaoPos]

In the pic below, ive outlined my main concern for friday (other than timing).

Up north, we have a 570dm Block over greenland with a 50-50 low and another one back up to its west ( in the RED circles). The BLUE circle is an area of high pressure due to confluence. ( WHERE THE FOOK WAS THIS IN WINTER?!?!?!) To the south, the ORANGE zig zag line is the approx area of the forecasted warm front. Lets just say the Mason DIxon line. How far North that WF advects will be high dependent on the strength of the block to the North. If the warm front doesn't pass you, you can almost forget about any chance of a thunderstorm/severe threat. We're gonna need that WF to advect north of us, get warmed sectored and cleared out to break the cap and get some instabilty. SHear will not be a problem here, unlike the other day. (Gotta love mid atl severe set ups.) anyhow, a 20 mile shift North would put phily burbs in play. Anyone just south of the warm front, and clears out, stands a good chance of some solid severe weather in the form of hail wind and tornados. Not an outbreak, but moreso than usual.

[tombo82685]

Just wanted to talk about the 18z nam, which has some of the most impressive parameters i have seen in a while "potentially" that could affect this area. As Bri and some others mentioned the whole key is how far north that warm front gets on friday. As we have seen during the spring a couple times where warm fronts were forecasted to blast through but never did. So this is definitely a legitimate concern. As of right now, and off the 18z nam the best area for "tornadic activity would be in the dc to ne md section. This isn't just the run of the mill svr threats we have seen so far this year. This threat has big time legs. I was worried before about the timing of the front, but now the models are speeding the front passage up. Also, the dynamics actually increase as the night goes on. Granted we may lose some Lift and cape, but the helicity and shear go bonkers. The 18z nam gets the warm front a little past philly so we do get into some of the fun. Below are some of the maps for some insane parameters.

The maps all are from the hr 54-57 timeframe on the nam.

First lets look at the cape, which is the measure of available energy for convection to form. This map shows the max cape over the region. anything above 1000 is decent for convection to pop. As you can see the warm front is drapped right over the region. The further south the better the dynamics.

LI, which is the amount of lift.

Helicity, which the measure of the amount of spin in the atmosphere

0-1km

Shear, is the change in wind direction over a short distance in the atmosphere...Values over 35 or ripe for supercell development

EHI, is the calculation of the energy of helicity and instability. To get supercells to develop you need an ehi of 2.5 or greater.

hr 51

hr 54

[NaoPos]

just to add what TOM TIMMER is adding (which is a great post tom). here's the sounding for baltimore hr 54:

look at the bottome right. look at the turning of the winds. Here's the associated HODO:

Thats pretty solid for the region. I know it's baltimores, but this is what the wind profiles/hodo's would look like just along the warm front.

[Boch23]

Awesome stuff guys, very informative. To Bri's point i feel like 20 miles isn't that much. And if nothing else gives me something to watch to get through the day thursday and friday.

[wederwarrior]

Great usage of helicity tombo. Good discussion

I don't think a shift of 20-30 miles is out of the question. We shall see what transpires.

[stormspotterlive]

Great post tombo and bri! I do think with the strong shear in place storms with the front will be moving east at a rather fast pace vs the slower pace we saw on Tuesday. The warm front like every other warm front will probably come down to nowcasting or last minute as we have seen earlier in the year. Any event interested to see how the spc responds to newer model data which is continuing to make things more interesting.

[MGorse]

It does appear that the Friday system is looking more and more interesting, but I am not quite sold on a decent severe thunderstorm threat for our area. Despite rather impressive wind fields overspreading the area, the timing is what may be against us. It looks like the best ascent and wind fields arrive after 00z Saturday and the gist of the guidance has what instabilty develops lowering during the night. I see the new 00z NAM has a 925 mb jet of 40-50 knots moving across most of the area after 00z Saturday. The southeasterly low-level inflow may also allow lower clouds to arrive sooner, cutting off the surface based CAPE. This could be an event where a convective line develops to the west and then it turns into not having much lightning with it as it becomes more low-topped with an eastward extent. This could be maintained through the night despite lowering instability due to decent height falls and a strengthening wind field.

[NaoPos]

It does appear that the Friday system is looking more and more interesting, but I am not quite sold on a decent severe thunderstorm threat for our area. Despite rather impressive wind fields overspreading the area, the timing is what may be against us. It looks like the best ascent and wind fields arrive after 00z Saturday and the gist of the guidance has what instabilty develops lowering during the night. I see the new 00z NAM has a 925 mb jet of 40-50 knots moving across most of the area after 00z Saturday. The southeasterly low-level inflow may also allow lower clouds to arrive sooner, cutting off the surface based CAPE. This could be an event where a convective line develops to the west and then it turns into not having much lightning with it as it becomes more low-topped with an eastward extent. This could be maintained through the night despite lowering instability due to decent height falls and a strengthening wind field.

Kinda like the other night! Killjoy :-)

[NeffsvilleWx]

Excellent post tombo, learned quite a bit. Thanks!

[Thunder Road]

I'm sorry but this has been bothering me.

LI is not a direct measure of "lift" in the atmosphere. It's just a crude approximation of instability (T(Parcel) - T(Environment) at 500 mb) and generally inferior to CAPE. It's better to look for significantly negative VV's (Vertical Velocities) specifically at 700 mb to isolate what the source of "lift" is.

I'm sure most of us know this already, but for those who are learning, here's another lesson.

[Thunder Road]

As for the threat overall, I'm still conditionally optimistic. I can recall more warm front busts that busted south than busted north. I think Maryland is game but I'm not so sure we are up here (although this could change).

That said, those are good dynamics for a Plains set-up (well one in June anyway), let alone an EC one, with a 50-knot LLJ at 925 mb and 850 mb and good veering with height. Remember that backed surface flow is going to mean we get a wind off the ocean. Even with the ridiculously warm SSTs we have up here, that it still a potentially-stabilizing marine layer. Again this is another reason why central MD might make out better than SE PA.

[SmokeEater]

Day 2 slight just issued, main threats widespread damaging wind and a possible tornado threat from VA to PA/NJ if discrete cells form ahead of the line, and sufficient destabilization happens in the area of the warm front. Also Moderate Risk may be needed in subsequent outlooks.