August 2024 Observations and Discussion

New Hope 1.25" at this point, no wind or thunder to speak of. Looking forward to more rain to take care of what has been a drought over the past month or so...

Here's the latest model from the NWS.



https://www.nhc.noaa.gov/refresh/graphics_at4+shtml/212535.shtml?rainqpf#contents

Aren't the same models used in winter forecasts exist for tropical events as well?

I want what Nick Gregory was smoking . His models said from today till Sun my area would have about 2.5 inches of rain..we currently bout to hit 3 inches and still coming down like cats and dogs..

1.2 inches of rain here. Looks like I dodged a big bullet.

3.5 inches of rain total so far..started raining again ....72 and swampy

Only around 1/2 inch as of 11 pm last night here.Cloudy, 64 degrees, light rain now.Jman, looks like your area got the most!

Rain total so far 1.58", power outage during the night here in New Hope...

The good news is (in addition to the heaviest rains from Debby staying to our west) that once we clear this system out Friday night, a beautiful weekend is ahead. Sunshine and temps in the low 80s. Also looks like the beautiful weather should stick around for most of next week with plenty of sun and warm but not hot temps. And that will take us into mid-August. Time marches forth . . .

Geez, and I thought the forecast was just 1-2 inches of rain and breezy as the storm will be moving through central PA.

NJBear wrote:Geez, and I thought the forecast was just 1-2 inches of rain and breezy as the storm will be moving through central PA.

This is what Rb was mentioning yest, in response to a jman post I believe, in the tropical thread.  I believe its because as described in the write up you posted the "extra tropical" nature means its linking up with a frontal boundary.  As a result it creates its own frontal boundaries.  Warm front out ahead of the main center of LP passing west brings in a warm tropical airmass.  BUT on its back side, since Debby is linking with the frontal boundary, creates a cold front that digs in on the back side of the LP as it lifts north, clashing with the warm moist air mass leading to the instability.  I think that's it in a nutshell.  Perhabs Rb(Ray) can add to correct me if Im wrong.  




Here was Rays comments from Tuesday. He was def all over that.

by rb924119 Tue Aug 06, 2024 10:26 pm

The trade off for missing the bulk of the rain, though, would be an enhanced severe weather threat along the I-95 Corridor, which isn’t any better. So definitely be on the lookout for that.

Yes, sroc is right. In the tropical thread rb made this point well in advance on Tuesday. What is headed into central PA is the steady, all-day downpours of rain that may total several inches. That will surely lead to major flooding concerns there (and likely would have put some towns here under water if it had moved east). But the individual thunderstorms that will pop up here from the instability ahead of the system are not to be underestimated in their ability to create severe weather tomorrow. Right on cue with rb's comparison to the tornado outbreak associated with Beryl's remains, the risk of some of these thunderstorms tomorrow producing tornados is actually heightened over NJ according to the SPC.

sroc4 wrote:

NJBear wrote:Geez, and I thought the forecast was just 1-2 inches of rain and breezy as the storm will be moving through central PA.

This is what Rb was mentioning yest, in response to a jman post I believe, in the tropical thread.  I believe its because as described in the write up you posted the "extra tropical" nature means its linking up with a frontal boundary.  As a result it creates its own frontal boundaries.  Warm front out ahead of the main center of LP passing west brings in a warm tropical airmass.  BUT on its back side, since Debby is linking with the frontal boundary, creates a cold front that digs in on the back side of the LP as it lifts north, clashing with the warm moist air mass leading to the instability.  I think that's it in a nutshell.  Perhabs Rb(Ray) can add to correct me if Im wrong.  




Here was Rays comments from Tuesday.  He was def all over that.  

by rb924119 Tue Aug 06, 2024 10:26 pm

The trade off for missing the bulk of the rain, though, would be an enhanced severe weather threat along the I-95 Corridor, which isn’t any better. So definitely be on the lookout for that.

To very little surprise, yet another absolutely fantastic discussion coming out of the Mt. Holly WFO. This belongs in an ATM 300+ level class because it's textbook. And, thanks for the shoutouts, gang

To your point, Scott, you're not entirely wrong, but if we zoom out a bit, I think it will become a lot clearer. As a tropical cyclone undergoes its transition to a non-tropical entity, you correctly stated that it starts becoming associated with baroclinic processes (i.e. becoming associated with fronts), which is correct, and it's all of the dynamics associated with that which lead to the severe weather threat.

Starting at the surface, the circulation is still clearly in tact and well-defined, so you have a very ageostrophic component, which is almost isallobaric (basically, the surface wind has a very strong cross-isobar component to it relative to a weaker, less-defined system). If you envision the center of circulation passing over Harrisburg, for example, there would be an east-southeast to southeast wind in the southeastern quadrant of it (I-95 Corridor), which is also what is evolving into the warm sector as the transition process continues. Moving above that, say, to the 850 mb layer, because it is transitioning, you are going from a well-defined low-level vorticity (spin) maximum when it's tropical, to now phasing into the broader mid-latitude trough. In order for that to happen, that local vorticity maximum opens up and shears out, which leads to an opening low-level trough over top of the surface circulation. Now, this same process occurs throughout the atmospheric column, but remember, as it becomes more non-tropical (less tropical), it begins to experience the westward tilting of its circulation with height. So, as the troughs at the 850 mb, 700 mb, and 500 mb layers open up and begin phasing into the broader mid-latitude trough, you begin to see a transition in the wind field from a concentric flow around the center of circulation when it's purely tropical (remember, tropical systems are vertically stacked, with all circulations located on top of each other), to a sheared environment. Thinking of a vertical profile, the wind in a transitioning tropical cyclone would look something like this, conceptually, from top to bottom, as the surface circulation begins to find itself downstream of the opening/shearing circulations above it:

500 mb: southwesterly
700 mb: south-southwesterly
850 mb: southerly
surface: east-southeasterly

Based on that profile, that is EXACTLY the directional shear profile of a classic supercell environment (think of a hodograph).

But we aren't done. In addition to the shear, you also have the warm, moist air in the same area (developing warm sector), which is inherently unstable itself. However, with the troughs opening up, now you enhance your differential voriticity advection in the vertical (atmospheric energy), which aids in broad forcing vertical motion/ascent. You also begin getting jet enhancement (in the right-rear quadrant, also favorable for broad ascent) from the upper-level heights compressing (convergence) in response to the upper-level ridge that was over top of the tropical entity now being forced downstream and my next point, and arguably, most important part of all of this - rapid height falls over the transitioning cyclone and increase in lapse rates (rate at which temperature changes with height). In the upper-levels of a tropical cyclone (i.e. above the 500 mb level), you actually have a ridge that develops over the top of the lower-level cyclones (i.e. below 500 mb). When it transitions, though, that ridge gets separated from the lower-level cyclones, and they begin to link up with the broader mid-latitude trough (bringing back the idea of the westward tilt with height). During that process, you get tremendous height falls over the lower-level cyclones. When you have height falls aloft, that also means that you also have a decrease in temperatures aloft. Now, temperature naturally decreases with height in the atmosphere, but, relative to the cyclone when it was tropical, when these height falls occur, they result in a much more drastic temperature decrease in the upper-levels, which makes the atmosphere significantly less stable (cooler, more dense air now over top of that warm, moist, buoyant inflow air at the surface). When you add all of this together, you have a very conducive environment for severe weather in general.

Each extra-tropical transition event is different, and does present different types of threats. Beryl had a very good setup for discrete tornadic cells for northern New York State as it passed through southern Canada. Mt. Holly feels that Debby presents more of a squall line risk. Regardless, I would expect severe weather tomorrow.

jmanley32 wrote:Wow looks like tomorrow will be wild even east of Debby, maybe even more o than where Debby tracks. Tornado watches already up south of here. I will porbably head back in the early AM. BTW check out the Jazz Saxophonist Grace Kelly (not to be mistaken with the classic actress) shes who I saw in Old Saybrook CT tonight, was incredible show in a intimate setting.

They had a confirmed tornado in Delaware 3 hours ago.  

https://x.com/NWStornado

THIS JUST IN..



From what I understand a 9.0 is about a strong as they get.  Horrifying.

Tornado watch issued until 2pm, I don’t remember seeing a tornado watch issued this early in the day here in a long time

68 degrees, heavy showers on and off.
Tornado watch is up here as well.Holy crow!

rb924119 wrote:

To very little surprise, yet another absolutely fantastic discussion coming out of the Mt. Holly WFO. This belongs in an ATM 300+ level class because it's textbook. And, thanks for the shoutouts, gang

To your point, Scott, you're not entirely wrong, but if we zoom out a bit, I think it will become a lot clearer. As a tropical cyclone undergoes its transition to a non-tropical entity, you correctly stated that it starts becoming associated with baroclinic processes (i.e. becoming associated with fronts), which is correct, and it's all of the dynamics associated with that which lead to the severe weather threat.

Starting at the surface, the circulation is still clearly in tact and well-defined, so you have a very ageostrophic component, which is almost isallobaric (basically, the surface wind has a very strong cross-isobar component to it relative to a weaker, less-defined system). If you envision the center of circulation passing over Harrisburg, for example, there would be an east-southeast to southeast wind in the southeastern quadrant of it (I-95 Corridor), which is also what is evolving into the warm sector as the transition process continues. Moving above that, say, to the 850 mb layer, because it is transitioning, you are going from a well-defined low-level vorticity (spin) maximum when it's tropical, to now phasing into the broader mid-latitude trough. In order for that to happen, that local vorticity maximum opens up and shears out, which leads to an opening low-level trough over top of the surface circulation. Now, this same process occurs throughout the atmospheric column, but remember, as it becomes more non-tropical (less tropical), it begins to experience the westward tilting of its circulation with height. So, as the troughs at the 850 mb, 700 mb, and 500 mb layers open up and begin phasing into the broader mid-latitude trough, you begin to see a transition in the wind field from a concentric flow around the center of circulation when it's purely tropical (remember, tropical systems are vertically stacked, with all circulations located on top of each other), to a sheared environment. Thinking of a vertical profile, the wind in a transitioning tropical cyclone would look something like this, conceptually, from top to bottom, as the surface circulation begins to find itself downstream of the opening/shearing circulations above it:

500 mb: southwesterly
700 mb: south-southwesterly
850 mb: southerly
surface: east-southeasterly

Based on that profile, that is EXACTLY the directional shear profile of a classic supercell environment (think of a hodograph).

But we aren't done. In addition to the shear, you also have the warm, moist air in the same area (developing warm sector), which is inherently unstable itself. However, with the troughs opening up, now you enhance your differential voriticity advection in the vertical (atmospheric energy), which aids in broad forcing vertical motion/ascent. You also begin getting jet enhancement (in the right-rear quadrant, also favorable for broad ascent) from the upper-level heights compressing (convergence) in response to the upper-level ridge that was over top of the tropical entity now being forced downstream and my next point, and arguably, most important part of all of this - rapid height falls over the transitioning cyclone and increase in lapse rates (rate at which temperature changes with height). In the upper-levels of a tropical cyclone (i.e. above the 500 mb level), you actually have a ridge that develops over the top of the lower-level cyclones (i.e. below 500 mb). When it transitions, though, that ridge gets separated from the lower-level cyclones, and they begin to link up with the broader mid-latitude trough (bringing back the idea of the westward tilt with height). During that process, you get tremendous height falls over the lower-level cyclones. When you have height falls aloft, that also means that you also have a decrease in temperatures aloft. Now, temperature naturally decreases with height in the atmosphere, but, relative to the cyclone when it was tropical, when these height falls occur, they result in a much more drastic temperature decrease in the upper-levels, which makes the atmosphere significantly less stable (cooler, more dense air now over top of that warm, moist, buoyant inflow air at the surface). When you add all of this together, you have a very conducive environment for severe weather in general.

Each extra-tropical transition event is different, and does present different types of threats. Beryl had a very good setup for discrete tornadic cells for northern New York State as it passed through southern Canada. Mt. Holly feels that Debby presents more of a squall line risk. Regardless, I would expect severe weather tomorrow.

I just had the chance to read this and actually digest it. I had to look up a few definitions, but once I did the image of the processes you were laying out came to light. Fascinating Ray!

Love getting my weather geek on.

Thanks, Scott!

These gusts are getting serious here in NEPA. Already had a few casualties in the form of limbs, but so far, no trees. Lost power twice, and lights continue to flicker. Squall lines are now getting their acts together as they’re swinging through east-central PA, and the wind potential with those has me pretty worried based on what I’ve seen here so far. We will see how it goes, though lol

rb924119 wrote:Thanks, Scott!

These gusts are getting serious here in NEPA. Already had a few casualties in the form of limbs, but so far, no trees. Lost power twice, and lights continue to flicker. Squall lines are now getting their acts together as they’re swinging through east-central PA, and the wind potential with those has me pretty worried based on what I’ve seen here so far. We will see how it goes, though lol

Thus far luckily the winds here in central NJ are not bad, hoping the storms are not too bad later

Just heard a top or a tree go somewhere. Not sure where, and I’m not venturing outside to go look lol the squall like approaches…..

Tornado watch has been extended to 10pm for essentially northern central NJ on northward.