12/1/10 convective threat

[weatherwiz]

When one thinks of late fall in the Northeast once doesn't usually think of convection and especially severe wx. By this time of year we aren't very warm, aren't very humid and due to this we generally don't see much instability. What we do normally see this time of year though is at times, pretty potent dynamic systems with strong cold fronts, strong dynamics, and some excellent lift. These are some of the factors that can compensate for the lack of instability.

As we all know by now we have been in a La Nina state for several months now and we are basically on the verge of entering a strong La Nina episode. What on earth does this have to do with convection? During moderate to strong La Nina events it isn't all that uncommon to see some late season severe weather episodes occur here in the Northeast, although as you enter into southern New England potential can rapidly decrease as you have stabilizing effects from Long Island Sound (for places like CT and parts of RI) and you have stabilizing effects from the Atlantic (for places out in eastern MA and RI as well). The flow off the now cooler waters tends to lead to an inversion just above the surface which can really inhibit stronger winds aloft from reaching the surface, even with the aid of convection.

We also have to deal with the fact that the surface low's usually begin to slowly weaken as they approach our area, the system begins to slowly lose its potency and dynamics begin to slowly decrease, lift isn't as solid, and everything can begin to become rather displaced, and often times our area will not quite make it into the favorable right rear quadrant of the ULJ. Sometimes the lows can actually take a too far northeastward track and move well into Canada, this allows the better lift and the better dynamics to miss our area to the northwest as well and we end up with an unorganized area of precip with embedded thunder.

As stated above, severe weather events are not totally uncommon during moderate to strong La Nina falls, while we didn't see anything occur during the fall of 2007 we did see a few events during the fall of 2006. One event was on November 16th, 2006, this event had zero impact on SNE in terms of severe but it did produce pockets of wind damage across portions of PA and upstate NY. This was a rather impressive event as it caused some pretty significant damage in areas of NY with reports of roofs being blown off and a measured wind gust as high as 74 mph!

The next and final event of that fall, which actually occurred on the first day of meteorological winter which actually much more impressive, not only causing damaging wind from PA to as far east as SW ME but it also produced several tornadoes in the state of PA. A nasty serial derecho rapidly developed in the early morning hours and continued to race eastward with embedded supercells. This setup actually warranted a moderate risk for a good portion of the Northeast. I also believe this was the FIRST time since late 2001 that the BOX CWA had been under a moderate risk...pretty impressive.

Prior to 2006 we have to go way back to 1989, probably one of, if not the most impressive late-season fall severe weather outbreak to strike the Northeast, again, the action just missing SNE to the west. NJ/NY were hit extremely hard. A total of 19 tornadoes were confirmed in PA/NJ/NY with 15 of those coming in NY/NJ alone! There were also 109 reports of damaging winds as well associated with convection.

As we head into next week and towards the first of December both the Euro and the GFS both agree that a rather potent storm system will be developing across the west and the strengthening as it moves through the Plains and into the Ohio Valley region before finally entering the Northeast. As the system advances eastward we will see a strengthening surface low as a pretty strong Arctic jet and sub-tropical jet work to draw in colder drier air from the north and warmer and more moist air from the south. As this surface low increases so will the southerly flow out ahead of it, this will allow for heights to begin building in the east which means warmer and more moist air will be transported northward, aided by a warm front which will be lifting northward. This system will have the potential to produce several days of several weather across portions of the Plains, upper-Midwest, and into the Ohio Valley as it appears there will be some quality moisture returns to go along with very strong dynamics aloft. With a very strong Arctic front and trough plowing into the warm sector we will see temperature in the mid-levels of the atmosphere begin to cool, this will aid in the development of instability aloft as well as increase the lapse rates.

As the system inches closer towards us here in the Northeast we will begin to enter the true warm sector of this system. As of right now it doesn't appear to be all that impressive, although timing will certainly dictate where we end up temperature wise. It does appear as if we will be dealing with some pretty nasty dynamics at 500mb/250-300mb. These dynamics coupled with a potent cold front approaching the region should be enough to generate a great amount of lift, with cooling temperatures occurring aloft helping to slowly increase the mid-level lapse rates this will further help to enhance the lift. It's quite possible we here in southern New England may see the potential for a low-topped squall line with the potential to produce some gusty winds.

This is still about a week or so away so too far out to go into specifics but the pattern being depicted certainly favors for this potential to occur. We've also already seen a pretty decent event occur in the Northeast, last Wednesday, while this produced some pockets of wind damage across our area it managed to produce an EF1 tornado in Columbia county NY at 5:18 AM as well as an EF! tornado/100 mph MACROBURST in Baltimore, MD hours before that.

Once this system clears our area it looks like we may be able to welcome a little taste of winter into the region as some colder air will finally work in and perhaps stay with us for a while as the models are beginning to hint at the idea of a -NAO/-EPO/-PNA pattern. The -NAO/-EPO should definitely help with getting some colder anomalies to quickly build into Canada and eventually potentially spill into our region and the -PNA should help to keep the pattern fairly active.

Fun times lay ahead over the next several weeks...doesn't look like it will be that boring and there should be at least plenty to discuss.

[nzucker]

Great post but this is not the subtropical jet causing the storm. It's actually a split flow in the polar jet, and you can see it pretty clearly on the 0z GFS.

[weatherwiz]

Thanks.

I agree there, Nate but I'm talking about December 1st...not this weekend

[nzucker]

Thanks.

I agree there, Nate but I'm talking about December 1st...not this weekend

I'm talking about December 1st as well...the origin of the storm is a split in the polar jet off the California coast which sends one branch to dig in the Desert SW while the other branch is a close 534dm low near the OR/WA border. When these two parts of the polar jet phase on the backside of the Pacific ridge, you have a deepening cutter over the Plains...

[free_man]

last warm sector system? lol

[Damage In Tolland]

LOL

[Tropopause_Fold]

Great post but this is not the subtropical jet causing the storm. It's actually a split flow in the polar jet, and you can see it pretty clearly on the 0z GFS.

you are such a dinkus sometimes.

[free_man]

you are such a dinkus sometimes.

Slight risk extended into Tri-state area.

[weatherwiz]

last warm sector system? lol

Well for now lol. Until January

[weatherwiz]

That is one sick jet streak at 500mb on the GFS

[weatherwiz]

Still looking good for some convection next week, probably more like elevated convection but still, maybe some decent lightning out of it. Very strong lift and forcing should be the main drivers here. Should end up with some decent elevated instability as well with WAA occurring in the low-levels and CAA occurring in the mid levels, this should help steepen the mid level lapse rates some.

[Damage In Tolland]

:weenie:

[MaineJayhawk]

:weenie:

I was wondering how many buns you were going to deliver.

[powderfreak]

You know you are not in a favorable pattern when Wiz is posting thunderstorm and severe threads for a December 1st event.

[weatherwiz]

I also just realized this but I had mentioned December 1st, 2006...well that occurred in a Nino, not Nina, I had stated that occurred in a Nina.

[New England Storm]

I also just realized this but I had mentioned December 1st, 2006...well that occurred in a Nino, not Nina, I had stated that occurred in a Nina.

That was one the first threads I read on Eastern, good times. Did a Tornado Watch get issued for some parts Mass, RI,Ct that night?

[weatherwiz]

That was one the first threads I read on Eastern, good times. Did a Tornado Watch get issued for some parts Mass, RI,Ct that night?

Yeah, as the line continued to race eastward and it continued to show areas of embedded supercells with strong rotation the watch was extended into eastern NY...when warnings continued to fly the watch was then expanded to cover W MA and W CT but it didn't get any further than that. I don't remember if there were any tornado warnings for MA but there was one in CT in Litchfield county.

[weatherwiz]

Well I think it still looks interesting next Wednesday for a possible forced low-topped line convection. Still unclear as to how warm we will become as if the sfc low moves anywhere further NW of us that will allow for more warmer and moist air to transport into the region. One thing that seems certain is we will be seeing some sick lift...pretty strong Arctic front pushing through and the dynamics at 500mb are through the roof...a 100-125 kt MLJ max is nothing to sneeze about.

[Damage In Tolland]

It will be December lol.

[weatherwiz]

It will be December lol.

It was also December in 2006.

[Collinsville]

Well I think it still looks interesting next Wednesday for a possible forced low-topped line convection. Still unclear as to how warm we will become as if the sfc low moves anywhere further NW of us that will allow for more warmer and moist air to transport into the region. One thing that seems certain is we will be seeing some sick lift...pretty strong Arctic front pushing through and the dynamics at 500mb are through the roof...a 100-125 kt MLJ max is nothing to sneeze about.

Wow, I forgot how much I miss your low topped supercell threads!! So what are we looking at for verification, gusty showers with two reports of sesame seed size hail?

[weatherwiz]

Wow, I forgot how much I miss your low topped supercell threads!! So what are we looking at for verification, gusty showers with two reports of sesame seed size hail?

Thanks!

As for verification purposes I guess if there are any reports of thunder/lightning

I'm not entirely sure if we'll be able to generate any winds for the line, despite the fact that winds aloft will be quite strong. Given how we may not break out into the true warm sector we will probably be dealing with a very strong low-level inversion, I could see places off to our west (like E PA/NY) getting some winds. Depending on how tall storms grow there could be a report of hail or two but probably nothing criteria wise.

The better chance for winds could come on the backside as the front passes and the secondary low potentially deepens fast enough, which if this occurs could give some snow showers on the backside to portions of the area. With strong CAA occurring with the passage could be looking at another evening/overnight period with some pretty strong winds.

[weatherwiz]

Well Wednesday still looks fairly good for some convection embedded within an area of pretty heavy rainfall. Luckily this will be a rather progressive system so flooding shouldn't be an issue although there could be some pockets of isolated poor drainage flooding.

[Damage In Tolland]

[weatherwiz]

Get ready, it's coming.

[Typhoon Tip]

What you are most likely to get in this scenario is a band of warm rains relative to the season with embedded 45 dbz showers, and general windy conditions, occasionally gusting to advisory in the valleys to marginal warning levels on the hill tops. Couple few power outages sure. Then, along and just ahead of the cfropa there will be a ribbon echo squall that will lower visibility to an 1/8th of a mile and back the wind rather abruptly into the west with damaging gusts possible. Then, 10 minutes later ...the wind drops to 10-15mph or so across the board and light rain goes to broken in moon light. Some two or so hours later there are a few good CAA gusts over the tree tops but your done. It would not shock me if very few hear any thunder.

[Damage In Tolland]

Moreso than storms..what we'll see if gust to 60 or higher even in valleys as this is sou easterly..not south..no inversion that way

[weatherwiz]

What you are most likely to get in this scenario is a band of warm rains relative to the season with embedded 45 dbz showers, and general windy conditions, occasionally gusting to advisory in the valleys to marginal warning levels on the hill tops. Couple few power outages sure. Then, along and just ahead of the cfropa there will be a ribbon echo squall that will lower visibility to an 1/8th of a mile and back the wind rather abruptly into the west with damaging gusts possible. Then, 10 minutes later ...the wind drops to 10-15mph or so across the board and light rain goes to broken in moon light. Some two or so hours later there are a few good CAA gusts over the tree tops but your done. It would not shock me if very few hear any thunder.

I love these setups

Moreso than storms..what we'll see if gust to 60 or higher even in valleys as this is sou easterly..not south..no inversion that way

Have to see how much we get warm sectored as well, if we can get sfc temps to get near 60F or just above that would definitely help.

[weatherwiz]

Man does Wednesday look fun. Going to get on the warm side with temps probably climbing fairly close to 60F mark and dewpoints probably rising close to that as well just south of the warm front which looks to briefly lift through SNE. Not too long after this occurs a very intense area of rainfall will approach us from the SW which will also have potential to produce some pretty strong wind gusts...wouldn't be shocked to see a dying band of low-topped convection approach us.

Depending on how well and long we warm sector this could create a period of time for some pretty strong non-convective gusts as well.

Once the front passes strong CAA works in and we may see a several hour period for some very strong wind gusts across the entire region. Maybe some snow flakes or snow showers to end for some?

[Damage In Tolland]

Man does Wednesday look fun. Going to get on the warm side with temps probably climbing fairly close to 60F mark and dewpoints probably rising close to that as well just south of the warm front which looks to briefly lift through SNE. Not too long after this occurs a very intense area of rainfall will approach us from the SW which will also have potential to produce some pretty strong wind gusts...wouldn't be shocked to see a dying band of low-topped convection approach us.

Depending on how well and long we warm sector this could create a period of time for some pretty strong non-convective gusts as well.

Once the front passes strong CAA works in and we may see a several hour period for some very strong wind gusts across the entire region. Maybe some snow flakes or snow showers to end for some?

Joe D not big on winds at all..though he tends to always play things conservatively