Severe Weather possible weekend of the 21st?

[weatherwiz]

When the Storm Prediction Center (SPC) issued their D4-8 convective outlook at 3:56 AM CDT on the morning of July 14th, they did something you very rarely see around these parts.  They included a large chunk of the Northeast, including all of New England in a D7 severe t'storm risk, which equates to 30% severe weather probabilities, or a 30% chance of seeing a severe weather report within 25 miles of any point within the shaded area.  Below is a graphic of the outlook:

 

 

Based on the image above, the SPC has enough confidence in the output of various model solutions that w could be dealing with perhaps a 3 consecutive day severe weather outbreak from the upper Mid-west all the way to the Northeast coast.  Based on the discussion of the outlook, it sounds as if we could be looking at the possibility of one or perhaps several very strong convective lines capable of widespread wind damage.  

 

For the SPC to include any area, especially the Northeast in a D7 outlook, there has to be very strong model agreement on the overall synoptic pattern, along with agreement on the timing/placement of features as cold fronts and shortwave energy and models also have to give the idea that a strong thermodynamic/kinetic environment will also be in place.  

 

Both the GFS/Euro are in very strong agreement that a strong piece of energy will slide through southeastern Canada.  This will allow for a trough to develop across the upper Mid-west and slide a very strong cold front eastward.  Both models are also showing very strong wind fields associated with the system as a strong pressure gradient between the developing trough and strong Bermuda High across the southeast tighten the pressure gradient.  Both models are forecasting winds in the mid-levels of the atmosphere to be strong enough to yield vertical shear values quite favorable for the development of organized convective lines.  

 

Both the GFS/Euro also suggest a pattern favorable for the advection of steeper mid-level lapse rates into the region.  While the pattern does suggest elevated mixed-layer (EML) potential, forecast soundings on the GFS aren't exactly EML-like, however, the GFS does have lapse rates in the 6.5-7 C/KM range which with surface dewpoints expected to be at least in the mid to upper 60's could yield to some moderate to extreme instability values depending on how much sun and surface heating we would receive.  

 

Being 7 days out, much can change here, especially in the Northeast where something always seems to go wrong.  As of now though, the Euro/GFS are in strong agreement with multiple features and seem to be handling the evolution of the pattern quite well.  

 

Some things to watch for too is how far south the piece of energy tracks across southeastern Canada.  If this tracks further south, we would see even stronger shear and even higher helicity values which could lead to the possibility of a tornado threat somewhere across the region, in addition to the threat for widespread damaging winds.  Steeper lapse rates and strong vertical shear values would also suggest large hail would be a threat.  

 

 

 

[ineedsnow]

hope it works out..

[weatherwiz]

I have to help my brother move on Saturday so I'm hoping this can get done early.  He's moving to Windsor Locks so I'll be in a decent spot!

[Ginx snewx]

AIT

[Damage In Tolland]

2-4 derechos seem possible, lolli to 5

[joey2002]

Somebody at SPC is feeling very bold issuing those 5-6-7 day forecasts... 3 day severe probs are difficult enough here.

[ineedsnow]

one if your lucky

2-4 derechos seem possible, lolli to 5

[mob1]

2-4 derechos seem possible, lolli to 5

Lol, labor day '98 redux? I wonder if there were a few places in extreme northern PA who got hit by both derechos that day.

[weatherwiz]

Somebody at SPC is feeling very bold issuing those 5-6-7 day forecasts... 3 day severe probs are difficult enough here.

 

The model agreement is amazing right now and the SP has even mentioned us the past few days.  Like BOX says, it's very difficult to escape this type of pattern without severe weather somewhere.  All the pieces are there...now it's virtually just getting the timing right...and this is actually the type of setup too where we can get severe at night.

[Typhoon Tip]

-Nice effort Wiz'

 

You're writing has improved over the years.  

 

Couple of quick comments:

-- Indeed ... MCS would seem plausible ahead of any cold fropa/trough -related convection, because as the core of the ridge node retrogrades, heights slowly receding out ahead of the trough.  The region should cross a stability threshold whence less inhibition begins.  Could see the old ESE thunderstorm cluster that's triggered by just about anything upstream, running down a degree and a half S of the isopleths out there beyond Wednesday.   Perhaps a couple of them. 

 

-- Big ridge and heat events don't have a very impressive "end with a bang" climatology.  You'd think they would, given to having so much ginormous energy stored below days of capping, such that when the cap recedes ...boom.  But no...  If you go back and look at big ridge events in the past, the heat tends to end with a whimper.   In fact, if we did get MCS exhausted that would of course mitigate trough -related potential.

 

Oy vay convection details are mind numbing.

[Ginx snewx]

most of the high heat spells I can remember end with a great thunderstorm

[CoastalWx]

Most of the recent spells ended meh.

[weatherwiz]

-Nice effort Wiz'

 

You're writing has improved over the years.  

 

Couple of quick comments:

-- Indeed ... MCS would seem plausible ahead of any cold fropa/trough -related convection, because as the core of the ridge node retrogrades, heights slowly receding out ahead of the trough.  The region should cross a stability threshold whence less inhibition begins.  Could see the old ESE thunderstorm cluster that's triggered by just about anything upstream, running down a degree and a half S of the isopleths out there beyond Wednesday.   Perhaps a couple of them. 

 

-- Big ridge and heat events don't have a very impressive "end with a bang" climatology.  You'd think they would, given to having so much ginormous energy stored below days of capping, such that when the cap recedes ...boom.  But no...  If you go back and look at big ridge events in the past, the heat tends to end with a whimper.   In fact, if we did get MCS exhausted that would of course mitigate trough -related potential.

 

Oy vay convection details are mind numbing.

 

Thanks!!

[weatherwiz]

Most of the recent spells ended meh.

 

Too be fair though, the setups at the end of them were rather meh.  For example, last week all the shear was post-frontal as were the steeper lapse rates.  This time, however, it appears we will have stronger shear out ahead of the cold front in response to a strong vortmax and steeper lapse rates will work over the ridge into the region...obviously that can change but this has been modeled for a few days now by both the Euro/GFS with great support and agreement. 

[Ginx snewx]

Most of the recent spells ended meh.

Have we had a high heat spell yet?

[CoastalWx]

Have we had a high heat spell yet?

 

I'm talking since 2010.

[Quincy]

This setup definitely has potential and timing will just be one of many important variables.

I've already taken Friday off from work in preparation as it could be a multi-day event from the upper Midwest into the Great Lakes and possibly Northeast. The greatest potential I've seen this far out all year...

[CoastalWx]

Shear looks decent if things can time right. Lapse rates are "ok."

[weatherwiz]

Shear looks decent if things can time right. Lapse rates are "ok."

 

GFS had 6.5-7 C/KM across much of the Northeast

[Ginx snewx]

I'm talking since 2010.

Oh, but yea I remember the July 2011 heat was broken on the 26th by a strong line which caused big power outages, June 2012 had the big T storm line on the 22nd which ended a heat wave. we really have not had many big heat outbreaks. This is in CT

[CoastalWx]

GFS had 6.5-7 C/KM across much of the Northeast.

 

6.5C on my product and that barely tickles us.

[Quincy]

Discussing lapse rate details this far out is not far off from talking about the freezing line in the winter 144 hours out.

[joey2002]

Discussing lapse rate details this far out is not far off from talking about the freezing line in the winter 144 hours out.

 

[weatherwiz]

6.5C on my product and that barely tickles us.

 

SO what are they here?  6-6.5?  As long as they are over 6 that's decent enough.

 

Discussing lapse rate details this far out is not far off from talking about the freezing line in the winter 144 hours out.

 

This is true

[CoastalWx]

SO what are they here?  6-6.5?  As long as they are over 6 that's decent enough.

 

 

This is true

 

But it's probably going to be close to reality.

[Damage In Tolland]

3 days of severe seems likely Thurs-Sat for all

[weatherwiz]

But it's probably going to be close to reality.

 

I'll still take 6-6.5 lapse rates...especially if we have dews touching 70F and strong shear/instability.  

[weatherwiz]

This is getting picky but the GFS has the strongest mid-level winds move through in the early AM...this just goes under the timing category I guess.  

[Quincy]

I'm actually skeptical of widespread severe east of let's say BGM, but we'll see what happens. Timing is either going to need to push back on Saturday or speed up Friday.

[Damage In Tolland]

The front comes thru Sunday