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2017 Severe Thread


mappy

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1 minute ago, George BM said:

I'm also wondering about any CAD Thursday. NAM seems to have some CAD during the morning.

That would be awful...especially since 1) CAD is slow to erode and 2) it's already coming in earlier than ideal. I smell a meh coming unless we can get some Bob magic. I'm not in at this time. 

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3 minutes ago, Kmlwx said:

That would be awful...especially since 1) CAD is slow to erode and 2) it's already coming in earlier than ideal. I smell a meh coming unless we can get some Bob magic. I'm not in at this time. 

Not always... if the WF comes through CAD will be eroded quickly

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1 minute ago, yoda said:

Not always... if the WF comes through CAD will be eroded quickly

         It may not be that the WF blasts through, but it may set up right across the DC metro area and enhance the SVR threat along and especially just southeast of it.   The low-level winds will be backed in a big way, such that even though the 500 flow is southerly, you might still have a lot of low-level shear.    And you have a 50 kt LLJ in place.     As has been noted, the timing is far from ideal, but this still has a chance.

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4 minutes ago, yoda said:

Not always... if the WF comes through CAD will be eroded quickly

You're still then left with timing issues. And I haven't even looked at cloud cover potential for Thur morning which would be another wild card that tends to screw us over. Your optimism is always appreciated. The WxWatcher007 scale needs to be brought out again. 

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I could see this being an event where the timing sucks but some mini sups put down a spinny or two in the favored areas. I don't think this will be a moderate or anything of that nature. Naturally, MBY will probably miss out. Besides...I'll be at work anyway. 

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1 minute ago, high risk said:

         It may not be that the WF blasts through, but it may set up right across the DC metro area and enhance the SVR threat along and especially just southeast of it.   The low-level winds will be backed in a big way, such that even though the 500 flow is southerly, you might still have a lot of low-level shear.    And you have a 50 kt LLJ in place.     As has been noted, the timing is far from ideal, but this still has a chance.

Very interesting... in which direction would the low level winds be backed?  Westerly?

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19 minutes ago, yoda said:

Very interesting... in which direction would the low level winds be backed?  Westerly?

       What I'm saying is that in terms of having the winds veering with height that you need for supercells, we're almost always screwed here (and same is true for most areas) when the winds in the mid levels are southerly, since the sfc winds are southerly, and you lose directional shear.    But you can work with mid-level southerlies IF the low-level winds are backed (in a direction more counterclockwise from the mid levels), and the 12z NAM shows southeast low-level flow.

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26 minutes ago, Kmlwx said:

The 12z NAM on the Nexlab site gets a nose of good parameters as close as Southern Maryland but no cigar for the rest of us. Hope to trend that better. 

        yeah, right now the NAM has the warm front only getting to Route 50, and lead showers destroying any chance of destabilizing.    To be clear, I'm not optimistic about the chances, but I do see a way it can work out.

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4 minutes ago, high risk said:

        yeah, right now the NAM has the warm front only getting to Route 50, and lead showers destroying any chance of destabilizing.    To be clear, I'm not optimistic about the chances, but I do see a way it can work out.

Timing is a problem with like 90% of our chances so I pretty much just roll with the punches. I'm not very good at severe anyways other than seeing a general setup that can do some fun things. Which I think we have on tap. 

We are lacking in the timing dept but the upper levels definitely point to an active period regardless. I'll take it. It's a pretty good ULL position and plenty of vorticity overhead. LLJ support is decent too. There will be "embedded fun" in the mix Thursday. I'd be happy with some prolific CG and heavy downpours. A fair number of us should see that type of action at least. 

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17 minutes ago, high risk said:

       What I'm saying is that in terms of having the winds veering with height that you need for supercells, we're almost always screwed here (and same is true for most areas) when the winds in the mid levels are southerly, since the sfc winds are southerly, and you lose directional shear.    But you can work with mid-level southerlies IF the low-level winds are backed (in a direction more counterclockwise from the mid levels), and the 12z NAM shows southeast low-level flow.

Ah okay... thanks for explaining.  I was a little bit confused

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42 minutes ago, Bob Chill said:

Timing is a problem with like 90% of our chances so I pretty much just roll with the punches. I'm not very good at severe anyways other than seeing a general setup that can do some fun things. Which I think we have on tap. 

We are lacking in the timing dept but the upper levels definitely point to an active period regardless. I'll take it. It's a pretty good ULL position and plenty of vorticity overhead. LLJ support is decent too. There will be "embedded fun" in the mix Thursday. I'd be happy with some prolific CG and heavy downpours. A fair number of us should see that type of action at least. 

We could probably manage with a storm period of 16z-18z as long as we can instability. I'm not sure if anything before 14 or 15z will be late enough to be a ton of fun. But yes, I'd say storminess is a good bet ;)

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10 minutes ago, yoda said:

I would also assume it is good for some severe with the SLP being that close, no?

 

      absolutely!    It would get most of the area into the warm sector.    The wind profile might be unidirectional, with better low level shear along the Mason/Dixon line, but I'd rather get the instability in place and worry about the shear later.      I'm glad I'll be back for this;  heading to Boulder today where I'll get a final taste of winter.

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Certainly looks like SEVA and maybe central VA will be the places to be for this one. Models continue to be pretty paltry with our composite parameters. Looks stormy at least...but a robust severe day would be fun. Maybe later into the season?

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LWX likes it; morning AFD diso:

Much of Wednesday expected to be quiet...as high pressure remains
over the area. Things begin to change late Wednesday as low pressure
shifts toward the area. Warm air advection precipitation ahead of
the main system expected to begin by evening and continue through
the overnight. Severe potential increases across the SW overnight as
wind field strengthens substantially due to cyclogenesis across the
Appalachians coincident with large area of lift near the nose of a
100 kt jet. Severe threat then spreads into the rest of the area
from Thursday morning through midday Thursday. While instability is
expected to be rather modest (generally 500-800 J/kg MLCAPE),
strongly veering wind profiles (especially at the lowest levels)
will create rather strong kinematics and the potential for supercell
thunderstorms. Furthermore...backed surface winds will contribute to
rather large low-level shear...with some potential for tornadoes.
Best chance for enhanced severe expected across central VA...where
boundary layer moistening will be greatest. Current SPC Day 2
outlook highlights the SW portion of the area in a marginal risk for
storms late Wednesday and then an Enhanced/Slight for Day 3
(Thursday) along and east of the Blue Ridge.

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From LWX morning HWO:

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

There is a slight risk of severe weather during the middle of the
day Thursday. South of Washington DC, there is an enhanced risk.
Localized wind damage will be the primary threat. A couple of
tornadoes will be possible.

A Gale Warning will be possible Thursday night into Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be required Thursday.

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