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General Severe Weather Discussion 2018


weatherwiz
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The biggest concern is going to be some weak height rises through much of the day and whether we can get a good forcing mechanism. Looks like the majority of the s/w forcing remains well to our west. We will be uncapped which will certainly help but our only source for buoyancy is just from unstable llvl air but nothing to really give an extra boost of support. 

EDIT: Nevermind...I was hovering over the wrong period :axe: looks like we will have subtle s/w moving through tomorrow but concern of height rises remain 

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10 minutes ago, CT Rain said:

Sooooo.... 21z SREF, latest HRRR, 00z NAM definitely have me concerned about a midday tornado threat. 

You’re not kidding...holy crap. Tremendous directional shear in the 0-3km layer with sufficient CAPE. Anything that gets going has plenty to work with 

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2 hours ago, CT Rain said:

Sooooo.... 21z SREF, latest HRRR, 00z NAM definitely have me concerned about a midday tornado threat. 

Figures. My car is out of commission so I can't chase this one even if something does happen - which it will because I can't chase. So it goes.

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15 minutes ago, Hoth said:

Lapse rates are pretty atrocious; not a lot of forcing either. But anything that does get going could certainly put down a spinner today given the CAPE, helicity, low LCL combo. Bad LRs are always a giant red flag for me though.

Depends on what you’re looking for. Many of our late July and August tornadoes occur with crap lapse rates.

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12 minutes ago, Hoth said:

Realize you're probably quite busy, but why don't lapse rates matter as much for tornadoes later in the summer? 

Part of the reason is typically later in the summer we have a higher likelihood for stronger llvl moisture which; 1) leads to lower LCL’s 2) enhances llvl instability and 3) combine this with strong shear in the 0-3km layer and you have potential for weak tornadoes. Basically we’re relying more on what’s going on in the llvls than the mid/upper llvls...especially when we aren’t really looking for storm tops exceeding 20,000-25,000’. I also believe with warmer SST’s this reduces the effects of marine air, especially in situations where dews are exceptionally high.

Also, steep mid-level lapse rates are typically more important when looking for significant severe widespread severe weather...this includes strong tornado potential. 

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41 minutes ago, Hoth said:

Realize you're probably quite busy, but why don't lapse rates matter as much for tornadoes later in the summer? 

If you want your classic supercell tornado like 1989 or 2011 you need the great lapse rates. This time of year we more often that not get tornadoes not from those epic setups but from setups like this. Deep moisture, anomalously strong mid level flow with a trough to the west, and a warm front coming through. 2013 Windsor, Revere, 2008 NH, etc are all examples of a super moist profile with enough shear to get the convective elements to spin.

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53 minutes ago, CT Rain said:

If you want your classic supercell tornado like 1989 or 2011 you need the great lapse rates. This time of year we more often that not get tornadoes not from those epic setups but from setups like this. Deep moisture, anomalously strong mid level flow with a trough to the west, and a warm front coming through. 2013 Windsor, Revere, 2008 NH, etc are all examples of a super moist profile with enough shear to get the convective elements to spin.

Thanks Ryan and Paul, that makes sense.

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49 minutes ago, Cyclone-68 said:

I wonder if the “if you want NE severe then see what happened in Michigan the day before” axiom applies this time?

We had unexpected tornado warnings in and around Detroit around midnight last night.

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Late last night at 2:00 am the HRRR and some other meso-models were clearly indicating isolated supercell activity along the CT coast and even Long Island around the 22z time frame... That's all gone now - no strong cells or helicity swaths of note in southern CT anymore, the show has moved northwest... Congrats POU indeed, although there's precious little even up there now. Anyway, don't feel so bad about having to sit this one out, it's looking like any spin-up will be transient, weak, and not very close to me.

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mcd1215.gif

Mesoscale Discussion 1215
   NWS Storm Prediction Center Norman OK
   1248 PM CDT Wed Aug 01 2018

   Areas affected...Portions of northern NJ...southern NY including
   NYC...and CT

   Concerning...Severe potential...Watch unlikely 

   Valid 011748Z - 012015Z

   Probability of Watch Issuance...5 percent

   SUMMARY...Thunderstorms moving northward across a warm front may
   pose a brief/isolated tornado and strong wind risk through the
   afternoon. Watch issuance is not expected.

   DISCUSSION...Lightning has recently developed with shallow
   convection across far northern NJ into southern NY. This activity is
   probably associated with a weak mid-level impulse and related
   low-level warm air advection. 17Z surface analysis shows a warm
   front draped west-to-east across this region. Although mid-level
   flow remains mostly unidirectional from the southwest, modest
   veering and strengthening of the low-level winds is present along
   the warm front per recent VWPs from KOKX, KENX, and KBOX. Related
   effective SRH values of 100-150 m2/s2 along and south of the warm
   front may be sufficient to support weakly rotating updrafts, with a
   brief/isolated tornado and strong wind gust possible. Lapse rates
   will remain poor across this region today, which coupled with
   widespread cloudiness will likely limit instability. Therefore, the
   overall severe threat is expected to remain quite marginal and
   isolated, with watch issuance not expected.

   ..Gleason/Grams.. 08/01/2018

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...BOX...OKX...ALY...PHI...
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