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General Severe Weather Discussion 2018


weatherwiz

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12 minutes ago, OceanStWx said:

I don't love how the CAMs seem to be trending towards convection arriving later in the day for WNE. 

Like the HRRR has a pocket of clearing, but it doesn't move into New England until 19z. That's not a lot of time to destabilize.

Do you think cloud cover is a bit overdone?  (This link I used to use to see cloud top temps doesn’t seem to have it anymore so not sure if there are indications of warning tops) but the IR doesn’t look horrible. 

But yeah I agree that the timing of things so late could be concerning. The NAM though does have some solid s/w energy moving through between 21z and 0z which I would think should initiate things sooner. 

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7 minutes ago, weatherwiz said:

Do you think cloud cover is a bit overdone?  (This link I used to use to see cloud top temps doesn’t seem to have it anymore so not sure if there are indications of warning tops) but the IR doesn’t look horrible. 

But yeah I agree that the timing of things so late could be concerning. The NAM though does have some solid s/w energy moving through between 21z and 0z which I would think should initiate things sooner. 

Could be, but the HRRR is attempting to fire things around dawn on the nose of the LLJ. That could certainly muck up clear skies for New England. 

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4 minutes ago, OceanStWx said:

Could be, but the HRRR is attempting to fire things around dawn on the nose of the LLJ. That could certainly muck up clear skies for New England. 

I wonder if we can escape that down this way. Seems like this tries to happen northwest of here and that activity that does develop may try to strengthen through the morning as it heads into central/northern New England. If things sort of time right with that seems like it’s also just ahead of the warm front so maybe a line of broken supercells? 

Down here in CT we may escape and be able to push well into the mid 80’s for highs...although nothing really approaches (per 3km NAM) until 0z and then completely falls apart but then a huge redevelopment around 6z. 

Not much of a cap tomorrow so and some of the soundings down here are quite impressive by 20-21z so if a cell can pop and there is enough upper support around it has plenty to work with 

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17 minutes ago, weatherwiz said:

I wonder if we can escape that down this way. Seems like this tries to happen northwest of here and that activity that does develop may try to strengthen through the morning as it heads into central/northern New England. If things sort of time right with that seems like it’s also just ahead of the warm front so maybe a line of broken supercells? 

Down here in CT we may escape and be able to push well into the mid 80’s for highs...although nothing really approaches (per 3km NAM) until 0z and then completely falls apart but then a huge redevelopment around 6z. 

Not much of a cap tomorrow so and some of the soundings down here are quite impressive by 20-21z so if a cell can pop and there is enough upper support around it has plenty to work with 

A lot of the flashy parameters are basically 3 km and lower, so I wonder if it is just a crappy day to be radar operator where storms are shallow and subtly severe or clearly tornadic.

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10 minutes ago, OceanStWx said:

A lot of the flashy parameters are basically 3 km and lower, so I wonder if it is just a crappy day to be radar operator where storms are shallow and subtly severe or clearly tornadic.

That’s certainly a possibility..and would virtually mean that the meh mid-level lapse rates don’t matter in this case. I know at least the 12z NAM bufget showed 0-1km CAPE values almost at 100 J. LCL’s too are quite low and there is a great deal of CAPE and shear around the LCL height. Storm motion too almost looks like that alone can enhance helicity even more 

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11 minutes ago, RUNNAWAYICEBERG said:

Nam been doing well with severe lately around these parts. Already prefered by OKX this morning. Severe day ahead, be prepared. 

Things this morning look quite intriguing although there are still some uncertainties...or disagreements. but instability is looking incredibly impressive...we could be looking at MLCape values approaching 2000-3000 when shear is increasing. HRRR/3km NAM do hint at some discrete like cells later on this afternoon and early evening and with secondary development around 6z. 

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20 minutes ago, Cyclone-68 said:

Not even a mesoscale discussion yet. Still a bit early maybe?

Yes. We really don't want things popping up this early (well if you want severe). The best overlap of ingredients doesn't seem to be until between like 6:00 PM and possibly as late as 2-3:00 AM. Butt he focus area seems to be 6-10 PM. Still torn on around 2-3 AM...really mixed signals but some of the signals are a bit impressive. 

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CAMs were always (well, since last night) showing basically two waves of storms, one around 19z which has already materialized, and then another after 0z (for some models well after) so it's playing out the way it was modeled, so far... That said, the good shear seems to be hanging back west well behind this first line of storms, and who knows how much instability will be left later on, so...

As always, we wait, and we'll see. It is what it is. I've learned never to get exited about these kind of setups.

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And we have an appropriately meh MD out. hard to get exited about "a few marginal supercell structures":

Mesoscale Discussion 1307
   NWS Storm Prediction Center Norman OK
   0142 PM CDT Fri Aug 17 2018

   Areas affected...Portions of central/eastern NY/PA...northern
   NJ...southern VT...and western MA/CT

   Concerning...Severe potential...Watch possible 

   Valid 171842Z - 172115Z

   Probability of Watch Issuance...60 percent

   SUMMARY...An isolated threat for strong to locally damaging winds
   should continue to increase this afternoon as thunderstorms develop
   and move eastward. A Severe Thunderstorm Watch may be needed within
   the next couple of hours.

   DISCUSSION...Airmass recovery is well underway across parts of
   eastern NY/PA behind morning showers and thunderstorms associated
   with a low-amplitude lead shortwave trough over New England as of
   1830Z. Continued diurnal heating across this region given cloud
   breaks noted on visible satellite imagery will allow surface
   temperatures to generally reach into the mid to upper 80s, and
   plentiful low-level moisture will contribute to MLCAPE around
   1000-2000 J/kg along and south of a warm front. However, poor
   mid-level lapse rates noted on 12Z soundings from ALB, BUF, and PIT
   will likely temper even greater instability this afternoon. The 18Z
   sounding from ALB modified for current conditions shows some
   steepening of low-level lapse rates, and this process should
   continue with eastward extent across western MA/CT and southern VT
   as the surface warm front lifts northward.

   Recent VWPs from BGM, CCX, and ENX show low-level southerly winds
   veering quickly to southwesterly in the 0-6 km AGL layer, although
   the magnitude of these winds remain generally limited (at or below
   30-35 kt). Even so, around 25-35 of resultant effective bulk shear
   should prove adequate for scattered thunderstorms organizing into
   multicell clusters. This convection will mainly pose an isolated
   strong to damaging wind threat this afternoon and early evening
   given the steepening low-level lapse rates and modestly
   strengthening low to mid-level flow. A few marginal supercell
   structures with some hail threat may also occur with south/westward
   extent where instability is stronger. A brief tornado cannot be
   completely ruled out along the warm front given the locally backed
   near-surface winds locally enhancing 0-1 km SRH. Given the expected
   increase in thunderstorm coverage and intensity over the next couple
   of hours, a Severe Thunderstorm Watch may be needed to address this
   threat.

   ..Gleason/Dial.. 08/17/2018
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