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Short-Term Severe/Flooding Discussion


Quincy
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26 minutes ago, mfgmfg said:

A bit off topic, but I was trying to get the outlook for Friday and keep running into this on and off - been having issues with other noaa.gov sites too, anyone else?

oAgFdWn.png

Yep... you can use http://kamala.cod.edu/SPC/ when this happens. It doesn't have as many features for the maps as SPC does, but it gets the job done, and usually updates faster than the actual SPC page. 

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1 hour ago, Wmsptwx said:

Looking like a few prolific hailers potentially this afternoon. 

Plenty of very large hail events showing up in the analog soundings. I generally take these with a grain of salt, since the matches are usually loose, but there's still a pretty strong signal there. 

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Quote

 ...Southern Plains into Ozark Plateau...
   An initial organized convective system, which evolved across
   central/eastern Oklahoma earlier today, now appears in the process
   of weakening across parts of northwestern Arkansas.  New convection
   is in the process of developing in its wake, near/east of the
   Interstate 35 corridor of Oklahoma, as a cyclonic 50-70 kt 500 mb
   jet streak noses east southeast of the Rockies, through the
   Texas/Oklahoma Panhandle region.  Subsequent evolution of this
   convection remains at least somewhat unclear, but due to the frontal
   progression and the influence of the initial convective cluster,
   strongest new convective development probably will eventually become
   focused near the Red River by late this afternoon.  This is within
   the thermal gradient along the northern periphery of a plume of
   warmer and capping elevated mixed layer air, where forcing for
   ascent will be aided lower/mid tropospheric warm advection.  The
   upscale growth of another mesoscale convective system accompanied a
   risk for potentially damaging wind gusts still appears possible. 
   Prior to this, early boundary layer based development may include a
   couple of supercells, particularly (roughly) near the Sherman
   TX/Durant OK area, where the environment could become supportive of
   an isolated strong tornado or two.

SPC still seems concerned about the potential of a strong tornado, albeit the potential is highly conditional.

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mcd0538.gif

Mesoscale Discussion 0538
   NWS Storm Prediction Center Norman OK
   0309 PM CDT Fri Apr 21 2017

   Areas affected...Southern OK...North TX...Southwest AR...Far
   Northwest LA

   Concerning...Severe potential...Watch likely 

   Valid 212009Z - 212215Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Severe thunderstorm development is expected later this
   afternoon. Very large hail, locally damaging winds, and a few
   tornadoes will be possible. Watch issuance is anticipated in the
   next 1-2 hours.

   DISCUSSION...At 20Z, an outflow-reinforced frontal boundary has
   become nearly stationary across north TX, southeast OK, and southern
   AR. Visible imagery indicates slowly deepening cumulus along and
   south of the boundary, though wave features noted in the cloud field
   are indicative that some convective inhibition remains. Ongoing
   elevated convection across central OK is being supported by ascent
   associated with a rather strong but low-amplitude midlevel shortwave
   moving into southwest KS. This ascent will likely only glance the
   region along and south of the boundary, but, in conjunction with
   continued boundary-layer heating, will help to support convective
   initiation later this afternoon into the early evening as the
   remaining CINH is eroded. 

   Along and south of the boundary, steep midlevel lapse rates atop a
   warm/moist boundary layer are supporting moderate-to-strong
   buoyancy, with MLCAPE of 1500-2500 J/kg noted in recent
   mesoanalyses. Effective shear of 45-55 kts is more than sufficient
   for organized storm structures, with initial discrete supercell
   development expected before consolidation into more of a linear mode
   along the boundary becomes more likely into the evening. Any
   discrete supercell that develops in the warm sector will be capable
   of all severe hazards. The tornado threat will be maximized with any
   supercells that interact with the frontal boundary, especially in
   areas where some heating/recovery has occurred north of the
   boundary. 

   While the timing of deep convective development remains somewhat
   uncertain, tornado watch issuance is likely when initiation appears
   imminent, which will likely be sometime in the 2030-22Z timeframe.

   ..Dean/Goss.. 04/21/2017
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30 minutes ago, jojo762 said:

SPC still seems concerned about the potential of a strong tornado, albeit the potential is highly conditional.

The only apparent red flag I see is how the shear vectors don't produce a large angle with the composite outflow/frontal boundary. Storm mode may become clustered relatively quickly. With that said, if any discrete cell that fires in North Texas can remain at least somewhat isolated, there will be significant tornado potential. The metroplex is going to be in the crosshairs, which is a bit concerning.

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21z FWD sounding shows a substantial cap, but favorable wind fields for severe. Storms should have little problem initiating (next 1-2 hours) to the NW of the metroplex where surface temps have risen into the upper 80s/near 90F.

264D5400-B6DB-4B0E-873B-96B1CE786263-4235-000003C1E1A27929.gif.8faa89ded236f9ffa050bfc496be8b3a.gif

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Just now, MattPetrulli said:

Cel near Springer, OK already exhibiting some low level rotation. Need to watch this one closely. 

Seems to be struggling a bit, both visually (I'm near Marietta) and on radar. As it moves east into an area of warmer near-surface inflow, it may better organize with time. 

Just now, cheese007 said:

What's the liklihood if cap breakage?

Cu fields popping down the line into North Texas. The cap is breaking. 

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Just now, Quincy said:

Seems to be struggling a bit, both visually (I'm near Marietta) and on radar. As it moves east into an area of warmer near-surface inflow, it may better organize with time. 

Cu fields popping down the line into North Texas. The cap is breaking. 

Yeah I'm noticing that via radar. Dbz going down slightly and everything becoming slightly less organized.

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