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April 13th-14th Severe Threat


andyhb
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13z stays moderate risk but with really strong wording

...SUMMARY...
   Tornadoes -- some potentially strong to violent (EF2+) -- are
   possible today from east Texas to central Mississippi.  Otherwise,
   numerous severe thunderstorms will pose a risk of large hail,
   damaging wind and tornadoes from central Texas this morning to the
   Tennessee Valley region overnight.

   ...Synopsis...
   In mid/upper levels, a leading/northern-stream perturbation will
   eject northeastward across from its present position over Lake
   Superior and northern Ontario, across Quebec.  To the southwest, a
   deep, high-amplitude trough is evident in moisture channel imagery
   over NM, far west TX, and northern MX.  This trough will pivot
   east-northeastward today, developing a closed 500-mb low by 00Z near
   the DFW Metroplex, and extending southwestward across Coahuila.  By
   12Z, that low should reach eastern MO, with trough southwestward
   over the Arklatex to deep south TX.

   At the surface, the 11Z analysis showed the primary surface low
   along a band of convection south of SJT.  A double structure was
   apparent to baroclinic zones to its east:  the first a
   quasistationary front across central TX to near a SHV-CBM-CHA axis. 
   The southern front was quasistationary just south of UVA and SAT,
   becoming a warm front over southeast TX and south-central LA, then
   quasistationary again over coastal AL and coastal western FL
   Panhandle.

   The primary surface low should deepen and cross the Arklatex region
   late this afternoon into early evening, reaching the lower Ohio
   Valley around EVV by 12Z.  The southern is expected to accelerate
   northward from mid/late morning, to and perhaps past the I-20
   corridor in northeast TX and LA, then over Mississippi, likely
   merging with the northern one.  By that time, a cold front should
   extend from the low south-southwestward across the MS Coast area,
   likely preceded by an organized quasi-linear MCS over the Deep
   South.

   ...TX to Lower Mississippi Valley, Mid-South and TN Valley...
   A regional outbreak of severe thunderstorms, with the main concern
   being damaging tornadoes, still appears possible today in and near
   the categorical moderate-risk area.  Only peripheral adjustments
   were needed for this outlook package, based on convective trends
   this morning and (on the eastern edge) continuity of overnight
   severe potential into the early day-2 period.

   Strong-severe thunderstorms are ongoing across portions of the Hill
   Country southward toward the Rio Grande.  This convection will pose
   a severe threat into central TX through the rest of the morning. 
   Refer to SPC watches 48-49 and associated mesoscale discussions for
   near-term details.

   East of the ongoing activity, the parameter space will become very
   supportive of supercell/tornado potential through the day in the
   warm sector, with the main uncertainties being longevity and
   discreteness of favorable storm mode.  As the southern front moves
   farther inland, a deeply moist boundary layer will spread across the
   region, with surface dew points commonly in the mid/upper 60s F and
   locally near 70, PW 1.5-1.75 inches, and mean mixing ratios
   increasing to 15-16 g/kg, with forecast soundings showing favorably
   low LCL.  Gradual diabatic heating in pockets will weaken already
   meager MLCINH from midmorning onward, enabling storm formation on
   pre-MCS sources for weak lift such as confluence/convergence lines,
   and perhaps persistent/relatively deep horizontal convective rolls. 
   Lapse rates will strengthen with westward extent, supporting
   preconvective MLCAPE ranging from 2000-3000 J/kg over parts of east
   TX to 1000-2000 J/kg over portions of LA and MS.

   Such buoyancy will be more than favorable for all forms of severe,
   amidst strengthening deep shear related to the approach of the
   mid/upper trough.  Furthermore, low-level shear vectors and
   hodograph sizes will be quite large along and south of the warm
   front, with forecast soundings yielding 250-600 J/kg effective SRH. 
   Any sustained supercells in this environment will be capable of
   significant tornadoes.

   With time this evening and overnight, convection should organize
   into a roughly north/south-aligned band over the lower Mississippi
   Valley region, as deep convergence becomes better-focused in the
   mass response ahead of the synoptic wave.  As this occurs, the main
   threat in a bulk sense may become damaging wind tonight.  However,
   given the strong inflow-layer SRH, tornadoes still will be probable
   from both embedded supercells and QLCS mesovortices.

 

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a severe thunder storm watch for San Antonio area?   

 

SPC had tornado watches all night long further west and suddenly they downgrade to a Blue Box even though instability is now increasing as the morning goes on  plus some storms will be moving near the warm front

 

 

 

 

 

 

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10 minutes ago, 1900hurricane said:

San Antonio cell is tornado warmed again. Looks like it might end up passing just north of the main city.

That said, most of the San Antonio metro area is north of the "main city" and the northern suburbs are well-populated.  It looks like this storm could be moving towards some of the suburban areas of the SA metro area.

I'm starting to get a little concerned for the areas near and along north/northwest Loop 1604 if this thing can hold together, especially if the rotation starts to tighten up.

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Golf-ball sized hail just reported in the area of Six Flags Fiesta Texas and quarter size hail at UTSA.  The KSAT live stream suggests more significant hail to the north.

EDIT: Baseball-sized hail north of Fiesta Texas (along Washita Way in Legend Hills).  At least golf-ball sized hail in the Dominion.  Seems like a major hail storm is underway in northern Bexar County.

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3 minutes ago, 1900hurricane said:

The cell near the KGRK radar site looks like it's getting together. That one looks right on the warm front. 

Yes, it looks like that storm (between Rockdale and Lexington) has developed a hook.  Would be concerned for the Bryan area if the storm tried to take a right turn, though it looks to pass north of there.

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Is anyone concerned that these early storms going up across the moderate risk area might keep a lid on things? We’ve seen so many Dixie events ruined by this in the past, particularly 4-27-2014 which, outside of the Vilonia tornado, didn’t do nearly as much as it could have.

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7 minutes ago, DanLarsen34 said:

Is anyone concerned that these early storms going up across the moderate risk area might keep a lid on things? We’ve seen so many Dixie events ruined by this in the past, particularly 4-27-2014 which, outside of the Vilonia tornado, didn’t do nearly as much as it could have.

It's all north of the warm front. The warm sector is open with minimal cloud cover, so they shouldn't affect instability much at all.

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I am concerned that the elongated north-south oriented low in Texas is now 1002-1000 mb.  That WF is only crawling to the north at present.  We may have to wait until later this afternoon and evening as initially expected for the tor potential to be maximized over LA and MS.   As Dave Reimer noted earlier in this thread these cells n of the WF can lay down boundaries to enhance svr potential later today once the WF gets in that area.

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