Severe Weather Discussion for April 12-15, 2012

Severe Weather Discussion for April 12-15, 2012.
Issued:  04/11/2012.
Highlights:
–  Severe thunderstorms are likely in the Texas/Oklahoma panhandles and far western Oklahoma on Thursday.  Destructive hail and a few tornadoes are the threats.
–  Severe thunderstorms are likely on Friday in the eastern Texas/Oklahoma panhandles and western Oklahoma.  Primary threats are tornadoes and destructive hail.
–  Active severe weather day is possible on Saturday.
–  Excessive rain and severe thunderstorms are possible on Sunday.
Discussion:
I am strongly tempted to use enhanced wording for Saturday but that is against the forecast rules, so for now will just use what I have.  Not smart to back myself into a corner.
12z/18z models have changed very little but have clarified some important details.  Thursday has more significance than it did 24 hours ago and is added to the highlight section.  SPC Day 2 covered the threat well and introduced a 30% area.  The likely threat is destructive hail and the reason for the 30% area.  Not sure if the hail threat will get a moderate risk (coverage and 45% hail area), but not out of the question.  Prior forecast reasoning remains the same.  NAM dewpoint issues have been resolved with it showing low 60s along the dryline in the central TX/OK panhandles.  CAPE values are @2000J/Kg by 4pm with some higher amounts.  Wind speeds surface to 500mb are good with impressive turning.  Wind speeds 200-300mb aren’t so good, but that probably won’t matter.  Big issue for tornadoes is LCL heights, which remain a little high.  However, as SPC noted, any storms that can survive into the early evening hours will have better tornado potential.
Thursday’s storms are likely to dissipate by mid-evening due to increasing CIN.  Models are rather quiet much of the night into Friday morning.  Friday afternoon, the NAM has taken a detour from the other models.  It now surges the northern part of the dryline well east while leaving the southern part near Hollis.  This appears related to a strong shortwave trof that ejects out late Thursday and it blasts the dryline eastward through NE/KS.  Unknown if this is a valid trend or not, so will need to watch.  The setup is favorable for severe thunderstorms and tornadoes as CAPE values are 3000 J/Kg across the threat area.  Wind speeds increase and directional shear remains favorable.  LCL heights are a little high early on near the dryline, but this suggests that storms may acquire tornado potential as they move into western Oklahoma or off the dryline.
Saturday certainly has the potential to be a significant severe weather day.  However, it is contingent upon storms from Friday night.  Storms do appear to go longer Friday night than Thursday and CAPE values are not as robust Saturday afternoon.  However, they are still greater than 2000 J/Kg, which in theory should be enough.  LCL heights are low and conducive for tornadoes.  Wind speeds and directional shear are very impressive.  So, given primary issue of overnight convection, there remains potential for a significant severe weather event.
Sunday is likely to be a heavy rain threat, but I’m not stupid enough to stick with just that answer.  Severe weather is certainly possible given deep layer moisture and any sunshine that might occur in the state.  For now, I’ll leave it at that.
Probabilities:
Risk area for any part of OK/TX (valid:  04/12 Day 1, Day 2, Day 3):
Slight:  100%, 100%, 100%
Moderate:  30%, 75%, 90%
High:  0%, 0%, N/A
Chase Status:
Level 3 – Monitoring chase potential Friday and Saturday.  Thursday also looks good, some part of the group may go out.
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