Severe Weather Discussion for April 12 – 14, 2012.

Severe Weather Discussion for April 12 – 14, 2012.
Issued:  04/09/2012.
Highlights:
–  A few severe thunderstorms are possible in the Oklahoma panhandle and western Oklahoma on Tuesday and again on Wednesday.  Primary threats are large hail and damaging winds.
–  Severe thunderstorms are possible Thursday-Saturday.  At least one medium-end event appears likely within this time period, but still a little far out to know which day(s) present said threat.
Discussion:
Complex weather setup for later in the week as a longwave trof develops across the western U.S.  Model outputs are in decent agreement but there are important differences.  The focus of this forecast is really on Thursday, since that is within the short range models (NAM).  On Thursday, a shortwave trof ejects northeast into Colorado with strengthening flow aloft across the threat area.  Models agree well here and even the overall setup.  There is disagreement on the dewpoints that will be in-place across the region.  NAM has widespread upper 50s while the GFS has low 60s and some mid 60s across the region.  CAPE values for both models are in the 2000 J/kg range but the upper 50s dewpoints results LCL heights much greater on the NAM while the GFS would be more favorable for tornadoes.  This is a situational awareness issue that won’t be resolved until Thursday.  The NAM has previously handled dewpoints issues decently but SREF 15z indicates 60F dewpoints are likely in the threat area with LCL values below 1500 meters.  Despite the ultimate moisture evolution of this event, sufficient deep layer moisture will be available for severe thunderstorms along  the drying in the Texas panhandle.  Storms will not move all that fast, so they’ll likely only get a little bit into Oklahoma before dissipating late Thursday.  GFS appears to be over-convecting into the night time hours and this would be supported by the current over convecting in Oklahoma.
On Friday, upper system continues to evolve across the western U.S. and flow across Oklahoma increases.  A dryline will remain near the TX/OK border.  Deep layer moisture return is expected to continue and despite CAPE values 2000-2500 J/Kg, this model does not develop convection until after dark.  At this time, there appears little reason for storms to not develop on Friday, but we’ll have to see.
ECWMF and GFS want to eject out a rather large portion of the western U.S. longwave trof on Saturday.  GFS is quite muddied and likely having extensive trouble with convection in the prior days and its own over convecting.  Either way, the available moisture and expected strong lift, will need to be monitored.
Probabilities:
Risk area for any part of OK/TX (valid:  04/10 Day 3):
–  Slight:   100%
–  Moderate:  20%
–  High:  N/A
Chase Status:
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