Severe Weather Discussion for April 9 – 15, 2012

Severe Weather Discussion for April 9 – 15, 2012.
Issued:  04/08/2012.
Highlights:
–  Severe thunderstorms are likely in northern Oklahoma on Monday.  Destructive hail and a few tornadoes are possible.
–  A few severe thunderstorms are possible in western/central Oklahoma on Tuesday.
–  Active severe weather period is possible Thursday – Sunday with multiple episodes of severe weather.  At least one medium-end event may be in the offering this time period.
–  Temperatures will be in the upper 70s Monday, mid 70s Tuesday, low 70s Wednesday, upper 70s Thursday-Sunday.
Probabilities:
–  Severe Thunderstorms in Oklahoma:  > 75%
–  Storm Chase:  60%
Discussion:
Active mid-April pattern looks to be setting up for Oklahoma with multiple rounds of thunderstorms likely, along with attendant threat of severe thunderstorms.  SPC has risks areas posted for Monday, Tuesday, Thursday, and Saturday.  The latter two are in their Day 4-8 outlook, indicating a 30% area.  Monday’s risk also has a 30% areas and a 10% hatched area.
Monday will see the formation of a mid-level ridge to the west of Oklahoma, putting this area in northwest flow aloft.  Not always a wet flow this time of year, but certainly transitions to such by late May.  However, the unusual amount of Gulf moisture will make this setup more favorable than is typical in mid-April.  Dewpoints of at least the low 60s is likely to be located just south of a synoptic front over northern OK/southern KS.  The ultimate location of this front remains in doubt as models disagree.  CAPE values are progged to be in the 2500 J/Kg range.  Models show storms developing during the afternoon hours and progressing southeast.  Directional shear will be maximized due to northwest flow aloft and speed shear will be decent.  As such, supercells are the expected storm type.
Upper ridge continues just west of the region and dryline retreats to the western Texas panhandle.  Cold front looks to hang up in northern Oklahoma or maybe into central.  NAM develops QPF during the afternoon hours and CAPE values are in the 2500 J/Kg range.  Winds aloft are slightly weaker than Monday but directional shear will still be maximized under northwest flow aloft.  As such, a few severe thunderstorms seem possible on Tuesday.  SPC’s slight risk is confined to the panhandle and far western Oklahoma, so we’ll see how that changes in the next day or so.
Upper ridge then shifts eastward and severe threat decrease on Wednesday.  GFS still has some QPF over Oklahoma but not going to add POPs for now.  By Thursday, the upper ridge has shifted eastward and a western U.S. shortwave trof takes aim on the area.  GFS and ECWMF disagree on the evolution of this system with the EC farther south and stronger.  Despite which model verifies, deep layer moisture return will continue across the region and wind speeds aloft will strengthen.  GFS is lower on instability than would be expected on Thursday afternoon, so this will be monitored.  The dryline is epxected to be in the eastern TX/OK panhandle.
Upper system shifts northeast of the region on Friday but the western U.S. longwave trof remains in-place.  As such, moisture will remain across the region and another round of severe thunderstorms is possible on Friday.  Speed and directional shear both look favorable for supercells along with CAPE values.  Prior convection on Thursday will likely drive what happens on Friday.  There is no obvious upper support this far out, but the potential for something seems plausible.  GFS weakens CIN values and develops QPF Friday afternoon.
Powerful western U.S. trof looks to develop by Saturday and translate eastward on Sunday.  This system will tropical moisture ahead of it with a surface pattern that resembles the prior few days.  Given the presence of deep layer shear and favorable thermodynamics, another round of severe thunderstorms seems possible in western/central Oklahoma.  By Sunday, the trof ejects northeast and should drive the dryline well into Oklahoma by Monday.
The forecast this week is certainly complex and the convective setup will change day to day.  However, the ovverall synoptic setup favors multiple rounds of severe thunderstorms.  Chasing potential seems decent this week, just have to find the day(s) that look best.  Special discussions will be needed starting tomorrow, focusing on the latter half of the week.  Not ignoring tomorrow, as SPC has medium-end probabilities already posted.
Did not get fancy with temperatures, but in-general went warmer than the going rate much of the week.  Next Sunday could be too warm, but that will be driven by convective processes.
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