Severe Weather Discussion for May 19-21, 2013

Severe Weather Discussion for May 19-21, 2013.
Issued:  05/19/2013.
*Active Severe Weather Day Expected across Oklahoma*
–  Several significant severe thunderstorms are expected across central and eastern Oklahoma.  The most likely area for the most intense thunderstorms will be Oklahoma City north and east.  Tornadoes, destructive hail, and damaging winds are all likely.  A strong tornado threat exists for northeast Oklahoma.
–  Another round of significant severe thunderstorms is possible on Monday.  However, the threat for Monday will be strongly governed by what happens today.
As with yesterday, this discussion will focus on the threats expected today and tonight.
Active severe weather event occurred yesterday but did not develop as expected.  Several limiting factors kept the storms from organizing and otherwise being in clusters.  I think this should have been obvious before hand but not my place to question a moderate risk with a 10% hatched tornado graphic.  SPC noted last night that a veer-back-veer profile was part of the problem and overall weakness in the mid-level flow.  Additionally, the previously noted dewpoint decrease immediately east of the dryline did occur.  Dewpoints lowered into the mid-50s in western Oklahoma.  I think this had a major impact on storms.  They did not get into deeper moisture until near sunset and but then there was way too much anvil debris and surface cold pool for organization.  It appears the storms tried a few times, especially the eastern storm near Lawton but alas RADAR only showed outflow dominated storms.
I really thought that yesterday would have some impacts on today and I’m still not convinced today will evolve like the models and SPC forecast.  However, I’m certainly not talking down the threat or talking it up, I just think the evolution will be different.
12z NAM/00z SPC WRF/12z HRRR all agree that CAPE values will exceed 3000 J/kg this afternoon as a dryline approaches central Oklahoma.  The HRRR is seemingly a little too aggressive with the dryline and lights off storms at I-35.  This model had a bit of an east bias yesterday with storms, so I’m not quite with that right now.  Best guess is the dryline will be just west of HWY 81 as consistently progged by the ECMWF and NAM.  Given that the SPC WRF is also on the same page, that is the going forecast.  The morning OUN sounding was rather impressive given the storms last night.  CAPE value was 1901 with temp 71 and dewpoint 67.  Tc 96F.  The hodo is a mess though and a veer-back-veer profile is obvious.  However, NAM sounding forecast shows a much better hodo developing by afternoon with a long curved environment, although there is a small dip in the mid-level but not going to worry about those items.
SPC seems rather concerned about T/Td spreads and I think this may be one of the items that doesn’t quite evolve like they’re thinking.  Either way, we’ll avoid playing tail-end Charlie as it may not be the best place anyway.  Not just related to T/Td spreads.  Okarche is on the south side of the nader threats but gives us plenty of options.  It also helps that the SPC WRF lights off a supercell at Okarche by 4pm.  12z NAM is similar.  Better likelihood of storms is north, but can go that direction if necessary.  None of the models are all that excited about storm chances south of I-40, so that will be monitored.  Given the close proximity to Oklahoma City and time of day (outdoor activities), there may be little time to react should a storm develop just west or southwest.  I’m still curious if any left over boundaries down south or “rolls” will create enhanced conditions for storm development.  The rain alone should create microscale temperature differences in that area.  And, still gotta wonder what the outflow boundary/heat burst in north-central Oklahoma will do.  As such, fascinating weather today, unfortunately some of it may be rather hazardous.
Tomorrow remains a threat and is very similar to today.  What happens will be strongly governed by today.  SPC has a moderate risk posted and this looks good.
Chase Status:
Level 1 – leaving at 2pm for Okarche.
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