Severe Weather Discussion for May 14 – 20, 2012

Severe Weather Discussion for May 14 – 20, 2012.
Issued:  05/13/2012.
Highlights:
–  Showers are possible across western Oklahoma on Monday.
–  Thunderstorms are possible Friday-Sunday.  Chance on any given day is on the low side, but probabilities are warranted for all three days.  Severe thunderstorms may become possible, currently Saturday in western Oklahoma and Sunday central/east.
–  Temperatures will be in the upper 70s Monday, low 80s Tuesday-Wednesday, mid 80s Thursday – Friday, upper 80s Saturday-Sunday.
Probabilities:
–  Severe Thunderstorms in Oklahoma:  30%
–  Storm Chase:  30%
Discussion:
Unseasonable min in severe weather potential will continue part of this week.  Models are in very good agreement through seven days and other than the current shortwave trof moving into New Mexico.  There are some weak signals of a weakening shortwave trof moving into the region on Saturday and north of the region on Sunday per the 18z GFS.  This trof provides enough wind aloft and moisture return to get CAPE values AOA 3500 J/Kg.  GFS has no QPF on Saturday but does develop sporadic QPF on Sunday along I-44.
The atmosphere will be a little more active this week across the CONUS but still not what is expected this time of year.  A broad western U.S. ridge will give way to a trof by Friday.  The system mentioned on Thursday undercuts the ridge and dampens as it moves eastward into the central U.S.  Models then show the ridge becoming pinched over the central/eastern U.S. by next Sunday as the lead western U.S. trof weakens as it moves into the central U.S. and a closed low develops near South Carolina. Probabilities are like throwing a wet noodle at a target but I have little choice to guess.  The < 5% isn’t appropriate but neither is a moderate/high-end event.
I’ve had to rewrite some of this given the 18z GFS, which I think represents the subtle nature of the atmosphere this week but grasps the potential for severe thunderstorms.  Models want to develop a western U.S. in the Day9-11 period but arrive at this differently.  This has also been the case for the past two weeks with no such development.  Given that such a trof is climatology, not a shocker the models keep insisting on it.  EC develops a huge ridge over the western U.S. in response to the trof upstream and the closed low over the western Atlantic.  GFS is a little more progressive and likely the more correct solution.  Another very interesting aspect of the GFS is the development of a tropical storm in the Carribean late this week.  We’ll see on that one.
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