Severe Weather Discussion for April 2 – 8, 2012

Severe Weather Discussion for April 2 – 8, 2012.
Issued:  04/01/2012.
Highlights:
–  Severe thunderstorms are expected Monday afternoon and evening across western/central Oklahoma.  The more significant storms, capable of destructive hail are expected in southwest Oklahoma.  Elsewhere large hail and damaging winds are the primary threats.  The tornado threat is rather low but one may occur.
–  Showers and thunderstorms are likely Tuesday with a lower but measurable chance on Wednesday.  A few cold air funnels are possible.
–  Severe thunderstorms are possible on Friday, with a somewhat better chance Saturday.  Showers and thunderstorms are possible on Sunday.
–  Temperatures will be in the mid 80s on Monday, mid 70s Tuesday-Wednesday, upper 70s Thursday, low 80s Friday-Saturday, and mid 70s Sunday.
Probabilities:
–  Severe Thunderstorms in Oklahoma:  30%
–  Storm Chase:  10%
Discussion:
Lots of record breaking going on weather wise the past few days.  March 2012 was the all time warmest in Oklahoma City and Tulsa, I’m sure a lot of other places.  Today tied a record in Oklahoma City from 1918.  The warmth looks to continue this week as deep layer moisture remains across Oklahoma with little to no significant change in airmass expected until next Sunday, if even then.
Models are consistent on progging a southern stream system to move towards the region on Monday and close/cut off from the main flow as it reaches New Mexico.  It will then inch towards the Texas panhandle and possibly lift east-northeast into Kansas or per the 18z NAM drift across Oklahoma.  Either way, this system is expected to bring a round of severe thunderstorms Monday afternoon and evening with the most significant activity in southwest Oklahoma.  CAPE values are progged near 3000 J/Kg east of a drlyine near the TX/OK border and directional shear is modest.  Speed shear is also modest but both will support severe thunderstorms.  Lack of better directional/speed shear should keep the tornado limited.  Farther north in northwest Oklahoma, a weak front should act to initiate severe thunderstorms during the afternoon with the primary threat being damaging wind and large hail.  Storms will continue into the overnight hours with the threat being large hail and damaging winds across the remainder of central Oklahoma.  Thunderstorms will be likely on Tuesday and Wednesday across much of the state with eastern Oklahoma getting the main activity on Wednesday.  As with two weeks ago, a few cold air funnels are possible.
Next system moves towards the west coast by the middle of the week and ejects our incoming friend eastward.  Little to no airmass change is expected in-wake of the prior system, although dewpoints drop into the 50s for a day or so.  By Friday, a surface low develops Wyoming, with rapid moisture return commencing across the region.  Upper system is progged to go well north of Oklahoma by late Saturday.  The GFS is rather insistent on storm chances in a rather moist atmosphere.  Winds are not overly impressive for early April but CAPE values look to be in the 2000 J/Kg range.  If the cap can be breached, then a few severe thunderstorms appear likely.  ECMWF and GFS do disagree on the speed of this system, so have started storm chances early on Friday as a nod to the EC and kept them in Saturday per GFS.  There could be storms both days and given that there should be little push on the moisture with this system, there could be storms into Sunday.  In fact the GFS is very robust for precip chances Sunday.  Real difficult this far out, so will include low POPs on Sunday.  It appears the only day I have POP free is Thursday, wow.
Followed all the models for temperatures, although did not go upper 60s per the NAM on Tuesday.  I feel that is a little cool given the recent warm conditions.  Other than that, continued the warm trend of the past week.  Sunday’s high may be a little too much if GFS progged storms do occur, but it is an appropriate downward trend from Saturday.
Severe probability is kept in the low-end (slight risk) category for all chances this week.  I do not see a medium or high-end event at this juncture.  Chase potential is set at 10% for a “gotcha” factor should something materialize.  Lots going on in the weather world this week and the forecast for Easter weekend is rather muddied, especially by Sunday.
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