Severe Weather Discussion for March 16 – 22, 2012

Severe Weather Discussion for March 16 – 22, 2012.
Issued:  03/15/2012.
–  A few severe thunderstorms are expected Friday afternoon and evening across western Oklahoma.  Primary threat is large hail.
–  Severe thunderstorms are possible Sunday afternoon and evening in western Oklahoma.
–  Severe thunderstorms are possible Monday afternoon and evening across much of Oklahoma.
–  Heavy rain threat develops Monday into Wednesday across central/eastern Oklahoma.
12z models continue prior trends of developing a medium-end event across Oklahoma by Sunday.  Opportunities for medium-end impacts will continue into early next week, but are currently outside the scope of this discussion.
Intense western U.S. longwave trof is expected to take shape by Sunday and combine with unseasonable moist conditions downstream to produce two severe weather episodes, followed by an excessive rainfall event.  There is a threat of severe thunderstorms on Friday, but this is expected to remain in the low-end of the scale.  SPC has it well covered in the Day 2 product and I really can’t add that much to what they have typed.  Saturday is also well covered in the Day 3 product and while moist conditions will remain east of the drylne, lack of defined shortwave trof is expected to keep thunderstorm coverage limited.  As always, can’t rule out one or two boomers.
Sunday appears to be a little more spicy across western parts of the state back west into the Texas panhandle.  12z EC/NAM/GFS all hint at strengthening wind fields across the threat area during the day.  Additionally, moisture will remain in-place with upper 50s to low 60s common in this area.  Big difference among the models is the location of southwest winds, which typically mark the dryline.  In this case, deep layer moisture is sitting well east of the southwest winds and this eastward location appears to be the convective initiation point.  The GFS is farther east with the conventional dryline while the NAM supports the prior discussion on separation between the deep moisture and southwest winds, on the order of 150 miles.  Wind fields aloft will be quite favorable by late afternoon for severe thunderstorms, with crossover maps showing appreciable difference in wind direction between the surface and 500mb.  GFS has low-balled CAPE values the past several days, so that part of the model is ignored for the somewhat more reliable NAM.  WRT to the NAM CAPE values, there is an area of 2000 J/Kg in the eastern Texas panhandle by 4pm.  Models seem to want to light off storms by early afternoon and this would seemingly occur given presence of a shortwave trof moving into the region.  Time of year would not necessarily favor such an early start but given several warm days and temperatures starting off in the 60s, shouldn’t take much to reach the low/mid 70s.  As such, Sunday has some chase potential and am currently watching Shamrock, Texas to Woodward as a chase area.
Beyond Sunday potential continues for medium-end impacts Monday-Wednesday.  On Monday the impacts appear to be related to severe thunderstorms with a transition to an excessive rainfall event late Monday through Wednesday.  This is currently outside the scope of this discussion, but the threat will be monitored over the coming days.  The GFS wants to slam eastern Oklahoma with 9-10 inches of rain during mentioned time frame, which would certainly have a flood risk associated with it.
Risk area for any part of OK/TX (valid:  03/16 Day 3):
–  Slight:  100%
–  Moderate:  30%
–  High:  N/A
Chase Status:
Level 4 – Watching Sunday and Monday, both appear to provide decent chase potential.
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