Severe Weather Discussion for April 24 – 26, 2016.
– Severe thunderstorms are likely across west-central through north-central Oklahoma on Sunday. Primary threats are large hail to tennis ball size and winds to 65mph. However, a few tornadoes are possible.
– A significant severe weather event is possible on Tuesday across a large part of Oklahoma.
Guidance is in reasonable agreement re eastward progression of a shortwave trof from Nevada/Utah to western Nebraska by Sunday evening. Prior surface high moved deep layer moisture to the Gulf of Mexico, with low/mid 60s currently located across the Texas Gulf Coast. Models attempt to return at least low 60s dewpoints northward into Oklahoma by Sunday evening. Temperatures in the upper 70s/low 80s should yield SBCAPE near 3000 J/Kg with MLCAPE near 2500 J/Kg based on a location at Enid. Convective inhibition may be low to nil by 4pm, so storms could start between 4-5pm across northwest Oklahoma. Wind fields will favorable supercells, capable of large hail and strong winds. The tornado threat may not present until 7pm when the LLJ develops. Indeed, moving the 4km NAM time frame to 7pm results in a better tornado threat than earlier in the day, even through CAPE (SB/ML) both decrease. There is a sharp cutoff to the instability axis, with east of I-35 AOB 1000 J/Kg CAPE.
Potential looks decent enough for a chase on Sunday, current plan is to leave at 3pm. Target area remains in-flux due to model differences WRT initiation location. Models usually tend too far east with convective initiation, so am attempting to move this location west. See attached image from Pivotal Weather website, noting potential chase location, along with expected convective initiation zone.
Monday appears quiet, as shortwave ridging moves across the region. Moisture remains across the region, so a few storms may develop. 4km NAM shows a few storms east of OKC Monday afternoon.
Attention then turns to Tuesday, which has serious potential to be a high-end weather day. Sunday’s upper system will move quickly northeast and be absorbed into the northern jet. The next upper system will progress rapidly into the region. Moisture will remain nearby and rapidly return northward as this system approaches. Models indicate upper 60s/low 70s surface moisture with 14C dewpoints at 850mb. 12km NAM does it usual weird 850mb sink, which is a characteristic bias of this model and is ignored. The resulting SBCAPE values are greater than 5000 J/Kg, indicating extreme instability across the region by Tuesday afternoon. Issues arise with the placement of the upper system Tuesday afternoon and subsequent influence on the dryline and mid level jet features. Models (EC/GFS/12km NAM) are quite varied in the location of the dryline and from intra-model time lapse (run to run).
There are several concerns about Tuesday, given the potential for significant severe weather. Dryline location typically shifts westward as an event nears, which is the case for Sunday. However, this westward shift has not occurred and the models have trended eastward with the dryline to near HWY 81 by 4pm. Additionally, the 12km NAM/GFS both erode CIN by early afternoon (2-3pm) time frame near HWY 81, irrelevant of dryline location. The potential also exists for a pre-dryline convergence area to setup near HWY 81. A 700mb speed max of 47kts is located across central OK by 4pm along with a 50kt 500mb jet max moving into this area. Models do tend to agree on these features, although ultimate placement of the upper system and dryline location remain elusive. Additionally I think there is decent potential for storms to develop before 4pm, whether they are just west of OKC or farther west in western OK. 18z GFS again moves the dryline location around but lowers CIN in central OK by early afternoon. All of these considerations will be tracked the next few days. Despite system timing/dryline location, the potential exists for a significant severe weather day across Oklahoma accompanied by tornadoes and destructive hail. SPC has been highlighting the potential for a few days and expect at least an enhanced risk on the morning D3 and potentially a moderate. Second attachment is from Pivotal Weather, 18z GFS valid 1pm Tuesday.
Risk area for any part of OK (valid: 04/24 Day 1, Day 3):
Slight: 100%, 100%
Enhanced: 60%, 100%
Moderate: 0%, 40%
High: 0%, N/A
Going on Sunday, Enid to Watonga is the initial target area.by