– Severe thunderstorms are possible across western and central Oklahoma Monday afternoon and evening.
– 18z 12km NAM – 78 hour forecast CAPE with dryline and dewpoint gradient.
Upper system will move into the western U.S. by Sunday, which marks the beginning of a rather large closed low forecasted across the southern U.S. A lead shortwave trof will eject northeast across northern New Mexico and southeast Colorado Monday afternoon and evening. A dryline will develop and mix slightly eastward during the afternoon, reaching western Oklahoma. Gulf moisture is in plentiful supply, although will be kept mostly south due to residual surface ridging. Despite this issue, models show at least upper 50s to low 60s dewpoints across Oklahoma Monday afternoon. Placement of upper system and surface low indicates good wind shear near and east of the dryline. As such, supercells should be the favored storm type. Earlier progs indicated veer-back-veer, but do not see this as an issue right now.
Models are in surprisingly good agreement, with dryline placement being the main difference. Either way, severe thunderstorms are expected Monday afternoon into the evening hours across parts of Oklahoma. Models do show a rather significant drop off in CAPE at I-35 and east. This appears related to low temperatures on Monday due to cloud cover. While models do show widespread clouds, including some cirrus, I’m not convinced temperatures will be in the low 60s. A few degrees higher, will raise CAPE values @I-35.
I’m not sure this event will rise to a medium-end threat, especially due to the limited moisture. There is a non-trivial threat for tornadoes due to good wind shear and decent moisture. This threat appears most likely west of I-35, but any increase in moisture or temperature would increase severe weather potential across central Oklahoma.
Risk area for any part of Oklahoma, valid: 03/05/2015, Day 3
Chase Status: Normal
(Forecast CAPE value for Monday afternoon and location of the dry line. Storms would be near or east of the dry line.)by