Wednesday, June 4, 2014

Weekend Severe Weather Outlook - June 6th-8th

It's looking like we'll see some marginal chances for severe weather this upcoming weekend.


Forecast instability (contours) and stability (blue shading) for Friday evening
Short range model guidance indicates we will begin seeing a reservoir of instability be pulled up en  masse from the Gulf of Mexico, a rather common occurrence for this time of year. Instability/CAPE values in the neighborhood of 2000 j/kg over the Upper Midwest and north Plains tell me we could see some light convective activity, though the lack of lower and upper-level wind support means any convection here would likely be of the pulse-storm variety. These pulse storms would likely have the ability to put down some gusty winds and small hail. The relatively-high precipitable water values over these regions would also allow for torrential downpours in these pulse storms.

Attention will then focus to the central and southern Plains for a much more dynamic environment. NAM instability projections above have CAPE exceeding 5000 j/kg in northern Oklahoma by Friday evening, an incredibly high amount of instability for any time of the year. Despite this impressive statistic, upper and lower level wind support again looks marginal, though slightly improved over the environment in the Midwest and northern Plains. The blue shading inching its way across the Plains on that instability projection above tells me there will be a limited window for convection in Oklahoma, and the capping inversion (which suppresses thunderstorms) will rapidly take over in the coming hours after sundown in Oklahoma. A closer look at forecasted sounding analyses (see below) over Oklahoma for Friday evening actually shows considerable low-level veering of winds, which could allow for some more formidable convection, if any is able to fire before the cap sets in. Right now, I'm pessimistic on opportunities for large-scale convection due to the lack of wind support and capping inversion.

Forecast sounding in north-central Oklahoma for Friday evening

Instability and stability forecast for Saturday evening
By Saturday evening, the sector of instability has been shunted east into the states of Louisiana, Arkansas and Mississippi, among others. We still see the capping inversion eager to take over the Gulf Coast, once again limiting the timeframe for thunderstorms to fire. Instability exceeds 4000 j/kg in some parts of this region, and a formidable mid-level jet streak rounding the base of an upper level low in southern Illinois may provide for the opportunity for some organized convection among expected pulse storms. To the north of the Gulf Coast, CAPE values are less opportunistic, despite the increased wind shear. For now, I would feel better calling for pulse storms across the Gulf Coast, with the potential for some more organized convection if we see more wind support in the upper and lower levels.