2017-03-09 EVENT: AR/KS/MO/OK

[Quincy Vagell]

Thursday PM is gradually becoming more interesting with respect to a localized severe threat across the southeastern KS/southwestern MO/northeastern OK/northern AR vicinity.

The large scale pattern is not particularly interesting, but a wave of low pressure is modeled to develop over eastern Kansas Thursday afternoon and drop southeast into the Ozarks Thursday evening. The more conservative 12z EC and 00z GFS show a plume of modest instability, on the order of 500-1000 J/kg MLCAPE, streaming into southeastern Kansas by 00z Friday amidst mid to upper 50s dew-points and 40-50 knots of 0-6km shear. At face value, this supports at least a localized severe threat. The usually more bullish NAM brings dews into the lower 60s in the same area with CAPEs around 2000 J/kg.

Low level winds around south-southwesterly are still favorable given a vertically veering wind profile, as winds in the upper levels veer to WNW/NW Thursday evening. Forecast hodographs in the 0-3km layer become enlarged immediately ahead of the system with an increasing low level jet. A subtle vorticity wave in the progressive flow regime appears to be allowing a wave of low pressure to form along the front.

With respect to severe, the convective mode is complex, as elevated storms may form just ahead of an effective warm front Thursday afternoon, displaced from more favorable moisture to the south. A cluster of storms may ultimately initiate in the vicinity of the surface low shortly after peak heating, with a lack of large scale forcing. The 00z 4km NAM solution drops a broken line of storms into the Ozarks Thursday evening, but this may be overdone due to bloated moisture return/instability. Otherwise the shear profiles are favorable for severe, so if overnight model runs continue the trend of better moisture return, the SPC could introduce a slight risk area in upcoming day 2 convective outlook(s).

My guess is that this could, at least, be a conditionally chaseable event somewhere in eastern Kansas to western Missouri, especially if model trends continue. The NAM has been nudging north over the last few runs, but I opted to leave AR/OK in the title since this trend could stop, and/or storms may persist into Thursday night with southeast extent. If the surface low ends up stronger than progged, than the threat would become more pronounced.

 

[Quincy Vagell]

SPC has delineated 5% tornado probabilities for the immediate AR/KS/MO/OK border region, including Joplin, for today.

Assuming morning convection doesn't destroy the environment, some of the higher end model forecasts for instability (locally 2000+ J/KG) should be realized to about as far north as PPF-SGF. Early day convection could persist and become routed in/near the surface by afternoon/early evening. This has been shown in several consecutive runs of the HRRRX/HRRR and recent 00z NSSL WRF.

A conditional chase day continues, as the terrain and road networks remain favorable for the first few hours of robust storm development (SE KS/SW MO/far NE OK), before convection moves into the more hostile Ozarks through the evening.

I'd expect a somewhat messy storm mode with a cluster of storms during the afternoon, but an embedded supercell or two seems like a plausible scenario given the inflow environment and CAM forecasts.

 

[Steve Holmes]

Congratulations on calling the Slight Risk, Quincy. I wish I had that skill. Unlike in Monday's bout, the sun may get to stir things up this AM. Curious that there's no Hazardous WX Outlook on SGF's forecast page for Joplin. I'd think they'd be playing up a Slight risk by now.

 

[Quincy Vagell]

Congratulations on calling the Slight Risk, Quincy. I wish I had that skill. Unlike in Monday's bout, the sun may get to stir things up this AM. Curious that there's no Hazardous WX Outlook on SGF's forecast page for Joplin. I'd think they'd be playing up a Slight risk by now.

The morning AFD from SGF sounds very skeptical of today's threat, sighting "model guidance has [dew-points] us in the mid 40s by 09z which isn`t gonna happen."

While that's true of the GFS, which shows mid-40s, the high resolution guidance all show low to mid-30s dews, which is verifying just fine. The latest HRRR and 4km NAM models both still bring dews to near 60 around JLN this afternoon. There is some concern that morning convection may disrupt the moisture return a bit, but it's hard to go against the CAMs here. (not sure why one would trust the GFS over the HRRR for near-term convective forecasts)

There's also a sleeper/non-zero threat back in northwest Texas and parts of Hill Country. Here, despite warmer mid-level temperatures, daytime heating of the surface into the upper 70s may be enough to erode the cap to reach near the convective temperature and take advantage of moderate/strong instability. The only glaring issue is rather anemic winds in the 850-700mb layer, e.g. 10-20 knots or so, leading some doubt to storm organization and maintenance. I wonder if SPC will introduce a MRGL risk here later today.

 

[Quincy Vagell]

Rapid moisture return is underway with lower 50s dews already into southwestern MO as of the top of the hour. An enhanced risk has been issued for portions of the region, although there are still questions regarding how long before initial discrete/semi-discrete cells congeal into a convective system.

 

[Dan Robinson]

This is really a tempting setup, just within striking distance for me. I'm concerned though about how the cold front is shown really pushing south and potentially undercutting the storms, given how the steering flow aloft is westerly. I'd feel better about it if the surface low were a little stronger and could counteract the crashing cold front. If it were a couple of hours closer, I'd definitely bite, but will be sitting this one out.