An amplifying northern stream trough will dig southeast from the upper midwest into the central MS river valley tonight, progressing into the Great Lakes and OH valley during the day Tuesday. A southern stream upper low over southeast TX at 16Z today will slowly deamplify as it tracks eastward along the gulf coast tonight, then northeastward into the Carolinas late Tuesday afternoon and evening. The latest model guidance suggests that little if any phasing will occur between these features, with the deamplifying southern stream wave getting ‘picked up’ and absorbed into strengthening southwest flow aloft in advance of the northern stream trough.
The low-level trough attendant the amplifying northern stream trough is expected to sharpen along the Appalachians during the day Tuesday, progressing into western NC/VA by Tuesday evening. Although the best lower level forcing will remain west of the piedmont through early Tuesday afternoon, the 12Z NAM indicates that convection will develop downstream of the low-level trough over the central Carolinas/VA after ~09Z Tuesday morning, perhaps due to small amplitude perturbations progressing into the region via SW flow aloft in the presence of an increasingly unstable airmass associated with strong theta-e advection (attendant a strengthening southerly LLJ) and diurnal heating (after 12Z). Additional convection will be possible Tuesday afternoon into Tuesday evening as the deamplifying southern stream wave progresses into the Carolinas from the SW and the low-level trough approaches the Carolinas/Mid-Atlantic from the W.
Thermodynamic/kinematic profiles over the Carolinas and Mid-Atlantic on Tuesday are quite impressive, with 500-1500 J/Kg of MLCAPE (stronger south) in the presence of a 40-50 knot LLJ at 1 km AGL and 40-50 knots of 0-6 km shear (stronger north), with 0-1 km SRH in the 150-300 m2/s2 range over NC and 300+ m2/s2 over the Mid-Atlantic.
With this type of pattern, it is difficult to ascertain both the timing and mode of convection on Tuesday. Given that convection may develop downstream of the low-level trough in an increasingly favorable thermodynamic/kinematic environment after ~09Z, it is possible that isolated severe weather will occur over the central Carolinas/VA Tuesday morning. As the stronger deep-layer forcing approaches from the west Tuesday afternoon and evening, another round of severe weather, perhaps more potent, will be possible given the impressive thermodynamic/kinematic environment in place by that time. Even if convection develops during the morning, such strong southerly low-level flow and theta-e advection would suggest quick airmass recovery over the warm sector and additional convective potential during the afternoon and evening. Although damaging winds are likely to be the primary threat, isolated tornadoes will certainly be possible, especially during the afternoon when the strongest low-level shear and instability are progged. It appears that the best overall tornado threat (and perhaps an isolated strong tornado) will be over the Mid-Atlantic Tuesday afternoon, particularly in VA/MD/DE/NJ/eastern PA where a pre-frontal trough may aid convective development and where the most favorable juxtaposition of shear/instability is expected.
I’m off today and haven’t had a chance to take a more thorough look at the latest model data in AWIPS – I’ve been trying to piece things together from GREarth, BUFKIT and web-based resources, so, I’d love to hear any additional thoughts/opinions on tomorrow’s setup!
NWS Raleigh, NC