Forecasting the location and intensity of thunderstorms is challenging 6 hours ahead of time. Forecasting it 48 hours out is close to impossible. There are, however, signs that indicate the potential for severe weather over a region. Many of those signs are coming together on Wednesday.
The main ingredients for severe weather are lift, instability, and shear. Where the three juxtapose is where the best threat for severe weather is. The stronger the lift, instability, and shear the higher the risk.
On Wednesday all three ingredients may be present. Our computer models show a substantial amount of instability developing under a remnant elevated mixed layer. The EML allows temperatures to drop quickly with height in the mid levels making warm, moist parcels of air from near the ground very buoyant. CAPE values >2000 j/kg seem possible as long as dew points remain high and we’re able to see a good deal of morning and midday sun.
Shear will increase through the day as the 500 mb shortwave advances with strong mid level winds (500mb winds 45 knots) out of the WNW with SW or SSW winds near the ground. This shear will be more than adequate for storm organization and supercells.
The third ingredient, lift, is also present with strong lift developing late in the day ahead of the upper level disturbance and along a surface cold front.
All three will need to come together perfectly for a major severe weather event. If the shear lags behind the best instability, even by a couple hours, the threat becomes much more pedestrian. I will say, however, that this type of setup is similar to many significant severe weather and tornado days in the northeast so it bears close watching. By Tuesday night I’ll have a much better idea if this will become a “high end” type of event. Stay tuned!