Focus Area: Southern half to two-thirds of PA
Primary threats: Early chance of supercells and multi-cell clusters in the SE quadrant of PA. A squall line will form along the cold front during the afternoon. Timing of the storms will be very similar to yesterday's severe weather.
Instability: Lower than Tuesday
- SB CAPE: About 1000 J/kg (Tuesday's storms developed with similar amount of SB CAPE).
- ML CAPE: About 500 J/kg (Tuesday's storms had up to 2000 J/kg).
Shear: Very high. There was no shear on Tuesday
- 0-1 km SR Helicity = 200-400 m^2 / s^2
- 0-3 km SR Helicity = 250-500 m^2 / s^2
- Jet Stream Presence: CONFIRMED
Synopsis:
The set-up will be similar to Tuesday with notable exceptions.
1. Instability will decrease due to the passage of the warm front occurring on Thursday night and its proximity to the PA-NY border. There will be enough to touch off storms in similar fashion.
2. Shear will be dramatically high since we are near the triple point and close to a jet streak.
3. We're in an area of enhanced upper-level divergence from the jet streak. An upper-level trough at 500 mb (~18,000 ft) will tilt into the low, providing some occlusion -> necessary for severe storms.
Further details (probabilities) to come on Thursday and Thursday night. The SPC has issued a slight risk but if models runs over the next two daily cycles are consistent or the front is expected to move through a bit earlier, a moderate risk of severe could be necessary in one of tomorrow's Day 2 outlooks.
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