Hello world,
Today appears to be shaping into a rather spring day overall. For most of the region, temps should be into the 70s today. Humidity levels are up, and so is our chances for shower/t-storms.
There were some passing showers earlier in the day that have made their way into NJ, and another area of showers with embedded heavy rains to the west of the area.
Thunderstorm Parameters
Most Unstable CAPE – best possible potential energy. Currently the highest CAPE is in W. Pa with another area of increased CAPE in C. PA. The surface based CAPE in W. Pa is also over 1000.
Blow is an image of the mid-level lapse rates (MLLR), with higher numbers equating to more instability. Lapse rates are indicative of change in temperature with height. The less change in temperature there is, the steeper the lapse rates. MLLR help thunderstorms because
And lastly, we are looking at the current shear. Shear essentially helps to build thunderstorms and allows them to breath. Higher shear values can tilt a storm’s updraft and create a mini circulation. This circulation is conducive to strong thunderstorm development. You have higher shear out towards the OV and another weaker area in C. Pa.
Model Forecast
3 km NAM
The NAM is showing that our best chance of a thunderstorm will likely happen later tonight by 0z (7-8pm). The above image depicts in red/blue shading where fronts are being created (in between blue and red areas). Essentially there will be an increased area of mid-level frontogenesis near Philly, and a cold pocket behind that in C. Pa. This is a defined attempt to create a cold front and that will be the best opportunity for more developed thunderstorm activity.
It will depend on cloud cover and if the lower levels of the atmosphere can warm up to create more instability.
The NAM is showing (not in this image) several attempts with frontogenesis, periods of pulsations. This tells me there will be several upticks in tightening of the temperature gradient. It is likely we will see some more pop-up lines of thunderstorms/stronger showers throughout the day, but the best chance for our area will occur tonight.
W. Pa will have the best chance of severe weather this afternoon. Eastern Pa will likely have pulsatile thunderstorm/strong showers with an outside chance that something can go strong/severe later this evening (the more heating/sun, the higher the risk).
After the front passes through, comfortable and seasonal for tomorrow in the area.
Hope you all have a fabulous Thursday!
Keep an eye to the sky today!
Philadelphia Weather Authority 