A vigorous piece of shortwave energy is slowly tracking to the northeast through the upper mid-West region. Associated with this piece of shortwave energy is a trailing cold front with is draped south through the Ohio Valley and into the deep south and a warm front which currently just sits south of CT but is is pushing through the states of PA and NY. As this piece of shortwave energy tracks off to the north and east the associated trough and cold front will push east and this will result in rather decent height falls across PA and NY which will aid in ascent and forcing:
There are some rather impressive elements involved with this system which is paving the potential for a potent severe weather event this afternoon, however, like with most severe weather setups here in the northeast there are numerous negatives in play and we will evaluate those as well within this post. With this system are some very impressive dynamics aloft. Currently working through the Ohio Valley region is a very impressive 80-100 knots 500mb (~18,000' ASL) jet streak! This will continue to slowly work east into the PA and NY this afternoon and really enhance the degree of forcing:
In addition to very strong winds at 500mb winds at the 700mb level (~10,000') 850mb (~5000' ASL) and 925mb (~2,500' ASL) are expected to be very strong as well with 700mb winds expected to increase to between 60-80 knots, 850mb winds 40-50 knots, and 925mb winds 30-40 knots:
These strong winds aloft will work to help with forcing and storm organization. In fact, given the magnitude of the 700mb winds this will yield 0-6km shear values as high of 50-60 knots which is not only more than favorable for storm organization (typically want to look for at least 30-35 knots) but for the possibility of rotating thunderstorms as well (typically want to look for at least 40-45 knots). Another intriguing factor with regards to the winds aloft are the changes in wind direction between the 925mb level and the 700mb level. 700mb winds will be more out of the southwest with 925mb winds working out of the south (which will help to advect in higher dewpoints/moisture and theta-e air) and surface winds perhaps more southeasterly. This change in direction with height is known as directional shear and is one ingredient to look for with regards to the potential of rotating thunderstorms. Another aspect is how the winds increase with height. This is known as speed shear and when combined with the directional shear will further enhance the potential for rotating thunderstorms this afternoon. This combination will yield very large helicity values with 0-1km helicity expected to be as high as 150-250 m2s2, and 0-3km helicity values as high as 250-400 m2s2. This is shown rather well on several bufkit profile soundings across PA and NY. The 12z bufkit profile from the NAM computer forecast model for State College, PA shows this environment quite well with a rather large and elongated hodograph. This indicates the presence of both directional and strong speed shear and indicates the potential for rotating thunderstorms:
Surface temperatures are expected to rise into the 70's to perhaps even lower 80's if enough sunshine can break through the clouds with dewpoints climbing into the lower to near mid-60's. This combined with mid-level lapse rates will help contribute to a modestly unstable environment with 500-1000 J/KG of mixed-layer cape possible. If more sunshine breaks out than forecasted and temperatures warm well into the 80's these instability values will be higher. Typically when looking for higher magnitude severe weather events you would love to see values much higher (>2,000-2,500 J/KG), however, given how impressive the wind fields are aloft and degree of forcing, these values should be enough for thunderstorms to not only develop but have the potential to become strong to severe:
Extensive cloud cover is also yielding questions as to exactly how unstable the atmosphere will become, however, recent trends in satellite do show numerous breaks occurring.
As the day progresses showers and thunderstorms are expected to develop ahead of the cold front and push off the the northeast at 50-70+ mph. Given the ingredients mentioned above, the potential will exist for thunderstorms to quickly become strong to severe and have the potential to produce damaging winds in excess of 60-70 mph, large hail, and perhaps even a few tornadoes, however, the tornado potential is a bit in question right now. While we do have some directional shear in place this is confined to the the lower portion of the atmosphere. While initially storms may develop more discretely, enhancing the likelihood of them developing supercell characteristics, they are expected to become linear rather quickly which could limit the tornado potential, however, embedded areas of rotation within line segments will be possible and would have to be watched:
Another inhibitor on the tornado potential are rather high lifted condensation levels (LCL's). LCL heights have been increasing up to around 1000 meters which is on the higher side when talking about tornado potential:
Computer forecast soundings also show an inverted-v look which also favors against tornadoes but does increase the likelihood for damaging winds:
All in all today will be rather interesting to watch unfold. Given everything mentioned above, thunderstorms are likely across parts of PA/NY later this afternoon into the evening hours. Some of these thunderstorms will have the potential to become strong to severe and could produce damaging winds in excess of 60-70 mph, large hail upwards of golf ball sized, and perhaps even a few tornadoes, especially if any discrete cells get going.
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