Numerous Showers and T'storms Expected Saturday, September 5th, 2014 across Southern New England

Saturday is shaping up to be quite an active day across southern New England as an area of low pressure moving through Quebec will allow for a cold front to slide through southern New England during the afternoon/evening hours.  Out ahead of the cold front the combination of surface temperatures in the mid to upper 80's with surface dewpoints in the lower 70's will yield to quite an unstable airmass across the region.  While winds aloft will be on the modest side, shear should be sufficient, especially given how unstable the atmosphere will be for showers and t'storms to develop and a few of these t'storms may become strong to severe.

The day will start off predominately dry, however, there may be a few showers around during the early morning hours.  While there will be clouds around, strong surface heating is expected to occur.  This will allow for temperatures to quickly jump and soar well into the 80's, perhaps near 90F in a few locations.  As mentioned above, with dewpoints in the low 70's, this combination will yield to quite an unstable airmass:

Computer forecast models indicating we could see CAPE values approach or exceed 2000 J/KG, suggesting quite an unstable atmosphere:


The strongest winds aloft in the mid-levels of the atmosphere are expected to lag just behind the cold front, however, computer forecast models do suggest that these winds will slowly be increasing throughout the afternoon.  While shear values at this time aren't expected to be very impressive (perhaps only upwards of 25 knots of vertical shear) the degree of instability will be enough for t'storms to develop.  There are some differences within the computer forecast models with regards to the winds aloft.  One forecast model indicates winds will begin increasing earlier as opposed to later on.  If winds aloft do increase on the quicker side and ahead of the approaching t'storms, this could lead to more in the way of severe weather potential:

The NAM computer forecast model showing area of stronger winds aloft approaching southern New England late in the afternoon, a bit slower than a few other computer forecast models:


For tomorrow we will see showers and t'storms develop in the afternoon and become rather numerous.  While numerous showers and t'storms are expected only a few of these storms are expected to become severe and pose the threat for strong to damaging winds and perhaps large hail.  If winds aloft do increase earlier and ahead of the approaching storms than the risk of strong to damaging winds and hail would increase.  A few rotating storms can't be ruled out either but this all depends on the strength and intensity of the lower-level wind fields.  Besides the threat for strong to damaging winds and hail, a very moist atmosphere will lead to torrential downpours and with this we will see a risk for localized areas of flash flooding, especially for the typical flood prone areas.