From WPC:
The CAMs are in good agreement that convection will expand, although the exact placement of what will be primarily scattered cells or multi-cells through 20-25 kts of bulk shear is uncertain. This is reflected by modest 1"/6hrs EAS probabilities, but high(>80%) and moderate(>30%) neighborhood probabilities for 1" and 3", respectively, in 6 hours. There is high confidence that convection will expand as thermodynamic advection continues from the south pushing PWs to broadly over 2" and SBCAPE to nearly 2000 J/kg in much of New England and Upstate NY. These cells will generally lift northward progressively on 0-6km mean winds of 15-20 kts, but the widespread coverage should result in multiple rounds in many areas. Additionally, nearly unidirectional flow noted in morning soundings suggests brief training is possible along narrow N-S corridors. Rain rates will likely reach 1-2"/hr in most of these cells, and the HRRR 15-min accumulation product suggests locally 0.75"+ of rain is possible this evening which indicates brief intense rates to 3"/hr are possible. These axes of enhanced training are where the heaviest rainfall is expected, and this is most likely from far eastern Upstate NY into much of VT where 2-3" of rain is possible.
FFG across the region has been compromised from recent heavy rainfall, and there are some local minimums of less than 1.5"/3hrs in the Green Mountains and Northeast Kingdom of Vermont. This area is generally sensitive anyway due the terrain features supporting rapid runoff when rates become intense, but the antecedent rain has made the area even more vulnerable.