Confidence is continuing to grow as of this Wednesday evening posting that a major storm system will be taking shape by Christmas Eve into Christmas. Confidence continues to be much lower by comparison as to that storm’s impact in WNY. As you should expect 8 days in advance, there is model disagreement on storm timing and placement, and there is some ensemble disagreement as well. However, there is unusually good agreement this far out between the operational GFS and ECMWF on the broader details. That is, there is good agreement an initial low pressure area and its trough will undergo a transformation as that trough begins to tilt from NW to SE, known as a negative tilt. That tilt encourages more rapid and deeper strengthening of a surface low with a broadening of the precipitation shield associated with the storm. The negative tilt will spawn a deepening frontal wave along the initial low’s cold front. This secondary low will undergo strong cyclogenesis, coming up from the S or the SSE. The new intense low will eventually merge with the original parent low to the N and become a rather powerful cyclone. Both the GFS and ECMWF deterministic runs take the central pressure of the merged low down to 964mb! The ensemble means of the 2 models drop the center to around 978-980mb. The GEM has some similarity, but its cyclogenesis is less impressive than in the GFS and ECMWF. The actual path taken by the new deep low in the GFS is faster and farther east than the ECMWF depiction, which would put us in the cold wraparound snow and strong winds more quickly than in the ECMWF.
Also strong to possibly High winds will be favored. On Wednesday, a strong SE flow will increase coverage and intensity of rainfall, and winds will strengthen, strongest near the Lake Erie shoreline south of Buffalo. As the main low shifts north with its near bombogenesis, the cold wraparound circulation should change the rain into an uncertain amount of snow overnight on Christmas Eve into Chrstmas morning. As of this Wednesday evening, both the ensembles and deterministic models favor strong to possibly High winds in the cold advection as well. It is too soon to speculate as to how much synoptic snow will fall vs lake effect behind the storm. Signs do point to potentially dificult travel by or before Christmas morning, and there will be the chance for damaging gusts and a seiche–depending on the orientation of the pressure field. There may also be especially strong gusts immediately following passage of the cold front, with an isallobaric coupling (pressure fall/rise couplet) possibly causing additional problems.
Much can and probably will change over the days to come, of course. We’ll keep you updated. If things get really hectic, watch on air and/or go to wivb.com for details.