The synoptic evolution of the weekend storm appears somewhat similar to the Monday storm. Cyclogenesis along a cold front will occur as the northern and southern streams of the jet stream phase over the eastern United States. This will lead to two separate bouts of wintry weather: the first will occur from a leading shortwave Thursday night into Friday while the second will occur as the surface low along the Gulf Coast intensifies late Friday night into Saturday. Unfortunately, it appears that Bowling Green and Nashville will be on the wrong side of both of these systems.
The synoptic pattern shows two important clusters of shortwaves that are driving the development of this storm system. Late Thursday night, you can see three distinct shortwaves associated with a 110 kt jet streak over the southern plains, as well as a more diffuse region of positive vorticity and a digging 90 kt jet streak over the northern plains. If you cycle through the various 6 hr forecasts, you can see that the surface low along the Gulf Coast does not deepen appreciably until the two clusters of shortwaves merge Saturday morning. (42 hr, 48 hr, 54 hr, 60 hr, 66 hr) Once the two branches of the jet stream phase Saturday morning, the storm becomes negatively tilted and the surface low deepens into a blizzard over the Appalachians with heavy rain and wind along the East Coast.
So what does that mean for snowfall for south-central KY? As the southern stream shortwaves move northeastward along a stalling cold front late Thursday night/early Friday morning, wintry precipitation will spread along that baroclinic zone. The models show ample moisture over Bowling Green (around 0.50″ liquid precip) but boundary layer temperatures favor rain or sleet over snow as 850 mb temps are between 0-3C and the 540 line is well to the northwest. The model trends starting over the past 24 hours continue to move the rain/snow line to the northwest, as has been the case with winter storms all season. Models suggest that by Friday afternoon, boundary layer conditions become more favorable for snow in Bowling Green, but by then, most of the moisture will be to the north. Precipitation should taper off by Friday evening such that there might be some light snow showers but no major accumulations.
The lull in precipitation should continue until the phasing occurs Saturday morning and the low begins to rapidly deepen. The heaviest snow from this second bout of wintry weather will mainly be confined to far eastern KY and into Ohio. Light snow showers should continue in Bowling Green into Saturday afternoon, but accumulations will not be significant.
Looking at model comparisons, both the NAM and GFS have been trending NW and warmer for Bowling Green. The main difference is that the NAM is more aggresive with the snow Saturday morning. I tend to lean toward the GFS here.
Bottom Line: My first call on this storm is for a mix of rain/sleet/snow to begin early Friday morning. This may briefly changeover to all rain before noon Friday but should mix back to rain/sleet/snow and turn back to all snow Friday afternoon. Daytime accumulations should be minimal but could be up to an inch. Light snow showers/flurries should continue Friday night into Saturday morning before tapering off Saturday afternoon; an additional accumulation of an inch or so is possible. Total storm accumulation of 1-2 inches of snow seems reasonable. I will update the forecast on Thursday.
Here is a snowfall model based on the 00z GFS. Note how south-central KY sits right between two regions of 6″+ snowfall. Bummer.
