Complicated Forecast

So much for attempting a forecast yesterday. There was and still is too much uncertainty with this storm system.

A slight southward shift has occurred with the models albeit not enough to bring the heaviest snow into our area. However, the Louisville NWS and local television mets will probably be yanking a few hairs from their scalp before this one is over.

The track of the low is still the most important part to watch. Yet, other significant variables are vying for closer inspection.

Surface-based instability - a fetch of -2 to -4 readings keep showing up in the forecast just south and southeast of Louisville. That could be a fair indication of convection that leads to thunderstorm activity.

CAPE Values - this is also an indication of convective activity that may flare up today in those same areas south of Louisville; values around 250, not bad for no atmospheric heating.

The above factors do not appear to have much influence on the snow that will be falling well north. Many areas today in the Louisville CWA will be seeing rain or a mix of rain/sleet/snow the farther north one goes.

However, as sunset approaches, temperatures in the upper levels will begin transitioning any liquid precipitation to frozen precipitation.

Right now, it looks like the transition to all snow in Louisville will not be till after 8pm tonight. HRRR models are indicating possible snow accumulations as close as the northern part of Louisville CWA by 5pm.

Core of cold air with low pressure - ahead of the low, warmer air will be in place. As the low moves overhead and just east, colder air will quickly change from rain to a mix to all snow though temperatures will be well above freezing. If the snowfall rates are heavy enough, accumulations will occur especially on grassy surfaces.

Just north of Louisville, surface temperatures will be cooling rapidly. Accumulations will be affecting travel before midnight.

I still think a slug of heavy wet snow will affect the Louisville area sometime between 11pm and 4am. Although roadways should generally stay wet, as we continue to cool and the snowfall rates are heavy enough, we could start to see slushy roadways just before morning rush.

This is nowcast mode. My current thinking is that Louisville could get 0.7 to 1.5 inches of wet snow by rush hour tomorrow. After that, convective snow showers could put down another inch in places during the daylight and evening hours. But roadways should be in better shape after rush hour and during the daylight hours.

MS