Sunday Afternoon Thoughts

Sunday Afternoon Thoughts- Afternoon data has trended a bit more robust with the moisture and the strengthening of the low pressure as it pulls NE. This is a bit different than the models trending colder as they really have not, temps overnight still warm, and temps tomorrow morning are also above freezing in many locations.

So what’s changed? The biggest development is the blossoming moisture field associated with the deepening low pressure, and the timing of the strengthening. Let’s talk through this with the images attached.

First two images are the latest HRRR and NAM modeled snowfall, both very similar but also showing more snow further south across the region. The next series in images are the simulated radar from the NAM and 5pm,8pm,1am,8am,noon.

Let’s talk about those images- precipitation arrives around 5pm, it may start as a brief burst of snow across the lower Hudson Valley but it quickly changes to rain. By 8PM the rain/snow line is pushing north to about i84 and it continues to push north through midnight where snow at that time may only be falling across the higher terrain and parts of Delaware and Greene Counties.

Snow accumulations of a coating to an inch or two is possible and will be highly dependent on who stays snow the longest with the northern most zones likely to see the 1-2” with a coating or less as you get south towards i84 and beyond where change overs occur sooner. The exception to this rule is the higher terrain and counties mentioned above that may stay snow for much of the overnight period, where several inches of snow may accumulate by daybreak.

Now tomorrow morning is where things will need to be watched and where those traveling need to keep their guard up. As the low pressure organizes to our SE, colder air aloft will begin pouring back into the region, this will begin to change rain back to snow during the morning hours. At the 8AM time stamp you can see how the rain/snow line has collapsed southward. So areas seeing rain just before daybreak may be back into the snow during commute times. In addition the low pressure will be deepening, the data shows very good atmospheric lift occurring over the Hudson Valley. This may result in banding developing as the moisture shield begins to backup into the region. You can see this sudden expansion of precip when you compare the 8am and noon radar stamps.

While surface temps will be above freezing, upper air temps will support frozen precipitation, the intensity of the precipitation will be enhanced by the upward motion of the atmosphere as our storm deepens. This will aid in dynamic cooling, and more importantly snowfall rates can overcome warmer surfaces. This could lead to rapidly deteriorating road conditions as heavy snowfall begins to slush over and snow cover roadways. While the data has been inconsistent and only begun catching onto the idea of earlier deepening of the LP in the last few runs. Given the fact it is both a work day, school day, and that conditions may not look “bad” predawn, it’s important to highlight this potential so sound decisions can be made around travel.

Final image is our snow forecast, we have added a circled area where if banding does occur, could result in accumulations on the high end or exceeding the current forecast. In addition it’s worth mentioning that the higher peaks of the Catskills may exceed 8” of snow within that forecast zone. More to follow.

-Alex