Weekend Forecast
This weekend’s forecast could potentially contain snow for some across ENC. Models seem to agree with the overall setup this weekend with strong high pressure over Canada and low pressure forming over the Plains in response to a mid-level energy moving over the Rockies.
18Z GFS surface and precip. Model image from tropicaltidbits.com.
There is some uncertainty around the strength of the mid-level energy as it dives southeastward Friday night and into Saturday so we will have to wait and see how this progresses over the next few model runs. If this pattern were to verify there are a couple of features that are of interest concerning precipitation type Saturday night and into Sunday. The first is the location and strength of the high pressure which is forecast to be over Quebec. This will create a CAD event as the system approaches the area.
18Z GFS surface temperatures, pressure, and 10m wind.
There are a lot of things that have to go right for portions of ENC to see snow. Which brings us to our next challenge.
18Z GFS forecast sounding at 78 hours. Model image from tropicaltidbits.com.
GFS forecast soundings show us a couple of things that have to happen for wintry precipitation. As the system approaches low levels remain mostly dry and above freezing. We can see the temperatures drop below freezing at around the 950mb level. You can also begin to see the CAD from the two wind barbs above the surface with southwesterly to westerly flow in the layers above that. As we move forward, the low level moisten up and the surface temperature approaches freezing.
18Z GFS forecast sounding at 84 hours. Model image from tropicaltidbits.com.
At this point precipitation is reaching the ground and surface temperatures drop to near freezing. If the GFS were to verify the above profile would support snow for areas generally north of 264. However, we also have to take other things into consideration. We still see a southwesterly flow aloft hinting that the upper-level temperatures could potentially be above freezing while the low levels remain at or below freezing. We would see frozen precipitation but it would be in the form of sleet. We also need to take a look at moisture availability in the dendritic growth zone. This is just a forecast sounding and not an observational data but it does show a hint of drying near that level. This would also bring down snow chances as well.
Cross section depicting the warm nose aloft (blue dotted line). Model image from tropicaltidbits.com.As we go forward from there, we begin to see the effects of the southwesterly flow aloft warming the mid to upper levels above freezing while the low levels remain at or below freezing due to CAD. We begin to see drying within the upper levels including the dendritic growth zone once again reducing changes of snow.
I would like to point out I used the GFS for the better part of this discussion for a reason. The models are running similar to the GFS (with the exception of the CMC) and the GFS was on the colder end of the scale and it shows where the uncertainty lies.
So by looking at the data from the models I can say the southern half of ENC is likely to see all rain. The northern half could at some point see the precipitation fall as snow, especially early in the event but change to a mix and end as rain before dry air filters into the area.
It’s a little early for me to be talking about forecast totals but I wouldn’t expect much in the way of accumulations.
We are still a couple of days out and things could change between now and then and due to the things I mentioned above, finding the rain/snow line will be difficult.
I will update the forecast as needed over the next couple of days.