The second issue with the long range pattern comes on Monday or Tuesday, depending on which model forecast proves to be more accurate. Figure 4 once again compares the GLB and GFS forecast models, but this time I will show surface pressure and QPF (Qualitative Precipitation Forecast, which simply means amount of liquid precipitation) forecast. Reason being is to demonstrate the large difference in the timing of the system and the large scale pattern. The difficulty here comes with the Bermuda high pressure system located in the Atlantic and the Arctic high pressure system located over Canada.
High pressure systems are rather difficult to track and forecast and thus where the Arctic high ends up situating will determine how much cold air gets pushed south and how fast the system will move east. The location and strength of the Bermuda high will ultimately determine how much warm air will be fed into the low and determine just how far east the low can be pushed. The one thing that the GLB and GFS forecast models agree with is the fact that just about all of Ontario and most of Québec end up cold enough to see mainly snow or a rain/snow mix with the chance of accumulations being significant. The other issue that arises is these systems that get sandwiched like this between two highs tend to have the precipitation shield elongated in a north/south orientation and compressed in the east/west. This makes for a narrow but potent band of precipitation, which can lead to large errors in the forecast when trying to pin point where the band will set up.
Luckily, the pattern looks to remain rather progressive with a vigorous upper level flow, which will keep systems on the move and lead to a somewhat better result from models. The one glimmer of hope is the ECMWF forecast model (not shown). Rather than bringing everything as snow Monday or Tuesday it favours a more westerly track with the low bringing much milder temperatures until late Tuesday. Unfortunately, given the general pattern, I don’t believe the ECMWF has the right idea at this point in time (as of the Wednesday morning solutions). For Atlantic Canada, things don’t look too bad Tuesday into Wednesday as the strong southerly flow from the Bermuda high will likely keep temperatures mild enough to give mainly rain with some rain/snow mix possible at times.
Given the way the pattern is trending it would seem it’s best to get out and enjoy as much of the spring-like and above seasonal conditions as much as possible now as winter is certainly attempting to give what I can only hope is one last hoorah, mainly for the Prairies, Ontario, Québec, and Labrador. Atlantic Canada and British Columbia look to stay on the spring side of things. Alberta is certainly no stranger to the extreme swings and this will continue for the province through to next week. Friday to Monday looks mainly cooler and below seasonal with a brief reprieve Monday and Tuesday through to mid-week with a return to slightly cooler conditions.