Spring or winter: A look at what is to come
Thursday, April 10, 2014, 8:51 PM -
After having a few days of more spring like weather across the country, with even some record breaking temperatures across southwestern Saskatchewan, I think the question on everyone’s mind is, "Is spring is here to stay?"
Well the answer is not a simple “yes” or “no” and I will look into the upcoming pattern changes and difficulties involving the current long range forecast.
Large temperature swings and an active pattern like we are seeing is not uncommon in the shoulder seasons (spring and fall). The brief explanation for this is that these are the times of year when the contrast between the cooler arctic air to the north and the milder air coming up from the south is greatest. This contrast helps fuel potent spring and fall storms and leads to the extreme swings that we experience. It doesn't look like the remainder of this spring will be any different as we look to the weekend and into next week.
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The scenario begins with the low pressure system currently tracking through the northern Prairies, which was responsible for the record highs in Saskatchewan on Tuesday afternoon.
Figure 1 shows the location of this low pressure system early Wednesday morning through northern Saskatchewan.
As the Pacific wave tracks northeastward, temperatures will be at or above seasonal into Manitoba and northwestern Ontario Wednesday and a little more seasonal behind the cold front as it pushes through Alberta and Saskatchewan on Wednesday.
By Thursday, the mild Pacific air mass will work its way into southern Ontario, which will bring temperatures into the mid to upper teens. This will begin to push milder air into Atlantic Canada as the cooler air pushes northeast from the low currently affecting the region. Of course the good comes with the bad in the form of showers along the cold front Thursday evening for southern Ontario as well as some spotty showers along it on Saturday and Sunday as it tracks eastward into Québec and Atlantic Canada.
Figure 1. Analysis of current systems across the country. Emphasis on the low in Saskatchewan and arctic front trailing it into Alaska
As the arctic front (the stationary front in figure 1 that extends through the Northwest Territories into Alaska marks the arctic front boundary) begins to drop south on Friday we will gradually see temperatures shift to below seasonal once again with showers and snow returning for the Prairies and Alberta. Figure 2 shows an ensemble mean of temperature departure from normal (not actual temperature, but a departure from seasonal values) from April 11 through to April 16.
Examining figure 2 we can see once again that the polar low centred over Hudson Bay will be driving cold arctic air back across the Canadian Prairies, as well as northern and central Ontario. British Columbia will benefit from a persistent ridge that will begin to build in over the weekend and persist maintaining generally mild temperatures. The other important item here is the sharp divide through southern Ontario into Atlantic Canada. This marks the boundary of the arctic front, which also approximately indicates the storm track. This will become problematic come Sunday through to Tuesday, but the take away here is up until early next week eastern and western Canada will benefit from more spring like conditions with the Prairie provinces, Alberta, as well as northern and central Ontario still feeling the grip of winter or at least below seasonal temperatures.
Figure 2. CFSv2 4 ensemble average of temperatures departure from normal from early morning April 11, 2014 to early morning April 16, 2014.
As mentioned above, the problem with this sharp frontal zone through southern and eastern Ontario as indicated by the ensemble forecast in figure 2 is visualized in figure 3. This compares the GLB and GFS weather model’s temperature forecasts and has the approximate location of the forecasted 0C line analysed for the first of two lows that will push in on Sunday. The huge differences here will lead to drastic changes in precipitation type and the amount of snow accumulation on the north side of the 0C line. If the GFS proves to be the more correct solution we can see a sloppy mess of rain/snow and as far south as Montreal to Sault Ste. Marie on Sunday.
NEXT PAGE: OTHER ISSUES WITH THE LONG RANGE
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.