•A chance of freezing rain or rain late tonight into tomorrow AM
•Warmer temps looks to linger till around Wednesday, this weekend will have the warmest days
•A storm system may brush the southern half of the HV with light snow Sunday PM into Monday
•Tuesday PM into Wednesday the probability of a significant storm impacting the region continues to increase
•The final track, strength, timing and availability of cold air will determine the type of precipitation and amounts
•Colder air filters back into the region in the wake of the storm
•More unsettled weather may impact the region by next weekend
As mentioned in the previous blogs, we are going into a potentially stormy pattern that looks to kick off by next week. At the moment it appears that after a potential brush with wintery weather on Monday, our warm up and fairly calm weather will come to an abrupt end on Tuesday PM into Wednesday. First we will have a storm system track to our north on Saturday and potentially bring a period of snow,sleet,freezing rain and plain rain to the region Saturday afternoon and evening. This precipitation may end as a brief period of snow showers on Saturday night, especially across the higher elevations. Then on Monday a storm system tracking to our south may brush the lower HV with a period of light snow, although the models differ on this possibility it is worth mentioning, seeing how it may have implications on the Monday morning commute. So lets start in chroniclogical order and take a look at the Monday situation, below are two model forecasts one from the Global Forecast System (GFS) and one from the European Model (Euro)
These models are depicting precipitation in it liquid form with colors that correspond with the keys on the right side, I have circled our region and also used a black line to show the difference between the two models in terms of how far north they forecast the precipitation to reach. The GFS model says that Monday morning there will not be a flake of snow in sight, while the Euro model shows just enough moisture for a dusting to possible an inch or so of snow across the mid and lower HV. While this isn’t a lot of snow, it is certainly enough to make for a potentially slick AM commute and will need to be monitored over the next day or so. Now on to the bigger threat that looms for Tuesday overnight into Wednesday, this will be a complex storm with some forecasting difficulties that will not be able to be ironed out until at least Sunday night or Monday. Here is what we know as of today, what makes this forecast a bit complicated is the fact that there may be two areas of low pressure, one to our west across Ohio and into PA, and another that will develop of the coast of NYC. Basically one low pressure dies out and transfers its energy to a new low of the coast. What makes the forecast difficult is that our region will be on the eastern side of the first low pressure, the circulation around a low pressure is counterclockwise, this means we will have southwesterly winds driving warm air aloft into the region. The more warm air that is pumped into the region, the higher the likelihood of our region have more of a mixed precipitation and not a pure snow event. Once the secondary low off the coast takes control we are now west of the low pressure and therefore the winds will be out of the NE/NW and colder air can pour back into the region and turn all precipitation back to snow.
The questions that can’t possibly be answered at this timeframe is just how long does it take for the secondary low pressure to take over? The longer it takes, the further the western low pressure can track north and in return drive more warm air into the region and extend the period of mixed precipitation and lessen the snowfall. If the secondary low pressure does not develop at all, the warm air may completely take hold of the region and cause rain to fall. On the other hand, if the secondary low pressure takes over sooner not only will the cold air win the battle but the snowfall amounts would be higher and the storm may deepen faster over the warm water and therefore lead to a more intense system overall. Lets try a few graphics to explain what the models are showing, try to stick with me here, first image is the European model showing the storm and its associated moisture. In western PA you can see the primary low and I have added a red arrow to depict the warm air being pushed into the region. Have also added a circle off the coast off NYC to show where the secondary low pressure is starting to form.
In this next image I have applied the temps at about 5000 feet during this point of the storm, the dotted red line shows the 0 celsius mark (32 degrees) freezing line, I have applied red arrows to simulate the counterclockwise rotation around the low pressure and the warm air it is driving north. This scenario shows that the mid and lower HV would be seeing mixed precipitation during this period with heavy snow falling to the North, you can slow see the low pressure beginning to develop off the coast.
Now in this next image watch the power of the secondary low as it takes control, look how the cold air collapses back towards the low pressure and the freezing line moves to the coast, it is at this point in the storm that our region would turn back over to all snow. The blue arrows depict the cold air now pouring in from Canada as the region is now on the western side of the low pressure (ignore the one red arrow).
Finally is the Euro model forecast for (POTENTIAL) snow from this system, you can clearly see the impacts of the warmer air on the snow accumulation across the HV. The period of mixed precipitation holds down the snow amounts, meanwhile just to our north up to a foot of snow has fallen. Now you see why this is not a clear cut forecast, factor in that these models are often very inaccurate past three days and you are left with nothing more than an outline of the final picture. So at this point we know that a storm will impact our region, what we don’t know is what those specific impacts will be. We will be monitoring the situation over the coming days and will keep you all abreast of the changes as they occur, in the meantime factor a potential storm into your plans for next week, but hold off on the milk and eggs.