The steering level begins to move
I can already hear it now. Mike, have you gone nuts? Why are you showing us this light ball of fluff over the Northwest Territories? It's the hand that holds the cards for how the steering pattern plays out through Saturday and is the table setter for what is to come for next week. It looks irrelevant, that little gem riding over the western ridge is what is going to touch off a chain reaction and move things along.
If you watch this loop of upper-level energy from start to finish at 7 PM Saturday and look specifically at that energy source over the NWT, its the driver that brings cold air into the state and determines the junky mix on the way.
Looking at it from a forecast surface map point of view may be easier to understand. While there is so much emphasis on the surface maps, and justifiably so since that is the eventual outcome for people to deal with, our atmosphere operates from the top down.
At times the important upper-level energy sources that determine the outcome are over areas of the continent that have poor radiosonde (weather balloon) sampling. This causes guidance to be jumpy at times, and cases where there are significant changes in a short period of time.
I bring all of this to your attention as I see a strong ridge building in the west. The upper-level energy sources that will determine our weather will ride over the top of that. In a case like this where that energy over the NWT is racing toward our region in 36 hours, forecasts could shift in either direction of higher or lower impact. This is common in active winter patterns. Our pattern is about to become more active as we head into January.
The outlook through Saturday
With the trough driving energy over the NWT holding the cold air card along with the recipe of a junk storm on the way, my confidence in how this is going to play out for precipitation types and amounts is on the low side. How much ice and or sleet is going to factor in to how much snow comes out of it. The element of bust potential is fairly high looking at all of the ingredients in the bowl.
Thursday Noon to Saturday 2 PM - Where confidence is good is the offshore storm tracking just south of Nova Scotia brings rain showers to the region through the day, and a bit of a breeze to the coast overnight into early Friday. Then confidence goes down heading into the overnight.
The key to the flip to freezing rain will be the northeast wind shift that hauls cold air down from the north. How quickly the cold air bleeds in, how far south it goes, and when will determine how much ice accretes and when some areas of sleet work in. The convergence of cold and warm air at the low levels appears to battle it out through Friday.
The cold air driver arrives Friday night. This is when the junk turns to snow as low pressure along the cold front passes through. Precipitation ends from west to east Saturday morning into the afternoon.
Outside of slippery roads and untreated surfaces, not a whole lot of ice to be concerned about. Again, where cold air damming sets up will determine how much accretion and for how long. Elevation plays a role in this to the west. Given the amount of liquid equivalent involved here, the accretion appears to be more annoying if anything. No concerns with power outages.
The snowfall amounts out of this appear to range from a few flakes in the south to upwards of 6" over the north. The arrival of the cold will dictate how much snow is produced from this. The quality of the snow isn't the greatest, and that may cut totals down over the west and the east. I expect that this idea will get tweaked, and I will update this on Friday.
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