BigThicket wrote:In the past having as much snow on the ground, in such close proximity, as we do...well let's just speculate. 1st does this inhibit the moderation of temperature up stream? 2nd, as the next front comes thru by around the 1st of Jan, do the models not pick up on the lack of moderation and therefor over do the forecasted temperature?? 3rd, how does that effect the dew point? 4th, if the colder air coming in is shallow is it deep enough for sleet or will the warm nose aloft erode the cold air enough to just be a cold rain that actually holds the temperature up? Maybe so of you real weather guys can help out here??? Thanks!
First off, Welcome BigThicket. We are glad you found us. To your first question, that is somewhat of a wildcard regarding upstream moderation. The West and the Rockies into the Southern Plains have snow on the ground, thus typically we see less moderation. Our source Region of Western Canada has been 'warmer than normal', but there is abundant snow across Canada. For example Yellowknife was -33C this morning. That is fairly chilly. What typically allows a warm nose is the warmer air streaming in off the Eastern Pacific with the sub tropical jet. The guidance is hanging the upper low much further N in the Great Basin versus the bowling ball cold core upper low that just exited our Region. I see the NWS offices to our West are indicating a wintry mix during the overnight hour of Thursday into Saturday, depending on the timing of the disturbance moving across our area. Right now I think a chilly rain is the most likely solution, but that may change as we near the Wednesday timeframe and see just how much cold air is associated with the Thursday front.
I am carefully watching the mid January timeframe as the upper air pattern could become much more conducive for much colder air entering the Lower 48, particularly along and East of the Continental Divide. The 12Z guidance in the longer range are really 'hinting' of a blocking regime with a strongly +PNA (Western Ridge) nosing well into the Arctic. That and a crashing Arctic Oscillation (-AO), -EPO as well as other indicators suggest a total breakup of the current Polar Vortex structure over the Arctic Circle allowing the potential for a cross Polar flow to develop driving very cold air from Siberia into North America. There are some indications that the Polar Vortex will setup shop near Hudson Bay in Canada favoring that cross Polar flow. Typically it takes a couple of weeks for the pattern to fully transition. That would put us into the mid/late January timeframe. For now, we will wait, watch and see exactly how the pattern evolves.