Raleigh Weather Discussion
We will see a chilly day tomorrow with clouds, scattered showers, and temperatures likely in the 50s followed by a cold Wednesday through Thursday morning with lows around or just below freezing and highs Wednesday in the low 50s.
But as we head into the weekend and next week, we see the reason why a lot of folks from up north who hate the cold/snow move south. As we see a very mild weather pattern set up for early December as a Gulf of Alaska trough initiates a very warm semi-zonal jet stream pattern across the US with cold being confined to Canada and a very warm pattern for much of the US, with most locations above normal.
Here in Raleigh, it looks like we will probably see a few days in a row at least with highs cracking 70 early to mid-next week as we get the meteorological winter off to a warm, dry start. This coming on the heels of what will be our 4th straight below normal temperature month. Will the warm pattern hold for a while? That is open for debate below.
National Extended Weather Discussion
Unfortunately for cold lovers like myself, what looked like a sure cold pattern coming shortly after December began is much less sure today. We have seen the pattern evolution to a cold pattern be constantly pushed back in the modeling and as of this morning while blocking signals remain (strong –AO on most model charts), the NAO is now only looking a little negative as opposed to the strong negative forecasts of last week. This combined with a persistent trough in the Gulf of Alaska (+EPO) will make it difficult for long-lasting cold to set up over the US.
It does look like we will see some cooling in the Ohio Valley/East by late next week as a storm moves through with some cooler air behind it. However, the GFS Ensemble maintains a +EPO look with a trough in the Gulf of Alaska and western Canada. The ECMWF/GGEM Ensembles do to a degree as well although they are weaker and allow for more ridging along the West Coast.
So let me summarize my thoughts currently. There is still a great deal of day to day model oscillation with regards to the pattern as we head into December which continues to lead to low confidence. We do see two key features remain and essentially until these features weaken or chance their ebbs/flows will likely force pattern oscillations. 1. The Gulf of Alaska Trough (+EPO) and 2. Blocking (-AO, -WPO, and at times a –NAO). If factor 1 is stronger that we will see the US flooded with mild, Pacific air like we look to see in early December. If factor 2 is stronger like it has been most of November, we will see cold air masses drop into the US. To begin December the GOA trough is going to be the key pattern forcer, as the ensembles keep showing a general cooler pattern by mid to late in the 11-15 day pattern but this seems to keep being pushed back as the GOA trough shows up stronger in subsequent model runs. I think December could be a back and forth month with an eventual turn to a colder pattern but rather it is 12/8, 12/10, 12/15 or 12/25 is hard to say.
Eventually, I think this pattern goes one of two ways. 1. The lack of a sustained El Nino influence on central equatorial Pacific convection allows for the Pacific warm influences to rule and we see the +EPO/-PDO signal dominate the weather pattern as blocking potentially fades through the winter as the –QBO influence weakens and we see a pretty warm winter. 2. The Gulf of Alaska low feature weakens, while the –NAO remains formidable and we see the –WPO/-AO/-NAO regime force a cold to very cold pattern that has some stability as the GOA trough influence wanes. OF course there is room for an in-between solution which would be a constant warm between the two factors through the winter which would produce volatility.
This is not an easy forecast with some cold indicators (blocking) vs warm indicators (GOA trough). Unlike last winter where there was no blocking and an active GOA trough which allowed for the blow torch. We will see which idea starts to win out!