Friday, 11:50 a.m.
It's halftime in the month of November, and the report card is pretty simple. Sub-par performance from the Plains to the East Coast in terms of temperatures, and excellent grades from the Rockies to the West Coast. In plain English, in areas from the Plains to the East Coast, it has been a cold first half of the month, while the West has been warm.
The interesting thing about the pattern is that it hasn't been your 'typical' pattern for a lot of cold. In other words, there has been virtually no downstream blocking that you would normally get with a persistently chilly weather pattern. Look at the North Atlantic Oscillation (NAO) since summer:
At the same time, the Arctic Oscillation (AO) has been strongly positive, indicative of a strong jet stream, but one pretty tightly wound around the polar regions. It is forecast to trend negative in the next couple of weeks, though, a sign that the circumpolar vortex and all of the very cold air locked up around it is about to expand:
That change is probably not going to take place much in the next five to seven days, so I'm not going to discuss its ramifications here. Instead, I'm going to look back quickly at the recent cold shots and look ahead to the next few days.
In looking back, while knowing the teleconnection indices have been suggestive of little cold, and certainly not sustained cold, we have a lot of amplification in the pattern nonetheless. So, any time there has been a strong system coming through the Northwest or the West, it has then dug a deepening downstream trough into the East in some fashion. None have had any semblance of staying power, need I remind you. However, they have been full-latitude troughs, with large surface highs in back of the cold fronts driving the cold air deep into the South and into the East.
What lies ahead if a flatter pattern, one much more zonal in nature. Look at the 12z Nov. 15 NAM 500mb forecast for Monday evening:
In this fast flow aloft, there's not much time to dig a deep trough, and if the feature driving the cold front eastward isn't immediately followed by something else to sharpen the trough and prolong it, then the cold will be limited in scope and duration. I believe that will be the case next week. The surface high coming into the Plains and Mississippi Valley is not a 1040mb high or greater. In fact, it may not even reach 1030mb, so it won't carry as much weight going forward. Tuesday and Wednesday will be the chilly days in the East, lingering into Thursday morning. West of the Appalachians, the coldest days are likely to be Monday and Tuesday, followed by moderation thereafter. The 12z Nov. 15 GFS surface forecast for Thursday morning:
The next cold front won't reach the northern Rockies and northern Plains until Thursday night and Friday, so there should be at least a couple of days where temperatures make a nice recovery from the Plains on eastward, limiting the chill next week.
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