Raleigh Weather Discussion
It will be warm again today as we stay in a warm southwesterly flow. The main band of rain though which is oriented SW to NE will likely stay near or just west of the Triangle. Therefore it may look like rain is imminent all day but we may end up seeing only some periodic light rain around Raleigh, with more consistent, substantial rain staying west. Temps will likely climb well into the 60s again today.
A surface high pressure will slide into the Northeast tonight and wedge down east of the mountains tomorrow. This will result in a much colder day tomorrow, as temperatures which will likely be in the 55-60 degree range around midnight, fall during the day and likely reside in the 40s most of the day tomorrow with cloudy skies and some intermittent light rain. Again, the most significant rain will likely stay west of the Triangle.
The whole storm system it appears will weaken and lift out Wednesday with the wedge front lifting back north as a warm front allowing for clearing Wednesday afternoon and highs back near 60.
The main item of weather interest will move towards and into our area Thursday night and Friday. An upper level disturbance which will form into a cut off low over the lower Mississippi River Valley will head east and weaken as it encounters strong confluent flow in the eastern US thanks to the massively strong polar vortex (PV) over southeastern Canada. However, the models have shown varying solutions to how much oomph this system will retain. For instance yesterday’s 12z ECMWF showed enough moisture and cold air for a moderate snowfall across the upper Southeast including much of the NC mountains and piedmont. Some runs of the Euro, GFS, and Canadian have suppressed the moisture well to the south with little precip in NC or some minor wintry precip south of the Triangle. Other runs have shown more moisture but also warmer temps meaning mostly rain. The very latest guidance shows:
00z ECMWF: This run of the model showed most of the significant precip south of the Triangle, across MS/AL/GA/SC, southern NC. And while the model shows 850mb T’s below zero in NE Ga/SC/southern NC, the boundary layer appears to be too warm and thus the model shows very little to no snow in those regions. The Euro Ensemble shows a little colder scenario with a mean of 1-3 inches across eastern Ky/TN, western/central NC and Va. However, it is difficult to gauge much form this as again I can see the individual ensemble model runs.
06z GFS: This run of the model is a little quicker showing the bulk of the precip Thursday evening and night. Despite the model snow accumulation parameter showing snow across the Southeast, the boundary layer warmth in the model forecast profiles look to be too warm. The wet-bulb zero line does get down to around 900-950mb in place like CLT and RDU, but the boundary layer remains in the upper 30s to low 40s. So this run of the GFS would likely be mostly all rain. Many of the GFS Ensemble members this run, curiously enough, are dry and suppressed.
For now, with continued model uncertainty, and concerns on my part about boundary layer warmth Thursday night and Friday morning, I am going to go with a forecast for some cold rain Thursday night into Friday morning. However, there is potential this could trend colder and there could be some snow around late Thursday night and Friday morning. The best chance will be in the southern Appalachians of NC/SC/TN/Ga.
After a brief warm-up Saturday and Sunday into the mid 50s, a major league arctic air mass and cold front will drop into the Plains and it appears rapidly plunge south and east by early next week. The models have consistently shown a 1047-1053mb high moving into the Plains which is big-time for mid to late January. It looks like this front will clear North Carolina during the day or evening on Monday with much colder air by Tuesday and much of next week. We see multiple days with highs in the 30s and lows in the teens to low 20s.
So the moral of the story is that although winter has appeared dead the last few days and in reality much of this winter, it will make its presence known in the coming days.
National Extended and Long Range Discussion
The ensemble models show the cold moderating and relaxing as we head into late next week and next weekend as the polar vortex that is forecast to move into southeastern Canada early next week lifts north. At the same time a new trough will form over western Canada and we will see ridging return to the southern and southeastern US, although likely it a much weaker and transient state.
Thus we will likely see warmth build over the interior Southwest, southern Plains and lower Mississippi Valley, and eventually into the southeast and mid-Atlantic later in the 11-15 day period.
However, the models do continue to maintain strong blocking signals near the North Pole through the period. The CFS weeklies have continued to maintain an overall cold pattern into early to mid February as well. The presence of the blocking to me, means that whatever moderation period we see in the 1/26-1/29 time frame, will likely be short-lived and renewed cold air could move into the US in the last few days of January and into early February. The current MJO pulse is holding together very well and is about to pass out of phase 6 into the colder phases for the eastern half of the nation, phase 7, 8, and 1. This correlates very well with the colder pattern coming up. It is interesting that the latest MJO plume forecasts do show the phase stalling in phases 7 and 8 though. If this happens we could see the colder pattern stick around for a while in general.