After another very cold morning this morning, we will see temperatures warm into the 40s across the state today and into the mid to upper 40s on Saturday and Sunday. However, an approaching storm system will increase our clouds tomorrow and bring a good chance of rain by Saturday night into Sunday.
There are some differences in the models for Saturday. The NAM is showing an in-situ damming event which would keep temperatures for many areas east of the mountains in the 30s tomorrow with light rain and drizzle. The GFS is not as pronounced with this nor is the ECMWF and these models allow temperatures into the upper 40s to low 50s. I think the NAM may be overdone, but if it isn’t Saturday will be colder than I have forecast. As it is we will likely not get out of the 40s, with clouds and possibly a passing shower tomorrow.
We will see temperatures warm up Sunday morning and a band of rain will move through prior to sunrise west of the Triangle and around sunrise in the Triangle. We may see a 0.25 to 0.5 inch of rain with this as it passes by. There is a slight chance the rain ends as snow across the foothills and piedmont but the chance is so small I do not mention it in my 6 day forecast and even if it did occur it would likely be an hour or less of snow flurries that do not accumulate.
It will turn very cold Sunday night and into early next week as very cold temperatures blast in behind this system. We are looking at the very real likelihood that the first half of December will be the coldest first half of December on record for Raleigh. We will likely go below freezing around 10pm or so Sunday night and may not get back above till Wednesday afternoon. It will be windy and very cold Monday and Tuesday as temperatures struggle to get to 30 and we will likely see lows in the mid teens in the Triangle Tuesday and Wednesday morning and in the 10-15 range in the western piedmont and foothills. Many mountain locations will go below zero.
The massive 500mb low over New England should lift out some by Thursday allowing temperatures to moderate some, but then our flow aloft will become southwesterly which could increase our cloud cover and increase our precipitation chances starting Thursday and going through the weekend, as several weak impulses aloft could move through the area. The 6z GFS painted a wintry scenario on Thursday with a wintry mix across the state but the 00z GFS though was warmer with rain. The 00z ECMWF brought in some very light precipitation Thursday evening and night which looked to be in the form of a wintry mix as well (especially in the west) but changes it to light rain by Friday. Many of the GFS Ensemble members are either dry or warmer with rain on Thursday and no other members look as supportive as the 6z operational GFS for wintry precip on Thursday. Another impulse could move through Saturday and we would have to watch to see if the low levels are cold enough to support wintry precip with it as well. Confidence is low, but we have to watch this time frame.
Temperatures will moderate some for mid to late week, but the models all show a massive west-based –NAO Greenland block which will likely serve to keep a cooler than normal pattern around through the rest of the month. In fact there are some signs we could see another arctic air mass drop in around or just prior to Christmas time.