Coastal Storm Updates
Last update 3-12-18 at 07:38 PM
As of Sunday Evening (March 11, 2018), forecast models have been showing a coastal low pressure system tracking and deepening off the NC/SC coast on Monday. This is a system that I have been keeping an eye on for the past couple of days as it has serious impacts to ENC. The details of the impact have been uncertain to this point but we are beginning to narrow down what we could expect over the next 48 hours.
As we go into this evening, the Mid-Level Energy will continue to dive southeastward as surface low develops off the SC coast. As the northern energy approaches it will begin to lift the low northeast off the coast on Monday and into Monday night.
Areas across the northern parts of ENC have already seen some light rain or drizzle throughout the day and will continue for the rest of the afternoon. Widespread heavier rain will begin to cover the entire area later tonight and last into the early morning hours. Some areas will see rainfall totals range from from 0.50″ to 0.75″ before a brief break in the rain by late morning.
Rainfall begins overnight.
Brief break in the rain during the morning hours.
Things become a little complicated as we head into Monday afternoon and into the evening. As the low pressure begins to deepen off the coast, winds will begin to increase especially along the coast where Wind Advisories have already been issued. Coastal sections could expect to see winds around 20-30 mph with gusts up to 40-50mph. Inland sections will also see increases in wind though not to the same extent as the coastal sections and not nearly as bad as the previous coastal storm.
Rain should pick back up during the afternoon from west to east as a deep upper-level trough moves over the area. As the low pulls away, colder air will begin to filter into the area. Timing of this colder air will be critical in the forecast for Monday Evening. Looking at the forecast soundings from the GFS, the vertical profile shows the air column above freezing through the afternoon into early evening for areas in the northern half of ENC. There will be a period where the upper-levels will drop below freezing while some precipitation lingers in the area. The problem is the surface temperatures will take longer to cool and these models show the air column drying during this time as well leaving a very narrow window of potentially seeing some snow in the air.
The NAM on the other hand has a much more aggressive approach to the atmospheric conditions during this same time frame. In its solution, it has a narrow field of strong lift with heavy precip rates. If this plays out, it is not unreasonable to consider some accumulations in this region. I am still skeptical of this solution and will keep this out of my forecast for now. I will reevaluate in the morning and post any adjustments I feel are needed.
As for those in the southern sections, the chances decrease of seeing snow as I do not think the cold air will catch the precip soon enough to see a change from rain to snow. Accumulations will also be unlikely as surface temperatures are forecast to stay above freezing prior to the precipitation pulling away Monday night.
I will keep an eye on the evolution of this storm and update if any changes to the forecast need to be made. At this time, my forecast is mostly all rain Sunday night through Monday evening with a potential quick change to snow before ending late (no accumulations). To the south, an all rain event. Coastal sections will see strong winds through the duration of the storm.
I will not be creating any forecast maps for snowfall totals for this system as there are way too many variables.
Update: Not much change in forecast thought for Monday-Monday night. The models have held steady overnight with the NAM still aggressive with precipitation rates leading to some accumulating snow (albeit low and on grassy surfaces) and GFS, Euro, and CMC holding steady at the moment. Surface temperatures will remain above freezing while precipitation is falling and only dropping below freezing later after the precipitation moves out of the area limiting any accumulation.
Update: I would like to remind viewers that the models show forecast accumulation but those numbers may not pan out due to warmer surface conditions. Some snow could accumulated in areas of high precipitation rates but nothing significant and mainly on grassy or elevated surfaces. Not everyone will receive these heavier bands and it is difficult to know where it will setup. We will have to wait until the storm unfolds later today.
Update: Snow in Greenville is coming down at a good rate. Have already received a dusting on grassy surfaces while elevated surface have now been covered. 
This band of heavy snow associated with the deformation zone of the coastal system will push eastward as the evening moves forward. The heavy snow will not make it to the coast but some areas could see some flakes in the air before the system completely departs the area.