Weekend Storm Update
Update (Thursday Night): Had to work later than usual tonight so I am a couple of hours behind. I have been monitoring the models throughout the day and I am currently working on the forecast and shortly I will begin working on tonight’s update. For right now, I can say nothing much has changed with yesterday’s forecast. I did bump up forecast totals from 2-4″ to 4-6″ inland and 1-2″ along the coast.
We continue to see some general consistency among the models though confidence remains slightly below avereage. There are a few details that need to be fine-tuned prior to this weekend’s storm. As of Wednesday afternoon, all models forecast a system to form over the Gulf of Mexico and shift eastward and emerge off the east coast of Florida. It is then forecast to move northeastward parallel to the east coast. The exact path of the low pressure center will be a major factor in determining the type of precipitation that will fall over the area.
At the time of this writing, we have received the most recent 12Z and/or 18Z forecast models which I will cover briefly because a detailed assessment of each would take too long to write. I’ll start with the 12Z CMC:
The CMC and Euro (not pictured) are very similar in forecast track at this stage. Both show the forecast track to be close to the coast. This will bring more moisture over ENC which means higher precipitation rates and totals however that doesn’t always translate to more snow. The forecast from these two models indicate rain as the dominant precipitation type at the onset Friday afternoon. Warm air ahead of the low will push onshore warming the layer above the surface just enough to melt the snow as it falls through. This warm layer will eventually retreat and the entire column of air should be cold enough for snow. For inland sections this transition from rain to snow will occur faster than for areas near the coast. The amount of snow that will accumulate is difficult to predict as there are other factors to consider which I will describe later.
The snow would be moving out of the area on Saturday night with increasing winds and much colder temperatures following.
The NAM is similar to the CMC and Euro except for timing. This run brings rain into the area a few hours earlier at the onset. With this model, the rain to snow transition along the coast would take longer to occur.
Then we have our friend: the GFS. Over the past few runs the GFS has been further east with its track than the other models and has been consistently colder. The GFS solution has the northern half of the area starting and ending as snow. It has rain/snow mix at onset transitioning to snow slowly. The GFS currently has the highest forecast totals among the models but there is another issue to consider at this time.
Right now, I am leaning towards the Euro/NAM/CMC solution.
I do not have a detailed forecast total map to post at this time. However, I will be continuing to monitor the situation so I can narrow down some accurate numbers. There are some things to consider with a forecast like this:
Over the past couple of weeks the weather has been changing frequently and quickly from day to day. There have been a couple of days where the temperature went from 40 degrees one day to 70 degrees the next then down to 35 degrees the day after that. Overall, its been warmer than average over ENC. The soil temperature has been warm with the lack of consistent cold weather. The temperature is unlikely to drop much if any before this weekend. The snow that falls is going to have a hard time sticking to the ground which is going to limit exactly how much snow will accumulate. On elevated surfaces this will not be a major factor.
The forecast models do have a tendency to add ice(sleet/IP) to a snowfall total estimate which would inflate the forecast totals significantly in most cases so if ice is involved in the forecast, you must take this into consideration. The GFS has the highest forecast snow totals near areas that could experience ice at some point.
At this moment, if I had to say the most reasonable numbers at this stage look to be 2-4″ over far inland sections to a trace to 1″ over coastal sections. I will hopefully have a map made out for tomorrow’s post.
Update (Thursday morning): I am very skeptical of the forecast totals showing several inches of snow for the reason mention a few paragraphs ago. While under normal winter conditions I believe a storm of this magnitude could produce totals > 5″. I believe that the models (especially the GFS) are underestimating the amount of warm at at 800 mb further inland resulting in more sleet than show early in the event. Eventually the warm air retreats but by that point, there isn’t as much moisture available to obtain these totals. While the snowfall totals on the model approach double digits, those numbers occur in the areas where ice is forecast to fall at the onset of the storm. If you take that and the warm ground temperatures, your final total (on the ground as opposed to raised surfaces) will be less than its overall potential. For now, I am going to change my forecast to 3-6″ west of highway 17 and 1-2″ closer to the coast. Highest amounts appear to be along a line from Wilson to Virginia Beach where I could see totals possibly ranging in the 6-8″ Of course that is if the forecast doesn’t change much between now and Saturday. Check back for more.
And for your joke of the day:
Really “The Weather Channel”? Are you serious with this map? Even the National Weather Service has a lower forecast than you. Saving this for later.
