Thanksgiving week East Coast storm could be travel troublemaker

cwg_JunkerAn East Coast storm threatens to produce precipitation, possibly heavy, across the area between Tuesday and Thursday next week. We think that any precipitation that falls will be in the form of rain but there still is a slight chance of seeing snow towards the end of the event late Wednesday. The possibility that the storm skirts us with little rain or even misses us altogether, is waning.

Wet weather is likely for people traveling south towards the Carolinas and Georgia starting Tuesday, with snow possible at high peaks in the mountains. By Wednesday into Thursday the storm *may* (lower confidence) move up towards the Northeast, with rain along the coast and snow in the mountains. Given this storm may well coincide with the busiest travel time of the year, travelers need to keep abreast of local forecasts.

Model discussion

The operational models (GFS, Euro, UKMET and GGEM) all bring a developing low pressure system across the Gulf Coast states into the Southeast early next week. Considering the storm is still 5 to 7 days from now, they are in pretty good agreement that there will be rain across the Carolinas and much of Virginia. There are some important timing differences in the model simulations: the onset of the precipitation in the GFS model (early Wednesday morning) is at least 12 hours slower than in the European (during the day Tuesday).

Today’s run of European model shows one of several possible scenarios for the southern stream system in the Mid-Atlantic. I show it below because I think it more right than the operational run of the GFS model which keeps the bulk of the precipitation south of us.  This run of the European  illustrates how wet the system could be. Aside from the operational GFS model, most other models look somewhat similar.

Simulation of precipitation between 7 p.m. Tuesday night and 1 a.m. Wednesday morning of the European model (WeatherBell.com)

Simulation of precipitation between 7 p.m. Tuesday night and 1 a.m. Wednesday morning of the European model (WeatherBell.com)

As the storm is pulling away, the European model shows a strong high pressure system building across southern Canada (see above) which should bring more cold air into the area late Wednesday into Thursday. How quickly this air comes in and how long the precipitation lingers could determine whether we see a few flakes towards the end of any event. Right now that seems to be a long shot.

While the European model hit us with a pretty decent slug of precipitation mostly in the form of rain, the last two runs of the operational GFS having the storm skimming us with only light precipitation.   However, as shown in the graphic below, most of the GFS ensemble members are predicting precipitation – a few of them with hefty amounts – in the area.

Plume diagram showing precipitation totals over time from different simulations (ensemble members) of the GFS model.

Plume diagram showing precipitation totals over time from different simulations (ensemble members) of the GFS model.

Remember – in the graphic above-  when each line has its steepest slope that is when the precipitation rate is heaviest. Most indicate their period of heaviest precipitation will occur  late Tuesday or Wednesday.   I’m not sold on the almost two inches of rain that some members  are showing. Those lofty numbers seem unlikely to me given that there is not a lot of interaction with the northern stream and there is unlikely to be any convection (thunderstorms) involved in the storm.

Our snow lovers will note a few members do indicate snow – especially the members that have the precipitation coming into the area slower allowing more time for the cold air to reach us.  Our snow haters will note that most members do not forecast snow of note.

Bottom line

The threat of precipitation Tuesday into Wednesday is rising. The bulk of it is likely to be in the form of rain with southern areas having a somewhat better chance of getting heavy rain than areas farther north. We can’t rule out a period of snow towards the end of the precipitation but feel the probability of seeing snow is only in the 10 to 20 percent range.

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