The big storm for the weekend may end up as two minor storms instead of one major one.
The first would be on Saturday, with a surface low passing to our south. The models differ on whether the storm would graze the area or miss us to the south.
A second more significant upper level low will be approaching the area on Sunday. That storm offers more potential for getting a decent snow, but could end up having the associated surface low track to our north.
Either way, the weekend looks unsettled, and there still have been too many model permutations to really get a firm handle on the systems. There is a chance of rain or snow, but right now any precipitation is more likely to be on the light side than heavy.
That’s a change of thinking from the last two days. The likelihood of a major East Coast storm for us is diminishing. Yet, with the models still in flux it is not yet quite dead.
Why so wishy-washy when discussing this weekend’s weather?
The operational models and various ensemble guidance have not shown a lot of run to run consistency and even now differ on how they handle the two potential weekend events.
Let’s first look at their handling of the first wave forecast to track to our south. Below, I’ve chosen three 06Z GEFS ensemble members that capture the three main clusters of model forecasts in handling the feature on Sunday. Remember that the only differences in the ensemble forecasts shown below are slightly different initial conditions. The model physics is identical in all the runs.
Each of the model forecasts are valid Saturday at 7 p.m. All the models and ensemble members, including ones not shown, predict a wave off the Carolina coast, but they differ on the strength of the low and how far off the coast it will develop. Therefore, the models differ on how that wave might impact our area.
The simulation at left is essentially last night’s 06Z GFS solution, shown at a lower resolution. Quite a few of the ensemble members have some variation of its basic idea. It keeps the low so weak and so far offshore that it produces no precipitation across our area on Saturday. The middle solution is the ensemble guidance from last night’s second most common solution. It depicts a weak wave just far enough north to offer a dusting of snow. Today’s GFS is in its camp. The solution on the right side has the least ensemble support developing the surface low close enough to the coast to give us light accumulations.
Last night’s European solution was a compromise between the two snow bearing solutions, and today’s run of the same model more or less backed up its offering last night, meaning some light snow is possible. All these solutions are viable ones.
The uncertainly ratchets up on Sunday and the range of solutions widens. The large differences in handling the low for Sunday is dependent on how far south a northern stream upper low will track. That system is coming into the U.S. at the latitude of the state of Washington.
Earlier in the week, a number of models were taking the southern stream system that will be exiting the coast on Saturday and were phasing it (combining it) in such a way to produce a major East Coast storm. Rumors about that storm went viral. Now almost all the models are handling the southern stream and northern stream features separately.
Below, I’ve attached three ensemble solutions from the 06Z package.
The most common solution was for the weak low from Saturday to scoot offshore with either no snow or dusting or so, and then for the northern stream system to produce a low that tracks to our north. The last two GFS solutions have pretty much mirrored the solution on the left hand side of the figure below.
That cluster of solutions takes a low towards the Ohio Valley, and then either tracks it to our north or redevelops a low off the coast north of us. Such a solution could offer us a little snow or mixed precipitation, but generally leaves us in the dry slot as the low level winds take on a westerly component which leads to downsloping winds (off the mountains), a recipe for drying out the local atmosphere.
However, not every member showed such an evolution.
A few runs the last couple of days have mimicked the middle panel solution developing a second low near the coast of North Carolina. Last nights European solution tried to develop such a low, but so far off the coast that it only produced very light precipitation across our area, and not from the low but from the upper level system passing by. While such a solution is still possible it looks like a long shot.
Still another possible solution offered by the ensembles is having a strong low track to the eastern Great Lakes region. That solution appears to be an outlier, but still is probably a viable one. The wrapped up low solution would argue that any precipitation associated with it would fall as rain.
The bottom line is light rain or snow is possible Sunday, but the area also could escape pretty much unscathed. However, enough uncertainty remains to keep monitoring the system.
Moving from the weekend to next week
The various GEFS member forecasts of precipitation amounts and types are displayed in the figure below. When the lines are showing steep slopes, heavy precipitation is being predicted, when the slopes are gentle, light amounts are being forecast. Periods when the lines are flat and parallel to the x-axis, are dry periods with no precipitation.
The ensembles are divided on whether precipitation will fall on both Saturday and Sunday. However, the members that do predict precipitation on Saturday suggest it is more likely to be snow than rain.
Sunday, is a different story. A number of members depict snow changing to rain reflecting the possibility that the second low will track to our north. Snow lovers can take solace that one member is predicting a moderate to heavy snowstorm. That snowy solution still looks like a long shot. The more likely scenarios are either light rain, snow or even for the storm to miss us to the north.
Another possible winter weather event is now starting to show up on the models around next Wednesday. Right now there is little that can be said except that a number of model runs are now suggesting that the Wednesday-Thursday time frame is one to watch.
The way the model forecasts have been jumping around lately, there is way too much uncertainty about any possible storm in that time frame. At such a long time range, I wouldn’t put much stock in any precipitation amounts or type being forecast by any model.
All the ensembles are saying is it’s a time period worth monitoring closely.