Weather Update - 4:45 PM Sunday

Winter storms are rarely "well-behaved" here in the Mid-Atlantic and this storm is no exception. However, as this storm approaches the area, the picture continues to become more and more clear. With that said, this is not 100% etched in stone yet.

Here is my forecast for snow totals from Monday night into Tuesday night.

***Update 10:20 PM***
I just looked at the latest data and have slightly adjusted this graphic so that it can be more specific. I think some areas west of I-95 have the potential to pick up a little more than the 1 to 3" I previously posted.



Yesterday I showed you a forecast sounding from the GFS computer model. It's a forecast of temperatures from the surface (bottom of image) all the way up to 50,000 feet in the upper atmosphere (top of image). I highlighted the freezing line in red. The right pink line is the temperature forecast. When it is to the left of the red line, temperatures are below freezing. When it is to the right, it is above freezing. Notice a large area of above-freezing temps at around 5,000 feet, indicated by the red arrow. This is your typical sleet scenario (ice pellets).

I think it's safe to say that we will see a mixture of sleet and snow in Richmond and areas to the south and southeast. In fact, far southeastern VA will be seeing mainly rain. This will eat away at our snow accumulation potential. There is also the threat for some freezing rain in south central and southeastern VA, but this band will be very narrow.



This is a difficult forecast because the powerful storm system currently moving across the Deep South is going to weaken when it moves into our skies. Once the surface low develops off the coast, it will receive reinforcing "lift" from a large upper level wave moving in from the northwest. From 7 PM Tuesday to 1 AM Wednesday (00Z to 06Z), this low will explode. You can see this on the ECMWF ensemble forecast below.





During this time, heavy bands of snow will redevelop, however, it might be too late to affect Central VA. That is why I'm going for higher amounts in Northern VA. I've posted all of the computer forecasts for snow accumulations. Notice how the NAM, ECMWF and RPM all reflect this trend (though NAM and RPM are very aggressive with snow totals in eastern North Carolina).

Tuesday Storm Update - Saturday 7 PM

Here are the maps of the ECMWF and GFS ensembles from earlier this morning. Both computers have a very similar track with rapid cyclogenesis (storm intensification) from 7 AM to 7 PM Tuesday. It's during this time that the heaviest snow bands will form.









As with previous runs, the GFS is hinting at a mid-level warm layer moving into southeast Virginia. I've posted the forecast sounding for Tuesday afternoon. The right pink line is the temperature forecast. The bottom is the surface, the top is around 50,000 feet. I've drawn in red the freezing line. Everything to the left of this line is below freezing, everything to the right is above freezing. Notice the red arrow at around 5,000 feet, where temps are very close to freezing. If it gets a little warmer in this location, then snow would melt, then refreeze in the colder air below. In other words, we would get sleet (ice pellets).



Although I think we could get some sleet in Richmond, most of the mixing will occur in south central and southeast Virginia. That's why I'm giving a higher probability to the ECMWF solution below. Notice how the heaviest band starts in central Virginia, right when the low intensifies off the coast. This heavy band then extends south of D.C. and into Philly.



If we see more sleet, then our snow accumulations will be less. Right now I think this is less likely, but still a plausible outcome.

Weather Update - Friday Morning

As always, I will start this discussion by saying that nothing is etched in stone and that things will change as this storm moves closer to our area.

Yesterday I presented two possible scenarios with Tuesday's storm. The data last night was fairly consistent with the track, so the overall picture is becoming more clear.

The maps below show the forecast of the upper atmosphere next Monday and Tuesday (500 mb heights and vorticity). What you will notice is that the smaller storm in the deep south races ahead of the low in the Pacific Northwest. This is important because there really isn't a phase, or merge, of the two storms. Instead, the storm in the northwest becomes the main feature by early Tuesday.

Also notice that the jet stream flow is more flat - east/west as opposed to north/south orientation. This could take away from our accumulation potential. The Christmas storm was deeper and slower, which allowed it to dump a lot of snow.

Although this storm doesn't look as big as the Christmas storm, it still has the potential to bring an accumulating snow to our area. We will have more updates in the coming days!