Saturday, March 26, 2011

Weather Update - Saturday Afternoon

This is my latest forecast for the area. Again, there are no major changes. One thing to note - a lot of the snow will melt in the afternoon, so these numbers can be deceiving. Also, most of the accumulation will remain on grassy surfaces and other things detached from the ground. Temperatures will drop below freezing Monday night, though ground temperatures will remain well above freezing. Most of the major roads will remain wet, while untreated bridges and overpasses could become icy or dangerous.

Midnight to 4 AM
Rain with a few ice pellets will overspread central VA. It will be snowing in northwest VA.

4 AM to 10 AM
This will be the peak of the storm. Central VA will see cold rain and wet snow with a few ice pellets mixed in. It will be all snow for the northern half of the state.

10 AM to 2 PM
Precip will slowly taper - mix in central VA, rain farther south.

Here are several things to consider before this storm hits tonight and early tomorrow:

1) Duration of event

This storm system will race past the area, which will shrink the window of opportunity to see an accumulating snow. In fact, the best chances for Richmond to see an accumulating snow will be during the peak of the storm from 5 AM to 9 AM.

2) Intensity of precip

Most of the precip will be light to moderate, though we could see an occasional burst of rain or snow. This will also impact our accumulations.

3) Surface temperatures

Temperatures will hover around the freezing point in central VA during the peak of the storm (upper 20s in northern VA and mid 30s southern VA). Remember, the magic number is typically 35 for the rain/snow line. Most of the precip will be gone by early afternoon, so we could see temps rise to near 40, which will melt a lot of the snow.

4) Ground temperatures

Ground temps will remain well above freezing for the entire event. This means that most accumulations will stay on things detached from the ground: grassy surfaces, cars, rooftops. Ground temps will stay well above freezing Sunday night, so most roads should remain wet. However, bridges and overpasses could quickly become icy/dangerous.

Winter Weather Update Saturday Morning

A Winter Weather Advisory is in effect for western parts of Virginia for this evening through Sunday afternoon for a developing storm system in the Southeast US that will expand a winter mix of precipitation into the Commonwealth tonight into Sunday. Snowfall of 1"-3" is expected in the purple highlighted counties, but elevations higher than 2000 feet can expect snowfall accumulations as high as 4"-5" by Sunday evening.

Much of the rest of central Virginia will experience a winter mix of wet snow and rain Sunday, too. Precipitation will expand into central Virginia from the southwest late Saturday night into early Sunday morning. Most temperatures will still be in the upper 30s to around 40 degrees with the onset of wet snow and cold rain. These air temperatures combined with mild ground temperatures will inhibit a big snowfall accumulation.

There may be some sleet (ice pellets) that mix in with the snow and rain in the pink areas.

Temperatures will be in the 30s above freezing Sunday while the slushy snow is falling and melting at the ground, except for northern locations from around Tappahannock to Charlottesville and north through Fredericksburg.

That is where more snowfall could stick to the ground and elevated objects when temperatures there fall below freezing Sunday while the snow is still coming down. Snow and rain should taper off from northwest to southeast during the afternoon. Notice the temperatures in the afternoon are in the mid to upper 30s where the snow is still falling, so some of that will melt on its way to the ground.

Here is the potential accumulated snowfall for Sunday, with most of this sticking to the grass and elevated objects:

Notice that the Metro Richmond area is right on the 1" borderline for that wet snow. Our surface temperature will be very close to freezing for a few hours Sunday. If we can get to the freezing mark, that will help more of the snow to stick on the grass and objects off the ground.

Any wetness on pavement Sunday night that doesn't evaporate will freeze for Monday morning as low temperatures plummet into the mid to upper 20s. This will likely create black ice and slick spots on the roads for your Monday morning commute. But any snow that does stay on the ground into Monday morning will melt off quickly Monday afternoon with highs in the upper 40s and low 50s in central Virginia. Stay with CBS 6, we'll keep you ahead of the storm.