Friday, March 25, 2011

The Latest On This Weekend's Wintry Mix

I want to first start off by saying that it is not uncommon to see wintry weather this late in the year. In fact, check out some notable snowfalls I found while digging through climate data this afternoon.

The forecast hasn't changed much from earlier this morning. I have posted temperatures along with the precipitation forecast below (Rain=green, Mix=pink, Snow=blue). Most of the precip should taper by early Sunday evening.

You can see that temperatures will hover above freezing. In addition, ground temperatures are relatively warm. This will be a tough forecast to verify because a lot of the sleet (ice pellets) and snow will melt. Nonetheless, here is my early forecast for accumulations. I want to emphasize that this is not etched in stone and you should check back on Saturday for the very latest information.

Most of the accumulations will stay on things detached from the ground, however, there could be slick spots on the roads...especially to the north and west. We will continue to track this and have another update tomorrow morning!

Friday Morning Update on Weekend Winter Weather

Here is the latest data as of Friday morning on the rain and winter mix expected this weekend in central Virginia. This data will likely change some over the next model runs today and tomorrow.

Overnight Friday into pre-sunrise Saturday, a weak upper wave currently tracking through the Midwest and Great Lakes will pass overhead and could produce some rain showers that may also have a few sleet or wet snowflakes mixed in.

However, temperatures at and near the ground will be above freezing in the mid to upper 30s and low 40s when this precipitation falls, so nothing will stick and there will not be icy patches Saturday morning. The light rain and mix will exit south before sunrise Saturday.

The rest of Saturday looks mostly cloudy but dry, so if you have outdoor plans during the day, you should be good to go!

Rain will begin moving back into the Commonwealth late Saturday night, and by Sunday morning, there should be a wintry mix of precipitation occurring in the area. On the maps to follow, green is rain, pink is a mix (snow, sleet, rain), and blues/whites are snow:

Sunday does look like it will be a cold washout day with a winter mix likely.

However, surface temperatures look like they will remain above freezing and hinder much, if any, accumulation or ice development during the day Sunday.

As colder air aloft is pulled southward into the Commonwealth Sunday night, a changeover to all snow may occur from north to south. Yet with surface temperatures still above freezing, accumulation may only occur on the grass and elevated objects.

Precipitation should quickly taper off after Midnight:

The snow map below should be taken lightly as it will likely change. Also, I think this represents how much snow may fall while it's mixing in with the rain, but not this much snow will literally "accumulate" on the ground because the surface temperature will remain above freezing Sunday and Sunday evening. We shouldn't fall below freezing until after the precipitation is done shortly after Midnight early Monday morning.

There should be wetness on the pavement Monday morning, and with temperatures by then falling to and below freezing, we could certainly develop icy patches on pavement Monday morning.
Stay with CBS 6, we'll keep you ahead of the storm!

Wintry Mix This Weekend?

Over the past couple days, computer data has been hinting at the possibility of wintry weather this weekend. I just got done looking at the latest data this evening, and it continues to show this scenario.

A few rain showers could clip the area during the day Saturday, especially in southern VA. Precip will intensify Saturday night into early Sunday as an upper-level storm system approaches. During this time, central VA could see a mix of sleet (ice pellets) and rain. Northern VA could see a mix of wet snow and rain.

A lot can change from now until Sunday, so we will continue to track this system and bring you more updates over the next couple days.

Legend for the maps below: Rain (green/yellow), Mix (pink), Snow (blue).

Technical Discussion

The key to the forecast in central VA will be the mid-level temperatures. I've posted a Skew-T diagram below. This shows temperatures and humidity from the ground (bottom of the diagram) all the way up 50,000 feet (top of the diagram). I've marked the freezing line in red. You can see the temperature line (pink line) is very close to freezing at 6000 feet, then much below freezing at around 4000 feet. This is your typical sleet profile (snow melts at 6000 feet then refreezes at 4000 feet). This will be something to watch when the new data comes out tomorrow.