Monday, January 31, 2011

Wintry Weather Possible Overnight

A light mix of sleet and freezing rain will be possible overnight in central VA. I stopped our model data at 2 PM to show how the precipitation will expand over the area after midnight. Although the model shows rain in the green color, this rain will be falling into sub-freezing temps and will freeze on contact, creating a glaze of ice. The amounts will be light, but it doesn't take much ice to cause big problems, so take it easy out there tonight through early tomorrow. A massive winter storm will cripple much of the nation this week with several feet of snow and strong winds. Temperatures behind this system could stay below zero. We'll be on the warm side of this system Wednesday, with highs near 70 degrees and a chance of thunderstorms.

Sunday, January 30, 2011

Update On Wintry Weather This Week

Warm air is going to surge into our area by midweek. The leading edge of this warm air will create a wintry mix of rain, freezing rain, and sleet (ice pellets). The best chances to see this mix will be from 7 PM Monday until 7 AM Tuesday. In addition, it will generally stay along and west of I-95. I've posted some maps below to give you a timeline of the event. We should be in the clear by 10 AM Tuesday as the precip lifts north and temperatures rise into the mid 30s.

As you can see on the map below, the accumulating snows will stay well north of our area.

Another storm system will pass our area Friday into Saturday. Normally I would be worried about a storm moving in from the south along the coastline, however, right now it loooks like a rain event to me. There are two problems with this storm.
  1. The track is too close to the coast
  2. Cold air moves in too late (if at all)
I've posted a map of the ECMWF ensemble: a very reliable computer forecast. It has been consistent with this storm for the past couple days and brings rain to our area late Friday evening and into early Saturday. I think this is a plausible solution and will keep a 30% chance for rain on both Friday and Saturday.

Saturday, January 29, 2011

Dense Freezing Fog This Morning

Patches of dense fog have developed across central and southeastern Virginia. Temperatures are currently below freezing, so the fog is freezing on anything detached from the ground. This could produce an icy glaze on bridges and overpasses, so use extra caution if you are on the roads this morning. I'm expecting the fog to lift and temperatures to rise above freezing between 9 and 10 this morning.

Friday, January 28, 2011

Snow Season 2010-2011 Update

If you feel like it's been a "snowier" Winter so far this season as compared to this time last season, you may be right--by one definition. It's not from snow accumulation, but by the number of days we've received at least some snow. By this time last Winter, we'd had 10 days where it snowed at least a trace or more. Our accumulated snowfall at Richmond International Airport was 17.8" from December 2009 and January 2010. That definitely surpasses our total snowfall so far this Winter season (10.7" through 1/27/11), but we've already had 13 days (before Friday) with at least a trace of snow. Here's a comparison of last Winter to this Winter so far, including what an average Winter snowfall season is like in Richmond:

But this morning we added another snow day with this light snow that passed through Richmond mid-morning. It will probably only register as a trace officially at the airport, but I'm counting that as a "snow day" in my tally of "Days it Snowed." So our total today for the season is now up to 14 from 13. Even though we've missed the bigger snow dumps just to our north and west (as evidenced by the snow depth maps pictured below, indicative of multiple snowstorms reinforcing snowcover), we've still had more snow days so far this Winter than we had at this time last Winter. And we're closing in quickly on the 19 day tally from last Winter, especially with another potential winter weather event coming next week in the Tuesday-Wednesday time-frame. Not to mention, February is typically Richmond's "snowiest" month out of an average Winter season. January is 2nd snowiest, December: 3rd, March: 4th, November: 5th, and April: 6th snowiest.

We'll provide updates on that next potential winter weather maker as the track, timing, and expected impacts become clearer. Right now, it looks like central Virginia could initially receive snow and sleet beginning Tuesday morning, then eventually change over to all rain for Wednesday. However, some of that rain may be freezing rain with surface temperatures expected to dip below freezing Tuesday night into Wednesday morning. That would create ice at the ground and on elevated objects (like trees, powerlines). The potential impacts from this system could be disruptive, so we are tracking it and will provide updates!

Thursday, January 27, 2011

Light Snow Possible Friday

A strong disturbance will move through the area Friday, bringing most of central VA a good chance for light snow. The surface temperatures will range from 34 to 42 degrees as the snow falls, so aside from a light accumulation on grassy surfaces, the snow should melt on contact. The precip rates will be lower than last evening's snowfall, and the flakes will be smaller. The image above shows the upper-level pattern at 1 PM Friday. If you look closely, you'll see the state borders in white, and you'll notice a blob of yellow and orange in southwest Virginia. That "blob" is the upper-level vorticity maximum, and it creates strong atmospheric lift just ahead of it. This "vort max" will move through the upper-level long-wave trough, and will give central VA a period of strong lift and resultant periods of light snow, between 10 AM and 4 PM Friday. You can't always assume that a vort max such as this one will produce snow, but in tomorrow's case, the lift/moisture should be more than sufficient. -ZD

Snow Depth Thursday Morning

Even though much of yesterday's snowfall melted overnight in central Virginia, there was still just enough of it left on the grass and other elevated surfaces to see this Thursday morning. Here's the snow depth analysis for our region after yesterday's snowfall:

Here is a selection of submitted snow totals from central Virginia:
Haynesville (Richmond Co): 2.8"
Corbin (Caroline Co): 2.0"

Sandy Hook (Goochland Co): 2.0"
Newland (Richmond Co): 1.5"
Bon Air (Chesterfield Co): 1.2"
Midlothian (Chesterfield Co): 1.0"
City of Richmond: 1.0"
Cumberland Co: 1.0"
Mechanicsville (Hanover Co): 1.0"
Farmville (Prince Edward Co): 1.0"
Bumpass (Louisa Co): 1.0"

And here is the updated map of northern and western Virginia of the highest snowfall totals in our region:

Wednesday, January 26, 2011

Snow Totals & Storm Recap

The last band of light to moderate snow is now moving east of I-95 and should be out of the state by 11-11:30PM. Western and northern Virginia got the lion's share of the snow today. Here is a glimpse of some of the totals as of 9:30 PM:

Totals were much less in Central VA. Here are some of the totals reported on our weather chat in the Storm Room:

1.0" Hanover
1.0" West Henrico
1.0" Louisa
1.0" Buckingham
1.0" Appomattox
0.8" Woodlake
0.5" Powatan Courthouse
0.5" Tappahannock
0.3" Brandermill

Temperatures will drop into the upper 20s tonight, so untreated roads could become slick. You can find the latest road conditions at We're expecting temperatures to climb above freezing from 9 to 10 AM Thursday morning.

Mapping Out The Next 12 Hours

Here are some maps to help you plan the next 12 hours. The shades of purple represent snow, pink is a mix, green and yellow are rain and gray is cloud cover. You can see that most the the wintry weather will end just after midnight.

Updated Winter Weather Map: 12:30PM Wed

As of 12:30 p.m. Wednesday, this is the updated Winter Storm Warning and Winter Weather Advisory map for central Virginia:

North-central Virginia counties are now included in the Winter Storm Warning, including Spotsylvania and Stafford Counties. This warning lasts until 4 a.m. in northern Virginia for heavy accumulating snow. The expected accumulations remain about the same in our area:

The change over to snow is already occurring in western Virginia at Noon as the potent upper low pressure system approaches. I still expect bursts of heavy, wet snow to occur this afternoon and evening as this upper system passes overhead. The Richmond metro is still on track to see the change over from rain to snow in the 4-7 p.m. window. Here's a snapshot of the upper vorticity max directly over central Virginia this evening at 7 p.m., when nearly all of central Virginia will have seen the change from rain to snow:

Snow will end from west to east tonight, exiting the state shortly after midnight. The wet pavement in the area will freeze by Thursday morning as temperatures dip into the upper 20s. This will create slick and hazardous conditions on the roads Thursday morning.

Wednesday 4:30AM Winter Weather Update

As of 4:30 a.m. Wednesday, here is the updated Winter Storm Warning and Advisory map for central Virginia:

Rain is falling in most of central Virginia right now, with the only locations receiving snow in northern Virginia around Fredericksburg and locations north and west. Surface temperatures where the snow is falling are still just above freezing, so much of this is likely melting as it reaches the ground, other than accumulating some on the grass and other elevated objects. We still expect periods of rain through the day Wednesday, so keep your umbrella handy. Deeper, colder air will begin surging into central Virginia this evening from west to east as our low pressure system tracks east and northeast of Virginia's coast, pulling that colder air into our region. As this colder air arrives, rain will change over to snow, which will be heavy and wet at times. The changeover to snow should begin in the western Richmond metro area beginning at 5 p.m., with the eastern Richmond metro at all snow as well by 8 p.m. This means that a heavy, wet snow may be falling in the metro during the Wednesday evening commute. Please prepare extra time to get to your Wednesday evening destinations, and be careful driving in what will likely be reduced visibilities because of the snowfall. Temperatures while this snow is falling will still be just above freezing, so some of this will be melting as it hits the roads. Here's what we expect for wet snow accumulation:

The snow should end in the entire area by 3 a.m. Thursday, but surface temperatures will dip below freezing into the upper 20s, allowing many icy patches to develop on any pavement. This will impact the Thursday morning commute with slick and hazardous conditions.

Tuesday, January 25, 2011

Watches, Warnings, & Advisories Issued

Here's the latest on the watches, warnings, and advisories in effect for the area on Wednesday:

Winter Storm Watch Expanded South

The winter storm watch has been extended farther south. Several inches of wet snow will be likely Wednesday night. Additional advisories should be issued farther south to include the metro area either late tonight, or early Wednesday.

Winter Storm Watch in VA for Wednesday

A Winter Storm Watch is in effect for the approaching storm system from the south for southwest, west and north-central Virginia, including the cities of Charlottesville and Fredericksburg. As of this update, the rest of central Virginia is not included in the watch for Wednesday.

The low pressure system that will produce rain and snow in the Commonwealth is currently overspreading rain through the Southeast U.S. Here's a breakdown of the precipitation, including surface temperatures. Green is rain, pink is wet snow, and blue/white is snow. This shows rain moving into central Virginia around midnight, but I think it will arrive a little sooner, closer to 9 p.m. in southern Virginia.

The precipitation will all fall as rain initially in our area, but notice that the pinks (wet snow) appear closer to sunrise in the areas included in the Winter Storm Watch:

Rain will continue through the morning in most of central Virginia, with surface temperatures above freezing. At Noon, the Watch area is still receiving a wet snow that is probably only accumulating on grass and other elevated surfaces because surface temperatures may be just above freezing.

By sunset, colder air will wrap around the low pressure system (to the east of Virginia by this time, offshore) and allow rain to change over to snow from west to east. However, notice the temperature remains above freezing in most of the area, keeping accumulations to the grass and other elevated objects.

Snow will end from west to east before sunrise Thursday. Much of the snow that falls Wednesday night, even though it may be heavy at times, will be melting as it hits the ground because of surface temperatures remaining slightly above 32 degrees.

Those bursts of heavy snow may occur Wednesday night because of the upper vorticity max, shown in the image below, passing directly over Virginia. This could lead to bursts of heavy, wet snowfall.

Despite these bursts, the wet snow will still be falling into surface temperatures just above freezing, resulting in some of the snow melting as it lands. Still, here is an estimate of measurable snow accumulation by early Thursday morning:

By Thursday morning, temperatures should dip below freezing, which could lead to freezing of the wetness on the roads from the rain and snow. I expect there to be some icy spots developing around sunrise Thursday, which could impact your commute with slick and hazardous conditions. We'll be providing updates on any threats to travel. Stay with CBS 6, we'll keep you ahead of the storm.

Monday, January 24, 2011

Rain to Snow Looks Likely for the Metro

The storm system that will move into the area this week will be mostly rain (by duration), but will end as snow. I expect to see rain arriving after dark Tuesday night. Here's how I think things will look at 11 PM Tuesday (It's likely the rain will arrive a little earlier):

I expect to see all rain in central VA during the day Wednesday. We'll see a transition from rain to snow occur across the area close to sunset. Here's how things should look around 5 PM:

By 9 PM Wednesday, the metro should be seeing a wet snow that could be heavy at times. This snow will be due to the upper-level low that will be very intense. It wouldn't surprise me to hear a rumble of thunder or two as it is snowing, especially in areas to our east. The snow will be falling into surface temps that are still a few degrees above freezing, so although I think we could see a couple of inches of accumulation, it will occur on grassy surfaces, rooftops, etc. Roads might still be slick for the Thursday AM commute as the roads will be wet and temps will likely fall below freezing by sunrise. Here's a look at the way things should look at 9 PM Wed, followed by the temps at 7 AM Thursday:

Update on Approaching Storm: Monday 6:30 AM

A weak upper-level impulse will pass over the Commonwealth today, producing more clouds from mid-day through the afternoon. There may be a few flurries as a result, which I've shown here in this snapshot of late this afternoon:

There is light snow falling in the mountains of southwest Virginia early this Monday morning, so I do think it's feasible to get some of those flurries surviving into central Virginia later. However, those chances are slim, and any flurries that do fall would only briefly stick on the grass or other elevated objects. This would not be disruptive for travel today.

So now our attention turns to the developing low pressure system in the southern Mississippi Valley region that will impact the Commonwealth late Tuesday night through pre-dawn Thursday as the low tracks through the eastern Carolinas and Virginia. I've taken snapshots of the precipitation type for you during this time-frame, shown below. The green is rain, the pink is wet snow mixing with rain, and the blue/white is snow.

Because of the mixing and "wet" potential of this snowfall, it's difficult to nail down expected snowfall accumulations amidst the rain, but our working map still looks like a legitimate estimate for now:

Sunday, January 23, 2011

Tuesday/Wednesday Update & Timeline

Precip will not start for another two days, so we can still see some shifts in the forecast. Generally speaking, this storm has been more "well-behaved" than previous storms. The computer data has been very consistent, so I haven't changed much from yesterday. Regardless, I encourage you to keep a close eye to the forecast tomorrow and Tuesday for any adjustments. Below you will find a timeline of what to expect with this storm.

1PM to 7PM Tuesday
Most of Tuesday looks cloudy and dry, though an isolated shower could sneak into Southern VA during this time.

7PM Tuesday to 1AM Wednesday
Precip will move into the area from the south at this time. It could briefly start as a wintry mix, especially along and west of I-95. As you can see below, temps will be above freezing in central VA, so I'm not expecting major problems on the roads.

1AM to 7AM Wednesday
Scattered rain showers likely across Central VA with a wintry mix still possible in Northern and Western VA. Accumulations will start in far Southwest VA.

7AM to 1PM
Periods of rain still likely in Central VA. Accumulations start building in Northern and Western VA.

1PM to 7PM Wednesday
Rain will briefly change over to wet snow in Central VA. With temps in the mid 30s, most snow will accumulate on grassy surfaces or anything detached from the ground (if at all). Accumulating snows will taper in Western and Northern VA.

Here is a map of vorticity, or spin, in the atmosphere for Wednesday afternoon. The red blob indicates a very potent upper-level storm system. These types of storms are notorious for creating a quick burst of snow, especially north of the vort max (red blob). The track of this vort max, along with surface temperatures, will be the keys to this forecast.

This is an early look at the accumulation potential. If anything will change with this forecast, it will be this map below. Be sure to check back tomorrow and Tuesday to get the very latest updates!