Ice Potential Sunday

6pm Tuesday

The ingredients are on the table for significant icing in Greater Lynchburg and Southside Virginia.

First off… remember it will be unusually warm Thursday and Friday.  After several hours of rain Friday night, the colder and drier air will follow for Saturday, setting the stage for some ice on Sunday.

As always, there are a few things that we feel good about, and some things that we do not. Preliminary thoughts…

Timing of Precipitation

Beginning Sunday between daybreak and noon. Ending between late Sunday night and daybreak Monday.

Precipitation Type

Mostly freezing rain. Remember, freezing rain is liquid that reaches the ground and freezes on contact, giving the icy glaze that accretes on surfaces.  Cautiously optimistic there will be a change to rain a couple of hours before ending, but not particularly confident.

Up to an hour of light snow is possible at the onset of the precipitation, but a quick transition to freezing rain is expected.  Accumulating snow is very unlikely.

Amount of Precipitation

Low confidence here, but expecting about 0.50-1.00″ liquid equivalent.  On the higher end of that range in Greater Lynchburg and north… toward the lower end across Southside Virginia.

Feel pretty good in areas north of the Staunton River and Smith Mountain Lake that there will be at least be a thin coating of ice on elevated surfaces (tree limbs, power lines). But there may be more, depending on…

Temperature

Most critical will be the temperature when the precipitation is at its strongest.  This will be governed by how dry the air is here at the ground on Saturday (we use the dew point temperature to measure the amount of absolute moisture in the air).

As precipitation falls into the dry air, there is cooling of the air, but a rising of the dew point.  The temperature at which these meet is called the wet bulb, and the wet bulb would be the temperature at which the heaviest precipitation will fall.

While we can have freezing rain at 31°F, that ice tends to be soft and does not usually cause big travel impacts during daylight hours, as there is still some solar energy getting through the clouds.  But freezing rain at 26°F is a different story. Ice is harder and poses more of a transportation hazard.

Right now, that wet bulb temperature appears like it will be in the middle to upper 20s, but a small break in that number in either direction has large repercussions on the amount of ice on surfaces.

Riskiest Areas

The places at greatest risk of large ice accumulation are north and west of Lynchburg. These counties for example: Albemarle, Alleghany, Amherst, Augusta, Bath, northern Bedford, Botetourt, Craig, Floyd, Nelson, Rockbridge.  These locations will likely be coldest the longest and have the most precipitation.

Lowest Risk Areas

We do expect some ice as far south as the northern counties of North Carolina.  But precipitation amounts will probably be smaller and temperatures will be a few degrees higher in Charlotte, Halifax, Henry, and Pittsylvania Counties.  This includes Danville. Even there, however, the storm should be followed closely over the next few days.

In Between

The remaining areas could have anything between a small nuisance or a 1-inch coating on surfaces.  At this point, it is still too far in advance to tell with any certainty.  Those remaining areas include the following counties: Appomattox, southern Bedford Buckingham, Campbell, Franklin, Montgomery, Patrick, Prince Edward, Roanoke. This includes Lynchburg and Roanoke City.

As always, it is imperative to remember that this is a forecast made 4 days before the precipitation begins.  So expect changes and modifications in the forecast.

Small changes in temperature and precipitation amounts have large real-world effects on travel, vegetation, and the electric grid.

Update 6pm Wednesday

No big changes to forecast thinking.  It does look more likely that however this plays out, the worst conditions will still be in the Riskiest Areas in the paragraph above.

If anything, the precipitation may start a bit earlier than envisioned yesterday, between 2am and daybreak Sunday… not ending until Sunday evening.

A colleague in Richmond, Dave Tolleris, who runs a comprehensive site called wxrisk.com pointed me to the Sperry-Piltz Ice Accumulating Index:

ice impact index

Sperry-Piltz Ice Accumulation Index. Developed by Sidney K. Sperry and Steven F. Piltz. More about their work at spia-index.com

On the above scale, I would guess that those Riskiest Areas (Lexington, Lovingston) would have an index of 3, In Between Areas (Lynchburg, Appomattox) a 2, and Lowest Risk Areas (Danville, South Boston) a 1.  To reiterate, as more data come in over the next 72 hours, modifications will be made to the forecast.

Wind should not be an issue with this storm.  Any damage would be from the weight of ice.

Those in charge of the Lynchburg Christmas Parade, scheduled for 4:30pm Sunday, tell us that the parade (for now) is still on as scheduled.

Update 6pm Thursday

Again this evening, no dramatic changes.  Hints that it may be a degree or two colder at the beginning of the precipitation… a couple of hours either side of daybreak Sunday morning. This timing suggests a little more ice, and perhaps a 1-2 hour period of snow or sleet before the changeover to freezing rain, mainly north of line between Roanoke and Lynchburg.

But the greatest risk is still in Amherst, Botetourt, Nelson, and Rockbridge Counties. These are locations that will likely have more than a half-inch of ice on elevated surfaces.

Road surfaces will also be impacted, but we are cautiously optimistic that areas south of the Staunton River and Smith Mountain Lake will be impacted the least. Those are areas where a modest decrease in speed may be sufficient to travel safely.  Farther north is still an open question.

And as always, remember bridges and overpasses freeze before road surfaces.  Bridges and overpasses cool from the top and bottom.

Below is a very, very rough estimate of ice potential. Again, areas north of Lynchburg may have a brief period of snow (coating or so) before a chageover to freezing rain.  Expect modifications in the ice forecast in the coming 48 hours.

 

ice5

Ice potential this Sunday. Precipitation should start between 5-10am. Lighter amounts of total precipitation (e.g. liquid equivalent) in southern areas. Higher amounts north.

 

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About seansublette

Meteorologist at Climate Central. Broadcast meteorologist in Virginia from 1995 to 2015. Born and raised in Richmond, VA. Penn State alumnus. Loves baseball and the rock band Rush. Views are independent of my employer. Past performance does not guarantee future results.
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