1pm Saturday Update
No substantial change to going forecast below. Winter Storm Watch has now been upgraded to a Winter Storm Warning for all locations. Still think the areas north and west of Lynchburg City get it the worst, with Southside Virginia getting only minor or nuisance icing.
And going with the original graphics below. For Metropolitan Lynchburg, an estimate of one-quarter to as much as one-half of an inch of ice before a slow melt begins to take shape Monday afternoon. Road conditions will be tricky, but my gut tells me that roads in the metro area will not be impassible.
Even when temperatures creep above freezing later Monday, the sky remains cloudy and there will be areas of rain to contend with. Do not look for the sun until at least Tuesday afternoon. Perhaps not until Wednesday.
Using the SPIA Index, I would still characterize the storm with the following indices:
1 in Southside Virginia
2 in Greater Lynchburg, including Appomattox, southern Amherst, southern Bedford, and Campbell Counties.
3 in areas north and west of Lynchburg (northern Amherst, Albemarle, Alleghany, Augusta, Bath, northern Bedford, Botetourt, Craig, northern Nelson, and Rockbridge Counties).
Potential for Index 4 damage in scattered parts of Alleghany, Augusta, Bath, and Rockbridge Counties.
Confidence in the precise amount of precipitation is unusually low, so there is a distinct possibility that the storm could break a little worse or a little better at the last minute. As I have always been taught, prepare for the worst and hope for the best.
But there is absolutely no way that Sunday is sunny and more than 45°.
Original post follows below:
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Surprisingly, the overall forecast philosophy has not changed too much since Tuesday. Having said that, I will admit to upping the precipitation forecast over the last 24 hours. There is still a small part of me that is worried this storm is going to lay an egg in Central and Southside Virginia. This comes out of respect for the NAM model. However, the quantitative precipitation forecast (QPF) from that model is suspect more than 36 hours in advance. And the QPF message has been consistent from the ECMWF simulations over the past three days. So we are leaning toward that idea in concert with the GFS.
While remote, there is a small chance to pull back the strings on the amount of ice. After all, we have about 30 hours before the onset of precipitation is expected.
Still looks like it moves in from south to north around daybreak or a couple of hours before, and covering all parts of the viewing area by 9am.
There will probably be some breaks in the precipitation on Sunday afternoon, but even so, we may find ourselves in spots of freezing drizzle, which is only less bad.
A longer break should take shape late Sunday night, then another wave of precipitation comes in Monday morning… and another Monday night into Tuesday morning.
Everything is out of the area around midday Tuesday.
Temperatures will be slightly above freezing at the onset of the precipitation Sunday morning, then fall several degrees as the atmosphere saturates. Expect temperatures Sunday afternoon between 27°-30°, and holding nearly steady overnight.
A small rise in temperatures above freezing is expected late Monday morning and through the afternoon, and they are expected to remain above freezing Monday night and during Tuesday.
That shift above freezing comes a few hours earlier in Southside Virginia, and will likely be delayed a few extra hours in areas along and west of the Blue Ridge Parkway.
Snow and Sleet
A brief period of snow or sleet will lead the freezing rain, probably lasting 1-3 hours. Southside Virginia is more likely to have only sleet before a rapid change to freezing rain. Areas farther north (Alleghany, northern Amherst, Augusta, Bath, northern Nelson, and Rockbridge Counties) look at about an inch or so of snow/sleet before the changeover.
Ice is the biggest concern. The amount of precipitation and the vertical atmospheric temperature profile are the primary factors in the forecast. However, time of day, precipitation rate, wet-bulb temperature, and ground temperature are also important.
With that, the icing potential is 1/2 to 1 inch in the white-pink shade. This includes Alleghany, northern Amherst, Augusta, Bath, Botetourt, Craig, Giles, Montgomery, northern Nelson, Roanoke, and Rockbridge Counties.
Hot pink shaded areas look for 1/4 to 1/2 inch of icing. This includes Greater Lynchburg and most of Appomattox and Bedford Counties, west across upper Smith Mountain Lake, and into Floyd County.
A thinner coating to as much as 1/4 inch of ice in areas just southward in the deep blue shaded area. This includes southern Campbell, Charlotte, Franklin, northern Halifax, Henry, Pittsylvania, and Prince Edward Counties.
Danville and areas eastward toward South Boston and Buggs Island Lake will have a thin coating, but serious icing is not forecast in those locations.
Something I have never tried before, but wanted to take a shot at. This is the chance of losing electricity. For example, areas in the red shaded area have a 60% chance of losing power during the storm. Most likely, this would occur between Sunday afternoon and Monday morning.
Greater Lynchburg is close to that 20/40 line, meaning there is a better chance of losing electricity in Forest, Boonsboro, and Elon than in Concord, Rustburg, and Evington.
Overpasses and bridges will be the most vulnerable to freezing, as they are cooled from top and bottom. Road beds will become increasingly slick as Sunday afternoon wears into evening and remain slick through early Monday morning.
Road conditions will be highly variable, as there will be pockets that are wet and pockets that are icy. Conditions will be worst along and west of the Blue Ridge Parkway. At this time, I am not convinced I-81 will become a skating rink, but that is a distinct possibility if the temperatures drop closer to the middle 20s. Again, Rockbridge County and areas to the north are at greatest risk.
Remember that even on cloudy days, some sunlight gets through and warms the pavement, slowing down ice accumulation, so if travel is necessary, it is best to get it finished before nightfall. Even if the air temperature does not change, surfaces will become more slick once the sun goes down.
Would suggest getting any travel out of the way as soon as possible on Sunday morning, but even that will bring a risk.
For many locations, it will be a game-time decision. Continuously updated traffic information can be found at VDOT’s travel site: http://www.511virginia.org/
Last bit of data before this thing gets started comes in late Saturday, so we’ll try to squeeze in one more update late in the day Saturday.