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| Snow, sleet, and rain: Messy tonight into Saturday, worst conditions north and west | Snow, sleet, and rain: Messy tonight into Saturday, worst conditions north and west |
| (about 2 hours later) | |
| * Winter weather advisory 6 p.m. Friday evening to noon Saturday, except for southern Maryland * | * Winter weather advisory 6 p.m. Friday evening to noon Saturday, except for southern Maryland * |
| * Winter storm warning from Winchester to Hagerstown along I-81 and west * | |
| A moisture-loaded storm coming out of the Gulf of Mexico up the East Coast is likely to produce a period of moderate to heavy precipitation overnight, before tapering off Saturday morning. Depending on where you live, you may experience rain, snow or a mix of precipitation. | A moisture-loaded storm coming out of the Gulf of Mexico up the East Coast is likely to produce a period of moderate to heavy precipitation overnight, before tapering off Saturday morning. Depending on where you live, you may experience rain, snow or a mix of precipitation. |
| The far northern and western areas from just north of Baltimore to Winchester have the best chance of seeing accumulating snow that could end up being heavy if everything comes together right. | The far northern and western areas from just north of Baltimore to Winchester have the best chance of seeing accumulating snow that could end up being heavy if everything comes together right. |
| The precipitation should start as early as around 4 p.m. this afternoon around Charlottesville and then should rapidly spread northeastward across most of the area by around 6 p.m. this evening. | The precipitation should start as early as around 4 p.m. this afternoon around Charlottesville and then should rapidly spread northeastward across most of the area by around 6 p.m. this evening. |
| For the immediate metro area, we think it’s unlikely that this is a high impact event, for three reasons: | For the immediate metro area, we think it’s unlikely that this is a high impact event, for three reasons: |
| Having said that, because the ground is somewhat cold and precipitation will be coming in at night, caution should be used on roads this evening and overnight. A coating or so of snow and sleet cannot be ruled out. | Having said that, because the ground is somewhat cold and precipitation will be coming in at night, caution should be used on roads this evening and overnight. A coating or so of snow and sleet cannot be ruled out. |
| Across the region, we expect the heaviest precipitation between about 7 p.m. and 2 a.m. tonight. | Across the region, we expect the heaviest precipitation between about 7 p.m. and 2 a.m. tonight. |
| In our colder north and west suburbs, a moderate impact is possible as temperatures fall to near freezing as the precipitation gets going and the wintry mix of precipitation lasts longer. A slushy accumulation of sleet and/or snow is possible roughly along a line running along the north side of Warrenton, Fairfax and Baltimore. | In our colder north and west suburbs, a moderate impact is possible as temperatures fall to near freezing as the precipitation gets going and the wintry mix of precipitation lasts longer. A slushy accumulation of sleet and/or snow is possible roughly along a line running along the north side of Warrenton, Fairfax and Baltimore. |
| More significant winter storminess is possible from around Winchester, Va., to Reisterstown, Md., and to the northwest — where a few inches of snow and sleet could fall. Travel may become challenging in this region overnight. | More significant winter storminess is possible from around Winchester, Va., to Reisterstown, Md., and to the northwest — where a few inches of snow and sleet could fall. Travel may become challenging in this region overnight. |
| However, even in these colder areas that get accumulating snow, precipitation may change to rain or freezing rain in the pre-dawn hours before possibly shifting back to a period of wet snow before ending. | However, even in these colder areas that get accumulating snow, precipitation may change to rain or freezing rain in the pre-dawn hours before possibly shifting back to a period of wet snow before ending. |
| Locations south and east of the city are likely to be dealing with a mostly rain event, though the precipitation could start as a brief period of sleet and/or snow. | Locations south and east of the city are likely to be dealing with a mostly rain event, though the precipitation could start as a brief period of sleet and/or snow. |
| For much of the region, precipitation should taper off during the daylight hours Saturday with just lingering light drizzle (most locations) or very light snow (colder locations to the north and west). We should gradually dry out in the afternoon. | For much of the region, precipitation should taper off during the daylight hours Saturday with just lingering light drizzle (most locations) or very light snow (colder locations to the north and west). We should gradually dry out in the afternoon. |
| Above we have laid out what we think is the most likely forecast. However, we should stress there is significant uncertainty in the specifics pertaining to exactly where the rain-snow line sets up. We see two possible scenarios and the above description is based on a blend of the two but slightly leaning more toward the colder, snowier scenario. | Above we have laid out what we think is the most likely forecast. However, we should stress there is significant uncertainty in the specifics pertaining to exactly where the rain-snow line sets up. We see two possible scenarios and the above description is based on a blend of the two but slightly leaning more toward the colder, snowier scenario. |
| Here are the two scenarios, which give a sense of the range of possibilities: | Here are the two scenarios, which give a sense of the range of possibilities: |
| Scenario 1 – Colder and snowier | Scenario 1 – Colder and snowier |
| Areas around the city and points east and southeast start as a brief period of snow or sleet and then transition to rain as warm air aloft pushes north. | Areas around the city and points east and southeast start as a brief period of snow or sleet and then transition to rain as warm air aloft pushes north. |
| However, as the low starts to deepen near the coast, the northward push of warm air slows, possibly allowing light accumulations up to an inch or two across the near-in western and northern suburbs before changing to a wintry mix and then rain. This is the type of storm where the precipitation may alternate between snow and rain as the precipitation intensity waxes and wanes. | However, as the low starts to deepen near the coast, the northward push of warm air slows, possibly allowing light accumulations up to an inch or two across the near-in western and northern suburbs before changing to a wintry mix and then rain. This is the type of storm where the precipitation may alternate between snow and rain as the precipitation intensity waxes and wanes. |
| The region north and west of line from Winchester to Reisterstown maintains enough cold air to support all snow that possibly mixes with sleet at times with accumulations of two to five inches. If a heavy snow band sets up, accumulations could exceed six inches, especially at higher elevations. | The region north and west of line from Winchester to Reisterstown maintains enough cold air to support all snow that possibly mixes with sleet at times with accumulations of two to five inches. If a heavy snow band sets up, accumulations could exceed six inches, especially at higher elevations. |
| Even as significant snow is possible in this colder zone, the NAM model forecast sounding for Frederick, Md., valid at 1 a.m. Saturday, shown below, helps illustrate how tricky the precipitation type forecast will be. The red line on the sounding represents the temperatures. The light blue line is the 0 C (or 32 F) line (the line at which snow or ice begins to melt). | Even as significant snow is possible in this colder zone, the NAM model forecast sounding for Frederick, Md., valid at 1 a.m. Saturday, shown below, helps illustrate how tricky the precipitation type forecast will be. The red line on the sounding represents the temperatures. The light blue line is the 0 C (or 32 F) line (the line at which snow or ice begins to melt). |
| The big takeaway is that the temperature is within half of a degree of freezing from the ground surface to a depth of almost 2,500 meters (8,000 feet) through the overnight hours. | The big takeaway is that the temperature is within half of a degree of freezing from the ground surface to a depth of almost 2,500 meters (8,000 feet) through the overnight hours. |
| Lighten the precipitation a tad and the temperatures in that layer would probably be a little warmer, resulting in more rain and sleet instead of snow. But keep the precipitation heavy for an extended period and the entire layer might stay just below freezing, supporting snow. Even our colder areas are right on the rain-snow line — and that’s our big forecast dilemma. The GFS model (not shown) is not as wet and is warmer — supporting Scenario 2 described below. | Lighten the precipitation a tad and the temperatures in that layer would probably be a little warmer, resulting in more rain and sleet instead of snow. But keep the precipitation heavy for an extended period and the entire layer might stay just below freezing, supporting snow. Even our colder areas are right on the rain-snow line — and that’s our big forecast dilemma. The GFS model (not shown) is not as wet and is warmer — supporting Scenario 2 described below. |
| Scenario 2 – Rainier | Scenario 2 – Rainier |
| A similar storm track to Scenario 1 but the cold air erodes quickly and temperatures rise and stay above freezing for most areas except the western Maryland toward Garret County and adjacent parts of West Virginia. The precipitation might start as a brief period of sleet (or snow in our far western areas) but would change over to rain across most of the area, from southeast to northwest. Outside of the high elevations, even our colder areas would not see much accumulation of snow and/or sleet in this scenario. Such a scenario has been forecast by a series of GFS and SREF model runs. | A similar storm track to Scenario 1 but the cold air erodes quickly and temperatures rise and stay above freezing for most areas except the western Maryland toward Garret County and adjacent parts of West Virginia. The precipitation might start as a brief period of sleet (or snow in our far western areas) but would change over to rain across most of the area, from southeast to northwest. Outside of the high elevations, even our colder areas would not see much accumulation of snow and/or sleet in this scenario. Such a scenario has been forecast by a series of GFS and SREF model runs. |
| Interested in the details for the possible storm Sunday night and Monday? Follow this link: Good chance of accumulating snow Sunday night into Monday |
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