DC region braces for first accumulating snow of 2019 this weekend
WASHINGTON (FOX 5 DC) - After what was a quiet start to 2019, winter is starting to rear its ugly head around the Washington, D.C. region as we approach the middle of January. Strong winter winds held temperatures below 40 degrees for the first time this year on Thursday, which ended a 28-day streak of above normal temperatures at Reagan National Airport, our longest stretch of "warmth" in winter in over a decade. The colder air is setting the stage for this weekend, cooling the ground and ensuring that more of what falls this weekend sticks, instead of melting away.
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This storm is not a blizzard, it is not a nor'easter, and we are not expecting this to be a major snowfall for the D.C. region. However, because ground temperatures are cold enough it really will not take all that much to get the ground and roadways coated in some snow. Travel across our area is expected to be awfully tricky Saturday night and Sunday. For those with weekend plans, let us go hour by hour with the latest data that we have so you know what to expect, when.
While this is a single storm system, it generally has two parts to it. The first is a process that we call overrunning, which is expected to occur on Saturday night. The second is from a developing coastal storm off the coastline. Each of these will bring its own unique challenges to the forecast period.
The storm itself started to gather strength in the Southern Plain on Friday afternoon, tapping into some warm and moist air from the Gulf of Mexico, pulling it northward. As that occurred, an area of high pressure across southern Canada is forcing cold and dry air southward. Cold air is heavier than warm air, so it gets stuck near the surface. The warm, moist air is lighter so as it collides with the cold air it is forced to rise and "overrun" the cold air. As it rises, it expands, and when it expands, then voila! You get your snow falling.
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This is the process that will bring the initial waves of snow into our region during the second half of day on Saturday. It is this feature that will bring those who live west of Interstate 81, in the Maryland and West Virginia Panhandle, and the Mason-Dixon Line most of their accumulation with this event. The longer the storm system pushing north through Tennessee can hold onto its strength, the longer this snow will last, and the most snow these regions could see.
Due to upper atmospheric features, this interior storm will eventually weaken and a new storm will start to develop and gather strength off the coastline of the Carolinas. As this storm strengthens it will increase the northwestern flow on the storms western side. This will allow the drier air to begin to intrude from the northwest, leading to the snow machine shutting down across our far northwest zones likely before the morning hour are done on Sunday.
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For those south and east, closer to the storm itself, overrunning will occur once again as Atlantic moisture is thrown around this new storm system. It is with this storm system from Sunday morning through the afternoon that gives our southern zones their greatest snowfall chances. It is the feature that will bring most of the accumulations to areas like Central Virginia, the Northern Neck, Southern Maryland, and the Eastern Shore. If this storm is stronger and tracks a little bit closer to us, the metro area could see some higher snowfall totals compared to our current outlook. We will have to see how the afternoon models perform with these weather features.
The vast majority of our weather models has scattered, light snow showers working their way east of the Interstate 81 corridor sometime after 1 p.m. on Saturday. Steadier light snows are expected to slowly advance eastward after about 4 p.m. in the evening.
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Weather models are suggesting a coating is possible around the Interstate 95 by about the 7 p.m. hour, if not earlier, with over an inch on the ground west of the Interstate 81 corridor (see above). Travel should still be manageable on the major roadways, but watch out for the untreated roadways to get slick pretty quickly once the snow starts coming down at a steady pace.
Most of the snow in the immediate D.C. area and areas north and west of the city is expected to fall during the late evening and overnight hours. If you're a late night traveler, I am concerned about area roads as the lack of traffic would allow them to cool faster, and they could quickly get a coating of slick snow.
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Latest guidance we have says to expect around 2-inches of snow or more in and around metro D.C. by the time you wake up on Sunday morning. The light snow machine will then begin to wind down to the far northwest (Maryland and West Virginia panhandles) as dry air starts to intrude from the northwest. This is when the coastal storm system is starting to develop, and more snow should start pushing into central Virginia, working its way northward towards Southern Maryland and eventually parts of the Eastern Shore.
By Sunday afternoon, most areas would have generally picked up what they are going to with this storm. Snow falling will be most likely from the Interstate 95 and areas south and east during Sunday afternoon. The morning run of the European model brought the 4-inch line right up to Washington, D.C. meaning it added about 1-inch to 2-inches of additional snow after sunrise on Sunday. More falls to the south and east where over 4-inches is a real possibility, although totals across all of these zones on Sunday will heavily depend on the track and strength of the coastal storm. If it's a little stronger or closer, then totals locally could go up. If it's a little weaker or farther away, totals will likely go down around the metro.
By Sunday night the storm should have pulled far enough away that snow is done falling across the majority of our zones. Much like with many storms of this nature, locally higher amounts will be possible but are most favored down across eastern portions of Virginia where the snowfall has the potential to be heavier. Clearing skies overnight will lead to falling temperatures and any wet areas will likely freeze up. There could be some morning commute issues due to this. As always, we cannot rule out the possibility of some local school systems having delays or closings, but that will all depend on whether or not we get what models are suggesting we will, a little more, or a little less.
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