Severe storms possible tomorrow. Derecho Tonight?

As seen above, a series of strong thunderstorms are currently forming near the Great Lakes region.  This series of storms, a Mesoscale Convective System (MCS) will have severe weather and could potentially spawn the feared derecho.  However, compared to last year, the CAPE (atmospheric potential energy) is significantly lower, so any derecho that forms in the Midwest is unlikely to impact the area and make it past the mountains. To answer the question posed in the title, derech-no would be a more accurate headline.   However, some potentially severe thunderstorms could impact the region late overnight, delivering strong winds and rains in the 1-4 am time range.

Now, moving on to tomorrow evening's severe weather potential, which also has a chance to give us some significant storms.
Yesterday, it seemed as if the Thursday evening storms could be a historical event, as there was a possibility for a strong (and strengthening) system to traverse over Southern Pennsylvania right after sunset. The timing and strength of this system combined with a particularly volatile air mass could have brought about some of the strongest storms that this area sees.  However, recent guidance suggests that the threat for such a strong event has decreased, as the storm now seems likely to arrive in the afternoon, before the sun has completely energized the atmosphere, with a weaker low pressure as well.  Nonetheless, the potential for strong and severe thunderstorms remains, but it is unlikely that they will impart significant damage on the scale of the derecho.

Winter Storm on Track, School Forecast

Storm Update

11 PM UPDATE: The temperatures are much lower than initially forecasted, and it seems as if we will get very little, if any rain. In addition, the storm is picking up intensity, and thundersnow is verypossible tomorrow morning.  This is supported by the latest forecast models.  I'm upping the storm totals to 8-16 inches, with 3-6 possible tonight alone.   

The winter storm is starting to make its way into the area, and while it may start out as a bit of drizzle, precipitation will quickly switch over to snow overnight. I'm sticking with my initial forecast of 6-12 inches, with more possible northwest and less southeast.  While the temperatures now are too warm for snow, in the lower 40s, the dew points are in the low twenties, so once precipitation starts, evaporative cooling in the atmosphere will allow snow to fall, relatively quickly after the onset of precipitation. 

School Prediction

At this point, it is almost a foregone conclusion that school will be closed tomorrow (Wednesday), as it will be snowing throughout the day, and at least 2-4 inches will have already fallen overnight.  I wouldn't be surprised if MCPS and other area school systems announced closings sometime tonight.  Since latest guidance suggests that the snow will taper off late Wednesday night, school will also probably closed Thursday, if everything goes according to plan.  Friday is more iffy, but a delay or even closing is not out of the realm of possibility. 

I'll post another update tomorrow morning as the snow starts to ramp up (hopefully).

Major Snowstorm to Impact Area Wednesday

A major and potentially crippling snowstorm seems all but certain to impact Washington D.C. on Wednesday. While temperatures will not be ideal, the heavy precipitation will cool the atmosphere enough for some significant snowfall in the area, the likes of which have not been seen for over two years.

Precipitation Details

The models are pretty much in consensus in forecasting 1.25-2" of precipitation to fall in the area.  IF accompanied with the 10:1 or 15:1 ratios that are often in January and February, we could be talking about one of the largest snowstorms in DC history.  However, due to temperatures that will hover around freezing the whole event, we will rather see ratios of around 7:1 or 8:1, and it is not out of the question that rain could mix in on Wednesday, which could drive down totals to the 3-6" range. However, this looks unlikely at the moment.  Still, this will be a very wet snow that could stick to the power lines and, combined with moderate winds, cause some power outages.

Timing

The first effects of the storm will be felt Tuesday evening, starting as light rain.  As it gets colder and temperatures fall overnight, it will start mixing and eventually switch over to all snow.  The snow will get heavier throughout the night, and will continue during the day Wednesday, until it tapers off Wednesday night.  It is also possible that some rain could mix in during the day Wednesday, but this seems unlikely, especially north and west of the District.

Impact

I would predict around 6-12 inches of snow throughout Montgomery Country, with 12 or more inches being more likely out west near Poolesville, with 6 or so inches more likely near Silver Spring. Along with this, schools have a very high chance of closing Wednesday, a good chance of closing Thursday, and may be delayed Friday.

UPDATE: Latest guidance suggests the possibility that the temperatures do not fall enough and that this is mostly rain, with a couple of inches of snow on the front and back end of the storm.  While unlikely, it is important to remember that this remains a possible scenario.

I'll post another blog update tomorrow afternoon, and minor updates on Twitter, where you can follow me @samdman95

Light Snow Expected Tomorrow Night

The Alberta Clipper that rolled in last night brought a nice half inch of snow (along with an unexpected two hour delay), and more of the fluffy stuff is on the way for tomorrow evening into the night.

As I'm sure everyone has noticed, it has been downright frigid this week, and it will stay that way for tomorrow's little event, meaning that any precipitation will fall as snow.  While the wet snow that we're accustomed to in DC has 10:1 snow:liquid ratios, tomorrow's powdery dendrite flakes will lead to ratios somewhere around the 15:1 range, amplifying our snowfall total.

However, there really isn't much precipitation to help us out, as the NAM forecasting model (the most generous in terms of snow), only gives us .09 inches of precipitation, which would lead to a measly 1-1.5 inches of snow.   While I think a decent coating is likely, this storm could fizzle out into flurries. On the other hand, there is little possibility for this weak system to pick up steam, and anything more than 2-3 inches isn't happening.

Our recent storms have mildly overperformed their quite modest predictions, so I think about an inch of powdery snow is what we'll end up with Saturday morning.  While aesthetically pleasing, it will be the 730th day without two or more inches of snow, a drought that has been active since the storm on January 26, 2011.