From the ABC 7 Weather team

Plenty of talk about snow next week

November 7, 2013 - 12:43 PM
Text size Decrease Increase

Many of you have already seen weather models displayed prominently on social media sites. Here are some of my thoughts.

This happens every winter. A potential snow storm develops about 7 days out, a number of people post about the chance of it occurring, and suddenly I get asked about every 10 minutes if it will snow next week. Okay, I understand it comes along with the territory of being a meteorologist, and I don't mind it at all. But I want you to know what we are looking at and what actually needs to happen for a snow storm to materialize.

First things first. Snow in November has been rather absent over the past 16 years. There has been a trace of snow (meaning not even 0.1") recorded in 5 of the past 16 years. The last measurable snow recorded in November was in 1996, when two-tenths of an inch was recorded at Reagan National. The month itself only averages one-half inch, but that doesn't mean it never occurs. Many can remember the Veterans Day storm which dropped 11.5" of snow (still the record for the day and month) back in 1987. This is a giant outlier, however, as in 126 years of record keeping, there are only 15 November months that have recorded more than two-inches of snow.

This incoming system in the middle of next week still has many more questions than answers. Here are a few things we're keeping an eye on and will continue to do so over the next few days through the weekend. We should have a much more solid grasp on what is going to happen by then.

Where is it coming from?

We really like to look at where the energy from a potential storm is originating from, to see if it's logical the system could really come together. The energy with this potential system is moving in from northern Canada. It gets some big time help through a giant ridge setting up over the western U.S. which allows high pressure to dive into the Northern Plains and Midwest. We are banking on this ridging to occur, as if it doesn't, this incoming cold push might not be as potent.

Strong area of high pressure moving into the Plains and Midwest next Tuesday (Courtesy: WeatherBell Models)

This is expected to bring the coldest air of the season into the U.S. We are currently banking on this to occur, whether there is snow or not. It appears likely it will be cold by Tuesday through Thursday of next week in the D.C. area. Temperatures should be in the 40s Tuesday through Thursday, and could possibly be in the 30s at least in the western suburbs on Wednesday. Low temperatures may fall into the 20s and teens in the suburbs and Reagan could potentially (I really like that word in this blog) see its first day at or below freezing Wednesday night.

Run to run consistency (Or inconsistency)

0Z Model Snowfall Output from the ECMWF, see next graphic below showing just how different (Courtesy: WeatherBell Models)

Since we are still five to six days out from this system, and the energy is currently located nearly 3000 miles away, there is going to be a lot of variability in modeled outcomes over the next few days. A change in a few hundred miles has incredible impacts on where precipitation would fall, particularly over the east coast where so many other factors come into play.

12Z Model Snowfall Output from the ECMWF, juuust a bit different (Courtesy: WeatherBell Models)

This very thing has been seen in model runs over the past 12 hours, where D.C. was in the path of incredible snowfall, then the next run is forecast to see much less. This all occurs based on where low pressure develops along the east coast, which is never an easy thing to determine even 2 days out let alone 5. For instance, the latest GFS develops a coastal area of low pressure about 250 miles southeast of the latest European model solution, which in itself over the past 12 hours has developed a surface low off the VA coast, and in the latest just off the NC/SC coast.

Big differences in 0Z and 12Z ECMWF Model Runs, typical this far out (Courtesy: WeatherBell Models)

We have confidence that a cold front will push into the region next Tuesday, the questions lie in what will happen next.

What to look for next?

We'll have plenty of cold air in the vicinity, energy swinging into the region from the northwest, a strong jet overhead, we just need each to play its part for there to be snow. We'll also have to wait and see how everything interacts with the warm gulf stream as that typically helps develop these strong coastal lows.

250mb Winds Tuesday evening showing a digging jet "phasing" off the east coast allowing for even more convergence at the surface off the east coast (Courtesy: NEXLAB Models)

If everything is still coming together come early next week, we'll need to consider where the low is anticipated to develop, as how far off the east coast will determine the supply or depth of the cold air over the D.C. area. Even smaller things such as ground temperatures will need to be considered as each of these play a big part in determining snowfall amounts. Then there is the model guidance itself, which has been forecasting colder conditions so far for the month than what has been observed. More and more information that we'll need to take note of.

We'll need to determine depth of cold air available at some point

This is where we play the waiting game, taking everything as it comes to us, keeping an eye on each scenario and trying to determine how far of an outlier we think each is. Changes will occur, as forecast confidence is about 20% right now. (My completely subjective number)

Take every model run that you see online or on social media with a grain of salt. These are just forecasts which are all subject to change. Do I think they do an injustice to the overall forecast for next week? Not entirely, as the chance is there for snowfall to occur. Do I trust it right now? Not really, forecasting such a big event to occur this far out isn't usually the smartest move as such big changes often happen.

Follow the Stormwatch 7 Facebook Page

I do know one thing though, our team is on it. We have it on our inner radars so to speak, and will be keeping an eye on it tomorrow, into the weekend and next week. We'll relay the latest information and our thoughts to you, so be sure to stay tuned, this is when meteorologists really begin to have fun.

comments powered by Disqus