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Weather models continue to debate the strength and position of a weekend storm system.
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The most likely scenario calls for rain Sunday morning changing to a mix and then wet snow by Sunday evening.
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Accumulation threat has emerged over the past 24 hours, with most models suggesting between 1 and 5″ of snow in the DC region.
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Some extreme solutions suggest that 6″ or more might be possible.
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WASHINGTON – Compared to previous weeks in the DC region, last week wasn’t so bad. Sure, it’s been pretty cloudy and cold, but temperatures have been consistently above freezing, allowing the region to slowly but steadily break free of the so-called “snow concrete” that has blanketed the DC area for nearly a month now.
Temperatures are expected to stay above freezing into next weekend, with the best day of the entire week potentially Saturday, with partly sunny skies and 50 degrees by mid-afternoon.
By Saturday evening, the pattern begins to change as a strong drop in the jet stream sends temperatures back into the low 30s overnight Saturday into Sunday. At the same time, a storm system is forecast to develop ahead of this cold push, which could bring a wide range of precipitation to the DC region, including the threat of accumulating snow.
The great snow debate
The big question, of course, is how much snow? It’s a question that remains relatively difficult to answer, even just days ahead of the potential storm system.
The key to any potential storm system is its track and intensity. These are two features that weather models have continued to struggle with.
Our general thoughts in the weather department this evening lead a little closer to the European pattern. With temperatures well above freezing at the start, the system would likely begin as a predominantly rain event through the early part of Sunday.
Then, as a surface storm pushes eastward into the Atlantic, cooler air fills in as the storm moves away, along a weather feature known as an inverted surface trough. This would bring the risk of rain changing into the mix and perhaps a period of potentially heavy wet snow Sunday night.
Now, the tricky part of forecasting with an inverted trough situation is the area where the snow accumulates tends to be in a relatively narrow band that follows the axis of the trough, so not everyone in the region would see decent snowfall, would be located in this band.
Forecasting exactly where it will set up is very difficult and we wouldn’t have a good idea of where this feature sets up until probably closer to Saturday night.
If this solution, which the European Model has been suggesting for the past couple of days, is the correct solution, then parts of our region could see a potential of 1-3″ with a risk of 3-6″ increase by the time the storm exits late Sunday into early Monday morning.
On the other hand, you have the American model solution, which for most of a day suggested the storm could have much more impact. With a stronger jet stream tilt, the weather model suggests a more intense storm system will develop that stays much closer to the coast. Although it also begins as rain Sunday morning, low surface intensification quickly pulls cold air into the storm, dropping temperatures in the DC region and changing precipitation to widespread heavy snow.
The model is aggressive with heavy and impactful snow for everyone with final snowfall totals in the double digits.
Now, most forecasters agree tonight that this solution is pretty extreme and unlikely to be the case for this storm. While we can’t rule out the realm of possibility, it’s generally on its own, with most other advisories starting Thursday night suggesting smaller snowfalls are more likely.
So if we don’t believe the American model solution, what is the debate tonight? The problem lies in the consistency of the model. The weather models were of course extremely bad with their forecast solutions for Sunday’s storm system. Even the European, which has a history of being more accurate than the American model, was extremely “cheeky” with this storm system. Sometimes bouncing the system to the east, showing less snow, then bringing the storm back to the west, showing more snow. Forecasters look for consistency between runs, and so far we haven’t seen that from any weather model.
The reason why has everything to do with the model. It’s not just one piece of atmospheric energy that helps drive this storm system, but more. The more pieces you have involved in a developing storm system, the more prone you are to errors in forecasting. This is why we may not have a really good understanding of what this system might do to the DC region until closer to Friday night or even Saturday when the pieces of energy involved in the formation of this storm system are all well sampled and better analyzed.
What to be prepared for
It will come down to the wire in terms of determining snow amounts. What I can guarantee is that this will not be a repeat of the late January storm.
Temperatures won’t be as cold, even after the system – this time without “snow concrete”. This would also be wet snow and we would likely lose some to ground melt in areas no longer snow covered from the January system as temperatures have been above freezing for much of this week.
One key thing we want to mention: a lot of people say, “but it’s too warm to snow on Sunday! The weather app says it will be in the 40s!” While yes, it’s too warm for snow to begin with…remember your weather app gives you the high temperature for the day.
Through a process known as dynamic cooling, temperatures can cool as you bring cooler air up the backside of a storm system due to the upper level trough passing by. Therefore, temperatures would drop throughout the day.
The time period we are most concerned with right now it is Sunday afternoon and especially evening. While we are not currently anticipating this to be a major, city-shutting down type of snow, the most likely timing means there is a risk of closing and delaying schools and other activities Monday morning.
Of course, how extensive these could be really depends on the final track and intensity of this storm system, and in the interest of forecast integrity, we’re not yet confident in any snowfall numbers that will raise our expectations.
stay tuned
What we will continue to do is keep you updated and informed ahead of this potential Sunday.
To reiterate, we are currently leaning towards the potential for a lower impact winter accumulation type event as opposed to a major snowstorm.
FOX 5 will continue to monitor the threat and let you know if we think a more impactful system will hit the region.