Snow appears likely for DC region Sunday evening
Weather models continue to debate the strength and position of a weekend storm system, but the most likely scenario involves rain on Sunday morning changing to a wintry mix and then wet snow by Sunday night. FOX 5’s Mike Thomas has the details.
The threat:
WASHINGTON – Compared to the previous several weeks in the D.C. region, this past week has not been so bad. Sure, it has been rather cloudy and chilly, but temperatures have been consistently above freezing, allowing the region to slowly but steadily free itself from the so-called “snowcrete” that has blanketed the D.C. area for the better part of a month now.
Temperatures are expected to remain above freezing into the upcoming weekend, with the best day of the entire week potentially being Saturday, with partial sunshine and middle 50s expected in the afternoon.
By Saturday night, the pattern does start to shift though, as a strong dip in the jetstream sends temperatures falling back into the 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 D.C. region, including the threat for accumulating snowfall.
The big snow debate:
The big question of course, is how much snow? It’s a question that remains relatively difficult to answer even with just a couple days to go ahead of the potential storm system.
The key to any potential storm system is its track, and its 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 model. With temperatures well above freezing at onset, the system would likely start as a predominantly rainfall event through the front part of the day on Sunday.
Then, as a surface storm pushes eastward into the Atlantic, colder air fills in as the storm pulls away, along a weather feature known as an inverted surface trough. This would bring the risk for rain to change over to mix and a perhaps a period of potentially heavy, wet snowfall on Sunday night.
Now, the tricky part of the forecast with an inverted trough situation is the area that gets accumulating snowfall tends to be in a relatively narrow band that follows the trough axis, so not everyone in the region would be looking as a decent snowfall, it would be localized in this banding.
Forecasting exactly where it would setup is very difficult, and we would not have a good idea of where this feature sets up until likely closer to Saturday evening.
If this solution, which the European Model has been hinting at for the last couple of days, is the correct solution, then parts of our region could see a 1-3″ with an upside risk of 3-6″ snowfall potential by the time the storm exits late Sunday night into early Monday morning.
On the other hand, you have the American model solution, which for the better part of a day now has suggested the storm could be much more impactful. With a stronger tilt in the jetstream, the weather model suggest that a more intense storm system will develop that stays much closer to the coastline. While it also starts as rainfall on Sunday morning, the intensifying surface low pulls cold air quickly into the storm, dropping temperatures in the DC region and changing rainfall over to a widespread heavy snowfall.
The model is aggressive with a heavy, impactful snowfall for everyone, with final snow totals in the double digits.
Now, most forecasters agree this evening that this solution is rather extreme and unlikely to be the case with this storm. While we cannot rule it out of the realm of possibility, it is generally on its own, with most other guidance as of Thursday night suggesting lesser snowfall totals are more likely.
So, if we do not believe the American model solution, what is the debate this evening? The issue lies in model consistency. Weather models have admittedly been extremely poor with the forecast solutions for the Sunday storm system. Even the European, which does have a history of being more accurate than the American model, has been extremely “jumpy” with this storm system. Sometimes jumping the system east, showing less snowfall, then bringing the storm back west, showing more snowfall. Forecasters look for run-to-run consistency, and so far we really have not seen that from any weather model just yet.
The reason why has everything to do with the pattern. It is not just one piece of atmospheric energy helping steer this storm system, but multiple. The more pieces you have involved with a developing storm system, the more prone you are to errors in the forecast. This is why we might not have a truly good hold on what this system could do in the DC region until closer to Friday night or even Saturday, when the energy pieces involved in the formation of this storm system are all well sampled and better analyzed.
What to be prepared for:
This one is going to come down to the wire in terms of figuring out snowfall amounts. What I can guarantee is this will not be a repeat of the late January storm.
Temperatures will not be as cold, even after the system — no “snowcrete” this time around. This would also be wet snow, and we would likely lose some to ground melt in areas no longer covered in snow from the January system, as temperatures have been above freezing much of this week.
A key thing we want to mention: A lot of people are saying, “but it is too warm to snow on Sunday! The Weather App says it will be in the 40s!” While yes, this is too warm to snow at onset…remember that your weather app is giving you the high temperature for the day.
Through a process known as dynamic cooling, temperatures can cool as you bring in cooler air on the back side of a storm system, due to the upper-level trough swinging through. So, temperatures would be falling throughout the day.
The time frame we are most concerned with at the moment is Sunday afternoon and particularly the evening hours. While we do not anticipate at this time this will be a major, city shutdown type of snowfall, the most likely timing of it does mean that the risk is there for closures and delays to schools and other activities on 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 are not yet confident on any snowfall numbers to put out our expectations.
Stay tuned:
What we will continue to do is keep you updated and informed ahead of this potential on Sunday.
To reiterate, at this time we are leaning towards the potential for a lower impact accumulating winter snowfall 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.
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