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3/8/2021 – Loudoun Weather Outlook has Warmer conditions through Friday and then some cooling. We likely will break 70 Thursday, but believe Wednesday and Friday may break 70 as well! With warmer weather… HERE COMES THE POLLEN! Tree pollen starts popping! I know Juniper and Maple are already up and by Friday Pollen levels will be Medium-high for trees! The cooler air next weekend MAY bring some interesting weather Sunday/Monday of the following week with some mixing. I will watch but feel it is unlikely. The longer-range is showing colder than normal temps with above-normal precipitation, which is a change from this dry stretch and the brief warm-up this week.
First – A Wintry Period will persist for the next two weeks. This could include multiple winter weather threats as well as some super cold temperatures at times.CONCERNS: Thursday and Thursday night keep fluctuating between a more snowy look and a sleety look. If it turns to icy, we could see enough for a sizable ice storm. It is possible the ice is sleet and not freezing rain which would be better! But someone in Northern and Central Virginia could see a significant ice storm. Please keep posted. BUT, it would be a good idea to prepare for potential power losses.
What in the world is causing this?
A light southerly wind is overriding some Arctic air that has worked into the area
The initial amount of cold air above us is cold enough that snow is more likely than other precipitation.
Southerly winds will bring in warmer air, and that will start to erode the colder air above us.. but the surface cold is dense and being reinforced from the north. So we get the Cold Air Damming set up, which is pretty strong Wednesday Night through Friday. I show a chance of some showers Friday here, but, honestly cold air like this is almost impossible to forecast right and the models always break it down too fast – so do not expect that to be likely.
On Saturday, a coastal system will be forming along this front that is hanging out in the area all week and causing the wintry weather. This could lead to a significant snowstorm Saturday into Sunday.
Where does that cold front separating colder from just marginal cold set up?
It is super difficult to figure it out, but I would say the confidence through early Thursday is that we are going to see snow. Mid-day Thursday through Thursday Night could be a constant switching back and forth and could end up dominant one type versus the other. The current look at the models leads me to think that we will be competing more with Sleet and Snow than Sleet and Freezing rain.
Saturday is low confidence now, but has possibilities!
2/3/2021 – We did have some more snow showers overnight and it coated the ground. This was the last upper support for the storm that is finally leaving but causing some blowing snow! Cold and windy today with a high in the mid-30s. Milder tomorrow and Friday. We may see some wintry mix tomorrow night, but it should turn to all rain. Showers Friday and one of the mildest days in a long while. Colder air expected next week is starting to fade from the original look. This may come back. We have to watch Sunday and mid next week for the chance for some snow, but I am no longer counting on a snowstorm at either time (but Sunday bears watching)
Very cold weekend with a winter storm possible. Snow could be 3 to 5 inches Sunday and possibly 2 to 4 or more inches on Monday. Monday has some upside potential, but slowly this is looking like a moderate storm and not a big dog. Many things have changed on these maps the last few days.
The European still shows a big storm, especially for the western areas.
What is so different about these two models?
I will summarize.
To the north, we have some “blocking” occurring that is causing storms to slow down as they head north. The blocking stops the storminess and the energy of the storm from going further north when the storm is west of Virginia. The blocking also keeps colder air in place. If the storm gets too far north (like the American Model shows) then we get into southerly winds since the low is due west or northwest of our area, and the colder air is eroded out of the area when the precipitation comes. In this setup, on the American Model, we have had about 4 to 8 inches of snow. The point where the winds change from the north to the south is a warm front (Warm air advancing into colder air). Once the warm front is north of you, you will change to rain or a mix. We do have the added help of Cold Air Damming in the region, so the warm air can push overtop the colder air and we will mix with sleet and freezing rain before seeing just plain rain. One note, however, is that once the warm front pushed through the precipitation will often cut off as the main low is way west of the area. The moist air overrunning the warm front and being pushed into our area is not uncommon to cause snow. Our failure earlier this week was related to this setup. We would have had more snow if the ground temperatures were colder. We will have cold air in place as we head into this Sunday’s event, so we will not waste the precipitation on getting the air cold. So we get the warm front assisted snow. Since the low and energy cannot push further north, they transfer this energy to the coastal front that is along or near the East coast. This Low-pressure system death to our west and transfer is known as a Miller B type set up.
Finally I can explain the potential and the potential busts for this forecast. THE KEY is “WHERE and when does that transfer take place?”
Scenarios that would cause a “bust”
IF the transfer is at our same latitude or further north, we may get the front end snow, but not the snow from the new low pressure that formed off the coast.
If the Primary low remain strong and transfers the energy slowly, we get into southerly winds and get too warm for snow
If the primary transfer is just slow and we stay between the heavier precipitation from the primary low, and too far west of the coastal low.
Another potential impact to lesser amounts of snow will be how close to the coast the new low-pressure tracks. IF it gets too far inland the warmer ocean water could turn the snow to sleet. This does have some possibility and will need to be watched (especially eastern areas)
Now, we do pretty well in the American Model setup on Sunday, and we get into the warmer sector of the storm, but we may not have too much precipitation after the warm front aided snow so we get some drizzle. Then the new storm takes over, but it is too far north to get us any of the coastal aided snow. THIS has been the setup on the GFS for days, but even now it has upped the totals to more than 6 inches from this front end snow!
BUT, THE EUROPEAN model is different! The Primary low on the European does not make it as far north to get us into southerly winds, and transfers the energy to a Low along the front down in North Carolina! The low begins to strengthen and organize which is sending precipitation over us in light to, to increasingly moderate, and then heavy snow. Because it is organizing, it slows down its forward speed for almost 12 hours.. so we are getting snow the entire time…then, as it strengthens and lifts northwards, we get in very cold and heavy snow. This is the snow on the Northwestward side of the system that has the moisture from the ocean, but is also pulling in the cold from the north! It is referred to as the Cold Conveyer Belt (or CCB). We get real heavy snow from this, and, sometimes, higher ratio fluffy snow which makes more snow with less moisture! We appear to get into this snow for a while on the European!
So now I will share the loops of the two models with the same system:
So what does that mean for snow totals?
IF we trust the snow output, from the models, the totals are quite different!
And now – the BIG DOG – European
SO WHICH ONE IS RIGHT?
It is all about the tracks, transfer of energy, timing.. etc!
I am leaning with a forecast of 6 to 12 inches, with the upside of 16 inches if all comes together correctly.
I will say, IF.. IF… IF the European is correct, the amount of snow may INCREASE for the region on the subsequent runs. It will also be windy!
2/26/2021 – What is next? Cold temps and then.. maybe.. a Snow Storm! After we clear up late today we now look to stay dry until Saturday Late through Monday when a winter system does look like it will visit the area. Unlike the system failure for Thursday, this system has a lot of support from all models! That gives me confidence that we will see some kind of weather. The question – How much and what types? I am leaning towards the idea that we get some snow and it will be enough to shovel. The upside potential is good, but we have been burned a lot by the setups this year. So, I will keep watching! Again, unanimous support of something happening from all models! Exactly what, when, and how much are all still a question! AND I HAD TO ADD.. Plenty of time for this to fail and become not a big deal.. or to become a REALLY big deal
Since this is on my Website – Here is the European model!
Colder conditions will be felt mid-week and next weekend. In general, the week looks dry. We will need to watch the longer range.
What about wintry weather?
One way to look into the possibility of wintry weather is by looking at weather models that blend a variety of possible outcomes. The next set of maps are that set up, but I will not be able to show these all the time as they belong to Weather Bell (if interested, check out https://weatherbell.com – too expensive for a hobby!) This is the European output for next Monday!
DO NOT GET SUPER EXCITED by the snow on the map as these show snow a lot and many times it does not come true! The thing that is interesting is the chance of at least 3 inches of snow in the next week is up to 60 to 70% – AGAIN, this can be incorrect, so we take it with a grain of salt, but I do like seeing the higher percentage.
The European is many times wrong, so lets not get ahead of ourselves.
We need to see this keep showing up. The thing that is a bit encouraging has been that both models show something around the same time. What is very discouraging is that both are SO VERY different in the may they get precipitation to fall! So I will keep watching!