Loudoun Weather

The Mid-Atlantic has a lot of factors because of the proximity to the Atlantic Ocean, Mountains, and even the Great Lakes. I want to outline the impacts of these AND the Pacific which will all impact this winter, especially early in the year!

Atlantic Temps are WAY WARM!

The Atlantic Ocean is currently much warmer than normal. I think this will impact us in several ways:

1. Storm systems will have a lot more moisture to work with! The heat should evaporate more moisture and juice up any storm system. This is part of why I think each time the forecast models say it will be a dry period, they back off pretty quickly
2. The Western Atlantic Ridge (which at times is known as the Bermuda High) will be strengthened by the warmer air. This could slow the infiltration of colder air and stall fronts away from the coast and make them just inland. This could have a significant effect on the rain/snow line!
3. Warmer temps from the ocean will also make marginal (close to frozen events) more likely to be a mix or even rain. That heat will make it inland! This becomes less of a factor for the western zones, but does impact the upper levels which could make sleet and freezing rain a problem. This is not new, but could be a more common set up

The Greenland Temperature Gap

There is often a cold pool off the Northeastern United States that is linked, many times, to a better negative NAO (See previous posts for information on the NAO)

Great Lakes

You would not think the Great Lakes would have too much impact on our weather, but it really does! The Great Lakes can provide additional moisture to some storm systems, and, if it is warm, it can help moderate temps that are being impacted by winds that go across them. I am not saying this is a huge factor, but it does have an impact.

The Pacific Looks Poor

Probably one of the worst looks I have seen in a long while. The colder weather will encourage cold storms and the Jet Stream to be in a poor setup for us. I will discuss the Pacific Decadal Oscillation, the Pacific North American weather patterns, and the Eastern Pacific Oscillation in a post soon. All I can say is the pattern will favor milder terms for us and drier than normal conditions. I just do not like it.

Of course, we also have La Nina which will not bode well for big storms.

Summary

Most of the ocean looks terrible for us for winter. It is also the biggest signal that the winter may be warmer than normal and have less snow.

Snow Advance Index

The Snow Advance Index is a feature that is not always the best indicator for how our winter will be. The basic principle is that the advancement of snow cover in October is closely linked to the phase of the North Atlantic Oscillation.

North Atlantic Oscillation

The North Atlantic Oscillation (NAO) measurement is a KEY FEATURE needed to help get snowstorms on the East Coast of the United States. For example, the NAO is currently negative, which helps to slow down and aid in the development of big Nor’easters like the one we are having this week (October 26 – 27, 2021)

Really, though, the negative NAO (NAO-) is not the key to these storms, it is as the NAO flips back and forth between the negative and positive (NAO+) that usually signals a storm

Anyways, when the Snow Advance Index shows a great increase, the NAO *COULD* end up being more negative for the winter.

So what is the Snow Advanced Index Looking Like?

Snow Progression

The index is actually below where I would like to see it, but it is higher than last year!

The NAO Has been running Negative for a long while now. We will see if this can continue into November and Beyond! That would be a good sign for offsetting the La Nina impacts. (The line is below the 0)

Arctic Oscillation

Another factor for colder conditions is the Arctic Oscillation! As noted yesterday, when the Polar Vortex gets disrupted, it can turn negative! WE NEED THE NEGATIVE (if you like snow)! That is a better indication for more snow in the east! It has been running back and forth between positive and negative phases. We will see how this works out, but it looks like it is heading to negative again so the colder long-range seems to be linked to this as well! (Observed in black and red the various model predictions)

I am not super convinced we get non-stop help from the Arctic Oscillation this year, but I do expect a lot of variabilities which could help us at times be colder and have a chance of winter weather.

In Summary

I do not think we have much to count on from the Snow Advanced Index, North Atlantic Oscillation, or Arctic Oscillation. The negative NAO has been encouraging, but that alone will not set us right for winter weather.

The Polar Vortex is not something new and makes visits into the Lower 48 states every winter. The news media LOVES to over hype when it comes into play for the United States. Additional names to this Arctic region airmass could be the Polar Express (the streams of air that bring in the Vortex, or at least portions of it), or the circumpolar vortex.

What is it exactly?

The polar vortex is a large area of low pressure and cold air surrounding both of the Earth’s poles. (that comes straight from the NWS) In the winter it strengthens.

When it is very circular, it is considered stable and the jet stream is usually very strong. Storms likely will rip across the United States and the coldest air stays “locked” in Canada.

Disruptions

If you want there to be colder air masses in the United States, you would want the Polar Vortex to be weaker than normal so that storm systems can disrupt and dislodge the colder air into the United States. Another thing that can help to split and disrupt the Polar Vortex is something known as Sudden Stratospheric Warming. This is warming above the vortex that can “split” the vortex in some situations. When it splits, this also will bring colder air into the lower latitudes. This does not always mean the United States! The Warming and Splitting can take some time and air masses and weather patterns can take some time to respond.

SO WHAT!! What about our winter?

Two things I am noticing this fall! The first is that the Polar Vortex appears weaker! Remember, this will allow for the influence of storm systems that could dislodge the colder air and give us cooler weather. I am also ALREADY SEEING THIS HAPPENING!

If you have been following me on the My Facebook “Speculations” I mentioned some “signals” that we could see some cold early. It was SPECIFICALLY related to the disruptions being forecast by models for November. The disruptions started showing on models two weeks ago and are now happening. It looks like this disruption pattern could come in a few waves in November! Some is coming into play next week, and some other long-range speculations show the middle of the month. Just because we get disruptions does not mean we will get cold here. That mid-month intrusion seems pointed towards the middle part of the country, and maybe down into Texas! Remember, when you get past 5 to 7 days in forecasting, the forecasts become much more speculative as the models may be failing to pick up on some things. HOWEVER, these Polar Vortex disruptions do seem likely, again, because the vortex is so weak. And, while in this stage, we could see some below normal spells in November! Snowflakes would not surprise me at some time. However, sustained cold air may be a challenge, as it should be, since it is so early in the colder months.