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Here is a blog post by Mrs. Pam Knox discussing some colder temperatures foretasted for our area.

Over the last few days I have received several questions about media reports of much colder weather that is expected to move into the Southeast over the next couple of weeks. In many cases this has been tied to ominous pictures of snowfall maps showing up to a foot of snow falling in one location or another in the Southeast sometime in the next ten days. I want to address some of these questions as well as tell you what we can and cannot say at this point.

Just because someone shows a scary snowfall map on social media it does not mean it will happen or even that it is likely to occur. It might be one out of 50 or so model runs, with the rest of the maps (not shown) with much less or no snow at all. They are also a snapshot of conditions at one point in time, and the same model might show a very different map in the next run a few hours later. You cannot trust any snowfall map that is more than 2 days out, because the conditions for snow to occur require very specific weather conditions that include cold air to hit a spot at the same time that there is enough moisture there to form wintry precipitation. In the Southeast, this is quite rare and the main reason that we don’t see snow very often, since usually the moist air has moved off to the east before the really cold air moves in from the northwest. Any weather map showing a forecast for 10 days out is just wishcasting their desire for a snowstorm (and looking for clicks to monetize their site or get attention), not providing any skill. Weather forecasts generally have some skill out to about 7 days, although we can see general patterns farther ahead than that.

Let’s start with the temperature. The current 6-10 day temperature outlook from NOAA’s Climate Prediction Center shows the map below. It has a large area of very dark blue right over the Southeast. That might lead you to conclude that our temperatures are going to drop into Arctic territory, but this is not the correct interpretation of this map. The CPC maps show how likely it is that a temperature will be above or below normal but not HOW MUCH it will be above or below normal. So this map shows that we have a very high confidence that it will be colder than normal from January 7-11, but not how much below normal it will be. That is because all the models agree that a pattern shift bringing air in from across the Arctic has started to occur with the passage of a front on New Year’s Eve. A storm that is brewing in the central US will bring an even colder mass of air into the Southeast as it passes this coming weekend. There is the potential for an even colder blast to occur around January 10-12, which would bring the coldest temperatures so far this year into the region. In fact, it might be the coldest temperatures in several years. It is also the coldest time of year for the Southeast in general, so it is not a surprise that we have seen this change to a more wintry pattern in the last week.

You may also have seen maps showing predicted temperature anomalies across the region. I am not going to show one here because they are constantly changing, but let’s assume it shows a temperature anomaly of -15 F. Note that this is an anomaly, or difference from the normal, and not the expected temperature. Dennis Mercereau posted this helpful map (below) showing some normal temperatures for January 10 on his blog earlier this week. If there is an anomaly of -15 F during the cold snap, that would mean we could expect Atlanta to observe a high temperature of 38 F and a low of 22 F instead of what they usually get.

While it is not as cold as -15 F, that is cold enough to potentially do some damage to areas and animals exposed to the cold, especially if the anomaly is more negative than this (and a few of the forecasts show anomalies of -20 F or even higher) depending on snow cover and the exact pattern of the cross-Arctic flow. In addition, this pattern looks like it will stick around for a while, so pets and livestock, pipes, plants, and outdoor workers might have to endure the cold conditions for longer than the brief cold blasts we most often get. This means pipes are more likely to freeze, livestock to experience frostbite and reduction of body temperature (especially calves and older animals on their extremities like ears and tails), power outages to last for a while, and outdoor workers to be exposed to frostbite, hypothermia, and other dangerous conditions. The coldest air is not going to get here until after the next storm, so you have around the 9th to figure out how to protect your houses, livestock, workers, wells, and heating from the cold. But you should be prepared for it to last for a few days before we return to warmer conditions, and it may well last through mid-January. Note that both the strength and timing of the temperature anomalies are going to change over time as new observations and forecast model results come in, so you need to keep monitoring forecasts for updated conditions. It’s important not to just use general weather apps and social media like “Joe-Bob’s Extreme Snow Lovers” (I made that one up) but to use credible scientific sources like the National Weather Service, who will be continuously monitoring conditions and giving you unbiased information that you can trust. Once we get within 7 days of the actual event, we will have a much better sense of the timing and strength of the cold outbreak, although predictions will continue to adjust over time to newer forecasts.

Now let’s talk about wintry weather. The storm that forms in the central US is not expected to cause significant wintry weather for us since it will most likely stay to the north of most of our region. The exception is Virginia, which could see snow, sleet or freezing rain late in the forecast period. In the rest of the region, we should see mostly rain, although we could experience some freezing weather at higher elevations in the Appalachians. The map below shows the most likely hazards to occur with this storm. Note that areas in northern Florida have not experienced much freezing weather yet, and so agricultural folks there will need to watch the temperatures closely, especially those growing citrus, blueberries, or other sensitive crops.

The next storm system, assuming it does form, could reinforce the cold air coming in from the Arctic. That means even colder air, deeper temperature anomalies, and the chance for the intersection of frigid air with moisture from the storm, which means a higher chance of snow around January 10-12. There is no way we can predict this with any accuracy ten days out, either in terms of amount, timing, location, or type of precipitation, but we know based on the pattern that we need to start watching and preparing just in case.

So the bottom line is that we know it’s going to get colder and the temperatures will continue to fall over the next week or two as the low pressure centers pass by, so we need to get ready for that now. We also know that the chance of winter precipitation will increase over time, with the most likely occurrence around January 10-12, but it is far too early to put snowplows on your trucks or make any time-consuming changes before you know what weather will actually happen where you are. I will post again with updates as things progress.

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