~Cameron (Severe) Derek (Winter)
As we kick off the first weekend of December, we may be having severe weather on our hands here in the natural state.
A powerful and potent storm system will approach The Natural State as we move towards the Friday/Saturday timeframe. This system will pull up a good bit of gulf of mexico moisture and will also pull up some instability towards the state. At the same time, as drawn on the maps, this system will take on a negatively tilted position over our area resulting in the possibility of strong/severe thunderstorms over our area. Shear will be sufficient over our area for severe weather but instability & timing will be the huge question in regards to how significant this threat could be. If it's overnight as current guidance has it, the threat will be marginal and main primary threat will only be damaging winds along the front and possibly heavy rainfall. But if this system trends towards the afternoon hours then the tornado threat may increase as instability will be greater during the afternoon hours.
This is the GFS and EURO's idea on the instability and Precip as they both have the system moving through in the overnight hours. Marginal instability + High Shear = Damaging Wind Threat and possibly a spinup or two along the line as its moving through our area.
While the thunderstorm and warm air threat to start the month is becoming more certain another thing is the cold side to the start of December. Also along with the colder air, there are storm systems showing up as well. Below I have added the GFS loop through the middle of December, the GFS FV3, which will be replacing the GFS in January, Images for the 2 systems on the 4th and the 10th, as well as the the CMC and the EURO for comparison. As you can see, the system shows up on some but not all. This is very common this far out to see systems show up in the long range but not come to fruition. Comparing the differnt guidance members, clearly there is a system to watch, but the details are far from certain. One thing that is agreed upon is the colder air coming in. To get snow in Arkansas you have to have the cold air in place and the system coming in with the cold air already entrenched and this is the main thing to watch for and also much easier to predict. Lets take a look.
Below are the temperature anaomlaies into the first week of December. As you can see, there is remarkable consensus that colder air will invade the the eastern half of the U.S. Temepetaures below to well below nornal are seen on all of the latest opertaional members. This would support the cold start to December that we have talked about and this is the start of Meterological winter so therefore, the start of winter being cold. This would obviously be after the Saturday system. Again if we can get an active subtropical jet into this cold air, we will see the potenital for winter weather and one of those systems mentioned above could be our snow maker with the setup we are heading into.
Now, you can't simply look at temperature outputs alone to get a forecast or potential forecast. You also have to look at the upper atmosphere to see if the models hold any weight. To do that we look at the three main Oscillations that affect our weather here, the AO, NAO, and PNA. To get cold weather and the potentail for any type of wintry weather in the state, you want to see a negative AO and NAO and a netural to slightly Positve PNA. The more negative the AO and NAO are, the greater chance we have to see colder air. The more neutral the PNA or positve, the stronger the ridging is the west. You need this ridging in the west to bring cold air south. Below are the latest outputs for what is mentioned above and as you can see, it fits into the idea of a colder pattern setting up.
Below I have included the CPC outlooks for the upcoming 6-10 and 8-14 day periods. As you can see the Climate Prediction Center has a colder pattern moving across which also favors a colder pattern setting up and goes along with what we are seeing in terms of colder weather. On the storm system side, they as well have above average precip. So with that, as stated above means that we will need to watch the systems being advertised by some of the guidance as even the CPC is hinting at the possibility of an acitve pattern as we head into December.
So as you can see, there is definitely something to watch other than quiet and sunny. Will we have warmer days? Yes. But in the midst of that, there will be a lot more colder days as we head into December. With the pattern starting to really get going, we could see one of those systems meet up with the colder air and bring us a round of winter weather, but that remains to be seen. Unfortunately, we will have to get through what looks like a round of strong to severe thunderstorms to get to the colder air first. Stay tuned as we continue to update as things get wild and crazy as we head into December.
~Cameron (Severe) Derek (Winter)
It has been a rather benign pattern since our snowvember setup a week or so ago. That pattern looks to persist into the following week. However, we are watching a couple of systems late in the period, just beyond the 7 day timeframe for some active weather. After our cool down next week, we will see a moderation in temperatures and moisture levels ahead of our next storm system. How this system affects us remains to be seen. One thing is certain looking at the setup, it does favor both rain and thunderstorms. Could it favor a strong or severe threat though? Let's take a look.
First is the GFS.. If you watch closely, you can see the evolution of what appears to be a low pressure developing in the Plains and shifting to the northeast. This is not a snow setup for us but more of a rain and thunderstorm setup. You can see it developing a squall line along a cold front as it moves east during the afternoon hours on Saturday. Looking at temps and soundings, it's a marginal setup but does support the idea, especially with a deepening low pressure. However, these systems in the past tend to produce late fall, early winter severe weather events so it definitely needs to be watched.
Now let's compare to the GFSFV3. This model will be replacing the GFS in January as the global model. Looking at this model, the setup is somewhat different, a tad faster with the front but the strength of the low and placement is about the same. It has the same concept of a squall line setup through the state. As with the GFS, temps are similar. Not significantly warmer, but has the same idea. This would support a marginal severe risk. Soundings on both do indicate some shear and with the strength of the low, shear would be present. The position of the low is most important in looking at the long range when watching for potential active setups, and both have that similarity.
Last but not least the EURO. This is looking at the pattern for the same time frame, and even the Euro shows a strong low pressure with a trough going somewhat negatively tilted. This is another we look for when watching for ingredients to come together for a severe weather event. Moisture increase and warm temps along with shear and instability are all needed to support severe weather. While this far out it's impossible to know if all of those ingredients will come together, you can watch for similarities in the guidance to see how things will set up. With the EURO showing a similar setup to the other two, a stormy Saturday next weekend could definitely be in the works. With a progressive pattern though, things tend to come together to our east and less so here models tend to not pick up on this until late. But all of this will be watched closely.
Just for fun I Wanted to show what the LONG RANGE is showing. This is way far out and has been tossed around as an idea. Being this far out, I don't buy this exact setup but just showing you how the relaxed pattern is slowly becoming more active. With the oscillations we talked about in previous videos and blogs going to a colder setup, Negative AO, Neutral to slightly positive PNA, a colder pattern is supported but how soon that gets here will determine whether or not we will see any type of wintry weather as we head into the first week of December.
As you can see, both show a system around the 6th of December, both have some sort of wintry weather and both have a system. This is beyond the Euros reach so this is just something to look at and totally for fun. As stated above, while possible a lot has to change with the pattern first.
So as far as our weather in the near term goes, December could come in like a Lion with an active weather pattern setting up across the Natural State. How active does it get? That remains to be seen. But with the Pineapple express open for business as the storm track comes across the southern U.S., we will have to watch each system for both winter weather and severe weather chances. For now, rain and thunderstorms look like a good possibility to start December. Could we see anything else? Stay tuned…..
For people traveling on Thanksgiving Eve and Thanksgiving Day...You should expect dry/cool conditions across The Natural State. A ridge of high pressure will keep our weather dry and cool for Thanksgiving eve and Thanksgiving Day for the natural state!
Beyond Thanksgiving and into December
As we head into next weekend, A powerful system will approach from the west and will have the potential to bring winter weather and severe weather on both sides of the system. Depending on the overall track and speed of the system...Severe Weather can not be discounted for south Arkansas as we head towards next Sunday into Monday and Winter Weather can not be discounted for far north Arkansas. This is the European model's idea of how instability values could look like by then. Weak yes, but with decent shear in place, Marginal severe weather would be possible across south Arkansas. As the system moves away, it would draw in cold air over a building snow pack in the Mid-West and could change the rain to a rain/snow mix across far north Arkansas before completely leaving.
The GFS, on the other hand, says no to severe weather and winter weather as it is progressive with the system (Which fights against what the current pattern is showing). At this time, If the GFS were to be right then we would see scattered showers and possibly a thunderstorm or two with the snow remaining well to the north of Arkansas.
As we close out November and dive into December...It could very well be a very cold December for the natural state. This is the EURO's idea on temperatures during the first week of December and it follows suite with our winter outlook with well below normal temperatures across the central, southern and eastern half of the United States and I don't even want to show you the snow maps....lol...But the overall picture is with -NAO, -AO and +PNA setting up as we close out November, this will lead to a cold December for much of the central and eastern half of the United States.