Active Pattern Over The Next Week
There is potential for some wintry precipitation which could cause some problems with ice here in Kentucky during the weekend into next week and another wave may bring rain later in the week so that's what I want to focus on. All the typical caveats are on the table for this right now because of the usual small-scale uncertainties that you see but as long as you know that then there is no harm in taking a look at what we've got going on now and how I think things will evolve going forward. I'm not going to be posting any specific predictions regarding snow/ice accumulation, rainfall, or any of that at this time because there is just too much uncertainty regarding whether we will see snow, freezing rain/sleet, or rain and I feel like it would only be for show if I did. Regardless of accumulation, even rain will cause problems because it will not have any trouble at all freezing, leading to ice issues.
So here's the plan: We'll look at the current conditions across the region and walk through what we can expect over the next 36hrs. After all, you've got to get to the end-zone before you can cross the goal line. Then we'll get to know some of the players involved in our weekend setup. I'll briefly get into the model guidance and share my thoughts on what they're suggesting and where I think they're tripping up but I think the data that comes out over the next few hours will have a little better grasp on things. That's as far as we can go for now so the next step is to monitor the features upstream to see what they do through tonight and through the morning (Friday) while keeping an eye on the forecast models. I'll reassess things, post an update sometime Friday, and take a shot at precipitation predictions for Sunday-Monday. By Saturday we'll see key features come into focus so I'll update my precip predictions during the AM and then we watch what happens.
The good news about the mid/late week system is that we will experience a warm up preceding it and won't have to deal with snow or ice. It's still a bit too far out for any real confidence about anything else though so we'll roll with this first system through the weekend and just monitor things upstream. There's never a reason to make a "forecast" based solely on model guidance unless you just want to throw spaghetti at the wall and see if anything sticks so you can brag about being the first one to predict something, IF the random model you choose happens to be correct. In this case, it's unlikely it's correct. There is basically a North to South conga line of waves from western Canada to California with a closed-low in the mix too. So think, the models have to resolve how each one of those waves evolve over time while also accounting for how they affect each other. That is a difficult scenario for them to handle. On top of that, every mistake amplifies with each step forward in time. I think the next milestone to say anything meaningful about this setup will be Saturday night when we can see if the vort max (vorticity is a measure of spin in the atmosphere) way out in the Pacific is able to eject from its parent low. Then we watch to see if it can be seeded by a shot of energy associated with a closed-low off to its East. IF that happens it would likely deepen into a sharp trough but that's as far as I can speculate and at this point the models can't agree on what the background environment will look like as a whole, let alone how one specific wave will behave.
Current Weather: Dangerously Low Wind Chills Continue
Frigid temperatures will be the main issue going into the weekend as Arctic air still has us in its grip. We do have some snow showers moving through southern Illinois that will make their way into western Kentucky through the overnight hours. These showers/flurries are associated with an area of upper-level divergence as a jet-streak passes overhead. Moisture trajectories from Lake Michigan aren't quite streamlined into KY like they were last night since the upper-trough has shifted a little bit so we don't have the same moisture support as we did, which is why we saw a few brief heavy snow bands last night, but soundings are still showing enough moisture over Illinois, Iowa, and Missouri to support continued flurries over the next few hours.
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| Snow Showers Moving Southeast Through Illinois. 11:08PMcst |
The pattern aloft right now consists of deep troughing and progressive winds aloft over the eastern CONUS with ridging in the West. We're looking at split flow off of the West coast with the Pacific jet coming into California and the Polar jet rounding the ridge in western Canada and diving southward through central Canada. The Pacific jet merges with the Polar jet as it enters the longwave trough over the eastern CONUS.
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| 300mb Analysis Showing Upper-Level Flow. You Can See an Area of Divergence Near MO/IL Border As A Speed-Max Within the Polar-Jet Passes Through. This Is Aiding The Current Snow Development In Western IL. |
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| 500mb Analysis Showing Mid-level Flow With the Eastern Trough and Western Ridge. Notice the Progressive Flow Throughout the Trough. |
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| Surface Analysis Showing the Extensive Reach of Very Cold Air. |
High-pressure is building into the Midwest in the wake of the trough. The southern extent of the polar-front and surface high-pressure to our northwest, which is still firmly tapped into Arctic air for now, are driving very strong cold air advection. Unfortunately, that means we will be waking up to temps in the single-digits and seeing our highs only reaching 20 degrees or so. Wind chills will be between +5F and -10F. That kind of cold is dangerous. That's not sensationalism either. Temps that low can literally hurt you if you're outside for more than just a few minutes, especially if you don't dress appropriately.
Storm System #1 Sunday-Monday
You can clearly see the pair of shortwaves expected to work together to be our system as we close out the weekend (I've circled them black and also outlined the Polar-Jet axis and the Pacific-Jet axis). The southern wave will continue riding the Pacific-jet before crossing the Rockies to the North and diving southward across the Central Plains and into the Mississippi Valley region. The northern wave, which is less progressive and embedded in weaker flow aloft, will hang out in Canada as it slides East before it takes a southeast jog toward the Great Lakes. The southern wave should deepen as it exits the top of the ridge and crosses the Central Plains. I expect deepening at that time due to strengthening baroclinicity as it gains access to a relatively warmer air mass to the South while already being tied to the colder air mass to the North. It's at this time, sometime early Sunday most likely, that it should trigger cyclogenesis and we'll see a surface-low develop in the Southern Plains. This is where things get tricky. Not so much that I'm not confident in the setup because I am, it's how the setup affects things, particularly temperatures which dictate whether we see rain, snow, sleet etc. With high-pressure to our South/Southeast and low-pressure to our South/Southwest we will be firmly under the influence of southerly low-level wind. I don't have any concerns regarding whether or not we'll have the moisture to fuel everything given that the Pineapple Express is well-connected to out initiating shot of energy AND we'll have Gulf moisture streamlining into the region from the South. The moisture trajectories resulting from the low-level flow are actually really favorable because we will be set up for substantial isentropic ascent and the expected trajectories would continually overrun the warm front in the area. That warm front is the kicker for me though. We will see strong warm-air-advection with surface winds near 20mph. Near/North of the warm front I'm expecting sleet/freezing rain/mixed precip with rain South in the warmer air mass. I currently think it will be near the Ohio River which would mean rain for Kentucky but we'll have to watch closely. Regardless, since we have had such extreme cold sustain over the region, if we have temps in the mid-30's we'll still see some ice develop and travel hazards will ensue. Models have been trending colder but the spread has temps either at or just above freezing. What seems to be tripping them up is the retreat of the Arctic air. They can't seem to figure out exactly how that plays out and that has a lot to do with inconsistent runs. Expansive snow cover across much of the northern CONUS is also reinforcing the cold air, potentially altering the output.
That's where we will stop for now as it's 3:30AMcst and I have things to do but I suspect we will see the model runs in a few hours agree a little more, for better or worse. As I said, I'll reassess things later on and take a shot at precip predictions with today's update. In any case, we could see things get a little messy in the next couple days so stay tuned.
Everybody stay warm.
DKK
