Joe’s Weather Blog: Snow and lots of cold are coming…your flakes may vary (12/23)

On the Eve before Christmas…the weather is going to get briefly more interesting…it won’t be a long term thing…and you’ll probably be sleeping and not see it until you wake up…but I’m still expecting snow in the area early Sunday morning that will accumulate to various amounts through the region. For snow lovers there will be more snow for areas north of KC…potentially enough to shovel in far northern MO…there will be markedly less the farther south you are away from KC…and there will be something in between for the KC area. I don’t think we’ll really need to shovel here but some may have the option too, especially on the north side of the KC metro area. I’ll post a map of my forecast as of this afternoon in the discussion part of the blog.



Forecast:

This afternoon: Variable clouds…more north of I-70 and less south of I-70. Cold with highs in near 30° north and closer to 35° on the south side in the sunshine

Tonight: Dry through 12AM…then increasing snow chances after 12AM…especially around or after 2AM-3AM. The snow may be moderate at times in parts of the area. The snow will also start in far north MO earlier than in the KC metro area.

Sunday: The snow quickly ends between 6AM-8AM from the west to the east. Then gradual clearing and turning sunny by the afternoon. Highs should be around 25-30°

Monday (Christmas): Lots of clouds in the area with highs in the 30-35°



Discussion:

Several items of note today…for evergreen purposes…on Friday’s climate sheet for the month through the 21st…we were running 7.3° above average for December. I note that because I want to see where we are after the 31st from that number because the trends are mostly cold for the rest of the month with the potential for some bitterly cold air…Tuesday>Wednesday then later next week into the weekend look very cold. IFwe can get some snow on the ground…it could be even colder…especially next weekend…potentially sub-zero lows…but we’ll deal with that later obviously.

The main item of interest is what’s going to happen tonight. Remember several things about the playout of the snow in the KC region (at least).

1…this “event” won’t last long…4-6 hours or so. 2…the air will be nice and cold…so the fluff factor is rather decent…again this gets into the snow ratios I’ve written about this week. Typically 1/10″ of liquid means 1″ of snow…but with the cold atmosphere in place…1/10″ liquid equates too about 1.5″ of snow. 3…there may be some evaporation of the snow before it reaches the ground…the length of time this occurs could impact snow totals…especially from the I-70 corridor southwards. 4…I’ve seen numerous cases where these disturbances track a bit farther south than what guidance says…as a result there can be a tendency to see some higher totals closer to “home”. It’s the reason, why when looking at some of the new data this morning I wanted to add about 1/2″ to the potential totals. This map is my current thinking.

Notice the wording…UP to 1.5″ for the KC Metro area. The farther south you go from I-70 the lessor the snow accumulations look to be…odds favor a dusting at best from near Ottawa to Paola to Clinton and Sedalia or thereabouts. I wanted to give myself some upside for the KC Metro in case this wave travels a bit farther south.

Areas north of KC…towards the 36 highway corridor up towards the IA border may be more in line for 2-3″ of snow. It won’t melt enough tomorrow…so a White Christmas looks more promising up there than in KC.

Remember a White Christmas means you have to have 1″ of snow on the ground on Christmas. This is the “official” definition. Some consider a White Christmas if there is actual flakes on Christmas Day…but it comes to what’s on the ground…a dusting/coating won’t do it. That’s why there is better hope the farther north you go. We can have a White Christmas in KC…BUT the system will have to really overproduce for us and/or trend even farther south. There will be some melting on Sunday…so IF the Metro gets 1″ of snow out of this…it probably won’t last into Monday.

As I mentioned yesterday this little disturbance has to track a bit father south for us to have something a bit more decent in the KC area. I typically like using the RAP model in this time frame…and you can see how it cranks out the “liquid” which we convert over the snow totals…this is the early afternoon run showing the liquid equivalent through 8AM Sunday. So this shows the 12 hour amount of moisture…the precip in KC will be ending around or before 8AM…this shows the area getting about 1/10″ of liquid…allowing for some evaporation and factoring in the somewhat higher snow ratios…that’s why I wanted to open things up to potentially UP to 1.5″ of snow in the KC metro area.

You can see why the areas up towards the IA border have a better chance of needing to shovel a bit…that would equate to over 3″ with a fast pick-up to near 5″ up there into southern IA…plus they will have near 20:1 ratios…so all of a sudden a 1/4″ of liquid would be about 5″ of snow

Let’s get into the weeds a bit now…one of the “issues” for us is getting enough “lift” to happen for long enough to produce some sustained bands of snow. It will happen BUT this next chart also shows something that needs to be mentioned…the best “lift” actually never really occurs in the part of the atmosphere where snowflakes best form…it mostly occurs above that layer.

The lift is represented by the phrase “Omega”. The “best” part of the atmosphere to create snowflakes is roughly between -12° and -18° Celsius. Note the areas of green in between the two RED lines (showing the -12–18° range). That’s weak left in the better “snow growth” area. Note the lighter blues…notice that it’s above the range that we want them to be at.

Why is that -12 to -18°C layer important? That’s the area where you get your best flakes to form…called dendrites. The chart below shows this better. Dendrites accumulate easier than other types of snowflakes…

Other “types” of snowflakes (their structure) don’t accumulate as easy. That’s why sometimes it can snow for a long time and really not accumulate as much (in the scheme of things). IF the best lift isn’t in that zone…these other types of snowflakes don’t accumulate as easily!

So there is a LOT that goes into snow accumulations.

The other theme of the forecast is cold…and I may be trimming more from the temperatures down the road. I’m impressed that today we’re not really warming up much at all. We started in the teens and have only come up about 10° or so into the early afternoon.

So after all that…KC will get a solid dusting to upwards of 1.5″ from this…higher totals may tend to favor the north side of the KC Metro area…while amounts of 2″ or higher will favor areas from 36 highway northwards to the IA border. The farther south you get away from KC…about 50 miles south…amounts will be about a dusting to 1/2″ or so.

I guess it’s a start…but don’t be too disappointed tomorrow IF, when you wake up, you see blades of grass through the snowcover in the Metro.

Let’s also start paying attention to Thursday for another snow event…right now looks “minor” in terms of totals.

Our feature photo comes from our own Michelle Bogowith, who’s in St Louis…they had some nice snow earlier this morning.

Joe

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