It’s a special Sunday edition of the blog with an incoming diffuse system that may create a combination of brief rain/sleet switching over to snow Monday night.

Temperatures will be critical in terms of road impacts but we should be OK for the Monday morning rush tomorrow and the afternoon rush with surface temperatures nicely above freezing.

That will change overnight Monday into early Tuesday with snow expected. Temperatures should drop to around 32° and some road issues are possible on Tuesday morning for the AM rush. IF it’s a bit colder… then more issues. Something to be watching for as we should get a light accumulating snow from this scenario.

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Forecast

Today: Sunny and chilly with highs near 40°

Tonight: Increasing clouds overnight and not as cold as this morning with lows in the mid 20s

Monday: Increasing clouds which will lower and thicken as the day goes along. There may be some light rain showers in the afternoon. Highs in the lower 40s

Monday Night: A wintry mix changes over to snow not too long after sunset. A coating to 1″ is possible… perhaps a bit more on grassy surfaces south of I-70. Temperatures drop to the 30° range.

Tuesday: Any flakes end near daybreak then gradual afternoon clearing with highs in the upper 30s. The snow should be gone by later in the day.

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Discussion

It’s been a cold weekend around here and I thought before we dive in on the winter part of the next few days… a little perspective. This cold is somewhat unusual for mid November. Not unusual in the sense of highs in the 30s, for a day or two, but unusual because this cold air mass, with a re-enforcer pop of colder air coming on Wednesday and then again perhaps on Friday has staying power.

Essentially we’ll be below 45° for highs into early next week it appears. That would be about 10 days with this cold regime, which is impressive for November. Maybe not during the winter, but at least for this month.

I don’t have an easy way at my disposal to query that for this time of the year. My guess is that would be rare, if not unique.

For perspective the average high for today is 55°. We’re not getting there till right around Thanksgiving I think.

Onwards.

For the last five days or so I’ve been watching for the potential of snow later Monday into early Tuesday. Data over the weekend hasn’t really changed that drastically. This does not look to be a big event for us; it sort of looks like our typical first event of the season running about three weeks ahead of schedule and with the cold air mass in place.

And with it having the staying power that I mentioned earlier, this doesn’t surprise me in the least.

Just because you have cold weather though, it doesn’t mean everything is easy to figure out. The system coming our way has trended farther north than some model data showed last week.

I was expecting this scenario in previous blogs and so far that looks to play out. It’s not a particularly strong system…it doesn’t have a lot going on with it now as a matter of fact.

It’s out toward Nevada…

At this point the system is sort of moisture starved. There isn’t a lot of rain or snow with it.. even in the mountains. It’s missing low level moisture and that will change as it comes into the southern Plains Monday.

As it does so it will start to tap into moisture from the Gulf region at the surface and really through the atmosphere. You can see this a bit more clearly when taking a look at the precipitable water in the atmosphere.

This shows us the available water that the mid-lower atmosphere has to work with. Notice the change from this afternoon: We’re very dry until tomorrow when we’re not as dry. Note as well where the best moisture ends up across southern Missouri. We definitely moisten up but it’s not as if the Gulf is wide open as this system comes through.

Data is from the EURO model. Note how we go from the teens to about 1/2″ of moisture in the column above us. This basically means that the atmosphere can squeeze out 1/2″ of moisture in the form of precipitation. It DOESN’T mean it will… just that it can.

So as the wave comes closer the atmosphere is moistening up… hence the clouds will start to lower and thicken tomorrow. Radar will start to show activity sometime later in the afternoon.

One of my concerns though is that the surface moisture and the moisture in the lowest part of the atmosphere may be slower to get northwards. I looked a the upper air report from the balloon launch down towards Corpus Christie this morning, and well, let’s just say it’s dry… really dry along the Gulf region.

The red line is the temperature…the green line is the dew point as you go up through the atmosphere…this is from the surface to about 18,000 feet. The further the spread in lines the drier the air is…note it’s RELLY dry below roughly 850 mbs…or about 5,000 feet down to the ground.

The reason I wanted to look is one of my concerns is that it may take a while for the atmosphere to saturate tomorrow afternoon. This combined with an overall weak system and weak broad lift to the atmosphere may play a role in limiting just how much moisture we can squeeze out of this.

In other words we may waste some of the snow potential just in saturating the bottom part of the atmosphere.

This happens A LOT around these parts, and I won’t be surprised if it happens again tomorrow late afternoon/early evening.

Eventually though as whatever rain falls, since temperatures will be in the upper 30s, and that rain falls and evaporates in the dry air closer to the surface, it will cool the lowest part of the atmosphere down. It will be enough to support snowflakes, hence what I think will be a quick transition to ice pellets perhaps and then light snow.

This should happen between 6-9PM or so on Monday. The meat of the accumulating snow would be after that as the atmosphere close to the surface is cooled to near or below 32°.

Then the issue is how much moisture can we squeeze out of this in roughly a 6-9 hour window.

The NAM model from 9PM onwards squeezes out about .15″ or so, give or take a few hundredths. The hi-res NAM that came out this morning is about the same with not much happening south of US 50 (Warrensburg to Sedalia). Most of the other modeling is about the same as well with the moisture totals.

Now we need to take that moisture and convert it over to snow, assuming it’s all snow at 9PM onwards. Snow ratios won’t be great with this because the surface temperatures may still be in the 32-34° range for one, common is 10:1 meaning 1″ of rain is 10″ of snow. We can sort of use that as a rough guideline for this. So that would give us roughly up to 2″ snow potential.

Let’s allow for some melting initially, especially on the pavement. So now we’re cutting a bit more from this. Grassy areas may do a bit better than the pavement…

Overall my thoughts are roughly 1/2″ to 1 1/2″ or so with lighter totals north and south of the Metro. So for the 5-6 counties in the Metro…1/2″-1 1/2″ is sort of my thought right now.

There is a way that some may exceed that. If some weird band of moderate snow gets established, which isn’t too crazy of an idea with this. I think though the overall average should be in that range for accumulations.

Again, it’s like forecasting 1/10″ of rain during the summer and getting 1/4″ instead. Few if any would care, but in the winter that’s the difference between 1″ of snow and almost 3″ of snow. Some would be more interested in that potential.

How impactful will this be on the roads? It’s tough to say because road surfaces will put up a fight for awhile tomorrow night. If it snows in some areas hard enough, then will become snow/slush covered and that could lead to slick areas for the Tuesday morning commute. As usual treatments will be the main factor in this…and that I can’t predict.

I won’t be surprised though if there are some problems on the roads Tuesday morning in some areas.

The feature photo is from Matthew Reinschmidt. The frost formed quickly last night and it was all over the place this morning.

Joe