Snow…Ice…Rain…Oh My

5

Well were one day closer to the Wednesday night-Thursday AM storm and, as expected, there isn’t much clarity in what exactly is going to happen. Here are some of the things that I do have confidence about.

1) we’re going to get wintry precipitation. Regardless of whether or not there is a changeover to liquid rain/drizzle on Thursday afternoon, when things get going Wednesday night sometime, it will be frozen at first and the odds favor snow at the beginning of the event. This snow should stick right away.

2) Temperatures, throughout the “atmospheric” column, will be the key to how long the snow falls. This will be a storm that brings “warmer” air into it from the south at various parts of the atmosphere. Should the warmer air invade enough it will melt the snow as it falls. It’s too early to figure the exact aspect of that…

3) The entire region won’t get the same precipitation part. Some may get rain while others are getting heavy snow. Some may get sleet while others are having freezing rain while someone else is having snow…while someone else is having something else. This is a forecast headache at this point with tremendous bust potential in specifying who gets what.

4) Model trends today seem to be a bit colder to me. GFS seems to imply more snow and the Canadian hasn’t given up the ghost of a significant snowstorm for a large part of the area. The EURO is pretty snowy as well. I’m still concerned about the potential of a “warm” layer of air above 5000′ that could melt the snowflakes as they’re coming down to the ground as the atmosphere morphs through the storm’s timeline.

5) Precipitation amounts look to be between 1/2″ and 1 1/4″ or so. How much of this total is in snow form or sleet form or ice form is questionable. The rain aspect of this system while present may be the lessor of the totals and may not occur till the PM on Thursday and might be under 1/4″. That leaves the rest to be of the frozen kind.

6) There should be a large and fast moving dry slot with the storm that cuts the significant falling precipitation during the day on Thursday. NOT saying it will be dry, just saying it will not be coming down that much, especially in the afternoon.

7) The main track of the upper level feature looks to be NW of here while the track of the surface storm looks closer to the I-70 corridor. That complicates the atmosphere a bit and also adds to the precipitation type headache that meteorologists may need a bottle of aspirin for!

Finally as I look at the models I’m reminded of the funny cartoon that I saw last week that was created by @MikeFavetta with an assist by @Scott_Derek.

It shows the studious EURO model taking a test while the GFS model peaks over to look for the correct answer and the NAM model, well I think you can see what the NAM model is doing. Basically pointing out the superiority of the EURO model in forecasting the big NE snowstorm as well as Hurricane Sandy.

Let’s start with where the storm is now…it’s in the eastern regions of AK. It’s not the energy off the SW Aleutian Islands.

That upper level core of the storm will drop into N CA Tuesday then head towards the Las Vegas area on Wednesday then swing out towards Dodge City on Thursday AM then move up towards Fargo, ND on Friday. That part seems pretty good although we really will have a better idea when the storm gets sampled in our upper air network of balloon sites beginning with the morning computer runs on Tuesday. So I think Tuesday night’s runs of the models will be critical for a better idea of what may happen with the storm’s future and KC.

Assuming this path is correct take a look at the GFS forecasted Precipitable Water chart or PW chart. This helps us investigate how much moisture there will be in the atmospheric column…more moisture with enough lifting equates to more precipitation on the ground (whatever form it takes). Click on that image to make it larger.

PW

Clearly you can see the moisture being brought in from the south, throughout the atmosphere and the dry punch of air that will overtake our area by Thursday afternoon taking shape in the SW Plains area.

Really the issue is can the atmosphere stay cold enough through the column to support snow for the majority of the event. IF it can. we’re probably looking at 4-8″ of snow with some upside to those numbers from KC northwards. The problem with this is that this fetch of air coming from the south and southeast may be strong enough and warm enough to bring in some above freezing air through some part of the atmosphere below 10000′. This means that even if it’s snowing up there, the flakes may melt as they come down, perhaps then going through another layer of below freezing air closer to ground level. This means that the melted snowflakes will refreeze in the form of sleet. Should this happen for any prolonged period of time it will kill the snow accumulations dead in their tracks and instead now you’re getting a bunch of sleet and not accumulating snow. So instead of getting 8″ of snow you get a couple of inches of snow and then a bunch of sleet that adds up accumulation wise much slower than snowflakes do.

Another possible scenario is that the layer of air closer to the ground that is below freezing is thinner than the above scenario. Then the melted flakes don’t have enough time to refreeze and you get some ice pellets and a bunch of freezing rain. That effectively kills the snow accumulations and then we worry about the ice accumulations and the headaches that that aspect can bring to the region.

Oh and did I mention that these transitions will be happening in different places and at various times. Meteorologists hate these types of storms. Give us one or another and a difficult forecast to begin with is simplified somewhat.

The bottom two scenarios are tied to where the surface low decides to go. IF it stays south of KC, then we stay in the colder surface air, IF the surface low goes to the NW of here as well, the liquid rain chances increase as temperatures nudge to 32-35°.

Don’t be surprised if temperatures in the afternoon on Thursday go up above freezing as the dry slot shuts down the best precipitation.

So with that said here is my updated timeline for the KC area. Areas farther south towards the Lakes region should see less snow with a bit more ice and then a more rapid change to liquid rain, while areas farther north towards the IA border may get more snow with some sleet and the potential is there for a 6-12″ snowstorm closer to the IA border.

Wednesday: Highs near 35-40° with increasing clouds

Wednesday night : Clouds lower and thicken fast…perhaps some snow/sleet developing (accumulations possible) changing more to sleet as the night moves along. Temperatures steady 26-29°. The duration of the snow will be critical to potential accumulations obviously.

Thursday 12AM-6AM: Snow/sleet (moderate/heavy at times) This may be a large chunk of the storm’s precipitation. Temperatures steady 26-29°

Thursday 6AM-10AM: Snow/Sleet transitions to some freezing rain/drizzle. Temperatures start rising to freezing

Thursday 10AM-2PM: Dry slot of the storm moves into the region effectively shutting down the significant moisture…temperatures go above freezing. We should see some melting until the surface low passes…then temperatures will fall again refreezing what’s on the ground.

To reiterate what I talked about yesterday this timeline and snowfall thoughts and amounts will change A LOT. This forecast will be a nightmare to figure out into Wednesday night (unless the mostly snow scenario plays out-then it gets a bit easier). I put these thoughts into my blog for the blog readers and I can’t really go through all the possibilities in a few minutes on the air…there are just too many variables. Personally on the air, odds are I wouldn’t touch forecasting snow totals till Tuesday evening/night when the storm finally is ashore. I might throw out there we could see more than ___” of snow out of this and do something general, but with transitioning precipitation types in the mix (pun intended) the potential for a busted forecast is through the roof already. I seem to remember the great KC ice storm in 2002 (click on that for the weather maps from the Ice Storm…this is a different set up in a large way…sort of similar aloft but different at the surface although there are similarities with the big expansive cold high pressure across the upper Midwest) looking like a big snow from several days away and then as we got closer to the event it shaping up to be mostly an ice event for the KC area.

If I was a young one hoping for a snow day…odds are Thursday could be one, and for some perhaps Friday as well, especially for the more rural areas.

So with all this said I will be increasing the FOX 4 Snowfall Potential Index to a 5 starting this afternoon. Hey it’s a start at least.

Thanks for reading all this…I know it’s like a term paper. I may post some additional maps later this afternoon. Time for me to go back to work!

Joe

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s