A look at the weather

Posted by RC on Feb. 22, 2016, 10:51 p.m.

As some or most of you already know, I'm very much interested in the weather and meteorology… at least sometimes. I tend to lose interest in a lot of things after a while and meteorology is no exception, though I always come back to it anyway. Since my area is supposed to be getting a decent winter storm in the coming days, I thought I'd give you guys a glimpse at what I like to do when such events arise.

A brief look at the impending storm

See this Texas booger butt that's within that big, red circle? This is what's heading my way for the "big" winter storm of 2016. Note that I live in Indiana and the arrow is tracked to Ohio - there's a reason for this and that reason is because it's not going to directly hit my area, but that doesn't mean I won't be getting any precipitation. It's a big system, after all.

The system is to arrive in the area in about 30/36 hours which puts us into Wednesday. Of course, the track and timing is still uncertain as the weather is unpredictable despite our best efforts at predicting it. It's a guessing game, really - a guessing game in which patterns and history play a massively major role.

Looking at this radar image alone isn't enough to determine anything, really, so this is where other data comes into play.

Atmospheric soundings and models

I might not actually be a meteorologist, but that doesn't stop me from making my own forecasts. Atmospheric soundings and various forecast models help me when trying to predict what's going to happen in my area. I get area specific data, analyze it, and try to determine what the future will bring in terms of weather related happenings.

Let's take a look at a Skew-T for Wednesday afternoon:

I never really use Skew-Ts much when forecasting winter weather as the software I use (Bufkit) to analyze atmospheric data has a handy dandy overview section which provides all the data I need. Still, Skew-Ts are an important part of forecasting the weather, so it's nice to take a look at it anyway.

This Skew-T is for 18Z on Wednesday. Z time is pretty much the same as UTC or GMT, so for my time this is 1PM on Wednesday. The green line on the Skew-T represents the dew point whereas the red line represents the temperature. The higher up on the graph the lines go, the higher up into the atmosphere the readings are for with the lowest points being the surface readings.

The green and red lines are pretty tightly bound together - this means that the air is saturated with moisture which in turn means that there is most definitely going to be some precipitation going on. We can tell what kind of precipitation it will be based on the temperatures.

On this Skew-T you can also see the colorful numbers and barbs on the right-hand side; these represent the wind in knots (I think). If you convert this to MPH, you can see that the winds are going to be around 40MPH. This is going to make for a very windy, snowy day on Wednesday.

A look at the real toy: the overview

This is probably my most used tool when it comes to forecasting the weather. It does pretty much everything I would have to do myself when it comes to reading the Skew-T for forecasting the weather, so hurray for shortcuts!

Basically, what you're looking at here is a heap of different types of formulated data overlaid atop one another. The colorful, blocky looking greens and purples represent the relative humidity, whereas the red numbers and circles represent the omega values. The pink and yellow lines represent the ideal area within the atmosphere in which dendrites (snow flakes) would form - this is the area between -12C and -18C. The white line represents the amount of snow accumulation based on the given snow-to-liquid ratio.

I can't really go into too much detail because I can't remember every single thing about what all of this actually means, but I'll try my best to explain what's going on here.

Negative omega indicates vertical lift within the atmosphere - this is needed for snow to happen and probably some other things I'm not thinking about at the moment. The lower the omega value, the heavier the snow could possibly be. The negative omega, however, needs to be within an area of high relative humidity and within the ideal area for dendrite growth.

I'm not sure if you can tell through that picture or not, but we've got values of omega at -26 within a 95% relative humidity zone - the only thing is that it's not really within the snow growth area. The higher numbers are, such as -8, though, so not all hope is lost for heavy snowfall.

Now onto the more interesting bits

Now that you hopefully know a tiny bit about what the crap I'm about to talk about, it's time to move onto the point where I'm going to forecast the snow accumulation for the Wednesday/Thursday event.

We know it's going to snow. We know the storm is coming from Texas. We've got the latest data from the NOAA for my area which shows that it's going to be a somewhat heavy snow as well as pretty windy outside. How do we determine the amount of snow accumulation that I'm going to get from this system?

It's not really as simple as opening up Bufkit and checking out the overview, though it also is in a way. Bufkit does a lot of things so I don't have to, but I still have to figure out what the snow-to-liquid ratio is going to be.

Before I get too deep into this, I should probably explain a little bit about the snow-to-liquid ratio. The average snow-to-liquid ratio is 10:1, which means that for every 10 inches of snow is the equivalent of 1 inch of liquid precipitation. A colder snow won't be contain as much liquid as a warmer snow would, so colder snows would have a higher snow-to-liquid ratio than a warmer snow would. Snow with higher ratios are more powdery and not really good for making snowmen whereas snows with lower ratios are more wet and great for making snowmen.

Earlier tonight using older data, I decided to go with the method which uses the maximum temperature within the sounding profile. By doing this, I came up with a 5:1 snow-to-liquid ratio which brought the accumulation estimate to 3 to 4 inches of snow for my area, but this was considerably lower than what the local media was saying - it was, however, right on target for what the National Weather Service was saying. I trusted the data and my assumption on the 5:1 ratio and went ahead and posted it to my Facebook page for my local area weather.

Now that I've got the new data in, though, the amounts are a bit different. When using the initial 5:1 ratio, we're getting about 5 inches of accumulation in the area. What I actually neglected to do originally is use historical data based on the system's track to determine a better and most likely more accurate ratio for the storm.

This system originated in the Colorado area before moving into Texas. Based on this information alone, I can determine through historical patterns that this system's snow-to-liquid ratio will likely be 7:1 or 8:1; Colorado systems typically yield a ratio of 8:1, though systems originating in the Gulf of Mexico typically are around 6:1. Since the storm is going through Texas and close to the Gulf, assuming a ratio of 7:1 should be okay.

This system - using a 7:1 ratio - will bring snow accumulations of between 7 and 8 inches to my area. This is a big difference from my original 3 to 4 inch estimate. Had I used this ratio on the old data, my estimate probably would been about 5 inches. Still not the same, but not as off as it's portrayed in the currently available data.

This is all subject to change as more data comes in, of course. Nothing's ever certain this far from the actually event, and even then you can't be 100% certain about what's going to happen. It's all a guessing game - a fun guessing game, nevertheless, but a guessing game.

Something something end of blog bit

I hope that you found this at least somewhat interesting. I know I didn't really go too in-depth with things and a lot of it probably made no sense, but I just felt like giving you a peek at what goes on when I try to forecast snowfall. It's different for thunderstorms and whatnot, though snow is more fun in my opinion because you have to guess how much snow you'll get instead of just checking if the conditions are right for thunderstorm development.

I might update this blog if you guys are interested in seeing how the storm pans out and if my predictions are right. This 7-8 inch estimate is more in line with what the local media is saying, but I'm honestly still not 100% convinced that we'll get as much snow as it's looking like now. Maybe it's just because I'd hate to see my initial estimate get burned.

Comments

Kamira 8 years, 3 months ago

That storm really hasn't done much in Texas, though I guess it's a little too far to the west. It's just been a little cloudy the past couple of days.

DesertFox 8 years, 3 months ago

We got a bit of light rain here in Austin, but not much.

RC 8 years, 3 months ago

Time for a bit of an update!

A lot has changed since last night's soundings, with models showing a more westerly track than before which means that the band of heavier snow is forecast to go farther west of me. This means less snow for me and more snow to the west.

Here the 12Z NAM data visualized for snow depth (not total snowfall) towards the end of the storm. It's showing about 1.5 to 2 inches of snow for me with higher amounts to the west. As this tool is new to my arsenal, I'm really not sure how much I can gauge total snow accumulation on this visualization, so I'm much more comfortable analyzing the data through Bufkit to make an actual prediction.

Compared to last night's soundings, this one might look a little bit more promising for heavier snow due to the grouping of negative omega within the snow growth zone, but higher level temperatures will mainly cause this to be rain, as is evident in the Skew-T below.

As you can see, we've got temperatures at higher levels that are 2 to 3 degrees (Celsius) above freezing which will likely melt the snow into liquid rain before it reaches the ground.

Atmospheric temperatures won't be cold enough until the end of the lowest omega values within the snow growth zone, which means less heavier snow is probable for the area. Using our 7:1 snow-to-liquid ratio from last night due to historical patterns from the storm's track, total accumulation of about 3 inches is shown in the NAM model.

Another model we can take a look at is the GFS. It works similarly to the NAM but uses different methods, thus possibly producing different results. There's also the Euro and Canadian models, but I'm not going to look at those (I don't actually have access to the Euro myself, so I have to wait on that from Twitter or something).

The GFS pretty much says the same thing as the NAM this time around, which is good for forecasting as the more models that agree, the better the chances are of your predictions being right. This, of course, isn't 100% truth. I'm not sure if you guys remember the east coast US snow storm a couple of years back that was forecast to be massive but turned out to be a little dinky thing - all of the models correlated with one another which lead forecasters to believe that it was going to be huge, but it wasn't until the data came in merely a few hours before the storm that they realized it was all wrong.

Anyway, the GFS is showing less precipitation to happen, with 1 to 2 inches of snow accumulation at 7:1. Based on both the NAM and GFS, it's somewhat safe to assume a 1 to 3 inch range for total snow accumulation from this system for me, with higher amounts to the west and northwest. To be safer, one could say 1 to 4 inches, but this system is likely going to produce a very wet snow which means less lower snow-to-liquid ratios and less accumulation.

So yeah, today's update as of noon EST is 1 to 3 inches of accumulation. A far cry from last night's 7 to 8 the NAM was showing, but at least it's correlating well enough with my original prediction of 3 to 4 inches. We'll see what happens once I get home from work and can check out tonight's soundings, though. Local media and meteorologists are being quick to dismiss these soundings and are still calling for higher amounts of snow, so I could be missing something important.

Edit: For what it's worth, the Canadian model is showing 8+ inches for my area. Usually that and the Euro are more accurate, but I can't check the Euro. I guess we'll see what happens tonight.

Seleney 8 years, 3 months ago

Quote:
See this Texas booger butt that's within that big, red circle?

Actually I'm a but further south. Jk I know bad joke.

This is interesting. There are so many factors that goes into these predictions. I am sometimes amazed how they can be accurate. Other time I just wonder if they get tired of all the math and just make up the formats for a day or two : P.

But seriously this complex stuff. Kudos that you understand it. Do become weather man.

Edit: storm is defiantly close though. No rain but the wind and sudden cold is astonishing…. And wrecking havoc on the power grid.

NeutralReiddHotel 8 years, 3 months ago

become a weatherman. do it. take screenshots. pics or it didn't happen

your knowledge should not be wasted. and if it is, shame on you and i'll take all the money you don't make on your knowledge and spend it on taco bell

RC 8 years, 3 months ago

Becoming a weatherman is too much work. I'm mainly suited to be an armchair meteorologist who posts on the internet and acts like I know what I'm talking about.

Anyway, onto more updates!

Here's the current radar image. The system's pretty much out of Texas now and probably in Mississippi. It's a bit difficult to tell precisely where the low is in this image, at least it's difficult for me to tell.

Right now, pretty much everything is the same. NAM and GFS soundings are still showing 1 to 2 inches of accumulation at the 7:1 ratio, but the Canadian model is showing upwards to 10+ inches for the area now. To make things even more difficult for me, just to the northwest is where the amounts go up drastically in the GFS soundings, with amounts of 3 to 6 inches just miles apart in places.

There's no point in me showing anymore Bufkit images and whatnot because there's nothing useful to be taken from them at this point, though the NAM 4k (high resolution) visualization does show about 4-5 inches of accumulation in my area. It's scattered, which makes it difficult to tell.

The National Weather Service has placed my area within a winter weather advisory and is calling for snow accumulations of 3 to 5 inches. If you trust the NAM 4k visualization, I'd say this is a decent enough range to go by. Local media outlets are still placing me within a 6+ inch accumulation zone, but I just don't see us getting that much with as wet as the snow's probably going to be.

All of this conflicting data is definitely making this forecast difficult for me, but I personally feel that a 2 to 4 inch range forecast for my area is good enough. The Canadian models might be accurate a lot of the time, but the GFS and NAM models have been steady all day for the most part. As I've said, it's all a guessing game anyway, so I'm going to go with my gut. I guess we'll see how right I am tomorrow or Thursday.

Kamira 8 years, 3 months ago

I was wrong about it being too west for me. Yesterday it was cold with light rain and winds maybe even over 25 mph. It was really annoying.

RC 8 years, 3 months ago

Yeah, we're supposed to be getting some high winds out of this too, but I haven't really seen anything yet. It's still early, though.

The snow is here! My current measurement is at 1 5/8 inches of accumulation, though I'm measuring 2 inches of snow depth in places. I'm not really sure why as the snow should be compacting due to how wet it is and giving off a lesser value snow depth, but I guess the sleet from earlier today could be playing a role in the greater snow depth than measured accumulation.

NAM and GFS are both showing between 4 and 5 inches of accumulation at 7:1, though the high-res NAM 4k visualization is showing around 10 1/2 inches. I still think that's way too high. Let's take a look at the Canadian model.

We're using precipitation data instead of snow totals as the snow totals image uses a 10:1 ratio. We need 7:1 or so for what we're doing. My area is in the 1-1.25 inch zone, so that means 7 to 9 inches of total snow accumulation at the 7:1 ratio. Of course, I can't see what the Euro has to say, so I'm going to disregard that.

The National Weather Service has put up a Blizzard Warning to my immediate north and also upped the expected accumulations to 8 to 12 inches for my county. I guess I might be missing some important factors, but based on the current conditions outside and all of the data I see before me, I cannot get myself to believe we're going to get that much snow.

I'm going to be making my final prediction as the system's already here, so here it is: 4 to 7 inches of accumulation. If I had to give an exact number, I'd say 5.25 inches of accumulation. I don't like going against the media or National Weather Service as I'm sure they know more than me, but hey… it's a learning experience either way, right?

aeron 8 years, 3 months ago

Quote:

Becoming a weatherman is too much work. I'm mainly suited to be an armchair meteorologist who posts on the internet and acts like I know what I'm talking about.

This is how I feel about all of my hobbies �

Omega_Squid 8 years, 3 months ago

It uhh, It rained a lot and made my day in the field miserable.

MAKE IT STOP

PLEASE MR. TROUT.