WWU080 - Severe Weather Friday (1/9)

Weather Weenie
Jan 8
4 min read

Good evening Weenies.

I'm not terribly impressed with tomorrow's setup.

Which I guess is probably a good thing.

WWU080

Tornado Season is November-May

Just a Reminder.

Weenies, I was so busy today I barely had time to be a Weenie.

I do know that there were a handful of tornado warnings further West.

I'm not anticipating too much of that for us. Here is the most updated graphic from NWS Birmingham. Another mostly daytime event! Hurray!

Let's look at the Storm Prediction Center: First the categorical outlook, Level 2/5 risk for us.

But why? It's not really tornadoes this time.

If we look at the tornado outlook, the highest risk is certainly close to us.

But based on the latest models, I wouldn't be surprised if it was shifted further away from us.

What I'm more worried about tomorrow is a gusty wind threat.

Which if you remember last summer's storms, they sure did a number on our area in particular.

Not to mention the excessive rain tomorrow.

oooooooo new tool!

This is the precipitation forecast for the next 72 hours, cumulatively.

Turn around, don't drown, folks.

Let's Break it Down

So why am I not impressed?

It seems, to my simple weenieocrity, that things just won't line up well enough to cause problems.

If we look at the predicted supercell development from the 00z HRRR (the most angry model), it's um... underwhelming.

Which I have to tell myself is a good thing.

Yeah, nah. But what about the rain and wind?

First let's cover the rain. Lots of green, lots of rain. For quite a while. That one is easy.

How about the wind though? How can we see that from the reflectivity?

If you watch the first few images of the gif, you can see a distinct line form.

(Also called a QLCS - I'll give a cookie to whoever sends me what that is an acronym for)

(Two cookies if you don't look it up)

The line is the leading edge of the front that will be producing the storms tomorrow.

Therefore, front=sudden strong winds from a new direction.

This is an issue if we have lots of rain and lots of wind.

Trees don't like to hold on to squishy ground in strong wind.

So there you go, stay aware tomorrow, certainly, but I also won't be putting the cool magnets on my car either.

That's quickly becoming my equivalent to the weatherman removing his coat.

Not sure how I feel about that.

Wanna see something cool I learned?

WEENIEINGS

Warning - this may be a particularily nerdy Weenings section.

As if this entire report isn't bad enough.

BUCKLE IN WEENIES.

First, here is my cool new tool. A single source for the daily state-wide graphics.

Ok now here is the painful part.

I want to dive into the use case for each model. I've alluded to the uses for years now, and I hope at least a few of you have caught on to which ones I use when.

There is so much more to this than my madness for this topic.

There's science!

And math!

Wahoo!

If we cover the main ones, we have:

GFS
ECMWF (aka: Euro)
NAM (3km and 12km)
HRRR

Yeehaw! Let's go!

The GFS (Global Forecast System) and ECMWF (European Centre for Medium-Range Weather Forecasts) are the global models. These are best used for predictions 3-10 days out. The GFS goes up to 16 days out, with grid spacing of 13km (more on that later). The ECMWF goes up to about 10 days out, with a grid spacing of about 9km.

Notice that I said starting at Day 3. These models are pretty rough to use as 'day of' forecasting, primarily because of the grid spacing. You may have noticed that the rain forecast days out is bigger and blobbier. That's for two reasons. First, it's just really far away in weather time so they calculate it safer. Second, again, grid spacing.

Grid spacing - the size of the chunk the model is predicting.

Long range, global models simply use far more processing. It is easier to forecast for 12km chunks around the world than 3km chunks around the world. There are 4x more if we calculate 3km chunks. That is a whole lot of processing power put toward something that will still be so very wrong. But big chunks work really well for large scale, synoptic forecasting.

Quick note before you Google it, (12km~7.5 miles, 3km=1.8 miles).

Hopefully I haven't lost you. This is cool stuff. So why are the HRRR and NAM used?

The HRRR (High-Resolution Rapid Refresh) and NAM (North American Mesoscale Model) both use 3km grid spacing. Which means they can be much more specific. These allow storms (Convection allowing) because a storm literally fits within a 3km square. It is able to calculate it. Isn't that neat?

Since these take up a lot more processing juice, they are only calculated up to about 3 days out, but they're remarkably useful in that Day 1-Day 2 timeframe.

I also mentioned that the NAM has a 3km and 12 km version. Yes, same model parameters, but differing grid spacing. Makes for interesting comparisons.

Is one model always better than another? No.

Models are intended to be used all together since they each have known strengths and weaknesses. Often new models are created to compensate for faults of other models.

They all matter and complement each other. They can really only be fully understood in the context of one another.

I hope at least one of you found this as interesting as I did.

Be safe and stay Weather Weenie Aware

KR4BZF

I have my resources on a page here - I'm working on adding all of them. The most important ones are already on there - check them out!

During the event make sure you keep tabs on what is going on with your favorite local weatherman.

Whether that's James or Wes. I don't care.

I hope you have enjoyed today's weather weenie update.

Stay Weather Weenie Aware.

Kaila - Weather Weenie - KR4BZF