Joe’s Weather Blog: Weekend storm looks ‘impressive’
I’m taking a couple of days off and will be back on the air on Sunday but with everything happening the blog has to keep going since so many of you rely on it so I may run a bit late with updates.
All eyes are focused on the storm for later Saturday into Sunday and it does look to be impressive…and very complicated. It’s amazing to think about but we have thousands of sensors here on the ground giving us pretty accurate temperature reports every few seconds…minutes…whatever. Think about this though…we have very LITTLE temperature information just a few thousand feet up above us…and with this storm what happens up at 5000′ or so will determine whether we get slammed by snow or sleet or both. A change of 1-2° up there will virtually make the whole forecast. It has to be reiterated…you’re driving along and you look at your car thermometer and it changes a few degrees…no big deal right. Now IF the air aloft changes just a couple of degrees the whole weather aspect of the impeding storm is dramatically different.
So with all that said lets talk about where the storm is and where it’s going. It’s plainly visible across the western part of the country. This is our infrared satellite picture.
I think you can clearly see the spin off the coast of CA. The storm will come ashore on Saturday and will move through the western part of the country Saturday night before moving into and through the Plains on Sunday. You can follow the storms progress by looking at one of our models…the NAM model and going up to about 18,000′ or the 500 mb level. It’s there that the storms track is best seen aloft.
What I’ve noticed over the past 24 hours…and this is not surprising to me is that the storm is stronger looking now on the model data…and that trend may continue over the next 36 hours as the storm makes landfall. This does a couple of things…1) it will allow some “warm” air to lift northwards above the surface. How “warm” this air is will goo all the way to determine if we get all snow…or sleet…or both. The stronger the storm the stronger the warm air moving in aloft…but by the same token the stronger storm will allow more moisture to wrap into it and behind it and that will then fall as snow in the colder air behind the storm and this may be where we end up with most of our significant accumulations of snow.
The loop above is our latest NAM model…the RED colors represent sleet while the blue colors represent snow. For timing purposes 00Z is 6PM (00Z SUN is really 6PM SAT)…06Z is 12AM…12Z is 6AM and 18Z is Noon.
Something else that I noticed today in the model data is that the warm air aloft, while still present is not as warm as what it appeared on the data yesterday. It’s still there but now we’re talking only about 32-34° as opposed to 34-36° like yesterday. This while the air on the ground will be in the single digits, amazing to think about, and I don’t recall seeing anything like that in the past in my 20 years or so in KC.
So how do we see this on the model data? By looking at the forecast soundings. Twice every day the NWS sends up a weather balloon and obtains what’s happening aloft. The information is basic but so important because that is put in to the complex modelling that is run and helps us figure out what is going to happen. From that data…then we try and figure out of the track of the storm is going to be what the model says…if not…for example if it goes farther south…then the “warm” layer aloft is deflected farther south…should the opposite happen then more of the region gets into the “warm” layer aloft meaning lots of sleet for more areas.
Here is the forecast sounding for 6AM Sunday…
Now let’s go forward 12 hours…to 6PM Sunday…
There is a subtle change…the layer of air aloft that was near to above 32° is now colder…that means the flakes no longer melt when they fall and refreeze…now they stay as snowflakes all the way down…unlike earlier in the day when the flakes encountered the warm air aloft and melted…then refroze as they dropped to the ground through the colder air from the surface up to the “warm” layer.
So what can happen with this scenario…should the air aloft be warmer or colder than what is forecast the precip types will alter between more snow accumulations or less accumulations and more snow.
So let’s say everything that falls between the start of the storm Saturday evening into Noon Sunday is sleet or some sort of majority sleet/snow combination…
Then as the “warm” layer disappears everything that falls after that is snow…how much will fall? Model guidance suggests the potential for up to 1-2″ of some sort of sleet/snow mess…then the potential for 2-8″ of snow on the backside of the storm that takes over from Sunday afternoon through Sunday night. So in essence the bulk of our snow accumulations will come from the back side of the storm…and that amount is still the iffiest in terms of how much it will produce.
As a result of all this the NWS has issued a Winter Storm Watch for the region.
A lot can and will change…check in with MB and MT through tomorrow…then I’ll see you 1st thing Sunday morning…