Hello Wednesday... Middle of the week, and a little activity on the maps to digest.
This particular blog post is going to be a little heavy on the imagery, so please bear with me. I'll also try to separate the really wonky weather-geek stuff from the general extra information that various folks may be interested in (I'd like to cater to all comers).
The first thing I want to talk about is the approaching cold front that has been in our discussion for the past several days. In particular, the early afternoon time-frame:
|HPC Analysis - 2pm Weds|
This map is of the Ohio River valley right in the afternoon today. It shows a cold front (in the blue) and a warm front (in the red). The warm front is already past us, so the wind flow will be encouraging warm, moist air to arrive from the south. This is a naturally de-stabilizing force for the atmosphere (explained in a bit more detail in the upcoming wonky section). The cold front is going to slice into the area and provide the main firing line for showers and storms. Notice how there is a little region right along the Ohio River where enhanced rainfall/storms are suggested. Basically, the idea is that a squall line is going to form along this front as it sags through our area, with a thin "window of opportunity" for these storms to turn severe open at the same time. Now, at the outset, it appears that downpours, gusty winds, and larger-than-pea-sized hail are the main threats, with tornadoes being not as likely. Here's what the simulated radar shows for the area around the same time:
|ARW 4km Simulated Radar - 3pm Wednesday|
It doesn't look like much, but the idea is that we have to watch things in case a storm or two decide to pack a punch because of the eclipse of several elements that phase right here in our area, whereas everywhere else there's just something missing.
The Storm Prediction Center is characterizing the area as a 'slight risk' for severe weather, which puts it ahead of most random areas as a place to keep an eye on.
---Wonky Weather-Geek Section--- (skip over if uninterested)
Okay, hopefully I don't overload this too much, but feel free to ask questions in the comments section and I'll try to clarify as best as I can :-)
I'm going to post a series of graphics and model data that will help hone in on exactly what is the cause for concern about this particular line of storms. Before I do so, I want to let you know that this sort of thing happens often in the summertime, so I'm not doing this because of some ungodly outbreak event that will rival what we've already seen this year. There have been many Severe Thunderstorms over the last several weeks, some that come and gone without many lasting impacts. Nevertheless, it is a duty of ours to track these storms and investigate/anticipate their intensities. I debated listing these maps individually, but I think it might a 'little' more clear if I post them all at once so you can examine them more easily in relation to each other. I'll throw them up here and then explain them afterwards: (click for larger view)
|NAM - Lifted Index - 2pm Weds||NAM - CAPE - 2pm Weds
||NAM - Wind Shear - 2pm Weds
So we'll take the maps from left-to-right...These are all from the NAM Model
"Lifted Index" - We've talked about this one before, but it refers to the temperature difference between two different altitude levels (in celsius). If you think about a hot-air balloon, the air in the balloon needs to be hotter than its surroundings in order for it to lift higher. If the air arround it keeps getting colder, and the balloon stays warm, then the balloon will accelerate upward. This sort of mechanism is at work on a "lifted Index" map. The greater the difference (measured in negative numbers because the upper level air must be increasingly colder than the lower level in order for the acceleration to occur), the more unstable the atmosphere is. Currently on the model, we see a good chunk of unstable air from central Kentucky through to West Virginia and southern Ohio.
"CAPE" - Stands for Convective Available Potential Energy. This is just a big phrase for storm juice. This number is measured in joules per kilogram of air (not important). Suffice it to say the higher the number, the juicier the air is for stronger storm development. On any given day, there is often very juicy air for storm development in "tornado alley" and the gulf coast, but there will be a 'trigger mechanism' lacking in the equation such that nothing happens. Picture the best dry kindling available locked up in a safe where no one can use it. It's still good kindling, but nothing's going to happen. In our area, there is a decent nose of CAPE nudging in this afternoon (anything over 1000-1500 J/kg is good for our area), and if you recall the arrival of the cold front as depicted on the earlier map from HPC, you have your trigger.
"Wind Shear" - This is another important map, particularly when investigating the potential for severe thunderstorms. When you've got unstable air with a lot of juice, the amount of wind-shear in the atmosphere overhead can change a garden-variety event into something more dire. When we talk about shear, what is happening is that the winds in the upper level of the atmosphere are moving much faster than the air below it. This creates swirls and eddies in the wind pattern (think about what happens when you are canoeing and you toss an oar into the water and move it much faster than the river current-- you get those little swirlies to form in the water; that is the effect of 'shear'). On the above map, the shear that is present is modest, but there. The concern with this kind of shear is that it will take the faster wind at the higher level of the atmosphere and spin it down to the surface, resulting in some pretty gusty winds. The National Weather Service qualifier for 'severe' weather when only counting winds are gusts to 57mph (which is quite the gust), but it can happen. If the shear was much higher than what we see there, then it's an even more dangerous scenario, because it can create wholesale circulations in the atmosphere itself right within a thunderstorm, and that can lead to tornadoes. As a point of reference, the March 2nd outbreak of this year had wind shear values over 65kts, which is exponentially more difficult to get to than the 30-40kt variety we're looking at on these models.
It bears repeating: with any one of these variables, it can look like there are other spots in the country that are featuring much more extreme values, but it's actually the combination of all of them (where they are all occurring over the same place) that is where the storms are going to happen. This is what meteorologists look for. Add to that the expectation that there will be a decent 'trigger' mechanism present as well. This could be as simple as the lift created by general wind-flow forced up a mountain range (which is why they often get more rain/snow than the rest of us), but in this case, it will be that slowly sagging cold front that we'll be watching. The way the models are advertising this, I would watch this front slowly sag southward with barely anything to show for it, then fairly quickly in the afternoon it will hit this combination of elements waiting around overhead, and we should kick up some storms, and possibly track some severe weather.
---End Wonky Weather Section---
Severe thunderstorms are always more a place of concern rather than fun for the folks that are directly experiencing them, so the hope is that one way or another things fizzle instead of spark. This can happen several different ways (by taking out a piece to the puzzle for example), but usually when the models are putting forth a multi-variabled description of the atmosphere in this way, there are at least some fireworks to be had. With that, y'all get a full slate of tracking tools today, and I will post updates if necessary and if time permits :-)
Update 10:00am - The Storm Prediction Center is updating their products, continuing the indications that this approaching severe weather threat will be more of a damaging wind/hail thing compared to seeing possible tornadoes:
|SPC - Hail Threat||SPC - Wind Threat||SPC - Tornado Threat|
Keep in mind that even though these percentage numbers you'll see on these maps are small, they represent the probability of such an event can occur within a 25 mile radius of any particular point. When you get up around a 15% probability, considering there is a large area that we cover, the chances of seeing such an event becomes much greater when the whole area is taken into account.
Update 3:30pm - The National Weather Service (a little while ago) issued a Severe Thunderstorm Watch for our area until 9pm. It should be noted that with this line of storms most folks will really only get one or two storms in a single time-frame within this watch period, with breezy but quieter skies on either side of it. Nevertheless, folks that are thinking of heading outdoors at this time should only do so with a firm look at the radar before doing so. You don't want to get caught out in this stuff (like out on the golf course). The boomers will be on the I-64 corridor soon, and the storms may still strengthen a bit before they get here. Again, the main threats with this system continue to be the potential for gusty winds and hail larger than 1" in diameter. Pay attention to WSAZ for all warnings that may be broadcast (you should also be able to see them on our updating warnings and doppler maps below).
Update 4:30pm - The storms are oriented in a singular line, and are assuming the form of a row of individual cells:
In this environment, it's 'possible' that some folks somehow thread the needle and miss some of the 'big' stuff, while others will actually get hit by a 1-2 punch of storms...But I still think everyone's going to get a piece of this (hear thunder, see lightning, get a downpour, etc.)
Update 5:30pm - The storms have now made it (mostly) south of I-64, and skies will be improving in Ohio and interior WV. Temperatures in the storms were noted to drop into the lower 60s, while other areas stayed in the upper 70s. Soon we'll be able to turn to "rainbow watch". I can explain this concept in a future blog post perhaps, but suffice it to say that some folks should be able to catch some as the day comes to a close. The environment in the southern part of the area remains very unstable, and the opportunity for strong/severe storms remains (again, hail/winds the main issue).
|Regional Radar/Satellite with Warnings Tracking||
From the Storm Prediction Center (below): Click For a Larger Image
|Activity Overview||Storm Outlook||Watches||Potential Watches||Storm Reports|
|Temperatures||HD Doppler Radar||Estimated Rainfall||Active Warnings|
|Click For Larger||Click For Interactive Radar||Click For Larger||Click For Larger|
Have a great day everyone!