Updates Below (most recent 12:00pm)
A good Sunday to one and all.
As we talked about yesterday, we've got another heightened severe weather potential coming through today. Let's talk about what the threats are, and then we'll discuss why I'm worried more about something else.
When meteorologists talk of "severe" thunderstorms, the requirements are that they either have (a) wind gusts inside them that are 58mph or greater; (b) hail around 1" in diameter; or (c) a funnel cloud/tornado. So with that in mind, here's some of the data that's important to look at:
1. Surface Support
|HPC - Surface Map - Sunday Afternoon|
In the middle of August, usually we'd be just asking for something, anything related to a cold front moving in. There's not a whole lot of temperature difference between the northern and souther parts of the US, so the fronts get pretty weak. This particular front is better than the last few-- but because the actual area of low pressure bringing it is way up in Canada, the part that will hold together is north of us as well. (I'm expecting a larger threat for severe weather to our north along the front). Down our way, the front has the potential to either wash out or get hung up in the mountains.
2. Upper Air Support
As I've said several times before, every storm system has surface features and upper-air features. Sometimes the upper-air picture drives the forecast much more than the surface fronts.
|NAM - 500mb Chart - Sunday PM||NAM - 500mb Chart - Sunday Evening|
The upper-air energy (denoted by the 'Vorticity' couplets of purple and red) looks great during the afternoon, but is weakening by the evening as it gets a little closer. The situation looks a lot better for severe weather up to the north toward New York state.
3. (Thermo-) Dynamic Support
Connecting the upper air and the surface data would be the thermodynamic support-- what can drive convergence at the surface into billowing storm clouds that have the chops to produce severe weather while also maintaining a high-level of incoming fuel to keep it going.
|NAM - Available Storm Energy - Sunday PM||NAM - Wind Shear - Sunday PM|
Examining the thermodynamic picture of this event makes me come up with a conclusion that there isn't going to be as much going on here in terms of 'severe' weather. We certainly get some marginally severe thunderstorms, but something akin to an outbreak is not likely. The best spots (for severe weather) in our area later today appear to be in our western Ohio/Kentucky zones where we could perhaps catch the phasing of vorticity with the front in the afternoon before things fall apart a little. Up in Canada/New York, there is considerable wind shear there, and combined with the stronger surface-front forcing up that way I would expect that to be your best potential for tornadoes and wind damage over-all.
All that said, I would be putting more of your weather vigilance on a different issue that technically isn't part of the suite of 'severe' weather but impacts us with far more regularity and usually with a larger capacity for devastation-- flash flooding.
|GFS - Precipitable Water - Sunday Afternoon||NAM - Vertical Velocity / Humidity - Sunday Afternoon|
Now this to me looks more intriguing. We've got "precipitable water" values over 2" in our area this afternoon (this is seen on the left-hand map). We also have a solid pulse of vertical velocity (the red contours on the right-hand map), that happens to line up with good humidity levels that stretch into the mid-levels of the atmosphere. Using yesterday's blog post, we see that as far as "precipitable water" values go, anything over 1.8" or so should raise eyebrows.
The National Weather Service has certainly seen this as well, as most of us are under "Flash Flood Watch" alerts today. If you live next to rapid-rising creeks, or areas of poor drainage-- you will be vulnerable today.
Here's the antipicated rainfall forecast today:
|HAS Precipitation Forecast||HPC Precipitation Forecast|
And here's the "Flash Flood Guidance" for selected counties (around what would need to fall in various time intervals to generate flash flooding:
The most vulnerable areas are in Eastern Kentucky and in the southern coal field counties of West Virginia. Be prepared to take action where necessary.
I will update this post today with any new information as time permits. Please feel free to post reports of the weather in your area, and post/e-mail pictures too. Flash flooding events can strike like lightning, and documenting it can sometimes be difficult.
A full suite of tracking maps today...
Update (12:00pm) - The latest severe weather potential breakdowns are now out from the Storm Prediction Center:
|SPC - Hail Threat||SPC - Wind Threat||SPC - Tornado Threat|
Threats are more notable along the Great Lakes in the northern tier of New York. Locally we're not expected to see tornadoes, and only an isolated spot of wind/hail. In any thunderstorm, the biggest threat today will continue to be for flash flooding, but there is at least a little potential for marginal severe weather in terms of wind or hail.
|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!