It's Thursday... and that means it's time to see where those storms pop up.
I've got two images in my head that come to mind in this particular weather pattern that are appropriate descriptions of a forecaster's perspective:
Simply put, there's a general circulation pattern, with high pressure below us to the south/southeast. Air flows clockwise around these things, which means the TN/OH Valleys are in a windflow that comes directly in from the Gulf of Mexico:
This map shows what is called "Advection". You don't have to worry about this term too much, it doesn't end up being too technical. "Advection" merely refers to the air overhead changing because the wind is blowing. Think of that steak on the grill, and a gentle breeze blowing such that everyone in the yard is salivating. That is because the aroma of the steak is being 'advected' around the yard by way of the wind. In the same way, warm air can be advected from the southern states up into the Ohio Valley (the yellow arrow depicts the flow of wind). In addition, the wind can also bring up moisture-- and the Gulf of Mexico has plenty.
Now, going with the earlier idea of 'herding cats', where specifically the heat and humidity result in thunderstorms is somewhat of a crap-shoot, which is why a map like this should be taken with a grain of salt:
|HPC - Thurs - Sat Rainfall|
The total precipitation here may indeed end up being correct, but what the map can't tell you is that you can get it all in just 90-minutes or so during the entire period. This means you shouldn't go around canceling all sorts of outdoor plans, but if you are doing something that requires 24-hours straight of guaranteed dry sky (painting a house, curing hay, things like that) this isn't the time for that.
Now, that's not to say that it's completely unknowable, specifically in the near-term, when/where storms will pop up. We do have a small disturbance approaching the area today that should provide the spark that gets a fire going:
|GFS - Vorticity - 8pm Thurs||GFS - Precip - 8pm Thurs|
(Remember 'Vorticity'?) I don't mean to belabor that point, except to show you that you can clearly see how that big red blob on the left image is responsible for the flare-up of precipitation on the right-hand image. This is more useful for the timing rather than the specific location of where all the storms will form. You can see that the potential exists for storms to be popping up just about anywhere. The threat of severe weather with these storms is low at this time, but certainly cannot be ruled out. I would plan on the idea that by Saturday everyone will have had at least one turn with the rains, and thunder should be a part of the mix. But like I said before, most of each day will be partly sunny and warm-- the folks who put in a full 8 hours of work outside shouldn't be canceling business ahead of time. Just keep an eye on the radar, and you should be fine. Speaking about radar, here are some tracking tools to keep you ahead of the game (below). I'll probably jump on here again later today if need-be and update the situation, so do check back when you have time. I'm also tracking a big storm entering the Pacific Northwest that figures to be a game-changer in the weather pattern around here late next week (always good to change things up every once in a while, stagnancy is not all that great).
7am Update - We certainly are off to a fast start with the showers and storms this morning. Frequent lightning, downpours, and small hail have been reported. Hail will be the biggest threat if any storms go severe today, and the reason for this is some deep cold in the middle levels of the atmosphere. If you think of a thunderstorm cloud, it can be pretty big vertically (sometimes as high as several miles high in the sky). Just as there are snow covered mountain peaks year-round, temperatures in the clouds up high are cold enough to be below zero even on the hottest summer day. Well, right now the freezing level is around 10-11,000 feet. It is quite easy to get a thunderstorm cloud to have a significant portion of itself both above and below this line-- perfect for hail formation. A raindrop would get caught in the updraft-downdraft cycle of the thunderstorm, and repeatedly go above and below this freezing line. Each time it goes up and down, a new layer of water freezes...This continues until the hail stone is too big to be kept up in the air, and it will then fall to the ground (at speeds upwards of 100 miles per hour). Conditions will still be ripe for hail formation right through this afternoon because of the cold pool of air aloft.
8am Update - A vertical line of slow (or no) moving storms has put down a radar estimated 1.5"- 2.5" of rain this morning (see the HD Doppler estimated rainfall map below). This is going to put that area in a precarious position for possible street flooding, especially if they get hit again this afternoon. It will be something to watch, but it's a great thing we had so much dry/warm air overhead for a couple days prior to this, or else we could have had even more problems on our hands.
9am Update - The Storm Prediction Center (SPC) has updated their products, and now has sections of our area under a 'slight risk' for severe weather (see the "Activity Overview" image below). These are the same areas that were hit hard by tornadoes on March 2nd, but this time around, tornadoes are NOT anticipated in this environment. This is definitely a breeding ground for hail though. The National Weather Service dictates that any hail 3/4" (penny) in diameter constitutes 'severe' weather. A 57-mph wind gust would also be considered 'severe' in conjunction with a thunderstorm, but those are also not as likely. I would add that we may get some flash flooding issues this afternoon if we see the same type of slow-moving storms appear.
10:30am Update - The National Weather Service has issued a Flash Flood Watch for much of the area through this evening. As we've been discussing, the storms of earlier in the day have set the table for any future storm to cause street flooding. For example, there is currently a Flash Flood Warning for Logan / Lincoln / Boone counties through 11:15am. This flooding has caused some temporary road closures, and more could be expected if we get another round of storms overhead. Pay attention to the Watch/Warning map (below) and the Doppler Estimated Rainfall map. Actually, the whole lot of 'em can be pretty useful :)
12:30pm Update - The National Weather Service has now issued a Flash Flood Warning from Gallia County, OH straight down to Mingo County, WV (see the Warnings image at bottom right)... Speaking about images, check out this picture I got off the Huntington Tower-cam at noon:
This thunderstorm has what is called a 'shelf cloud' developed underneath it. This is a sign of a strong storm. The heavy rain that is falling down in unison can be said to compress the air column beneath it (like what happens to the air when you tip over a piece of plywood-- it rushes forward out ahead of it). This downdraft of air is generating turbulence on the leading edge of the storm, creating this cloud (also associated with 'gust fronts'). The winds are particularly notable with this storm, but the downpours are. There are more storms upstream of this one that are also heading our way (follow it on the radars below). Even though the hail is the main threat of 'severe' weather, flooding is already appearing to be the main issue for today.
2:15pm Update - A Severe Thunderstorm Warning has been issued for the Knott County, KY area until 2:45pm. I won't be able to mention every single warning here in the blog (you can follow all of them below), but I mention this one to underscore that hail is the main severe weather threat today (not tornadoes). Eastern KY remains the most likely spot for the severe storms, while farther into WV is the anticipated zone for the most flooding. If you notice on the temperature map (below), many parts of southeast Kentucky have benefitted from warm sunshine and a lack of heavy rain. This now works against them when thunderstorm energy finally comes their way. The atmosphere above them is more unstable.
4:15pm Update - Even though the current plume of moisture is passing through the area enough to get us a breather, note on radar how the middle of Kentucky, having spent a lot of time in sunshine without the flooding rains, is now filling up with strong thunderstorms and a Severe Thunderstorm Watch. The warmer temperatures will be associated with the best placement of severe weather, but the region that's cooler has spent the most time in downpours (so that's the biggest flooding threat). There are still more things to watch this afternoon.
All of this water now has to flow down their respective basins into the local rivers and streams (the creeks rise and fall quickly, the rivers do so more slowly as all the localized flooding funnels in, and the Ohio River last). Each river has the best potential to flood when the entire basin gets soaked with flooding water (not when a single thunderstorm brings street flooding to only part of an area). Looking at the HD Doppler Rainfall Estimates (below), the river that may need to be watched the most is the Guyandotte. Here's the river gauge in the Branchland area:
|Guyandotte River At Branchland|
Definitely a rapidly rising river at the moment. Actual flood stage is all the way up at 30-feet at this location, so no immediate concern just yet.
7pm Update - Check out the radar, particularly our 'interactive radar' (below). Two storms that are 'Severe Thunderstorms' are heading toward the West Liberty area. These storms are similar to the ones we've had today in that heavy downpours, frequent lightning, and hail are all parts of these storms-- but not tornadoes. Sometimes it has been said that the presence of hail is a harbinger for a nearby tornado, but for this we're really talking about large hail (> golf ball size). So far, nothing like this has been reported with these storms. Any appreciable downpours will definitely exacerbate an already tenuous flash flooding situation. (You can follow the storm reports from SPC below)
|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!