Updated Below (most recent 5:00am Thursday)
Good Wednesday morning to one and all...
This post builds on yesterday's, as a lot of the models are continuing with the same themes of warmth and approaching rain. However, there are a few things to point out beyond what was said yesterday...
1. That whole 'dirty' high pressure thought is getting more traction... expect periods of clouds today...
|NAM - Wind-field - Wednesday Afternoon||NAM - Cloud Cover - Wednesday Afternoon||NAM - Surface Map - Wednesday Afternoon|
The winds pick up from the south and west across the Ohio Valley, capable of generating those above normal temperatures but also capturing a bigger chunk of cloud cover from the storm brewing in the southern Mississippi Valley. It's not a big deal or anything, just if you notice the shade from above at times today, remember that the forecast wasn't for all-day sunshine ;-) As far as actual showers today, I would expect them to be few and far between, with most of the rain reserved for later in the week.
2. The timing still looks good, but add another storm to the conga-line...
|GFS - Surface Map - Thursday PM||GFS - Surface Map - Sunday AM||GFS - Surface Map - Monday PM|
The way this works, is that there's an elongated zone of unsettled weather that channels moisture and warmth in a line virtually parallel to the Appalachian mountains but offset to the west a bit. This region then becomes the primary highway for low-pressure systems to travel northward, and will continue the conveyor belt until the last storm in the chain is strong enough to push the whole mess across the mountains. In our case, this record just keeps repeating and repeating, continuing our risk of showers and well-above-normal temperatures right into next week. Fortunately, as we discussed yesterday, the bulk of the heavy rain (and the risk for thunder) will stay off to our west, but figure on things getting pretty soggy anyhow even if the threat for river flooding ends up being on the low-side, particularly in West Virginia.
-----<tangent> Reading A Commonly Used Weather Map -----
I was inspired by a commenter to try my hand at working more of the basics into a blog post here or there, particularly when the meat of the forecast lies well beyond the here and now. I may do a bunch of these over time, so feel free to make suggestions so that I can help where I can.
I know a lot of folks flock to the blog because they want more information about an upcoming (winter) event ;-), more than just the for-everyone presentation provided on-air, or the slightly more technical discussion always available at www.wsaz.com/weather . I know a lot of blog-watchers are weather-fanatics, completely follow what's going on here, and even offer their own takes on future model runs and snowfall forecasts ;-) That's great. However, I've also found there are people that simply have a thirst for information-- and feel just out of arm's reach of what's going on in the blog despite their passion for the weather. I want to speak to these folks when I can too. So here goes.
Today's foray into this is a little ironic, because I want to break down a map I use commonly, but didn't in this post :) Oops. Might as well break it out now. It is the surface maps provided by HPC. Here's today's map:
|HPC - Surface Map - Wednesday|
There is a bunch going on here, and some of these things you already know to be sure...but let's break down some elements that are important because they show up all the time.
1. Highs and Lows - This is all about air pressure. Just like a topography map (here's one of Huntington High School):
Perhaps some of you are more familiar with these (or maybe not). Anyway, just like our land has high spots and low spots when it comes to elevation, so too does our atmosphere have areas of high air pressure and low air pressure. The most glaring difference is that air pressure changes and moves all over the place in a given week-- so we have to track it. High Pressure, depicted by the "H" on the map, is typically associated with sinking air, less clouds, and more Sun. Low Pressure, the center of which is shown by the "L" on the map, indicates rising air, cloud formation, and the best spots for precipitation. So in a nutshell, if you see an "H" coming closer, the weather most likely will turn sunnier, while the "L" is going to bring rain.
2. Isobars - keeping with the topography analogy, on the map of Huntington above, you can see lines that mark a certain height, say, 800 feet. Lines inside that contour are higher, while outside are lower. It works the same way with air pressure.
On this map, the faded gray lines represent these lines of equal pressure, or "isobars". Notice how they envelope the "L" to represent the "valley" of lowest pressure, while the higher numbers represent contours of higher pressure farther away from the center. The unit of measurement in this picture is "milibars" or "mb". This is the standard scientific measurement for air pressure that differs from the "inches of mercury" found on most American barometers. It's like feet vs. meters, the math always works out better and easier when using the standard scientific measurements. If you have the opportunity to get a barometer that has milibars as a measure, get it :-)
3. Wind-flow around Isobars - The neat thing about isobars is that they can tell you the general wind direction as well. The reason for this involves a bunch of math/physics, so I'll spare you the details of that. Here's the 'skip-to-the-end' version:
Wind will flow along these isobar lines in whatever direction necessary to keep lower pressure to the LEFT and higher pressure to the RIGHT.
|Wind Flow (example 1)||Wind Flow (example 2)|
Here are two examples from the above map with the wind arrows drawn in (the first one is just a blow-up of the previous image. Notice with each example, low pressure is kept to the LEFT and high pressure is kept to the RIGHT.
When meteorologists talk about the wind direction, we always discuss the direction FROM WHICH the wind is blowing. Thus, a "south" wind is coming toward us from the south, while a "north" wind is coming toward us from the north. The reason why it's important to do it this way is because the wind will be bringing the weather from its source region to our area (we call this "advection"). Thus, a "north" wind is usually a colder wind, and a "south" wind is a warmer one. It makes much more sense that way.
There are other things we can talk about on this map, like the fronts and the precipitation symbols, and I would be glad to do so if there's interest. Also, if anyone wants more explanation put to other maps we talk about, we can do that as well on a similarly quiet day. I may just do it anyway, but I do like reader-participation.
----- </End Tangent> -----
Update (5:30pm) - Well, as some folks have observed in relation to point #1 of this post, the "dirtiness" of this area of high pressure was quite underdone. At least I had some company with the National Weather Service (no offense to any NWS followers here, just trying to be less depressed)...
Anyway, so here's what happened...
I'm going to discuss this using the HPC image from above that looked at yesterday.
|HPC - Surface Map - Wednesday|
Armed with our newfound understanding of how wind flows along isobars and highs and lows, the rectangle indicated a bit of a "no-man's land" where currents were pretty weak. Remember, the tighter the isobars are, the faster the wind is moving. In this case BOTH isobars were 1024mb, indicating just the slightest of a high pressure ridge in there (really not much of anything), but more importantly, no good steering winds. You would figure that in order to channel the Gulf moisture all the way up our way, or bring down the Lake moisture from the north, better ingredients needed to be present (at least that was my thinking). In reality however, there was juuust enough interaction between the Low in the Great Lakes and the Low in the Gulf to create a deformation zone between the two of them that allowed the moisture to fill from both top and bottom-- but only right at the tri-state.
|Surface Station Plot / Radar - Late Tuesday||Surface Station Plot / Radar - Midday Wednesday||Surface Station Plot / Radar - Now (Wednesday Evening)
Click on any of the above images for a larger pop-out... But, you may not need to since the only thing I want you to stare at are the radar imagery in green and the locations of the H's and L's. You should be able to see that a weak area of high pressure initially kept these two systems separate, but the northern Low was just strong enough to extend downward from the lakes a little more, and managed to capture some of the northward moving moisture flow from the low down in Texas. Just a piece broke off and sailed up through the Ohio Valley, but obviously it was enough to dreary up our day. Then, once the mountains had their say, the connection between the two systems was broken, and the moisture once again retreated to their corners.
I hope this doesn't become an issue in the coming days as well, because we'll be teased and flirted with by these showers each of the next seven days. Yes, each day to come will have at least some measure of rainfall opportunity. Spots farthest west of the mountains have the best shot at the bigger rains. Places in the Kanawha valley (Charleston area) may well get but a fraction of the rain others get, so be prepared for a diversity of weather experience across the tri-state.
...Except for the warmth of course :-)
Update (5:00am) - The uninvited rain from yesterday is causing further complications this morning-- namely very thick fog. Be VERY careful this morning as you head out to work. Here are some maps to track the fog.
|GOES-13 Fog Product (Experimental)||GOES-13 Fog Depth Estimate|
The biggest threat areas are places where the temperatures are dipping below freezing in the fog. Fog in sub-freezing temperatures can actually create an icy glaze on the roadways and walkways, made even more invisible by the fog itself. In January, the Sun angle is quite low still, so it takes longer into the day before it can successfully chip away at the fog. We may be stuck with it right through the morning drive.
|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!