WSAZ - Blogs - Brandon Butcher

Is 80° In Range?

Skipping March, and perhaps even April this week with all the warmth in town. Model comparisons, output statistics, and some tracking tools :-)

Welcome to your Tuesday.

I hope you're ready for some warmth, because it's going to be sticking around for a while. One question of the forecast is whether those showers will also hang around with us. We looked at this last week, and it's a good thing to do when trying to parse the weather in 'not strong' environments (it's sometimes easier to forecast when there are huge storm systems roaming the country, rather than a morass of 'maybes' running around). So, here's a comparison chart of the different models showing their 'vorticity' (relative rotational energy) and 'precipitation' solutions for the early afternoon hours today:

NAM - Vorticity - 2pm Tuesday CMC - Vorticity - 2pm Tuesday GFS - Vorticity - 2pm Tuesday
NAM - Precip - 2pm Tuesday CMC - Precip - 2pm Tuesday GFS - Precip - 2pm Tuesday

Okay, if I've confused any of you, feel free to stop me. The top row shows the vorticity, and the bottom row indicates modeled precipitation for the 6-hour time frame that ends at 2pm today. What I wanted to show you is what I've drawn in yellow on each of the vorticity maps. This shows couplets of 'positive' vorticity (more associated with clouds/storms) and 'negative' vorticity. These are called 'shortwaves' as opposed to 'longwaves' that would represent actual coldfronts and warm fronts. Sometimes a shortwave will actually cause a slight kink in the pressure pattern to let you know they are there (the solid black lines in the images), but in the summer time most often you're just tracking these wandering disturbances of vorticity all over the place. They're small, they're fickle, and they're often represented differently across different models (as they are here too). You can see how they are triggering precipitation in different places, with the GFS being the weakest in its vorticity field (making it difficult to be sure of anything popping up). The NAM and the CMC look a little more tidy, but something else we talked about can screw up the modeled representation when it comes time for verification: grid-space resolution. These models all have their own resolutions and terrain schemes, and the precipitation representations are smoothed across that space (and integrated across 6-hours of time). It's great for a general will-it-or-wont-it when it comes to rain, but during close-in situations like this, more powerful models with a tighter resolution but smaller forecast range can help settle the score. This is what the high-resolution 4km simulated radar is showing for the same time-frame:

NAM 4Km SimRadar - 1pm Tuesday

Admittedly, this output is modeled after the NAM physics and initialization, but right away you can see the differences that higher resolution grid-space and terrain can have on more deterministic accuracy (whether it comes true or not can be another story, but it's certainly not looking wishy-washy). Anyway, this imagery creates a picture that I'm happier with: the idea of clusters of patchy rain showers sweeping through the northern counties around lunchtime into early afternoon. This sort of thing is at-best hinted at in the other models, but now seems to have more of a consensus look to it. We'll have to watch and see if those showers actually do pop up-- and keep in mind that there also appears to be plenty of opportunity to slide in some sunshine at times, which will do wonders to get those temperatures up (as we talked about last week). I have my doubts that these showers can actually slide down far enough to make an imprint locally, but do see this trailing cold front idea playing out to our north.

And about those temperatures... There are many different ways that meteorologists attempt to forecast what those high temperatures will actually be, and usually what they pursue depends on time and availability (often a whole mess of them will be looked at to try to get the best assessment). This is the easiest method that involves the least amount of initial forecasting: The "consensus" method. Simply put, a forecaster will simply try to find as many different forecasts that exist out there and average them all together to get the most representative 'consensus' number. This doesn't necessarily work in all cases (naturally), but over the long-haul a 'consensus' forecast will turn out to be very good at keeping you in the ball-park. So, what participates in a 'consensus' forecast that's readily available? Well, all the models we've been discussing all produce a product that is called "model output statistics" where the model is programmed to stop at various intervals and spit out various numbers for meteorologists to inspect and analyze. Sometimes they can be crazy weird, but most often they just reflect the same things as the images above except in digital form. Here are some model outputs for Today/Tomorrow's high temperatures:

Tuesday's High 76 77 77 78 73
Wednesday's High 76 78 78 77 76

 This would yield a 'consensus' forecast for Tuesday's High of 76°, and a high on Wednesday of 77°. Now, this will understandably get you in the ballpark, but will do so without any sort of explanatory power (how would you describe 'why' the temperatures would be where they are). Also, it's possible that the 'consensus' view is incorrect. Notice how the National Weather Service is seeing something for tomorrow that all the models aren't describing (perhaps a reduced high temperature in response to lingering cloud cover from these nearby showers). The other thing to keep in mind is that we cover a HUGE area at WSAZ, so one number is never going to be correct. Often in the mornings there is as much as a 20-degree difference from one area to the next.

Okay, that's enough for now :-) Enjoy your temperatures in the 70s. Don't look now, but there actually is a model outputting a high of 80° on Thursday, but 'consensus' is still staying in the upper 70s. The threat of severe weather is not pronounced today, so I'm wondering if y'all can get by with a diminished but appropriate amount of tracking tools today. I can certainly update things if necessary.

Regional Radar/Satellite with Warnings Tracking

Accuweather Radar


Temperatures HD Doppler Radar Estimated Rainfall Active Warnings
Current Temperatures HD Doppler Radar Estimated Rainfall Active NWS Warnings
Click For Larger Click For Interactive Radar Click For Larger Click For Larger

Have a great day everyone!



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