MWN Blog: Early look at potential weather trends for the eclipse

The BACKGROUND

If you are a longtime follower of this site/blog and our content in general, you know I'm not real keen on looking beyond a week out in our forecast, especially when details unresolvable several days out could end up producing wild swings in the resulting weather. For instance: pinpoint temperatures that could mean the difference between rain, snow, or ice. Or temperatures, dewpoints, magnitude of the wind, and cloud cover that could mean the difference between severe storms and rain showers. All of these details can make a big difference in forecasts beyond 3-4 days, let alone a week.

However, trends in the overall meteorological pattern are a little different. While specific timing or forecast details may not be discernible, a colder/warmer or wetter/drier pattern CAN be discerned out to a week or more. So I may not be able to say WHEN on day 6 or 7 an upper level trough will drive a cold front through the Mid-South. But I could say if there is some overall model agreement on the pattern and can probably tell you that we'll see a cool-down, or a wetter than average pattern, a week or more out.

All that said, we have a MAJOR astronomical event occurring about 10 days from now that I know you are all aware of, and many of you (like me) are greatly anticipating! A total eclipse, like that which that will cross the state of Arkansas and block out 97% of the sun here in Memphis for a couple of minutes on April 8, will not occur again for another 21 years. And far be it from me to withhold information for such an event once we start to creep into the "forecast-able period" of said event.

The DISCLAIMER

Information presented here, on March 28, is provided as a very early look at the possibilities, or trends, and includes NO guarantees. Do not change any plans you have based upon information presented. Do not tell me on April 9 how good/bad my "forecast" was on March 28 (believe me, I will be well aware!). Do not sue me. Do not TP my house. And do not call me or my family bad names. This is NOT a forecast - it is general "trend" information. It is presented vaguely on purpose, because anyone who will tell you on March 28 exactly what will happen at 2pm on April 8 is lying. I present the trends, because there is agreement amongst our various computer model sources on those trends - but certainly not the details. Moving on...

The OUTLOOK

To get to April 8, we start with the general trends leading up to it.

The next several days will be influenced by building high pressure aloft and surface high pressure sliding to our east. That means dry weather and warming temperatures with increasing southerly breezes. That trend continues through the weekend. By early next week, models are in concurrence that low pressure will form in the Plains and move by to our north on Monday/Tuesday with an upper level trough advancing from the southwest U.S. This will lead to a generally wet and possibly stormy pattern to start next week. (Without diving into too many details, because we're 4-5 days out, the most likely severe weather threat appears to be to our west and north Monday and then to our southeast Tuesday.)

Behind that system, high pressure builds back in for the latter half of next week and into the weekend. Then (are you sensing a pattern?), by the weekend of April 6-7, long-range models generally concur on upper level troughing (low pressure) forming in the Plains again. With surface high pressure to our east, southerly flow sets up over the Mid-South by the 8th. This pattern typically results in building cloud cover and increasing rain chances. BOOOOO!!!!! 👎

Comparisons of the mid and surface level pattern on April 8 from the European and GFS (American) ensembles show fairly remarkable agreement on the overall pattern for an 11-day forecast. (WeatherBell)

Below, I have placed graphs from three of the major global model ensembles - the European, American (GFS), and Canadian. Ensembles basically are iterations of the model, run many times with slightly different parameters and schemes, to provide a range of potential outcomes. They are the BEST way to look at long-range trends. The models themselves can change multiple times a day. An ensemble effectively averages out all of those different possibilities. The averages, or oftentimes probabilities, of a particular scenario give us a much better idea of the range of possible outcomes than a single model does.

I've chosen to show precipitation in 6-hour increments, since if the model shows rain falling, that would also mean some amount of cloud cover - which ultimately is the forecast element we most care about for an eclipse! Each of the three model ensembles are shown below. Each ensemble is run four times a day, and those "runs" are stacked horizontally (oldest on top, most recent at the bottom) with time going out into the future from left to right and precipitation amounts shown in dark grey to green boxes for each 6-hour time increment.

On each graph, I have boxed April 8 in red. There is one thing that stands out to me immediately when looking inside those red boxes (and either side of the box to see what might happen before and after the 8th). Each model ensemble, and each of the previous several times that ensemble has run (going back at least a few days), shows precipitation occurring on April 8 in Memphis. Essentially, what is shown is the culmination of hundreds of runs of the three models over the past 3-5 days. And each of those averages has rain falling in Memphis on April 8.

The RECAP

Now, before we break all the guidelines and disclaimers mentioned above and cancel all our plans, it is still many days before the eclipse happens. A "pattern" is NOT a "forecast!" There is not enough detail in this outlook to make any rash decisions. All we really need is partly cloudy skies for a few minutes on April 8 (preferably around 2pm) to see a pretty amazing astronomical spectacle. I'll continue to watch the trends, and as we get within a week, our daily forecast found on our website or app will reflect the latest information.

A final p.s.: For those that spent a bunch of money on a place to stay in Arkansas to see totality... I looked at this same data for Little Rock and there was almost no difference. They are in the same pattern we are according to the data. It is also too far out to define the details that could make a difference between here and there. Keep those reservations (I am!) and go chase the eclipse! If the sun doesn't shine, hopefully you still have had a nice day or two away from the daily grind.

Erik Proseus
MWN Meteorologist

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