2017 Eclipse Weather Forecast (updated 17 Aug)

(Please see my earlier post for an introduction to what/why I am forecasting for this.  Also remember I am focusing on Indiana and the portion of the totality from central NE to central TN.)

As we get closer to the eclipse, forecast confidence increases as the details become clearer.  We’re just outside the reach of the short range models, and their additional data will really help.  This post will focus on some things to look for.

First, let’s revisit the Weather Prediction Center to see their map.

WPC forecast for Monday.

Not much change from a few days ago.  Conditions still look good in the Northeast and upper Midwest; iffy from Nebraska to South Carolina.  Consistency in forecasts = greater confidence.  But, there is still a front hanging around the area of the totality.  Humidity levels in August are high and that makes it easy to create clouds / showers / storms.

To forecast clouds, look at a map of relative humidity at 2 miles above ground (700 mb for you weather geeks).  Most clouds thick enough to block the sun pass through this level.  Thus, high relative humidity = cloud cover (and maybe rain).  Low relative humidity may show clear skies, but here could be fog/very low clouds, so more information is needed.  (There could also be cirrus clouds, but these are less problematic.)  Here is a forecast from the GFS model (via Penn State E-wall).

Forecasted relative humidity at 2 PM EDT August 21. Green colors indicate cloudy areas, while tan/orange colors indicate areas where skies may be sunny.

Skies in the West look good, though remember that this map doesn’t show fog/low stratus.  The Northeast and Midwest are generally clear, though we see clouds are forecasted now for MN/WI/MI.  Along the totality, clouds are a potential problem in eastern Nebraska, eastern Kansas, and western Missouri.  Many other areas along the totality have relative humidities in the 30-70% range, which probably indicates scattered clouds.

Areas where the model things precipitation will fall from 2 PM to 8 PM EDT on August 21.

The precipitation map above shows where the model thinks precipitation will fall from 2 PM to 8 PM EDT on Monday.  This is vague.  It may rain for 30 minutes or 6 hours; it may rain at 2 PM or 7 PM; but areas in white are forecasted to remain dry.  Take away points:

  • Eastern NE is likely cloudy but dry during the eclipse since no accumulation is shown.
  • Northeastern KS and western MO will likely experience clouds and rain.  Since precipitation typically moves west to east, rain is more likely closer to 2 PM EDT.
  • Clouds may be starting to build or arrive in Eastern MO/southern IL during the eclipse, but they may be OK.  (Precip. probably occurs closer to 8 PM EDT.)
  • KY/TN/SC may have clouds, but since they are not getting rain, the clouds may be too small to cause widespread problems for eclipse viewing.
  • IMPORTANT: Again, this is all preliminary.  Do not change travel plans until the weekend!

Based on these maps and previous forecasts, if you are planning to travel to Missouri to see the eclipse, you might need to have alternate plans.  Folks in Kansas and Nebraska will probably need to head west.  Kentucky and Tennessee may be OK.  I am surprised by the dry forecast for South Carolina — we’ll see about that.  And finally, if you are watching in Indiana, things still look good!

1 Comment

  1. We ended up going to southern Kentucky. There were high clouds and it was humid, but no low clouds so things worked out well.

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