Missed it by THAT much…

One of the toughest weather issues we deal with as far as the Upstate is concerned is how our temperatures and moisture behave once some cool, damp air slides in from the northeast and gets wedged up against the mountains. This becomes especially critical to our weather forecasts during the winter, as how this cold air lines up can make the difference between all rain and an icy mess across parts of the area. I’ll probably have more on that down the road at some point.

This time of year, the biggest forecast challenge relating to this can be in determining the exact timing of when low clouds will break up…and exactly where the clearing line will end up. The sun is still strong enough this time of year to create a huge temperature difference in areas that see sun versus areas that are stuck in cloud, but the heating may not be strong enough to completely erode the clouds themselves. And a good forecast can go horribly wrong…but only in some parts of the area.

Pictured on this page is a satellite picture taken from 12:15 pm Tuesday, 10/7/08. Prominently displayed is the batch of low clouds stuck over parts of the Upstate and into the North Carolina Piedmont. Also obvious is the clearing over western North Carolina, the southern Upstate to the Midlands, and even into the metro Charlotte area.

With the moisture banking on the southern slopes of the mountains, seeing sunshine in the mountains themselves is expected. And farther away from the mountains, one is farther away from that trapped moisture and cool air. But where will the southern extent of the cloud cover end up? Will the clouds entirely dissipate, and will they do so in time to warm us all up? Will the clearing line make it to a certain point, and then stop? Or will the clouds hang tough…or even spread farther south and west? That’s a lot of questions, and a lot that we have to go over when making a forecast.

Well in this case, the clouds didn’t thin until late, with highs in the lower 70s around Greenville and Spartanburg, with upper 70s around Greenwood and mid 70s in Clemson and Anderson. As far as the temperature forecast went, it was exactly as planned across the area…with the exception of Greenville and Spartanburg where we came up a few degrees short. If clouds thin a bit at 2 pm instead of 4 pm, the temperatures are on target. Shows you how delicate and complicated a temperature forecast can be when we’re dealing with a matter of miles in where the edge of the clouds sits.

That was a relatively “mild” case: I’ve seen situations in which there’s been nearly a ten-degree difference in high temperature between locations relatively close to each other…for example, Anderson and Greenville…simply because Anderson clears out but the sun never makes it to Greenville.

Maybe we should change the saying to “if you don’t like the weather, just travel five miles.”