32 days and counting

No rain in sight

After a cold front sweeps offshore tonight, high pressure builds back in with lots of sun and cooler temperatures. Source: National Weather Service

After a cloudy, cooler-than-average day, we’ll have a sunny, cooler-than-average day for your Thursday. Lots of sun but temperatures will only get into the mid-60s as cool high pressure builds in behind yet another dry cold front.

Is it ever going to rain again?

That’s a damned fine question.

Our dry weather streak continues at 32 days barring an unexpected bit of rain before midnight. This is the fourth-driest streak on record, and based on the extended forecast, we should eclipse the third-longest streak of dry weather this weekend.

Record streaks of driest weather. #3 is solidly within reach. Source: National Weather Service, Charleston, SC

It’s raining, but not reaching the ground

An example of some virga from late last month.

It’s not that we’re not getting cold fronts. Quite to the contrary — in fact, we just had one come through tonight. But the moisture return from these is paltry at best — just enough to produce some clouds, with any precipitation turning gaseous before it reaches the surface. I got some reports of virga earlier today, in fact.

Ever wondered what one of these setups looks like to a meteorologist? Read on…

12z (7am for you mortals) sounding from NWS Charleston, SC on November 9 depicting a saturated layer just above a very deep dry air layer. Recipe for virga. Source: Storm Prediction Center

The skew-t chart above does a great job of depicting a typical setup for virga (precipitation that doesn’t reach the ground). This chart is from this morning’s weather balloon (the National Weather Service in Charleston, along with stations all around the world, launches two of these a day). The red line (to the right) is temperature; the green line (to the left) is the dewpoint. As those lines converge, that indicates a more saturated airmass, and vice versa.

So, between 4–5km up, there was a very saturated layer of air which resulted in clouds and precipitation. However, between 4km and the surface, extremely dry air with dewpoints as low as -20C could be found. Precipitation would have an extremely tough time surviving that dry layer.

The fun part? That precipitation started out in a layer below freezing, so it was likely snowing before it hit the layer of dry air. Said layer of air was so dry that it very well could have converted the precipitation from its solid form directly into a gas, a process known as sublimation.

Science is cool.

The next seven days

Spoiler alert: No rain. We’ll get very close to the all-time record of 41 days without measurable rain next week if this forecast holds. Source: National Weather Service

We’ve got a lot of the same over the next seven days, with some particularly cool weather in store for the weekend. (Check out that low of 39 on Sunday!) We’ll start to see temperatures moderate a bit more starting Monday. Mid-70s are forecast to return by midweek next week.

Note that if we remain without measurable rainfall through Wednesday, that’ll be 39 straight days without rain, second-longest streak on record at the airport. All-time record streak is 41. It’s gonna be close…

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