weather map spacex launch 05272020
Meteorologist explains why historic launch was scrubbed
03:11 - Source: CNN
CNN  — 

The first crewed spaceflight to take off from US soil in nearly a decade will likely come down to the wire once again Saturday.

The latest weather forecast puts the odds of a go or no go decision at 50/50 – just as it was when the launch was scrapped on Wednesday.

“Saturday and Sunday could turn out to have very similar weather as Wednesday did,” CNN meteorologist Haley Brink said, referring to this week’s scrubbed launch. “We may be waiting on a game-time decision again this weekend.”

The next launch opportunity is Saturday at 3:22 p.m. ET, with a backup window of 3 p.m. ET on Sunday.

But the 45th Space Wing Weather Squadron says the odds are once again the same as a coin flip.

Friday morning, the weather squadron says there is a 50% chance of favorable conditions for Saturday’s attempt. This forecast is 10% better than the 40% chance issued Thursday.

weather spacex launch forecast 20200529

The primary concerns Saturday are that rain or even thunderstorms could form near the launch site, the Weather Squadron said.

There had also been a 50/50 chance Wednesday that the weather would clear, and 10 extra minutes might have given the launch team the green light. But the timing had to be just right for a proper rendezvous with the International Space Station.

“Weather is the one thing that we actually cannot control on our missions so unfortunately, it did cause us to scrub today,” tweeted NASA.

During this time of the year, it is not uncommon for a sea breeze along the east coast of Florida to cause pop-up afternoon thunderstorms.

It isn’t always easy to forecast precisely where one of these storms will pop up. Still, forecasters can look at the overall pattern to see if conditions present themselves for thunderstorm development.

Check the forecast from CNN’s team of meteorologists >>>

There is an area of possible tropical development out over the Atlantic that could become the third named tropical system of the year.

But the weather squadron says the tropical development possible over the next few days will stay well east over the open Atlantic. So, this plausible storm should not threaten the criteria for a go launch.

The good news is that the weather squadron is now forecasting more favorable conditions for Sunday.

Sunday has rain chances in the forecast as well, albeit a slightly lower chance than on Saturday, Brink said Thursday.

The weather squadron is saying there is a 60% chance of favorable conditions on Sunday.

This outlook is slightly more optimistic than their forecast Thursday.

“Although it seems a welcome drying trend over Florida will soon be upon us, it’s not clear if the timing will be soon enough for Sunday’s attempt,” the weather squadron said.

Rocket-triggered lightning is a launch hazard

A whole team of meteorologists is on hand from the 45th Space Wing and SpaceX to determine if the weather will scrub the launch. As on Wednesday, the decision can be made right up to liftoff.

During the NASA broadcast on Wednesday, disappointment was evident as the weather team called it a no-go for launch.

Launch weather officers must be “clear and convinced” that no NASA “criteria are violated in order to give the weather GO call for launch,” the 45th Space Wing Weather Squadron states.

For example, lightning in the area will cancel a flight, as will a cloud with a large enough electrical field to produce rocket-triggered lightning. This happens when a giant spark of electricity occurs when a large rocket flies through a strong enough atmospheric electric field.

The electric field needed to induce rocket-triggered lightning is much lower than for natural lightning.

“Either type of lightning could cause serious damage to the rocket and endanger public safety,” the weather squadron states.

Forecasters also have to monitor the winds.

If there is a sustained wind of 30 mph or more at 162 feet above the launch pad, the mission will be canceled.

Here’s a list of all the weather scenarios that will prevent a launch

The weather squadron also has to monitor the weather downrange because if the Crew Dragon capsule encounters a problem, it needs to have a safe splashdown location.

Earlier this month, NASA had to delay its launch of the Atlas V rocket, US Space Force mission due to Tropical Storm Arthur. It launched the following day after the storm cleared out.

CNN meteorologist Jennifer Gray contributed to this report.