The launch weather guidelines involving the Space Shuttle and expendable rockets are similar in many areas, but distinctions are made for the individual characteristics of each. The criteria are broadly conservative to assure avoidance of possible adverse conditions. The criteria are reviewed for each launch. Weather outlooks, which are provided by the Cape Canaveral Range Forecast Facility begin at Launch-minus-5-days. The outlooks include weather trends and their possible effects on launch day.

During the countdown, formal weather briefings occur approximately as follows:

The basic weather parameters on the pad at liftoff must be as follows:

Temperature
Prior to external tank propellant loading, tanking will not begin if the 24-hour average temperature has been below 41 degrees F. After tanking begins, the countdown will not continue if the temperature exceeds 99 degrees F for more than 30 consecutive minutes.

After tanking begins, the countdown shall not be continued nor the Shuttle launched if the temperature is lower than the prescribed minimum value for longer than 30 minutes unless sun, wind, and relative humidity conditions permit recovery.

The minimum temperature limit in degrees F. is specified by the table below and is a function of the five-minute average of temperature, wind, and humidity. The table becomes applicable when the observed temperature reaches 48°F. In no case may the Space Shuttle be launched if the temperature is 35°F or colder.

Wind
Tanking will not begin if the wind is observed or forecast to exceed 42 knots for the next three-hour period. For launch, when the wind direction at the launch pad is between 300 degrees and 060 degrees, the highest wind allowable is 34 knots. When the wind direction is between 150 degrees and 200 degrees, the highest wind allowable is 20 knots. The peak allowable wind speed is on a descending scale between the directions of 060 degrees and 150 degrees, and an ascending scale between 200 degrees and 300 degrees.

The upper atmosphere wind profile must conform to either one of two wind loading programs developed by the Johnson Space Center. This profile is determined by a series of Jimsphere wind balloon releases from Cape Canaveral Air Force Station. A final recommendation is made by the JSC Launch Systems Evaluation Advisory Team (LSEAT) to the KSC launch director at Launch minus 30 minutes. The Space Shuttle will not be launched within 30 minutes of the time a determination has been made that the upper wind profile will adversely affect the performance of the launch vehicle.

Precipitation None at the launch pad or within the flight path.

Lightning (and electric fields with triggering potential):

Tanking will not begin if lightning is observed within five nautical miles of the launch pad or is forecast to occur during the next three hours.

Launch will not occur if lightning has been detected within 10 nautical miles of the pad or the planned flight path within 15 minutes prior to launch, unless the source of lightning has moved more than 10 nautical miles away from the pad or the flight path. The one-minute average of the electric field mill network, used to measure electric fields, shall not exceed -1 or +1 kilovolt per meter within five nautical miles of the launch pad at any time within 15 minutes prior to launch.

The above rule need not apply if the following two conditions are observed to exist:

1. There are no clouds within 10 nautical miles of the launch pad. If clouds are present they may not have been previously associated with a thunderstorm, or associated with convective clouds having tops greater than the -4 degrees F. temperature level (approximately 23,000 feet) during the last three hours. The clouds must be thin optically transparent clouds, or a cloud cover less than or equal to 25% of the sky with tops below or equal to the 41 degrees F. temperature level (approximately 10,000 feet).

2. It can be determined that abnormal readings are the result of smoke, fog, or a maritime inversion associated with an onshore or alongshore wind present over the electric field mills, causing those mills located near the ocean to be elevated with a positive polarity between 1 and 1.5 kilovolts per meter.

Clouds (types known to contain hazardous electric fields) The Space Shuttle may not be launched if the planned flight path is through a layer of clouds with a thickness of 4,500 feet or greater where the temperature of any part of the layer is between 32 degrees F. and -4 degrees F. This frequently corresponds to the altitudes between approximately 13,000 feet and 23,000 feet.

The Space Shuttle may not be launched if the planned flight path is through any cloud type that extends to an altitude where the temperature is between 32 degrees and -4 degrees F. if this is associated with disturbed weather within five nautical miles of the flight path. (Again, this may correspond to the region between approximately 13,000 feet and 23,000 feet altitude.)

The Space Shuttle may not be launched through an opaque cloud which has become detached from a thunderstorm within three hours before launch, or within 5 nautical miles of thunderstorm debris clouds not able to be monitored by the field mill network, or producing a radar return showing light rain.

The Space Shuttle may not be launched through cumulus type clouds with tops extending into a temperature 41 degrees F. or colder (located at approximately 10,000 feet), or within 5 nautical miles of clouds with tops extending higher than the 14 degree F. temperature level (located at approximately 18,000 feet).