Let's try to have a look on the Boeing Manuals...
I just take a copy-paste from the manuals onto here so you guys can read it with no interference from my language issues.
Cold Weather Operations <XXX>
Considerations associated with cold weather operation are primarily
concerned with low temperatures and with ice, snow, slush and standing
water on the airplane, ramps, taxiways, and runways.
April 28, 2011
737 Flight Crew Operations Manual
Supplementary Procedures -Adverse Weather
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
SP.16.2 D6-27370-8XX-XX(XX)
At all times the Commander is responsible for ensuring that the aircraft is
operated in a safe manner appropriate to the aircraft and ambient weather
conditions. Cold Weather Operating procedures may be required at any
temperature. Whenever the Commander feels that the aircraft or ambient
conditions require the application of the following procedures, he/she is
authorised to take whatever action is required to ensure safety.
CAUTION: Do not use engine or wing anti–ice when OAT (on the
ground) or TAT (in flight) is above 10°C.
Icing conditions
Icing conditions exist when OAT (on the ground) or TAT (in flight) is 10°C
or below and any of the following exist:
• visible moisture (clouds, fog with visibility of one statute mile
(1600m) or less, rain, snow, sleet, ice crystals, and so on) is present,
or
• ice, snow, slush or standing water is present on the ramps,
taxiways, or runways.
CAUTION: Do not use engine or wing anti–ice when OAT (on the
ground) or TAT (in flight) is above 10°C.
Freezing conditions < XXX >
Freezing conditions exist on the ground when the OAT is +3°C or below
and any of the following exist:
• visible moisture (clouds, fog with visibility of one statute mile
(1600m) or less, rain, snow, sleet, ice crystals, and so on) is present,
or
• ice, snow, slush or standing water is present on the ramps,
taxiways, or runways.
737 Flight Crew Operations Manual
Supplementary Procedures -
Adverse Weather
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-8XX-XXX(XX) SP.16.5
Engine Anti-ice Operation - On the Ground < XXX >
Engine anti-ice must be selected ON immediately after both engines are
started and remain on during all ground operations when icing conditions
exist or are anticipated.
WARNING: Do not rely on airframe visual icing cues before
activating engine anti-ice. Use the temperature and
visible moisture criteria because late activation of
engine anti-ice may allow excessive ingestion of ice
and result in engine damage or failure.
CAUTION: Do not use engine anti-ice when OAT is above 10°C.
When engine anti-ice is needed:
ENGINE START switches .......................................................CONT
ENGINE ANTI-ICE switches .......................................................ON
Verify that the COWL VALVE OPEN lights illuminate bright,
then dim.
Verify that the COWL ANTI-ICE lights are extinguished.
Note:
If the COWL VALVE OPEN lights remain illuminated
bright with engines at IDLE, position APU BLEED air
switch to OFF and increase thrust slightly (up to a maximum
of 30% N1).
When engine anti-ice is no longer needed:
ENGINE ANTI-ICE switches ..................................................... OFF
Verify that the COWL VALVE OPEN lights illuminate bright,
then extinguish.
Wing Anti-ice Operation - On the Ground < XXX >
Use wing anti-ice during all ground operations between engine start and
takeoff when icing conditions exist or are anticipated, unless the airplane
is, or will be protected by the application of Type II or Type IV fluid in
compliance with an approved ground de-icing program.
WARNING: Do not use wing anti-ice as an alternative for ground
de-icing/anti-icing. Close inspection is still needed to
ensure that no frost, snow or ice is adhering to the
wing, leading edge devices, stabilizer, control
surfaces or other critical airplane components at
takeoff.
CAUTION: Do not use wing anti-ice when OAT is above 10°C.
When wing anti-ice is needed:
WING ANTI-ICE switch .............................................................. ON
Verify that the L and R VALVE OPEN lights illuminate bright,
then dim.
Note:
The wing anti-ice VALVE OPEN lights may cycle
bright/dim due to the control valves cycling closed/open in
response to thrust setting and duct temperature logic.
When wing anti-ice is no longer needed:
WING ANTI-ICE switch .............................................................OFF
Verify that the L and R VALVE OPEN lights illuminate bright,
then extinguish.
As you will understand I have deleted any reference to the airline this procedures come from (XXX added) but anyways, this is written by Boeing.
