One of the most accurate way to determine Qibla direction is by looking at the direction of the sun (or looking at the sun’s shadow) when the sun is directly above the Ka’bah in Makkah, Saudi Arabia.
Times the sun above Ka’bah
During the year, there are two specific times when the sun transits or lies directly above the Ka’bah. These two times are: 28 May at 9.18 GMT and 16 July at 9.27 GMT. After converting to your local times, if you can see the sun at those times, then your sight is directly to the direction of qibla. Alternatively, you can put a stick on the ground vertically and observe the shadow. It should create a straight line opposite to the direction of Qibla.
Times the sun below Ka’bah
At the above mentioned times, there are part of the worlds that are on the night side. Therefore they would not be able to use the sun to guide them to the qibla direction. However there are also exactly two times in a year when the sun is directly below the Ka’bah (antipode). These times are: 28 November at 21.09 GMT and 16 Januari at 21.29 GMT. At these times, the sun would be on the opposite direction of the qibla. So, by observing the shadow of a vertical objects at those times, one can see the qibla direction pointed by the shadow.
What to do if overcast
You can observe the qibla direction using the above methods during several days around those times.
Alternatively you can check the Prayer Times Widget which should give you information for determining qibla direction using the sun for any location for the current date.