B737-800
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 180; Flight Crew Type 2000
Communication Breakdown
Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Flight Crew Executed Go Around / Missed Approach
Environment - Non Weather Related; Human Factors
Moderate turbulence below 14;000 feet.  Heavy winds as well. 290/19 G29 on the ground.  Cleared Visual Approach 34L. Approach was normal; but Captain very busy dealing with speed fluctuations and turbulence.  I was double checking the winds with Tower. Watching terrain as well.  Adjusted REF speeds for gusts and prevailing winds. Captain called for flaps 30; I inadvertently moved flap handle to 25 and did not know it.  Everything was good until short final; we got Too Low Flaps" aural alert.  We executed go-around immediately. Need to look down and see if correct flap detention is selected."
On flight to RNO we received a Too Low Flaps warning from the GPWS around 500 feet AGL on an approach to Runway 34L. We had continuous moderate turbulence below 13;000 feet MSL on our approach and that was distracting. We were on a high right base leg because of the terrain. We were cleared for the visual on the right base leg. Also; on base we were gear down flaps 15; and near flaps 15 approach speed. I called for flaps 30 and the Before Landing checklist well above 1;000 feet AGL; because I wanted the extra drag. I did not notice the flaps were at position 25 during the Before Landing checklist. Our REF speed was plus 9 and then increased to plus 15 with the new Tower winds.  At about 500 feet AGL we received the Too Low Flaps warning and I did a go-round. We were vectored for another approach to Runway 34L and did a normal landing.I felt task loaded on the approach. I was concerned about the turbulence; terrain; and changing surface winds. I let these additive condition distract me while doing the Before Landing Check List.  I should have bought myself more time by asking for a longer down wind on the approach.
B-737 flight crew reported executing a go-around upon receipt of a configuration GPWS warning.