Narrative:

The weather was marginal VFR with low ceilings; but pretty good visibility. I cleared aircraft X for takeoff; knowing that his flight direction would be west. I told him that a left turn to the west was approved; he never read it back; but I saw him start his turn and proceed westbound. I then got an IFR release on a light transport. I then cleared the light transport; 'turn left heading 290; maintain 2000; runway 35L cleared for takeoff; proceeding aircraft is west bound.' by the time the light transport started his takeoff roll aircraft X was two miles west of the field; so I turned to watch the light transport take off. When the light transport got airborne; I looked at the stars to watch for a tag and I saw that aircraft X had turned and was now due northeast bound and climbing. I asked him right away what his intentions were and he said he needed to maneuver to remain clear of the clouds; but continued climbing. I called the light transport traffic to him; but he did not see him. The light transport pilot saw aircraft X at the last second and made a drastic turn to avoid him. In a later conversation with the light transport pilot; he said that the only reason he saw aircraft X was because he happened to be in between the cloud layers; and had he not turned when he did; he would have run right into him. The aircraft X pilot; however; did not seem to notice. Recommendation; make sure I get a readback on everything. Next time in this same situation; I would probably have sent the light transport southwest bound until he was clear; just to make sure this doesn't happen again. I will not hesitate next time to change the heading of the IFR to avoid collision.

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Original NASA ASRS Text

Title: DWH Controller described conflict event between IFR and VFR departures when the VFR aircraft maneuvered to avoid weather placing aircraft in direct conflict with the IFR aircraft; requiring evasive action to avoid collision.

Narrative: The weather was marginal VFR with low ceilings; but pretty good visibility. I cleared Aircraft X for takeoff; knowing that his flight direction would be West. I told him that a left turn to the West was approved; he never read it back; but I saw him start his turn and proceed westbound. I then got an IFR release on a Light Transport. I then cleared the Light Transport; 'turn left heading 290; maintain 2000; Runway 35L cleared for takeoff; proceeding aircraft is West bound.' By the time the Light Transport started his takeoff roll Aircraft X was two miles West of the field; so I turned to watch the Light Transport take off. When the Light Transport got airborne; I looked at the STARS to watch for a tag and I saw that Aircraft X had turned and was now due Northeast bound and climbing. I asked him right away what his intentions were and he said he needed to maneuver to remain clear of the clouds; but continued climbing. I called the Light Transport traffic to him; but he did not see him. The Light Transport pilot saw Aircraft X at the last second and made a drastic turn to avoid him. In a later conversation with the Light Transport pilot; he said that the only reason he saw Aircraft X was because he happened to be in between the cloud layers; and had he not turned when he did; he would have run right into him. The Aircraft X pilot; however; did not seem to notice. Recommendation; make sure I get a readback on everything. Next time in this same situation; I would probably have sent the Light Transport Southwest bound until he was clear; just to make sure this doesn't happen again. I will not hesitate next time to change the heading of the IFR to avoid collision.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.