diff --git a/src/AIModel/AIAircraft.cxx b/src/AIModel/AIAircraft.cxx
index 40c790a16..ab293b98b 100644
--- a/src/AIModel/AIAircraft.cxx
+++ b/src/AIModel/AIAircraft.cxx
@@ -54,11 +54,12 @@ FGAIAircraft *FGAIAircraft::_self = NULL;
 FGAIAircraft::FGAIAircraft(FGAIManager* mgr) {
    manager = mgr;   
    _self = this;
+   _type_str = "aircraft";
+   _otype = otAircraft;
 
    // set heading and altitude locks
    hdg_lock = false;
    alt_lock = false;
-   _type_str = "aircraft";
 }
 
 
diff --git a/src/AIModel/AIBallistic.cxx b/src/AIModel/AIBallistic.cxx
index 0e7249e4e..c712a989b 100644
--- a/src/AIModel/AIBallistic.cxx
+++ b/src/AIModel/AIBallistic.cxx
@@ -30,6 +30,7 @@
 FGAIBallistic::FGAIBallistic(FGAIManager* mgr) {
     manager = mgr;
     _type_str = "ballistic";
+    _otype = otBallistic;
 }
 
 FGAIBallistic::~FGAIBallistic() {
diff --git a/src/AIModel/AIBase.cxx b/src/AIModel/AIBase.cxx
index 123a936e8..bb1af2279 100644
--- a/src/AIModel/AIBase.cxx
+++ b/src/AIModel/AIBase.cxx
@@ -52,6 +52,7 @@ FGAIBase::FGAIBase() {
     x_shift = y_shift = rotation = 0.0;
     invisible = true;
     model_path = "";
+    _otype = otNull;
 }
 
 FGAIBase::~FGAIBase() {
@@ -103,6 +104,12 @@ bool FGAIBase::init() {
    return true;
 }
 
+bool FGAIBase::isa( object_type otype ) {
+ if ( otype == _otype ) { return true; }
+ else { return false; } 
+}
+
+
 void FGAIBase::bind() {
    props->tie("id", SGRawValuePointer<int>(&id));
    props->tie("velocities/true-airspeed-kt",  SGRawValuePointer<double>(&speed));
diff --git a/src/AIModel/AIBase.hxx b/src/AIModel/AIBase.hxx
index a9a00408c..44ebd61e8 100644
--- a/src/AIModel/AIBase.hxx
+++ b/src/AIModel/AIBase.hxx
@@ -41,6 +41,9 @@ public:
     virtual void update(double dt);
     inline Point3D GetPos() { return(pos); }
 
+    enum object_type { otNull, otAircraft, otShip, otBallistic,
+                       otRocket, otStorm, otThermal };
+
     virtual bool init();
     virtual void bind();
     virtual void unbind();
@@ -103,6 +106,7 @@ protected:
 
     static FGAIBase *_self;
     const char *_type_str;
+    object_type _otype;
 
 public:
 
@@ -129,6 +133,7 @@ public:
     static double _getRotation();
 
     static bool _isNight();
+    bool isa( object_type otype );
 };
 
 
diff --git a/src/AIModel/AIManager.cxx b/src/AIModel/AIManager.cxx
index 394951f09..ceffc4c4a 100644
--- a/src/AIModel/AIManager.cxx
+++ b/src/AIModel/AIManager.cxx
@@ -37,6 +37,7 @@ SG_USING_STD(list);
 FGAIManager::FGAIManager() {
   initDone = false;
   numObjects = 0;
+  _dt = 0.0;
   dt_count = 9;
 }
 
@@ -54,6 +55,7 @@ FGAIManager::~FGAIManager() {
 void FGAIManager::init() {
   int rval;
   root = fgGetNode("sim/ai", true);
+  wind_from_down = fgGetNode("/environment/wind-from-down-fps", true);
 
   for (int i = 0; i < root->nChildren(); i++) {
     const SGPropertyNode * entry = root->getChild(i);
@@ -127,10 +129,16 @@ void FGAIManager::unbind() {
 
 
 void FGAIManager::update(double dt) {
-	
+
+        // initialize these for finding nearest thermals
+        range_nearest = 10000.0;
+        strength = 0.0;
+
+        _dt = dt;	
+
         ai_list_itr = ai_list.begin();
         while(ai_list_itr != ai_list.end()) {
-                if ((*ai_list_itr)->getDie()) {
+                if ((*ai_list_itr)->getDie()) {      
                    freeID((*ai_list_itr)->getID());
                    delete (*ai_list_itr);
                    ai_list.erase(ai_list_itr);
@@ -138,10 +146,15 @@ void FGAIManager::update(double dt) {
                    --numObjects;
                 } else {
                    fetchUserState();
-                   (*ai_list_itr)->update(dt);
+                   if ((*ai_list_itr)->isa(FGAIBase::otThermal)) {
+                       processThermal((FGAIThermal*)*ai_list_itr); 
+                   } else { 
+                      (*ai_list_itr)->update(_dt);
+                   }
                 }
                 ++ai_list_itr;
         }
+        wind_from_down->setDoubleValue( strength );
 }
 
 
@@ -277,7 +290,7 @@ int FGAIManager::createThermal( double latitude, double longitude,
         ++numObjects;
         ai_thermal->setLongitude(longitude);
         ai_thermal->setLatitude(latitude);
-        ai_thermal->setStrength(strength);
+        ai_thermal->setMaxStrength(strength);
         ai_thermal->setDiameter(diameter / 6076.11549);
         ai_thermal->init();
         ai_thermal->bind();
@@ -313,3 +326,13 @@ void FGAIManager::fetchUserState( void ) {
      dt_count = 0;
    }
 }
+
+
+// only keep the results from the nearest thermal
+void FGAIManager::processThermal( FGAIThermal* thermal ) {
+  thermal->update(_dt);
+  if ( thermal->_getRange() < range_nearest ) {
+     range_nearest = thermal->_getRange();
+     strength = thermal->getStrength();
+  }
+}
diff --git a/src/AIModel/AIManager.hxx b/src/AIModel/AIManager.hxx
index 5b0e962b1..537d5145e 100644
--- a/src/AIModel/AIManager.hxx
+++ b/src/AIModel/AIManager.hxx
@@ -29,6 +29,7 @@
 #include "AIBase.hxx"
 
 SG_USING_STD(list);
+class FGAIThermal;
 
 
 class FGAIManager : public SGSubsystem
@@ -53,8 +54,6 @@ private:
 
 public:
 
-    enum object_type { otAircraft, otShip, otBallistic, otRocket, otStorm, otThermal };
-
     FGAIManager();
     ~FGAIManager();
 
@@ -120,6 +119,7 @@ private:
     bool initDone;
     int numObjects;
     SGPropertyNode* root;
+    SGPropertyNode* wind_from_down;
 
     double user_latitude;
     double user_longitude;
@@ -128,9 +128,15 @@ private:
     double user_pitch;
     double user_yaw;
     double user_speed;
+    double _dt;
     int dt_count;
     void fetchUserState( void );
 
+    // used by thermals
+    double range_nearest;
+    double strength;
+    void processThermal( FGAIThermal* thermal ); 
+
 };
 
 #endif  // _FG_AIMANAGER_HXX
diff --git a/src/AIModel/AIShip.cxx b/src/AIModel/AIShip.cxx
index d9fc379fe..c1d4ce809 100644
--- a/src/AIModel/AIShip.cxx
+++ b/src/AIModel/AIShip.cxx
@@ -29,9 +29,11 @@
 
 FGAIShip::FGAIShip(FGAIManager* mgr) {
    manager = mgr;
+   _type_str = "ship";
+   _otype = otShip;
+
    hdg_lock = false;
    rudder = 0.0;
-   _type_str = "ship";
 }
 
 FGAIShip::~FGAIShip() {
diff --git a/src/AIModel/AIStorm.cxx b/src/AIModel/AIStorm.cxx
index fa09aad79..532a3f106 100644
--- a/src/AIModel/AIStorm.cxx
+++ b/src/AIModel/AIStorm.cxx
@@ -40,6 +40,7 @@ FGAIStorm::FGAIStorm(FGAIManager* mgr) {
    manager = mgr;   
    _self = this;
    _type_str = "thunderstorm";
+   _otype = otStorm;
 }
 
 
diff --git a/src/AIModel/AIThermal.cxx b/src/AIModel/AIThermal.cxx
index 812f5e01e..7ceafcee9 100644
--- a/src/AIModel/AIThermal.cxx
+++ b/src/AIModel/AIThermal.cxx
@@ -40,8 +40,10 @@ FGAIThermal::FGAIThermal(FGAIManager* mgr) {
    manager = mgr;   
    _self = this;
    _type_str = "thermal";
-   strength = 6.0;
+   _otype = otThermal;
+   max_strength = 6.0;
    diameter = 0.5;
+   strength = factor = 0.0;
 }
 
 
@@ -51,8 +53,7 @@ FGAIThermal::~FGAIThermal() {
 
 
 bool FGAIThermal::init() {
-   wind_from_down = fgGetNode("/environment/wind-from-down-fps", true);
-   scaler = 8.0 * strength / (diameter * diameter * diameter);
+   factor = 8.0 * max_strength / (diameter * diameter * diameter);
    return FGAIBase::init();
 }
 
@@ -100,13 +101,13 @@ void FGAIThermal::Run(double dt) {
    double range_ft = sqrt( lat_range*lat_range + lon_range*lon_range );
    range = range_ft / 6076.11549;
 
-   // Set rising air if within range. 
+   // Calculate speed of rising air if within range. 
    // Air vertical speed is maximum at center of thermal,
    // and decreases to zero at the edge (as distance cubed).
    if (range < (diameter * 0.5)) {
-     wind_from_down->setDoubleValue( strength - (range * range * range * scaler) );
+     strength = max_strength - ( range * range * range * factor );
    } else {
-     wind_from_down->setDoubleValue( 0.0 );
+     strength = 0.0;
    }
 }
 
diff --git a/src/AIModel/AIThermal.hxx b/src/AIModel/AIThermal.hxx
index c4eb171d1..1da663ff8 100644
--- a/src/AIModel/AIThermal.hxx
+++ b/src/AIModel/AIThermal.hxx
@@ -40,8 +40,10 @@ public:
         virtual void unbind();
 	void update(double dt);
 
-        inline void setStrength( double s ) { strength = s; };
+        inline void setMaxStrength( double s ) { max_strength = s; };
         inline void setDiameter( double d ) { diameter = d; };
+        inline double getStrength() const { return strength; };
+        inline double getDiameter() const { return diameter; };
 
 protected:
         static FGAIThermal *_self;
@@ -50,10 +52,10 @@ private:
 
         double dt; 
 	void Run(double dt);
-        SGPropertyNode* wind_from_down;
+        double max_strength;
         double strength;
         double diameter;
-        double scaler;
+        double factor;
 };