AN ACR LGT CAPT ATTRIBUTES HIS SINKING FEELING TO THE DIKE AT THE END OF LGA RWY 31. THERE WERE VERY BIG WINDS ABOUT THIS NIGHT.

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WE WERE CLRED FOR AN ILS RWY 4 LGA; CIRCLE TO LAND RWY 31. WX WAS APPROX 1200 FT OVCST; WINDS 310/25 GUSTS 35; LIGHT TO MODERATE TURB. WE ADDED 20 KTS TO OUR FINAL APCH SPD. AT APPROX 150 FT ON SHORT FINAL TO RWY 31; OUR AIRSPD INCREASED BY 15-20 KTS. WE LANDED AND MADE A PIREP TO THE LGA TWR. THEY ISSUED A WARNING TO THE NEXT ACFT. HE LANDED AND RPTED A WINDSHEAR ON SHORT FINAL. HE SAID HE WAS TOO BUSY TO FIGURE OUT EXACTLY WHAT HAPPENED. AS YOU KNOW; LGA RWY 31 HAS A DIKE THAT IS SHAPED LIKE A RAMP AT THE APCH END. SINCE I HAVE EXPERIENCED THIS PHENOMENON SEVERAL TIMES TO A LESSER DEG ON THIS SAME RWY; I THOUGHT I WOULD WRITE IT UP. MY THEORY IS THAT A WIND STRAIGHT DOWN RWY 31 HITS THAT RAMP SHAPED DIKE AND RISES CAUSING ACFT TO BE FORCED UPWARDS. THIS CAUSES THE ACFT TO RISE NECESSITATING NOSE DOWN ACTION INCREASING AIRSPD ON SHORT FINAL. IF YOU HAVE OTHER RPTS OF THIS PHENOMENON; PERHAPS A WARNING OF SOME SORT SHOULD BE IN THE COMMERCIAL APCH PLATES. ALSO; NEXT TIME STRONG WINDS FROM 310 DEGS EXIST; PERHAPS A SMALL SMOKE GENERATOR OR A SMALL BALLOON BEING RELEASED MIGHT CONFIRM THIS WIND.