AN INSTRUCTOR AND STUDENT PLT IN A C172 ENCOUNTERED LOWERING CLOUD COVER THAT WAS NOT RPTED BY TWR OR PREVIOUS METAR AS THEY TOOK OFF FOR SOME LCL PATTERN WORK. THEY STAYED LOW AND RETURNED FOR A FULL STOP LNDG.

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I WAS CONDUCTING A TRAINING LESSON AT FRG ARPT. THE LESSON WAS CONDUCTED ON MAR/XX/97 AT XB00Z THROUGH XB10Z. THE LESSON WAS TO ENTAIL PATTERN OPS AND LNDG TECHNIQUE. AFTER TKOF AND LEVELING OFF AT 900 FT MSL IN THE L DOWNWIND FOR RWY 19; MY STUDENT AND I ENCOUNTERED SCATTERED CLOUDS AT 1100 FT MSL (WHICH WAS THE REASON FOR OUR LEVELING OFF AT 900 FT MSL). AFTER WE LEVELED OFF ON THE DOWNWIND I PROCEEDED TO CALL THE TWR OF OUR POS ON THE DOWNWIND AND I ALSO VERIFIED THE ACFT'S DISTANCE FROM THE RWY. THE TWR GAVE ME INSTRUCTIONS TO FOLLOW A PIPER CHEROKEE ON THE L DOWNWIND. MIDFIELD TO THE DOWNWIND THE SCATTERED LAYER BECAME 1000 FT MSL. AT THIS POINT THE TWR REQUESTED MY ALT. MY ALT WAS 900 FT MSL; WHERE I XMITTED THIS INFO TO THE TWR. THE TWR ADVISED ME THAT THE FIELD WOULD BE GOING IFR. I RESPONDED WITH A REQUEST FOR A FULL STOP LNDG. THE TWR GRANTED MY REQUEST. DUE TO THE PIPER CHEROKEE HAD BEEN FLYING IN THE AIR TFC PATTERN NUMEROUS CIRCUITS PRIOR TO MY TKOF I BELIEVE THE TWR CTLR COULD HAVE POSSIBLY ISSUED A SPECIAL WX METAR INDICATING THE CHANGE IN CLOUD ALTS. THE CHANGE WAS APPARENTLY -800 FT MSL FROM THE TIME OF THE RPTED METAR RPT.