A C172 INSTRUCTOR AND STUDENT DEVIATED FROM THEIR IFR ALT AND TRACK CLEARANCE IN UNFORECAST TURBULENCE; ICE AND SNOW.

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THIS WAS A TRAINING FLT WHERE I WAS INSTRUCTING AN INST STUDENT ON HIS FIRST INST XCOUNTRY. WE HAD FLOWN INTO HQM 1 HR BEFORE AND HAD BRIEFLY FOUND A TRACE OF ICE AT 4000 FT BUT HAD A SMOOTH RIDE IN AND OUT OF MIXED CLOUD TYPES. WE WERE NOW GOING TO RETURN TO ZZZ AND RECEIVED A WX BRIEFING; FILED A FLT PLAN AND PICKED UP OUR CLRNC ON THE GND AT HQM VIA FSS. THIS TOOK A BIT MORE TIME THAN PLANNED AS THE STUDENT'S NATIVE LANGUAGE WAS NOT ENGLISH. WHILE HE IS VERY SMART; HIS ACCENT SOMETIMES CONFUSES THE CTLRS; FSS PERSONNEL; ETC. WX WAS FORECAST FOR RAIN SHOWERS WITH CEILINGS AT ABOUT +/-1500 FT AND A FREEZING LEVEL OF ABOUT 6000 FT. ANY ADVERSE WX WAS NOT FORECAST FOR THE NEXT FEW HRS. I ADVISED THE STUDENT TO REQUEST EITHER THE MEA OR 4000 FT; HOWEVER; WE WERE ASSIGNED 5000 FT. WE DEPARTED VFR AND CLBED IN GOOD VFR FOLLOWING THE DEP PROC TO 5000 FT AND TURNED FOR V27. MY STUDENT AND I DISCUSSED THAT IF WE FOUND ANY ICING WE WOULD REQUEST A DSCNT TO MEA BY SHN WHERE WE KNEW WE WOULD BREAK OUT INTO VFR CONDITIONS AND COULD CONTINUE THE FLT IN VMC. AHEAD WE NOTICED AN AREA OF 2 BUILDUPS OF MODERATE HEIGHT ON OUR COURSE THAT WEREN'T THERE ON THE ARR. THERE APPEARED TO BE EITHER VIRGA OR SNOW FALLING FROM THEM. AS WE GOT CLOSER IT WAS APPARENT THE SNOW WAS VERY THIN; HOWEVER; I ADVISED THE STUDENT WE PROBABLY SHOULD GET A CLRNC FOR LOWER; AS I DIDN'T WANT US TO FIND ANY ICE. HOWEVER; CTR WAS WORKING WITH OTHER ACFT AND WE COULDN'T GET A WORD OUT. BY THEN; WE HAD ENTERED THE SNOW AREA BUT IT WAS NOT STICKING; WITH THE OUTSIDE AIR TEMP FLUCTUATING FROM 0 TO -2 DEGS; AND THE RIDE WAS SMOOTH; THEN IT GREW VERY DARK -- VERY QUICKLY -- AND IN A MOMENT WE WERE HIT BY A COMBINATION OF MODERATE OR GREATER TURB IN THE FORM OF A DECISIVE DOWNDRAFT THAT DROPPED US ABOUT 500 FT AND HVY SLEET OR WET HAIL. MY STUDENT WAS VERY SHOCKED BY THIS (ME TOO!); YET HE STARTED TO SET UP VA SPD; BUT BECAME DISORIENTED IN THE TURB. I TOOK CTL OF THE ACFT AND STABILIZED IT AT 4500 FT CONCURRENTLY I NOTICED A VERY LIGHT AREA TO MY STARBOARD (R) AND SINCE I WAS STARTING TO ACCRUE ICE AT A CONSIDERABLE RATE I BANKED TOWARD THE LIGHT AREA. I ASKED MY STUDENT TO CALL CTR AND TELL THEM WHAT WAS GOING ON; BUT THE POOR GUY WAS TONGUE TIED AND WHITE AS A SHEET. SO I PUSHED THE BUTTON AND GAVE THEM OUR ALT (4500 FT) AND SAID WE HAD DEVIATED TO THE R TO GET OUT OF THIS 'HAIL SHAFT' AND WANTED LOWER -- NOW. BY THEN WE FLEW OUT OF THE SHAFT AND I GAVE THE CTLS BACK TO THE STUDENT; HOWEVER; HE CONTINUED TO TURN R AND I AGAIN TOOK BACK THE CTLS AND STARTED US IN A L TURN BACK TO COURSE. BY NOW MY STUDENT WAS SAYING PRAYERS. THE CTR CTLR WAS UNHAPPY WITH OUR DEV AND ALT LOSS AS THERE WAS TFC BEHIND US AT 4000 FT; HOWEVER; HE DID 'SPIN' THAT TFC BACK TOWARD HQM AND THEN GAVE US THE MEA AS WE CAME BACK ON COURSE. I WAS ABLE TO COACH THE STUDENT AND HE RESUMED CTL OF THE ACFT AND WE STARTED OUR DSCNT TO 3200 FT. ANY ICE THAT HAD ACCUMULATED STARTED MELTING OFF AS WE LEFT 4500 FT; AND BY 3200 FT WE WERE AT AN OUTSIDE AIR TEMP OF 4 DEGS AND ONLY LIGHT INTERMITTENT CHOP. IN A FEW MINS WE WERE IN VMC; HOWEVER; I PUT THE HOOD ON THE STUDENT AND HE 'WORKED' HIS WAY BACK TO ZZZ; WITH A RENEWED RESPECT FOR THE WX. THE CTR CTLR ASKED THAT I CALL THE FACILITY; WHICH I DID. THIS WAS NOT A FUN FLT FOR US. IT WAS THE FIRST ACTUAL INST TIME THE STUDENT HAD EXPERIENCED. THE WX INTENSIFIED QUICKER THAN EXPECTED. WE WERE IN AN AIRPLANE THAT WAS NOT EQUIPPED FOR ICING CONDITION (OTHER THAN PITOT HEAT) AND THERE WAS A PERIOD WHERE THERE WERE SEVERAL EXCHANGES OF THE CTLS TO STABILIZE THE AIRPLANE. I WAS COMPLETELY SURPRISED OF THE INTENSITY OF THE DOWNDRAFT AND CONCURRENT SLEET FROM SUCH A MODEST BUILDUP. AND THIS IS AFTER FLYING 35 YRS FOR THE AIRLINES. I DID NOT WISH TO DEVIATE FROM THE AIRWAY; HOWEVER; I CONSIDERED IT THE BEST COURSE OF ACTION CONSIDERING THE MESS WE (I) HAD STUMBLED INTO.