EMS FLT ENCOUNTERS DETERIORATING WX. DECLARES EMER; DIVERT LAND.

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AT THE COMPLETION OF A FLT FROM XXX MEDICAL CTR TO YYY; WX AT MY DEST WAS APPROX 7000 FT OVCST; VISIBILITY 10 NM. APPROX 5 NM FROM MY DEST I ENCOUNTERED VIRGA. I LANDED XA19 HRS AND SNOWFALL ON THE GND WAS ALMOST NONEXISTENT. DEPARTED YYY FOR THE RETURN TRIP TO XXX AT XA48 HRS. DEP VISIBILITY WAS NEARLY IMPOSSIBLE TO DETERMINE FROM THE GND DUE TO NOW FALLING LIGHT-MODERATE SNOW SHOWER. AFTER DEP VISIBILITY WAS ESTIMATED TO BE 3 NM BUT I WAS EXPECTING VFR CONDITIONS AT ANY TIME BASED ON OUR INBOUND FLT JUST 30 MINS PRIOR. AS I REACHED 3500 FT MSL ALT; I CONTACTED OUR DISPATCH CTR TO CHK WX AT XXX. CONDITIONS WERE RPTED AS SIMILAR IN OUR DEP WX (7000 FT OVCST; 10 NM VISIBILITY). APPROX 10-15 MINS INTO THE FLT; CONDITIONS HAD NOT IMPROVED SO I CONTACTED CTR AND REQUESTED AND RECEIVED CLRNC FOR THE ILS RWY 24 APCH INTO ZZZ. WX AT ZZZ WAS RPTED TO BE ABOVE VFR CONDITIONS ACCORDING TO AWOS BUT THE CONDITIONS I WAS EXPERIENCING WERE LESS THAN VFR. ENRTE ON THE FEEDER LEG FROM THE ABC VOR TO THE INITIAL APCH FIX; I REQUESTED A FREQ CHANGE FROM CTR TO CHK WX AT XYZ AND AWOS WX AT XXX. BOTH STATIONS WERE STILL RPTING VERY GOOD WX. I RETURNED TO CTR'S FREQ AND ADVISED THEM I WAS REQUESTING A CLRNC FROM MY PRESENT POS DIRECT TO CDE VOR TO ENCOUNTER VFR CONDITIONS. CLRNC WAS ISSUED AND I TURNED DIRECT TO CDE. ABOUT 1/2 THE WAY IN BTWN FAF AND CDE; XXX DISPATCH ADVISED ME THEIR WX WAS DETERIORATING TO APPROX 23 SCATTERED; 28 BROKEN; 50 OVCST; 7 NM VISIBILITY. WX AT MY LOCATION WAS MUCH WORSE THAN THAT AND I THOUGHT WX WAS PROBABLY DETERIORATING RAPIDLY. WITH ONLY ENOUGH FUEL FOR A VFR RESERVE THE THOUGHT OF CONTINUANCE ONTO XXX WAS TROUBLING ME. OUR DISPATCH CTR CALLED AGAIN TO RPT THAT SOMEONE IN ZXY (APPROX 10 NM S OF MY LOCATION) SUGGESTED IT WAS SNOWING VERY HARD THERE. DISPATCH ALSO RPTED WX WAS DETERIORATING AND WAS NOW 28 OVCST WITH REDUCED VISIBILITY IN SNOW SHOWERS. MY FUEL WAS LIMITED TO ABOUT 10 MINS PLUS A VFR RESERVE OF 20 MINS. I STILL HAD APPROX 10 MINS TO REACH MY DEST. THE THOUGHT OF CONTINUING OUTBOUND FOR 10 NM; THEN DOING A PROC TURN AND RETURNING 10 NM INBOUND LEFT ME WITH FEELING FUEL WE HAD ON BOARD WAS LESS THAN COMFORTING. THE VOR/DME COPTER APCH INTO XXX WAS BECOMING LESS AND LESS A VIABLE OPTION WITH THE EVER DETERIORATING WX. I REQUESTED A 10 DEG HDG CHANGE TO FLY OVER ZYA EXPECTING TO SEE LIGHTS FROM THE TOWN BELOW. I TURNED TOWARD ZYA. APPROX 2 NM FROM THERE THE SKY WAS AGLOW FROM THE LIGHTS BELOW. ALTHOUGH I COULD NOT ACTUALLY SEE ANY DIRECT LIGHTING THE LIGHTS FROM THE GND AND MY NAV EQUIP CONFIRMED I WAS OVER TOWN. I DECLARED AN EMER AND REQUESTED AND RECEIVED CLRNC TO 2000 FT MSL; AN ALT I KNEW WOULD PROVIDE ADEQUATE OBSTRUCTION CLRNC. AT APPROX 2600 FT I SAW THE STREETS OF TOWN. I CANCELED MY IFR FLT PLAN AND THE EMER CONDITION WITH CTR AND LANDED AT ZYA HOSPITAL HELIPAD IN WX CONDITION OF APPROX 1 NM VISIBILITY. THIS SIT WAS CAUSED BY MY INSISTENCE IN BELIEVING THAT THE WX AHEAD OF ME WOULD CLR UP AS IT WAS ON THE FIRST LEG OF THE FLT. I SHOULD HAVE REALIZED THAT IT WASN'T; I COULD HAVE LANDED UNEVENTFULLY AT ZZZ. FUTURE OCCURRENCES WOULD NOW HAVE ME RECONSIDER BYPASSING AN ARPT WITH AN INST APCH WITHOUT; AT LEAST; STOPPING TO REFUEL.