Date: 201401
Local time of day: 0601-1200
Location: ZZZZ.TRACON, US
Flight conditions: IMC
Weather elements / visibility: Icing; Turbulence
Light: Daylight
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Initial Approach
Airspace: Class D ZZZZ
ATC / advisory: TRACON ZZZZ; Tower ZZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Workload
Second reporter function: Pilot Not Flying; Captain
Anomaly: Ground Event / Encounter Other / Unknown; Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Diverted; Flight Crew Executed Go Around / Missed Approach; Flight Crew Landed As Precaution; General Declared Emergency
Contributing factors: Procedure; Weather
Primary problem: Weather

Narrative: Departed then diverted for unforecasted adverse weather. Weather at destination was forecasted to be windy but good visibility and high overcast. Our alternate was filed as ZZZZ. The destination runway was reported as BRAKING ACTION GOOD; BARE DRY TRACE.  Upon reaching the filed destination Terminal frequency; the controllers advised us that there was holding delays for weather at ZZZZ. We reminded them that we were landing at a different airport. We received destination ATIS and immediately noted that we would need to execute an instrument approach to land. Visibility was ATIS reported to be 1 3/4; sufficient to fly the ILS.  We received vectors for the ILS and near final decent were informed that the RVR was less than the required for the approach of 4;000. We heard the visibility reported as low as 3;000-3;500.  Hearing this; we flew the missed approach and received vectors for a second ILS. Fuel was noted; visibility was not increasing but going lower.  Prior to FAF; Terminal advised us that Braking Action (not previously reported) advisories were now .18 MU... degraded. We were experiencing continuous moderate turbulence; below required visibility; winds were gusting to 30 knots creating the need; per company profiles; to fly a higher approach speed. We applied WET; A/I ON numbers for landing plus wind correction plus a 15% Landing Field Assessment for unforecasted weather that existed at arrival. Visibility was reported as 2;500-2;800 RVR; further degraded from the first approach.  We decided to divert to ZZZZ; our planned alternate landing field and a much more capable airport with better facilities. ZZZZ Terminal then advised us that the; 'Only way for us to land ZZZZ was to declare an emergency;' that in; '15 minutes the airport would be closed for 30 minutes for snow removal.' At this point we had IFR reserve plus 25 minutes of fuel in a terminal environment doing approaches with degrading weather. We confirmed that the only way for us to land was to declare a low fuel emergency. The Terminal Controller confirmed this fact. A 'technical ATC required fuel emergency' status was declared and we landed without event. It was also noted that the conditions at ZZZZ AFTER we landed continued to degrade with an Airbus aircraft reporting runway braking action of POOR-NIL on Runway XX as more snow and strong wind continued to pound the airport after our decision to land sooner than later. In retrospect; after destination conditions deteriorated so quickly; our decision to land promptly was confirmed as the best one possible. Of note; is that the owners were very pleased in the decision to move departure to ZZZZ given the surprise winter storm; per Owner Services and comments made to us by them. I think that company procedures are adequate. We followed them and made sure that our flight was operated firmly on the side of safety even though authorities requested additional information on the matter. I'm not sure that anything except filing an alternate airport farther away from the planned destination would have prevented the technical emergency declaration from occurring due to degrading weather. The airport was incapable of maintaining continuous operations due to the accumulating snow; gusty winds; etc. It was a bad weather day. Even with adequate pavement options (runways); the airport couldn't keep up. We; as a company; picked the best option available given weather forecast at the time of arrival.


Second narrative: [Report narrative contained no additional information.]


Synopsis: A Corporate flight crew decided to declare a fuel emergency and divert to the filed alternate ZZZZ because the weather at their filed destination went below approach minimums.