Small Aircraft
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 15; Flight Crew Total 800; Flight Crew Type 650
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Regained Aircraft Control; Flight Crew Returned To Clearance; Flight Crew Diverted
Weather; ATC Equipment / Nav Facility / Buildings; Human Factors
After passing over LNS which was in the clear; I continued on my flight plan to land at MQS; about 20 miles further east and in between areas of precipitation on the XM and ADS-B weather.  As I approached the airport and after requesting vectors for the ILS 29 into MQS; it became clear this was not safe.  I lost 1000 feet of altitude within a few seconds and had trouble controlling the airplane.  Philly approach told me I was descending below their radar coverage to which I replied that I was trying to climb back to 2500 and would like to head back to LNS (my listed alternate) to wait out the weather at MQS.I regained altitude; Philly handed me off to Lancaster tower and I landed there uneventfully. I am sure I deviated from the assigned altitude due to downdrafts and windshear.  Even though Chester County Airport looked clear on both radar sources; in fact the weather was worse than depicted.  Lesson learned:  I should have just requested a deviation to the alternate before getting close to potential weather issues.
Small aircraft pilot reports approaching his destination and noting it is between weather cells on his XM and ADSB NexRad weather displays. While on vectors for the ILS; 1;000 feet is lost due to downdrafts. After regaining the lost altitude the reporter diverts to his alternate to wait out the weather.