Best time to fly Johnstown to Washington
Every month pooled across the years on record, so "July" means July generally rather than one particular July. Full JST to IAD record →
Best month
May
92.5% on time · 53 flights
Worst month
December
60.3% on time · 62 flights
| Month | Flights | On time | Cancelled | When late, by |
|---|---|---|---|---|
| January | 61 | 78.6% | 8.2% | 278 min |
| February | 56 | 62.7% | 8.93% | 225 min |
| March | 62 | 76.3% | 4.84% | 225 min |
| April | 52 | 78.4% | 1.92% | 169 min |
| May | 53 | 92.5% | 0% | 138 min |
| June | 51 | 80.4% | 0% | 261 min |
| July | 62 | 82.3% | 0% | 78 min |
| August | 62 | 79% | 0% | 121 min |
| September | 60 | 85% | 0% | 173 min |
| October | 62 | 87.1% | 0% | 93 min |
| November | 60 | 74.6% | 1.67% | 146 min |
| December | 62 | 60.3% | 6.45% | 159 min |
What a seasonal pattern can and cannot tell you
Months differ for reasons that repeat — summer thunderstorms in the American interior, winter fog and de-icing in northern Europe, school holidays filling every seat and leaving no slack in the schedule. Those are real and they come back each year.
What the pattern cannot do is forecast a particular flight. A quiet month has late days and a bad month has punctual ones. Treat this as a way to choose between two dates you are indifferent about, not as a promise.