The government jet prowling the atmosphere over the North Pacific now is riding above a solid cloud mass and probes directly into the upper-level weather system affecting Northern California.
The Gulfstream IV, operated by the National Oceanic and Atmospheric Administration, just flew over a jet-stream wind of 138 m.p.h., stronger than that of a Category 3 hurricane.
Those strong winds, measured about 1,600 miles northeast of Honolulu, are on the east side of the upper-level that is giving a kick to the system now affecting northern California.
That same feature may bring what flight meteorologist Jessica Williams describes as a "heavy precipitation event" to her hometown, Willow Grove, and the rest of the Philadelphia region by Sunday.
Her best guess right now would be rain, but coming up with a more-precise answer obviously is an important one, and Williams says that's one reason the Gulfstream IV is up here.
That wind reading is significant, because the U.S. computer model yesterday was forecasting a wind of about 120 m.p.h.
But the tiny computer board on the "dropsonde" device, about 18 inches long and 2 ½ inches in diameter, came back with the 138 m.p.h. real-time reading. That's a significant difference.
In the end, the details that can make all the difference in a forecast as a system moves downstream.