Pilot report: “Stronger winds than forecast”

April 5th, 2009 |
GOES-11 6.5 µm water vapor image + satellite winds + PIREP

AWIPS image of GOES-11 6.7 µm water vapor + GOES satellite winds + PIREPs

There was a pilot report (or PIREP) received over Annette Island, Alaska (station identifier ANN) on 05 April 2009 which noted “stronger winds than forecast” at an altitude of 29,000 feet. The winds reported by the aircraft were from a direction of 190º at a speed of 76 knots — and nearby GOES-derived atmospheric motion vectors (above) generally had speeds of around 50 knots or less.

However, note the strong dry-to-moist (dark blue to white) gradient seen on the 8-km resolution GOES-11 water vapor imagery above — this is a common signature that often occurs along the axis of a strong jet streak. This strong water vapor gradient is more well-defined when viewed on a 1-km resolution MODIS water vapor image from 21:40 UTC (below).

MODIS 6.7 µm water vapor image

MODIS 6.7 µm water vapor image

An animation of 4-km resolution GOES-13 6.5 µm water vapor imagery (below) also shows this strong “jet streak gradient” signature just to the west of Annette Island (ANN). Even though the viewing angle from the GOES-13 satellite (positioned over the Equator at 105º West longitude) was quite large, the 4 km spatial resolution of the data still allowed the gradient to show up quite well.

GOES-13 6.5 µm water vapor images

GOES-13 6.5 µm water vapor images