Wednesday, 12 February 2003: 1:30 PM
Impact of GPS-IPW data on RUC forecasts
GPS integrated precipitable water (GPS-IPW) data have been available
at FSL for more than five years. A long-term impact study using
the original 60-km RUC with and without GPS data has been ongoing
since November 1997. Verification of the analysis and forecasts
from the two parallel runs has been performed against RAOBs at 0000
and 1200 UTC daily, resulting in a longterm, data-rich sample.
These statistics show a consistent, modest impact in relative humidity
forecasts at 850 hPa, 700 hPa and 500 hPa, important levels in
forecasting weather potential. The impact increases with
the density of the data.
Individual cases have also been assessed, both with the 60-km
RUC and the new 20-km RUC. A 20-km case study has been run
for 24 May 2000. The case includes a widespread severe weather
outbreak in the south central US, where most of the GPS receivers are
located. Assimilation of GPS-IPW in this case resulted in drier
(more unstable) conditions aloft and an increase in
precipitation in this area.
An additional case will be run for February 2001 to assess the impact in a cold weather situation.