Dear RUC users,

A relatively small set of changes for the RUC is scheduled
to be implemented next Tuesday May 4 for the 1200 UTC run.
Most of these changes involve post-processing. Another
change regarding the speed of RUC processing has already
been made and is discussed further below.

------
The code changes include
- consistency fixes and a bug fix to surface temperature
and dewpoint diagnosis from RUC native fields
- a CAPE/CIN change
- more smoothing of isobaric level winds
- use of different ice and vegetation fraction files
- GRIB identifier changes

-------

Effects:
-------

-- Improved diagnosis of surface temperature and dewpoint
temperature.
BACKGROUND: The RUC surface temperature and
surface dewpoint fields are diagnosed from the RUC native
grids using lapse rate information to a topography grid that
is closer to actual METAR elevations. This has been done
with the RUC1 and RUC2 systems.
With the fixes, biases of analyzed surface temperature and
dewpoint compared to actual METAR observations are reduced
from 2 deg C to 0 in the western United States, and standard
deviation differences of temperature are reduced from about
2 deg C to a little over 1 deg C over the United States as
a whole. These improvements also benefit the Lifted Index
calculations.

-- The diagnostic of convective available potential temperature
has been modified to better detect potential for elevated
convection by considering cloud parcels in the lowest 300 mb
near the surface, rather than the previous 180 mb thick layer.

-- Additional smoothing of RUC isobaric wind fields in the lower
troposphere and at the tropopause improves their accuracy.
This modification is only in the post-processing, not in the
model or analysis.

-- The ice fields from the NESDIS snow/ice analysis are much
more precise than the previous ice analyses used in the RUC.
This NESDIS ice field was used this past winter with the Eta.

-- The use of a GRIB-based vegetation fraction field has no
effect on the RUC output. It simply reads from a compressed
format, and is still the detailed NESDIS AVHRR-based
0.14 degree monthly greenness fraction also used by the Eta.

-- GRID identifier changes:
 number conc. for ice particles from 180 to 198
 surface runoff from 234 to 235
 sub-surface runoff from 198 to 234

Speed of processing
-------------------
The processing of the RUC at NCEP has speeded up fairly
dramatically since late last week, as some of you may have noticed.
NCEP allocated 10 processors on the Cray for all runs for the RUC
as part of improving the use of the Cray for the overall NCEP model
suite.

The effects of this change are that RUC forecast grids at 0300,
0600, 0900, 1500, 1800, and 2100 UTC are available about 25-30
min earlier than previously. Analyses at all times are available
about 5-8 min earlier, as are the 3-h forecasts at non-3-hourly
times.

CAUTION: This change is likely to continue for the duration of
the Cray before the changeover to the IBM SP-2, but this is
not yet certain. NCEP/NCO will decide by next week on whether to
make permanent this modification in the processors allocated to
the RUC.

----------

As always, please send questions or comments to the RUC forum
at http://maps.fsl.noaa.gov/forum/eval, or email or call me
directly.

Stan Benjamin