changes to the NWS upper air program 9/1/93

• To: l.miller.ucar(rec), j.hoke(rec)
• Subject: changes to the NWS upper air program 9/1/93
• From: C.ALEX
• Date: Wed, 11 Aug 1993 14:40:20 -0600

Posted: Wed, Aug 11, 1993   2:32 PM EDT              Msg: FGJD-5842-4582
Subj:   changes to the NWS upper air program 9/1/93   
I sent the following message to internal and external NWS users this aftn.  I 
know in the past, the universities have been especially interested in changes 
to the upper air program.
----------------------------------------------------------------------------
WSHPNSNMC
NOUS41 KWBC 111805

NATIONAL TECHNICAL INFORMATION MESSAGE 92-33
NATIONAL WEATHER SERVICE HEADQUARTERS
200 PM EDT WED AUG 11 1993

TO:       ALL USERS OF NWS UPPER AIR DATA

FROM:     MARY M. GLACKIN
          CHIEF, SERVICES DEVELOPMENT BRANCH

SUBJECT:  CHANGES TO NWS UPPER AIR PROGRAM EFFECTIVE
          SEPTEMBER 1, 1993


(THE FOLLOWING INFORMATION WAS PROVIDED BY MR. TOM McCLELLAND,
NWS UPPER AIR PROGRAM LEADER)

********* NOTICE TO UPPER AIR DATA USERS ****************

Effective September 1, 1993, all National Weather Service
operational upper air offices will install a new version of the
MicroArt software which is used to take and transmit the upper
air coded messages.  A brief summary of the software changes
follows:

1)  CHANGE IN CALCULATION OF GEOPOTENTIAL HEIGHTS

The constant used in the calculation of geopotential heights
(sometimes referred to as the "gravity constant") will be changed
from 9.8 meters per second squared to 9.80665 meters per second
squared.  This will have an effect on the geopotential height
calculations.  Future retrospective users of upper air data will
have to contend with this change.

2)  CHANGE IN RESISTOR VALUE IN THE VIZ RELATIVE HUMIDITY
    EQUATION

The replacement of the 1.2 megohm parallel resistor value in the
VIZ relative humidity equation with a corrected 1.0 megohm value,
which affects only higher humidities.  This change will again
introduce a discontinuity in the climatological record for VIZ
sonde soundings for the period September 1988 though August 1993.

3)  CHANGES IN REPORTING OF RELATIVE HUMIDITY BELOW 20 PERCENT
    AND AT TEMPERATURES COOLER THAN -40 DEGREES C

Relative humidity cutoffs below 20 percent and -40 degrees
Celsius will be eliminated.  The practice of cutoff of the
dewpoint depression when the temperature reaches -40 degrees C is
being changed for the first time.  The practice of truncating
relative humidity below 20 percent began in April 1973 until
August 31, 1993.

If you need additional information about any of these changes,
call Tom McClelland or Bob Thomas at (301)-713-0722.

END
SENT - W/OM23 - C. ALEX

Posted: Mon, Aug  9, 1993   3:38 PM EDT              Msg: LGJD-5838-5786
Subj:   three changes to AVN/MRF on 8/11/93           
I sent the following NTIM out this afternoon:

WSHPNSNMC
NOUS41 KWBC 091845

NATIONAL TECHNICAL INFORMATION MESSAGE 93-32
NATIONAL WEATHER SERVICE HEADQUARTERS
240 PM EDT MON AUG 9 1993

TO:         ALL USERS OF THE AVIATION (AVN) MODEL AND THE MEDIUM
            RANGE FORECAST (MRF) SYSTEM

FROM:       MARY M. GLACKIN
            CHIEF, SERVICES DEVELOPMENT BRANCH

SUBJECT:    THREE CHANGES TO THE AVN MODEL AND THE MRF SYSTEM


(THE FOLLOWING INFORMATION WAS PROVIDED BY WAYMAN BAKER OF THE
DEVELOPMENT DIVISION OF NMC.)

On August 11, 1993, with the 1200 UTC cycle, three major
enhancements to the global aviation and Medium Range Forecast
system are scheduled:

1)  The model's vertical resolution will be increased from 18 to
    28 levels;

2)  A simplified Arakawa-Schubert parameterization of convective
    precipitation will replace the Kuo convection scheme;

3)  Satellite temperatures retrieved at 40 levels instead of 15
    layers will be used in preparation for the "interactive
    retrievals" to be implemented soon.

With the above enhancements, an improvement in model performance
is expected in the upper troposphere and in the stratosphere in
the Southern Hemisphere.  Forecast precipitation should be more
smoothly distributed and the precipitation threat scores much
improved over the continental U. S.  Little change is expected in
the global model guidance for the hurricane track forecasts. 
However, the precipitation associated with tropical cyclones
should be much improved.

An evaluation by forecasters in the NMC Meteorological Operations
Division indicated a slight improvement in the aviation wind
analyses and forecasts at 250 mb in the Northern Hemisphere. 
Objective evaluation by NMC's Development Division showed a
significant improvement at 250 mb in the Aviation wind analysis
and forecast in the tropics and in the Southern Hemisphere.

A Technical Procedures Bulletin (TPB) which describes these
changes to the Aviation and Medium Range Forecast system is in
preparation, and will be distributed to TPB subscribers as soon
as possible.

If you need further information on these changes, please call
Masao Kanamitsu at (301)-763-8301.

END