Policy and Procedures for Precision Digital Barometer Comparisons

NATIONAL WEATHER SERVICE
SILVER SPRING, MARYLAND 20910-3283
Operations Manual Letter
07-99

Date of Issue: Effective Date:

In Reply Refer To: W/OSO14 File With: B-10, B-11, B-12, and B-66

Subject: Policy and Procedures for Precision Digital Barometer Comparisons

References: National Weather Service Operations Manual Letter, 2-98, Policy Statement on NWS Barometry, Filed with: B-10, B-11, B-12, and B-66

Attachments:

(1) Procedures

(2) Summary Table

(3) Comparison/Verification Form

Policy

The Precision Digital Barometer (PDB) shall be used as the barometric home station standard (HSS) for the upper-air program and other meteorological programs not associated with the Automated Surface Observing System (ASOS).

In accordance with the reference, ASOS shall be the HSS for the surface observing program at offices collocated with a commissioned ASOS. At offices with both a surface observing program and an upper-air program, ASOS will be the HSS for the surface observing program, and the PDB will be the HSS for the upper-air and other meteorological programs. The PDB will be used as a back-up instrument to the ASOS. There is no requirement to compare the PDB operationally against the ASOS. All PDBs shall receive initial calibration at the NWS Pressure Standards Laboratory.

John J. Kelly, Jr.

Assistant Administrator

for Weather Services

WSOM-B-10-07-99

Procedures

1. NWS offices with an upper air program: At the time of annual calibration, the NWS field office will receive a replacement PDB from W/OSO321 and notification to return the current PDB. The point of contact for replacement of these instruments is W/OSO321, 301-713-1834. A verification of the PDB readings shall be conducted at least once every 6 months with the NWS Digiquartz Paroscientific Inc. model 760-16B Traveling Standard.

a. The verification will be done by comparing the sensor pressure of the PDB with the Traveling Standard.

b. The PDB and Traveling Standard must be positioned within 1 foot of each other in the vertical and 3 feet in the horizontal during the verification. The procedure shall consist of two verification readings taken at least 15 minutes apart. For each verification, the uncorrected sensor pressure shall be read to the closest 0.001 inch of mercury (Hg). The verification shall be documented using WS Form B11-11 (3-99) (attachment 3).

c. If both readings are within 0.007 inch of Hg when compared to the Traveling Standard, no further action is required.

d. If either of the readings of the PDB deviates more than 0.007 inch of Hg from the Traveling Standard discontinue use of both instruments and consult with the regional surface program manager and W/OSO321 to determine which of the instruments may be deficient.

2. NWS offices without an upper air program: The PDB will not be calibrated annually by the Pressure Standards Laboratory at these locations, but shall be compared at least once every 6 months against the Traveling Standard.

a. The comparison will be done by comparing sensor pressure of the PDB with the Traveling Standard.

b. The PDB and the Traveling Standard must be within 1 foot of each other in the vertical and 3 feet in the horizontal during the comparison. The procedure shall consist of two comparisons taken at least 15 minutes apart. For each comparison, the uncorrected sensor pressure shall be read to the closest 0.001 inch of Hg. The comparisons shall be documented using WS Form B11-11 (3-99) (attachment 3).

c. If both readings are within 0.02 inch of Hg when compared to the Traveling Standard, no further action is required.

d. If either of the readings of the PDB deviates more than 0.02 inch of Hg from the Traveling Standard, the PDB shall be removed from service and returned to the NWS Pressure Standards Laboratory for recalibration.

e. Every 5 years W/OSO321 shall inform each NWS field site of the 5-year recalibration through the delivery of a replacement PDB.

3. ASOS Backup: No correction shall be applied to the PDB when used as the operational backup to ASOS. If for any reason the ASOS pressure data is not available, PDB readings for altimeter and sea level pressure shall be read and used to

backup those elements in the surface observation.

4. Notification Procedure: W/OSO321 shall be notified immediately of any deficient instrument. A replacement PDB will be shipped via overnight delivery. W/OSO321 shall maintain the computer storage disks containing station dependent data, including r-values. The data files from these disks shall be entered into the PDB's memory by W/OSO321 prior to a new PDB being delivered to field locations. NWS field staff should verify station dependent data within the PDB's memory upon receipt of the PDB.

Precision Digital Barometer Comparison Policy

Program Function Calibration WFO Comparison Requirement

NWS Offices with an Upper Air Program and No ASOS

Home Station Standard/ Operational Barometer 1) Initial calibration before deployment.
2) Annually after initial deployment.

3) Consultation with region and W/OSO321 if PDB deviates more than 0.007 inch from Traveling Standard.
A verification of the PDB readings shall be conducted at least once every six months with the Traveling Standard.

NWS Offices with an Upper Air Program and Collocated with a commissioned ASOS 1) Home Station Standard/ Operational Barometer for Upper Air
2) Operational Backup to ASOS
1) Initial calibration before deployment.
2) Annually after initial deployment.

3) Consultation with region and W/OSO321 if PDB deviates more than 0.007 inch from Traveling Standard.
A verification of the PDB readings shall be conducted at least once every six months with the Traveling Standard.

NWS Offices with an ASOS and no Upper Air Program Operational Backup to ASOS 1) Initial calibration before deployment.
2) Recalibration every five years

3) Recalibration required if PDB deviates more than 0.02 inch from Traveling Standard.
The PDB shall be compared at least once every six months with the Traveling Standard.

NWS Offices with no Upper Air and no ASOS Programs

Home Station Standard/
Operational Barometer
1) Initial calibration before deployment.
2) Recalibration every five years

3) Recalibration required if PDB deviates more than 0.02 inch from Traveling Standard.
The PDB shall be compared at least once every six months with the Traveling Standard.

Summary Table

WS Form B11-11 U.S. Department of Commerce
(3-99) National Oceanic and Atmospheric Administration

National Weather Service

Precision Digital Barometer (PDB) Comparison/Verification Form

(See detailed instructions for preparation of form on reverse side)
Station:

Station
Elevation:
PDB Elevation: Field Elevation
(If applicable):

Year/Quarter
(1)
Traveling
Standard

Serial Number

(2)
PDB Serial
Number

(3)
Readings from
Traveling Standard

(4)
Readings from
PDB

(5)
Differences from
Traveling Standard (6)

1st reading
(4a)
2nd reading
(4b)
1st reading (5a) 2nd reading (5b) 1st reading (6a) 2nd reading (6b)

WS Form B11-11

(3-99)

Guide for Preparing Form

Headings: Enter Station name in plain language, e.g., WFO Green Bay, Wisconsin

Enter Location as Latitude/Longitude e.g., 44.29 North 88.08 West

Col. 1 Enter the year and quarter the comparison is made. The required verifications/comparisons should be made during the first month of each alternating quarter. The format for Year/Quarter should be consistent, e.g. 99/1st.

Col. 2 Enter the serial number for the Traveling Standard used to compare the PDB.

Col. 3 Enter the serial number of the PDB being compared.

Col. 4a Enter the first sensor pressure reading from the Traveling Standard to the closest 0.001 inch of Mercury (Hg), e.g., 30.014

Col. 4b Enter the second sensor pressure reading (taken at least 15 minutes away from the 1st reading) from the Traveling Standard.

Col. 5a Enter the first sensor pressure reading (taken at same time as reading in 4a) from the PDB to the closest 0.001 inch of Hg.

Col. 5b Enter the second sensor pressure reading (taken at same time as reading in 4b) from the PDB to the closest 0.001 inch of Hg.

Col. 6a Enter the difference between 4a and 5a to the closest 0.001 inch of Hg.

Col. 6b Enter the difference between 4b and 5b to the closest 0.001 inch of Hg.

For the upper air locations: Notify the regional surface observing manager and W/OSO321 at National Weather Service Headquarters if either 6a or 6b exceeds 0.007 inches of Hg.

For the non-upper air locations: Notify the regional surface observing manager and W/OSO321 at National Weather Service Headquarters if either 6a or 6b exceeds 0.02 inches of Hg.

Comparison/Verification Form (back side)

Date of Issue:				Effective Date:
In Reply Refer To:			W/OSO14	File With:	B-10, B-11, B-12, and B-66
Subject:	Policy and Procedures for Precision Digital Barometer Comparisons
References:		National Weather Service Operations Manual Letter, 2-98, Policy Statement on NWS Barometry, Filed with: B-10, B-11, B-12, and B-66

Precision Digital Barometer Comparison Policy
Program	Function	Calibration	WFO Comparison Requirement
NWS Offices with an Upper Air Program and No ASOS	Home Station Standard/ Operational Barometer	1) Initial calibration before deployment. 2) Annually after initial deployment. 3) Consultation with region and W/OSO321 if PDB deviates more than 0.007 inch from Traveling Standard.	A verification of the PDB readings shall be conducted at least once every six months with the Traveling Standard.
NWS Offices with an Upper Air Program and Collocated with a commissioned ASOS	1) Home Station Standard/ Operational Barometer for Upper Air 2) Operational Backup to ASOS	1) Initial calibration before deployment. 2) Annually after initial deployment. 3) Consultation with region and W/OSO321 if PDB deviates more than 0.007 inch from Traveling Standard.	A verification of the PDB readings shall be conducted at least once every six months with the Traveling Standard.
NWS Offices with an ASOS and no Upper Air Program	Operational Backup to ASOS	1) Initial calibration before deployment. 2) Recalibration every five years 3) Recalibration required if PDB deviates more than 0.02 inch from Traveling Standard.	The PDB shall be compared at least once every six months with the Traveling Standard.
NWS Offices with no Upper Air and no ASOS Programs	Home Station Standard/ Operational Barometer	1) Initial calibration before deployment. 2) Recalibration every five years 3) Recalibration required if PDB deviates more than 0.02 inch from Traveling Standard.	The PDB shall be compared at least once every six months with the Traveling Standard.

WS Form B11-11 U.S. Department of Commerce (3-99) National Oceanic and Atmospheric Administration National Weather Service Precision Digital Barometer (PDB) Comparison/Verification Form (See detailed instructions for preparation of form on reverse side)					Station:

					Station Elevation:	PDB Elevation:	Field Elevation (If applicable):

Year/Quarter (1)	Traveling Standard Serial Number (2)	PDB Serial Number (3)	Readings from Traveling Standard (4)		Readings from PDB (5)		Differences from Traveling Standard (6)
Year/Quarter (1)	Traveling Standard Serial Number (2)	PDB Serial Number (3)	1st reading (4a)	2nd reading (4b)	1st reading (5a)	2nd reading (5b)	1st reading (6a)	2nd reading (6b)