Frost-depth gauge Installation,
Maintenance and Observation
This instruction sheet provides guidance on the installation, maintenance and procedure for taking
observations utilizing an NWS Model 5 frost-depth gauge.
The inside tube of the frost-depth gauge should be stored in a dark storage area away from any sunlight
or indoor lighting prior to installation. Prolonged exposure to light will cause the dye/water solution to
lose its consistency and/or body.
Tube Length Selection
The length of the frost depth tube should be selected to match the maximum frost depth of a
geographic location. Figure 1 below should be used as a guide to select the appropriate frost depth tube
Figure 1. Approximate maximum frost-depth contours. Frost-depth tube length should be selected to
capture the appropriate frost depth in a given geographic area.
The frost-depth gauge is typically co-located with other NWS observing equipment. The frost-depth
gauge should not be installed within a 20-ft distance of a heated building. In addition, the gauge should
not be installed within 10-ft of any marked underground utilities (see Utility Location). The selected site
should be reasonably level.
All utilities must be located and marked by a professional utility location service, prior to digging a hole
for the frost-depth gauge. As a general rule of thumb, all underground utilities must be located within
100-ft of the selected frost-depth gauge location. Contact the local utility location service and make a
request to have the utilities located on the property. Place a stake or other marker in the ground at the
selected site, prior to the utility location. The stake/marker will serve as a reference when describing
the location to the utility location service. Typically, it takes two to four full working days for the utility
location service to mark all the utilities. Do not install the gauge in a location that is within a 10-ft radius
of any utility line.
Installation Supply List
NWS Model 5 Frost-Depth Gauge:
o ¾-in diameter PVC outer tube with end cap (length varies from 2 ft to 6 ft)
o Flexible-clear inner tube assembly with top cap and handle (length varies from 2 ft to 6
ft). The clear tube is filled with green fluorescein dye.
o 4-in diameter PVC frost-depth gauge outer tube with lid
Small 4x4 in or similar size piece of scrap lumber
Post hole digger or hand auger or gasoline-powered auger or post-hole driver/black iron pipe.
Broom handle or similar flat-bottomed stick
Wooden stake or similar marker
Offices must have utilities located by a professional utility location service prior to boring a hole for the
Equipment Rental or Purchase Procedure
Offices may have to purchase or rent equipment to install the frost-depth gage. Central Region will fund
the rental or purchase of equipment to install one frost-depth gages on the property of each WFO.
There is a budgetary limit of $100 for the installation of a frost-depth gage at each WFO. Offices that
must rent or purchase equipment for the installation of frost-depth gages should follow the procedure
Regional Point of Contact (POC): Bob Brashears (Bob.Brashears@noaa.gov) 816-268-3161
1. Obtain an estimate for the purchase or rental of the necessary equipment required to bore a
single hole on WFO property to a depth that will accommodate your WFO frost-depth gage.
2. Once you have obtained an estimate, have the station MIC enter the following information in
the Central Region Facilities Project Request System:
a. SUBJECT: Frost-Depth Gage Installation
b. WFO Name
c. The handbook 5 ID (NSWLI) of the frost-depth gage that will be installed on WFO
d. An itemized list of the equipment to purchase and/or description of the equipment
rental that will be ordered and the associated costs.
e. The name of the person that will charge the purchase to your local office’s Government
Visa Purchase Card (for accounting purposes).
3. The POC will review the parts and/or repair request. Upon review:
a. If the purchase request is approved, the POC will approve the request in the system,
upon which the MIC and the person who entered the request will be notified via e-mail
that the equipment and/or rental have been approved, and the purchase can be
ordered. The charge code to be used will be included in the approval email for
reconciliation of office bank card statements.
b. If the purchase request is not approved, the e-mail generated by the request system will
notify the requester that the equipment and/or rental cannot be purchased.
4. Once the request has been approved, make the purchase and/or arrange for the equipment
rental. Charge the purchase to the office’s Government Visa Purchase Card. Notify the POC
immediately if the final costs are different from the initial estimate previously provided in the
Facilities Project Request System.
There are two basic approaches to creating a hole for installation of the frost-depth gage. A hole may be
excavated with a manual post-hole digger, gasoline-powered auger, or manual soil auger. A hole may
be pierced in the soil with a manual post-hole driver and iron pipe combination.
The excavation method requires removal of soil in layers to create a void space for the installation of the
frost-depth gage. This method should work in all soil conditions. A manual post-hole digger, gasoline-
powered auger, or manual soil auger may be used to excavate the soil layers. During excavation, soil
layers should be extracted in sections, and the soil sections should be preserved, in order of extraction
from bottom to top. The layers will be used to backfill void space once the gauge has been installed,
thus it is important that the layers are replaced in the order that they were extracted.
The diameter of the tool used to excavate can range from 1 to 12 inches in diameter. A 1 -in diameter
hole is the minimum diameter that will accommodate the frost-depth gauge. A 6-in or 8-in diameter
auger is the ideal size. The 6 to 8-in diameter hole may be easily backfilled with a tamping stick.
When excavating the hole, it is critical to maintain a 90-degree angle between the auger tool and the
ground surface. A bubble level can be used as a guide to ensure that the frost-depth tube is installed at
a 90-degree angle. After the gauge has been set in the hole, adjust the gauge depth so that the black
ground line mark on the outside of the gauge lines up with the ground surface. Use a yardstick laid
horizontally to line up the black line with the ground line.
After the gauge is adjusted to the proper height to match the ground surface, backfill the hole slowly
making sure the gauge stays as vertical as possible during the backfill process. Using a flat-bottomed
stick, tamp the dirt down tightly around the gauge. If possible, return the soil layers back in the hole in
the order they were taken out. The soil should be tamped down as closely as possible to the original
state of the compactness. Backfill and tamp the soil right up to the black line on the gauge.
Figure 2. A frost-depth gauge installed inside the 4-in diameter PVC cover. The tube is positioned so that
zero inches of depth reading is level with the ground surface.
The piercing method consists of driving a length of threaded black iron pipe into the ground to create a
void space for the installation of a frost depth gage. This method may not work in rocky soils or soils
with heavy clay deposits. The piercing method requires a single or multiple lengths of threaded black
iron pipe, depending on the depth requirement of the gauge, and a two-handled metal post driver. The
black iron pipe should be approximately the same diameter or slightly larger than the frost-depth gage
PVC casing. A 4-ft to 6-ft length of black iron pipe can be driven into the ground, and a second section
may be threaded onto the initial section to keep the above ground length of the pipe at a manageable
length for operation of the post driver. Once the desired gauge depth has been reached, remove the
entire length of threaded black iron pipe and install the frost depth gage. The black ground line mark on
the outside of the gauge should align with the ground surface. No backfilling is required with the
PVC Cover Installation
Using a short piece of scrap lumber and a sledge hammer, pound the 4-in diameter PVC cover into the
ground around the gauge. Use the piece of scrap lumber to protect the PVC cover from direct contact
with the sledge hammer. Secure the screw-on top.
A post, stake or marker can be placed near the gauge so that it can be easily found under deep snow
NWS CSSA Station Documentation
The frost-depth gages should be documented in the Cooperative Station Service Accountability (CSSA)
system in the "Other Equip Info" section. Complete the CSSA form as follows:
Equip Category: MISC
Azimuth and Distance: the direction and distance from the primary precip gage
Backup: Enter "N"
Equipment Description: NWS MODEL 5 FROST DEPTH GAGE / DEPTH "X" FEET / INSTALLED ON
"XX-XX-20XX" / DEPTH OF FROST PENETRATION (GD) AND DEPTH OF SURFACE FROST THAWED
(GT) REPORTED VIA WXCODER ( "ON MONDAY AND THURSDAY / OR DAILY" ...as appropriate )
FROM NOVEMBER UNTIL THE FROST IS OUT OF THE GROUND IN THE SPRING.
Once a year, a service check should occur prior to the reporting season (September to October). Key
Items to view during the annual inspection:
The gauge and the 4-in diameter PVC cover should be removed, inspected and cleaned.
Check the elevation of the zero line on the gauge in relation to ground level. Ground settling
may have occurred, and readings will be inaccurate if this zero line is higher or lower than the
ground level. If the zero line on the gage falls below the ground surface, then add soil so that
the ground line matches up with the black line (zero inch line) on the gauge. If the gauge is too
high, pound it down in the ground to the proper depth using a piece of scrap lumber and a
The dye/water mixture should be inspected. The dye/water mixture should maintain a green
color that is similar in color to automotive antifreeze. The dye should not appear faded, very
light green in color or “washed out.” If this is the case, then the dye and water mixture must be
drained and replaced.
The clear plastic tubing that contains the dye must be visually inspected. If the clear plastic
tubing appears foggy or cloudy, the whole inside clear tubing must be replaced.
Lubricate the cap threads lightly with white lithium grease or Vaseline. This will prevent the cap
from freezing in place.
Procedure for Taking Frost-Depth Observations
The objective of the frost-depth gauging program is to capture the formation and degradation of the
frost throughout the reporting season. The reporting season begins in Fall and ends in Spring, but may
vary widely by geographic region. The WFO must capture a minimum of two weeks of baseline zero-
frost depth data prior to the onset of frost. The WFO must capture a minim of two weeks of baseline
zero-frost depth data after all frost has melted. The WFO should coordinate with their RFCs to
determine the best date to begin and end the frost reporting season for their geographic area.
Reading the Instrument:
The instrument reports frost depth below ground level in units of inches. Ground level is designated as 0
in and units increase as the distance below ground increases. The inner tube must be removed from the
Figure 3. A frost-depth gauge being removed from the 4-in diameter PVC cover.
Frozen ground conditions will cause the liquid in the clear tube to freeze. Ice formation in the flexible-
clear tube will change the color of the liquid from a green color to a clear or opaque color, so that the
observer may visually identify the depth of frost penetration. In addition, a ball bearing has been
installed inside the clear tube. The observer may tip the clear tube upside down and take a reading at
the location where the ball bearing travel is restricted by the ice.
Observers are requested to report Depth of Frost Penetration and Depth of Surface Frost Thawed at
each report; however, Depth of Surface Frost Thawed need only be reported if there are at least 2 inches
of frost depth. Observations should be rounded to the nearest inch.
Depth of Frost Penetration is defined as the distance from the zero reading on the flexible clear
tube to the end of the frozen zone (clear) on the frost-depth gauge. As a second check, this is
the location where the ball bearing meets the ice in the tube.
Depth of Surface Frost Thawed is defined as the length of thawed (green) liquid that extends
from the ground level or zero to the top of a frozen zone of liquid (clear) on the frost-depth
gauge. Depth of Surface Frost Thawed is only recorded when there is at least 2 inches of total
frost depth. Depth of Surface Frost Thawed may not exist during periods of persistent cold.
Figure 4. An example gauge reading that shows 9 in of Depth of Frost Penetration and 2 in of Depth of
Surface Frost Thawed. Depth of Surface Frost Thawed needs only be reported if there are at least 2
inches of frost depth present.
The frost-depth readings should be reported and SHEF encoded through WXCODER. In WXCODER, these
elements are listed and SHEF encoded as Depth of Frost Penetration (GD) and Depth of Surface Frost
Thawed (GT), respectively.
Frequency and Timing:
CO-OP observers should take readings and report every day, if possible. At a minimum, CO-OP
observers should take readings twice per week on Monday and Thursday mornings before noon. All
observations should be submitted through WXCODER.
Weather Forecast Offices should take readings and report twice a week. Readings should be taken on
Monday and Thursday mornings before noon and should be submitted through WXCODER.
Special Precautions and Troubleshooting:
Try to keep snow or rain from falling into the outside tube of the frost-depth gauge. The flexible tube
should be kept in a dry environment. If water does get into the outside tube, try to remove it. A stick
with a sponge secured to the end can be utilized to remove any moisture/dirt that may have seeped into
the outside tube of the gauge.
The screw cap may freeze up and become difficult to remove in cold weather. This problem can be
eliminated by lubricating the cap threads lightly with white lithium grease or Vaseline. The cap should
also be tightened only enough to keep moisture from entering the measurement instrument.
The gage may be difficult to locate in deep snow. A marker or flag that sits above the snow pack will
help with the location of the device.
MSDS Safety Sheet for Green fluorescein liquid dye
Note: The fluorescein dye and distilled water in the clear tube have been mixed at a ratio of 1 part
fluorescein dye to 750 parts distilled water. See attached “MSDS.pdf” for the Material Safety Data