Grooming Guidelines




Snow grooming conducted by Bureau of Forestry (Bureau) personnel shall follow the guidelines in this document to obtain optimal productivity and grooming results.  Grooming is conducted to obtain a long-lasting trail by removing moguls and acquiring a consistent density.  The denser the snow, the longer the trail will last.

The overall objective of snowmobile trail grooming is to provide smooth trails that are suitable for all levels of rider experience. This can mean many things: establishing a trail base at the beginning of the season, having to reestablish a trail after heavy snowfall and/or winds have obliterated it, or having to work a heavily moguled trail back into a smooth surface (also called “restoring” the trail).

Where possible, grooming objectives may be met by “night grooming” (non-standard business hours).  Adequate equipment operator staff, employee availability and willingness to work beyond normal business hours, personnel safety, budgetary limitations, and AFSCME Union issues may be a basis for restrictions on grooming in specific forest districts.  Such issue may need to be addressed with AFSCME or other parties through the Bureau’s Division of Operations and Recreation and/or the Bureau of Human Resource’s Division of Employee Relations and Safety.

Where areas have traffic levels that are generally low, with little night riding and low weekday traffic, there is typically more flexibility as to when grooming efforts can be effective and few grooming repetitions per week will generally be required to have good trails.  If traffic levels are high everyday of the week, areas must look closely at scheduling factors to be as effective as possible with grooming expenditures. It is likely that 3 to 5 or even 7 repetitions per week may be needed to have good trails.  While some high traffic areas choose to groom mid-day to keep moguls from getting too deep, such efforts should be secondary to regular grooming.

The District Forester is permitted to use snowmobile clubs to assist in grooming roads and trails that have traditionally not been groomed nor are planned to be groomed by Bureau personnel to help meet the snowmobile user group needs.

Local Bureau personnel will assess snow and weather conditions prior to and during grooming so that, within equipment, personnel and budgetary limitations, optimum conditions are provided for snowmobiling. The groomer operator should examine the snow, by trying to make a snowball, for example. Very warm, wet, or saturated snow will not be cohesive. However, if the temperature is dropping, wet snow may refreeze overnight. Also, freshly fallen, cold, dry snow will not readily stick together. However, grooming and compacting this type of snow will enhance its ability to form bonds or “setup.”

A record of grooming, including schedules and trail / road names, will be maintained in each forest district office.  Main corridor trails and roads shall be groomed when favorable conditions exist.  All groomers owned and operated by the Commonwealth shall be equipped with a 2-way radio, a cell phone (when a particular district has them available to their employees and when deemed appropriate to supplement radio communications), fully functioning front and rear lights, and a fully functioning orange beacon mounted atop the groomer cab.  Groomers owned by an outside organization, such as snowmobile clubs, and operated on State Forest Land, shall be equipped with fully functioning front and rear lights and a fully functioning orange beacon mounted atop the groomer cab. 


Early Season Trail Preparation

The first snowfalls that are processed on the trail often create the base for the remainder of the winter. An early solid, smooth base of snow will help keep the trail smoother throughout the rest of the winter. Early winter snowfalls can contain more free water and can compact well. Therefore, vigorous smoothing and heavy compaction is often important for early snows.  Typically 4-6 inches are all that is required to begin base building.  Managers and operators must use their own discretion as local factors and conditions will dictate when base building can begin.  Newly fallen snow layers should ideally be cut to 6 inches or less, using only the blades, before compacting to ensure full compaction throughout the layer. Thick layers of newly fallen snow typically do not compact well.

In areas prone to wetness, such as low swampy crossings, it is advantageous to keep the snow thickness to a minimum in the early part of the winter. This allows the underlying soil to freeze and become stable. This frozen layer of earth will also help to keep the trail solid later into the spring season. Since snow is an excellent insulator, these areas should be kept thin so the ground remains frozen. Banked snow can be pulled onto these areas later in the season if bare spots occur.

Mogul Formation

Figure 1.5 demonstrates how moguls are formed. In the top view, a small rut is created in the trail by a snowmobile that has either braked suddenly or accelerated too quickly. Views 2, 3, and 4 show how the rut develops into a run of moguls as the suspensions of many successive snowmobiles react to the uneven trail surface, each one compounding the other, as each snowmobile passes.

Figure 1.5 Mogul formation

Removal of Moguls

Ideally, moguls should be completely cut away from the snow that forms the trail base. Beware that if the top is simply cut off a mound and dropped into the depression of the adjacent dip, it can result in the same mogul returning in no time at all. By completely removing the mound, all the way down to the bottom of the adjacent dip, the profile of the mogul is eliminated from the trail. However, also beware to not cut into the layer of snow that forms the compressed trail base below the bottom of a mogul’s dip. The mogul should be removed, but not the solid trail base below it, so care must be given to cutting no deeper than the bottom of the dips that form the moguls. This requires that the cutting depth must be continually monitored and adjusted by the Groomer Operator.

 There may be limitations to successfully removing the entire mogul: 1) if there is bare ground showing at the bottom of the dips in the moguls, do not attempt to cut the whole mound off since it could damage the equipment and result in destroying whatever hardened trail base there is; 2) if using a single blade drag and the moguls are deep, it is likely that snow could be lost out the sides of the drag when cutting deep enough with the blade to successfully remove the entire mogul. In this situation it is better to “save” the snow on the trail base rather than spilling it out the side where it may be “lost” for the purposes of grooming; 3) if using a tiller, the front blade on the tractor is the most effective tool for mogul removal prior to processing the snow with the tiller. However this has limitations since it cannot duplicate the planer effect of a drag; and 4) if using a multi-blade drag, it will not cut any deeper than the depth that the planer blades extend below the bottom of the side rails of the drag when it is fully lowered. If the trail bed is soft, the side rails may cut into the trail bed. But if the trail bed is hard, the rails will typically ride on top and limit the cutting depth. In all cases, the goal should be to remove all, or as much of the mogul as is reasonably possible, to produce a trail that will stand up better to snowmobiling traffic. Oftentimes, multiple grooming passes may be required to achieve this.

Multi-blade drags accomplish mogul removal by using multiple sets of planer blades angled to cut into the moguls. As shown in Figure 1.6, the preset cutting depth of the planer blades are typically stepped slightly lower from the front to the rear of the drag, which results in the deepest cutting depth when the drag is fully lowered so it rides flat on the side rails. Again, if the depth of the moguls exceeds the depth of the drag blades, multiple passes may be required to accomplish complete mogul removal.

Figure 1.6 Step 1: Removal of moguls. The planer blade cutting depth should cut to the bottom of the mogul’s dip, but not into the compacted trail bed.

Processing the Snow

At any given time, there may be several types of snow on a snowmobile trail – hard packed snow, soft snow, wet snow, dry snow, ice, freshly fallen snow, wind blown snow that is typically small granules and some of the hardest snow, or snow that has been pounded by snowmobiles and worked so hard by groomers that there is little consistency left in it. It is critical that all types of snow be “processed” to achieve proper trail compression and set up. In many drag designs, the multiple blades are angled so the snow moves from side to side further mixing and homogenizing it.  The more the blades are in contact with the snow; the more the snow will be processed.  While the snow is being mixed, it is also de-aerated (air space between snow particles is removed to make it denser).

This churning, tumbling, or milling action removes air from the snow and, at the same time, breaks up the compacted snow from which moguls are formed into smaller granules of various sizes. It also breaks away points from individual snow flakes so they can be compressed more tightly.

Figure 1.7 Step 2: Processing the snow. A churning action should be created in front of the planer blade to help process the compacted snow from the mogul into granules of various sizes.

The mechanical action of the churning and tumbling has another important purpose in that it can sometimes introduce moisture into the snow mix due to friction. This friction causes the temperature of the snow to actually rise, be it a very small fraction of a degree, which can create a small amount of moisture in the processed snow. This is especially valuable when snow is very dry. Introducing this moisture into the processed snow is also very important to achieving good trail “set up.”

It is critical that the rolling or churning action is achieved. If snow is allowed to ball up or plow along in front of the blades without this rolling action, the snow is not being properly processed (doesn’t de-aerate, doesn’t mix and break points, doesn’t produce friction). This can be caused by the tractor traveling too fast (not enough time for the snow to properly roll and process), grooming conditions being too warm or too wet, or improper drag blade height (set too deep if “plowing” or too shallow if no snow in blade).

The height of the drag’s blade(s) is critical to proper processing of the snow. If the trail is fairly smooth or only slightly moguled, only a minimum of snow will need to be processed since it isn’t desirable to disturb any more of the trail base than what is needed to remove the moguls. In such cases, there may only be a need to have snow churning in the rear sets of blades on a multi-blade or only a partial blade full on a single blade. If the trail is heavily moguled or if there is lots of new snow, more blades on the multi or greater depth on the single blade will likely be required. Remember – process only as much as is needed to remove the moguls, but no more.

Proper ground speed is also critical to proper processing of the snow. Too slow and the proper churning, rolling, and mixing to produce the friction that is needed to improve trail set up is not achieved. Too fast and several factors work against effective grooming, particularly with multi-blade drags. First, too high of a ground speed results in the angled blades spraying snow out the sides of the drag where it is lost and wasted for the purposes of grooming. Snow is precious to the grooming operation and most areas can ill afford to deliberately throw it off the trail. Second, the rolling and churning action is partially dependant upon forces of gravity, so proper time must be allowed for the snow to roll, churn, and fall out. Third, going too fast can sometimes, in effect, over-process the snow and prematurely wear it out. Processing snow can be similar to using a blender – low to mid speeds can achieve good mixing and blending, but setting the speed too high can actually start to change the consistency and even liquefy what’s being processed. The same can be true with grooming in that the quality of the snow can actually be adversely affected by going too fast. And fourth, regardless if using a single blade, multi-blade, or tiller to groom, too high of a ground speed results in a side-to-side rocking that produces a rough versus smooth finished trail. Irrespective of the type of groomer, the best quality trails, in terms of both smoothness and durability, result from grooming at speeds between 5 and 7 miles per hour.

After the processed snow passes through the last set of blades or the tiller, there should be an even blend of loose particles ready for compression.

 Compression of the Processed Snow

The moist, loose snow created by the processing step must be “compressed” into an even covering of uniform density with a smooth surface. This process further de-aerates the snow and provides for a denser trail surface.

Figure 1.8 Step 3: Compression of the processed snow. The loose snow created by the cutting and churning action of the blades is distributed by the spreader pan, then compressed into a new layer of compacted snow on the trail bed.

On a multi-blade drag, the front of the pan is angled so loose snow that is contained by the side rails is captured and pulled under the spreader pan where it is then compressed by the weight of the moving drag. Since single blade drags typically do not have side rails, the snow must pass under the single blade of the unit and then be compressed by the drag’s pan. If too much snow is carried in the single blade, it spills out the sides. This difference means that the multi-blade typically increases the finished snow depth/base of the trail with each pass, while the single blade increases trail depth only when there is an accumulation of new snow on the trail.

Trail Set Up

Set up is simply allowing the snow that has been disturbed by cutting, processing, and compressing the proper time required to refreeze. Generally, the longer the set up time that is allowed, the more durable the trail will be and the longer the newly created smooth surface will last.

Once the drag or tiller has passed, the snow from the moguls should have been fully removed, processed, and redistributed as a new layer of denser, smoother “snow pavement.”

The last step in the grooming operation allows the moisture that was created during the processing step to refreeze. This binds the individual granules of tightly packed snow firmly together, creating a hard surface that will withstand passing traffic much better.

The length of time needed for a trail to set up correctly can vary from two to six or even more than ten hours, depending upon the ambient temperature and snow moisture.

Trail set up can be similar to freezing a tray of ice cubes – after a short time there may be a crust but the cube isn’t entirely solid and it generally takes a few hours for it to become fully firm. A snowmobile trail is no different. Therefore, it is vital that the trail remain as undisturbed as possible during this set up period for firmer, better quality trails that will stand up longer to snowmobiling traffic.

Ideally, a snowmobile trail would be closed during set up time, but that isn’t practical. Consequently, the best time to groom is generally at night when traffic levels are typically lower and air temperatures are generally colder.

It is recommended that daytime grooming be done in areas only if there is little or no daytime snowmobile use on the trail being groomed. Other exceptions would include special circumstances such as when daylight would aid operator visibility for initial early season trail set up and establishment or for trail reestablishment of the trail after big storms, extremely heavy snowfalls, and/or significant wind events.

General Operating Guidelines

How Much Snow is Required to Start Grooming Operations?

The amount of snow depth required to begin grooming operations will vary by area and is affected by the type of terrain and by the type of snow. Remember that it requires a lot more snow to safely and effectively operate a groomer than it does to operate a snowmobile. And it can be a good thing to let snowmobiles run on the snow first before you start grooming operations because it starts the de-aeration and compression process. Generally, at least 8 to 12 inches of wet snow on smooth terrain like a road is enough to begin grooming operations. However, if the snow is drier, or if the terrain is rough or uneven, at least 12 to 18 inches of snow (or more) may be required to safely begin effective grooming operations.  Pleased be advised, however, these are general depth recommendations and goomer operating manuals should always be consulted prior to beginning any grooming operations.

Best Grooming Temperatures

Generally when using a drag, grooming operations should be suspended when the air temperature is below -25 degrees Fahrenheit or above +40 degrees Fahrenheit because it can cause snow to stick in the blades or build up on the packing pan enough of the time to make grooming a smooth trail impossible.  The ideal grooming temperature is approximately 25 degrees Fahrenheit.  Groomer operators may often have to use their own discretion and base grooming operations on other local factors including presence or absence of sunlight, terrain, expected weather conditions, etc.

Grooming Basics

Building Trail Base vs. Maintaining Trail Base

Anytime there is “new” snow to work with, either through new snowfall, blown in snow, or snow that is pulled in from the trail edges, grooming will build (increase) the trail’s base/depth. If “new” snow is not available, grooming will simply maintain the trail base, which is a much less desirable situation.

Ideal Groomed Trail Width

In most areas, the ideal groomed trail width will be 1½ to 2 groomer widths (typically 12 to 18 feet). However, local conditions and equipment widths will dictate what this means on any given trail segment. The clearing width in some wooded areas may only accommodate a single drag width, while other trails located on improved roadways may provide as much as 60 feet of width. However in these situations on wide roads, do not try to groom too wide. Pick a route and stick to it to ensure that the trail base is built from the ground up. If varied routes are groomed on wide roadways, it can result in soft pockets of snow and rough trails because the same designated trail route was not consistently compacted.  By keeping the groomed route on these wide roads narrower, the middle of the road/trail can be hardened and result in a better quality trail.

Think Visibility!

Grooming tractors should be operated with their warning beacon/strobe and lights on at all times to increase their visibility to snowmobilers approaching on the trail. A slow moving vehicle (SMV) sign should be displayed at the rear of all units since a groomer is nearly stationary when compared to a fast moving snowmobile.

Groom When Traffic Is Low

Always try to groom when traffic volumes are at their lowest.  This helps allow adequate time for the trail to set up properly and can also enhance grooming and snowmobiling safety.  The greatest single key to effective grooming is low traffic. So if traffic is heavy, consider an alternate time to groom. 

Pull Snow to the Middle of Trail

If there is a lack of snow in the middle of the trail, which is often the case since that is where snowmobiles most often operate, use the front blade to pull snow in from the trail’s outer edge or operate the drag on the outer edge of the trail. The outside two to three feet of a trail will often be softer than the middle of the trail due to the compaction that snowmobile traffic contributes in the middle of the trail.

Don’t Set the Drag Blades Too Low on Smooth Trails

When grooming a trail with little fresh snow cover and only minimal moguling, care should be taken to not have the drag adjusted too low because it would unnecessarily process the hard-packed trail base. Cut only as deep as the bottom of the “dip” of the moguls. If the trail is relatively smooth, only cut or “skim” with the rear set of blades. Following this method can help build/increase the depth of the hard-packed trail base.  

Deep New Snowfall Can Mean Starting Over

Moguls under a deep new snowfall cannot usually be completely removed. Process the fresh snow and compact it so a smooth finish is established as a new base on top of the moguls. Two passes may be required to achieve sufficient processing and compression when there is extremely deep new snowfall. A longer set up time will be required.

Grooming Wet Snow

Processing wet, heavy snow is more difficult and requires more operator finesse since it has more surface tension and will not flow as well as cold, dry snow. To groom in wet conditions, adjust the drag somewhat higher than if in below freezing conditions and pick up the speed of the tractor slightly. Monitor the snow to ensure it flows freely. If the snow begins to collect in the drag, raise it high enough to clear the snow and lower it again, but make sure not to deposit a hazardous pile of snow on the trail when doing so.

Grooming Hills

Hills can create another special challenge for groomer operators. There is likely to be a lack of snow at the crest/top of the hill and an abundance of snow at the bottom. Oftentimes, the hillside may be either icy, or even bare, from snowmobiles spinning their tracks while climbing it. It may also be bare due to southern exposure to the sun. As much as anywhere, hills are an area where the operator must anticipate and plan ahead. Also, always keep to the right so the groomer is not a hazard. The drag may need to be raised as the groomer begins climbing a hill.

Grooming Curves

Curves can create special challenges since there is typically low snow or no snow in the bottom of a sharp curve. At the same time, berms three to five feet (0.9 to1.5 meters) high (or more) can form on the outside edge if the curve is not regularly groomed and reformed. First, always beware that dropping too far down into the center of a sharp or blind curve can be dangerous for approaching snowmobile traffic. Therefore, never deviate over/inside the mythical centerline of the trail by more than a couple of feet so as to still allow room for an oncoming snowmobile to meet and pass the groomer in the curve. Second, if the groomer gets too high on the outside edge of the berm, it risks

becoming high centered and stuck. Use the front blade on the tractor to pull snow from the outside berm into the bottom of the curve. At the same time understand that it is difficult to “carry” much snow into the curve with a multi-blade drag because of its tendency to build trail depth versus “carrying and dumping” snow like what can be done with a single blade drag.

One other thing to keep in mind about grooming curves is that there is only one location in a curve where there is ever “extra” snow that may be available for the drag to move into the snow-deprived bottom of the curve. That location is the outside end of the curve and, sometimes, some of it can be tapped on the next reverse direction grooming pass. This is further explained as follows: Imagine the curve as an upside down U, like this: . The direction of travel and grooming is counterclockwise, on the outside/top edge of the curve, which means any “extra” snow will be deposited on this grooming pass by the drag at the end of the upper left corner of the , where it transitions from curve to straightway. If the grooming direction is reversed on the next shift (by grooming clockwise on the trail loop), the groomer will be on the inside/bottom of the curve as it enters the curve. By moving over to the left a couple of feet/half a meter (but no more so as to not create a safety hazard!) as the groomer approaches the curve, the drag can be swung slightly into the area with the extra snow, which is slightly before the outside left corner of the . Then, by dropping back into the bottom of the curve, the groomer can deposit any snow that was picked up with the drag into the bottom of the curve. This is a slow process, but by keeping at it, trail conditions on curves can be slowly improved.

Proper Use of the Front Blade

Don’t Over Use the Front Blade

When using a drag, the front blade of the grooming tractor is best used to level drifts or to pull new snow into the trail. Snow worked by the front blade is then processed, compressed, and leveled out by the drag. Operators are cautioned to not “over groom” by continually raising and lowering the front blade which can lead to accentuating dips and rolling trail surfaces. Rather, trail leveling is best accomplished by the planer effect of a drag pulled behind the tractor. When using a tiller, the front blade must perform the important process of removing moguls, so the front blade needs to be in use nearly fulltime. Still, overworking (too frequently raising and lowering) the front blade can lead to uneven trail surfaces and should be avoided. Try to use the tilt adjustment instead.

Blade Use at Grooming Speed

While operating the tractor at grooming speed when using a drag, it is recommended to run with the bottom of the front blade set about 4 inches above the bottom of the tracks, not at ground level. This can allow it to be used for day-lighting out finger or pillow drifts, while at the same time keeping it a safe distance above the trail bed and away from rocks, stumps, and other hazards. Watch behind the front blade to monitor the blade height in relation to the bottom of the tracks. If there is a need to use the front blade for heavy dozing or for building trail across a drifted side slope, slow down and operate with caution.

Tips for Operating Tracked Vehicles

Keep the Vehicle on Top of the Snow

Snow can have a top crust that is harder than the underlying base due to various melt-freeze or wind-packing conditions. It is to the operator’s advantage to try to keep the groomer on top. Try to not spin the tracks through that crust if at all possible.

If Stuck, Don’t Spin

If the groomer gets stuck, DO NOT spin the tracks. It is important to remember that a tractor is rarely stuck in a level position, unless it has spun out while climbing a hill on a hard packed, icy trail. Raising the implement and backing the unit down the hill will often remedy this situation. If not, the groomer is stuck, so proceed with caution.

More often than not, the tractor will be tilted to the right / outside edge of the trail because it fell off the compacted trail base. The first thing to do is get the tractor level. This is particularly true with gear drive tractors since the lubricants can run out of the differential into the axle tubes that are lower, which can leave the ring gear and pinion empty or low of grease. In such cases, spinning the tracks is the last thing that should be done since it can severely damage the tractor. Get the tractor level to protect it. At this point, a long handled, plastic scoop shovel is the operator’s best friend, and they should start digging. The tractor will most likely be high-centered, so snow must be removed from beneath the tractor’s front blade, frame, and undercarriage.

Once the tractor is level, the vehicle should be rocked gently back and forth which can help pack the snow. It is better to unhook a drag sooner versus later – it can save a lot of time, effort, or even damage to the equipment. If that doesn’t work, a winch or come-along may be needed to free the vehicle. Otherwise the operator must shovel some more.

Descend in Low Gear

When descending steep grades, use a sufficiently low gear and always keep the tracks revolving to permit steering. A good rule of thumb for descending steep grades is to use the same gear as is required for climbing the hill.

Raise the Drag in Deep Snow

In deep snow or in drifts such as can occur along fence lines or in a road ditch, raise the drag to prevent too much snow buildup. Also remove accumulated snow from the pan. If track slippage occurs, try to wriggle the unit through the excessively deep area of snow.