Call-In Criteria for|
Eastern Utah and Western Colorado
Please call the NWS at (970)243-7007|
email us at firstname.lastname@example.org
If you observe any of the follow:
|Snowfall Rates||1 inch per hour in the valleys, 2 inches per hour in the mountains.|
|Wind||Sustained of 30 mph or more, or with gusts greater than 40 mph, or if you do not have a wind gauge, difficulty standing or flying debris or any damage.|
|Fog or Blowing Snow||Restricting visibility to < 1/4 mile.|
|Thunderstorms||Anytime you see lightning or hear thunder, especially when snow is falling ("thundersnow!").|
Now you are prepared for taking snowfall measurements. Here are the three critical measurements when reporting solid precipitation:
But it is not always that simple. As winds increase, your gauge will collect less and less of the precipitation that actually falls. Generally speaking, the stronger the wind and the drier the snow, the less is captured in the gauge. If you notice that less snow is in the gauge than accumulated on the ground, first empty any existing snow from inside the 8-inch cylinder, then use it to take a snow sample, sometimes referred to as "take a core" or "cut a biscuit" from your snow board with the 8-inch overflow can. Melt the biscuit of snow, pour the liquid into the small measuring tube to measure the water equivalent.
If snowfall occurred several times during the period, and each snowfall melted either completely or in part before the next snowfall, record the total of the greatest snow depths of each event and enter in your remarks "snowfall melted during the OBS period". For example, three separate snow events during your 24-hour reporting day, say 3.0, 2.2, and 1.5 inches. The snow from each event melts off before the next accumulation and no snow is on the ground at your scheduled time of observation. The total snowfall for that reporting 24-hour day is the sum of the three separate snow falls, 6.7 inches, even though the snow depth on your board at observation time was zero.
Snow often melts as it lands. If snow continually melts as it lands and the accumulation never reaches 0.1 inches on your measuring surface, record the snowfall as a trace (T), and record in your remarks that the "snow melted as it landed".
It is essential to measure snowfall (and snow depth) in locations where the effects of blowing and drifting are minimized. Finding a good location where snow accumulates uniformly. In open areas where windblown snow cannot be avoided, several measurements may often be necessary to obtain an average depth. The measurements should not include the largest drifts. In heavily forested locations, try to find an exposed clearing in the trees. Measurements beneath trees are inaccurate because large amounts of snow can accumulate on trees and never reach the ground.
Report snow depth to the nearest whole inch, rounding up when one-half inch increments are reached (example 0.4 inches gets reported as a trace (T), 3.5 inches gets reported as 4 inches). Frequently, in hilly or mountainous terrain, you will be faced with the situation where no snow is observed on south-facing slopes while snow, possibly deep, remains in shaded or north-facing areas. Under these circumstances, you should use good judgment to visually average and then measure snow depths in exposed areas within several hundred yards surrounding your weather station. For example, if half the exposed ground is bare and half is covered with 6 inches of snow, the snow depth should be entered as the average of the two readings, or 3 inches. When, in your judgment, less than 50 percent of the exposed ground is covered by snow, even though the covered areas have a significant depth, the snow depth should be recorded as a trace (T). When no snow or ice is on the ground in exposed areas (snow may be present in surrounding forested or otherwise protected areas), record a "0".
When strong winds have blown the snow, take several measurements where the snow was least affected by drifting and average them. If most exposed areas are either blown free of snow while others have drifts, again try to combine visual averaging with measurements to make your estimate.