March Moisture: Storms bring Wyoming to average snowfallWritten by Christy Hemken
“Basically they’re giving us a forecast that says we’re on our own,” says Wyoming State Climatologist Steve Gray. “There’s no clear indication that we’ll be cooler or warmer than historical average for the months of April, May and June.”
On the other hand, he says predictions for precipitation over the next three months call for a fair chance of dryer than normal conditions across the state, but particularly for western and southwestern parts of the state.
“But what that means is hard to say,” he notes. “Historically they’ve had some trouble predicting what’s going to happen at this time of year, but the current forecast could have some serious implications for us in Wyoming, because that time of year tends to be the wettest portion and it’s important for generating forage.”
Gray says these forecasts are generated through analysis of historical weather patterns and trends. “They also look at conditions in the oceans surrounding North America and how their temperatures affect the way moisture gets from the ocean to interior areas of the country like Wyoming,” he explains. “That also has a big effect on the way storms track off the Pacific and into Wyoming.”
The USDA’S National Agriculture Statistics Service (NASS) reports that east of the Rockies temperature and precipitation patterns were consistent with conditions expected during a La Nina winter. However, the agency reports conditions in the West were a “patchwork quilt” of above and below normal precipitation totals not typical of La Nina.
“Winter temperatures averaged at least two degrees below normal in Maine and from eastern Montana into the Great Lakes region. Readings averaged as many as four to eight degrees below normal in North Dakota, Minnesota and Wisconsin,” says NASS. “Farther south, however, December through February temperatures averaged at least four degrees above normal in parts of the southern Rockies and southern Plains.”
Unfavorably dry weather prevailed from the Rockies westward in January, except for pockets of heavy snow across the Intermountain West and early-month downpours and flooding in the Pacific Northwest. An area from California into the Great Basin, where drought developed during the winter of ‘06-‘07, was of particular concern due to already low reservoir levels and the risk of completing a third consecutive year of drought. NASS reports, “At month’s end, California’s 151 intrastate reservoirs cumulatively held just 66 percent of the normal volume of water for January 31. At the same time, the Sierra Nevada snow pack contained a meager average of 10 inches of liquid, 59 percent of average for the date.”
Warmer than normal conditions were observed during February in a broad area stretching from the Rockies into the Midwest. Monthly temperatures averaged at least five degrees above normal across the southern half of the Plains. In contrast, cooler than normal weather prevailed across the northernmost Plains, the lower Southeast and the Far West. February readings averaged at least five degrees below normal in much of North Dakota.
In February much needed precipitation doubled the water content of the Sierra Nevada snow pack and aided California’s drought-stressed pastures and rangeland. According to the California Department of Water Resources, the water equivalent of the Sierra Nevada snow pack climbed from 10 to 20 inches (from 58 to 77 percent of average for the date) during February.
Gray says the moisture Wyoming recently received in March has brought the state back to somewhere in the neighborhood of historical averages. “We may seem wet based on recent experience, but most of the state is just at or slightly below average,” he says, noting that some areas, like the southern Green River Basin and parts of the Wind River Basin remain 10 to 20 percent below average in terms of snow currently on the ground.
“We’re ok up to this point,” Gray summarizes of spring moisture so far. “What will make or break us in terms of water supply and rangeland productivity is what’s going to happen over the next few weeks and months. That’s the critical time for determining what our growing season will look like.”