Oregon Climate Service, March 2005
Overview
March was like two very different months stuck together in the middle. The first half was a continuation of the very dry, mild conditions we “enjoyed” in recent months (at least, we enjoyed them until we thought about summer water shortages!). And then along came a major change in air circulation patterns, a succession of storms, and lots of rain and mountain snow. Most of Oregon received a month's worth of precipitation in the past 2 weeks of the month, and most of the state ended the month near- or above normal. We’re still facing the prospects of water shortages in parts of Oregon this summer, but we’re WAY better off than we were a month ago!
Table 1 is a summary of monthly
averages and totals at selected stations throughout the state. Table 2 lists
daily temperatures and precipitation for most of the locations listed
in Table
1. In Table 3, monthly and
seasonal precipitation totals throughout the state are listed.
Basin Summary
Here is a summary of precipitation, water supply, and snow pack as of the end of the month, by river basin:
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| OWYHEE | 75 | 94 | 83 | 75 | 20 | 34 | -2.0 |
| MALHEUR | 122 | 84 | 72 | 38 | 11 | 33 | -2.3 |
| GRAND RONDE, POWDER, BURNT | 102 | 78 | 67 | 44 | 52 | 60 | -2.8 |
| UMATILLA, WALLA WALLA, WILLOW | 80 | 54 | 60 | 26 | 47 | 52 | -3.0 |
| UPPER JOHN DAY | 46 | 70 | 66 | 39 | 30 | 37 | -2.5 |
| UPPER DESCHUTES, CROOKED | 78 | 64 | 60 | 48 | 36 | 43 | -1.9 |
| LOWER DESCHUTES, HOOD RIVER | 106 | 60 | 56 | 22 | 45 | 48 | -3.3 |
| WILLAMETTE | 107 | 59 | 58 | 35 | 41 | 45 | -3.0 |
| ROGUE, UMPQUA | 101 | 72 | 67 | 43 | 43 | 44 | -2.1 |
| KLAMATH | 68 | 68 | 64 | 40 | 44 | 57 | -2.2 |
| LAKE COUNTY, GOOSE LAKE | 82 | 98 | 78 | 85 | 35 | 38 | -1.4 |
| HARNEY | 65 | 87 | 73 | 48 | 28 | 53 | -1.9 |
| NORTH COAST | 90 | 63 | 54 | 17 | 70 | 57 | -2.6 |
| SOUTH COAST | 93 | 72 | n.a | n.a. | 79 | 59 | -2.4 |
n.a. Not available
(1) Percent of normal March precipitation, from NOAA Cooperative
sites
(2) Percent of normal seasonal precipitation (since Oct. 1), from
NOAA Cooperative sites
(3) Percent of normal seasonal precipitation, from Natural Resources
Conservation Service (NRCS) SNOTEL sites
(4) Percent of normal snow water equivalent, from NRCS SNOTEL
sites
(5) Percent of normal March stream flow, from U.S. Geological
Survey (USGS)
(6) Percent of normal seasonal stream flow (since Oct. 1), from
USGS
(7) Surface Water Supply Index, from NRCS (-4 = very dry, 0 =
normal, +4 = very wet)
Forecasts
The Climate Prediction Center’s (CPC) forecasts for April-June appear below. Temperatures for Oregon (and all of the West) are likely to be above normal, while precipitation probabilities are near normal.
Oregon Climate Service predicts normal temperatures and precipitation for the
next three months.
The “March Miracle”
Well, maybe not a “miracle, but it seemed like it. After the very disappointing
winter (at least to those of us who were hoping for a reasonably wet season),
the first half of March was very disappointing: very mild and extremely dry.
Irrigators began to prepare for exceptionally early crop watering, as the growing
season approached and very dry soils prevailed.
And then came a major change in large-scale weather patterns. The ridge of high pressure which had blocked storms all winter gave way to a “zonal flow” situation: this is a situation in which fast-moving storms, moving from west to east, hit our area every 2-3 days, bringing rains, clouds, and strong winds. This is exactly what we DIDN’T have during the winter, though we usually do. And now spring, which is supposed to be warmer and drier, is acting like winter.
Most of Oregon was above average for March, making this the first above-average month since October. Among the higher amounts reported was at Lee’s Camp in the northern Coast Range, where 5.9 inches fell in one day and nearly 9 inches was recorded in three days (last weekend). Here in the mid-valley we had 4.34 inches, which is .21 inches short of the long-term average for March – close enough so we can call it “near-average.”
The U.S. Geological Survey (USGS) is responsible for federal measurement of stream flow in the U.S. In Oregon, they operate about 100 stream gages. According to Tom Herrett of USGS, on March 18, 55% of the stream gages were reporting record low stream flows for that date. Ten days later, on March 28, none of the gages was reporting record lows, but 20% reported record HIGH flows for the date. What a turnaround!
In the Drought Council, we were asked, “do these rains help erase the drought?” My answer: at the very least, they buy us time by delaying the beginning of irrigation. They also have caused reservoirs and streams to rise significantly: Detroit Lake, for example, rose more than 30 feet in late March (see chart below).
That’s because spring rains, coming as they do very close to the growing
season, have a much bigger effect on summer water supply than do fall or winter
rains. An inch of rain in April might be the equivalent of 4 or 5 inches in
November, when it comes to summer water, when demand is highest.
When it comes to rain, it’s not just HOW MUCH rain falls that matters,
it’s WHEN it falls. The Bible says that love covers over a multitude
of sins. In weather talk, one might say that a wet spring can cover a multitude
of dry winter months.
The diagram above shows lake levels at Detroit Lake in the Cascades. The “water control” level, or “rule curve,” shows the ideal or target lake level: low during winter months to accommodate possible flooding, and rising during spring snow melt months. In mid-March the lake level was only 1484 feet MSL, about 50 feet below target, but by April 1 the lake had risen to 1516 feet and has continued to rise since that time.
Cloud
Seeding – A Dry Year Panacea?
Q. Why can’t we start a cloud seeding program in dry years like this
one to make sure we get enough rain?
A. This question pops up whenever we have a dry year here. The answers:
1. We can.
2. But it doesn’t work well in our truly dry years, because cloud seeding
requires CLOUDS – which were in unusually short supply last winter.
3. And it’s not cheap, either.
Q. How does cloud seeding work?
A. In the 1940s, Irving Langmuir and Vincent Schaefer performed an experiment on cold clouds inside a home freezer. They found that if they dropped tiny chunks of dry ice into the cloud, some of the “supercooled droplets” could be turned into ice crystals. The ice crystals grow rapidly, finally reaching a large enough size that they fall out of the cloud. The result is precipitation.
The supercooled droplets are the key to this. Small cloud droplets can remain liquid even when the temperature is as low as 40 degrees below zero. Aircraft flying through clouds can experience severe icing when droplets freeze upon contact with the fuselage or wings. Winter fogs also contain supercooled droplets that freeze on contact with objects such as fences, overhead wires, and vehicles.
During winter cloud seeding operations, aircraft fly above storm clouds and
drop dry ice into them. If the clouds are already producing some precipitation,
seeding can be very effective in increasing the snow pack over mountains. Long-term
winter seeding programs in California and Utah have demonstrated that the process
works well, producing increases in precipitation on the order of 10-20% higher
than if no seeding were done.
Other substances besides dry ice can be used as seeding agents. The most common
is silver iodide (AgI), a compound whose crystal structure closely resembles
that of ice. Some scientists think it “fools” the supercooled droplets
into freezing when they encounter AgI.
Utah experimented with using an unusual seeding agent, propane gas, in the Wasatch Mountains. The scientist in charge of Utah's project, Arlin Super, a retired professor of meteorology with 30 years of experience in cloud seeding, said the propane method appeared to increase snowfall by at least 7 percent. And propane seeding (from ground generators rather than aircraft) is far cheaper than dry ice or silver iodide seeding.
Summertime seeding is tricky, and not as effective, probably because there are fewer supercooled droplets.
Q. Do they use cloud seeding for other things besides rain and snow making?
A. Yes. Seeding can be used to clear up fog. This is practiced at some airports and air bases, including Fairchild AFB in Spokane. It is sometimes used in the Midwest to try to reduce hail.
The National Hurricane Center at one time tried to seed of hurricanes to reduce their intensity. This was called Project Stormfury. Unfortunately, it failed to modify hurricanes significantly, probably because there is already an abundance of ice crystals in hurricane rain systems, so the production of new ice particles through cloud seeding has little if any effect.
Q. Is there anything we can do this year?
A. Forget about cloud seeding. But how about conservation? Now is a very good time to conserve water, in anticipation of a typical warm, dry Oregon summer. In fact, conservation is a very good thing to do every year. Even in those wet years when we wouldn’t even THINK about doing cloud seeding!
Ref: Lyons, Walter A. The Handy Weather Answer Book. Visible Ink Publishers, Detroit, 1997.
Oregon Climate Service
George H. Taylor, Oregon State Climatologist
Wayne P. Gibson, Programmer/GIS mngr.
Eileen Kaspar, Research Assistant/Manager of Data Services
Melanie Mitchell, Undergraduate Assistant
Wolf Read, Undergraduate Assistant
Emily Gibson, Student Assistant
Cadee Hale, Publications Assistant
Kelsey Kuykendall, Undergraduate Assistant
Sara Joos, Student Assistant
Sean Daly, Student Assistant
Kirk Borgerding, Undergraduate Assistant
Oregon Climate Service, Strand 326,Phone: (541) 737-5705 Oregon State University Fax: (541) 737-5710 Corvallis, Oregon 97331 E-mail: oregon@coas.orst.edu Web: http://www.ocs.oregonstate.edu