By Rod Hill on 2013-01-23
With talk of freezing rain in some spots today, especially the Columbia River Gorge, I want to clarify the differences between frozen precipitation types.
Freezing Rain: Simply liquid rain in the air that freezes into a glaze of ice when the drops make contact with freezing objects on the ground. This is the precipitation type that can cause the most damage, coating trees and power lines with ice until the weight brings them crashing down. Freezing rain is the classic ice-storm. Just more than a trace of freezing rain can coat roadways and sidewalks with a sheet of ice making driving and walking impossible. Forecast models give meteorologist a temperature profile showing all warm air just above the surface. Under such conditions, when ground temps are 32 degrees or less, freezing rain will be in the forecast. The worst ice storms usually occur with ground temperatures in the 20s.
Sleet: A warmer layer of air in the atmosphere melts snowflakes into raindrops, after which the rain then falls into a freezing layer, turning the raindrops into ice balls or pellets. The frozen pellets then fall to the ground. Sleet, although formed differently does appear similar to hail stones to the casual observer. Sleet can fall onto a frozen or above freezing ground surface. Heavy sleet falling onto frozen roadways and lawns can coat the surface with thick ice, also making driving nearly impossible.
Hail: As mentioned above, hail appears at ground level much the same as sleet. The difference between sleet and hail is how the two are formed. Hail is formed through convective weather and for much of the country is most common in severe spring and summer thunderstorms. Liquid droplets in a cumulus cloud formation are carried high in the atmosphere into freezing temperatures where the droplets freeze into icy balls known as hail stones. The hail stones then fall from the top of the cloud to the bottom and back into above freezing temperatures where the icy stones are coated with liquid then carried by updraft winds back to the top of the cloud into freezing temperatures. The new liquid coating freezes into ice, making the hail stone larger. The process repeats until the hail stone is too heavy to be supported by updraft winds and falls to the ground. Single hail stones can be as small as peas and as large as soft balls! Here in the Northwest, hail is most common during the fall, winter and spring months when cold upper level lows, lower the freezing level and cause convective activity.
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By Rod Hill on 2013-01-12
Heavy snow the last two weeks, including more than 60 inches at Timberline Lodge, has pushed Oregon's snowpack to near normal across most areas. Overall, the snowpack is in much better shape than one year ago. Using Mt. Hood as a comparison, the first week of 2011 had a snowpack of 54 percent of normal. This year, the snowpack stands at 82 percent of normal on Oregon's highest point. The map below shows snowpack zones as a percentage of normal to date.
Summer streamflow forecasts are already being calculated and project normal to above river conditions. Keep in mind, the snowpack is measured through May 1st. We still have lots of weather to get through before we claim this winter's snowfall a success. The Mt. Hood test site currently has an 88 inch snow depth that would melt into 26.5 inches of water. The season average is 65 inches of runoff at the end of April. Obviously we still have a way to go. At this time, forecast charts show little snow the remainder of January. Last year, saw Mt. Hood snowfall between March and April drop more than 200 inches, making a big finish to the season.
Remember, my Mt. Hood Winter Forecast called for near normal snowfall this season, which would be less than the last two seasons. To date, Timberline as received 299" of total snowfall, the annual average is 400-500 inches.
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By Rod Hill on 2013-01-09
Let's not worry about the debate of man made or natural and just focus on the fact our planet is in a warm cycle. Temperature data for the United States shows a mean temperature for 2012 of 55.3 degrees Fahrenheit. The temperature is a new record for a data set that begins in the 1800s. The record is more than three degrees above normal and a full degree warmer than the old record of 1998. I likely do not have to tell you that Portland bucked the trend with temperatures last year near normal. However, 19 states did set all-time heat records for the year. Last July, was the warmest on record for our country. Last summer was the 2nd hottest on record. Extreme warm temperatures far out-paced record lows.
The headline of the warm year is the severe drought gripping the nation's heartland. Making the drought more harsh was the nearly one-third of the country that coped with at least 10 days of 100 degree or hotter temperatures during the year. 2012 was the 15th driest year on record. So far this winter, much of the upper midwest snow pack is well below normal. If the trend of little snow and below normal spring and summer rain continues, vital waterways such as the Mississippi river may not be able to support river commerce. Watch for the drought to be a huge story this coming summer if mother nature does not deliver much needed precipitation.
More information is available at: www.noaa.gov
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By Rod Hill on 2012-12-26
Here is an update to the soaker of a year 2012 has been so far. Usually we talk about the water year, which runs from Oct. 1st through Sept. 30th. The dates correspond with the mountain snow pack. Records are also kept for the calendar year, January 1st through December 31st. The normal precipitation for PDX is 36.03 inches. Record go back as far as 1941. So far, Portland has received more than 50 inches of moisture and still counting. The total is better than 15.00 inches above normal! The surplus represents roughly 3 extra months of winter rainfall! Here is the list of wettest calendar years at PDX:
1. 1996 63.20 inches
2. 1950 51.09
3. 1968 50.89
4. 2012 50.33 (as of Dec. 26th a.m.)
5. 1953 48.59
If you go back through the records dating back to 1990, 2012 becomes the 7th year Portland has received 50 inches or more. This year we had a soaking spring and a very wet fall, starting around mid October and of course December!
Enjoy the liquid sunshine.
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By Rod Hill on 2012-12-20
I have always thought winter weather begins weeks before the calendar agrees. The winter solstice officially changes the season at 3:12 a.m. PST Friday morning.
At that moment, the sun sits over the Tropic of Capricorn and the Earth's northern pole is tipped away from the sun. As seen from Portland, the sun will reach it's lowest southern point in the sky at 21 & 1/2 degrees on the horizon. The low angle will produce the longest and most spectacular sunrises and sunsets of the year, assuming we get to see. The shortest days of the year in terms of daylight hours are December 18-21st. Each day receives roughly 8.5 hours of sunlight minutes. Although the sun continues to rise later in the morning, sunset has already been occurring slightly later each evening. By February we will have gained enough daylight to produce warmer days with the average high warming back into the 50s. February is famous for a period of mild weather, often the first since the cold rains of December.
Happy Winter!
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By Rod Hill on 2012-12-10
Mild temperatures this fall are not producing records, but they allowing flowers to bloom. So far, the lowest temperature at PDX has been 35 degrees, reached twice in November. This is the latest in the season without an official freeze since the fall of 1999. In fact, since 1999 this year becomes only the third fall to not have a freezing temperature before December 1st. I remember, because the fall of 1999 was the year I moved here and my roses were still blooming Christmas week! That year stayed above freezing at PDX until Dec. 24th when the low dropped to 30 degrees. The average 1st freeze in Portland is November 8th. The year of 1934 holds the record for no freezing temperatures all year.
A few stats to highlight our mild weather include: since October 1st, 45 days have averaged above normal temperatures, only 21 days have been cooler than normal and we have had more overnight lows in the 50s than the 30s as of today's date. The normal low today is 35 degrees, the normal high is 46. The 7day forecast for Portland has no freezing numbers, but it does show a cooler pattern with temperatures likely to be near normal. The snow on the ground at Government Camp and Skibowl represents one of the few times this season the snow level has been below 4,000 feet for a number of days, but by the end of Sunday, rain was once again falling at Timberline.
Forecast charts are hinting at colder, wet weather with heavy mountain snow below Cascade passes the days leading up to Christmas.
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By Rod Hill on 2012-12-04
Below is my response to a friends email about climate change. I thought the article to be a good write and interesting read:
Rod, as a TV weather forecaster I see your job as serving two functions:1) Forecasting tomorrows weather 2) Educating the public as to what could be happening long term. I have tried to educate myself by looking at the literature of what has occurred and what trends are occurring and thought you might find them interesting.We often hear that global climate change is coming in the next 50 years, etc. I believe it has already arrived. Look at the recent arctic ice levels (http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm ) Note that even now at the end of Nov. that we are at 20% lower levels of ice than the average even though there is no sunlight there now. Climate scientists have predicted that an Arctic Ocean loosing a lot of ice would result in 2 changes: 1) Lack of ice will cause more sunlight to be absorbed on a dark surface rather than be reflected; this is a strong feedback mechanism 2) The jet stream would be affected; first, by delaying its advance southward starting in the fall/winter months and an earlier advance in the spring and, second the troughs and ridges would be longer lasting. As the Arctic loses its temperature difference from land and waters to the south, there is not the energy to create as strong a jet stream that will allow for more rapid changes. Therefore, the troughs and ridges in the path of the jet become more pronounced. As an example look at spring of this year in the Midwest where a long lived high pressure area led to temperature more than 30 degrees warmer than average in early March. These temperatures dried out the soil, the high pressure prevented rain and a severe drought was the result. At the same time the jet stream plunged all the way to Mexico in the West. It was cool and wet in the American Southwest. It snowed in northern Mexico. The jet stream became so deformed, it broke off forming a “closed” or “cutoff” low pressure area. In mid-July this high pressure ridge shifted slightly west leading to a long dry spell in the NW and record level of fires in the West. This year the Rocky Mountains, at the highest elevations, did not get their first snow until the third week of October and then only a dusting. While growing up in this Rocky Mountain region 50 years ago the high elevations often got their first snow from mid-August to Labor Day. Last year where the average was 45” of snow for the winter season only 4” fell, a new record low. An omega block high pressure lasted over the area almost all winter. Now the year before the blocking ridge was in the east and a trough in the West, resulted in record snowfalls. Both were extremely long lasting events. As the climate warms further these snowfalls will be more likely to be rainfall. Just a few days ago it was raining in Stanley, Idaho (elevation 7800 ft), usually the “icebox” location of the nation. There is no snow cover there as of 12/03/2012. Local residents say this has never occurred before. Once again there is an “omega block” high pressure ridge over the Rockies.In summary, we all know that water is slow to heat and equally slow to cool. Once ice has melted, very much heat must be shed before it freezes again, especially freezing to a large depth. The Arctic Ocean melted much more quickly than predicted and all the efforts to curb greenhouse gases will not refreeze it, except over a period of hundreds of years. We are once again talking climate change, but now the climate has changed. The high Arctic is much warmer on land and at sea than it used to be just a generation ago. Now, the Arctic Ocean will not refreeze except for a meaningless couple feet in late winter. Its deep blue waters will soak up more of the sun’s heat and make the Arctic warmer still. Melting permafrost is releasing billions of tons of carbon dioxide and methane gas. The normal daylight temperatures will raise slightly, but because of the 30 year running average the weather service provides, will not be obvious to most observers who get their weather from the television. The rising night time low temperatures will be more obvious but not noted by the average lay weather watcher.After writing this blurb I came across a recent article (see Dec 2012 Scientific American by Charles Greene pp 50-55) and the references cited therein.
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By Rod Hill on 2012-11-28
Do you remember last May 5th, when we told you about the "Super Full Moon?" The story that day was your chance to see what appeared to be the largest full moon of the year, as the moon made it's closest pass to earth. The close position of 221,705 miles from earth is called the perigee.
Today, November 28th, the moon will make it's farthest pass from earth at 252,503 miles. This most distant position, called the apogee will happen at 11:35 a.m. PST. This distant passing is called by some the, "Super Tiny Moon," as the moon may appear slightly smaller than usual. The moon was full this morning at 6:46 a.m. Of course, today's cloud cover will take away our viewing opportunity.
It is interesting to note that the large size of the moon near the horizon is a trick our eyes play, called the moon illusion. The illusion is a matter of perception, a trick the brain plays. When the moon is seen along the horizon, the brain perceives the object to be farther away and will make it appear larger in size. When an object is perceived to be nearer, the brain may compensate by making it look smaller to us. This smaller perception is what we see when the moon is overhead, high in the sky.
Moonrise today at 4:23 this afternoon.
Rod Hill
Courtesy: Jim Todd, OMSI Director of Space Science Education
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By Rod Hill on 2012-11-20
As of 6:00 pm Monday, here is the storm summary. The heavy rain and strong winds were produced by a Sunday evening warm front and the high wind field that followed, advecting a belt of deep moisture overhead Monday.
Coast Wind Reports: Columbia River Bar, sustained 74 mph, gust of 97, Lincoln City gust 85, Garibaldi 79 mph gust.
Coast Range: Elevations at 2,000' & higher saw gusts to 114 mph.
Valley: Newberg gust 60 mph, McMinnville gust 51, Hillsboro gust 48 mph. The Portland metro mainly saw gusts near 40 mph.
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Rainfall: Up to 7.00" reported over the Coast Range. 24-hour rainfall at Astoria 3.48"/ Seaside 3.89"/ Scappoose 3.71"/Portland 2.00"/Salem 2.29" / Hillsboro 2.50". Storm total at PDX 2.15"
Numerous reports of high water, including area rivers near flood stage. Power outages reported, roof damage in Newport and scattered trees down across the area.
As forecasted, this storm will likely be one of the strongest we see all winter, in terms of wind speed and heavy rain.
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By Rod Hill on 2012-11-19
Rain forecast Sunday evening Through Tuesday morning calls for: 3-5" or more at the coast, up to 8" over the Coast Range and 2-3" over the Valley. Many area rivers & streams will reach near or over flood stage Monday night, including the Wilson River, Johnson Creek, Nehalem, Grays River and the Clackamas at Estacada. The Willamette river is expected to rise 10 feet by Thursday, but remain well below flood stage. Here are the rain totals as of early Monday morning:
Astoria 2.35" / Tillamook 2.23" / Newport .69"
Portland 1.06" / Salem .70" / Kelso 1.56" / Scappoose 2.35" / Vancouver .94" / Hillsboro 1.46"/ McMinnville .38"
Hood River .60"
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A cold front Tuesday will break the flow of heavy moisture and return the forecast to showers or occasional rain through Thanksgiving day.
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