Rod's Weather Headlines

Let me begin by saying, the skill level for seasonal forecasting is less then 20% better than pure chance or guessing.  The skill does increase with strong La Nina and El Nino episodes.  With that said, this winter is expected to be a Neutral or weak El Nino season, meaning equatorial water temperatures in the Pacific are likely to be near normal or less then one degree celsius above normal.  This means, the forecast skill for this winter is on the low side of prediction.  The method I use to reach conclusions is comparison, meaning I look for similar La Nina, El Nino or Neutral years and compute the average of such seasons. 

Last winter was the 2nd of back-to-back La Nina seasons.  My research showed the 2nd La Nina is typically weaker.  My projection was for Mt. Hood to see 50" less snow than the previous year.  The forecast was correct!  Timberline 2010-2011 received 696" of snow for the season.  Last winter has a total of 550 inches.  (Yes more than 50" less, but the trend was correctly projected).  I predicted the valley water year would be drier by 5-7.00" of total moisture.  Again the prediction was correct.  PDX water year 2010-2011 saw 44.74", the water year ended 2011-2012 had 39.73 inches.

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Here is my 2012-2013 Winter Prediction:  

Neutral to Weak El Nino Winter Season Will Be Drier Than Normal With Low Odds of Significant Snow.  

Comparison years:  1953 - 1954 / 1958-1959 /1976-1977 / 2004-2005

Portland Water Year Precipitation Forecast:  A below normal 33. 71"  /  Normal is 36.03"

Snow Forecast:  3.4" for the season

Mt. Hood Snow:  400-500 inches at Timberline would be near normal to below & the driest since 2006-2007. 

We are not "due" for any extreme weather events.  The last valley windstorm was December 2006, last major snow event was Dec. 2008.  The winter season had 23.7" including a white Christmas!  

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Keep in mind, to reach my conclusion, I took the average of a data set.  The years of comparison include the following weather events:

1.  January 1954:  10.6" of snow

2.  November 1958:  Wind Storm, PDX sustained to 51 mph with a 71 mph gust. Coast Range over 100 mph.

3.  My strongest comparison season is 2004-2005.  The Mt. Hood snowpack that season was 44% of normal.

4.  January 2005:  Bad ice storm, freezing rain all day.  

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The two patterns I will be watching:

1)  Will Mt. Hood have it's first low snowpack in years, matching 2004-2005?

2)  Will this coming spring continue a shift of our wet season into the months 

of March - June?  The past few years have been nearly as wet in spring as winter!

Any questions, or comments please let me now on the PortlandWeather Facebook page or email if you are a Concierge member.  

Happy Rainy Season!

The 2011-2012 water year and September come to an end.  Despite our recent dry stretch, the water year, thanks to another wet spring and especially June, finishes with a surplus.  The water year ends with:  39.73" of precipitation.   

Normal Water Year 36.03"  /  2011 - 2012 surplus:  +3.70"

Interesting to note that the adjusted 30-year water year average is drier than the 1980 - 2010 average which was 37.07".

September ends with .04" of rainfall, which is the 4th driest at PDX. Here is the dry list:

September 1993:  Trace

September 1965:  .01"

September 1991:  .02"

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The combo months of August & September were the driest in the record book which dates back to 1871!  The two month rain total was .04 inches.  Only three times in recorded history, have the two months produced less than .50" of total rainfall.  There does not seem to be any correlation between our recent dry weather and up-coming winter precipitation.

Looking forward, very little if any rain is expected the first two weeks of October.  The driest October at PDX was .19" of rainfall back in 1988, 2nd driest was .27" in 1987.  Normal October rainfall is 3.00".  Our rainy season is said to begin November 1st when 19 of 30 days typically see rainfall during the month.  

The .04" of rain at PDX last night ended 51 days in a row with a trace or less of rainfall, good enough for 8th place on the dry list of days with less than .01 inches.  The rainfall today also ended 22 days in a row with not even a trace of rain.  The streak of 22 days has been equaled nearly 10 times over the years.  The record for no rain is 41 days back in 1967.  The record for only a trace of rain is 71 days, also back in 1967. The summer of 1967 was a neutral to weak La Nina season that had a trace of rain between June 23rd - Sept. 1st.  Now that is a dry summer!  Below is the report from the NWS.  

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PUBLIC INFORMATION STATEMENT
 NATIONAL WEATHER SERVICE PORTLAND OR
 540 AM PDT MON SEP 10 2012
 
 ...51-DAY DRY STREAK COMES TO AN END AT PORTLAND AIRPORT...
 
 A POTENT COLD FRONT IS MOVING ACROSS THE PORTLAND AND VANCOUVER 
 METRO AREA EARLY THIS MORNING...BRINGING WITH IT A BRIEF PERIOD OF 
 RAIN AND A SHARP WIND SHIFT TO GUSTY NORTHWEST WIND. THIS WILL USHER 
 IN THE FIRST REAL AUTUMN-LIKE COOL AIR MASS OF THE SEASON. PERHAPS 
 IT IS APPROPRIATE THAT THE FIRST MEASURABLE RAIN IN 51 DAYS COMES 
 ALONG WITH AN AUTUMNAL CHILL.
 
 SO FAR...AS OF 540 AM THIS MORNING...0.04 INCHES OF RAIN HAVE FALLEN 
 AT PORTLAND AIRPORT. THUS THE 51-DAY DRY STREAK AT PORTLAND AIRPORT 
 HAS COME TO AN END.
 
 BELOW ARE THE TOP 10 DRY STREAKS AT PORTLAND AIRPORT...
 
            NUMBER 
           OF DAYS     YEAR          DATES
    ==========================================            
      1.   71 DAYS     1967     JUN 23 - SEP  1 
      2.   62 DAYS     1984     JUN 30 - AUG 30
      3.   55 DAYS     1960     JUN 20 - AUG 13
      3.   55 DAYS     1952     JUN 30 - AUG 23
      5.   53 DAYS     1980     JUL  5 - AUG 26
      6.   52 DAYS     1951     JUL  7 - AUG 27
      6.   52 DAYS     1985     JUN  8 - JUL 29
 ***  8.   51 DAYS     2012     JUL 21 - SEP  9  ***
      9.   47 DAYS     1998     AUG  1 - SEP 16
      9.   47 DAYS     1981     JUL 13 - AUG 28
 

August 2012 at PDX goes into the record book with a trace of rain.  The lack of moisture ties the years 1998, 1970, 1967 and 1955 for the driest August on record at PDX.  Back in 1885, no moisture was recorded.  Normal rainfall is .67 inches.  The wettest August all-time was 4.53" in 1968.  

The average high temperature was 83.3 degrees, which is 2.2 degrees above normal.

The average low temperatures was 58.9 degrees, which is 0.9 degrees above normal.

The mean temperature was 71.1, which is 1.6 degrees above normal. 

No days had total cloud cover.  11 days were clear and 21 partly cloudy. 

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Meteorological summer is June, July, August. 

June was 2.4 degrees below normal, July was 1.2 degrees below normal.  The summer average for 2012 was 2.0 degrees below normal. 

June was the 2nd wettest on record at PDX with 4.10", July was dry with .21" and August only a trace.  The summer rainfall total is 4.31", 3.02" is considered normal. 

It should be noted that the July & August rain total of .21" is the driest combo since the summer of 2003, when July had zero rainfall and August .19 inches.  The summer of 1967 had only a trace during the two months!

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Forecast outlooks continue to show below normal rainfall through October.  Very little if any rainfall is expected through mid-September.

August 19th kicks-off the slow march towards the rainy season, which is considered to begin November 1st.  According to the climate record, the following is the progression of Portland's daily rain chance. 

Driest Part Of The Year:  July 11th - August 18th /  Daily Rain Chance 10%

August 19th - Sept. 13th:  Daily Rain Chance 20%

Sept. 14th - Oct. 5th:  Daily Rain Chance 30%

Oct. 6th - Oct. 19th:  Daily Rain Chance 35%

Oct. 20th - Nov. 3rd:  Daily Rain Chance 50%

Nov. 4th - Nov. 30th:  Daily Rain Chance 60 - 70%

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The above are "eye-ball" averages and not exact.  

Forecast outlooks continue to show mostly dry weather through August.  Below normal rainfall is expected through October. Temperatures the next two months are expected to be near normal to cooler than average.  It still looks like we could have a spectacular fall season!

Rod Hill

Peak viewing of the Perseid Meteor shower tonight around 9:00 pm.  Dark areas in the country could see 40-60 meteors per hour.  Visibility near the city lights will be closer to 10-20 at most.  The meteors, often the size of a grain of sand produce amazing light as they enter the earth's atmosphere.  The shower is produced as the earth enters the path of debris left by the comet Swift-Tuttle.

OMSI and the Rose City Astronomer club will hosts viewing parties tonight, starting at 8:00 pm at Rooster Rock state park in the gorge and Stub Stewart Park in the Coast Range.  Parking is $5 per vehicle. Telescopes will be set up free of charge for you to enjoy!

Skies will be clear tonight with a crescent moon.  Sunset in Portland will be 8:22 p.m. 

REVISED FORECAST: The CME launched toward Earth by yesterday's X-flare is moving faster than originally thought. Analysts at the Goddard Space Weather Lab have revised their forecast accordingly, advancing the cloud's expected arrival time to 09:17 UT (5:17 am EDT) on Saturday, July 14th. Weekend auroras are likely.

EARTH-DIRECTED X-FLARE: Big sunspot AR1520 erupted on July 12th around 16:53 UT, producing an X-class solar flare and hurling a CME directly toward Earth.  Forecasters expect the cloud to arrive on July 14th.  Its impact could spark moderate to severe geomagnetic storms, allowing auroras to be seen at lower latitudes than usual. 

Check http://spaceweather.com for more information and updates.

http://www.swpc.noaa.gov/SWN/index.html

Jim Todd

OMSI Director of Space Science Education

Here is a look back at another cool and wet June:

PDX Rainfall:  4.10"  / 2nd wettest in history, behind June of 2012, 4.27"  Normal for month is 1.70"

Average High:  69.7 degrees / 3.8 degrees below normal

Average Low:  52.7 degrees / slightly below normal, -0.9 degrees

Mean Temp:    61.2 degrees / 2.4 degrees below normal

12 days had partly or sunny skies / 14 is average

18 days were overcast /   16 is average

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Does it surprise you that June had only 2 more cloudy days than average?  This is a reminder that June is not a sunny month for us.  With that said, the high temperatures were cooler than normal and of course total rainfall was nearly a record.  16 days had measurable rainfall, normal is 10 days. 

The updated summer outlook calls for July - September to see near normal temperatures.  The forecast for the 3 month period continues to call for below normal rainfall, which would mean extremely dry conditions. 

I was thinking yesterday, that the start of summer is truly more special for the Northwest than most of the country.  For most, summer weather, meaning sunny, hot days began weeks ago.  Summer fun in warm lakes, boating with sun screen and complaining about 90 degree heat has been going on for weeks.  But for the Northwest, today brings hope to many of a changing season.  Dreams of days of sunshine and warm temperatures near 80 degrees will begin this afternoon.  Most of us will have renewed hope that rainy, cloudy days that struggle to reach 60 degrees will vanish until October or November.  For us, the summer solstice truly is the start of a new season of hope and childhood dreams.  I say bring on summer, a new season of fun and laughter and let us rejoice!

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The below information is courtesy of Jim Todd, OMSI planetarium manager:

For the Pacific Time Zone, summer officially begins with the summer solstice on Wednesday, June 20 at 4:09 p.m. PDT.  The earth is tilted so that the north pole is at its closest point with the sun. (Yet, the earth will be at its farthest distance from the sun, called aphelion, on July 5)  As a result there will be more minutes of sunlight in the northern hemisphere than there are at any other time of the year.  The word “solstice” is derived from the Latin sol-stitium, for sun-standing.  The summer solstice is the time of the year when the sun stops its northern climb and stands briefly before turning back toward the equator. As seen from Portland, the sun will reach its highest northern point in the sky at 67.54 degrees from the horizon on June 21 at approximately 1:12 p.m.  From March 21 until September 24, there are more hours of daylight than darkness.  After June 21, the days will gradually grow shorter until December 21, the winter solstice.

Not everybody is celebrating. Far to our south, across the equator, winter has arrived. For people in the southern hemisphere, June 21st, will be the shortest day of the year. It also means the beginning of their winter. 

Six months from now, when the earth has made half of its yearly trip around the sun, the northern hemisphere will experience that cold weather. December 21 will be winter solstice. That's when we have the fewest hours of sunlight and winter officially begins.

Friday's thunderstorms and .63" of record rainfall for the date, put PDX over the top, both for the month of June and the water year!  The June average for the entire month is 1.70"  Portland began today with 1.98" in the rain gauge.  What is more impressive is the water year total that stands at 37.36", which is 5.22" above normal for the date.  Normal annual rainfall between Oct. 1st and Sept. 30th is 36.03 inches.  So, if PDX does not receive a drop of rain until October, we will finish the water year above normal!  

Forecast charts do show promise of much drier weather over the coming weeks.  Charts this morning give Portland roughly .25" of rain through June 30th.  The summer outlook continues to call for below normal rainfall July and August.  So, just maybe, we are about ready to enter our dry season.  As you know, holding your breath is not recommended.