Rod's Weather Headlines

Do you remember how October began?  The first 14 days of the month had at least a trace of rain and most days were simply wet.  Since that time, only one day as been on the wet side.  Well, that is about to change!

Forecast charts have been very consistent in showing a long stretch of mostly wet days, beginning this coming Wednesday night.  In fact if the pattern holds November 3rd - Nov. 15th would be mostly wet.  Cold air arriving this coming Thursday will likely bring Cascade snow down to 3,000 feet.  I am not expecting a snowstorm, but accumulating snow Thursday at Government Camp looks likely.  Motorists may need chains for the first time this fall. Snow levels could be 3 - 4,000' Thursday through Monday.  Timberline could see significant snow accumulation.  

Weather outlooks continue to show above normal precipitation patterns November - January and possibly into March.  No confidence to predict much of a temperature departure.  A reminder that November 1st is the start of our rainy season. The big four months, November - February average 20.57" of precipitation which is 55% of our annual total.  

This past Saturday's daily record for the high-low temperature of 58 degrees, got me looking at just how warm this October's low temperatures have been.  The month begins with a normal low of 48 degrees and currently, the seasonal norm is 45 degrees.  To date, all but five mornings at PDX have had low temperatures in the 50s.  In fact the lowest of the month to date is 45 degrees, which equals our normal low.  The first 16 days of the month saw low temperatures above normal.  Talk about mild!  If you are wondering, the warmest October low temperature for the entire month is 63 degrees, back in 2003. 

Here is a brief timeline to our fall cool down:

October 28th, the normal high, currently 61 degrees, becomes 59.

November 10th, the normal low drops to 40 degrees. 

November 16th, the normal low becomes 39 degrees.

Standard Pacific time begins 2:00 a.m., the first Sunday of November.

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Don't forget to keep updated this week as the first frosty weather of the fall season takes hold.

Just for fun & interest, here is a brief comparison of the summer months of July - September, last year verses 2011.  I decided not to include June, because June of 2010 was so chilly and record wet, it would have blown the doors off of any comparison!

High temperature average, July - Sept. 2010:  77 degrees  / Mean temperature:  66.7 degrees

High temperature average, July - Sept. 2011:  79 degrees /  Mean temperature:  68.0 degrees

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Rainfall July - Sept. 2010:  4.18" (3.36" Sept.)

Rainfall July - Sept. 2011:  1.76" (wet July, dry Aug. & Sept.)

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Mostly sunny to clear days, July - Sept. 2010:  42 days

Mostly sunny to clear days, July - Sept. 2011:  47 days

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The above shows the heart of the summer was warmer by 1-2 degrees in 2011.  This past summer was much drier despite a wet July.  This past summer saw 5 more sunny days than a year ago.  So, nearly an extra week of sunshine, less than half the amount of rain and 1-2 degrees warmer.  After a slow start, summer of 2011 was a success!

The 2010-2011 water year ended Sept. 30th.  Portland's precipitation total of 44.74" was the wettest since 1998-1999.  The total of 40.00" or more, ends the longest streak of less than 40.00" water years since records began back in 1870.  I personally use 40.00" as the bookmark of what is considered to be a "wet" water year.  By the way the new 30 year average water year precipitation total is 36.03".  (Portland finished the season +8.71" above normal.)  

The climate average is reset each 10 years, for a 30 year period.  Our new climate normal is the 30 year average from 1980 - 2010. The old water year average was 37.07", the new average is slightly drier at 36.03 inches.  The 2nd longest streak of less than 40.00" years ended in 1994 and was followed by the wet & flooding years through 1999.  Remember, the atmosphere always fights to maintain balance.  Almost always, dry is followed by wet, hot followed by cold and so forth and so on. 

Current forecast outlooks call for wetter than normal weather October - December.  

October starts the process of wondering about winter.  All outlooks continue to call for a wetter than normal October and wet months on average through December.  In fact precipitation outlooks call for mostly wet months through March!  Temperature outlooks show less confidence but are leaning toward the cool side. 

A weak La Nina began to take hold back in August and will likely strengthen somewhat into winter.  It is true that La Nina's typically bring normal to above precipitation to the Northwest as the Pacific Jet takes aim at our coast line. This year's La Nina is expected to be weaker than last seasons.  This fact points at less water than we saw last winter.  Below are 3 factors I have researched:

1.  An active hurricane season often means a wet winter for the Northwest.  To date, the current tropical season has 16 named storms, 11 is average.  Thus, WETTER THAN NORMAL WEATHER IS LIKELY. 

2.  La Nina facts:  The last 5 strong La Nina's have averaged 40.04" of precipitation.  (Last year was a strong episode with 44.74" of water;  8.71" above normal).  The last 5 weak La Nina's, which we expect this year have averaged 35.07" of water.  Thus, YOU WOULD EXPECT  5.00" LESS RAINFALL THAN LAST SEASON. 

3.  Our place in history has Portland coming off the longest streak of non-soaking years in the record book.  The water year ended Sept. 30th was the wettest since 1998-1999.  The last time Portland went more than 10 consecutive seasons without a wet winter, the following years brought some of the heaviest rains on record, including the floods of 1996.  MY POINT IS THAT WE ARE DUE FOR A NUMBER OF WETTER THAN NORMAL WATER YEARS.  My benchmark number for a wet year is 40.00" or more. 

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My conclusion:  Normal to above normal rainfall for the valley.  I expect a drier year than last, in fact 5-8" less precipitation this water year looks likely.  My forecast calls for PDX to receive 36.00 - 40.00" of total water through Sept. 30, 2012.   

Mt. Hood at Timberline Lodge received 696" of snow last season.  This year I would look for another good year with season snow totals 600 - 650" of snow.  I have no guess as to when the season will begin, but current forecast projections look favorable for Thanksgiving weekend!

So, look for a wet winter but not as wet as a year ago.  Temperatures will likely be normal to below. 

Rod Hill

All information courtesy of Jim Todd:

The latest information shows UARS will pass over Portland at 9:17 pm tonight, moving from WSW to NE with maximum altitude of 60 degrees NNW.  The brightness will be about -1.2 magnitude which will be fairly easy to see.  It will appear as a bright 'star' lasting for about 3 minutes.  The time is subject to change by Heavens Above and NASA.  Still no firm prediction when UARS will fall.

Jim Todd

OMSI Planetarium Manager

http://www.heavens-above.com/PassSummary.aspx?satid=21701&lat=45.524&lng=-122.675&loc=Portland&alt=61&tz=PST

NASA:
As of 7 p.m. EDT on Sept. 23, 2011, the orbit of UARS was 90 miles by 95 miles (145 km by 150 km). Re-entry is expected between 11 p.m. Friday, Sept. 23, and 3 a.m., Sept. 24, Eastern Daylight Time (3 a.m. to 7 a.m. GMT). During that time period, the satellite will be passing over Canada, Africa and Australia, as well as vast areas of the Pacific, Atlantic and Indian oceans. The risk to public safety is very remote.

Autumnal Equinox – Friday, September 23

Fall officially begins with the autumnal equinox, which takes place on Friday, September 23, 2011 at 2:05 am PDT).  At that point the Sun is directly above the Earth’s equator, and the significance of this is that every point on Earth will, for one day, experience nearly 12 hours of darkness and 12 hours of daylight. The Sun rises due east and sets due west on the equinox. At the South Pole the penguins will be celebrating the first appearance of the sun in six months. By the same token, at the North Pole the polar bears will be bracing themselves for six months of darkness.

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The above is courtesy of Jim Todd,  Planetarium Manager, OMSI

Now that our hot September streak has ended, you may be wondering what the coming weeks will bring.

Forecast models are showing a number of days with afternoon sun and highs in the 70s to near 80 as September continues and ends.  This month has a likely chance of ending with above normal temperatures and below normal rainfall.  

The October outlook does call for above normal rainfall with temperatures close to normal.  Current forecast charts show a wet week as the new month begins.  

You may find this surprising, but the record book now shows most of the daily record cold - high temperatures in the 50s.  In other words, it would not be unusual for high temperatures to only be in the 50s!

More to come on the winter forecast in a few weeks.  Fall begins September 23rd - a little later than most years. 

Don't let our current cool spell discourage you, warm sunny days will return Labor Day weekend!  Extended forecast charts show above normal temperatures the first 10 days of September, along with mostly dry weather.  There are indications of a wet, cool October and start to November.  

Remember, this fall and winter are likely to be either a neutral pattern or weak La Nina.  Forecast confidence of what to expect will be lower than last winter.  Remember a year ago, confidence was very high that a wet winter would develop. We know now, our current water year ending Sept. 30th, will be the wettest since 1998 - 1999!

Much more to come on this winter's forecast.  I am planning on giving my outlook this October.  For now, let's all look forward to a nice September!

Portland's high of 96 degrees Saturday was not only the first 90 degree day of 2011, but also a record high for the date.  The old record was 95 degrees, back in 1986.  

Here is the list of the latest in a year to reach 90 degrees for the first time:

1.  1954 - no 90s all year.

2.  1957 - Sept. 13th

3.  2011 -  Aug. 20th

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 There is plenty of time for more 90 degree days.  The latest in the season PDX has reached 90 degrees is Oct. 5th, back in 1980.  The average date for the 1st 90 degree temperature in Portland is June 30th. 

Other notable temperatures Saturday was 82 degrees at Astoria.  Not a record, but the warmest of the year to date.