Thursday, July 18, 2013

Nighttime Heat Wave Hits Victoria, Paradise Melt-Out, and a Very Dry July

Nearly every summer day Northwest temperatures follow a familiar routine, with temperatures hitting a minimum around 6-7 AM and rising until roughly 5 PM, followed by falling temperatures during the evening and morning hours.

But something very different hit the western suburbs of Victoria B.C. Wednesday morning, with temperatures rapidly rising around midnight.  How could this be?

Let's start with a plot of temperatures at Victoria's Lakewood Elementary School during the last week.  Yes, temperatures are in Celsius (30C=86F, 20 F-68F, for those metrically challenged).  Temperatures on the 12th, 13th, 14th, and 15th do the normal diurnal thing, rising and falling
at the typical times (the big tick marks indicate midnight). But something weird happened early on the 17th.  The temperature rose right after midnight, and then fell again.  Strange behavior.
Here is a plot of the temperatures and winds at midnight on Wednesday around Victoria...nothing too strange.  A lot of temperatures in the upper 60s. (circles indicate calm, lines with pennants are winds).
 But two hours later at 2 AM something weird has happened...temperature zoomed up into the mid to upper 70s in the western part of the city, with one site hitting 79F.
The warmth is explained by the winds.  While most of the city had light winds, westerly winds had pushed into the eastern suburbs.  Such flow is descending off the terrain to the west of the city, being compressed as it sinks and mixing down warmer air down from aloft.

Here is a terrain map around Victoria to give you a better idea of what I am talking about.



A few hours later the the westerly winds weakened and the temperature dropped to levels similar to the rest of the area.

As long as I am talking about anomalies....it has been quite dry around here, even for July.  So far we have only had a trace at Seattle-Tacoma Airport (a trace is less than .01 inches).  If we get no more precipitation for the rest of the month there (a real possibility), we would enjoy the driest July since 1960.   You will tell your grandchildren about this one day.

And another big meteorological event happened yesterday....the snow finally melted out at Paradise Ranger Station on Mt. Rainier (see graphic).


According to Mark Albright, past state climatologist, over the past 30 years, the median melt-out date at Paradise is 11 July.  (The mean melt-out date is slightly later on 15 July.)  During the first 15 years of operation from 1981-1997 the mean melt-out date was 10 July.  Since then the mean melt-out date has moved 8 days later to 18 July over the 15 year period from 1998-2012.  Over the past 5 years (2008-2012) the mean melt-out date has been 2 August.  The earliest melt-out was 5 June 2005 while the latest melt-out was two years ago when the snow pack didn't melt out until 25 August 2011.

Bottom line:  the Cascade snow pack is NOT melting out earlier during recent years.

8 comments:

Tara K said...

NicePost :-)

Unknown said...

"The Cascade snowpack is NOT melting out earlier during recent years."

Serious question (not doubting your statement) -- why are so many area glaciers retreating then?

Warning: horribly formatted website:
http://www.nichols.edu/departments/glacier/bill.htm

Lindsey said...

That is interesting. When I think of a WESTERLY wind during summer in the Pac NW, I always think of that as COOLER air "advecting" in.

Patrick said...

I love the weather at this time of year. Sunny afternoons, but the morning clouds keep it from getting too hot in the afternoon.

Karl Bonner said...

Don't you mean WESTERN suburbs, since the warm temps were to the west of downtown Victoria?

Dani Moreno Orellana said...

great blog

wynneforplants said...

I've a question.

What is up with the persistent winds this year? I see whitecaps most days out on Georgia Strait, almost no calming in the evening. Definitely atypical up here on Lummi Island, at least for the 13 yrs I've lived here.

Don't know if you have any thoughts on this but I'd enjoy a post if you do.

David Schowengerdt said...

Fascinating post. Another thing about Victoria that I've always been curious about is, after living here for 6 years, I see that especially Victoria, but also even Vancouver and Bellingham, get far fewer 'low cloud' mornings than the central and southern sound. I'd love to know why that is. I'm guessing subsidence?