First Freeze?

September 23, 2008

   Well it has been a few days since the last post so I thought I might put one up for all us weather nuts.  So After this mornings rain, PDX is at about .43" for the month.  Before the rain this morning we were about 1.3" below average for the month alone.  For the year we are about 5.3" short.  So lets hope for some more… plus it's nice to hear when I am trying to go to bed at 10 AM after the morning show.  As for the first freeze, on average it is around November 8th.  The earliest first freeze record that I could find was on October 5th, 1993, with a really old record on October 13th, 1881! (who knows how accurate that is…1881) 
    I don't think we will see any freezing temps here in Portland in the next few weeks but it is going to be cold for a few nights7day_640x480
.  The average minimum temperature for this time of year is 51F.  We will see some mornings colder then that with tomorrow morning being around 44F.  If you goto the Cascades and some Central OR areas they will be at or below freezing tomorrow morning.  The NWS put out a special weather statement this morning about that. 
   For the rest of the week, I see some more rain Wednesday evening into Thursday.  After that we will be warming up to above average temps for the weekend.  Have a good night everyone!

Rob Martin

*UPDATE*

Ok so in response to Eternal Yamcha’s question posted at 1:08AM: One easy,
one REALLY geeky/long.

 

For the easy answer, the overall pattern does not support
east to west movement for this specific Low. 
This means that it gets blocked so to speak.  In terms of precip, in washington,
from say Bellingham
to the Cascades on the East, the precip amounts will range from .2” to maybe 1”
towards the Mountains from this cycle. 
Storms like this can die off when it hits land just because the
“ingredients” to keep it going are not available on land anymore, where over
the oceans, it has an abundance of “ingredients” 
  

 

Really Geeky/Long (w/ help from my class notes in college)-

 There are many
different ways you can explain this depending on what methods you start
from.  I am going to use Rossby Wave
Thinking.  If you are not familiar with
it you can Google or Wiki it and get an idea who/what  Rossby was/is. 
To start easy, let’s think of a wave. 

 

The top of the wave is a HIGH and the bottom is a LOW.  A wave is Progressive a lot of the time (not
always), but the over all flow of the “weather” is generally, usually, most of
the time, progressive.  Progressive means
moving “forward” or in our case (N Hemisphere) from west to east.   Another term I am going to use is Zonal
Flow.  Zonal flow is the flow of the
“weather” moving DIRECTLY west to east(Progressive Flow) where the opposite is
Retrogressive, or moving “backwards”. 

 

Back to Rossby… I am going to take a Synoptic Scale approach
to the Rossby thinking.  The significance
is that as the mean Zonal Flow increases, the wave number of the stationary
wave decreases, there are fewer stationary or retrogressive waves, and the
overall pattern become Progressive.  

Experience:  In Strong Zonal Flow, embedded waves move
rapidly from west to east. With Weak Zonal Flow, we often have blocking
situations, as in its stalls.  So in this
case there is Weak Zonal Flow.  If you
look at the same time frame for the GFS at two levels (say 300mb and 850mb) you
will notice that as the “low” stalls, the upper levels have Weak Zonal Flow (
Over Vancouver Island at that particular time, the flow is strong SW, not
W).  This would lead to blocking/stalling
in Rossby Thinking. 

-RM


Fire Maps

September 19, 2008

Gnarlridge  I love Google Earth…I assume most of you reading this have used it in the last few years.  The uses for it (beyond planning my future vacations), are just becoming more and more varied.  I've noticed this summer there is quite a bit more "real-time" fire mapping with Northwest wildfires.  For example, on www.inciweb.org, I found this map showing exactly where the Gnarl Ridge fire has burned.  I took the view from the north;  you're looking to the southwest, up towards Cooper Spur itself…it's an "arm" of Mt. Hood.  Cloud Cap Inn is at the top of the zig-zagging road you see…a little ways above the word "Gnarl".  It'll be interesting to hike up there in a month or so and see how much actually burned.  Of course you can click on the image to get a better view.  The file to plot this on your own Google Earth is at the link above.  In fact you can also see the spread of the fire well beyond the August 18th fire boundaries when you download that file.

We are getting some convection to our east tonight…at least so far it's staying to our east.  Some fresh strikes, first of the day in fact, have shown up in the last 15 minutes near Sherar's Bridge (Tygh Valley) and Pine Grove.  Also a fresh strike just now near Criterion Summit north of Madras…hmmm.  We may see some flashes to the east very soon!  

I don't expect a fresh marine layer overnight tonight with the mid-upper level clouds moving overhead, so we just get leftover clouds and probably no rain tomorrow.

On Sunday a dying cold front gives us a better chance for a shower.

I changed the 7 Day forecast for the middle of next week since a warm front runs right over the Northwest Wednesday as a ridge tries to build overhead…must be Fall.  Have a good weekend!  Mark Nelsen


That Darn Marine Layer

September 18, 2008

1996_IceStorm Now that cooler weather has arrived, I can finally start thinking about the upcoming winter…even though it's still at least 2 months away.  In between we have lots of gray skies and plenty of boring weather.  So…anyone know what year and ice storm this picture is from?  It can be found on the NWS home page.  Answer at the end.

A very tough forecast day with a much thicker marine layer than anticipated.  Looks like the cool air was about 3,000' thick.  I see Wanderer's Peak at midafternoon was 77 degrees (at 4400'), while at the same time the Willamette Valley below was lingering near 60.  This was quite a strong inversion which was tough to break.  I'm anticipating the approaching upper-level trough to the southwest along with cooling in the upper atmosphere will allow a return to sunshine tomorrow afternoon…or at least that's the plan.  Either way the temperature damage has been done.  We went from 90 to 80 to 63 in just 48 hours.  Instant Fall!  Looks like the cool weather is going to stick around through at least Monday.  I notice a trend of the 00z models is to just give us drips of rain Sunday/Monday, instead of a good soaking.

There seems to be some sort of longwave ridging returning to the West Coast Tuesday and beyond, but details are different on each model run.  The 12z/18z GFS and 12z ECMWF were nice and warm with 850 mb temps back up around 10-12.  That would push highs back into the mid 70s.  00z GFS is flatter with even some rainfall Wednesday.  Hopefully future model runs don't flatten the ridging even further.  Mark Nelsen

The date of the picture?  It was from those rare back to back ice storms between Christmas and New Year's Eve…1996.  At the west end of the Gorge where I lived there was just about 6" of solid ice on the windward side of objects, which included school buses tipping sideways and trees down all over the place.  The first storm was Christmas Night and the 26th, the 2nd was 2 days later, before the ice from the first had melted.  I remember during the night of the 2nd storm it was 23 in Corbett with sheets of rain coming down, while the wind was gusting to 60+ mph.  That was a wild night!


Finally! 90 Degrees

September 16, 2008

Snapshot A very interesting picture was sent to us this evening from Becky Collins in Gresham.  She says some ash was falling out of the sky there, as well as where her husband works a few miles away.  Did any of you see it at your homes?  The windflow from the south-southeast is bringing smoke from several fires up into the metro area this evening.  I happened to see the setting sun…very cool!

We finally hit 90 degrees today after two days at 89.  There is a very shallow push of marine air in progress this evening, but it's barely made it into the metro area.  So 10 degrees of cooling tomorrow looks good.  In the latter half of September it shouldn't be too hard to cool our high temperature to five degrees ABOVE normal.  Then more marine air Thursday and Friday means it's back to the morning clouds, afternoon sun routine.

Quite a change in the 7 Day forecast is due to the GFS coming around to the ECMWF point of view.  850mb temps with a cold trough Monday-Tuesday are forecast by both models around 0 to +1.  Seems a bit extreme, but not unheard of the 2nd half of September.  According to my 850mb temp chart, the coldest 00z temp over SLE in the 6 Septembers 1997-2003 was +2.  That means this upcoming chilly spell is at the bottom of the chart, just 5 days after the "top of the chart" weather yesterday and today (see previous post).  So it's going to be quite a change…get the woodstove ready!  Mark Nelsen


Underachieving Hot Spell

September 15, 2008

Moon The moon SEEMS really big tonight, so I figure it's worth a large picture.

Many of our viewers have been writing, wondering about the freakishly red full Harvest Moon.  It's due to smoke from the Rattle Fire, near Diamond Lake in S.W. Oregon.  The flow in the upper atmosphere has turned southeasterly, sending a surge of smoke north.  The flow stays generally the same way through Wednesday, so I think we have a smoky/hazy day on the way again for tomorrow.

Now…for the "cool" heat wave.  850 mb temp was 24.4 degrees at SLE this afternoon!  That is the highest on my September chart for the years 1997-2003…this is the warmest airmass you can get this time of year.  So why only 89 degrees?  Not enough easterly flow.  Anemic east wind only made it to Troutdale…just barely.  I looked at the maps from the 1981 heat…On September 15th that year we hit 96 at PDX.  I'm assuming the east wind made it to PDX that day.  This warm of an airmass would have produced a 100-103 in August.

No reason to think there will be any change tomorrow.  Easterly flow won't be any stronger, so that's why I left the high at 90.  Cooler starting Wednesday, then models are in disagreement from Thursday onward.  Mark Nelsen


A Record Setting Day

September 11, 2008

Snapshot  A new record for the day here in Portland.  The easterly flow did it's trick at the Airport.  The wind did not actually surface at the ASOS location itself, but it must have been REALLY close.  850mb temp at SLE was 18.8 this afternoon, which gives us a high around 86 with no onshore/offshore component, so the 91 was way up at the top of the chart I use for forecasting temps in the warm season.  We really overachieved today.

We still have all of 1 mb. gradient from PDX-DLS through the Gorge (technically -1 I suppose).  But the flow quickly turns onshore during the day tomorrow.  I hope we don't get a surprise high of 83-85 tomorrow.  I'm anticipating a good 10 degrees of cooling…or at least that's the plan.

No changes for the long range forecast.  I notice the GFS 850mb temps for Sunday/Monday are slightly cooler, even though the 500mb heights are now higher…hmmm.  We'll see what future model runs show, but I think with the upper-level ridge directly overhead for the first time this month, we should be able to exceed today's 91 degree high.

Busy right now so I'll check out for this evening…Mark Nelsen


A Record Setting Day

September 11, 2008

Snapshot  A new record for the day here in Portland.  The easterly flow did it's trick at the Airport.  The wind did not actually surface at the ASOS location itself, but it must have been REALLY close.  850mb temp at SLE was 18.8 this afternoon, which gives us a high around 86 with no onshore/offshore component, so the 91 was way up at the top of the chart I use for forecasting temps in the warm season.  We really overachieved today.

We still have all of 1 mb. gradient from PDX-DLS through the Gorge (technically -1 I suppose).  But the flow quickly turns onshore during the day tomorrow.  I hope we don't get a surprise high of 83-85 tomorrow.  I'm anticipating a good 10 degrees of cooling…or at least that's the plan.

No changes for the long range forecast.  I notice the GFS 850mb temps for Sunday/Monday are slightly cooler, even though the 500mb heights are now higher…hmmm.  We'll see what future model runs show, but I think with the upper-level ridge directly overhead for the first time this month, we should be able to exceed today's 91 degree high.

Busy right now so I'll check out for this evening…Mark Nelsen