Another Cool Summer?

July 18, 2012

Let’s talk long-term weather, then discuss some possible fun action tomorrow evening/night.

First, it’s a pregnant woman’s dream, or so I’ve been told by a co-worker.  Long range models show average or cooler than average temps will continue most likely through the rest of the month.  A 90 degree temperature in Portland appears unlikely during the next 2 weeks.  If so, it’s going to be the first time in PDX history that we haven’t hit 90 through the end of July for 2 consecutive years:

The reason?  We had 10 days of warm ridging nearby; that began on the 4th of July.  Now it appears upper-level troughing is going to linger closer to us (or overhead) for the next 10+ days.  At this point I don’t see an excessively cloudy and chilly pattern, but definitely one that will keep the heat away.  When those upper-level troughs linger nearby, most of the time that maintains a thicker than average cool marine layer; basically the cold Pacific Ocean dominates our weather a bit more than in a “regular” summer.  Get used to lots of 70-82 degree high temps; many would say those temperatures are just perfect.  But this also likely means more gray than we are used to during this normally sunniest time of year.  Models are in very good agreement on the general pattern.  Check out the 850mb temperature ensemble charts from the 18z GFS:

and the 12z ECMWF:

Both models, and their ensemble members, have a chilly upper low just to our north Sunday and Monday, the recover to slightly above average much of next week, then below again after a week from now.

Now lets talk short-term.  Some severe thunderstorm action today, but only over Union County, around La Grande.  Reports of golfball size hail and even a funnel cloud spotted too. 

Real quiet west of the Cascades with just one or two weak storms over the Cascades.  West of the mountains we had a very deep marine layer that kept us socked in low clouds all day long.

Tonight and tomorrow the upper low offshore moves slightly farther offshore, allowing warmer air aloft to move in along with weak easterly flow above about 3,000′.  This should break up the marine layer and bring us a much warmer day (80-85 degrees).

The the fun might begin, all models show the upper low suddenly moving north tomorrow evening through Friday morning.  The strong diffluence in the upper atmosphere on the northeast side of the low (over us) tends to promote rising motions in the atmosphere below it.   Not unlike a wood stove or fireplace starting much quicker when a breeze or wind is blowing over the top of the chimney, pulling air up through it.  The WRF-GFS is showing a large are of storms and showers developing starting tomorrow evening and into the night.  This COULD be a nice little overnight thunderstorm outbreak.  Now our RPM has the action and upper low moving slightly farther east.  It produces nice storms in a line from about Madras to Mt. Rainier.  I trust the WRF-GFS a bit more.  Either way SOMEONE in the Pacific Northwest is going to get a nice light show tomorrow night!

Chief Meteorologist Mark Nelsen



GolfBall Size Hail In Heppner

July 17, 2012


Very impressive, our hail tracker says 4″ size hail possible just south of Heppner, official storm report says 1.8″…that’s huge.


Thunderstorms Finally Beginning To Pop On Cascades

July 17, 2012

The radar screens have been relatively quiet today.  There was a quick burst of thunderstorm action around Albany at 5am, then 3 strikes from east-west moving storms between Wilsonville and Newberg at 11am.  Since then just warm and partly cloudy. 

Now finally some action showing up around Mt. Adams, Mt. Hood, and Detroit Lake.  It remains to be seen whether we actually get storms here in the Valley.

As mentioned in yesterday’s posting, we have great instability, lots of moisture, and plenty of sunbreaks.  We just need a good trigger and things can happen quickly (note Albany at 5am during the coolest part of the day!).

So now it’s a wait and see weather game…anyone COULD see a thunderstorm in the next 8 hours, but some of us won’t.  We’ll keep on top of it.

Chief Meteorologist Mark Nelsen

2-3 Days of Weather Action: Thunderstorms Possible

July 16, 2012

Just about anyone in the FOX12 viewing area  could see a thunderstorm during the next 72 hours, but not everyone will; a challenging forecast ahead.  By the way, in case you ever wondered where our signal goes, it’s generally in the blue area.  Some people receive us via satellite outside the blue counties; but these are the counties we “service”.  Specifically, in forecasting weather and severe weather warnings we pay attention to these.

For those just wanting the basics:

1.  Warmer temps today and tomorrow, highs closer to 80 with a mix of sun/clouds.  We won’t see the gruesome clouds/drizzle we had Sunday morning!

2. We can’t (no one can) forecast exactly who or what spot will get thunderstorms or at what time.

3. We do know the best chance appears to be from later today through Tuesday evening. 

4.  Storms that DO develop will move from east to west; the opposite of our normal weather pattern.  They will come from the east (Cascades).

5. Don’t do anything outside that requires 24 hours of dry weather (staining, spraying etc…)…too risky.


More Details:

This morning an upper-level low, basically a circulation in the upper atmosphere, is moving south along the Oregon Coast.  It’s near Newport at 11am.   Click for a better view below, map shows the airflow at about 30,000′ or 300mb: Circulation around an area of low pressure is counter-clockwise, which means most of us are on the north and northeast side of the low by later today.  By 11pm tonight it’ll be right on the Oregon/California border.  But look ahead to Thursday afternoon:

Still in the same spot!  That means for the next 3 days we’ll have easterly or southeasterly flow in the upper atmosphere overhead.  This is usually a good setup for getting thunderstorm action west of the Cascades.  Indeed we’ve already seen storms on the north side of the low this morning up in SW Washington:

This is never a guarantee of widespread thunderstorms; I’ve seen this pattern end up with almost nothing over some spots.  But the screaming message is the potential is there for anyone to see a thunderstorm and just about anytime of the day or night the next 72 hours.  Take a look at the Lifted Index forecast for tomorrow afternoon from the NAM, it’s a measure if instability in the atmosphere.  When it gets to zero or below, that’s good: 

Very impressive -4 to -6 over the Cascades of Washington and very close to the Portland Metro area!   Easterly flow could bring storms out over the lowlands west of the Cascades.  Tuesday does appear to have the best dynamics/forcing for stronger storms too; it might be our best bet.  Afternoons/evenings do tend to have more “action” due to the stronger rising motions from daytime heating, but in a pattern like this the action can occur anytime of the day/night as small curls or eddies move around the big upper low setting off storms.

Once this all moves out of here on Friday, models show the hot upper-level ridge over the desert SW pushing closer to us again.  That’ll give us another run at 90 degrees over the weekend or early next week.  The 12z GFS ensemble chart shows above average 850mb temps Saturday and beyond.  The ensemble average generally agrees with the operational model:

The ECMWF is similar:

Chief Meteorologist Mark Nelsen

Much Cooler and Wet At Times Today

July 15, 2012

As expected a huge change in the weather this morning; a major push of cool ocean air is thick enough to give us showers in spots west of the Cascades.  Instead of high temps in the 80s today, it’ll struggle up to around 70.  That’s a good 10 degrees below average.  You can see the change on the satellite image.  All areas west of the Cascades are socked in, but totally sunny east of the mountains. 

Today is an excellent day to head to the Eastern Gorge or Central Oregon if you want blue skies, because we’ll likely see little or none west of the mountains.  All the thunderstorms from the past two days will avoid these areas; but take a look at the past 24 hours worth of strikes:

We never saw lightning too close to the metro area, just up around Mt. Hood during the early afternoon only.

Another upper level low (disturbed area of weather) drops in over us tonight, with a third later Wednesday and Thursday.  That means this week will be much cooler than average for the middle of July.  In fact Wednesday could actually be a wet day as Low #3 moves in…another 70 degree day (at best).

Chief Meteorologist Mark Nelsen

Watch Out For Weekend Showers & A Chilly Sunday

July 13, 2012

I’ve seen lots of fields with freshly mowed hay drying in the sun the last two days.  Get it taken care of today or tomorrow morning; or it may get wet!  

Showers are definitely possible this weekend, in fact anytime from Saturday evening through Monday morning in NW Oregon and SW Washington.  An upper level disturbance is sitting in Western Washington this morning and slides south right over Mt. Hood by Saturday afternoon.  The flow around that will cause thunderstorms to break out over the S. Washington and N. Oregon Cascades Saturday afternoon.  They MAY move to the west out over the Portland/Vancouver Metro Area.  Look at what happened last night over the western part of Puget Sound!

This could happen Saturday afternoon or night over us…so the risk of something getting wet is definitely there.

As that moves east Saturday night, strong onshore flow develops down near the surface. That means thick low clouds could take much of Sunday to dissipate; likely even some drizzle in the far eastern suburbs.


A 2nd low dropping in Monday keeps temps below average Monday (75-80) then it’s back to more reasonable summer weather again.

Chief Meteorologist Mark Nelsen

Summer Vacation

July 8, 2012

Vacation time…no postings (unless we get a tornado somehow) from Sunday the 8th through the 15th.  I’ll be back at work on the 16th. 

Chief Meteorologist Mark Nelsen