Snow In Hills Thursday A.M.

April 20, 2011

A very chilly airmass moves into the Pacific Northwest briefly later tonight and tomorrow.  A burst of showers late tonight and before 10am could bring sticking snow down around 1,000′ in the foothills of the Cascades and Coast Range too.  That means ANY OF US could see snow mixed in with the rain later tonight through tomorrow morning.  Not a whole lot of anything, but a nice curiosity for late April don’t you think?

The picture above is an oldie but I still love it.  It’s from Jerry Kinney.  The top photo is the mill pond in Vernonia on April 19, 2008.  It was the last dusting of snow down around 1.000′ during that cold La Nina Spring (like this year!).  The lower picture was taken 3 weeks earlier in 2007.  Notice how delayed the vegetation was in 2008 compared to 2007.  Of course we have similar conditions this year as well.  And Vernonia could easily see a dusting tomorrow morning.  The sticking snow level tomorrow afternoon will jump back to around 3,000′.

There is a bright spot in the forecast…we get offshore (easterly) flow and a warmer airmass Friday and most of Saturday.  We should actually see above average temps Friday and Saturday.  The beginning of a rainy spell arrives by sunset Saturday.

By the way, there has been some incorrect information floating around weather circles the last 30 days about latest snowfall in Portland.  Part of the confusion is the fact that in the past snow and hail were BOTH included in daily “snowfall” totals.  Obviously that means it could snow in early October or May!   Here is the pertinent info:

1. Measurable snowfall has never been recorded at PDX in April…those records go back to 1940, or about 71 years.  The latest measurable snowfall at PDX is March 20, 1995 (.4″).

2. Measurable snowfall HAS been recorded in downtown Portland in April, 5.4″ on the 1st back in 1936, and 1.4″ in April 1933 as well.  Otherwise less than .30″ in a few years in the late 1800’s and early 1900’s.

Chief Meteorologist Mark Nelsen


Cold (but drier) Spring Continues

April 19, 2011

Here’s a nice chart showing how chilly the first 19 days of April have been.  Today was below average again, by 6 degrees on both the high and low temps at PDX.

The chart is from the National Weather Service in Portland.  You can see the green area is the 30 year average for high and low temperatures.  The blues and reds are the record low and high temperatures…the warmest and coldest we’ve seen on any one day.  Note that we’ve only seen two days at/above average for the high temperature (out of 19!).  Notice also that most record highs are now in the 80 degree range…wouldn’t that be nice? 

It’s fair to say this is becoming a cold spring historically.  Not an “epic” cold spring…unless the current pattern continues through May, but one of the coldest we’ve seen (so far) in this area.  We’ve only seen 3 60 degree days so far, which is the lowest number ever at PDX. 

That’s the fewest number of 60 degree days by April 19th in 70+ years! 

If you look at Downtown records, we’re at the 2nd lowest in 137 years…just as unusual.  We’ve seen a rare combination of:  a cold period in the 2nd half of February, a slightly cooler than average March, followed by a very chilly April.  In most other years, even if late Winter and Spring is chilly, we get some sort of brief warm spell.  Sometimes it’s in late February, other years in March, or April of course.  In fact during the very cold La Nina Spring of 2008, we hit 80 degrees in parts of the Metro Area the 2nd week of April…then the cool weather resumed.  But this year we haven’t even seen a hint of warming, not a single briefly warm ridge.  Very strange indeed.  And we are alone here in the West, take a look at the USA temperature anomaly for the last 30 days (Celsius):

It has been unusually warm across the southcentral and southeast USA, but about average from the Great Lakes eastward up north.

A nice change the last few days has been the dry weather and sunshine.  Saturday was a screwed up forecast, but the bright sun Sunday, Monday, and today was a welcome change.  Keep in mind the sun angle right now is similar to late August, which explains why it FEELS warmer than 55 degrees at mid-afternoon in the sunshine.  But once the sun goes down it feels like Halloween weather.  I was at my daughter’s first softball game yesterday evening and we could see our breath by the time the game ended at 8pm…about 45 degrees!

My eyes are on that 70 degree record for May 5th…that’s the latest we’ve had our “first 70” of the season.  The year was 1967.  Anybody remember that one?  A searing hot summer followed (a 107 degree day too), so keep in mind that a cold spring doesn’t mean anything with respect to our upcoming summer.

Chief Meteorologist Mark Nelsen


One Last Rainy Day

April 14, 2011

It appears our long spell of consistently wet and snotty weather is about to come to an end.  Of course the bad news is that we have one more excessively gloomy and wet day ahead.

We broke a rainfall record today.  As of 10pm we’ve seen .74″ of rain, which breaks the old April 14th daily record of .62″.  We’re just a few tenths of an inch below our average April total rainfall right now too.  It’s quite possible that we’ll have our normal “allotment” of monthly rainfall by halftime (tomorrow).

For those of you gardeners out there, bad news for Sunday and the rest of next week.  With clear skies, a cool airmass lingering overhead, and dry conditions, that’s the perfect setup for late season frosts.  Luckily most fruit trees are just starting to bloom (if they are at all).

Next week may not be totally dry, but in general I just don’t see much rainfall…more typical for mid Spring.

Chief Meteorologist Mark Nelsen

By the way, there were 3 earthquakes in SE Portland tonight too…(OMSI TO AROUND DIVISION/30TH)

8:49pm: 2.1, 10 miles under

9:26pm: 1.7, 10 miles under

9:56pm: 1.2, 10 miles under


More Soaking Rain Ahead

April 12, 2011

I didn’t know whether to cry or laugh looking at the models tonight.  We have a very wet 3 days on the way, especially Thursday and Friday.  Just when we get a totally dry day, hopes rise and we make plans to get some yardwork done or something planted in the garden.  Then our La Nina Spring slams us upside the head with another soaking.  Yuck…I think my fruit trees at home and native broadleaf trees are about 3 weeks behind normal right now.

The image above is from our 00z RPM model, showing the 72 hour precipitation forecast.  Note the precipitation falls as mainly snow in the Cascades…maybe 15-20 inches at the higher resorts by Saturday morning.

There does appear to be a break in the steady rainfall beginning this weekend.  Upper level heights rise (slightly), and no significant systems move through our area.  This would be more typical April weather rain-wise.  However the upper level flow is still from the northwest, so a cool airmass remains.  More frost in the outlying areas is definitely possible Sunday-Monday.

Chief Meteorologist Mark Nelsen


Rainy Season SLOWLY Fades Away

April 11, 2011

Does it ever feel like Spring progresses very slowly here in the Pacific Northwest?  You’re right!  The “wet season” (denoted by high probability of .01″ or more precipitation in any one day) peaks in late November, then stays quite high through February. 

The most obvious feature is the sudden ramp up in daily precipitation in the Fall (20% to 60% from early September to early November, or 2 months).  Then in the Spring, it takes DOUBLE that time to go from 60% back down to 20%.  That’s early March to early July.  So yes, it takes much longer to dry out in the Spring than turn wet in the Fall.  On the positive side, we go about 5 months with less than a 50% chance of rainfall on any one day.  That would be May through September.  On the negative side, our real dry period only lasts about 6-8 weeks.  It sometimes seems longer at the time (it’s TOO HOT!), but really never lasts more than 8-10 weeks even in the hottest/driest years.  This is the period in which I like to take the majority of my vacation time as well, for obvious reasons.  I could work every day from November through January, as long as I get those weeks in midsummer off!  Luckily that lines up with our busy weather season too.  So hang on…we’ll slowly dry out over the next couple of months.

Chief Meteorologist Mark Nelsen


A Nice Day!

April 8, 2011

Finally, I think today was the first day that gave us warm temps AND solid sunshine.  We hit 61 degrees here in Portland, one of the few days 60+ so far this season.

A weak system moves through tomorrow, but probably no rain…definitely not a blue sky.

Sunday and Monday it’s back to the same slop.  The “slop” Monday will be accompanied by much cooler temps; the snow level may drop as low as 1,500′ again.

Next chance for dry weather is Tuesday.  ECMWF is hinting at more ridging late next week; NCEP seems to think that might be the way to go.  If so our 7 day temps will be too low for next Thursday and Friday.

Check out the national rainfall map for March.  No big surprise eh?  REAL WET on the West Coast!

Chief Meteorologist Mark Nelsen


Hail and Possible Funnel Cloud Today

April 6, 2011

As I was heading to work around 2pm I was thinking today was a bit disappointing so far…then things changed.  We had two areas of heavy showers move through the Metro Area.  First from 3:30-4:00pm from Lake Oswego to Clackamas a heavy hail shower brought traffic to a standstill in spots.  There may have been a funnel cloud as well.  We received several pictures, and both viewers say there was some rotation.  Radar showed some weak shear, nothing that would scream “FUNNEL CLOUD!”, but could explain the brief rotation.

The 2nd batch of showers moved from NE Vancouver through Orchards and into the Hockinson area.  That one dropped a ton of hail and some snow too.  The picture above is from Steve Pierce.  It’s rare to see so much hail accumulate in our area, a testament to the very cold air up above.

Speaking of cold air, it’s down to 37 here at the station, and the top of our transmission tower (1,800′) is at 32 degrees.  Sticking snow is down around 1,000-1,500′ right now.  If you’re looking for a white start to Thursday though you’ll probably be disappointed.  Precipitation should taper off the next few hours.

Thursday we’ll see a bright day (after brief morning clouds), then showers develop mainly over the hills and mountains.  This time they’ll drift from north to south since we’ll be on the back side of the cold upper-low.

Still a nice, dry, and mostly sunny day on tap for Friday…get ready for some AVERAGE TEMPS!

Then it’s back to more rain over the weekend.

Chief Meteorologist Mark Nelsen