Rare March Snow; In 50+ Years, Measured Just 5 Times In Lowest Parts of Portland

March 5, 2019

5:30 pm Tuesday

Portland Snow Last Few Times In March

Portland Snow Last Few Times In March2


Below I’ve copied over portions a March 2012 blog entry… Some good info for the weather geeks!  Note that one week later we received our latest-ever measurable snow at PDX (in graphic above).  Nice timing!

March 14, 2012…

During the Oregon AMS Meeting last night, a brief discussion about Portland’s latest snowfall revealed some slight disagreement over what the date is.  Remember, we’re talking MEASURABLE SNOW, which is 0.1″ or more.  A trace is recorded even if it snows but nothing sticks, which could happen anytime in an extremely heavy hailstorm, even in May or October.  On the NWS website it says the latest date is March 20th, 1995, which you see in my graphic below.  I made the graphic below a few days ago.  Of course I heard that and said “what about March 25th, 1965”?  According to the Western Regional Climate Center site which I use, it shows that as the latest measurable.

So I looked at the hourly observations…the LOW temperature on the March 20th date was 43 and the high was 55!  Obviously it didn’t snow on March 20th, 1995.  NWS folks agree so that one is gone and they will correct their records.  They also did some checking on March 25th, 1965.  The temp was 33 early and 43 in the afternoon.  Sure seems like it could have snowed briefly that morning.

But now that date is out as well…why?  It was hail on both those dates.  In the past, snow and hail were both recorded as the same thing, or at least in the same column.  I’ve known that for quite a few years, alerted to it once when I heard another TV person and the Oregonian claim it snowed in the first week of October here in Portland.  I looked it up and found the low temperature on that date was something like 51 degrees!  It must have been hail.  Also, watch out for lots of “traces of snow” in March-April-May in the record books.  Many of those in the past may have been hail.

The NWS guys are still checking on the new “latest snow on record” of March 15th, 1946.  I think I saw Vancouver had a few tenths of an inch of snow that day too, so maybe it’s real.   Either way, just remember, the latest recorded is in mid-March now.

Keep in mind that these records are for PDX (1940-1995) and the Portland Forecast Office (1996-Now).  Earlier daily records (a bit sketchier) downtown date back to 1928, and even earlier records than that go back to the late 1800s.  It did snow the first few days of April, 1935 downtown, and the latest measurable down there is 1.4″ on April 7th, 1933.

Now all this discussion of March and April snow in Portland makes it appear that it’s relatively common, but it isn’t.   Looking through the records, I noticed large periods of time where little or no snow fell after late February in the records.

1875-1890 (Downtown):  16 years with no measurable snow except 0.1″ in one March

1907-1919 (Downtown):  13 years with just 3 months measurable, none more than 1.9″

1921-1928 (Downtown):  8 consecutive years with none

1966-1988:   21 consecutive years with none

1990-2005:  16 consecutive years with none.

This also shows how much elevation plays a role with marginal snow events at the end of each cold season.  There are many years where at least an inch or two falls up in the hills (even in the city) in March, but it doesn’t stick all the way down to the floor of the valley, or city in this case.

Chief Meteorologist Mark Nelsen


A Rare March Snowfall Possible Wednesday

March 5, 2019

11am Tuesday…

A very cold airmass continues to linger over the Pacific Northwest today.

Portland’s low of 24 is the coldest March low since I was in college (1989).  That’s a long time; quite a cold spell!  I see The Dalles made it down to 6, which is the all-time coldest March temperature there.  But now we’re done with the really cold nights since clouds move into tonight.

Quick Summary

Between now and Wednesday night we transition from this really cold and dry stuff to a more typical “cold March shower weather pattern”.  That’s when we get snowflakes in the lowlands in the mornings, then by afternoon it’s in the 40s and you’ve forgotten about it as those change to rain showers.  The next morning the higher hills have a wet/slushy dusting again before melting etc…you get the idea.  That’s the pattern through early Saturday.  In that setup it’s very tough to get sticking snow to sea level, or below 500′ elevation.

But late tonight and Wednesday, during the transition to the “milder” weather pattern, we have a pretty good chance of seeing at least a little sticking snow all the way down into the lowest elevations

Snow Headlines Metro Tonight

WEDNESDAY AM COMMUTE IN METRO AREA & SALEM/ALBANY

  1. Snow showers, a trace to 1/2″ accumulation
  2. Many roads will remain bare since snow could be very light
  3. Expect a few snowy roads in spots, but many of us should see good driving conditions for the commute

WEDNESDAY DAYTIME & EVENING COMMUTE

  • Snow showers continue and may turn to steady snowfall
  • Through the daylight hours it’ll be too warm for snow to stick to roads (strong March sun energy coming through the clouds)
  • Not much additional accumulation

WEDNESDAY EVENING (after 6-7pm)

  • Snow showers continue
  • Temps cool to near/just above freezing so sticking snow is possible again
  • Nothing to 1″ additional snow, could even stick to roads again IF temps drop down to freezing and snow keeps falling.

TOMORROW NIGHT & THURSDAY

  • Snow showers, change to mainly rain showers after morning commute
  • Little or no freezing of roads
  • Dusting to 1″ on hills, little or nothing in lowest elevations

 

HOPEFULLY YOU’RE GETTING THE IDEA THAT MUCH OF THIS MAY BE “CONVERSATIONAL SNOW” IT MAY NOT HAVE MUCH EFFECT ON OUR LIVES, BUT WE’LL SEE PLENTY OF IT IN THE AIR AND ON OUR LAWNS.  WE’LL ALL BE TALKING ABOUT IT (WHINING?).

 

TECHNICAL DISCUSSION

We’ve only seen measurable snow three times in the past 20 years at the Portland NWS Office.  That shows you how rare it is.  Last time was 7 years ago.  It’s MUCH easier to get sticking snow up around 1,000′ and above and there will be plenty of that the next three days.

All models in pretty good agreement bringing the moisture north for snow late tonight through Wednesday evening, then the flow turns westerly and showers move in off the Pacific tomorrow night through early Saturday.

ECMWF Snow Accumulation

Once again the ECMWF and GEM models are “wettest”, showing up to .40″ precip by tomorrow night over the metro area.  It’s interesting that none of them generate much precip through the morning hours, but then some sort of convergence in the afternoon/evening as westerly flow begins to take over.  Most precip is the 2nd half of the day, but in March that means it’ll be above freezing.  The GEM is still producing sticking snow at temps above freezing tomorrow.  I’m quite confident it’ll be cold enough in the morning with 6 millibars dry/cold flow still coming through the Gorge.  But then it goes flat by sunset.  From that point forward we’re into the usual onshore-flow cold shower pattern.  Plenty of evaporative cooling to go around through early afternoon due to the cold easterly flow.  So if we get steady/moderate snow in the afternoon hours it could stick anywhere in the metro area, although roads would still be too warm at that point.  The HUGE question for tomorrow evening is whether snow keeps going after sunset and we get 1-2″ in the central/east metro area.  The WRF-GFS is a bit too warm through the entire day/evening and only generates a little snow for us; most areas under an inch.  It also shuts of snowfall around sunset.

wrf_snow_4pm-4pm

Beyond tomorrow evening I think models are overdoing snow forecasts, they typically do in these onshore-flow type patterns.  I’ve been burned by that several times.

By the way, the ECMWF is back on top folks!  This is the 2nd event in the past two weeks where it was the first to show snowfall over us.  A few days ago all other models were dry and keeping all that to the east/south.  Then they fell into line.  I’m just obsessed with model competition; a bit weird I know.

That’s it for now; see you on TV this evening!

Chief Meteorologist Mark Nelsen