Patchy Frost Possible In Spots Next 2 Nights

It doesn’t take brain surgery (sorry neurologists) to figure out that we have a very cool air mass for this time of year sitting overhead.  You don’t need a meteorologist to tell you that with temps in the low 50s across the metro area at 5pm.  Typically we’d be well into the 60s on an early May afternoon. 

Showers will end overnight tonight, and models punch some drier air into our area.  This is a typical spring setup for a chilly night.  The areas that clear out away from the big cities will see temperatures plummet.  So who clears out and might see frost?  Here’s a still image from our RPM model showing forecast cloud cover at 6am:

With air flowing west to east, clouds tend to bank up against the Cascades, so eastern suburbs and outlying areas will be relatively warm compared to the west side.  Out there I expect mainly clear skies tonight, allowing maximum radiational cooling (objects radiate heat out to space).  Whew!  I live way out eastside to I think all my blooming fruit trees (apple, pears, plums & cherries) are probably safe.  But if you live in Vernonia, Hillsboro, Gaston, Forest Grove, Scappoose, or McMinnville, you might get a light frost tonight.  That does fit the average last frost dates for our area…earliest in the city, latest out to the west and northwest of the metro area. 

It’s not on this map, but Downtown Portland’s average last frost is February 24th!  Portland Airport and most of the lowest elevations within 10 miles of downtown Portland (south, east, & north) is the last week of March or first week of April.

Saturday will be a cool day with increasing sunshine, but then we have another very cool night tomorrow night.  No clouds or fog around to hold temps up tomorrow night, so some of us (my trees!) might see a light frost in the outlying spots north and east of Portland…those spots that escape it tonight.  But…

I don’t expect frost either night in the main part of the Metro area either of the next two nights.  It’s only possible in outlying areas.

Starting Sunday it’s on to Summery weather for a few days.  Light offshore (easterly) flow Sunday continues with a warmer atmosphere Monday.  Check out the WRF-GFS cross-section:

Easterly flow from Sunday morning to Monday evening from the surface up to around 4,000′.  By the way, time goes from right to left.  07/12 is Monday morning at 5am, 04/12 was this morning at 5am.  That, along with solid sunshine, will give us maximum heating…lower 70s Sunday and right around 80 Monday.  We didn’t get too crazy with temps Monday since it appears 850mb temps top out around +11 to +12. 

After a strong onshore push later Tuesday and Wednesday, weak ridging seems to come back later next week.  Hmmm, looks like the marine air see-saw is starting up for the season.  Both the ECMWF and GFS imply we are heading into a period of very mild May weather with temps more above average than below.  If I lived in the lowest elevations here in the western valleys, I’d consider planting the warm weather veggies (corn, beans, tomatoes) Sunday or beyond.  It’s worth a shot, the 2nd week of May isn’t too early IF we stay in a generally mild pattern the rest of the month.  If you live in a cooler spot like I do…wait for another couple of weeks to make sure.

Here are the two 12z ensemble charts.  The GFS operational would say well into the 80s next weekend, ECMWF not as warm but still mild:

Interesting to note the GFS is warmer than its ensemble members for the Mother’s Day weekend, but the ECMWF is cooler than it’s ensemble:

Chief Meteorologist Mark Nelsen

10 Responses to Patchy Frost Possible In Spots Next 2 Nights

  1. bgb41 says:

    5/4/2012 Oregon (All) Temperature Summary

    High:65 at Castle( 283 ft)
    Low: 47 at CW1075 Boardman(322 ft) & Rufus(185 ft)

    High:29 at CW7477 Lostine(7002 ft) & HOWARD Mt Howard(8150 ft)
    Low: 18 at HOWARD Mt Howard (8150 ft )

    Largest Diurnal Change: 28 degrees
    DW0460 Sisters (57/29 ) (3251 ft )

    Heaviest Rainfall:
    0.92″ at DW4118 Sandy(1250ft)
    0.91″ at DW9126 Brightwoo(1336ft)

  2. karlbonner1982 says:

    I just posted a status update on Facebook about how solar summer began at 7:13pm PDT tonight, and will end at 7:26pm on August 6. Solar summer is the quarter of the year with the highest (northernmost) midday sun angle and longest days in the Northern Hemisphere. Funny how the first two nights of solar summer could see patchy rural frost!

    I’m gonna plant the corn this weekend and tomatoes around Mother’s Day in The Dalles. Peppers can wait until Memorial Day…

  3. Mr Data says:

    I have a funny feeling that with both models (GFS and Euro) disagreeing with each other the most likely solution is somewhere in the middle.

    I am not sure what word I am looking for that means (somewhere in the middle of 2 different extremes to please everyone.) Oh well.

    I just hope we don’t have any 90s till July then have a whole week of 90s.

    • Dave in SW PDX (235') says:

      A “happy medium”?

    • Mr Data says:

      Never heard that phrase but I like it!

      I find it funny how when Mark gets his kickers in a twist about an anti global warming post it always happens on a weekend and the discussion continues the next few days.

      Looks like I won’t be reading this blog…… least for this week until the fuel dies off especially from the pro global warming alarmist who blame everything and anything on Global Warming when a lot of data suggests otherwise.

      The only thing I’ll say is after my enlightment:
      Don’t always trust the models as they are imputed by humans and THERE ARE people out there in high positions with an evil agenda that want to slowly depopulate us that aren’t *worthy* to them and will exaggerate studies done.

      Do extensive study of the climate and use your own intuition as it’s unique to YOU plus always read between the lines even though you may have to squint to do so. :p

    • Mr Data says:

      Oh! And then Mark gets after Rob for *flipping out*. :p

  4. Garron near Washington Square says:

    I totally agree with Brian, it looks like we’re in that 3rd year make up session. The last 2 – 3 year cycles have been like this. So, if this were to continue, the greenhouse I built this year will be money well spent over the next two springs.
    BTW, I planted my maters about 3 weeks ago, and I’ve only had to have them in the greenhouse about 1/3 of that time, and they have already grown about 11-16″ depending on the variety of tomato.
    I used to do my tomatoes in Hillsboro at a friends house with really good soil, but, back about 5-6 years ago, I experienced one of those nasty late frosts around the 5th of May, and that sold me on using my other friends house in SE Portland to do the majority of my gardening as I can get a lil earlier start, and later finish than I could out here.

    • Mark Nelsen says:

      I planted 7 tomatoes in my new greenhouse (in ground) last weekend. Hoping for the first time I actually get lots of tomatoes this year since it’s hot in there every day it’s over 65 outside. Localized climate change.

    • Dave in SW PDX (235') says:

      Anthropogenic, even!

  5. bgb41 says:

    Nice to see ensembles above normal for an extended period. After the last two years of cold wet springs, its almost to be expected we have a summer-like equalizer coming now.

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