Nice Weather Ahead, But Tough Temp Forecast

What an incredible day today.  I visited a school up in Battle Ground and while driving away it felt like spring.  Of course we’re in the middle of fall, but for some reason it felt a bit more like spring to me.  It might be due to all the rain last month; it’s greener than what we would typically expect this time of year?  I don’t know…anyway, a real nice day with temps up around 70 in the metro area.  Quite impressive considering we were down in the 30s this morning.  Easterly wind made it to about I-205, helping to warm us up a bit.

The Big Picture:  It’s going to stay sunny and warm for at least another week!

The devil is in the temperature forecast through the period.  The reason is that we are right on the cusp of “inversion season”; that’s when the decreasing sun angle gets so low that there isn’t enough midday/afternoon heating to get rid of the overnight inversion (cool air in valleys).  From November through late February I suppose one could say “the night rules the air mass”.  During that time easterly offshore wind doesn’t warm us up.  When we get a big ridge of high pressure and 60s/70s in the foothills, the warm air rides right over the cooler low-level air mass.   During the transition times (late October and early March), it’s really tough to tell how much the easterly wind will warm us up.  By the way, during this period, our “warm” weather then occurs with southerly winds, usually near/ahead of frontal systems.  All our record highs from mid-November through mid-late February are from some sort of southerly flow.

Typically a very good guide for short-term temp forecast is MOS (model output statistics) based off of models.  As opposed to just reading raw model output (usually not a good idea to read it literally), MOS uses algorithms that are based on what actually occurred in the past when certain atmospheric conditions were present.  For example, such and such 850mb temp plus a certain wind condition led to a certain temperature at a specific site.  Got that?  The problem the past few days is that MOS has been cooler than what actually occurred.  So it’s not real helpful for the next few days.  Actual model surface temps at Portland (NAM, GFS, ECMWF) warm a few degrees (4-6) from Wednesday through Friday.  So that would put us in the 70-75 range.   But easterly gradients just about go flat Wednesday, then turn breezy easterly again Thursday and Friday.  So we dropped tomorrow’s forecast down a notch to 68, then up a couple degrees Thursday and again Friday with the increasing easterly gradient.  Back to mostly flat flow Saturday/Sunday, so we’ll struggle to hit 70 again.  One more surge of easterly wind Monday-Tuesday next week with even warmer low level atmosphere should push us back up in the low 70s again.  One thing that can really mess us up this time of year is a wet air mass at the surface giving us fog through at least half the day.  I’m not worried about that for now since we’ve dried out quite a bit the last few days.  And I don’t see any low level moisture source the next few days either.   Add it all together and here’s what I get for a 7 Day forecast right now:



By that time it’ll be October 21st/22nd, definitely near the end of easterly flow helping with any warming, so the middle of next week might be the last of our warm/sunny weather.  Or at least the “warm” part of that.  Models are definitely sticking with dry theme through the next 7-10 days.  The 12z GFS broke the ridge down quickly just before Halloween, and the ECMWF seems to be trying to do that.  We’re probably going to stay dry through at least a week from Thursday or Friday, who knows what happens after that.  Notice the huge variation in solutions on the 12z ECMWF:


and the 18z GFS has a cold (but dry) trough dropping in on us for an early season cold spell right around Halloween:

tseries_850t_000-384_Portland (1)

Look at how different ensemble members want to bring in a cold trough at different times too.  Some nice variability in there!

Chief Meteorologist Mark Nelsen

177 Responses to Nice Weather Ahead, But Tough Temp Forecast

  1. It seems BG is one of the few clear areas still in the valley’s of SW Washington. This has enabled my temp to drop to 31.7 for my first freeze of the year.

  2. Rob - Southeast Portland says:

    I am personally inviting bloggers to join our Facebook Weather Group. In the past 2-3 weeks we’ve already had over 50 members request to join from here alone! So feel free to join.

    Our Group is aimed at following weather events in the Portland/Vancouver metro area as well as all of the Northwest. Here you can find comprehensive, detailed thorough analysis and information when a weather event is expected or unfolding. We have 10 Professional Meteorologists, Specialists, and Experts. We also have knowledge on Climate information, Historical Research, Model Analysis, Radar Analysis/Storm Tracking, and even a few Storm Chasers.

    Our Staff, Professional Meteorologists, Analysts, Specialists, and Storm Chasers

    Some Basic Guidelines To Remember

    You won’t have to worry about certain ‘cliques’ of people, nit picking, arguing, fights, immature provocation, or profane vulgarities here. It won’t happen. When you’re here for the same thing, the same collective interest, which is weather discussion, then there is no need for other nonsense.

    How do you accomplish running an active group and keep it drama free? Easy really. Respect. If we’re discussing weather just do so respectfully. If there is a disagreement which is bound to happen, just make sure people go about it the right way. It’s okay to apply constructive criticism or even correct someone, but do so nicely with actual data to back yourself up. It isn’t okay however to do so and just nit pick the person to death.

    Also, another thing is appreciation. When one of our Meteorologists posts information, or I see another Expert chime in, or if someone posts pictures(just examples) I appreciate they did so and took the time to do so too, because nothing says anyone has to take the time to post in our group, so when people add to the discussion or offer their insight that needs to be noted and appreciated. Not enough people, or groups rather do that anymore.

    Look forward to having you there with us

  3. Timmy_Supercell (Klamath Falls @ 4200') says:

    00z GFS is outstanding tonight. This is for Klamath Falls.

    Average 68.2 degrees and its in the middle of Fall.

  4. schmit44 says:

    10/18/2013 Oregon (All) Temperature Summary

    High:80 at AGNESS2( 247 ft)
    Low: 60 at FLYNN PRAIRIE(1543 ft)

    High:44 at HOWARD Mt Howard(8150 ft)
    Low: 14 at FOSTER FLAT (5000 ft ) & Horse Ridge (US (4160 ft )

    Largest Diurnal Change: 55 degrees
    Beatty (71/16 ) (4320 ft )
    CROOKED RIVER FE (78/24) (2919 ft)
    Lorella (71/17) (4160 ft)

    • Rob - Southeast Portland says:

      Yup, it sure has been.

    • Rob - Southeast Portland says:

      More info here —>

      Great video by NWS Anchorage

      It is always good to look upstream in Alaska, Bering Sea, and the across the North-Central Pacific and their weather patterns as they have everything to do with our own patterns downstream.

      Credit to John Rinier for posting this in my Facebook weather group PDX WX Analysis.

    • Cool vid. Warm weather!

  5. Rob - Southeast Portland says:

    Hardly worth a mention, but if you can believe it tonight’s 00z GFS run was even more boring. lol

  6. ashley watson says:

    I may be moving to sw washington. Where is a good place for snow? Is yacolt pretty good?

  7. Mark Nelsen says:

    marinersfan: You’re on moderation after last night’s trolling. Note rule #3 and rule #4

  8. WEATHERDAN says:

    70 and sunny. It just doesn’t get much better than this for late October. I hope this weather lasts into November. There is plenty of time for the exiting stuff this Winter. For right now this sunny weather and clear cool nights makes for spectacular leaf coloration. Also helps out with heating bills. Hope you all have a nice weekend. See you at the weather conference at OMSI next Saturday. Peace.

    • David B. says:

      Took until after 2PM for the fog to burn off up here in Puget Sound country, so it never got above the mid 50s. Already in the 40s with clear skies, doubt we’ll get frost, though (the fog should greatly slow the cooling once it re-forms).

  9. BoringOregon says:

    All I can say is i’m “BORED”…………………………………

  10. W7ENK says:

    Rob (et al.), I hope you understand my comment yesterday wasn’t meant to be rude or criticizing or “trolling”? It was simply misplaced. I tried to convey that as best as I possibly could. (here: ) I hope that’s been clearly laid out for you… I am not pushing your buttons.

    Someone please acknowledge? 😕

  11. WEATHERDAN says:

    There has bee a lot of complaining recently about how because it has been so warm and dry this October we are going to have a mild and dry winter. HA! That as they say is just so much hogwash. And here’s why. First off it hasn’t been excessively warm this month. In fact so far we are a little colder than normal for the month. As far as being drier than normal, not so much. Normally Salem has about 2.88 inches of rain in October. With most of that falling the second half. Well we have had nearly 1 inch in the usually drier first half. Now as far as the rest of the winter goes what follows may be completely different. Hey that sounds so pythonesqe. October of 1976 was cool and wet. After that dry and mild. 1978 saw a warm and dry October and a super cold winter. In 2008 we had a warm October followed by a cold and snowy December. October it seems can sometimes be a carryover from the Summer months than a harbinger of what is to follow. Just relax and enjoy this nice patch of dry and mild weather. The rainy and stormy season will be here soon enough. I remember last spring when some posters were complaining about how this was going to be the coldest and worst Summer ever. Those of us who are older and have experienced many Autumns similar to this one understand that weather patterns can change on a dime. November and December of 1985 were very cold and snowy. Then in January it turned very mild for the rest of the winter. So will this Winter be cold and snowy or dry and mild or something in between. I don’t know the answer and neither does anybody else including Mark. We can make an educated guess, but that’s all it is. So have fun with the Winter forecasts but if you want to know for sure what this Winter will really be like you will have to wait until March of 2014. Peace

    • Rob - Southeast Portland says:

      Good post.


    • Punxsutawney (aka HIOPHIL) at work by Sunset High elev ~280 says:

      FWIW, there are some similarities between Sept-Oct 1978 and this year when I look at historical Hillsboro records. Sept ’78 was very wet, and October ’78 was fairly dry with long warm rainless streak in October. Oct 17, 1978 – 80 degrees for a high in here.

      Today 72, 73-74? here for a high.

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