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Thread: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

  1. #1
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    Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    I believe many pilots will find this posting to be educational. We don't always need to take a flight to verify the accuracy of the RASP. At the same time, we don't always know what the RASP forecast is really telling us. I've captured the Mtn Cam View for 11 AM today and copied the RASP fcst for 11AM today and will display the images below.

    Thomas D and I had planned to fly the 24's today, but opted to stay on the ground due to the fcst. I has developed exactly as I thought it would!

    ---
    A side bar note: I just wish we had one more mountain web cam, with it showing the Office area and the view towards Rumsey... but it's not very feasible... due to nothing more than the sunlight coming directly into the lens and burning out the camera (but maybe it could be pointed downward so it wasn't too high in the sky?). In any case, what we have is excellent - as is. Thank you Larry Roberts and Noelle.
    ---

    We can see from about "3 Sisters" on the left of the view, up to about Yolla Peak area, but Yolla Peak area is too distant to see much. On the 11 AM image I marked about where I think the turnpoints marked on the RASP are located. On the RASP forecast for the same time (11 AM, today) I have drawn lines corresponding to the view shown no the Mtn web cam.

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    Now I will display the RASP fcst for this same area at this same time.


    How much Cu cloud cover is in the fcst?
    Here is the RASP for 11 am ...
    blcloudpct.curr.1100lst.d2

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    And here is the zoom in, with the camera view marked wiith grey lines...
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    Clouds SW of Goat are in the fcst, clouds aligned with Goat are well to the West, Clouds this the red area (on the RASP) north of Goat is actually overdeveloped cu-nim which are now all fuzzy in the web cam photo.


    Now we look at the BS ratio - bsratio.curr.1100lst.d2

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    The feared areas marked in blue indicate very low BS between three sisters and goat, but higher ratios over Indian and towards Sites. Higher bs ratios under those tall fuzzy cu nim clouds north of Goat, this side of black butte.


    Now lets see the HCrit.
    hwcrit.curr.1100lst.d2

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    Blue- ie - zero lift over Montgomery (east of Goat) . Lift between 3 sisters and goat up to about 3,000 ish. Under the fuzzy cloud north of Goat you might find some lift as high as 9,000 in spots, but all very poor and not high enough for most of us.


    I'll continue this with a second posting to this thread.
    Last edited by Peter Kelly; 05-30-2019 at 01:39 PM.
    Peter Kelly

  2. #2
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    Continuing with analysis...
    A second posting, just to break up the image uploads...

    So what thermal strengths were in the fcst?

    wstar.curr.1100lst.d2 (Thermal Updraft Velocity, aka thermal strength)
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    xx
    zblclmask.curr.1100lst.d2 (OD Bases)
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    xx
    zsfclclmask.curr.1100lst.d2 (aka Cu Cloudbase)
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    Posting terminated at 11:30 PM
    Thread was OBE
    Last edited by Peter Kelly; 05-30-2019 at 11:31 PM.
    Peter Kelly

  3. #3
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    This is great! A few notes from my experience:

    I don't pay much attention to the B/S ratio plots. Look at thermal strength and wind and make up your own mind. I've successfully thermaled on awful B/S ratio days.

    Thermal strength is basically calculated from surface heating. So, if the forecast thinks clouds are going to be overhead, even a good atmosphere will say low thermal strength. If the clouds don't show up, the thermal strength will be better. It's common to see low thermal strength under OD for that reason -- even though often the best lift is under the OD. Thermal strength is about ground based thermals, not cloud suck. It is explicitly thermal strength under blue conditions, so if it's not blue it's pretty useless.

    This day is unusual for getting the exact location of overdevelopment right. The model sees conditions for overdevelopment and then guesses where it will pop up. But a thunderstorm here will suppress development there. So take it as a sign there are likely to be OD, and of course more likely on the best mountain and thermal spots, but not a guarantee of when and where it will show up.

    I find cloud base height and BL top the most useful. Thermal strength is pretty much proportional to height. And clouds need to be over the tops of mountains!

    John Cochrane

  4. #4
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    Peter
    Many thanks for the tutorial & the plan view to the west.
    -- from a beginner.
    Leon

  5. #5
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    John, Leon, thanks for the comments.

    Sorry I dropped off line for the last 12 hours.
    I went back and filled in where those "xx's" were in my last post - I had not posted the RASP source charts. I did not offer any further comments to that posting.

    The purpose of this thread was to demo that on Monday night the RASP charts foretold what conditions were gong to be on Thursday pretty accurately (although we couldn't make sense of it at first). Thomas and I reserved the 24's for Thursday on Monday morning. We couldn't make sense of it on Monday night but mid-day Tuesday I studied the RASP again and this time compared it to Windy.com to try to figure out what the RASP was telling me. I suspected but needed confirmation. After looking at the RASP on Wednesday morning, we cancelled our flying for Thursday before it was even 10 AM.

    The point is, you need to look at the big picture when doing a forecast, not just a single or even a couple of RASP charts. Look for inconsistencies between RASP charts, and Be sure to look at the soundings. The thing that alerted us the most was the 180 degree wind shift shown on the sounding in a period of one hour at WSC from 5,000 ft down to the surface.
    Peter Kelly

  6. #6
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    Peter,
    Excellent visuals, graphics, and explanations. It was great following the weather development with you from Monday to Wednesday.
    Thomas Duncan

  7. #7
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    I saved those 46 hour forecast soundings that had us baffled ... The big wind shift that was fcst to occur overhead, between 2 pm and 3 pm at WSC some two days later.

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    Peter Kelly

  8. #8
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    Cold marine air spilling through the pass from clear lake? I notice the speed profile as well suggesting that.
    John Cochrane

  9. #9
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    windy.com also showed the development of the t-storms using the Rain, thunder option which I wished I would have saved to share.
    Pete Alexander -- 98

  10. #10
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    Re: Reading the RASP while watching the Mtn Web Cam - another tutorial posting

    So a thunderstorm outflow could account for the cold air spilling in from the west in the forecast sounding too.

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