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    Default high icing index above freezing level

    Hi again,

    in a night raid report is said "High icing index above freezing level at 10.000 ft."

    So I understand that the possibility of icing problems would be quite high during ops. But what is actually meant by "index". Is it just a word for a high possibilty of icing or does it refer to some real index, percentage or something.

    Sorry for that question, but I am really not familiar with this wording.

    Thanks.

    Marcel

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    Marcel,

    Without going into the whys and wherefores a basic lack of information would have made it difficult in the extreme to apply a specific number to the risk of icing during WW2. That said the probability of icing in a forecast would have been given as Nil, Low, Medium or High depending on the weather situation; thus on nights with no cloud the probability of icing would have been Nil, whereas on a night of thick clouds extending to high altitude the probability could have been High. (I've taken the two extreme cases.) This covers the probability, but not the severity of icing.

    The severity of icing in a forecast would have been given as Light, Moderate or Severe, depending on the expected thickness of cloud, the proximity of weather fronts or deep convection (cumulonimbus cloud extending to high altitude).

    Thus as it stands your quotation ("High icing index above freezing level at 10.000 ft.") is ambiguous in that it could mean there is a high risk of some icing above 10000 ft, or there is a risk of severe icing above 10000 ft. Equally ambiguous is that the report does not say if this is a forecast of icing, or of the icing experienced during the operation.

    Because it is mentioned in the report I suspect it means severe icing was experienced during the operation, but if you could email the report to me I might be able to help further.

    I've a feeling I've missed something here in terms of how a forecast is presented, but no doubt someone (Resmorah?) will put me right.

    Brian

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    Hi Brian,

    thanks a lot for answering my questions.

    The quoted text is from the weather forecast. I will email you the report.

    Thanks.

    Best wishes.

    Marcel

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    The problem was somewhat intractable in WW2. It remained so after WW2 (introduction of much turbo-prop and pure-jet aviation). And it seems not to have changed since (see https://aviationweather.gov/static/a...g_Forecast.pdf)!!!! Too many unknown variables! Even if Met get the cloud, temperature, and absolute/relative humidity right it seems that the shape of whatever bit of the aircraft going through icing clouds can affect the accretion!! Too difficult!!
    Sorry not to make it any easier!
    HTH
    Peter Davies (c/s Resmoroh)
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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    If you could provide the date and the numbers of a couple of the squadrons which took part that would be a great help. I'm trying to cast my mind back to the forms we used, and I think one of the items listed was Icing Index (Nil/Low/Medium or High) but that was usually followed by the type of icing (Light/Moderate or Severe) - sorry it's a long time ago.

    Apropos to Peter's post an icing forecast always referred to airframe icing, there being no technique for forecasting carburettor icing at the time.

    Brian

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    Hi Brian,

    I have sent the Night Raid Report to you. It was the raid of 11./12.6.1943 against Dusseldorf and the follwing squadrons participated:

    9, 10, 12, 15, 35, 44, 49, 50, 51, 57, 61, 75, 76, 77, 78, 83, 90, 97, 100, 101, 102, 103, 106, 109, 115, 149, 156, 158, 166, 196, 199, 207, 214, 218, 300, 305, 405, 408, 419, 426, 427, 428, 429, 431, 432, 460, 466, 467, 619

    Thanks for your help.

    Best.

    Marcel

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    Hi Peter,

    thanks for your comments on this difficult topic.

    Marcel

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    Hi,

    I just wanted to mention that the Forecasters’ Reference Book Met.O1023 of 1997 can be downloaded from the address below. But maybe you know already.

    https://www.google.com/url?sa=t&rct=...5H6fRzCJ1NADrU

    Marcel

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    Thanks for this timely discussion on icing. Since we have a couple of meteorologists engaged, I am interested in your views on the likelihood of icing at very low level on October 4, 1944 on the operation to Bergen by 6 and 8 Groups.

    Dad recalled “Well we flew at 100 feet because we couldn’t see the sea, it was so dark and it was raining . Golly it was pouring buckets… And all of a sudden, and it was the most amazing thing, because these were all cumulonimbus clouds that we had over us. There was as I say, rain and hail and everything else, it was a real mess…and all of a sudden the sky just opened up and it was almost like a cathedral with great big hammerheads or the tops of the clouds looked like the claw of a hammer and it just looked like a massive cathedral with the sun streaming down and there was Norway ahead.”

    In his diary, F/O J.A. Anderson (DSO, DFC) recorded “…The icing level was 250 ft and cloud from 250 yo ti 30,000 ft. Cloud dispersed completely over the target…”

    So how likely is it that icing would be present at 250 ft in early October?

    Jim

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    There are a couple of items in this account which makes me wonder about its veracity, in particular Well we flew at 100 feet because we couldn’t see the sea, it was so dark and it was raining. I would have thought it dangerous in the extreme for 140 (from the Bomber Command Diaries) 4-engined heavies to fly at 100 ft in heavy rain which prohibited the crews from seeing the sea. So before I answer could you tell me which squadron(s) these two extracts refer to, please?

    Also, is there a raid report?

    Brian

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