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03jtrickey

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Posts posted by 03jtrickey

    Model Output Discussion - The Run In To Christmas

    in Forecast Model Discussion

    Posted

    Great now I have to get the dictionary out. Someone save me the effort.

    From my understanding the deterministic forecast (i.e. operational run) calculates one particular outcome/forecast at high resolution based on one set of initial weather conditions (which are estimated based on observations).

    However, the initial weather conditions can never be perfectly known due to incomplete geographic coverage of weather observation networks and uncertainty in measurements etc.

    To account for this uncertainty, ensemble predictions are created by running the same model multiple times at a lower resolution using a range of slightly perturbed/adjusted (but still plausible) initial weather conditions as input data. Examining the range of different forecasts that result from the set of slightly different weather conditions gives an idea of the uncertainty in the forecast and allows the deterministic run to be considered in the context of these possible outcomes (e.g. mild outlier etc.). However the deterministic run is still valuable because its higher resolution resolves weather features better, particularly small scale features that may be critical for how a forecast develops.

    • Like 6

    Geopotential height and pressure relationship

    in Spring Weather Discussion

    Posted · Edited by 03jtrickey

    Hi,

    I have a probably fairly basic question about geopotential height, which has bugged me for a while.

    What is confusing me is that...if pressure falls, this means that the atmosphere is less dense and therefore thicker. Therefore by my logic, since pressure would fall more slowly one would need to travel higher in the atmosphere in order to reach, say, the 500mb pressure level under low pressure conditions than under high pressure conditions. This seems to suggest that high heights ought to be associated with low pressure and low heights with high pressure.

    However, on the charts, low pressures seem to have low heights and high pressures typically higher heights, e.g. height rises over Greenland are associated with the establishment of high pressure in that area etc. Can anyone help to put me out of my confusion and explain why this is the case? I feel like there is something really obvious that I am missing!

    Thanks smile.png

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