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Ben Sainsbury

Pro Forecaster / Meteorologist
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Posts posted by Ben Sainsbury

    Storms and Convective discussion - 1st August 2022 onwards

    in Storms & Severe Weather

    Posted · Edited by Ben Sainsbury

    19 minutes ago, Eagle Eye said:

    Let's talk Supercells because they rarely happen in the UK so when there is the potential that one has happened its quite a big event, normally the whole of twitter is onto it in a flash to disprove or prove it.

    So let's talk facts (that I have just learnt so may not be facts).

    First of all

    For idealised mesocylone strength, a rare event here, then the Storm-Relative Wind coupled with stream wise vorticity would be equal with the change in distance along the direction of the increase of speed from outside the updraft core to the core itself which theoretically means that with a small SRW it could be counteracted and still become a Supercell if the updraft remained relatively stationary.

    If the max updraft speed is equal to or bigger than the SRW then that is a big component in deciding whether tilting happens as well. So a strong updraft does help streamline vorticity tilting which in turn hands itself to helping to create perfect conditions for Supercells.

    20220814_195935.thumb.jpg.293d1d2f43a472579a6e43395b4aab71.jpg

    Earlier in Scotland, the possibility that one of the Storms was a Supercell was mentioned,I had a brief look at it but never really went in depth.

    Polish_20220814_215244596.thumb.png.9f8c2a3140c009b1c6e593e9bfed6643.png

    Upshear is the change of shear upwards and so would be associated with inflowing updraft which is what we want here so from the cloud layer 150:211 is decent enough for a slight right turn in terms of when the Storm is strengthening as usually happens but more importantly,it suggests the net vorticity tilting was very close to 1:1. So a persistent mesocylone was quite likely and based off pictures of the event I would suggest this was probably a mesocylone but to confirm it we would need a time-lapse to know that he distance between the outside and the core of the updraft and the streamwise vorticity also worked together well.

     

    You've lost me😂 

    Just for the rest of the people here, it might be helpful to explain what "Storm-Relative Wind", "Streamwise Vorticity" and "Net Vorticity Tilting" is 🙂 

    • Like 8

    Model Output Discussion - Autumn arrives

    in Forecast Model Discussion

    Posted · Edited by Ben Sainsbury

    44 minutes ago, FetchCB said:

    UKV is part of the Met Offices unified model. Its not based on the UKM its part of it. 

    binary-code.jpg

    6554b6be8c0d829a8bf63ae0c82cf121_link.pn Unified Model

    WWW.METOFFICE.GOV.UK
    The Unified Model (UM) is a numerical model of the atmosphere used for both weather and climate applications.
    visual-cortex-of-uk-temperatures.png

    6554b6be8c0d829a8bf63ae0c82cf121_link.pn Numerical weather prediction models

    WWW.METOFFICE.GOV.UK
    The Unified Model is run operationally in a number of configurations for weather forecasting at the Met Office.

     

    It's not always that easy to understand, but the UKV is linked to the UKMO. The UKV utilizes the boundary conditions from the UKMO, so effectively the UKV will use the bigger picture (outside the map boundaries of the model) from the UKMO and then runs its own forecast based on the boundary conditions at that time (I think that's how it works).

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    Storms and Convective discussion - 1st August 2022 onwards

    in Storms & Severe Weather

    Posted · Edited by Ben Sainsbury

    Just thought I'd take a little bit of a deeper look into the Thunderstorm Risk for Sunday/Early Next Week.

    Saturday night would expect a few elevated thunderstorms to approach S Ireland/far SW England but nothing too much of note at this point. 

    Sunday we see some quite large CAPE developing across Ireland and less so for N England/Scotland. I'd expect a combination of strong surface heating/convergence zone/orographic lifting to initiate scattered thunderstorms, possibly strong/severe at times given modest DLS over Ireland.

     image.thumb.png.a4033ed2902b6a386f5dc19d46282ed5.png

    By Sunday night, as the low gradually drifts a touch eastwards, I would expect storms to become increasingly elevated as the boundary layer cools with some impressive lightning shows right across the Irish Sea and up towards NW England/Scotland, given the magnitude of MUCAPE.

    image.thumb.png.5fef5878c6ef175d64eb22b0b464ac98.png

    Monday looks to have a more widespread thunderstorm risk, with large instability (for UK standards). With a slack low sat right over the UK, wind shear will likely be weak, however given the magnitude of instability, some strong thunderstorms are likely to develop again; this time across much of England, Wales and into S Scotland. Shear across NW England/N Wales is less weak, so some organisation is possible for a time here. Storms becoming increasingly elevated overnight.

    image.thumb.png.712e8293c78eee2fc95a321503cfec81.png

    The last day I'm going to cover is Tuesday given there are still uncertainties on the positioning of the low near the UK. However, I would expect a similar day to Monday albeit the risk transferring a bit further south. Strong thunderstorms developing once again, however as the low pulls south there are some indications that modest wind shear will exist across C/E England. Assuming this (UKV) to be the case, then multicellular development is possible with the potential to upscale into a homegrown MCS into the evening. Flash flooding, prolific lightning and relatively large hail are the likely risks. But at this stage, this is all speculation and to be taken with a large pinch of salt.

    image.thumb.png.4c3483adb33e5204231f18b24033b1ab.png

    That saying, there is relatively good agreement between the models for Monday at least to be a fairly active day, some a close eye is being kept on model developments over the next few days.

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    Storms and Convective discussion - 1st August 2022 onwards

    in Storms & Severe Weather

    Posted

    10 hours ago, damianslaw said:

    Recent years have delivered barely any thunder and lightening here. We had a couple of strikes on the 2nd June but so far nothing.

    The exceptional heat 2 weeks came to an end with a whimper.. can only think due to the exceptional dry air. 

    Quite possibly, but I guess there is no concrete way of knowing! This has to be the worst year for homegrown activity that I can remember.

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    Storms and Convective discussion - 1st May 2022 onwards

    in Storms & Severe Weather

    Posted · Edited by Ben Sainsbury

    12 minutes ago, wimblettben said:

    I know!

    It seems to keep changing from one day to the next these day's and quite often a number of different forecasts will all be saying a different thing from each other on the same day.

    Never no what to even expect anymore or whats going to happen from one day to the next as it keeps changing so much.

    Models have been performing quite poor lately regarding any convective activity. Though at the moment today seems to be going to plan. Ed is right though, ConvectiveWeather for example is probability of lightning within a 25 mile radius. That's actually quite a large area and too often people will see they're under a SLGT for example and expect to see a storm when in reality that's only approx 30-45% chance of lightning with 25 miles.

    Storms and Convective discussion - 1st May 2022 onwards

    in Storms & Severe Weather

    Posted · Edited by Ben Sainsbury

    9 minutes ago, Peachy said:

    Folks who say it's too windy for storms need to remember that just because it's windy at lower levels doesn't mean it's windy higher up where the storms are building. 

    Definitely more chance of storms today than yesterday. 

    I'm not sure I agree with these statements. Technically, you want it windy higher up because this is effectively what wind shear is. Even if it is windy as the surface, it has a negligible impact on storm development.

    Personally, I wouldn't say there is more chance of storms today... if anything I'd say the opposite. But the important thing to note today, is the difference in storms. Those yesterday was elevated thunderstorms whereas today we're expecting a few surface-based thunderstorms.

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