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MattTarrant

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    South West and Central Southern England Regional Weather Discussion 22/02/2018 Onwards

    in Regional

    Posted · Edited by MattTarrant

    4 minutes ago, ajpoolshark said:

    EllyTech, you're interpretation of lapse rates is wrong.....the above definition is correct, yours isn't.......that is why convection is generally limited in frontal systems, the lapse rates are low.....have a look in the learning area of NW.......you're confusing lapse rates with the differences of T850 temperatures between different locations!......in this coming 'event'.....there will be a large difference in T850 temps between say the south coast and the midlands, but this will not aid convection as it has nothing to do with lapse rates!

    Thermal Gradient = Lateral (Horizontal) difference is temperature (850hPa/Surface Temp) between two areas. 

    Lapse Rates = Vertical difference between surface & upper atmosphere. 

    Should of quoted Elly, sorry. 

     

    • Thanks 1

    Wales/Cymru Regional Weather Discussion

    in Regional

    Posted

    Just to settle the nerves a little; 

    HIRLAM : More broad snow (Ie even Swansea West Gets 7/8 cm)

    ARPEGE: 5cm West Of Swansea

    EURO4: Likely to be over predicting the effects of the Brecon Beacons. They are a real annoyance but are they really going to wipe out all precipitation on SE to NW trajectory? Unlikely. 

    Met Office automated forecasts also show snow falling for the likes of; Swansea, Ammanford, Carmarthen. 

    • Like 4

    South West and Central Southern England Regional Weather Discussion 22/02/2018 Onwards

    in Regional

    Posted

    2 minutes ago, Jayfromcardiff said:

    Wish they'd issue snowfall amounts.

    Still too much uncertainty, I safe bet would be 5- 10cm at the moment. Though there will be areas seeing in excess of 20cm. I believe the ice threat is what causing the most issues with that having the potential to cause severe disruption though any the northern extent unlikely to be agreed upon until late Wednesday/Early Thursday. 

    Model output discussion - the beast arrives

    in Forecast Model Discussion

    Posted · Edited by MattTarrant

    Icon followed the GEM & UKMO in that is disrupted the energy east. 850hPa still very marginal but it does undercut the precipitation after a short period of rain/sleet along southern areas. I think we are all in agreement that whatever outcome, be it enegry going east or west uppers will be marginal along southern areas. 

    Model output discussion - the beast arrives

    in Forecast Model Discussion

    Posted

    3 minutes ago, Ben Sainsbury said:

    For what I see the ECM 12z will have produced some of the largest snow totals of all the runs so far.

    Exceptional chart, the hardest hit being the Dublin area receiving almost 65cm of snow between Thursday and Saturday. Whilst most other places looking in excess of 20-25cm.

    5a93043bf17e2_snowaccumulation.thumb.jpg.d61e1af2cc7e745d5a7a906c951cf800.jpg

    I do believe they are horridly inaccurate. The In & cm depths are completely different :wallbash:

    Wales/Cymru Regional Weather Discussion

    in Regional

    Posted

    1 hour ago, benytezz said:

    any model experts on? doesn't warm air rise when it encounters cold air, especially the VERY cold air we'll have over us when that low arrives? Why does an established block of cold air move out of the way so readily in the face of an encroaching spin of warm air?

     

    this is the bit i'm not getting about the models, but perhaps that's why i'm not a pro meteorologist as well? lol

    You make a valid point, cold air is very dense. Though its key to distinguish between 850hPa Temperatures (Approx 1500m) & Surface Temperatures in this situation. 

    Parameters of air (mass) resistance is a complex science. I would be under the assumption that as result of our minimal land surface area, the boundary level is more minimal in its affects to fluid flow than would otherwise be the case in a continental country. Such that as a result of minimal cold development at the surface 'warmer' air masses can easily override the cold air in place without disruption or turbulence (Ie remains laminar flow in essence), related to a dimensionless numerical value known as Reynolds Number.  

    The above hopefully will give a little glimpse at the complexities of air mass interchange, especially at the boundary level. You should also hence be able to decipher why there is a lag in surface temperatures over ridden by a warmer upper air component.  

    • Like 1

    Model output discussion - here comes the beast!

    in Forecast Model Discussion

    Posted

    4 minutes ago, chionomaniac said:

    That was not my point. I know colder air is denser but what I said is that I don't buy the theory that cold air is hard to dislodge once in place. It may be slightly harder to displace than warmer air but if the block isn't strong enough then the mild air will come marching through. Anyway I am hoping that the low pressure is further south on the next runs.

    Parameters of air (mass) resistance is a complex science. I would be under the assumption that as result of our minimal land surface area, the boundary level is more minimal in its affects to fluid flow than would otherwise be the case in a continental country. Such that as a result of minimal cold development at the surface 'warmer' air masses can easily override the cold air in place without disruption or turbulence (Ie remains laminar flow in essence), I believe this is related to something known as Reynolds Number. Anyway I do believe the macro - scale synoptics are just as important in the whole process. 

    • Like 1
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    Wales/Cymru Regional Weather Discussion

    in Regional

    Posted

    9 minutes ago, Jayfromcardiff said:

    What's your thoughts on Friday mate? People saying mild temps to turn snow to rain?

    Model analysis at such a range is based  on trends & the probabilistic nature of certain broad scale events happening. History would indicate that cold pooling is often readily removed too fast (often just before the onset of the cold),especially at the surface level. Once we are into the cold spell the models will adjust accordingly, largely a result of snow cover actually physically being in observations instead of in theory. Friday's system is simply conjecture at this range, though a mix of ECM & UKMO would currently be the favored outcome with support from MOGREPS. <10/20% GFS outcome.   

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