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Paul

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    Southeast England & East Anglia - Weather Chat >> 1st Feb Onwards

    in Regional

    Posted

    I wonder if some of the more knowledgeable can help me out on this. I'm under one of those showers affecting north Essex as we speak. I have an outside temperature of -1.2c and it was clear and frosty until this shower arrived. We have a dp of -0.5c and uppers of -8c. Somehow it is raining. The water is freezing on contact but it is most definitely rain. Where is the warm air coming from in the atmosphere to melt the snow on its journey to the ground? I thought it might be the sea but the air with current wind direction is having to track across about 60 miles of land which should allow it to cool especially and we have very light winds.

     

    The 850-1000 thickness is and important factor for snow forecasting as it looks at the temperature between 850hpa and the ground (essentially). At around 1290 in your neck of the woods you're not nailed on for snow - that's around a 60-70% chance of snow at that level, you'd want to be at around 1280 for a 90% + risk.

     

    post-2-0-36021500-1422999883_thumb.png

    Model Output Discussion - 23rd Jan - 12z onwards

    in Forecast Model Discussion

    Posted

    That doesn't explain why last night the radar showed snow going over me in bands yet it was bone dry on the ground.

     

    We're getting miles off topic here, but as snow tends to blow a long way it could well have been that - more info on the radar systems and what can cause it to show phantom prec, or miss prec here:

     

    http://www.metoffice.gov.uk/media/pdf/j/h/Fact_sheet_No._15.pdf

     

    Best we get backto the models now though please - can answer more radar questions if there are any over in the help section, or the learners area..

    • Like 3

    Model Output Discussion - 23rd Jan - 12z onwards

    in Forecast Model Discussion

    Posted

    Sorry if off topic

     

    can i ask a question, i have searched but not found what i am looking for and there are alot of knowledgable posters on here!

     

    I have heard that the rainfall radars we all look at are not live but a prediction based on the model runs and current observations, it was mentioned on few posts recently, is that correct? Or is the precipitation radar live but wether its rain, sleet or snow is what the prediction factor is?

     

    Thanks

     

    It is off topic, but the radar is live from the UK's radar network, the precip type detection is based on model data/observations. Feel free to pm me if you would like further info.

    Model Output Discussion - 23rd Jan - 12z onwards

    in Forecast Model Discussion

    Posted

    So in a case such as the ensemble chart posted above - Should we be going with the newly upgraded higher resolution operational, or the ensemble mean? It seems strange to update the operational but not the ensembles

     

    In the particular case of the chart above I'd go with the ensemble as it appears the grid square being used for the isle of wight by the operational is more sea based than land (will see if we can shift it to stop this happening). In most cases, when looking at detail on the ground then the operational will be the way forward. 

    • Like 2

    Model Output Discussion - 23rd Jan - 12z onwards

    in Forecast Model Discussion

    Posted

    GFS Op was definately on the warm side of the ensembles. Almost 40/40 for a break through from the west or a beasterly from next weekend. 20% go for a middle ground solution

     

    Some of the ensebles (esp south) show the Op to be completely out of sink with the operational, even from the start!  Any ideas on how this can be?

     

    attachicon.gift2mIsle~of~Wight.png

     

    It's the difference in resolution - ensembles are at 1 degree, gfs at 0.25 degrees, so you're essentially comparing quite different data, particularly when talking at ground level at the moment. The ensembles will be upgraded this year to bring them more into line with the GFS again. 

    • Like 1
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    Southeast England and East Anglia - Weather Chat

    in Regional

    Posted

    I think those going round in circles dissecting forecasts from different forecasters (or the same ones at different times) are just going to tie themselves in knots here. You're in the SE of England, so clearly northerlies aren't the ultimate for snow and real cold, but it's cold enough (in the main), and there is a risk of some snow. That should really be enough - no matter how many times you read a forecast that's a variation on the theme, it's not going to change - so perhaps relax a tad and see what happens rather than continually going through this whole weather angst thing?

    • Like 20

    RADAR Future time steps question

    in Help, support and feedback

    Posted

    Hi Quentin, funny enough was about to reply in the other thread. It looks like we had a bug on the forecast radar recently which was throwing it off course, that's literally just been fixed in the last 10 minutes though (may take a few updates to filter through).

     

    To answer your question, we use upper wind data to decide where the rain is moved to. 

    Southeast England and East Anglia - Weather Chat

    in Regional

    Posted

    What are the verification stats on this model & what data is it based on? I wonder how it compares with the EURO4, I use the NetWx model quite frequently and it to me, seems to suggest sleet when it would otherwise be snow 

     

    We find it verifies very well, and has handled a lot of recent situations when it comes to snow/rain/wind events strongly. As with any model it's never going to be 100% when it comes to things like localised snow showers - that's where the radar comes into play though! In terms of the green - that's not sleet, it's a rain/snow mix, so green areas can be rain, sleet or wet snow as they're in that borderline area.

    Need Help On The Site/forum?

    in Help, support and feedback

    Posted

    Hi Gangan, there is some info on this over in the help files here (under posting):

    https://forum.netweather.tv/index.php?app=core&module=help

     

    But in short, on the post editor, if you click the more reply options button you'll see there's an uploader at the bottom, clicking that will allow you to choose a photo from your computer to upload and add to your post. 

     

    post-2-0-93931700-1422459469_thumb.png

     

    Once it's uploaded, you'll see an add to post link above the upload button, which you can click to place the photo into your post wherever the cursor is. 

     

    Hope that helps :)

     

    Paul

     

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