Kasim Awan

Dry as a Sahara run for most of UK.

Not necessarily, we need some wind speeds for that and the flow looks very slack. Our chances are in the Iceland low moving south east and the low moving up from the Azores.

That shows 48 hours of slightly colder than average upper air temperatures before divergence.

If this morning's runs are correct snow chances will be very few and far between.

A cold but largely dry spell is a strong possibility here. The lows responsible for snow risk appear to weaken upon approach to the UK. Still a decent chance of changes.

What we get this morning from the output is a repeat of the late November cold snap.

If you animate the models through over the next 7 days you can clearly see the cold northerly / easterly being deflected away from the UK by the Iberian high.

A real lack of convective snow showers given the potential synoptics, the showery easterly going north of us and the northerly looks tame. This a result of heights to our South.

Merged polar low & Atlantic low snow maker moving South at 126 hours. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5006022

A significant number of GEFS members now produce a NW-SE runner which originates from energy over Iceland around the 120-150h mark. Some parse it into a front, and some keep it's circulation entact as a shortwave low. What is also of interest is the fact these GEFS members also struggle to process the potential big snow maker trough further North East, indicating that a more southerly track of the Azores low also increases the chance of this runner to develop well into the UK.

Depends if we get the front north enough, if we're on the northern flank the easterly winds will produce a moderate leeward effect west of the Pennines with reduced snowfall rates as a result. Get it far enough North or get a front with lighter winds and the leeward effect will be minimal. Any short scale troughs would bring lower levels a risk as there would be no leeward effect in these instances.

For a 25km model to show 30-40cm of snowfall indicates locally 60-70cm of snowfall is likely, say on hills or where streamers within the front align. This is due to the low resolution of the model missing the normal distribution associated with elevation and streamer activity. Combined with 40-50mph winds would likely result in very severe drifts.I can say the GFS18z would produce this with very high confidence. Objective analysis of a model run is not silly, it is factual analysis of data shown to us by the NWP.

Lovely chart to look at, meteociel GFS algorithm looks a bit stingy, 20-25cm widely central areas with 40-50mph gusts. Some are adamant of a southwards trend, which I agree is possible. However, the governing factor that is mostly responsible for the latitude of this system is the Azores high. Given we usually see trends northwards in this feature, I wouldn't discount a trend north in this system over time as opposed to a trend south. Very 5050 stuff and we can't bank anything at this point.

I wouldn't go so far at this stage.

Moving South rapidly on the back end though.

It's a bldy snowstorm that highly active front in very cold air and very little movement over time that chart takes us back to the 1800s.

Yes and it's a great run for longevity the GFS has absolutely been leading the way in the 168h-192h time scale in the past couple of weeks, time and time again we've seen it's changes be later picked up by other NWPs so I expect the ECM/UKMO00Z to be closely in line with tonight's GFS18Z.

Admittedly the snow prospects are far from nailed on, the GFS18Z looks pretty dry up this point once that initial low has moved South, so whilst the potential for heavy snow is there, so is the potential for mostly dry cold spell.

Merged polar low & Atlantic low snow maker moving South at 126 hours.

Ok so the ECM is not so good - it shows us the least we can probably expect from the upcoming pattern. These sorts of outputs are expected really when we're looking at a probabilistic chance of 70/30 of the cold staying in put after the initial slider 16th/17th/18th. We'll probably get the odd rouge run with those probabilities within the ENS/operationals. The main thing is ECM sticks to the plan broadly speaking within 192h so coldies should hope that it is just struggling with too much energy which it can do in these setups at this range. This does not discount the chance of a milder push around day 8 though which is still somewhat of a risk, personally I think GFS/GEM handling is more accurate.

Wrong post.

Everything went well. Home now .

This is a thread to objectively analyse model output. I am well aware of the caveats involved, however you really can't cough up a set up more promising for the potential for major snow events.

Not a fan of deep snow cover and severely cold temperatures? @Nick123 I think models are converging on the pattern now - and it's a very good pattern given the activity to our South West. Obviously details and potential warm sectors very uncertain but the trend that is gathering pace is highly supportive of eventful and cold UK weather.

This is highs of -2/-4C with deep snow cover.