fergieweather

As a UKMO colleague says, putting current NWP output in very good perspective: "... Looks like major hemispheric re-configuration after next weekend's disruption. Not surprising then to see a period of comparative chaos in deterministic output. But northern blocking looks a possibility, so we'll have to watch out for extrusion of low GPH out of the eastern Arctic. EC32 firming up on cold signal..."

They currently stick with the 30% PROB scenario for colder, dry / blocked into the 15d trend period. That's remained consistent recently. However, they note that it remains a continued theme, so they're in no way disregarding it. Doubt much stock given to GFS way into FI however - they'd be forever chasing their tails if they bothered with that stuff. They stick with ECM output (and MOGREPS of course) as the primary driver for the longer MR in any case above anything churning-out from the American model.

Oh absolutely - please don't get me wrong, I wasn't for a moment suggesting it shouldn't be discussed (!) but merely responding to specific queries as to what UKMO's take is on CFS. So, folk can make their own judgement... for my part, I'll take the wisdom of Exeter's boffins over it... one of whom wrote to me today, quote, "...CFS doesn’t get a look in (in MR preparation), and based on my own experience of its performance, nor should it..."

12z NAE is now in: issues resolved

12z NAE has failed to run, just in case anyone ponders why it will look same as 06z....

Yup, UKMO stress the flavour of expectations into 10-15d period, which (consistently of late) sees the blocked option continuing as a minority solution: " 4. Trend for Days 10-15 : Strongest signal is for an unsettled type to persist, bringing further spells of rain or showers to many areas and probably moving more towards a NW’ly flow bias. However, still an ongoing lower prob alternative (about a third of ensemble members) suggesting drier, colder conditions developing later in this period. 5. Discussion : Strong signal for generally very cyclonic and unsettled conditions to dominate through this period. An upper vortex becomes established over the NE’ern Atlantic next week whilst downstream ridge amplification also takes place, limiting progression and leaving a S/SW’ly synoptic type with further frontal zones and spells of showers across much of the UK through the week. There remains uncertainty over timing of frontal zones on Tuesday/Wednesday, with EC and GFS both suggesting waves running along the front. Later in this period EC, NCEP and MOGREPS ensembles tend to agree that the flow trends away from the SW’ly to more of a W, then NW’ly bias. This would make for a continuation of the unsettled flavour, but with temperatures falling below normal more widely..."

Incidentally, worth adding how the developments into Saturday as progged by UKMO-GM and EC also have support from ARPEGE (as shown here:)

Took part in interesting discussion last night with UKMO colleagues re potential snow possibilities for some areas into Saturday. We didn't bother discussing the longer range stuff this time...!!

Forecasting cloud amounts and areal spread of this over next 48hrs might benefit from some...!!

It will be interesting, one way or another...!!

Indeed so John. And yes: They really do 'forecast'. And have PhD's. And unblinkered view of models. And other important stuff...;-) I see innumerable changes made each day to the raw NAE / GM output by the Ch Forecaster, MR Forecasters etc., based on 'forecasting skill'. The recent snow event in W Country was a classic example of how they tweaked NAE with published methodology outside raw model scope to better account for evaporative cooling and WBFL lowering (with the correct result). I'm astonished the question even requires asking...!!

EC-32's output had already leaned in this direction and that was the driving rationale behind the recent BBC video. Rest assured the med-range stuff and updated UKMO seasonal has been subject of as much discussion today at BBC Weather as on this forum...!

I'm saying we tend to use 00 & 12z whenever either are available but the other runs shouldn't be loosely discounted or devalued per se (albeit in any case, UKMO invariably prefer ECMWF as their pointer versus GFS, in my experience)

As for this 'pub run' 18z GFS thing: to my knowledge the only difference between 06z / 18z runs and those initiated at 00z / 12z by NOAA is absence of US radiosonde network data input. In any event of course, thIs single run output remains unconvincing until we see better continuity.

I'm not going to pronounce any judgement on CFS as I'm wholly unclear on it's demonstrable performance or validation, but in my mind, it's noteworthy how I've never seen it cited / mentioned - ever - in any piece of UKMO guidance / briefing / analytical documentation looking into longer-range prospects.

No: it was produced to explain rationale for UKMO 30-d comments after internal discussion.

Yup: as on the pressure anomaly output I'm looking at now. Strong signal. We shall see. Anyway I'm sure it's all been gawped at on here before so apols for any duplication!

PS The EC anomaly prog remains strongly in tune with its previous output into the same period.

I think "fearing the worst this winter" has opposite meaning for many, who will be more than happy if it's mild & essentially non-descript! The model thread does seem to have an awful lot of cold-seeking / cold-wishing bias, which might be better served on other parts of the forum? Surely model discussion should be focused solely neutrally on the potentIal outcomes, rather than a wish-list for specific weather type? Just my thoughts... cheers!

Hi folks, just to reiterate a post I sent on 3 Nov quoting (see below) the UKMO Chief Forecaster; you will note again from this how they anticipated some snow potential and crucially also note how raw NAE was tweaked at Exeter using a technique they regularly employ to give more reliable indication of snow potential by evaporative cooling... so I don't think they were off the mark; the raw NAE is just that - raw - and rarely followed without many tweaks at Ops Centre throughout every day....  "New (NAE) run doesn’t suggest any snow but tweaking with Wilderspin/ Lumb (method) readily produces some, as also does UKv (which is considered overdone with its 5-10cm locally). Wet snow considered as low to moderate risk on N+W flank (UKV suggests some) but depends critically on ppn intensity and tracking..."

UKMO-UKV turned out to be the closest solution with prognosis for locally 5-10cm; back on Fri we called for 10% chance but low track was v uncertain as was ppn intensity in any one spot to lower WBFL. Tricky forecast per square mile of region to get right, but good UKMO models spotted it all by Fri and no others did...

P.S. see comments just posted in SW regional thread re latest prognosis from UKMO regarding Sunday snow potential

Snow signal has now gone in new NAE.

Probably already noted, but new NAE loses snow signal for Sunday with more southerly track. UKMO considers only v low potential N and W flank dependent on ppn intensity.

UKMO stance is currently based on MOGREPS-R, which has 50% members supporting the deeper wave further NE on Sunday. Last two runs have given same outcome. So, UKMO have moved in this direction , quote, "...but confidence remains low.... risk of snow on NW & W flank of this deeper solution assisted by intensity of PPN as well as the lower sfc pressure and it's corresponding decrease in WBFL..." Snow given 10% PROB and mainly Midlands, especially the north.