Jump to content
Will it snow? 7 day forecast Weather Radar Will it be cold?
Snow?
Local
Radar
Cold?

Davey80

Members
 View Profile  See their activity

  • Posts

    75

  • Joined

  • Last visited

 Content Type 

Posts posted by Davey80

    London & South East Regional Discussion 16/01/13 18z------>

    in Regional

    Posted

    So to tonights update:

    Most of use have been around a while, some of us lucky enought to remember 1987, some can remember 79 & some even 47 & 63-

    They are the archive charts that we search & find every year when we want to enjoy our memories of cold & snow-

    Note its nearly 50 years to the day for the famous winter of 63.....

    We stand on the cusp of charts ( like Dec 10 as well) that could stand in the archives years to come..- especially if the ECM vairifies tonight which would see the cold spell stretch to day 13 & beyond ( assuming Monday was day 1)-

    Without going into the background of whys & what nots the first thing we might consider is the rarity of this weekends pattern.

    We have had a 'few' undercutting type scenarios in the last few years but they all held one common theme - no blocking high to the east- usually we have low pressure in the north sea that allows low pressure from the atlantic to pass through with little or no resistance- so anything coming from the SW is either snow to rain or freezing rain to rain.

    last time we had a stalling frontal zone that delivered high quantities of snow was 5th feb 1996- thats 17 years ago. - so whilst theres a chance that it could miss the SE the pattern on the whole is RARE.

    Here is the 1996 chart-

    post-1235-0-48092400-1358364370_thumb.pn

    Crucially when we talk about 850 temps the -2c line is a good guide-

    heres those temps at 12pm that day

    http://modeles.meteo...996-2-6-0-2.png

    I recall the Kettley forecast saying ' the front is really getting a speed on now & its even snowing in the channel islands-... where we can see the -2line.

    So for this scenario if we look at mid term models in THIS scenario- any sliders or creepers along the channel- the -2 line is the guide.

    The event for friday for the SE has no marginality in terms of temps- except for the EXTREME SW of the region coastal areas- southampton sort of way- however you only need travel a few miles inland away from any onshore breeze to be secure.

    so there she is in all her beauty-

    http://www.meteociel...48-21.GIF?16-18

    The UKMO chart at T48 shows the low slightly positioned further south than 96 & the upper blocking high further North- this means V 1996 the atlantic should move further east into the country as the amplitude of the jet isnt quite as high. ( slightly lower wave )

    The SW taking a beating there with snow friday for 12 odd hours really building up-

    Then we enter the fray- around T54/T60 & out to 78/84- so 24 hours is a **POSSIBLE** bet.

    http://www.meteociel...60-21.GIF?16-18

    The T60 shows the low sliding SE- which is great as the PPN sheild ahead of it isnt actually getting any further east-

    The low is also pumping up moisture & instability across the SE which will enhance the PPN rates-

    so at T45/48 we are starting out-

    http://www.meteociel...8-594.GIF?16-18

    but at 60 we have that push & onshore flow from the SE

    http://www.meteociel...0-594.GIF?16-18 &

    The Raw output between 12pm Friday & 12pm Saturday are suggestive of 15mm widespread- especially to the south & SW of the region-

    Because the air is so dry & he dewpoint very cold the accumulation ration will be higher than your usual wet rubbish we get.

    I suspect being very light with high air content the ration could be 1mm : 1.5CM-

    That points to 22CM being the mean & 30cm being the TOP END-

    SO for forecast purposes & for the fact the low could fragment / weaken & stay west my forecast for the period is

    London/essex/ kent / East sussex 5-10cm.

    Surrey / West Sussex 7-15cm.

    Areas like the downs- all around banstead etc- ~ 20cm.

    this is based on the UKMO-

    For the ECM knock 3/4cm of all totals-

    **** remember the biggest caveat to this ISNT temperature for once- but how far east the PPN goes & holds together.

    **** Where it stalls will get persistent snow for 30 hours before it fragments ****

    So does it end there????????- NO, for this to be special & one for the archives you need a sustained period over 2 weeks- so lets open the ECM curtains for next week - after sub -10c minima sat night-

    Snow approaching from the west-

    http://en.vedur.is/p...16_1200_114.png

    http://en.vedur.is/p...16_1200_120.png

    http://en.vedur.is/p...16_1200_126.png

    another 12 / 18 hour event that rolls into convective snowfall post that- & very cold out to day 10-

    In Summary then:

    A snow event friday- DONT ramp it up to much on the PPN front as the ECM is fast through with no real stall- so amounts are in the sub 10cm camp- where as the UKMO is VERY aggressive with PPN..

    until then- total ice day tom & friday- freezing the ground & some ponds/lakes ready for the snow...

    S

    Great forecast Steve - What would you predicted snow depths be for North Hampshire . Alton/Basingstoke area?

×
×
  • Create New...