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This is the forecast for Lasham on 13th August 2017:
This forecast was last updated 12/08/17 22:19 GMT
Forecaster: David Masson
Synopsis: A rare event this year - a ridge of high pressure, light winds and having to wait for a proper trigger for thermals (which might be the most significant thing).
Depending on dewpoint (say 8C) a trigger tenp of 18C+ gives cumulus base 4000ft+ by midday-1pm. There is a risk of it being blue to start in which case a tenp of 19C should give depth of convection to 4000-4500ft+ anyway.
Then good conditions with good thermals 3-5kts+, shallow cumulus base 4500-5500ft+ under some top cover.
Best conditions east of 2W and I would stay east of 1.5W or further later in the afternoon.
Taskwise I'd just go straight north. South of Humber cumulus bases could be 6000-7000ft+ ASL.
Should be good for good for a fast 300-500km+ or for 600km+ (maybe a rare O/R to York or Sutton Bank)
Temperatures: Max/Min -> 20C / 10C, Dewpoint -> 7C
Wind strength/direction: 4 knots / 310 degrees
Cloud base/thermal top: 5000 feet
Thermal strength: 4 knots
Thermal start/finish: 1200/1900
Visibility: >21000 metres
Outlook: Mon: probably pants with southerlies and lots of top cover
Tue: probably ok, a bit windy with 20kt weaterlies, towering cumulus base 3500-4000ft+ not showering though???