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This is the forecast for Lasham on 18th July 2017:
This forecast was last updated 18/07/17 07:48 GMT
Forecaster: David Masson
Synopsis: Quick update 8:30am
- rather lot of top/medium cover, but the worst of it it is to our north and maybe it won't be too bad in southern counties for a few hours
- the trough line and thunderstorms to the SW is obvious. Be careful if they start hitting late afternoon / evening
The actual soundings (Herstmonceux 00Z and Larkhill 06Z) show actually if we get enough heating through it would be easy to get temperatures to 24-26C+ and even 24C would give blue to 4000ft+.
I would monitor it, but 25C would give blue to 4000-4500ft+ and, with dewpoints >13C (which might happen later or to our south) we could have shallow cumulus base 4000-4500ft+ under a weak inversion at ~5000ft.
So I'll still suggest it is MIGHT be ok for 100-200km or more.
--- last night's text unchanged, figures changed ---
Weak slow moving warm front on the south coast moves slowly northwards.
Slow to get going under some top cover with a temp of 22-23C needed to give blue thermals to 2500-3000ft maybe reached by midday to 1pm.
Thermals affected by the wind and on-and-off by the top cover but may get a bit more organised in streets. In the afternoon going to 3000-3500ft+ with more chance of shallow cumulus base 3500ft+ to our south and later in the afternoon.
Might be ok for a short XC 100-200k in the afternoon.
Temperatures: Max/Min -> 25C / 13C, Dewpoint -> 14C
Wind strength/direction: 21 knots / 100 degrees
Cloud base/thermal top: 4200 feet
Thermal strength: 2 knots
Thermal start/finish: 1200/1700
Visibility: 20000 metres
Outlook: Tuesday evening thundery low and trough coming up from Biscay with heavy thundery showers / storms possible through Tuesday night.
Wed: thundery showers moving north then warm and humid, clearing about in the afternoon with wind 210/18kst and vaguely soarable, cumulus base 2000-2500ft+. I probably won't bother with a forecast.
Thu: cold front(s) to clear and then a weak of ridge of high pressue. The air looks really quite nice over most of the country. Typical conditions wind 300-270/17kts, 1-3/8s Cu 4000-4500ft+, and maybe 5000-5500ft+ in the best bits. For most of the country and for those that can cope with the wind probably a 300-500km+ day, 400-600km+ in the better bits and the possibility of it being a 750km day...
[next forecast Wed evening for Thu, but I will try to do it a bit earlier]