Getting the thermals out

Libby Greenhalgh predicts a chilly weekend in the UK

Winter is now with us with possible snow showers inland over the hills in the east as air temperatures reach a maximum of 6degC on the Saturday and only 3degC on the Sunday in the Southampton area. But the wind chill could be as low as -2degC in the north easterly wind.

General Situation.
A trough in the high pressure system, 1050hPa, over Scandinavia covers the British Isles throughout the weekend. While a low pressure system, 1020hPa, develops tonight to the west of the British Isles. The low will remain a weak feature pushing eastwards as the high pressure persists into early next week.

Saturday will see the continuation of the chilly rather cloudy conditions of today with a north easterly wind of 050degs between 12-15 knots in the morning. This wind will strengthen in the late afternoon and veer more towards 070degs reaching 18 knots. With no strong frontal features associated with the high pressure system, there are no large cloud structures to bring wet and gusty conditions. Instead the northeasterly direction of the wind as it is coming straight off the land will produce shifty conditions with the land topography.

The wind direction over land tends to be backed by roughly 20deg from the wind on the water due to greater friction. As the wind from the land reaches the water, friction is reduced, the wind will try and veer back to its original position producing a wind bend near the shore. The effect of the land is relative to the height of the land, which is relatively low so will probably be within 500 metres of the shore. However the effect of the topography will dominate the shifty conditions, with the wind trying to take the easiest route, down valleys and around hills, and bouncing off the shore over the topographic obstacles.

Sunday will see a slight strengthening of the wind reaching 15-18 knots with a more easterly direction around 080deg. It will also be day of the most chance of wintery showers or rain as a shallow trough pushes across the country in early morning, looking to clear away by the start of the first race. Conditions across the day will remain fairly constant with the sea state being slight due to an offshore wind. It will again be the effect of the mainland causing shifty conditions that will be the key factor of the day.

Question: Will it snow on Christmas Day?
Sadly with climate change making our winters milder and January/February time being the coldest months with most chance of snow the outlook is bleak for a white Christmas - for the south coast at least...

If you have any questions about the weather or aspects of forecasting for Libby, then please email us at feedback@thedailysail.com or click on the Contact Us page above to use a message box...