Wet 48hrs For WestAdded : Tuesday at 9:43 Some impressive amounts of rainfall expected across parts of Northwest Wales, Northwest England and Western Scotland over the next 48 hours as a rather slow moving and moist frontal boundary system brings rain in from the Atlantic. In fact, it's not just the moisture, but orographic features come into play too. This is the chart for tomorrow :-
You can see the heavy rain across parts of Northwest and Western Scotland, then later in the day this front pushes South into the Northwest of England and Northwest Wales :-
This is a classic example of orographic or relief rainfall which happens when warm, moist air is forced to rise over higher ground. There is no rocket science to it, the airflow forces the air to rise which cools it. Cooler air holds less moisture than warmer air and it's a bit like if you were forced to walk up a mountain with a load of shopping you would start to discard some of it on the way up (in bins provided of course) as you felt less able to carry on with a heavy load.
The air is exactly the same, cooler air means it can't hold on to that water moisture as well as it did in warmer surroundings and therefore drops the moisture in the form of rain on Western facing and higher ground.
The GFS ► is progging some 25-50mm of rainfall across these regions throughout Wednesday which could give some surface flooding and swollen rivers. You can see this in the GFS ► surface run off algorithm which shows the areas most at risk :-
This chart basically shows areas where the amount of rainfall falling is greater than what the soil and soil type can cope with and hence the rainfall becomes run off.
So, some wet weather for Western areas on Wednesday and could be some local flooding issues in prone Western and Northwestern areas.
METEOROLOGIST : MARSH |