UKC

I'm planning to go up Ben Nevis on Saturday with friends. Obviously MWIS is a key place to look and its description for Saturday is appalling. I trust it, so I doubt we'll get much above Halfway Lochan, if even that. So far so bad!

I don't often look at the Synoptic Charts, but in my desperation for a window of good weather, I did. And I'm confused / showing my ignorance.

As I read the chart:-
1.the pressure's to be about 1012, which isn't too bad?
2.the isobars seem fairly well spaced, which doesn't seem too bad?
3.the line of the front has passed over to the east by mid-Saturday, it appears
4.the direction seems to be from the west, which i'd generally take to be squally but not wicked

So from these points, I get a big gap between above (blustery, bit wet, bit chilly) and the described donner unt blitzen, severe wind chill, snow, v strong winds, etc. etc.

Clearly MWIS is a very good and reliable source - it's my preferred site - so I'm not doubitng it in any way - can anyone tell me where my interp of the Synoptic is falling down? Can the front (i'm not sure of the symbols on it, in truth) still carry something pretty wicked in its trail, rather than it being the focus point of the worst of it?

many thanks.

In reply to andy hunter:
Which synoptic chart are you looking at? The MWIS forecast is from yesterday afternoon so will be based on forecast charts from yesterday noon, and you are likely looking at charts from midnight.

However, the airmass behind the front looks very cold and unstable: the 528dm thickness line is over Scotland, which is very cold for this time of year, and likely to produce heavy gusty showers, which a surface pressure of 1012mb is not nearly high enough to suppress.
The wind speed does look a little on the high side, but the isobars look like they may tighten during the afternoon in association with the next occluded front.

The Met Office W Highland forecast is broadly in agreement: "Breezy with widespread westerly gales over high ground, and severe gales for the northwest Highlands. Blustery showers will be most frequent north of the Great Glen, falling as snow above 600m, rising to 800m in the afternoon. Showers may merge into longer spells of rain or snow later in the day. Freezing level 800 to 1000m."

In reply to Mark Bull:

Thanks Mark. I looked at the 48 hours option, hoping that it would give me 48 hours from now = Saturday mid morning?

I didn't know that what comes behind the line of a front can mean as much as the area around the line of the front, thanks. (I was kind of guessing it might, having pondered it, I suppose.)

I didnt know about the thickness of the line, nor the relationship between the pressure cold air. That's interesting and useful thanks.

I've checked a number of sites and they all say, essentially, appalling, so I think a stretch to the lochan is about it - if that.

cheers

In reply to andy hunter:

48 hours is the time from the data collection on which the forecast is based, not from "now": if it's a Met Office chart them you are likely looking at a chart with a valid time of midnight Fri/Sat which is not quite what you want! The Met Office charts have the valid time in UTC (i.e. GMT) in the top left corner.