WXSIM forecasts not picking up Haar (sea fog) intrusion

Software WxSim
1

Tom - here in North East Scotland between April and September we can suffer from the Haar - a cold North Sea sea fog which spreads several miles inland. For the last few days - and it’s expected to continue for the rest of the week - we have sea fog extending across the North Sea from Scotland to Norway. Usually we only get Haar here at Glenbervie when the wind is SE less than 8kts but this week the wind is very light and from the ENE and as I speak I’m sitting in the Haar some 7 miles or so from the coast.

The trouble is that whilst the Met Office correctly forecasts the extent of the Haar - and adjusts the expected temperatures as a result - it seems that WXSIM misses it out for forecasts at this location. Yesterday WXSIM was forecasting 14C and a sunny day but we never got above 9.9C in the Haar and the same was true for the day before that. My current WXSIM forecast is attached showing double figure temperatures for the rest of the week and above it is the Met Office forecast for the BBC for a village two miles from here plus the WU forecast for the local town on the coast 7 miles away - all showing lower temperatures due to the Haar.

I have had fog set in WXSIM preferences for low as I kept getting forecasts of fog with NW winds - that never happens here. However I changed the fog setting back to Normal (50) a couple of days ago and it is still not forecasting this persistent sea fog - I have always had ‘Diurnal Breeze’ ticked by the way.

Any observations you have would be welcome. I’m running beta6 incidentally. Up until this Haar situation I have been amazed at the accuracy of WXSIM forecasts, especially in respect of temperature now that I have had over a year of WXSIMLite and Autolearn running and it would be great if it was possible to iron out this small problem.

EDIT 16/03: 0700 forecast for today, high of 14C and sunny…actual high 8.8C…sea fog or low cloud nearly all day, just 12 minutes of sun.

EDIT 17/03: 0700 forecast, high of 15C and sunny…actual high 8.2C…sea fog all day, 50-200 yards visibility, zero minutes of sun.

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2

Although sea fog at this time of year for us is unusual I have noticed that later in the year WXSim does indeed miss out on forecasting such an event as well. Because this happens at warmer times for us the sea fog is often restricted to within a couple of hundred yards of the high water mark. Especially for us at our house as we are comparatively high here, I find that WD also fails to detect it because we are high enough for my sunshine recorder to read sunny and if you look up it is indeed sunny but look horizontally and it is foggy!

Stuart

3

I don’t know if this is the best way to approach it, but there is a fog sensitivity control on the first tab (I think) under Preferences/Settings. My usual default setting is 45 (on a scale of 0 to 100), and more often than not, I’ve had reports that this is too high (making the forecasts too foggy) and needs to be turned down. However, your case (at least this time of year) could be the opposite. It might be interesting to experiment with that. I’d recommend running multiple forecasts using the same data but different fog settings. Let me know if that helps!

Tom

4

Thanks Tom - I also had the problem of too much fog in the forecasts so had previously reduced the preference setting to ‘low normal’. However after a day of the haar when WXSIM hadn’t picked it up I reset the preference to 50%but it still didn’t pick it up. When I know the haar is about to show itself I’ll up the setting some more and report back here…that could of course be a while in the future.