Predicting when fog will lift

[Captain]

I had to abort a flight last weekend because of fog at the destination (it was predicted by the BOM but hung around longer than the airport operator expected when I called him).

 

 

 

Does anyone have a formula or rule of thumb :thumb_up: on how to predict when fog will lift ....... or have you seen it ever being predicted anywhere?

 

 

 

I assume it is dependant on air temp & dewpoint & wind & local topography (:confused:) .... so apart from talking to a local or looking at what happened the day before, is there any easy & reasonably accurate way to guestimate when it might clear?

 

 

[facthunter]

Fog lifting.

 

All the factors you mention, plus a little local knowledge. and an idea of how thick the fog is. If you have an accurate idea of the wind direction likely (there is usually none unless it's a sea fog) the characteristics (air mass properties) can be assessed. It is usually only the raising of the temperature, or a drying wind, that will disperse it.. Nev..

 

 

[Yenn]

Very hard to predict. Here at Gladstone the fog usually starts to lift and then continues lifting, but it came back in again years ago when a pilot had taken off, knowing that it had started lifting and would continue. He had fly to Bundaberg to find a clear spot where he could land. So wait until it has all gone before setting out or at least have a good alternate. Don't forget that once in the air you may be able to see the ground, but if you need to land the visibility decreases when you get down into the fog.

 

 

[BigPete]

The Fogs dispersal rate is tied to your need to fly. :confused: I found this out only this morning.

 

Woke at 4.30 (I have no reason why :raise_eyebrow: ) tossed and turned for an hour and a half (well it is Saturday - sleep in day) decided to go flying nice and early. :thumb_up:

 

Showered, shaved (and the other one) went outside - BLOODY FOG.

 

YES I know it was forecast, but so is the rain we never get!! (How can they be so right and so wrong????) :yuk:

 

Now its 7.45am and its still FOGGY.

 

regards

 

 

[facthunter]

Why?

 

Bureau of Meteorology is a non-prophet organisation. Nev

 

 

[Geoff]

Same hear Pete Left the ground at 8:05 am But was worth the wait:big_grin:

 

 

[Ben Longden]

On the same day in question (for Big Pete), I had a news job to fillum in Cohuna. It was around lunchtime the fog started to lift there, but it was not VFR Kosher until about 2pm.

 

Ben

 

 

[skybum]

Captain, if you have access to Weatherzone and your aerodrome is close to a weather recording station, dew point goes hand in hand with fog. As soon as the temps start to separtate the fog will disperse.

 

A study of how the fog formed in the first place will give you an idea how quick it will disperse. TS events in the northern summer will result in huge amounts of radiation fog along the entire coastal plain. As soon as the TS dissipate and the sky clears. The ground starts cooling quicker than the very humid air above it. It doesn't take long for a layer of air to be cooled to saturation by convection and form a small inversion layer, enough to start forming fog. As the breeze increases , the fog will initially thicken under the inversion layer. The fog normally disperses after the wind has increased. General radiation fog as found under a high pressure system will tend to lift to form a layer of stratus under the rising inversion layer. Tends to hang around a bit until conditions improve. When it lifts , you may be able to get airbourne but you will still have a solid layer of crud between you and blue sky. Only time I flew to MIA we had fog north of Mt Macedon all the way to within sight of the Murray. As the morning went on I had to descend through a break in the stratus because it was lifting to my altitude. Once under the layer all was well again. The layer of fog stretched from west to east as far as the divide in the east and gawd knows where in the west. Initially was starting to worry if the forecast was correct for Mildura.

 

So, fog caused by TS activity will clear with the morning breeze. Fog by radiation and inversion way well hang around and still cause bother by lifting to a solid layer of stratus.

 

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter5/fog_intro.html

 

Good little link:thumb_up:

 

 

[Captain]

Captain, if you have access to Weatherzone and your aerodrome is close to a weather recording station, dew point goes hand in hand with fog. As soon as the temps start to separtate the fog will disperse.A study of how the fog formed in the first place will give you an idea how quick it will disperse. TS events in the northern summer will result in huge amounts of radiation fog along the entire coastal plain. As soon as the TS dissipate and the sky clears. The ground starts cooling quicker than the very humid air above it. It doesn't take long for a layer of air to be cooled to saturation by convection and form a small inversion layer, enough to start forming fog. As the breeze increases , the fog will initially thicken under the inversion layer. The fog normally disperses after the wind has increased. General radiation fog as found under a high pressure system will tend to lift to form a layer of stratus under the rising inversion layer. Tends to hang around a bit until conditions improve. When it lifts , you may be able to get airbourne but you will still have a solid layer of crud between you and blue sky. Only time I flew to MIA we had fog north of Mt Macedon all the way to within sight of the Murray. As the morning went on I had to descend through a break in the stratus because it was lifting to my altitude. Once under the layer all was well again. The layer of fog stretched from west to east as far as the divide in the east and gawd knows where in the west. Initially was starting to worry if the forecast was correct for Mildura.

 

So, fog caused by TS activity will clear with the morning breeze. Fog by radiation and inversion way well hang around and still cause bother by lifting to a solid layer of stratus.

 

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter5/fog_intro.html

 

Good little link:thumb_up:

 

 

So about 10.17 am then?

 

 

 

 

 

 

 

 

 

 

 

 

 

Seriously, thanks for that. In reality it looks like the best way out west here is to track the separation of dew point and actual temp and compare it with a known result, like when it lifted the day before.

 

 

 

Or move to a non-fog area.

 

 

 

However if the BOM can get it pretty right about what cloud will form about what time in their area forecasts like they can most times with Area 22, and they can predict that fog is likely after what time, why can't they have a lash about when it might bugger off? I guess that if it was more predictable, they would, so I may have answered my own question there. EG, like this evening the Area 22 prediction says:

 

OVERVIEW:

 

ISOLATED THUNDERSTORMS/SHOWERS NE OF YMGI/YSDU TILL 12Z. FOG/MIST PATCHES DEVELOPING SE OF YHAY/YSDU AFTER 16Z.

 

 

[skybum]

More like elevenses!

[Captain]

The BOM have done it today in our area. Told ya it's ten-zies.

 

FOG AND LOW CLOUD PATCHES E OF YMGI/YNAR TILL 24Z.

 

 

[youngmic]

No guarantee's and like many have stated wind and temp are usually the key to it.

 

A TAF is useful guide with a FM XXXX (From time) prefix indicating an increase in wind speed or direction. The other is the dew point temperature and reference against this the bottom line of temp's and QNH given for typically 3 hourly intervals from the period of validity of the TAF. If the temperature is forecast to increases significantly above the dew point then this time is a likely indicator.

 

Follow this up with the AWIS if available (number in the ERSA) and it usually includes dry bulb/wet bulb temp's, track this for an increase in the split and it's also a guide.

 

Similarly you can use this in reverse, ie, en-route to a destination regular checks of the actual temp v the dew point can give an indication of lowering cloud base in the late afternoon on an overcast low cloud day.

 

A phone call to Met briefing and speak to the on duty Met officer is often a good way to get a good picture, these guys are usually very helpful.

 

Having said all that even QANTAS and the like get caught out a couple of times a year coming east to west.

 

 

[Guest Fred Bear]

Yep, you should have seen it here the other day. Closed our airport. Anyway, if there is high humidity the day before and low temps through the night, perfect combination for fog. Next day, I look at the ARFOR, predict the rise in temp and forecast winds and go from there. Need a little bit of a breeze and some heating from the sun.

 

 

[facthunter]

Fog.

 

If the wet & dry bulb temps are ,say 1 degree apart and there is no cloud cover and the wind is non-existant you can have quite rapid fog formation. When you fly over the top, you can see down vertically through it ,but when you line up on final and descend into it , your horizontal visibility is inadequate for a safe approach. Nev..