A Case Study in Weather Forecasting:

Fog in the Gulf Coast Region





This case is told by Petty Officer Trisha Bednarczk, a forecaster at the NASP METOC. She has been forecasting since 1990, including service at NAS-Dallas, Crete and Baharain,. She has logged over 13,300 hours at forecasting and forecasting-related tasks.



Although this case involves a typical scenario of advective fog in the Gulf Coast region, is shows how even the "typical" scenario can involve variations on a theme. It also shows how forecasting can be difficult, not just because the uncertainties inherent in the weather, but also because of the many responsibilities of the METOC forecaster. This Case also serves as an excellent illustration of local heuristic rules, rules that go beyond what is taught in the Schoolhouse, including rules that may be of a kind that might be totally unexpected.

 


 

Event and Comments

Event type

February or early March, 1993.

NAS-Dallas

Daywatch, 6:00 AM

I was AFDO.

We discussed when and whether the fog would burn off.

There it usually burns off at about 10:00 - 11:00 AM

 

Observation or situation assessment

It was foggy when I came on watch, zero ceiling and zero visibility.

I couldn't see my car 25 feet away in the parking lot through the front door.

The fog sets in from a nearby lake.

 

Observation or situation assessment,

Local rules

 

Fog is tough to forecast there, like here at NASP, but it tougher here at NASP.

It can be clear off the Base and heavy fog here on the Base since it is closer to the water and at a lower elevation.

What's difficult about NAS Dallas is the question of when it will lift enough for flying.

I knew I'd be doing dash-1s, TAFs, and answering the phone.

The Forecaster mainly handled the fog situation.

I can't way what a less experienced person might have done.

It takes experience with a full season to get used to the local weather pattern.

Even if you study the typical cases and the Forecaster's Handbook.

 

Decision

 

 

 

Local rules

 

 

 

 

Local rules

Southerly flow off the Gulf, typical in the transitional regime for early Spring.

Typical of a foggy day.

 

Decision, Local rules

It is typical for fog to burn off.

It depends on the thickness of the fog.

It can burn off by 11:00 AM, other days you are socked in all day.

 

Decision, Local rules

If we were lucky it would get to 1000 feet by mid afternoon, but at sunset it would come back down.

It depends on the fog thickness and the cloud cover that blocks the sunlight that would otherwise burn it off even though the ceiling might rise.

There are lots of variations on this scenario.

If it is thick and it burns off at 200 feet per hour even that will not be enough.

The student pilots' attitude sometimes makes things hectic.

They would only have a couple of hours to do their stuff if they were to go out early in the day.

It is a rule learned at C-school.

As temperature drops, ceiling and visibility drop due to the loss of heating.

But lived experience helps.

You get to know when to put the knowledge to use.

 

Decision

 

 

 

 

 

Mental workload

 

 

 

 

 

Local rules

But we stayed at 300 to 500 foot ceilings all day.

A less experienced person or someone unaware of forecasting always knows to call other places to ask more experienced people.

 

Observation or situation assessment,

Local knowledge

 

By 11:00 AM I knew there was no way it would burn off

It hadn't gotten above 500 to 600 feet.

This was a measured judgment--the tops were at about 3,000 feet.

I was confident.

 

Decision, action

We knew because the Dallas airport gets lots of PIREPS.

We got plenty of PRIEPS from the Dallas-Fort Worth area airfields--7 or 8 of them, from about 7:00 on

I was envisioning that it would definitely not burn off.

 

Observation or situation assessment

We could tell that from the NWS charts (upper-air charts show the depth of the cloud layer), and the data from regional soundings, and the climatology.

 

Observation or situation assessment

 

A cold air mass had settled in after frontal passage.

Then the southerly flow returned from off the Gulf a day or so later.

That brings up warm air and moisture from the Gulf.

This is a typical scenario.

This is covered in basic training in C-school as a case of fog.

 

Decision

 

 

Local rules

You can see the stratus coming up on the GOES imagery.

It is thick and dark in the infrared (i.e., it is warm because it is at a low level).

This should be the first thing you look at.

It is taught in the satellite course in C-school.

This takes a bit more experience beyond the coursework, though, to reach the point where you can do the forecast off of satellite imagery.

 

Observation or situation assessment

 

Local rules

It was a warm air over a cold air condition, which trapped the fog.

 

Decision

Gulf moisture was coming up.

There was southerly flow due to a High pressure center over the Gulf.

 

Observation or situation assessment,

Local rules

 

The base was just high enough to condense the moisture.

Someone new to that Base wouldn't have known that though the foundation is laid in C-school.

 

Decision,

Local rules

The forecasting problem was if and when the ceiling would rise enough for flights. (F-14s, A-4s.)

This is where experience with the local pattern is necessary.

You need to know the local rules.

 

Action

 

Local rules

Pilots kept bugging me, the Forecaster, and the FDO, from as soon as the field opened up, and especially for flights of smaller aircraft that go out later after the C-9s go out.

"When is the ceiling going to rise?"

We kept saying "No way anyone would do air operations."

The phones rang constantly from early AM when the field opens at 7:00 AM until early afternoon.

It gets tedious.

My options were to post a "Go Away" sign on the door! (laughs), but you just continue handling the calls.

 

Observation or situation assessment, Action

 

Mental workload

Pilots kept bugging me, the Forecaster, and the FDO, especially during the 8:00 AM- 9:00 Am time period.

 

Observation or situation assessment, Action,

Mental workload

 

Guys needed to fly--Army, Air Force.

And it was midweek so they were busy.

Army Reserves want to play for a day.

 

Decision

Local knowledge

At about 1:00 PM it cleared enough for a while to see the downtown to the southeast in the early afternoon.

The downtown is 15 miles away.

If you could not see the top of a certain building, you knew the ceiling was 800 feet.

You could see the downtown but only for a little while

 

Observation or situation assessment, Decision

Local rules

We'd look over the Base towards the downtown hotels, and use the hotels as ceiling indicators.

 

Observation or situation assessment, Action,

Local rules

 

We knew from the visibility of the hotel floors what the ceiling was, and when it got up to 800 feet.

 

Decision, observation or situation assessment,

Local rules

 

There were other rules of thumb--if you could not see the tower you knew the visibility was less than 3/4 of a mile.

You use what you can.

 

Observation or situation assessment, Decision,

Local rules

 

They kept bugging me so I had to keep monitoring the situation--GOES loop, celiometer, every 5 to 10 minutes, observations out of the Dallas area airfields.

 

Observation or situation assessment, Action,

Mental workload

 

By about 10:00 PM I knew no one would fly.

Decision

 

The situation was difficult because everyone kept bugging us.

Every day at NAS Dallas, you deal with the USAF, the Navy, Marines, transients, Drug Interdiction, Reserves doing mid-week flight time, the Coast Guard.

 

Decision

Local knowledge

Takeoffs needed a certain ceiling for different planes and for different airfields.

For example, C-9s cannot take off in anything.

Flights may be able to take off or may not, but they could land elsewhere.

 

Local knowledge, Decision

The Base Operations Officer kept asking about it.

As soon as it would hit 700 feet he took off.

Then the ceiling came back down.

Once he got above the mid-deck and cirrus he was OK.

But he had to divert to Love Field (about 20 miles north of Dallas) on his way back.

 

Observation or situation assessment

By 2:00 PM the situation was over.

Stuff was shutting down.

Even if they took off they couldn't fly back in or into other fields in the region.

 

Observation or situation assessment, Decision

Analysis

 

You use what you can.

For instance, in Suda Bay there were two mountain ranges in the distance at different elevations.

You could tell from how far down in elevation the snow was falling by using the mountain ranges as a ruler.

 

 

 

 

Decision Requirements

 

Cues and

Variables

 

Fog forecasting involves forecasting whether fog (ceiling and visibility) will lift and when. There are many variations on the basic fog forecasting scenario in the Gulf region. Key data are Pilot Reports, local soundings, upper-air analysis, and GOES imagery.

 

        "We knew because the Dallas airport gets lots of PIREPS. We got plenty of PRIEPS from the Dallas-Fort Worth area airfields--7 or 8 of them."

        "We could tell that from the NWS charts (upper-air charts show the depth of the cloud layer), and the data from regional soundings, and the climatology."

        "You can see the stratus coming up on the GOES imagery. It is thick and dark in the infrared (i.e., it is warm because it is at a low level)."

 


 

Needed

information

 

 

 

 

Local Heuristics. Local rules are often critical, and represent a knowledge that comes only from experience and learning from the local experts.

 

        "It is typical for fog to burn off. It depends on the thickness of the fog."

        "Southerly flow off the Gulf is typical in the transitional regime for early Spring."

        "A cold air mass had settled in after frontal passage. Then the southerly flow returned from off the Gulf a day or so later. That brings up warm air and moisture from the Gulf. This is a typical scenario."

        "The base was just high enough to condense the moisture."

        "Someone new to that Base wouldn't have known that, though the foundation is laid in C-school."

 

Rules Of Thumb Sometimes Involve The Unexpected.

        "The downtown is 15 miles away. If you could not see the top of a certain building, you knew the ceiling was 800 feet. You could see the downtown but only for a little while in the early afternoon. We'd look over the Base towards the downtown hotels, and use the hotels as ceiling indicators. We knew from the visibility of the hotel floors what the ceiling was, and when it got up to 800 feet. There were other rules of thumb--if you could not see the tower you knew the visibility was less than 3/4 of a mile."

 

Training for Fog Forecasting

        "It is a rule learned at C-school. As temperature drops, ceiling and visibility drop due to the loss of heating."

        "This is covered in basic training in C-school as a case of fog."

        [Stratus in GOES] should be the first thing you look at. It is taught in the satellite course in C-school."

 

Experience Beyond Training

        "A less experienced person or someone unaware of forecasting always knows to call other places to ask more experienced people."

        "Lived experience helps. You get to know when to put the knowledge to use.

 


 

 

Local Knowledge

        "And it was midweek so they were busy. Army Reserves want to play for a day."

        "Every day at NAS Dallas, you deal with the USAF, the Navy, Marines, transients, Drug Interdiction, Reserves doing mid-week flight time, the Coast Guard."

        "Takeoffs needed a certain ceiling for different planes and for different airfields. For example, C-9s cannot take off in anything. Flights may be able to take off or may not, but they could land elsewhere."

 

Hypotheticals

 

 

 

Fog forecasting always involves hypothetical reasoning, and requires the forecaster to be comfortable in uncertain situations.

 

        "If we were lucky it would get to 1000 feet by mid afternoon, but at sunset it would come back down. It depends on the fog thickness and the cloud cover that blocks the sunlight that would otherwise burn it off even though the ceiling might rise. There are lots of variations on this scenario. If it is thick and it burns off at 200 feet per hour even that will not be enough."

        "I was envisioning that it would definitely not burn off."

 

Options

 

 

The main option is just to continue providing information to the clients (se Time/Effort, below).

 

         "This was a measured judgment--the tops were at about 3,000 feet. I was confident."

          

Rationale

 

 

 

        "Fog at NAS-Dallas usually burns off at about 10:00 - 11:00 AM."

        "Lived experience helps. You get to know when to put the knowledge to use."

        "This is where experience with the local pattern is necessary. You need to know the local rules."

        "You use what you can."

 

Situation

Assessment

 

        "This takes a bit more experience beyond the coursework, though, to reach the point where you can do the forecast off of satellite imagery."

 


 

Time/effort

 

 

        "Fog is tough to forecast there, like here at NASP, but it tougher here at NASP. It can be clear off the Base and heavy fog here on the Base since it is closer to the water and at a lower elevation. What's difficult about NAS Dallas is the question of when it will lift enough for flying."

        " The student pilots' attitude sometimes makes things hectic. It gets tedious."

        "My options were to post a "Go Away" sign on the door! (laughs), but you just continue handling the calls."

        "The situation was difficult because everyone kept bugging us.

        Every day at NAS Dallas, you deal with the USAF, the Navy, Marines, transients, Drug Interdiction, Reserves doing mid-week flight time, the Coast Guard."

 

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