This case is told by Mr. Robert Hollenbach, a senior civilian Forecaster at the NASP METOC. He has been forecasting since 1977, including service on the USS Independence, the USS Wisconsin, and the USS America. He served as Forecaster at NAS Kingsville, Staff Forecaster at Pearl Harbor, and as an Instructor at the USN Aerography School. He has logged over 47,000 hours at forecasting or forecasting-related tasks.
In the case described here, there was a question of whether severe weather would
occur at all, in a typical scenario in which one would not expect severe
weather to arise.A single key datum
triggered a line of hypothetical reasoning that led to successful prediction of
severe weather that other weather forecasting stations missed--until it was too
late.This case also illustrates the
need for the forecaster to possess an thorough knowledge of the needs of his
OSA = Observation /Situation
AssessmentD = DecisionA = Action
This was my first day of
I had watched the weather
channel before coming in.
This was a standard scenario.
When I walked in the guy at
the FDO station was just two years out of school.
He said, "Front is
through, NW winds, clear all day."
He wasn't looking at anything
This is what most people
The front goes through then
they do not look upstream, and assume that nothing will happen.
I want to limit the phone
calls and do not like to have the pilots standing around.
I want them in and out.
You end up repeating the same
answer to the same questions.
This gets frustrating after
about three times of explaining the same thing.
And you get multiple calls
from the same squadron.
Why don't they share the
Just yesterday, four guys from
VT-10 called about the same SIGMET.
When weather is happening the
weather itself creates work--warnings, TAF amendments, etc.
If you get ahead of the game
you can avoid the pile-ups of pilots in here.
Better early than later.
Better for them to call when
it is not yet happening.
Also, in the PM we get calls
about stuff being planned the next day.They have to do their schedules before they go home.If weather is happening in the PM (which
is when it commonly does) then there is a big crunch.
Radar showed mid-level
moisture--some spots of green in SATRADin the cirrus region.
A front had gone through.
Winds were out of the
northwest, no clouds.
(I can't recall if the 500 millibar chart showed a weak thermal high behind
Nothing was said at the
The forecast was for NW wind
all day long.
The satellite loop showed that
the cirrus was still there.
The 500 millibar analysis showed
an area of turning winds.
This was a key clue.
The area of cirrus shown on
satellite was atypical cloud cover.
The cirrus continued behind
Usually the negative vorticity
wipes the cirrus out.
This cirrus made it all the way
across to an area of negative vorticity (downward vertical motion).
My goal was to try to figure
out what would happen.
If it kept moving through
nothing would happen, but if it didn't, you get stung."
I've had that happen over the
If you pulled up the wrong
charts or charts without plots, you would overlook the turning and not ask
yourself why it was there.
You'd not keep the satellite
The wind shift implied that
something was happening.
A novice would have missed it.
If I had not seen the weather
channel that AM I would not have been concerned with it.
I would not have looked at the
winds and found the vorticity maximum.
I like to come in one step
ahead of the game.
The key is
Not so much the vorticity max
as the turning of the winds.
The vorticity max was at the
top of the ridge so it would not show up so much.
The turning of the winds was
enough to me.
Any turning in any amount
should be considered significant.
Then you look for support and
weigh all the factors.
Try to justify the turning, do
not try to not justify it.
In this case, the association
of the turning with the vorticity max keyed it off.
A vorticity of 6 is not enough
for most people to consider significant.(The vorticity scale goes from zero to 22 in 2-unit increments, and
can be positive or negative.).
If the front had not stalled
and there were no light and variable winds to hint of a sea breeze... light
and variable winds support land heating and thereby contribute to the
formation of a sea breeze.
The sea breeze linked up with
the front's tail moving back up.
The sea breeze nullified the
gradient associated with the ridge and allowed the front to move back
If the front had not stalled
there would have been no moisture for the vorticity to interact with.the cirrus would have de-enhanced and lost
the mid-level moisture.
It was dry at NASP.
The humidity was only 48% and
was going down over the AM hours.When the winds changed, the relative humidity increased to 78%.
If I had not been looking, the
wind shift would have been a cue since
the prognoses called for a
gradient and a small craft warning.The wind shift implied that something was happening.
I put a statement in the
Temporary Condition line in the Dash-1s that I was doing.
This was to let the pilots know
the potential was there through if one were to skywatch here at the station,
they would see clear skies.
So I knew there was something to
There was no time pressure at
The stuff was still a few hours
showed no change in the cirrus enhancement, implying that the cirrus was not
something to be concerned with.
Typically, as it cones down a
ridge it should dive and dissipate due to the negative vorticity.
It was not enhancing, but it
also was NOT going away.
It had turning and cirrus.
There must have been something
balancing the positive vorticity (or divergence with the trough) and the
negative vorticity as it was going down the ridge.
I could have done things
I do not like doing other
people's jobs, like giving brief explanations of synoptic situations and
stuff like that.
We needed to amend the five-day
forecast on the Home page, but with two forecasters working here we probably
could have done that.
Normally, whenI come in after two or three days off
watch, I do not question the forecast at changeover.
If I see something and ask about
it, they often haven't looked anyway!
I just decided to keep a look on
this over the next few hours, and wait for the next model output charts at
I always glance at the PUP and
LPATS as I walk in and out to go skywatch.
If you do not know what to look
at you continue to not look.
Once you get burned and bust a
forecast no one lets you forget it.
Even when you are
right--forecasting bad weather, they complain at you for saying they can't
I went back to the 00Z
analysis and thought he saw some turning over southwest Missouri, but not a
lot since it was at the top of the ridge axis.
There was moisture at 500
The depression was 2.
The winds were faster ahead
than behind, implying divergence.
Water vapor imagery showed no
dry slot, implying the air was homogeneous and there was no instability.
I was seeing that there was
Divergence on top of a front
will kick stuff off.
Something would happen.
The timing was the issue.
7:00 - 7:30 AM
No one else was going for
There was nothing in the
I decided to continue waiting
The error would be to ignore it
until it was too late to let anyone know.
Thunderstorms would kick off.
Pilots would get stuck out
The new 500 millibar analysis
He saw rotation, enough to call
it something--a disturbance.
The satellite enhancement
showed that the cirrus was not changing--but it was also not dissipating--and
was still moving to the south.
Being in this situation a
couple of times makes you want to look at everything so you do not get stung.
You have to be prepared to
explain why something did NOT happen in a standard scenario.
9:00 -9:15 AM
I decided there was something
out there, and that it could kick off.
Across the loop, the cirrus
stayed the same size and had no moisture associated with it, implying that it
was not a thing to worry about.
It would be localized and not
I decided to look at the
I wanted to look for any
tendencies to lessen the disturbance or keep it intact, or deepen it.
None of the charts showed
But the vorticity was there.
300 millibar chart showed a
little increase in winds.
Some of the models tend to
smooth out the little stuff, but the vorticity analysis does not do that.
Vorticity in the same area as
the increased winds implied divergence at 300 millibars, but not really a jet
It was not big enough to be
called a jet max.
It is called a "minor
short wave" since it is usually only at one level and is not as strong
as a jet max.
If the vorticity maximum was in
the same area as the winds, that would imply that the disturbance would not
A novice would not be looking.
They are trained in school but
tend to not do what they're taught, and they get stung.
After that, you always ask
He had to write a TAF in 30
He decided to keep watching the
satellite imagery and saw no change.
It implied that there was no
dissipation, but the disturbance might yet have fallen apart.
Still, I had to decide what to
put in the TAFs.
A novice would not be focusing
on the satellite loop.
I decided to put a thunderstorm
warning in the TAF.
I did it to cover my rear.
It would have been an error to
not out it out.
It is better to have them laugh
at you because you were wrong (forecast rain, but no rain) than complain to
you because you were wrong (no rain forecast but it rained).
A novice would have missed it
You are not ever supposed to
have to put out a T-1 and a T-2 at the same time, since if you do that
implies that you missed something and by the time you have to put it out it
is already there.
I determined that it would reach
the coast between 3:00 and 4:00 PM.
The decision was based on the
movement I saw in a four-hour satellite loop.
On that, and on two runs of the
analysis, I could do a simple calculation in my head of when the disturbance
would get here--where it was four hours ago, where it is now, the approximate
distance covered, then just divide.
The pilots get little training
Their mind set is due to the
basic training they get in weather:
After a front goes through the
weather is good and flying is good.
You have to convince them
In this case I had to get out a
T-1 to force them to ask and then get an explanation.
Pilots should get better
weather training--not more training but more savvy training.
I included the 3:00 - 4:00 time
in the TAF.
I called for thunderstorms
beginning about 2:00 or 3:00 and out through sunset.
Usually if they do crop up in
the PM they do not die down until after sunset.
Round-robin flights out of here
going north on VR, by the time they land up there, eat lunch, and then come
back down, that is just when stuff is popping up down here, the late
That is the key time for them
to get back in.
I wanted the pilots to be aware
that if weather would happen it would be at about the time they'd be coming
So, they would take a longer
lunch and wait a while before leaving to come back here.
If a novice were at the FDO
desk, they would never glance at the PUP.
SRF's get in a mind-set.
After they've done their fields
forecasts every two hours and their dash-1s they just sit.
The NEXRAD should be seen from
the FDO desk, not the SRF desk.
Idecided to wait for the rest of the model run to come in.
I knew to keep an eye on the
surface winds on station.
(see entry for 10:30 - 12:30 PM,
The error here would be to miss
It was always a possibility
that the later model runs would show a decrease in intensity implying that
the deepening had been counteracted by the ridge.
Or, the models could show an
increase, implying a change from isolated thunderstorms to severe
Also, the models runs would
include a revised lifting index, and if the lifted Index increased, that
would imply severe weather ant not isolated storms.
Severe weather has implications
for the Charlie areas--I have to put out special warnings.
So, missing this would be a big
Saw some pink in the radar.
It was at the edge of the Mobile
radar and showed pink,
This implied that there was
moisture at the high level, which fit with the cirrus to the east.
This all was fitting the
The cirrus continued to move
south and he noticed on GOES that it was enhancing.
There seemed to be some low and
mid-level stuff building up.
This implied that storms were
going to happen.
The disturbance was starting to
pick up low-level moisture.
The pink in the radar was not
the precipitation (yet)--it was showing the moisture being picked up.
New prognoses, NGM outputs, etc.
arrived.They still showed nothing.
The runs included no increase
in the Lifted Index.
No change in anything.
So, the biggest problem again
was that the models tend to smooth things out.
In this case, the GOES data was
critical, and radar too.
Nothing else was helpful.
There are not a lot of stations
out in Mississippi and rural Alabama,so there is a paucity of ground observations.
I've lived (and died) by satellite
data more times than not.
Winds at NASP shifted from the
northwest at 12 knots to the east-northeast at 3 knots.
This suggested that the front
was passing to the south now.
The front had stalled out and
gotten closer to the station.
A novice may not have noticed
it when the popcorn cumulus began showing up in the GOES imagery, at about
10:15 - 12:30 PM
I kept an eye on the local
surface winds--watching the front.
I hypothesized that either the
front had stalled and backed up or the land heating has counteracted any
gradient that was out there.
f the front moved down,
divergence would hit it over the water and nothing would happen here at NASP.
If the front stalled,
divergence would hit it over land and pull it back up.
Land heating is rare for that
time of year--not enough heating to cause a sea breeze.
And besides, you still need the
light and variables winds, even in the winter scenario.
So I figured that the front had
With stationary fronts, as the
upper-level system hits the front, there is a bit of turning on part of the
front.Part of the front turns back
up north and part turns down southward.
In this case, the
southward-turning part of the front was down in Mississippi--they had the
north-west winds there and to Mobile.
East of Mobile to here we had
So the center of the turning was
between Mobile and New Orleans, approximately.
I knew they would either have
northwest winds (steady gradient) or light and variable winds out of the
Light and variable winds out of
the east would be atypical because they would imply that the front had
stalled and was being pulled back up to the north on top of this region.
Winds were light and variable out
of the east.
There were still no clouds
associated with the tail of the front.
But there was the possibility
that clouds could increase in the low level along the front.
If the winds had stayed
north-west I would have amended the TAF--there would be no way we would get
low-level moisture here.
Winds were southeast at 10
This implied that the front was
right on top of us or just to the north and NASP was back on the warm side of
the front in the low-level moisture.
1:00 - 1:15 PM
I went outside and skywatched.
I expected to see low-level
If they were not there, I'd
have known that I'd blown the forecast.
I also looked for
enhancement--clouds going up and not just stratifying.
Stratification would mean
capping and subsidence can cap the development on the cold side of the front.
But on the warm side, the
inversion can be broken and the air goes unstable.
I could see low clouds scattered
and flowing up to the north
Over this next hour there was
Satellite showed clouds down in
the Alabama-Mississippi border region into southeast Mississippi.
There was a line of popcorn
cumulus at the I-10 corridor.
Showers began to show in radar.
I knew I'd nailed the forecast.
What was happening was what I
had told them was going to happen.
1:15 - 2:15 PM
Thunderstorms and the vorticity
max expanded along the cumulus line.
Everyone else had to change
Norfolk did a SIGMET but after
stuff started to develop.
I had not talked to any of the
other stations because I was busy with pilots.
Everyone thought it would be a
good flying day--lots of people were flying.
the National Weather Service
waited until stuff popped then they issued numerous amendments.
Stuff popped up.
The front moved through NASP and
things cleared out.
Winds shifted to the northwest.
None of my guys got stuck.
They left for their return legs
later than they would have and arrived at NASP later in the PM.
So no one had to divert, no one
out of about 14 flights.
4:00 - 4:30
·Although satellite imagery is often said to be the prime data source
for getting the bit picture, the satellite data can be critical in supporting
on-going situation assessment through long-term monitoring of the loops.Using a loop one can readily calculate the
direction and rate of motion of developing systems and thereby forecast the
onset time of severe weather.this
can be the only way to determine onsets for smaller-scale weather events that
are sometimes glossed over by the computer models.
"The runs included no increase in the Lifted
Index. No change in anything. So, the biggest problem again was that the
models tend to smooth things out. In this case, the GOES data was critical,
and radar too. Nothing else was helpful. There are not a lot of stations out
in Mississippi and rural Alabama, so there is a paucity of ground
observations.Sparse data. I've lived
(and died) by satellite data more times than not."
·Upper-air data on troughs and vorticity can be critical in
forecasting rapidly-developing severe weather.
·Awareness of overall weather situation at the beginning of a watch is
critical, but as pass-down very little is typically said.
"Nothing was said at the turnover.The forecast was for NW wind all day
"Normally, whenI come in after two or three days off watch, I do not question
the forecast at changeover. If I see something and ask about it, they often
haven't looked anyway!"
·The layout of the operations floor at the METOC clearly calls for
changes, including making the NEXRAD PUP directly viewable from the FDO desk
rather than the SRF desk.
·The key data in severe outbreaks of this sort seem to be moisture at
the low levels, the amount of lifting, convergence-divergence across levels,
and an energy source such as an upper-level trough running over a front.
·Computer models sometimes gloss over smaller-scale events, with the
exception of the vorticity charts.the forecaster needs to be alert to weather events that the models can
miss, and then look to data types that can be informative.
·Sometimes the decision to explore a possibility hinges on seeing a
single key clue:
"The satellite loop
showed that the cirrus was still there. The 500 millibar analysis showed an
area of turning winds. This was a key clue. My goal was to try to figure out
what would happen.If it kept moving
through nothing would happen, but if it didn't, you get caught stung. I've
had that happen over the years."
·The experienced forecaster never relies exclusively on the data
provided through mediated systems.They always directly observe the atmosphere and clouds at the
field.This dovetails on the notion
that the METOC facility and layout should be re-designed.Skywatching the region south of the field
is possible through easy exit from the operations floor, but skywatching
toward the field and north is possible only by a considerable traverse of the
building.Ideally, the operations
floor should look out onto the field through a panoramic window.
·Forecasting involves not just determining what will happen and when,
but sometimes involves determining why something that is expected in a given
typical scenario is NOT happening.
"Typically, as it cones down a ridge it
should dive and dissipate due to the negative vorticity. It was not
enhancing, but it also was NOT going away.It had turning and cirrus."
·There must have been something balancing the positive vorticity (or
divergence with the trough) and the negative vorticity as it was going down
·Hypothetical reasoning about severe weather outbreaks involves a
number of possible alternative scenarios.the highly experienced forecaster engages in a great deal of
hypothetical reasoning, sometimes in spite of the fact that incoming data cut
against a favored hypothesis or make one or another scenario less likely.
"But there was the possibility that clouds
could increase in the low level along the front. If the winds had stayed
north-west I would have amended the TAF--there would be no way we would get
low-level moisture here."
·It is important for the forecaster to know the usual activities and
routines of the clients and not just the bare flight plan (e.g., time of
departure to determine such things as ceiling and visibility at the
airfield).For example, pilots doing
round-robin flights will often eat lunch at their way-point then depart for
the return to NASP, bringing them into NASP in the PM hours just when summer
regime storms are developing.If
earlier in the day the forecaster anticipates the possibility for afternoon
severe weather, alerting the pilots to this before they depart NASP will let
them know to delay their departure for the return leg.
·Issuing a thunderstorm
warning sometimes constitutes justified over-forecasting.If severe weather does occur and a
warning had not been put out, that would be a worse error than putting out a
warning and then the bad weather does not happen." It is better to have them laugh at you because you were
wrong (forecast rain, but no rain) than complain to you because you were
wrong (no rain forecast but it rained).)
·Training in the Schoolhouse on the standard scenarios should include
gaming in which the students are set-up to "get burned," just as
was possible in this case.The
learning in the Schoolhouse is said to transfer only after lived experiences
in which errors are made, teaching the student to look for things to explain
why expected events do NOT occur and why the unexpected CAN occur. The
information you need depends on your knowing where to look.
·Novices are said to be weak in terms of picking up subtle clues for
small-scale events that the computer models gloss over.
"If you pulled up the wrong charts or charts
without plots, you would overlook the turning and not ask yourself why it was
there. You'd not keep the satellite loop going."
·Novices are said to fall prey to mindsets, such as the mindset that
says that after frontal passage the weather will be clear.Hence, they expect nothing to happen and
do not look to see if anything is happening.Schoolhouse exercises should help them break through such mind-sets.
"They are trained in school but tend to not do what they're taught, and
they get stung."
·Pilots do not appreciate the emotional impact of their casual
behavior, and through their own lack of understanding of the forecaster's
activities, they cause an unnecessary increase in forecaster workload.the emotional impact of the client's
behaviors on the forecaster becomes salient:
"Even when you are
right--forecasting bad weather, they complain (euphemism) at you for saying
they can't fly."
"It is better to have
them laugh at you because you were wrong (forecast rain, but no rain) than
complain (euphemism) at you because you were wrong (no rain forecast but it
It seems ironic that the
forecasters want their clients (the pilots) to leave them alone.But there is a reason:
"I want to limit the phone calls and do not
like to have the pilots standing around. I want them in and out. You end up
repeating the same answer to the same questions. This gets frustrating after
about three times of explaining the same thing. And you get multiple calls
from the same squadron.
that's frustrating. Why don't they share the
information? Just yesterday, four guys from VT-10 called about the same
SIGMET. When weather is happening the weather itself creates work--warnings,
TAF amendments, etc."
·Pilots and their wings should do a better job of sharing weather
presented to pilots should be explanatory and not merely descriptive.
·The training pilots receive in weather needs to be better, and not
just more, but more savvy:
"The pilots get little training in
weather.Their mind set is due to the
basic training they get in weather: After a front goes through the weather is
good and flying is good.
You have to convince them otherwise. In this case
I had to get out a T-1 to force them to ask and then get an
·It is important to possess the willingness and fortitude to inspect
incoming data stream frame by frame for long periods of time.