RADIATION FOG STUDYRADIATION FOG STUDY

Office StatsOffice Stats

00z ELM TAF00z ELM TAF POD for FG – 0.53 POD for FG – 0.53 FAR – 0.55FAR – 0.55

06z ELM TAF06z ELM TAF POD for FG – 0.68 POD for FG – 0.68 FAR – 0.50FAR – 0.50

Crossover TechniqueCrossover Technique

This method, by itself, showed skill in This method, by itself, showed skill in determining when at least BR would occurdetermining when at least BR would occur When FG/BR occurred, the low temperature at When FG/BR occurred, the low temperature at

ELM reached the crossover temperature about ELM reached the crossover temperature about 80% of the time80% of the time

However, it was less able to distinguish However, it was less able to distinguish between FG and BRbetween FG and BR When the “dense fog” threshold was reached When the “dense fog” threshold was reached

(Crossover – 3 deg. F) or exceeded, FG only (Crossover – 3 deg. F) or exceeded, FG only occurred about 55% of the timeoccurred about 55% of the time

Water Temperature vs. Low Water Temperature vs. Low TemperatureTemperature

No data available at this time for temp. of No data available at this time for temp. of Chemung River near ELM…closest gages Chemung River near ELM…closest gages are on the Tioga River in PA (Mansfield)are on the Tioga River in PA (Mansfield)

For this study, compared early morning For this study, compared early morning low at ELM to climatological value of water low at ELM to climatological value of water temp. on Cayuga Lake near ITHtemp. on Cayuga Lake near ITH For June into August of this year, this compared For June into August of this year, this compared

favorably to Mansfield (+/- 3 deg. F)favorably to Mansfield (+/- 3 deg. F) Need to look at this more closely over a longer Need to look at this more closely over a longer

time periodtime period

More Water Temperature vs. More Water Temperature vs. Low TemperatureLow Temperature

August through DecemberAugust through December When Delta T was 23 deg. F or more, FG When Delta T was 23 deg. F or more, FG

occurred the vast majority of the time (20 occurred the vast majority of the time (20 FG/only 3 BR)FG/only 3 BR)

When Delta T was between 14 deg. F and 23 When Delta T was between 14 deg. F and 23 deg. F, FG and BR occurrences were evenly deg. F, FG and BR occurrences were evenly split (20 each)split (20 each)

When Delta T was less than 14 deg. F, BR took When Delta T was less than 14 deg. F, BR took place the vast majority of the time (13 BR/only place the vast majority of the time (13 BR/only 4 FG)4 FG)

Yet More Water vs. Low Yet More Water vs. Low TemperaturesTemperatures

April through JulyApril through July When Delta T was less than 7 deg. F, BR When Delta T was less than 7 deg. F, BR

occurred the vast majority of the time occurred the vast majority of the time (30 BR/only 7 FG)(30 BR/only 7 FG)

When Delta T was 8 deg. F or more, FG When Delta T was 8 deg. F or more, FG and BR events were about even (9 FG/6 and BR events were about even (9 FG/6 BR)BR)

RADIATION EVENTS Average Wind Speed (knots)

SIGMA LAYERFG BR

8 10 18

7 10 19

6 11 19

5 11 18

4 10 16

3 8 12

2 5 9

1 3 5

SFC 3 5

59 FG CASES73 BR CASES

FG EVENTS

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0 5 10 15 20 25 30 35 40 45

WIND SPEED SIGMA 8 (knots)

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Series1

FG EVENTS

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0 5 10 15 20 25 30 35

WIND SPEED SIGM A 5 (knots)

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BR EVENTS

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WIND SPEED SIGMA 8 (knots)

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BR EVENTS

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WIND SPEED SIGMA 5 (knots)

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PRELIMINARY CONCLUSIONSPRELIMINARY CONCLUSIONS

Between sigma layers 5 through 8, the Between sigma layers 5 through 8, the average flow in BR events was twice as average flow in BR events was twice as strong as FG events. strong as FG events. FG – 10 knotsFG – 10 knots BR – 20 knotsBR – 20 knots

FG EventsFG Events Vast majority of events occur when the wind Vast majority of events occur when the wind

speeds at sigma layers 5 and 8 are 13 knots or speeds at sigma layers 5 and 8 are 13 knots or less.less.

A few extreme outliers but these came from two A few extreme outliers but these came from two minor fog events.minor fog events.

BR EventsBR Events Majority of events occur when the wind Majority of events occur when the wind

speeds at sigma layers 5 and 8 are speeds at sigma layers 5 and 8 are greater than 12 knots and less than 25 greater than 12 knots and less than 25 knots.knots.

There were several events that occurred There were several events that occurred with winds greater than 25 knots but with winds greater than 25 knots but mainly from short lived 5-6sm BR mainly from short lived 5-6sm BR events.events.

FG CompositesFG Composites Sea level pressure - indicates surface Sea level pressure - indicates surface

high pressure directly over region or high pressure directly over region or ridge axis just to our east. ridge axis just to our east.

H85 – Ridge axis generally to the west of H85 – Ridge axis generally to the west of ELM. Composites show a range from Erie ELM. Composites show a range from Erie PA to the central southern tier.PA to the central southern tier.

BR CompositesBR Composites Sea level pressure – indicates surface Sea level pressure – indicates surface

high pressure over the mid Atlantic high pressure over the mid Atlantic region or moving off the coast. region or moving off the coast. (Increased moisture advection but also (Increased moisture advection but also more mixing)more mixing)

H85 – A flatter ridge and axis generally H85 – A flatter ridge and axis generally to the east of ELM.to the east of ELM.

Late season events occurred with ridge Late season events occurred with ridge axis further east.axis further east.

GENERAL OBSERVATIONSGENERAL OBSERVATIONS

Null fog events depict that a Null fog events depict that a temp/dewpoint spread of 8 degrees or temp/dewpoint spread of 8 degrees or greater from sigma 3 through 8, will greater from sigma 3 through 8, will prevent fog formation.prevent fog formation.

Fog events that do occur with a NE flow Fog events that do occur with a NE flow are generally short lived events or have a are generally short lived events or have a late onset time. This due to greater mixing late onset time. This due to greater mixing and dry advection as surface high and dry advection as surface high pressure builds over region. pressure builds over region.

FWC MOS Prediction of Fog FWC MOS Prediction of Fog (FG) and Light Fog (BR) at ELM(FG) and Light Fog (BR) at ELM

Shows some seasonal talent in Shows some seasonal talent in predicting FG eventspredicting FG events

Shows better talent in predicting BR Shows better talent in predicting BR eventsevents

FG predictionFG prediction

FWC MOS able to predict FG events FWC MOS able to predict FG events better than 50% of the time in June, better than 50% of the time in June, August, and September.August, and September.

Accuracy increased slightly in 00Z Accuracy increased slightly in 00Z forecast over the 12Z forecast, for forecast over the 12Z forecast, for the following morning.the following morning.

Little ability shown other months of Little ability shown other months of the year.the year.

Explanation of Charts:Explanation of Charts:

Hit:Hit: MOS forecast visibility exactly MOS forecast visibility exactly matched ELM observed visibility.matched ELM observed visibility.

Near:Near: MOS forecast visibility was within MOS forecast visibility was within two categories of ELM observed visibility.two categories of ELM observed visibility.

Over:Over: MOS forecast visibility was more MOS forecast visibility was more than two categories lower than observed.than two categories lower than observed.

Under:Under: MOS forecast visibility was more MOS forecast visibility was more than two categories higher than observed.than two categories higher than observed.

FG or BR must have occurred within the FG or BR must have occurred within the three hour MOS forecast time window.three hour MOS forecast time window.

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12Z FWC Fog Fcst June, August, September

Hit

Near

Over

Under

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00Z FWC Fog Fcst June, August, September

Hit

Near

Over

Under

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12Z FWC Fog Fcst Other Months

Hit

Near

Over

Under

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00Z FWC Fog Fcst Other Months

Hit

Near

Over

Under

BR PredictionBR Prediction

Both 12Z and 00Z FWC MOS Both 12Z and 00Z FWC MOS forecasts showed year round ability forecasts showed year round ability in forecasting BR events.in forecasting BR events.

Very little seasonal variation in abilityVery little seasonal variation in ability

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12Z FWC BR FcstTotal 108 Events

Hit

Near

Over

Under

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00Z FWC Br Fcst108 Events

Hit

Near

Over

Under

FWC MOS SummaryFWC MOS Summary

Has skill in predicting BR events in Has skill in predicting BR events in ELM year round.ELM year round.

Has skill during June, August and Has skill during June, August and September in predicting FG events in September in predicting FG events in ELM, but little skill the remainder of ELM, but little skill the remainder of the yearthe year

The 00Z MOS is somewhat better than The 00Z MOS is somewhat better than the 12Z at predicting both FG and BR.the 12Z at predicting both FG and BR.

LAMP MOS FG Forecasts at LAMP MOS FG Forecasts at ELMELM

LAMP MOS showed similar skill to that of LAMP MOS showed similar skill to that of the FWC MOS.the FWC MOS.

Skill was directly related to month.Skill was directly related to month. June, August and September showed June, August and September showed

reasonable skill, while other months reasonable skill, while other months showed little skill showed little skill

Skill improved closer to event, e.g. the 23Z Skill improved closer to event, e.g. the 23Z LAMP showed better skill than the 17ZLAMP showed better skill than the 17Z

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17Z LAMP Fcst June, August, SeptemberFG Events

Hit

Near

Over

Under

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20Z LAMP Fcst June, August, SeptemberFG Events

Hit

Near

Over

Under

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23Z Lamp Fcst June, August, and SpetemberFG Events

Hit

Near

Over

Under

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30

35

17Z LAMP Fcst Other MonthsFG Events

Hit

Near

Over

Under

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20Z LAMP Fcst Other MonthsFG Events

Hit

Near

Over

Under

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23Z Lamp Fcst Other MonthsFG Events

Hit

Near

Over

Under