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RADIATION FOG STUDY

RADIATION FOG STUDY. Office Stats. 00z ELM TAF POD for FG – 0.53 FAR – 0.55 06z ELM TAF POD for FG – 0.68 FAR – 0.50. Crossover Technique. This method, by itself, showed skill in determining when at least BR would occur

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RADIATION FOG STUDY

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  1. RADIATION FOG STUDY

  2. Office Stats • 00z ELM TAF • POD for FG – 0.53 • FAR – 0.55 • 06z ELM TAF • POD for FG – 0.68 • FAR – 0.50

  3. Crossover Technique • This method, by itself, showed skill in determining when at least BR would occur • When FG/BR occurred, the low temperature at ELM reached the crossover temperature about 80% of the time • However, it was less able to distinguish between FG and BR • When the “dense fog” threshold was reached (Crossover – 3 deg. F) or exceeded, FG only occurred about 55% of the time

  4. Water Temperature vs. Low Temperature • No data available at this time for temp. of Chemung River near ELM…closest gages are on the Tioga River in PA (Mansfield) • For this study, compared early morning low at ELM to climatological value of water temp. on Cayuga Lake near ITH • For June into August of this year, this compared favorably to Mansfield (+/- 3 deg. F) • Need to look at this more closely over a longer time period

  5. More Water Temperature vs. Low Temperature • August through December • When Delta T was 23 deg. F or more, FG occurred the vast majority of the time (20 FG/only 3 BR) • When Delta T was between 14 deg. F and 23 deg. F, FG and BR occurrences were evenly split (20 each) • When Delta T was less than 14 deg. F, BR took place the vast majority of the time (13 BR/only 4 FG)

  6. Yet More Water vs. Low Temperatures • April through July • When Delta T was less than 7 deg. F, BR occurred the vast majority of the time (30 BR/only 7 FG) • When Delta T was 8 deg. F or more, FG and BR events were about even (9 FG/6 BR)

  7. RADIATION EVENTS Average Wind Speed (knots) 59 FG CASES 73 BR CASES

  8. PRELIMINARY CONCLUSIONS • Between sigma layers 5 through 8, the average flow in BR events was twice as strong as FG events. • FG – 10 knots • BR – 20 knots • FG Events • Vast majority of events occur when the wind speeds at sigma layers 5 and 8 are 13 knots or less. • A few extreme outliers but these came from two minor fog events.

  9. BR Events • Majority of events occur when the wind speeds at sigma layers 5 and 8 are greater than 12 knots and less than 25 knots. • There were several events that occurred with winds greater than 25 knots but mainly from short lived 5-6sm BR events.

  10. FG Composites • Sea level pressure - indicates surface high pressure directly over region or ridge axis just to our east. • H85 – Ridge axis generally to the west of ELM. Composites show a range from Erie PA to the central southern tier.

  11. BR Composites • Sea level pressure – indicates surface high pressure over the mid Atlantic region or moving off the coast. (Increased moisture advection but also more mixing) • H85 – A flatter ridge and axis generally to the east of ELM. • Late season events occurred with ridge axis further east.

  12. GENERAL OBSERVATIONS • Null fog events depict that a temp/dewpoint spread of 8 degrees or greater from sigma 3 through 8, will prevent fog formation. • Fog events that do occur with a NE flow are generally short lived events or have a late onset time. This due to greater mixing and dry advection as surface high pressure builds over region.

  13. FWC MOS Prediction of Fog (FG) and Light Fog (BR) at ELM • Shows some seasonal talent in predicting FG events • Shows better talent in predicting BR events

  14. FG prediction • FWC MOS able to predict FG events better than 50% of the time in June, August, and September. • Accuracy increased slightly in 00Z forecast over the 12Z forecast, for the following morning. • Little ability shown other months of the year.

  15. Explanation of Charts: • Hit: MOS forecast visibility exactly matched ELM observed visibility. • Near: MOS forecast visibility was within two categories of ELM observed visibility. • Over: MOS forecast visibility was more than two categories lower than observed. • Under: MOS forecast visibility was more than two categories higher than observed. • FG or BR must have occurred within the three hour MOS forecast time window.

  16. BR Prediction • Both 12Z and 00Z FWC MOS forecasts showed year round ability in forecasting BR events. • Very little seasonal variation in ability

  17. FWC MOS Summary • Has skill in predicting BR events in ELM year round. • Has skill during June, August and September in predicting FG events in ELM, but little skill the remainder of the year • The 00Z MOS is somewhat better than the 12Z at predicting both FG and BR.

  18. LAMP MOS FG Forecasts at ELM • LAMP MOS showed similar skill to that of the FWC MOS. • Skill was directly related to month. • June, August and September showed reasonable skill, while other months showed little skill • Skill improved closer to event, e.g. the 23Z LAMP showed better skill than the 17Z

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