Cloud Base How high (ALG) will the clouds be? Who Cares? –Public? …maybe… –Aviation? …hopefully… –What’s important? …It Depends… Airport/Runway Minimum Aircraft Minimum Pilot Minimums Airline Minimums Airport Instrumentation
MODCV Graphs 4 Graphs – 2 types! –Categorical Probabilities 1-Hour 3-Hours –Cumulative Probabilities 1-Hour 3-Hours Clicking on the graph expands the individual graphic for all the time ranges.
Example If it’s October in Cleveland and at 12Z the Wind was S and the ceiling was 1700, Climatologically, what time would the ceiling become VFR ?
Another Example It’s Nov 5 th at 05Z, it’s clear and wind is NE at 10KT. You confidently “forecast” BKN008 at 11Z, but you don’t know if the stratus will lift or not or will dissipate. Set MODCV to November at 11Z, place an initial ceiling of 800 ft and set the wind direction to NE
Don’t go for the largest number, but look for trends. Ensure there are enough observations in the data set. If observations are low (<50), set the wind direction to all and/or use unconditional climatology.
Conclusion Cloud height forecasts remain a challenge for forecasters. A combination of all the tools are needed: –Observations –Model Output –MOS –Climatology
Conclusion Cloud Forecasting Remains a “Challenge” Verification shows that forecasts are not very good. NWP models have a difficult time with moisture and clouds. Applied Climatology can help. MODCV (or its equivalent) is a “tool” that all aviation forecasts should use. Remember – The TAF is a FORECAST - NOT an Observation !