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Forecasting Ceilings in EVENTS

Forecasting Ceilings in EVENTS. Meteorology 415 Fall 2012. Low Ceilings. Any broken to overcast deck below 1000 ft Part of MVFR (3miles and 1,000 ft ) Processes in the PBL play the major role Elevation is a prime factor Precipitation (recent or current) has an influence

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Forecasting Ceilings in EVENTS

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  1. Forecasting Ceilings in EVENTS Meteorology 415 Fall 2012

  2. Low Ceilings • Any broken to overcast deck below 1000 ft • Part of MVFR (3miles and 1,000 ft) • Processes in the PBL play the major role • Elevation is a prime factor • Precipitation (recent or current) has an influence • Direction of surface air flow (upslope is a must) • Fog season climatology is very important

  3. Low Ceilings • Expected precipitation is a key to lowering ceilings • Advection of a low cloud deck, especially below a frontal inversion in the fall • Mechanical mixing plays a role in a moistened boundary layer

  4. Low Ceilings – Check List • Consider the following when predicting ceilings below 1,000 feet (IFR) • Is the station at or near sea level? • Does the station have less than 12” of rain per year (Is it in the desert)? • Is the station in the Tropics (even south Florida counts)? • ALL OF THESE ARE STRIKES AGAINST FORECASTING LOW CEILINGS

  5. Low Ceilings Also check out the RUC and HRRR

  6. GFS LAMP is a very good tool for short range ceiling forecasts: http://www.mdl.nws.noaa.gov/~glmp/glmp_expr.php

  7. GFS LAMP - Low Ceilings

  8. Low Ceilings • Consider the T-Tdwp Spread, but also look at the 850 REL (>90%)

  9. Low Ceilings - Summary • Consider advection of low ceilings • Decide on whether conditions warrant the formation of low ceilings • Rapid moistening of low levels • Winds become lighter or blow upslope • Surface convergence expected • Cooling of lower troposphere • Or warming in the winter over cold ground / snow cover • Remember instrument’s ability to detect low ceilings

  10. Low Ceilings • Become familiar with the Weather Depiction Chart showing ceilings and low visibilities…

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