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Understanding Low Ceilings Forecasting in Fall Meteorology

This guide explores the factors influencing low ceilings in meteorology, particularly during fall. Low ceilings, defined as any broken to overcast deck below 1,000 feet, can significantly impact visibility and aviation activities. Key contributors include processes in the planetary boundary layer (PBL), recent precipitation, and surface air flow direction. The document discusses the importance of environmental conditions, such as elevation and historical fog patterns. Tools like GFS and LAMP are recommended for reliable short-range ceiling forecasts.

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Understanding Low Ceilings Forecasting in Fall Meteorology

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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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