Experimental Mountain Obsuration Guidance

One of the products that is being tested in the winter experiment is a probabilistic mountain obscuration product based on the Short Range Ensemble Forecasting System (SREF).  The SIERRA G-AIRMET package includes a forecast IFR conditions due to ceiling and visibility, as well as a forecast of extensive mountain obscuration.  The image below depicts
the mountainous regions for which obscuration forecasts are produced.  As you would expect the the major mountain ranges in the US are depicted, but forecasts are also produced for smaller ranges like the Black Hills and the Ozarks.

Image depicting regions of mountains

Automated guidance based on the SREF was developed, using a 40km horizontal grid.  A USGS Digital Elevation Model (DEM) with a 30-second resolution (~0.9km) was used to defined mountains on this 40km grid.  A grid box is mountainous if the elevation within the box varies by at least 1000 feet.  Mountain obscuration is determined for each SREF member.  If a forecast ceiling for a grid box is lower than the highest elevation from the DEM, that point is defined as obscured for that particular member.  Probabilities are then constructed from the percent of members that indicated obscuration at that grid point.

Below is a loop of the mountain obscuration forecast from the 09Z SREF run issued today.  Probabilities are shaded starting at 40%.  Also shown are experimental mountain obscuration G-AIRMETs issued in today's Winter Experiment.

Probability of Mountain Obscuration from the 09Z SREF forecast on 13 Feb.  Overlaid are the experimental mountain obscuration G-AIRMETs issued by the testbed forecaster.